Optimization and Characterization of Hydrochar Derived from Shrimp

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Optimization and Characterization of Hydrochar Derived from Shrimp Waste Shrikalaa Kannan, Yvan Gariepy, and G.S. Vijaya Raghavan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b00093 • Publication Date (Web): 03 Mar 2017 Downloaded from http://pubs.acs.org on March 6, 2017

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Optimization and Characterization of Hydrochar Derived from Shrimp Waste Shrikalaa Kannan§*, Yvan Gariepy§ and G.S. Vijaya Raghavan§ §

- Department of Bioresource Engineering,

Macdonald campus, McGill University, 21111 Lakeshore road, Sainte-Anne-De-Bellevue, Quebec, Canada H9X 3V9.

*All correspondence should be addressed to Shrikalaa Kannan Department of Bioresource Engineering, Macdonald campus, McGill University, Room MS-1 101, Macdonald Stewart Building, 21111 Lakeshore road, Sainte-Anne-De-Bellevue, Quebec, Canada H9X 3V9. E-mail: [email protected] Tel: 1-514-582-8939

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Abstract Shrimp, a most consumed seafood, when processed results in an enormous generation of wastes. Current ways of shrimp waste utilization are uneconomical and far from being environmentfriendly. Alternative sustainable technologies to utilize shrimp wastes completely are essential. Hydrothermal carbonization (HTC) that converts moisture-rich biomass into hydrochar is mostly employed for pure lignocellulosic biowaste. However, the suitability of HTC to produce good quality hydrochar from pure non-lignocellulosic waste such as shrimp waste is unknown. Here, for the first time, a response surface design guided optimization of microwave hydrothermal carbonization (MHTC) process parameters, holding temperature (150-210 °C) and time (60-120 min), showed that a temperature of ~184 °C and a time of ~112 min yielded maximal hydrochar (~42%). The atomic carbon and ash content, and calorific value of hydrochar were ~39-49%, ~21-25%, and 18.26-23.22 MJ/kg respectively, depending on the MHTC operating conditions. Taken together, these results confirm that MHTC produces hydrochar from shrimp waste of quality comparable to one produced from low-grade lignocellulosic, sewage and municipal wastes. Keywords: hydrothermal carbonization; microwave; shrimp waste; hydrochar; and response surface design. Abbreviations: HTC, Hydrothermal carbonization; MHTC, Microwave hydrothermal carbonization; DoE, Design of Experiment; RSM, Response surface design methodology; CCD, Central composite design; SEM, Scanning electron microscopy; HHV, High heating value; EEF, Energy enrichment factor.


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Introduction Seafood has been an important part of the human diet for centuries as they are a rich source of energy and nutrients. Seafood processing industries have seen a rapid growth in the past few years due to the increase in their demand. This sector, like other food processing industries, produces considerable quantities of waste. It is estimated that every year 6 to 8 million tons of shellfish waste (crab, shrimp, and lobster) are produced worldwide1. During shrimp processing, the head, and the outer shell is treated as waste after recovering the meat. According to Sachindra et al2, 45-48% by weight of the shrimp is discarded as waste depending on the species. Managing the enormous amount of waste from shrimp processing firms is a major cause for concern especially in developing countries where most of the wastes are dumped in landfill sites and oceans. This constitutes a serious environmental problem as the populations of endangered species are directly affected3. In the case of developed countries, waste disposal can be expensive which is not economically viable for these industries. Therefore, innovative solutions are needed to minimize environmental damage and maximize economic returns. Shrimp waste consists of 40% protein, 35% minerals and 14-30% chitin4. Chitin is a valuable biopolymer that has been often targeted for recovery from shrimp waste. Proteins are also frequently extracted from this waste and marketed as animal feed. Current techniques of utilizing this waste for extraction of value added products suffer from several disadvantages. For example, the traditional chemical method for isolating chitin from shrimp waste uses 4% NaOH for deproteinization and 4% HCl for demineralization. The use of such strong acid was found to have detrimental effects on the molecular weight and intrinsic properties of the purified chitin5. Moreover, the current techniques of chemical extraction are hazardous and uneconomical due to the use of harmful and corrosive chemicals.


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Hydrothermal carbonization is a thermo-chemical process that converts biomass at elevated temperature and pressure into a carbon-rich product called hydrochar. This process takes place in the presence of water and therefore does not require an energy intensive predrying step as in the case of pyrolysis6. However, the use of HTC for animal wastes like seafood waste is a very challenging and unusual approach. This is because HTC was primarily and predominantly used to treat plant-derived lignocellulosic biomass to manufacture highly functionalized carbon materials7-9. The use of this technique has since extended to other complex waste streams such as municipal waste10-12, food waste13-15, human biowaste16, and sewage sludge17, 18. The main challenge with seafood waste being subjected to this technique is that these wastes are rich in complex proteins and fats with a lesser amount of carbohydrates as compared to plant-derived waste. They contain neither lignin nor cellulose and can be broadly called as non-lignocellulosic wastes19, 20. To our knowledge, there has been no earlier report on the production of hydrochar from a pure non-lignocellulosic waste source such as shrimp waste. Microwave hydrothermal carbonization utilizes microwaves to heat the biomass, unlike conventional HTC where heat transfer occurs through temperature gradients (conduction and convection). Microwaves heat the material from within as they work on the principle of dielectric heating. The high moisture content of the raw seafood waste is favorable for microwave heating as the water molecules that readily couple with electromagnetic fields results in microwave dielectric heating. This heating is a result of the dipolar rotation and polarization of water molecules in response to an applied electromagnetic field. There is a phase lag between the dipole polarization and the alternating applied electromagnetic field resulting in dielectric loss and friction between the molecules. This results in the generation of heat from within the


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material. Therefore, microwaves help address the shortcomings of conventional heating methods by providing a uniform and rapid heating method21. Microwave hydrothermal carbonization (MHTC) is still in its nascent stages and has been used thus far to carbonize lignocellulosic biomass and human bio-waste16, 22, 23. Recently, it was shown that a pure non-lignocellulosic waste such as seafood waste could be utilized by MHTC to produce hydrochar24 after enzymatic pre-treatment. However, the effect of the MHTC process parameters on the yield of hydrochar, and characteristics of hydrochar such as elemental and proximate composition, energy value, and morphological features are not known. The lack of this knowledge makes it hard to predict the potential uses of the hydrochar. This study, first, aims to optimize the process conditions to produce a maximal yield of hydrochar from enzymatically pre-treated shrimp waste using MHTC. Next, the chemical, material, energy, and morphological properties of the hydrochar will be characterized to facilitate the prediction of potential uses of hydrochar. Materials and Methods Sample preparation Shrimp waste comprising of heads, tails, and shells from a variety of shrimps including pink shrimp, tiger shrimp and brown shrimp were obtained fresh from the local market, stored, and processed as previously described in Kannan et al., 201524. Enzymatic hydrolysis Enzymatic hydrolysis was carried out using three commercial enzymes namely Viscozyme (catalog no.: V2010), lipase (catalog no.: L0777), and protease (catalog no.: P4860) as previously described24. Briefly, 20 g of minced shrimp waste was homogenized with a foodgrade blender. The enzyme cocktail (20%, w/w of each enzyme) was then added to the


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homogenized waste in the ratio of 1:1:1 (Viscozyme: Protease: Lipase; w/w/w). Then the digestion was carried out in a laboratory incubator/shaker (Incushaker mini, Benchmark Scientific, USA) at ~40 °C with rotation at 120 rpm for a period of 6 h. The enzyme concentration of 20% w/w, enzyme ratio of 1:1:1, and treatment time of 6 h were found to be the optimal conditions that resulted in the maximal digestion of the shrimp waste as described previously24 and further confirmed here (Supplementary data Figure S1). Microwave hydrothermal carbonization MHTC was performed using the Mini-WAVE Digestion Module (SCP Science, Canada) that operates at a frequency of 2.45 GHz as previously described24. The product of MHTC process was then subjected to vacuum filtration to separate the solid fraction (i.e., wet hydrochar) from the liquid, biocrude liquor. The wet hydrochar was then oven-dried at 105 °C for 24 h to produce dry hydrochar. The yield of the hydrochar was calculated on a dry basis.

ℎ % =

! " # $

× 100 …………. (1)

Screening of MHTC process parameters MHTC process parameters namely holding temperature (°C), holding time (min) and biomasswater ratio (biomass water ratio = mass of waste /mass of water) were tested for their impact on the yield of hydrochar produced. From a previous study, it was known that a holding temperature of 150 °C, a holding time of 60 min, and biomass-water ratio of 1 results in the production of hydrochar from shrimp waste24. As this is the first-time optimization of MHTC of shrimp waste is conducted, the parameters that significantly affected the yield of hydrochar from shrimp waste was first tested by conducting a screening study, where one of the parameter was varied while having the other two at constant values. First, the effect of holding temperature was tested by varying it from 150 °C to 210 °C while having a constant holding time of 60 min and biomass-


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water ratio of 1. Second, the effect of holding time was tested by varying it from 60 min to 120 min, while having the holding temperature and biomass-water ratio constant at 180 °C and 1 respectively. Finally, the effect of biomass-water ratio was tested by varying it from 0.5 to 1.5 while having the holding temperature and time constant at 180 °C and 60 min respectively. A significant effect was determined by students’ t-test at α=0.05. MHTC optimization protocol As the central composite design (CCD) renders an even distribution of the experimental points, it can be used in response surface methodology (RSM) to implement the design of experiment (DoE) approach to optimize the process parameters of MHTC, namely holding temperature and time to maximize the yield of hydrochar. Biomass-water ratio is excluded from the optimization study, as in the screening study, it was not found to have a significant impact on the yield of hydrochar (see Figure 1). CCD design involves the use of two-level factorial design with 2k factorial points, 2k axial points and n centre points; where k is the number of factors. The total number of experiments, N, is given by the following equation, ( = 2* + 2, + -……………………..(2) With two factors, namely the holding temperature and time, the CCD design has 4 factorial points, 4 axial points, and 5 center runs. Due to technical limitations, a face-centered non-rotatable design was implemented as the Mini-WAVE system has a very narrow operating temperature range. For holding temperature, the minimal and maximal limit (-1,1) was set to 150 and 210 °C. For the holding time, the maximal and minimal limit (-1,1) was set to 60 and 120 min. A 5-center run was adapted to improve the reliability of this model. As MHTC is being optimized for the first time for shrimp waste, DoE was performed in duplicates. MHTC was performed in a random fashion to account for any random hidden effects that may be present.


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Significant effects were analyzed using ANOVA (analysis of variance) through DoE suite in JMP. The main effects and a further model building were implemented by using F-test (Fisher test) and probability values (α= 0.05). This design resulted in total 13 runs per experiment. The second order linear regression model as below could be used to model the output variable i.e. hydrochar yield (%). = ./ + .010 + .2 12 + .02 10 12 + .00 102 + .22 122 + 3 ……………. (3) The experimental results from MHTC trials were fitted to the above equation using SAS statistical software, JMP licensed to McGill University. Characterization of hydrochar Chemical and energy properties of hydrochar Elemental and proximate analyses were conducted to characterize the chemical composition of the hydrochar produced at varying MHTC process parameters. The elemental composition i.e. C, H, N and S were determined using an elemental analyzer (Fisons Instruments CHNS-O EA 1108). Shrimp waste hydrochar and raw waste samples were analyzed for moisture content, ash content, and volatile solids per ASTM International Standard protocols. First, to decipher the moisture content, 1.0 g of hydrochar was placed in a hot air oven at 105 °C until a constant weight was achieved. Weights were noted initially after 4 h and after every hour after the initial 4 hour period (ASTM 871-82, 2006)25-27. Second, to measure the ash content, 1.0 g of the test sample was taken in an open crucible and placed in a muffle furnace that was at 600 ± 10 °C for 4 h. The weight was noted after the crucible was cooled (ASTM-D 3174-04, 2009)25-27. Finally, to measure the volatile matter, 1.0 g of test sample was placed in a muffle furnace that was at 950 ± 10 °C for 7 min (ASTM-D 3175-07)25-27. The total fixed carbon was determined by the difference from 100, considering the percentile amounts of moisture, volatile matter, and ash


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content. Energy value was determined using a Parr adiabatic bomb calorimeter (Parr Oxygen Bomb Model 1341EB, Calorimeter Thermometer Model 6772, Parr Instrument Company, Moline, IL, USA) to calculate higher heating value (HHV) as previously described28, 29. Scanning electron microscope (SEM) The raw shrimp waste samples and recovered hydrochar at various operating conditions were analyzed for their surface morphology and microstructure by a Hitachi TM-3000 (Tokyo, Japan) scanning electron microscope for comparative microstructural analysis. Varying resolutions from 50X to 1500X was used to analyze the morphological structure. Results and discussion Screening of MHTC process parameters An initial screening design was performed to assess the effect of the process parameters namely holding time, holding temperature and biomass to water (w/w) ratio on the yield of hydrochar. First, an increase in the holding temperature from 120 °C to 180 °C (holding time and biomasswater ratio was kept constant at 60 min and 1 respectively) resulted in an increase in the yield of hydrochar from 19.65 ± 0.98 % to 33.93 ± 0.81 % (Figure 1A, significantly different, n = 3, student’s t-test, P < 0.0001). However, upon further increase in the holding temperature from 180 °C to 210 °C, the yield of hydrochar remained stable at 35.53 ± 1.19 % (Figure 1A, significantly not different from hydrochar yield at 180 °C, n = 3, student’s t-test, P = 0.24). Therefore, MHTC holding temperature significantly affects the hydrochar yield albeit in a complex manner. Second, upon increasing the MHTC holding time from 60 to 120 min (holding temperature and biomass-water ratio was kept constant at 180 °C and 1 respectively), the hydrochar yield increased from 33.93 ± 0.81 % to 44.71 ± 0.51 % (Figure 1B, significantly different, n = 3, student’s t-test, P < 0.0001). This result indicates that the holding time significantly affects the


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yield of hydrochar. The yield of hydrochar produced from lignocellulosic waste12, 22, 23, 30, 31, algae32, sewage sludge16, human biowaste16, food waste14, 15, and municipal streams10-12 was found to be influenced by the holding temperature and time. A similar complex trend of hydrochar yield with respect to holding temperature and time is observed with sewage sludge16. In another study, the yield of hydrochar from MHTC of cellulose at 200 °C decreased as the holding time increased23. An increase in the holding temperature leads to increased loss of organic matter in the biomass as the volatile matter at higher temperatures increases33 and thus leads to a reduction of hydrochar yield as the holding temperature increases31. The complex macromolecular structure of the shrimp waste that consists of carbohydrates, proteins, and lipids might lead to the observed complex trend of hydrochar yield from MHTC of shrimp waste. Finally, upon increasing the biomass-water ratio from 0.5 to 1.5 (holding time and temperature were kept constant at 60 min and 180 °C respectively), the hydrochar yield remained constant (Figure 1C, not significantly different, student’s t-test, P = 0.38). This result shows that the biomass-water ratio does not seem to affect the yield of hydrochar. Taken together, these results indicate that the MHTC holding time and temperature significantly determine the yield of hydrochar. Optimization of MHTC process parameters For further thorough optimization of MHTC of shrimp waste, response surface design guided study of each significant parameter, i.e. holding temperature and time to maximize the yield of hydrochar were undertaken. Face-centered central composite design (Figure 2A) was adapted in this study due to technical limitations, as MHTC equipment used in this study cannot hold the biomass at temperatures higher than 210 °C reliably. Therefore, use of star points that could facilitate more sophisticated rotatable design could not be implemented.


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It is evident from Figure 2B that the hydrochar yield increases with increasing temperature and time up to a certain point and then hydrochar yield decreases with further increase in holding temperature and time, forming a response surface that looks like an inverted parabola. The surface plot indicates that there are slopes for both factors holding temperature and time suggesting that the response variable, i.e. hydrochar yield is affected by both the factors. First, upon examining the effect of each parameter, it was found that both the holding temperature (F(1,25) = 26.75; P ? @ A , >C = 0.2920 >D- -: -: + 7.0443……….. (5) One of the other common ways used to estimate the calorific value is based on the unified model developed by Channiwala and Parikh 200247, that is based on the elemental analysis of solid fuels that encompasses a wide variety of biomass including lignocellulosic waste such as agricultural waste, woody biomass, and also mixed waste such as sewage sludge, animal waste and municipal waste47. The model equation is as below (HHV = high heating value),


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C = 0.3491> + 1.1783 + 0.1005F − 0.1034G − 0.0151( − 0.0211H (MJ/kg) …....(6) The interesting fact here is that the unified model has incorporated data from animal waste to predict HHV. The composition of the kind of animal waste used in the model development is not known, however, it should be rich in non-lignocellulosic biomass. The above equation was used to compute the HHV values based on the proximate analysis of the hydrochar produced from shrimp waste. Interestingly, it was found that the HHV calculated from above equation and the actual calorific value calculated from bomb calorimetry matched well (R2 = 0.65; P = 0.042; Supplementary data Figure S3A and B). Despite the model being barely significant, it always predicted the HHV values to be higher than the actual values irrespective of the MHTC operating conditions. This is further evident from the percentage difference between the actual and predicted values that ranges from ~16 to 40%. The fit model equation is as below, H:A ? @ A = 1.0444 I : ? @ A − 7.5709 … … 7 The authors recommend the readers to exercise caution when using the model developed by Channiwala and Parikh 200247 to predict the HHV values of hydrochar produced from shrimp waste. Taken together, these results suggest that the hydrochar obtained by MHTC of shrimp waste has good energy densification and energy yield. The calorific value is in comparison to the hydrochar obtained from lignocellulosic biomass48, food waste13, sewage sludge16 and human biowaste16. The calorific value as obtained from the bomb calorimetry indicates that hydrochar from shrimp waste resembles lignite18. SEM analysis of hydrochar SEM micrographs enabled the analysis of the microstructure of hydrochar produced by MHTC of shrimp waste at varying operating conditions (Figure 6A). The SEM micrographs revealed interesting surface features of the hydrochar obtained at different operating conditions. At first


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glance, compared to raw shrimp waste (Figure 6B), hydrochar irrespective of the operating conditions looks very different. The raw material is unstructured, flaky, and appeared as blobs of clustered biomass. However, at MHTC holding temperature of 150°C, carbonization process has resulted in the transformation of the surface morphology of hydrochar as is evident from the improved surface structure of the hydrochar. Close examination revealed that at this holding temperature, microspheres can be rarely discerned. However, upon increasing the holding temperature of the MHTC process from 150°C to 180°C and 210°C, the microspheres formed during carbonization are clearly visible (Figure 6A and 6C). Other structures resembling a form that can be discerned as flower or snowflakes are also seen irrespective of the MHTC operating conditions (Figure 6D). In addition to microspheres, plate-like structures were also observed with cracks that had a higher incidence than microspheres. Such cracks are likely to be formed during the release of volatile substances during MHTC. These transformations are very interesting and thus indicate the decomposition of the monomers of the complex macromolecules such as carbohydrates, proteins and lipids and subsequent precipitation and growth into spheres. Different microstructures of hydrochar due to different operating conditions is also seen in other types of biomass such as lignocellulosic biomass49. In summary, this characterization study of hydrochar produced from MHTC of shrimp waste shows that it is of quality (elemental composition, proximate composition, morphological structure and energy value) comparable to one produced from low-grade lignocellulosic waste and mixed waste. These results strongly suggest that, like hydrochar made from lignocellulosic waste, shrimp waste hydrochar, firstly, can be used as a coal-substitute. Secondly, the microstructure of hydrochar, particularly ones produced at higher holding temperatures, suggests that the hydrochar is porous and could be suited for adsorbent and sequestration purposes.


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Hydrochar from lignocellulosic biomass has often been deemed to be unstable in soil for effective carbon sequestration43. Evaluating shrimp waste hydrochar for soil amendment purposes will be very interesting to check if hydrochar produced from non-lignocellulosic wastes exhibit higher stability in soil. Evaluating the heavy metal composition in shrimp waste hydrochar in future experiments would be critical in evaluating its suitability to be used as a soil amendment and in agriculture applications. Conclusions In this study, the MHTC process parameters were optimized to maximize hydrochar yield, and further, the chemical and material properties of the hydrochar were characterized. (1) It was found using RSM design that the MHTC holding temperature of ~184°C and holding time of ~112 min produced a maximal yield (~42%) of hydrochar. (2) The atomic carbon content and ash content of the hydrochar was found to be ~39-49% and ~21-25%, respectively. The elemental and material characteristics of the shrimp waste hydrochar was found to be comparable to hydrochar produced from lignocellulosic waste, sewage sludge, and human biowaste. (3) Interestingly, the calorific value of the hydrochar varies from 18.26 to 23.22 MJ/kg, and is found to be comparable to one produced from lignocellulosic waste, food waste, sewage sludge, and human biowaste. Thus, for the first time, it is shown that MHTC of pure nonlignocellulosic waste like shrimp waste could yield hydrochar of good quality. This process thus presents potential multifaceted benefits. First, this strategy is a sustainable utilization of shrimp waste without leaving behind or generating new waste. Second, this process yields hydrochar of quality comparable to one made from low-grade lignocellulosic and mixed wastes. These results suggest that hydrochar from shrimp waste could be potentially used for energy, carbon sequestration and agriculture applications.


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Author contributions SK designed experiments, collected and analyzed data, made figures, and wrote the manuscript, YG designed experiments, and GSVR designed experiments, analyzed data and helped write the manuscript. Acknowledgements The authors are grateful to Dr. Valerie Orsat for providing access to the FTIR equipment. The authors would like to acknowledge ‘Elemental Analysis Service’ at the University of Montreal, and Dr. Arif Mustafa and Mr. Wucheng Liu for their help with bomb calorimetry experiments. The authors would like to acknowledge Dr. Darwin Lyew, and Dr. Ramesh Murugesan for their helpful discussions during the research. Funding: This work was supported by operating grants from Natural Sciences and Engineering Research Council of Canada (NSERC) to GSVR and it was also supported by Faculty for the Future grant by Schlumberger Foundation to SK. Supplementary information Figure S1. Effect of enzyme concentration and treatment time on the enzymatic hydrolysis of shrimp waste. Figure S2. Comparison of actual calorific value to predicted value computed from carbon content. Figure S3. Energy value prediction model for shrimp waste hydrochar. Figure S4. FTIR spectra of raw shrimp waste and hydrochar produced after MHTC. Table S1. Elemental analysis of the hydrochar made from MHTC of shrimp waste. Table S2. Proximate analysis of the hydrochar made from MHTC of shrimp waste. Table S3. FTIR spectra of hydrochar produce from MHTC of shrimp waste.


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Figure captions Figure 1. Screening of MHTC process parameters of shrimp waste. Effect of (A) Holding temperature, (B) Holding time, and (C) Biomass-water index on the yield of hydrochar. Data indicate Mean ± S.E.M from triplicate experiments. *P

Optimization and Characterization of Hydrochar Derived from Shrimp

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