EVALUATION OF THE POTENTIAL TO PRODUCE BIOGAS AND

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Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Evaluation of the Potential to Produce Biogas and Other Energetic Coproducts Using Anaerobic Digestion of Wastewater Generated at Shrimp Processing Operations Mark E. Zappi,*,†,‡ Emmanuel Revellame,†,§ Dhan Lord Fortela,†,‡ Rafael Hernandez,†,‡ Daniel Gang,†,∥ William Holmes,†,‡ Wayne Sharp,†,∥ Ashley Picou-Mikolajczyk,†,‡ Krishna D.P. Nigam,⊥ and Rakesh Bajpai†,‡ Downloaded via UNIV OF SOUTHERN INDIANA on July 23, 2019 at 12:47:10 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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Energy Institute of Louisiana, University of Louisiana, Lafayette, Louisiana 70504, United States Department of Chemical Engineering, University of Louisiana, Lafayette, Louisiana 70504, United States § Department of Industrial Technology, University of Louisiana, Lafayette, Louisiana 70504, United States ∥ Department of Civil Engineering, University of Louisiana, Lafayette, Louisiana 70504, United States ⊥ Department of Chemical Engineering, I.I.T. Delhi, Hauz-Khas, New Delhi 110016, India ‡

ABSTRACT: Shrimp processors in the United States each year operate via a staggered schedule of harvest runs that usually encompass about two to four months per run staggered between two to three month intervals. They typically use aerobic biotreatment for their wastewater management which yields no coproducts. This study considered a scenario where intermittent use of an anaerobic digester to produce methane (via biogas) during treatment of the wastewater was evaluated as if the digester was restarted multiple times per year. The overall study goal was to determine if an anaerobic digester could meet treatment goals (set at 60% removal of the chemical oxygen demand or COD) while producing a biogas containing >60% CH4 (v/v). The results indicated that nitrogen amending coupled with adding a microbial seed collected at the digester from a local municipal wastewater treatment plant provides good performance in terms of both biogas production and COD removal. Digestion of the shrimp processing wastewater yielded high levels of methane in the biogas at over 70% (v/v). About 3.5 ft3 CH4 per pound of input COD was produced in the nutrient amended and seeded digester system. Anaerobic digestion can produce other valuable products other than biogas such as volatile organic acids (VOAs), including acetic, proprionic, and lactic acids. Approximately 2 g/L of VOAs could be produced via a 10 day hydraulic residence time using a similar system that was pretreated via conditions reported by others to enhance the production of VOAs, but the level of VOA production obtained was not considered economically attractive. An assessment of the economics of a centralized digestion system that could service multiple processors indicated that the centralized unit would produce a slightly higher return on investment than that typically observed with digestion systems at animal raising and food processing facilities.

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INTRODUCTION

operations run over a series of on and off staggered plant operations over the year. Treatment plants at shrimp processing plants experience periods of high daily loadings and then no waste input (thereby no loadings) for weeks. This results in long periods of dormancy between the processing runs essentially requiring the restarting of shrimp processing operations representing a start-up situation for the wastewater treatment systems at these processing facilities (which is one advantage of abiotic treatment systems because they are not impacted by intermittent use). However, on and off operations

Shrimp harvested in the United States (US) is a more than $700M per year industry, yet over $6B of shrimp is sold in the US each year with the majority of tonnage being imported shrimp (a 90% market share is imported into the US consumer market). The global shrimp production yield is estimated to be over 3000 thousand metric tons per year.2 The US production of shrimp is estimated to be over 120 000 metric tons per year with the primary harvested varieties being the brown and white species. US production rates have remained fairly constant from 2006 through 2015 with the Gulf of Mexico region representing over 60% of the US yield.1 The Gulf of Mexico region shrimp processing operational runs vary year to year, but commercial shrimping each year in the region typically processes shrimp via two to four month runs staggered between two to three month intervals. Hence, processing © XXXX American Chemical Society

Special Issue: Biorenewable Energy and Chemicals Received: Revised: Accepted: Published: A

March 20, 2019 May 15, 2019 May 30, 2019 May 30, 2019 DOI: 10.1021/acs.iecr.9b01554 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

Figure 1. Envisioned dual stage bioreactor system for producing VOAs in a digester followed by aerobic conversion of the VOAs into microbial lipids within an activated sludge bioreactor.

shrimp processing plant where reducing organics and potential food-based pathogenic microbes were key evaluation factors with results indicating that this concept was feasible (essentially full reuse of the treated water as a semipotable water at the plant).12 The concept of coproducts from shrimp processing wastes has been evaluated with the harvesting of the chitin in the shrimp shells being the most commonly researched.13−15 However, chitin and protein harvesting and the subsequent conversion into marketable products can be expensive and often require off-site processing that is fairly complex and not within the experience base of most processors. This complexity of operation results with the shells at most US plants being given away by the processor as a cheap bulk product or more commonly disposed of as a waste, often into landfills. Anaerobic digestion is a biological treatment process that utilizes anaerobic microbial consortia for the treatment of organics contaminated wastewaters. The process is welldescribed elsewhere; however, in general, it involves the stepwise anaerobic degradation of complex wastes (such as proteins, lipids, and carbohydrates) through the production of organic acids, eventually resulting in the formation of biogas which is primarily made up of methane with the balance mainly being carbon dioxide.16−20 Conversion yields of input pollutant mass into biogas of a digester system generally fall within the 2−6 ft3 per pound of COD removed range. Also, a biogas composition in the 60% or more methane volumetric content is also considered a decent performing digester. Digesters where the biogas yields exceed 3.5 ft3/pound COD removed with COD removals greater than 80% and a biogas methane composition exceeding 70% (v/v) are considered good performers. Nutrients required by microorganisms must be present in the digestion water at the appropriate levels to ensure growth and to drive targeted metabolic reactions. These nutrients are divided in two groups: macro- and micronutrients.19 Macronutrients include N and P, while micronutrients include a range of trace elements such as S, Na, Ca, K, Mg, Co, and Fe.16 Chowdhury et al. found that anaerobic digestion was a good option for seafood wastewaters, including shrimp processing wastewaters.21 Digman and Kim suggest in their review that digestion is a good option for producing energy from seafood processing wastes (including shrimp).22 Gunnarsdottir et al. evaluated digestion of halibut versus shrimp wastes and reported that the fish wastes were more digestible than the shrimp wastes.23 Linder found that shrimp processing wastes in Belize were digestible, but ammonia inhibition was noted as an

are challenging to biological treatment systems such as anaerobic digestion (which can be a disadvantage). The US shrimp industry has faced numerous economic challenges over the past few years with increased environmental regulations, world trade issues, and labor shortages.2−5 Therefore, any reduction in processing costs and/or introduction of new value-added coproducts could represent tremendous benefits to the struggling US shrimping fleets and processors. A large portion of this annual production produces two primary wastewaters: farming recirculation/discharge water (from shrimp growing operations) and processing wastewater (from shrimp processors readying the shrimp for market). Most of the wastewaters generated at US shrimp processing plants stem from the following processing operations: rinsing, deheading, peeling, gutting, and cooking. Shrimp processors generate a wastewater that has organic wastes in both solid and soluble forms and is composed primarily of shells, protein, lipids, feces, and inerts.6 Tay et al. presented a listing of the pollution parameters from different seafood processing wastewaters, including shrimp processing wastewaters.7 They list shrimp processing wastewaters as having a neutral pH and biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), and lipids (as fat, oil, and grease or FOG) ranges of 720−2000 mg/L, 1200−3300 mg/L, 800−900 mg/L, and 250−700 mg/L, respectively. Prabha et al. presented data on the wastewaters exiting a shrimp processor and observed pollutant concentrations similar to those reported by Tay et al., except Prabha and colleagues list total solids data an order of magnitude higher for their wastewaters tested.7,8 With shrimp processors commonly located close to coastal ecosystems, the treatment of their wastewaters is of great interest to the regulatory community in terms of preventing ecological damage to these sensitive areas.9 Several treatment systems have been successfully employed for treating shrimp processing wastewater. Aerobic biotreatment is commonly used at many US shrimp processors and is an effective treatment alternative; however, no value-added coproduct is produced, and thus, the use of this option only imparts costs with no payback.7,10 Dissolved air flotation is also effective, and this option has potential to produce a protein coproduct used for fish bait; however, dissolved air flotation can be a relatively expensive option.11 Constructed wetlands offer another option,11 but this process is land intensive and can be difficult to ensure full containment of pollutants during flood and storm events. Casani et al. evaluated reverse osmosis for the potential recycle of the treated processing wastewater effluents back into the B

DOI: 10.1021/acs.iecr.9b01554 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research issue to be managed.24 Anh et al. suggested that a centralized waste processing area that includes digestion is more economically appealing than singular units placed at each processor due to the economy of scale and reduced labor needs on a per unit power generated basis.25 Anaerobic digestion does have the potential to produce valuable products other than biogas. Both hydrogen and volatile organic acids (VOAs) such as acetic, proprionic, and lactic acids can also be produced from a properly operated digester system. Hydrogen has recently become of interest because of its use by regional oil refineries within their hydrotreaters (adds carboxylic groups to aliphatics) and/or as a potential for use in fuel cells, which is a future power unit for portable devices and, perhaps one day, vehicles. Thus, researchers have been evaluating the use of anaerobic digesters to produce hydrogen and/or VOAs. Note that with either coproduct, biogas will likely be produced to some level. Khan et al. reviewed the potential for biohydrogen production from anaerobic digestion and concluded that this coproduct could be a valuable process option in the future.26 Fortela et al. proposed a novel treatment system which utilizes anaerobic digestion followed by aerobic biotreatment (activated sludge) where the VOAs produced during anaerobic digestion are converted into lipids within the cells of the aerobes in the activated sludge system.27 This combination of anaerobic/ aerobic biotreatment results in the potential generation of both biogas and commercially valuable lipids that can be further processed into biobased diesels or any other lipid-based product.28,29 Figure 1 presents a schematic of this new dualbioreactor system under development. The digestion of wastes such as shrimp processing wastewaters may offer a good feed source into the digestion component of this process system to form VOAs that are later converted into extractable cellular lipids within the aerobic step. In this study, the shrimp processor where the influent samples were collected is currently using activated sludge (aerobic biotreatment) as a means of removing COD (∼1600 mg/L as the initial COD level) from the wastewater generated within the plant which imparts a considerable cost to the facility’s operational budget. No coproducts are currently generated from this system. The processing plant also has significant monthly electrical costs for the processing and cold storage areas of the plant. Hence, anaerobic digestion appears to be an attractive wastewater treatment option that can produce one or more valuable coproducts. On-site power generation using biogas would be of great value to them as a means of reducing their operational costs. Another benefit to anaerobic digestion is that it is also operationally more simple than the activated sludge system currently used at the facility (and at most other shrimp processors). The overall goal of this study was to first evaluate the amount of biogas that could be produced from an anaerobic digestion system that was fed actual shrimp processing wastewater as an influent. Inclusive to this goal were attempts to optimize anaerobic digestion fed this influent in terms of biogas output and quality using several different digestion system pretreatment strategies. In particular, because the US shrimp processing industry operates intermittently over the course of a year, each processing run at the processing plant represents essentially a new start-up for a candidate biotreatment process. For this study, anaerobic digestion was evaluated for use at the plant as a new start-up which represents the worst-case scenario that an anaerobic digester would face in

terms of operating via a series of on/off operational modes over the course of a year. Targeted performance metrics for anaerobic digestion were the rate and quality of biogas production (as CH4) along with removing at least 60% of the influent COD. This level of COD reduction would greatly reduce the loading of the aerobic bioreactors on-site (perhaps even eliminate them with higher removals). A methane production yield of over 2.5 ft3 CH4 per pound of input COD and a biogas having at least 60% CH4 were considered a successful performing digester system for this study. The biogas would fuel a power production genset used to offset power costs in the plant. Secondary goals were to (1) briefly evaluate if some slight operational modification could produce hydrogen and/or VOAs from an anaerobic digester treating the shrimp processing wastewater as an influent and (2) test the optimal anaerobic digester system for methane production within a large pilot system which better mimics a full-scale unit to see if the bench results could be replicated using actual process equipment.

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MATERIALS AND METHODS Test Influent for the Digester Studies. The test influent used in this study was an actual shrimp processing wastewater influent collected from a large commercial shrimp processing plant located in Delcambre, Louisiana (LA). Discussions with the processing plant owners and a review of information about other US shrimp processors indicated that the processing methods and resulting wastewaters were indicative of an average US shrimp processing plant. As needed, the influent samples were collected in 1-gallon plastic jugs at a sample point located before the existing solids removal screens and before the influent tank of their current treatment system (activated sludge). Upon receipt at the laboratory, the samples were stored in a refrigerator (4 °C) until used for testing when at that time they were allowed to come to room temperature prior to use in the experiments. A series of bench-scale experiments was performed to evaluate the performance of several digestion strategies toward treatment of the shrimp processing wastewater. Performance was assessed via the quantity and quality of biogas, percent COD removal, and/or the amount of hydrogen and/or VOAs produced. Anaerobic Digestion Biogas Production Optimization Runs. Initially, the biogas production potential of the influent sample was evaluated using duplicate sets of 500-mL microcosms designed for performance of batch anaerobic digestion screening tests (see Figure 2 for a photograph of the microcosms). Each 500-mL microcosm was seeded with 12.5 mL of thickened microbial sludge (yielding 9 g/L total solids) collected from a high-performing, large-scale anaerobic digester located at the Lafayette, LA wastewater treatment plant (yields a 5% v/v liquid addition). This seeding protocol was selected based on an initial screening test to evaluate the appropriate seed amount to be added (discussed in the Results and Discussion Section). Note that the use of a microbial seed from the anaerobic digester from the local wastewater plant (Lafayette, LA) was selected over one that was more acclimated to the shrimp processing wastewater (via laboratory acclimation) because shrimp processing is a seasonal industry which would require digester start-ups at the processor via microbial seeding at the initiation of another shrimp processing run. Each experiment was seeded with 12.5 mL of the thickened biosolids that are described above (representing a 5% volume addition; this seed dose was selected from a

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ature and pressure) as used by both the United States Environmental Protection Agency (EPA) and National Institute of Standards and Technology: Tstandard = 20 °C, Pstandard = 1 atm. The headspace gas within the microcosms was periodically sampled through the septum outfitted port via a 1mL glass analytical syringe inserted into the center of the headspace after microcosm swirling. The final port shown in Figure 2 was used to charge additional reagents and collect liquid samples as needed. Three pretreatments prior to initiating anaerobic digestion were evaluated: acidification, base (alkaline) addition, and ozonation (O3 sparging). Additionally, a digestion system where only nutrients were added was evaluated to determine if straight digestion coupled with nutrient amending would be successful (only total nitrogen was added as ammonia because P and S were present in sufficient amounts as detailed later in the Results and Discussion Section). As noted above, all systems had the microbial seed added. The digestion runs (which is almost all of them except where no N-amending was tested) involved adding N from the dosing of NH4Cl to achieve a mass concentration ratio of [COD]:[N] = 100. The [COD]:[N] mass ratio was based on pretest analyses of the influent for total nitrogen in the form of the summed concentrations of N as nitrite, nitrate, and ammonia. This dosed N and already present influent P and S levels are in agreement with the acceptable ranges reported by Hussain et al.33 In the case of the pretreatment runs, the nutrients were added after the pretreatment step, followed by the pH adjustment to neutrality, and then the N-nutrient and microbial seed were added. The pH adjustments were targeted to hit 7.0 (±0.2) using HCl or NaOH as needed. As mentioned above, several digester test conditions (i.e., operational strategies) were evaluated within the 500-mL microcosms using the wastewater influent: (a) nutrient addition (aka N-nutrient amended), involving the nutrient amending strategy detailed above; (b) acid pretreatment (acidification), involving 5 N HCl addition to pH of ∼2, stirring for a period of t = 24 h at room temperature, then readjustment via NaOH to pH ∼7, addition of the microbial seed, and nutrient dosing using the same N-amending as with N-Amended runs after pH neutrality was reestablished; (c) base (alkaline) pretreatment, involving the addition of enough 5 N NaOH to achieve a pH ∼10, stirring at room temperature

Figure 2. Photograph and schematic of the 500-mL microcosms.

screening experiment summarized in the Results and Discussion Section of this paper). All of the conditions tested in the 500-mL microcosm experiments involved the following: total liquid addition (including the 12.5 mL of microbial seed) of 250 mL yielding a sealed headspace of 250 mL. No pH adjustment was needed with the untreated influent because it consistently had a neutral pH. All 500-mL microcosm incubations were performed at T = 35 °C by placing the microcosms in a preset laboratory incubator. No mixing was applied to the microcosms except during sampling when the microcosms were gently hand-swirled prior to sample collection to ensure homogenization of the samples. All microcosms were purged with nitrogen gas prior to sealing to remove air from the headspace, and then the microcosms were placed into the incubator (t = 0 days). Biogas production was monitored via observation of pressure increases using a test pressure gauge inserted/sealed into the center threaded port of the microcosm (see Figure 2). Gas production volumes were estimated using the pressure readings and assuming ideal gas behavior. Biogas volumetric yields were standardized at NTP (normal temper-

Figure 3. Fifteen-liter anaerobic digester system used for evaluating hydrogen and/or VOA production using freeze/thaw and a slightly adjusted pH (pH 6.5) as pretreatment methods (operated using the microbial seed addition [9% TS seed], N-amended [C:H = 100], and continuously mixed [100 rpm]). D


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Figure 4. Schematic (A) and photographs (B and C) of the 250-gallon pilot anaerobic digester system. Photo B is the actual digester (250 gallon wetted volume), and photo C is the influent and effluent tanks with pumps.

for a period of t = 24 h, re-establishing pH to neutrality using HCl to pH 7, then addition of the microbial seed and Nnutrient dosing (using the nitrogen nutrient amending protocol); and (d) ozone pretreatment, involving sparging 3% (v/v) ozone into the influent via a sparge stone for 15 min, then checking the pH and adjusting to pH 7 with both the Nnutrient and microbial seed addition once pH neutrality was re-established. All chemicals for the pretreatment experiments were purchased as analytical grade from Fisher Scientific. Ozone was provided using an Ozonology oxygen-fed generator with turn-down capacity and oxygen used as the parent gas. Hydrogen and VOA Production Runs. After the optimal anaerobic digestion system (N-amending) for biogas production was selected from the 500-mL microcosm experiments, this experiment was performed to assess the potential for an anaerobic digester fed shrimp processing wastewater as an influent to potentially produce hydrogen and/or VOAs. The objective of this test phase was to use pretreatment methods

from literature that may be employed at the processing plant to perhaps produce hydrogen and/or VOAs as potential coproducts. The intent was not to perform a series of optimization runs but to evaluate a single candidate system. This experiment was performed in a duplicate 15-L laboratory fermenter (New Brunswick BioFlo 3000) setup to mimic an anaerobic digester (see Figure 3). Digestion in the 15-L digesters (fermenters) was performed under semibatch operations by allowing instantaneous release and monitoring of biogas produced via an online flow totalizer system (Model DFM 502, Challenge Technology) with the liquid components batch added at the initiation of the tests. With semibatch operation, the reactor was batch with regard to the influent/ microbial seed liquid and continuous with regard to the produced biogas which was continuously released out of the reactor. The fermenters were continuously mixed at 100 rpm. Upon arrival in the laboratory from sampling, the shrimp processing wastewater and microbial seed were immediately E


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both equipped with electrochemical detectors. One unit was dedicated for anion analysis, while the other unit was for cation analysis. Anion analysis involves a 2 mm ASRS suppressor and a KOH eluent generator. The ECD is set at 35 °C with a 2 × 250 mm AS 16 (+2 × 50 mm AG16) at a constant eluent flow of 0.30 mL/min. The gradient elution was set as follows: 23 mM KOH for 6 min, ramp to 50 mM at 9 min, back down to 23 mM at 12 min, followed by a 4 min stabilization period. The cation analysis used a 2 mm CSRS suppressor, a MSA eluent generator, and a column oven. The oven was set at 30 °C, suppressor at 50 mA, and eluent flow rate at 0.40 mL/min with a 2 × 250 mm CS 18 column (+2 × 50 mm AG18 guard column). The eluent concentration was 30 mM for the duration (30 min) of the analysis.

mixed into the fermenters and purged with nitrogen to initiate the digestion. The two fermenters were N-amended to hit a [COD]:[N] ratio of 100 and also seeded using the previously described method. The units were monitored over time for biogas composition (CH4, CO2, and H2), biogas volume produced, and for liquid phase concentrations of VOAs (acetic, lactic, proprionic, and butyric acids) and pH. The COD concentrations before and after treatment were also determined. The biogas rate was calculated via first derivative numerical differentiation of the biogas flow data using Cubic BSpline curves implemented in R using the D1ss function of the “sfsmic” Package. Pilot Study. A pilot-scale evaluation was performed using a 250 gallon digester system designed for conducting on-site evaluative R&D (see Figure 4). The system was semibatch operated in which the biogas produced was allowed to flow out of the digester with the liquid influent batch charged. The biogas flow exiting the digester was quantified using a gas flow totalizer (SmartTrak 100, Sierra Instruments). The same seeding and N-nutrient amending protocols used with the 15-L experiments were used. No form of pretreatment or other nutrient amending was applied over the course of the pilot study. A single pilot test run was performed; however, liquid samples were collected and analyzed in duplicate. Reactor content pH values were monitored over time in which these values remained in the neutral pH range, thus not requiring pH adjustment. The initial and final water COD concentrations were analyzed. Periodically, the exiting biogas was analyzed for CH4, CO2, O2, and H2; however, practically speaking, no O2 or H2 concentrations were detected in the biogas samples tested. As shown in Figure 4, the bioreactor temperature was maintained at 35 °C using an external water heater coupled with a heating water recirculation pump and the heating jacket surrounding the bioreactor. The bioreactor was mixed occasionally (at least every other day, but typically daily for about 10 min). This reduced mixing effort was done because most full-scale digesters are generally mixed using a similar periodic mixing protocol. Analytical Methods. This section presents a summary of the analytical methods employed in this study. More details on these methods are described elsewhere.30,31 COD was analyzed as soluble COD (filtered) via a Hach DR-5010 and digestion block using Hach COD precharged ampules (meets all EPA method requirements). The pH values were measured using a Fisher pH meter and probe that was calibrated using a 2-point calibration. Collected headspace biogas composite was analyzed via injection of ∼0.5 mL gas samples into a GCTCD (Agilent 6890N), which was calibrated for CH4, CO2, H2, and O2 analyses using an 80/100 mesh, 6 ft × 2 mm ID Porapak-Q and 80/100 mesh, 10 ft × 1/8 in. Molesieve 5A columns in series. The injector and detector were operated at 150 and 180 °C, respectively. The GC oven was programmed for 70 °C for 2 min, ramped to 130 °C at 10 °C/min and held at 130 °C for 2 min. A HPLC system (HP 1100) was used for analyzing the liquid samples for lactic, acetic, butyric, and propionic acids. Samples were filtered through 0.45 μm nylon syringe filter prior to analysis. Detection of VOAs was accomplished using diode array detector set at 210 nm. HPLC analysis was done at 40 °C for 30 min with 0.005 N H2SO4 as mobile phase at a flow rate of 0.60 mL/min. Ion chromatography (IC) was used to characterize the wastewaters in terms of the different N, P, S, Na, Ca, K, Mg, and Fe species. The IC procedure involved using two-Dionex DX600 units

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RESULTS AND DISCUSSION Characterization of the Shrimp Processing Wastewater Influent. Table 1 presents the analytical characterTable 1. Analytical Characterization of Shrimp Processing Wastewater Influent analyte

value

pH COD, mg/L nitrite-N, mg/L nitrate-N, mg/L ammonia-N, mg/L sulfate, mg/L phosphate, mg/L sodium, mg/L potassium, mg/L magnesium, mg/L calcium, mg/L chloride, mg/L flouride, mg/L total suspended solids, mg/L avg COD: avg total N ratio avg COD: avg phosphate ratio

7.55 1106−1998 8.6−12.6 0−7.5 3.0−6.1 0−1.1 36.7−60.8 89.0−239.3 31.7−42.9 15.5−23.6 0−56.7 88.3−350.2 3.1−3.9 984−1162 183.5 97.6

ization of the shrimp processing wastewater. Periodically, as the various experiments were initiated, the influents were chemically characterized for selected analytes which is why there is a range of concentrations listed for COD and the nutrients. From Table 1, the pH of the influent was consistently found to be neutral. The COD concentrations (1106−1998 mg/L) were well within the reported ranges expected for a shrimp processing wastewater. Phosphate and sulfur levels were all within a reasonable concentration range for maintaining an anaerobic digester.16 Nitrogen compounds were low in terms of a [COD] to [N] ratio (typically less than 30) where typically a ratio of 100 or higher is preferred.32,33 The [COD]:[phosphate] ratio of 98 for this wastewater was considered more than enough based on the reports of others.34,35 These nutrient data justified the nutrient amending protocol used throughout this study (see Materials and Methods Section), which involved only nitrogen amending (as NH3). Also, there was enough sulfur, so adding sulfur was not needed. Thus, the test influents were dosed with enough ammonium to hit a [COD]:[N] (as ammonium) ratio of 100. No other analytical data were considered of potential detriment to the digestion systems being evaluated. F


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Figure 5. Microcosm runs (duplicate runs) using shrimp processing wastewater to evaluate the potential benefits of seeding the bioreactors with an active digester microbial consortium (9 g/L TS as sampled) from the local wastewater treatment plant: (a) no anaerobic sludge seed added, (b) 2% (v/v) seeded, and (c) 5% (v/v) seeded with all units having the pH adjusted from 7.4 to 6.45 to assess low pH performance or no pH adjustment (pH 7.4).

Evaluation of Microbial Seed Amending Protocol. This set of experiments was performed to determine an optimal anaerobic consortium seeding protocol for use in this study. Because shrimp processing is seasonal, it was decided that this study would assume that each processing cycle at the plant would basically represent a new digestion start-up approach at the beginning of that processing plant run (worst case). Figure 5 presents a series of tests using duplicate 500mL microcosms where no seed was added (Figure 5a) versus adding a 2 and 5% (v/v) solution of thickened anaerobic digester sludge (∼9 g/L as TS) seed (represented as Figures 5b and 5c, respectively). This sludge was collected at the exit point of an active anaerobic digester at the local wastewater treatment plant. The nutrient amending protocol was used via the addition of ammonium to initially hit the 100:1 ([COD]: [N]) ratio for this series of runs. This method of seeding would be easy to implement at the plant during restarts (adding a volume of thickened digester sludge from a local wastewater treatment plant). During these test runs, a pH adjusted influent (pH 6.4 via HCl addition) was also tested against the unadjusted influent (pH 7.5) to evaluate the potential impact of a slightly lower pH during system restart (when acids are produced prior to the methanogens catching up). From Figure 5, there are clear benefits to adding a microbial seed for system start-up. The unseeded system started producing carbon dioxide at day 4, but no methane appeared until after day 6. The 2% seeded system started producing both methane and carbon dioxide at about the same levels by day 4. The 5% seeded system produced twice as much methane as carbon dioxide by day 4. Clearly, the addition of a well-functioning anaerobic consortium provided benefit in that the raw wastewater apparently did not have an optimal consortium present. The appearance of carbon dioxide prior to methane is indicative of an unacclimated consortium starting to digest. It is interesting to note that the slightly lower pH had no real impacts other than that the lower pH was more favorable in terms of carbon dioxide evolution over methane. It is well-documented that most methanogenic systems tend to favor neutral pH conditions (and, in fact, are very sensitive to lower pH conditions), although some acclimation to lower pH values has been reported.16,19 Table 2 presents the solids removal data for the three different seeding strategies evaluated. From the table, the three different seeding strategies produced volatile suspended solids (VSS) removal ranging from 45% (5% seed) to 64 (2% seed). The higher seeded sample does introduce a higher amount of

Table 2. Solids Data from the Microbial Seed Evaluation Experimentsa solids data

0% microbial seed

2% microbial seed

5% microbial seed

initial VSS, mg/L final VSS, mg/L VSS% removal initial TSS, mg/L final TSS, mg/L TSS% removal

1073 400 63 2175 1360 37

1181 420 64 2320 1460 37

1343 733 45 2537 1893 25

a

Note: The 5% microbial seeding strategy was selected as optimal and used in all subsequent digestion experiments within this study; the source of the seed was the anaerobic digestion from the Lafayette, LA wastewater treatment plant.

solids that had already undergone digestion within the anaerobic digester at the municipal plant from which it was collected (Lafayette, LA plant). However, it was clear that reaching 60% or higher was feasible with this influent. The TSS removal ranged from 25% (5% seeded) to 37% (both the unseeded [0%] and 2% seeded). The higher TSS is attributable to the small shell fragments from the shrimp that resulted from the peeling operations and the fixed solids introduced from the seed. The peels are fairly recalcitrant within a digester system. It was decided that all future experimental runs during this study would utilize the 5% seeding protocol and that the 5% (v/v) seeding before each plant operational restart would be of benefit at the plant if a full-scale digester were to be installed. Even though the higher seed amount (5%) did yield lesser solids removal, it was decided that this effect would be eliminated as the full-scale, continuously operated plant was operated within a larger time frame. No pH adjustment would be needed because the neutral pH of the unamended influent supported good anaerobic activity. These experiments indicated that at full-scale shrimp processing facilities, the use of a microbial seed collected from a well-functioning digester from a local municipal wastewater treatment plant using a similar solids loading to the 5% seed used in this study would be a good option to start/restart biological digestion operations at a shrimp processing plant. The results also indicated that the shrimp processing wastewater was a good candidate for anaerobic digestion in terms of appreciable biogas production. Evaluation of Various Pretreatment and Amendments for Optimizing Biogas Production. Appels et al. evaluated oxidation pretreatment a means of enhancing G


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Figure 6. Gas production (as CH4 and CO2) during the batch digestion testing of the shrimp processing wastewater using the 500 mL microcosms to evaluate (a) no nutrient amendments added (active control) but microbial seed added with COD reduction achieved = 68%; (b) nutrient amendment with microbial seed added and pH adjusted to pH 7 with COD reduction achieved = 68%; (c) acidification pretreatment then nutrient amended/microbial seed added/pH adjusted to pH 7 after pretreatment with a COD reduction achieved = 71%; (d) base (alkaline) added pretreatment then nutrient amended/microbial seed added/pH adjusted to pH 7 after pretreatment with a COD reduction achieved = 73%; and (e) ozonated pretreatment then nutrient amended/microbial seed added/pH adjusted to pH 7 after pretreatment with a COD reduction achieved = 67% (each data point shown represents the average of duplicate runs).

influent constituent solubilities and biodegradation potential of anaerobic digestion.36 They found that biogas production was increased by over 20% after oxidation pretreatment. Ozonation as an oxidative pretreatment was evaluated by Goel et al. with the results showing that ozone pretreatment of the effluents improved methane production.37 Carrere et al. evaluated base addition as a pretreatment to remove influent oils via saponification because lipids in the influents have been known to hinder the activity of the microbial consortium toward production of biogas with their results showing improved performance after base pretreatment.38 The use of acidification as a pretreatment method was tested by Devlin et al. with their results indicating significant effluent improvements and biogas yields with a pH 2.0 being optimal, yet the full range of pH 1−6 all showed some level of process improvement.39 Ariunbaatar et al. reviewed various pretreatment methods (mainly pH adjustments and physical methods) for a variety of influents to anaerobic digesters.40 Acid treatment was found to work particularly well when plant materials were present but also to stimulate hydrogen production. Base (alkaline) pretreatment was particularly effective with meat-based influents as the base enhanced degradation of lipids and proteins. The wastewaters generated from shrimp processing primarily contain shrimp meat, guts, and shells but also some small amounts of seaweed and algae mass. Hence, given this type of wastewater influent, it was decided to evaluate if acid, base, or oxidation (ozonation) pretreatment coupled with Nnutrient amending and seeding with the 5% (v/v) thickened

digester-derived seed would generate improved biogas production as defined as total volume of gas produced per pound of input COD and higher volumetric methane levels within the gas. Additionally, the impact of the different digestion systems on COD removal was of interest as well. Hence, this phase of experimentation focused on identifying an optimal digestion system for the shrimp processing influent using the 500-mL microcosms which allowed for the concurrent evaluation of multiple replicates and test conditions. Figure 6 presents the results of this testing in which an active control (straight wastewater without any amendments other than the seed were added [no N-addition/control, Figure 6a]), nutrient amending in the form of N-addition to hit the [COD]:[N] ratio mark of 100:1 (Figure 6b), and the evaluation of three influent pretreatments methods (Figures 6c−e). The three pretreatments evaluated were acidification (Figure 6c), base (alkaline) addition (Figure 6d), and ozone oxidation (Figure 6e). Note that the initial pH values for all of the pretreatments were adjusted back to a pH of ∼7 after pretreating prior to starting the digestion incubations. All of the noncontrol tests were nutrient-dosed (N-added) and then inoculated with the microbial seed (the 5% [v/v] of thickened digester sludge) after pH adjustment. The control test was only inoculated with the microbial seed (no N addition). All of the gas yields (CH4 and CO2) were normalized to cubic feet yield per pound of COD inputted basis to eliminate the effect of the slight differences in initial influent COD concentrations on biogas yield calculations. H


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Figure 7. Biochemical methane potential of the shrimp processing wastewater with various pretreatment strategies (note that all conditions had a microbial seed added after pH adjustment from the pretreatments): (A) no nutrient amendments added (active control), (B) N-amended, (C) acidification, (D) base (alkali) pretreatment, and (E) ozonation (B0 = maximum methane production (potential) as ft3/lb-COD loaded; k = kinetic parameter as day−1). Note: The experimental data (expt’l) are the data (also shown in Figure 6) produced from the actual tests (average of duplicates).

system, the different systems evaluated all yielded good quality biogas from a methane composition perspective. In terms of COD removal, a COD removal of 60% was targeted for consideration of successful water treatment. The COD removals achieved for the unamended, N-amended, acidpretreated, base-pretreated, and ozonated-pretreatment systems were 68, 68, 71, 73, and 67%, respectively. Thus, all of the treatments were considered successful in surpassing the 60% COD removal metric. No real differences are noted between the various treatments tested. Thus, from a water treatment perspective, it was shown that anaerobic digestion with Namending and no influent pretreatment would yield sufficient performance in terms of meeting the study target COD removal goal of 60%. The results from biogas optimization runs were further evaluated using a modified first order model (biochemical methane potential or BMP model) to estimate the maximum amount of biogas that each condition could produce. The BMP model is presented below as described by Da Silva et al.:41

Based on the graphs in Figures 6a−e, all of the systems produced appreciable amounts of both methane and carbon dioxide. At day 40, the acid-pretreated system (Figure 6c) yielded a slightly higher methane yield at 3.8 ft3/pound of input COD ft3/pound of input COD than did the N-nutrient amended and unamended systems with methane yields of 3.25 and 3 ft3/pound of input COD, as seen in Figures 6b and 6a, respectively. The ozonation-pretreated system yielded a day 40 methane yield at 3 ft3/pound of input COD. The basepretreated system had the lowest methane yield at day 40 at 2.8 ft3/pound of input COD. However, the day 40 methane yields for all systems were generally within 20% of each other indicating small differences in day 40 yields. What does separate the performances of the various systems tested is the rate of increase of methane production from initiation through 10 and 20 days of incubation. The two systems that were not chemically pretreated had much faster yield to the final methane levels than did the chemically pretreated systems (Figure 6). At day 10, the two systems not chemically pretreated both hit methane yields greater than 1.5 ft3/pound of input COD with the acid- and ozonation-pretreated systems, hitting 1.25 ft3/pound of input COD at day 10. Again, the base-pretreated was the worst performer with a day 10 methane yield of 0.75 ft3/pound of input COD. At day 20, the two systems not chemically pretreated and the acid-pretreated system all resulted in methane yields at about 2.8 ft3/pound of input COD with the ozonated- and base-pretreated both having yields of 2.3 ft3/pound of input COD. The carbon dioxide data did not show much difference in production among the different systems except with the ozonatedpretreated system, which produced almost twice the carbon dioxide yield at around 1.5 ft3/pound of input COD over the carbon dioxide yields observed with the other systems (∼0.75 ft3/pound of input COD). It should be noted that the different systems evaluated had biogas methane compositions calculated to be 74, 72, 76, 71, and 59% for the control, N-amended system, acid-pretreated system, base-pretreated system, and ozonated system, respectively. Other than the ozonated

B(t ) = B0 (1 − e−kt )

where B(t) = methane production over time, ft3/pound of input COD; t = volume methane/mass VSS input or volume methane/mass pound of input COD; B0 or BMP = the maximum methane production, ft3/pound of input COD; and k = the kinetic parameter (t−1). Figure 7 presents the methane production data shown in Figure 6 along with the fit of the applied BMP model. The estimated BMP values and rate constants are shown in Figures 7a−e) for each respective digestion system tested. A review of the BMP values indicates that the acid pretreatment system has the highest production potential, followed by N-amended and ozonated both performing about the same with the control following and the base-pretreated system showing the lowest BMP. The data in Figures 6 and 7 show that albeit the different chemical pretreatment did not appear to hinder the I


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Most of these studies focused on hydrogen yields, but most also observed the buildup of VOAs. The 500-mL microcosm biogas optimization experiments indicated that anaerobic digestion could yield a good quality biogas and target water treatment goals could be met. Thus, an experiment was initiated to evaluate if appreciable levels of hydrogen and/or VOAs could be produced within the Namended, microbial seeded system using some pretreatment options targeting hydrogen and VOA production. Because the appearance and disappearance of the VOAs would have to be observed during testing via the collection of multiple water samples taking much more than 500 mL total, the 500-mL microcosms with maximum working capacities of only 300 mL were deemed inappropriate testing vessels for this phase of study. Hence, a semibatch flow series of experiments was performed within 15-L reactor systems (large, benchtop fermentation systems [BioFlo systems] run in duplicate). These larger bioreactors were continuously using impellerbased mixing (set at 100 rpm) provided via an in-vessel mixing shaft with three axial-mounted paddle impellers (see Figure 3). The bioreactors were continuous in terms of biogas evolution out of the reactors (volumetrically quantified via the in-line gas volumetric flow totalizer) and batch operated in terms of the liquid influent. The larger bioreactors also allowed for periodic extraction of the liquid samples needed for VOA analyses. With this series of experiments, N-nutrient amending was performed along with the addition of the microbial seed that was exposed to two stages of freeze/thaw prior to initiating the digester runs (feeding the test influent). Also, the influent pH was reduced to a pH 6.0 to stimulate hydrogen production. This pH level was not found in the seed evaluation study to significantly hinder the activity of the acetotrophs; it was postulated that this level of pH adjustment may concurrently produce hydrogen. Thus, these two pretreatments designed around reviewed literature (detailed above), representing one pretreatment directed at the microbial consortia and another at the influent, were evaluated to determine the amount of both hydrogen and VOA production achieved along with biogas production. Figure 8 presents the results of the VOA and hydrogen production experiments. The results of this experiment showed that hydrogen was mainly produced during the initial five days of the incubation. After that period, no more hydrogen was produced as observed with the steady yield line seen from day 5 forward (Figure 8a). It is possible that more hydrogen was produced, but this production could have been removed via unicarbonic conversion of the hydrogen and carbon dioxide into methane via hydrogenotrophic methanogens.48 The methane and carbon dioxide production concentrations over time shown in Figure 7a exhibited generally the same production trends as seen with the 500-mL screening tests (Figure 6). However, the day 35 methane levels were about a full 1% lower than those observed in the 500-mL microcosm experiments (see Figure 6b for the data generated essentially the same system tested as shown in Figure 8). From Figure 8b, butyric acid was by far the most produced VOA in these tests at levels approximately 10 times higher than the other three detected (acetic, proprionic, and lactic acids). The acetic acid appeared early into the incubation but was quickly reduced through the remainder of the test starting at day 8, likely indicating that the methanogens were actively converting the acetic acid to methane, which does correlate well to the rapid production of methane seen in Figure 8a (around day 8). By

progression of anaerobic digestion, there appears to be minimal benefit toward the extra process equipment needed and cost associated with adding these chemicals (particularly true for ozone). The N-nutrient amended and unamended systems performed similarly, but given the ease of adding fertilizer as a N-source and the potential stabilizing effect of ensuring sufficient amounts of nitrogen were present, the Nnutrient amended system was deemed to be the optimal system for the shrimp processing wastewater tested. Do note that this system also involved adding the microbial seed from the anaerobic digester (as did all of the systems tested). The quick initiation of very active digestion through 10 days of incubation coupled with the ease of operation (no pretreatment) makes the potential use of this operations mode of the digester at the plant an even more appealing option given the seasonal operations schedule with processors of this type. It appears that anaerobic digester restart should be relatively easy, and a high level of performance is expected to be relatively rapid based on review of these data. Assessment of Hydrogen and/or VOA Production. There are two primary types of methanogens that produce methane within most anaerobic digesters: acetotrophs and hydrogenotrophs. The acetotrophic and hydrogenotrophic overall reactions of these two methanogen types are summarized below as eqs 1 and 2, respectively.42 CH3COO− + H+ → CH4 + CO2

(1)

4H 2 + CO2 → CH4 + 2H 2O

(2)

Taconi et al. reported the hydrogenotrophic pathway (eq 2) as being a significant methane production mechanism for the digestion of a simulated acetic acid wastewater.19 However, for the vast majority of anaerobic systems degrading complex organic substrates, like shrimp processing wastewater, the acetotrophic pathway is the dominant source of methane production. Note that the acetotrophs are responsible for the degradation of the VOAs into methane. If they are suppressed (or deactivated), then the VOAs will build up in the digester. If no acetogenic activity occurs, then the pH can drop to a point where the digester system fails. Hence, the balancing of a hindered acetogen population to allow for some buildup of VOAs while some methane is produced at the same time could yield two products: methane and VOAs. The VOAs would potentially be transformed via aerobic biotreatment into microbial-based lipids (as discussed in the Introduction Section of this paper). Also, as a complex organic waste is sequentially broken down by the various microbes within the digester, the hydrolyzing organisms are often considered the first key microbial consortia because they break down the complex organics into large organic acids and hydrogen. Hence, other than biogas, an anaerobic digester can technically produce three products of value: methane within the biogas (by far, the most common product used), hydrogen (a developing area for digesters), and VOAs (another developing area for digester that are coupled with a subsequent aerobic stage to actually yield lipids). Numerous studies have been done over the years to first suppress, but not totally eliminate, the acetotrophs.20,43−47 A variety of pretreatments to the influents and digester microbial consortia has been tested to suppress the acetotrophs, including sonication, thermal shocking (both heat and freeze/thaw), and reducing the digester influent pH to less than neutral levels (acidification). J


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be estimated. Assuming an influent flow of 50 gpm and an influent COD of 1500 mg/L yielding a total VOA concentration of 2 g/L with an aerobic microbial yield coefficient for converting VOAs into lipids of 0.5 (converted in the aerobic step), it can be estimated that approximately 600 lbs/day of lipids would be produced. However, assuming a 25% aerobic sludge wasting, this amount is reduced to only 150 lbs/day, which is only worth a daily economic value of around $50/day (assuming lipids selling at $0.30/lbs). Hence, the value of investing in a system capable of anaerobic/aerobic biotreatment solely for lipids production is not economically attractive for a typical shrimp processor. This is consistent with our past studies on lipid production from VOAs generated from anaerobic digesters in which influent COD concentrations should be much higher to yield appreciable amounts of lipids. It was concluded that the value of the thermal-stressing of the microbial seed along with the lowering of the influent pH does not appear to be an attractive option for the shrimp processing wastewater influent due to the low production levels for both hydrogen and VOAs. Past studies by our team indicate a much more attractive lipid production system using much higher influent COD levels.27 It was interesting to observe the VOAs produced and that if an incubation period (HRT) was to be selected where both VOAs and biogas production are at their mutual highest, the 10 day HRT would be the optimal selection. Pilot Scale Testing. Figure 9 presents the results from the pilot study. From the figure, the methane yield based on the pound of input COD was approximately 2.5 ft3 CH4/lbs. pound of input COD. The biogas produced had methane and carbon dioxide concentrations of about 80 and 20% (v/v), respectively, which is an excellent, high BTU biogas. It is noted that the methane yield was 24% lower than what was observed for the same system tested within the 500-mL microcosm. The reason for this slightly lesser performance is not known. It is likely that the large pilot digester had less than the ideal incubation conditions provided within the small microcosms such as a more consistent temperature control. However, the pilot results did support the opinion that anaerobic digestion is a good option for shrimp processing wastewater as both a treatment system and a source of a good quality biogas. The digestion test run in the pilot system did reduce the influent COD over the incubation by 69%. This removal level was considered successful.

Figure 8. Gas production (total biogas, CH4, CO2, and H2) (a). VOA concentrations (b) versus incubation time during the batch digestion testing of the shrimp processing wastewater using the 15-L bioreactors to evaluate nutrient amending/microbial seed added/pH adjusted to pH 7 with a COD reduction achieved = 55% (each data point shown represents the average of duplicate runs).

day 30, complete consumption of the VOAs was observed, which correlates with significant generation of methane during the same time frame. It appears that a 10 day hydraulic residence time within a digester would yield the highest amount of VOAs and a biogas containing approximately 50% methane. Further optimization and microbial consortium acclimation would likely yield more promising results, but this was not pursued in the current study. The extent of COD removal achieved over the full 33 days of incubation was only 55%. This lower level of COD removal could very likely be attributed to the freeze−thawing of the microbial seed. Thus, from a water treatment perspective, it does infer that care should be taken to ensure the integrity of the microbial seeds to ensure that a key microbial consortium member is not hindered or eliminated. The amount of lipids that could be potentially generated from a shrimp processing plant using the data in Figure 8 can

Figure 9. Gas production (total biogas, CH4, and CO2) and total biogas production rate versus incubation time during the batch digestion testing of the shrimp processing wastewater using the 250 gallon pilot-scale system to evaluate nutrient amending/microbial seed added/pH adjusted to pH 7 with a COD reduction achieved = 69% (each data point shown represents the average of duplicate samples collected). K


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Figure 10. PFD of the envisioned digester system implemented at the shrimp processing plant.

The organic content of this wastewater stream is a contribution from three main digestible compounds from the shrimp: proteins, lipids, and carbohydrates. Their relative digestibility is indicated by the plot of biogas production rate versus incubation time (see Figure 9), where Gaussian-like peaks are present. Each peak is believed to represent a different class of compounds based on their chemistries and metabolic source from the shrimp (carbohydrates, proteins, and fats and oils [lipids]). Digestion of carbohydrates is usually faster than proteins, and lipids tend to be the most recalcitrant among the three compounds.49,50 On the basis of this information, it can be inferred that the first peak represents the carbohydrates, the second peak the proteins, and the third peak shows degradation of fats present in the wastewater stream. These three classes of compounds have been found to be present in abundance in shrimp processing wastewaters.6,7,51,52 Generally, the carbohydrates, protein, and lipid compositions in shrimp wastes are in the 5−10, 30−50, and 5−20% range, respectively. The various rates of biogas produced also reflect three differing stages of substrate degradation. The pilot unit allowed evaluation of the optimized digestion system within a large bioreactor system similar to a full-scale system. The good quality biogas and gas production rates observed in the pilot study provide further evidence that a digester system could be effectively restarted several times over a year at shrimp processing plants with a very small lag phase (if at all) observed before a steady, effective digester system is quickly established. Economic Assessment. Using the experimental results from the anaerobic digestion of shrimp processing wastewater, the economics of the envisioned process in Figure 10 was estimated using Aspen Plus simulation software. It should be

noted that only electrical power was considered as product in this assessment. In the simulations, it was assumed that the feed streams are free and that the cost of electrical energy (as product stream) is $0.10 per kW-hr. Note that $0.10/kW-hr is often used as the US average industrial power cost.53 An initial economic analysis was performed to place a single digester at a typical processing plant with less than optimistic results being generated. It was decided to focus efforts on a centralized facility where multiple processors would collectively input their wastewaters into a large centralized system. Hence, the simulations were conducted based on a 2 MGD wastewater influent with a resulting power generation of 550 kW. The flow rate of 2 MGD is equivalent to two or three typical Gulf of Mexico Region shrimp processing plants combining their wastewaters. For this economic assessment, no tax credits or other financial benefits (such as selling coproducts other than the biogas) were included in the calculations. The 2 MGD wastewater influent might not be a realistic volume of wastewater coming from a single shrimp processor. However, this volume is reasonable by combining wastewater streams from multiple processors. Due to marginal economic outlooks for many digesters (biogas to power) from agricultural and food processing wastes, the concept of centralized or small-field regional digester systems is emerging.54 The economies of scale often offer a more attractive investment opportunity at larger facilities; plus, the capital and operational cost can be shared among multiple facilities, jointly contributing to the total influent. For example, Wolton and Lozo conclude that for siting anaerobic digester systems in Colorado, the breakeven number of cows at a farm needs to be larger than 2000 head, which they report is larger L


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Industrial & Engineering Chemistry Research than the state average head count of 1200.55 They further state that the concept of a “shared” centralized digester system would offer an economically viable option. Our results, shown in Table 3, indicate a payback period of about 9 years, which is higher than the one obtained by Carlini

time, not a consideration for a current to-date economic assessment. Other factors when evaluating the economic viability of anaerobic digestion should include odor issues/complaints, cost of treating the wastewaters using other treatment systems (such as activated sludge), sales credits as a green producer, and relative ease of operations. These factors are often difficult to place hard costs other than treatment costs, but they can provide economic benefits for a given situation. These were not considered for this study because the study was designed to be reflective of a typical shrimp processor within the North Gulf of Mexico Coast but not directed toward any one region or plant. Hence, these important secondary factors cannot be included in the present study.

Table 3. Summary of the Economic Assessment for the Use of a Centralized Anaerobic Digestion System (2 MGD) for Treating the Combined Wastewaters Generated at Several Shrimp Processing Facilities total project capital cost total operating cost total utilities cost total product sales desired rate of return payback period

$9.2M $2.8M/year $355 K/year $5.9M/year 20%/year 9.8 years

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CONCLUSIONS The shrimp industry along the Gulf Coast of the southern US operates on a part-time basis over the course of the year, meaning a series of starts and stops which results in a series of start-ups for a biotreatment process. Anaerobic digestion was found to be a sound option for this industry over traditional aerobic biotreatment. The addition of only the macronutrient nitrogen along with seeding via sludge taken from a digester from the local municipal wastewater treatment plant was found to provide an excellent anaerobic digestion system. This system produced a biogas with methane levels in excess of 70%, methane yield rates of 3.5 ft3 /pound of input COD, and COD removal generally above 70%. The various influent pretreatment methods targeting improved biogas production did not perform at levels supporting the additional cost and operational complexity. The impact of cycling operations appears to be well-handled by the selected anaerobic digestion system in that the start-up conditions evaluating with the Namended, microbial seeded system almost immediately produced an appreciable biogas yield and quality. The potential to produce VOAs or hydrogen using pretreatment methods targeting their production did not yield promising results. Even though the pilot system did not perform as well as the laboratory system, it did yield promising results for both treating the wastewater and producing a good quality biogas. A survey of economics indicates that the use of a centralized digestion system within a community of shrimp processors (small regional asset) is economically feasible for straight power offsets with a nine-year simple ROI calculated. Other monetary incentives (via state and federal policies) could likely reduce this ROI, as observed with other projects involving animal raising and food processing facilities using digester systems.

et al. for the economic performance of a codigestion plant fed with agro-industrial waste.56 They obtained a payback period of about 5 years for a 500 kW plant. However, a nine-year return on investment (ROI) is within the range reported by the EPA (2014) based on their analysis of six food waste to energy projects. They report that the ROIs for these projects ranged between 3 and 12 years. Note that the estimated costs for the centralized digester did incorporate both capitalization and annualized operational costs (O&M costs).57 Albeit not considered as part of the economic assessment, carbon trading (for methane emissions) and tipping fees (for received substrate or wastewater) can substantially increase the revenue of the centralized digester plant.58 These additional financial benefits are site-specific (regional, state, etc.). The economic analysis of this example aligns with the conclusions of Giesy et al., who report on their feasibility assessment of digestion treatment systems for power production at dairy farms that at a power rate of $0.10/kW-hr, engineered digester systems were not cost-effective options without government incentives.59 However, offsetting in-plant costs does enhance the economic attractiveness of the concept. Fersi et al. state that the offset of treatment costs via in-plant power production makes digestion attractive over simple wastewater treatment.60 In general, unless direct power is offset within the facility producing the wastes, digestion for power input into the grid is often not economically attractive.61 Oftentimes, unless secondary products such as fertilizer usage of the digestion residuals are used or nutrient displacement credits are available, longer payback times are to be expected without incentive programs (carbon credits, fuel credits, etc.). There is a developing market for biogas in which the gas is further energy-intensified (mainly through CO2 removal to a CH4 level of >90%) to become a “renewable natural gas” product.54 The US federal program, EPA Renewable Fuels Standards, allows biogas to be upgraded to a renewable natural gas and then be considered as an advanced biofuel.54,62 Thus, there exists a potential for biogas to serve as the primary fuel for meeting current and upcoming renewable fuel standards which could more than triple the value of biogas once converted to renewable gas standards (>90% CH4). Other coproducts from the digester could be evaluated such as the solids exiting the system, which in the case of shrimp will be mostly the chitinbased exoskeleton shrimp shells. There are emerging markets for chitin, but these markets are not mature and hence, at this

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Mark E. Zappi: 0000-0002-7608-076X Daniel Gang: 0000-0002-2565-0830 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to acknowledge the funding of this work from both Cleco Power (Pineville, LA) and the Energy Institute of Louisiana (EIL), located at the University of M


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V. A. The IWA Anaerobic Digestion Model No 1 (ADM1). Water Sci. Technol. 2002, 45 (10), 65−73. (19) Taconi, K. A.; Zappi, M. E.; Todd French, W.; Brown, L. R. Methanogenesis under Acidic PH Conditions in a Semi-Continuous Reactor System. Bioresour. Technol. 2008, 99 (17), 8075−8081. (20) Meegoda, J.; Li, B.; Patel, K.; Wang, L. Int. J. Environ. Res. Public Health 2018, 15, 2224. (21) Chowdhury, P.; Viraraghavan, T.; Srinivasan, A. Biological Treatment Processes for Fish Processing Wastewater - A Review. Bioresour. Technol. 2010, 101 (2), 439−449. (22) Digman, B.; Kim, D.-S. Review: Alternative Energy from Food Processing Wastes. Environ. Prog. 2008, 27 (4), 524−537. (23) Gunnarsdóttir, R.; Heiske, S.; Jensen, P. E.; Schmidt, J. E.; Villumsen, A.; Jenssen, P. D. Effect of Anaerobiosis on Indigenous Microorganisms in Blackwater with Fish Offal as Co-Substrate. Water Res. 2014, 63, 1−9. (24) Linder, M. Potential Study on Producible Biogas and Renewable Energy from Biomass and Organic Waste in Belize; Belmopan, Belize, 2016. (25) Anh, P. T.; My Dieu, T. T.; Mol, A. P. J.; Kroeze, C.; Bush, S. R. Towards Eco-Agro Industrial Clusters in Aquatic Production: The Case of Shrimp Processing Industry in Vietnam. J. Cleaner Prod. 2011, 19 (17), 2107−2118. (26) Khan, M. A.; Ngo, H. H.; Guo, W.; Liu, Y.; Zhang, X.; Guo, J.; Chang, S. W.; Nguyen, D. D.; Wang, J. Biohydrogen Production from Anaerobic Digestion and Its Potential as Renewable Energy. Renewable Energy 2018, 129, 754−768. (27) Fortela, D. L.; Hernandez, R.; French, W. T.; Zappi, M.; Revellame, E.; Holmes, W.; Mondala, A. Extent of Inhibition and Utilization of Volatile Fatty Acids as Carbon Sources for Activated Sludge Microbial Consortia Dedicated for Biodiesel Production. Renewable Energy 2016, 96, 11−19. (28) Dufreche, S.; Zappi, M.; Bajpai, R.; Benson, B.; Guillory, J. Today’s Lipid to Renewable Diesel Fuel Market. Int. J. Adv. Sci. Technol. 2012, 39, 49. (29) Shurtleff, W.; Aoyagi, A. History of Industrial Uses of Soybeans (Non-Food and Non-Feed): Extensively Annotated Bibliography and Sourcebook; Lafayette, CA, 2017. (30) Revellame, E. Activated Sludge as Renewable Fuels and Oleochemicals Feedstock; Mississippi State University, 2011. (31) Fortela, D. L. B. Enhancement of Microbial Oil and Biodiesel Production from Activated Sludge by Cultivation on Short Chain Fatty Acids; University of Louisiana at Lafayette, 2016. (32) Poggi-Varaldo, H. M.; Valdés, L.; Esparza-García, F.; Fernández-Villagómez, G. Solid Substrate Anaerobic Co-Digestion of Paper Mill Sludge, Biosolids, and Municipal Solid Waste. Water Sci. Technol. 1997, 35 (2), 197−204. (33) Hussain, A.; Mehrotra, I.; Kumar, P. Environ. Eng. Manage. J. 2015, 14, 769. (34) Banister, S.; Pretorius, W. A. Optimisation of Primary Sludge Acidogenic Fermentation for Biological Nutrient Removal. Water SA 1998, 24 (1), 35−41. (35) Suzuki, S.; Shintani, M.; Sanchez, Z. K.; Kimura, K.; Numata, M.; Yamazoe, A.; Kimbara, K. Effects of Phosphate Addition on Methane Fermentation in the Batch and Upflow Anaerobic Sludge Blanket (UASB) Reactors. Appl. Microbiol. Biotechnol. 2015, 99 (24), 10457−10466. (36) Appels, L.; van Assche, A.; Willems, K.; Degrève, J.; van Impe, J.; Dewil, R. Peracetic Acid Oxidation as an Alternative Pre-Treatment for the Anaerobic Digestion of Waste Activated Sludge. Bioresour. Technol. 2011, 102 (5), 4124−4130. (37) Goel, R.; Tokutomi, T.; Yasui, H. Water Sci. Technol. 2003, 47, 207. (38) Carrere, H.; Antonopoulou, G.; Affes, R.; Passos, F.; Battimelli, A.; Lyberatos, G.; Ferrer, I. Review of Feedstock Pretreatment Strategies for Improved Anaerobic Digestion: From Lab-Scale Research to Full-Scale Application. Bioresour. Technol. 2016, 199, 386−397.

Louisiana. Deep appreciation is felt toward the students and staff of the EIL for their assistance with this project. Finally, the project team acknowledges and thanks the Louisiana Public Service Commission for their support of the use of these funds and their dedication to finding cheap and effective alternative energy sources for the people of Louisiana, particularly with a strong focus targeted on waste generated at Louisiana industries.

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REFERENCES

(1) Spanos, T.; Hreinsson, E. United States Seafood Market Report. ́ Islandsbanki Research 2017, 1−52. (2) Debaere, P. Small Fish-Big Issues: The Effect of Trade Policy on the Global Shrimp Market. World Trade Rev. 2010, 9 (2), 353−374. (3) Keithly, W. The Southeast U.S. Shrimp Industry and Requests for Relief from the Increasing Import Base. In Proceedings of the Thirteenth Biennial Conference of the International Institute of Fisheries Economics & Trade, July 11−14, 2006, Rebuilding Fisheries in an Uncertain Environment; Portsmouth, U.K., 2006. (4) Keithly, W.; Poudel, P. The Southeast U.S.A. Shrimp Industry: Issues Related to Trade and Antidumping Duties. Mar. Resour. Econ 2008, 23 (4), 459−483. (5) Tabarestani, M.; Keithly, W. R.; Marzoughi-Ardakani, H. An Analysis of the US Shrimp Market: A Mixed Demand Approach 2017, 32, 411. (6) Mao, X.; Guo, N.; Sun, J.; Xue, C. Comprehensive Utilization of Shrimp Waste Based on Biotechnological Methods: A Review. J. Cleaner Prod. 2017, 143, 814−823. (7) Tay, J.; Show, K.; Hung, Y. Waste Treatment in the Food Processing Industry; Wang, L. K., Hung, Y.-T., Lo, H. H., Yapijakis, C., Eds.; CRC Press: Boca Raton, FL, 2006. (8) Rashmi Prabha, M.; Rout, S.; Navin, K.; Akhaya, P.; Chandrakanta, M.; Mishra, J. Assessment of Suitability of Processing Effluent Discharged from Quality Indian Seafood Exporter; Shimpo Exports: West Bengal, India, 2015; Vol. 4. (9) Islam, M. S.; Khan, S.; Tanaka, M. Waste Loading in Shrimp and Fish Processing Effluents: Potential Source of Hazards to the Coastal and Nearshore Environments. Mar. Pollut. Bull. 2004, 49 (1), 103− 110. (10) Boopathy, R. Biological Treatment of Shrimp Production Wastewater. J. Ind. Microbiol. Biotechnol. 2009, 36 (7), 989. (11) Cardoch, L.; Day, J. W.; Rybczyk, J.; Kemp, G. An Economic Analysis of Using Wetlands for Treatment of Shrimp Processing Wastewater - A Case Study in Dulac, LA 2000, 33, 93. (12) Casani, S.; Leth, T.; Knøchel, S. Water Reuse in a Shrimp Processing Line: Safety Considerations Using a HACCP Approach. Food Control 2006, 17 (7), 540−550. (13) Selmer-Olsen, E.; Ratnaweera, H. C.; Pehrson, R. A Novel Treatment Process for Dairy Wastewater with Chitosan Produced from Shrimp-Shell Waste. Water Sci. Technol. 1996, 34 (11), 33−40. (14) He, H.; Chen, X.; Sun, C.; Zhang, Y.; Gao, P. Preparation and Functional Evaluation of Oligopeptide-Enriched Hydrolysate from Shrimp (Acetes Chinensis) Treated with Crude Protease from Bacillus Sp. SM98011. Bioresour. Technol. 2006, 97 (3), 385−390. (15) Bueno-Solano, C.; López-Cervantes, J.; Campas-Baypoli, O. N.; Lauterio-García, R.; Adan-Bante, N. P.; Sánchez-Machado, D. I. Chemical and Biological Characteristics of Protein Hydrolysates from Fermented Shrimp By-Products. Food Chem. 2009, 112 (3), 671− 675. (16) Speece, R. E. Anaerobic Biotechnology for Industrial Wastewater Treatment. Environ. Sci. Technol. 1983, 17 (9), 416A− 427A. (17) Webb, A. R.; Hawkes, F. R. The Anaerobic Digestion of Poultry Manure: Variation of Gas Yield with Influent Concentration and Ammonium-Nitrogen Levels. Agric. Wastes 1985, 14 (2), 135−156. (18) Batstone, D. J.; Keller, J.; Angelidaki, I.; Kalyuzhnyi, S. V.; Pavlostathis, S. G.; Rozzi, A.; Sanders, W. T. M.; Siegrist, H.; Vavilin, N


Article

Industrial & Engineering Chemistry Research (39) Devlin, D. C.; Esteves, S. R. R.; Dinsdale, R. M.; Guwy, A. J. The Effect of Acid Pretreatment on the Anaerobic Digestion and Dewatering of Waste Activated Sludge. Bioresour. Technol. 2011, 102 (5), 4076−4082. (40) Ariunbaatar, J.; Panico, A.; Esposito, G.; Pirozzi, F.; Lens, P. N. L. Pretreatment Methods to Enhance Anaerobic Digestion of Organic Solid Waste. Appl. Energy 2014, 123, 143−156. (41) Da Silva, C.; Astals, S.; Peces, M.; Campos, J. L.; Guerrero, L. Biochemical Methane Potential (BMP) Tests: Reducing Test Time by Early Parameter Estimation. Waste Manage. 2018, 71, 19−24. (42) Rapport, J. L.; Zhang, R.; Williams, R.; Jenkins, B. M. Anaerobic Digestion technologies for the treatment of Municipal Solid Waste. Int. J. Environ. Waste Manage. 2012, 9, 100. (43) Wang, J.; Wan, W. Comparison of Different Pretreatment Methods for Enriching Hydrogen-Producing Bacteria from Digested Sludge. Int. J. Hydrogen Energy 2008, 33 (12), 2934−2941. (44) Shida, G. M.; Barros, A. R.; dos Reis, C. M.; Amorim, E. L. C. de; Rissato Zamariolli Damianovic, M. H.; Silva, E. L. Long-Term Stability of Hydrogen and Organic Acids Production in an Anaerobic Fluidized-Bed Reactor Using Heat Treated Anaerobic Sludge Inoculum. Int. J. Hydrogen Energy 2009, 34 (9), 3679−3688. (45) Carotenuto, C.; Guarino, G.; Morrone, B.; Minale, M. Heat Technol. 2016, 34, S425. (46) Bundhoo, M. A. Z.; Mohee, R.; Hassan, M. A. Effects of PreTreatment Technologies on Dark Fermentative Biohydrogen Production: A Review. J. Environ. Manage. 2015, 157, 20−48. (47) Sołowski, G. Biohydrogen Production - Sources and Methods: A Review. Int. J. Bioprocesses Biotechnol. 2018. DOI: 10.20911/ IJBBT-101. (48) Zabranska, J.; Pokorna, D. Bioconversion of Carbon Dioxide to Methane Using Hydrogen and Hydrogenotrophic Methanogens. Biotechnol. Adv. 2018, 36 (3), 707−720. (49) Angelidaki, I.; Ahring, B. K. Codigestion of Olive Oil Mill Wastewaters with Manure, Household Waste or Sewage Sludge. Biodegradation 1997, 8 (4), 221−226. (50) Alves, M. M.; Pereira, M. A.; Sousa, D. Z.; Cavaleiro, A. J.; Picavet, M.; Smidt, H.; Stams, A. J. M. Waste Lipids to Energy: How to Optimize Methane Production from Long-Chain Fatty Acids (LCFA). Microb. Biotechnol. 2009, 2 (5), 538−550. (51) Nargis, A.; Ahmed, K. N.; Ahmed, G. M.; Hossain, M. A.; Rahman, M. Bangladesh J. Sci. Ind. Res. 2007, 41, 63. (52) Ibrahim, H. M.; Salama, M. F.; El-Banna, H. A. Shrimp’s Waste: Chemical Composition, Nutritional Value and Utilization. Nahrung 1999, 43 (6), 418−423. (53) Moriarty, K. Feasibility Study of Anaerobic Digestion of Food Waste in St. Bernard, Louisiana; NREL: Golden, CO, 2013. (54) Ecoengineers. Anaerobic Digestion Systems & the WaterEnergy Nexus: A Study of the Impacts of Biogas Production in Iowa; 2016. (55) Wolton, L.; Lozo, S. Colorodo Market Assessment of Agricultural Anaerobic Digesters; Boulder, CO, 2009. (56) Carlini, M.; Mosconi, M. E.; Castellucci, S.; Villarini, M.; Colantoni, A. An Economical Evaluation of Anaerobic Digestion Plants Fed with Organic Agro-Industrial Waste. Energies 2017, 10, 1165. (57) Ely, C.; Rock, S. Food Waste to Energy: How Six Water Resource Recovery Facilities Are Boosting Biogas Production and the Bottom Line, EPA/600/R-14/240; EPA: Washington, DC, 2015. (58) Bishop, C.; Frear, C.; Shumway, R.; Chen, S. Economic Evaluation of Commercial Dairy Anaerobic Digester. CSANR 2010, 1−17. (59) Giesy, R.; Wilkie, A.; De Vries, A.; Nordstedt, R. Economic Feasibility of Anaerobic Digestion To Produce Electricity on Florida Dairy Farms. IFAS Extension University of Florida 2017, 1−7. (60) Fersi, S.; Chtourou, N.; Jury, C.; Poncelet, F. Economic Analysis of Renewable Heat and Electricity Production by Sewage Sludge Digestiona Case Study. Int. J. Energy Res. 2015, 39 (2), 234−243.

(61) Lazarus, W. Farm-Based Anaerobic Digesters as an Energy and Odor Control Technology Background and Policy Issues. USDA 2008, 1−37. (62) Jaffe, A.; Dominguez-Faus, R.; Parker, N.; Scheitrum, D.; Wilcock, J.; Miller, M. Feasibility of Renewable Natural Gas as a Large-Scale, Low Carbon Substitute. UC Davis 2016, 1−101.

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