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Enhanced biogas production from co-digestion of intestine waste from slaughterhouse and food waste S Porselvam, B Mahendra, S.V. Srinivasan, E Ravindranath, and R Suthanthararajan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01764 • Publication Date (Web): 11 Sep 2017 Downloaded from http://pubs.acs.org on September 13, 2017

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• Batch co-digestion with a uniform feed of IWS, FW and mixing ratios (1:1 to 1:5) were investigated. • Mixing of IWS and FW on VS basis was increased the C/N ratio • The maximum biogas production of 0.43 L/g of VS added was observed in 1:2 (IWS:FW) ratio which is 57% and 17% higher than the individual.

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Enhanced biogas production from co-digestion of intestine waste from slaughterhouse and food waste S. Porselvam, B. Mahendra, S.V. Srinivasan,* E. Ravindranath, R. Suthanthararajan Environmental Science and Engineering Division, CSIR-Central Leather Research Institute, Chennai – 600020, India Corresponding author email: [email protected] Abstract: Presence of higher protein and lipids contents of the Intestine waste from slaughterhouse affects the anaerobic digestion (AD) process due to VFA accumulation and ammonia toxicity. The aim of the present batch reactor study was to evaluate the effect of mixing ratio on anaerobic codigestion of intestine waste from the slaughterhouse (IWS) and carbon-rich food waste (FW) to enhance the biogas production and to optimize C/N ratio for improving the efficiency and better performance of AD. Biogas productions were estimated for various mixing ratios on VS basis (IWS: FW - 1:1, 1:2, 1:3, 1:4 and 1:5) keeping inoculum to substrate ratio maintained at 0.5 as per German method VDI 4630. Based on the present study, the biogas productions of different mixing ratio at the end of 30th day were found to be in the order of 0.43 (1:2) > 0.39 (1:3) > 0.38 (1:1) > 0.36 (FW) > 0.35 (1:4 & 1:5) > 0.18 (IWS) L/g of VS added. Similarly, the VS removal efficiencies were in the order of 64.02% (1:2) > 61.28% (1:3) > 60.91% (FW) > 60.34% (1:4) 60.21% > (1:2) > 60.15% (1:1) > 47.69% (IWS). Results of the study reveals that, the mixing ratio of 1:2 is found to be the suitable mixing ratio which resulted in enhancement of biogas production by 57% and 17% 1


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when compared with IWS and FW alone respectively. The lowest theoretical retention time of 12 days was observed in mixing ratio of 1:4 with biogas production of 0.28 L/g of VS added while in the mixing ratio of 1:2, the biogas production of 0.35 L/g of VS added was achieved in 13 days. Keywords: Slaughterhouse waste; IWS, Food waste; Biogas Production; VDI method; C/N ratio

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1. INTRODUCTION The slaughterhouse is one of the major industries cater to the needs of meat production industry, tannery and meat by-product recovery industries. Due to the demands of local and export market, commercial slaughterhouses are increasing day by day. It is estimated that the average solid waste generated during slaughtering of buffalo and small animals (sheep and goat) as 275 and 170 kg/tonne of live weight killed respectively.1 The quantity of solid waste generation from slaughterhouses is not uniform and varies depending on the kind of slaughtering process (manual, semi-mechanical & mechanical system) and scale of operation (small, medium and large scales).2 Currently, there is no specific treatment method or scheme practiced for slaughterhouse solid waste especially in municipal slaughterhouses.

3

The solid waste from the slaughterhouse is

being disposed along with municipal solid wastes in open dumps in most of the cities and towns. It leads to foul odor nuisance, groundwater contamination and also gaseous emissions like CO2 and methane contributing to global warming. Various treatment methods are available for treatment of slaughterhouse solid waste like rendering, controlled incineration, burial, composting, anaerobic digestion etc.4 However, few of the commercial slaughter houses have employed rendering plants for animal carcass waste and AD for dung. AD is a suitable method to treat animal wastes as well as recovery of energy.5 Moreover, AD is a better option as it requires less area and energy when compared to composting and controlled incineration and it is more suitable for Indian scenario where already availability of land is an issue in urban areas for waste treatment. The AD process involves series of reactions such as hydrolysis, acidogenesis, acetogenesis and methanogenesis during degradation of organics and recovery of biogas.6,7 The AD process is strongly influenced by


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operational parameters such as pH, VFA, alkalinity, C/N ratio, etc 8 which needs to be taken care during the operation of the plant. One of the major solid wastes from the slaughterhouse is intestine waste. Intestine waste from the slaughterhouse (IWS) contains high protein and lipid contents with low C/N ratio in the range of 2 - 5 9,10 whereas the optimum C/N ratio requirement for the anaerobic process is 25 – 35.11 During AD of animal waste with low C/N ratio, the rapid dissociation of ammonium into ammonia, higher pH value than the optimum12,13 resulting ammonia toxicity in the reactor and affects the biogas production.14,15 Similarly, the formation of long-chain fatty acids (LCFA) from lipids restricts the rate limiting step of hydrolysis resulting in accumulation of VFA in the reactor which harms the acetogenic bacteria and methanogens.16 Co-digestion is a suitable option to overcome the above problem associated with AD of animal waste. Co-digestion is a process to mix different wastes and treat wastes together17 in AD to reduce the concentration of nitrogen18,19 i.e., codigestion of protein and lipid rich IWS with carbon-rich FW. FW is more suitable co-substrate for anaerobic co-digestion as it contains high moisture, C/N ratio and VS content.20 Co-digestion improves the AD of animal organic wastes by providing several benefits to the process such as dilution of toxic compounds, improvement in balancing of nutrients including C/N ratio and hence ultimately resulted in higher biogas production21 and better stability of the reactor. Co-digestion of slaughterhouse waste with other organic waste such as fruit and vegetable waste (0.27–0.35 L/g VS);22 combination of manure, various crops and the organic fraction of municipal solid waste (0.65 L/g VS);23 organic fraction of municipal solid waste (0.40-0.50 L/g VS)24-26 and sewage sludge (0.43 L/g VS)27 have been reported. Based on the major research gaps identified from the literature, the present study involved novel approach of maximum biogas production from IWS and FW (VS/VS basis) with specific inoculum to substrate ratio of 0.5 at 35°C. The major objective of 4 ACS Paragon Plus Environment

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the study is to optimize the mixing ratio (IWS/ FW) and retention time for enhancement of biogas production and higher removal efficiency. 2. MATERIALS AND METHODS 2.1 Substrate and inoculum. Anaerobic sludge (inoculum) was collected from anaerobic digester from sewage treatment plant at Perungudi, Chennai, India. Intestine waste was collected from meat shops at Chennai, India and the co-substrate food waste (FW) i.e segregated canteen cooked waste without vegetables were collected from CLRI campus canteen, Chennai, India. 2.2. Experimental set-up. Experimental set-up of the batch reactor is shown in (supporting information) Figure S1. The capacity of batch experimental reactor is 600 ml and headspace of 400 ml was maintained for the accumulation of biogas. The batch reactor was closed with airtight silicone rubber lid, which is more suitable for measuring the biogas using needle arrangement connected to a manometer and also ensures complete tightness and also avoids biogas leakage. The batch reactor study was carried out in a temperature-controlled incubator and the temperature was maintained at 35º C.28 In the incubator, the individual batch reactor is provided with a magnetic stirrer for providing mixing arrangement in the reactor. In batch reactor studies, the inoculum and substrates were added in each batch as per the requirements with triplicates and head space of 400 ml were maintained in all the batch reactors as per German method VDI 4630. The biogas productions from each batch reactor were monitored at regular intervals by measuring the increase in pressure inside the reactor. For monitoring the batch reactor performance, one set of batch reactors were removed from the incubator at regular intervals of 10th, 20th and 30th day and the contents of the batch reactor were collected, analyzed and the values are reported.


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As per experimental investigations, control batch reactors were fed with IWS and FW separately. Experimental batch reactors were fed with a different mixing ratio of IWS and FW (1:1, 1:2, 1:3, 1:4, 1:5) based on VS content and wet weight basis. In this batch study, VS ratio of the substrate (10.59 g) to inoculum (5.3 g) was added to maintain inoculum to substrate ratio of 0.5 in all the reactors.20 Biogas production was calculated by using the following eq.1 ܸ‫ܸ = ݋‬.

ሺܲ − ܲ‫ ݓ‬ሻ. ܶ0 ܲ0 . ܶ

(1)

Where, Vo - Volume of dry gas at standard temperature and pressure (STP) in normal state (ml), V – Actual volume of the gas generated (ml); P – pressure of the gas phase at the time of reading (hPa); Pw – Vapour pressure of the water as a function of the temperature of the ambient space (hPa); To - Normal temperature (273 K); Po – Normal pressure (1013 hPa); T – Temperature of the fermented gas or of the ambient space (K). 2.3. Analytical methods. Initial characteristics pH, TS, VS and moisture content of inoculum and substrates were analyzed as per standard methods.29. The carbohydrate estimation was done according to the Phenol-sulphuric acid method.30 Protein concentration was determined as per Bradford method employing bovine serum albumin as the standard.31 The estimation of lipid was determined by the phospho-vanillin method.32 Volatile fatty acid was estimated by the direct distillation method. Total ammonia nitrogen was estimated as per standard methods and the free ammonia concentration was calculated based on Eqs 2- 3.33 ‫= ܣܨ‬

ܶ‫ܰܣ‬ 1 + 10 ܲ‫ ܽܭ‬−ܲ ‫ܪ‬

ܲ‫ = ܽܭ‬0.09018 +

(2)

2729.92 ܶ + 273.15

(3)


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Where FA is the free ammonia concentration (mg/L), TAN is the total ammonia nitrogen (mg/L), pKa is the dissociation constant for the ammonium ion and T is the temperature in ◦C. The methane content in the biogas of headspace of the reactor was determined using a Gas Chromatograph (Chemito7610 series) equipped with a thermal conductivity detector (GC-TCD) and Poropak Q column for this study. The temperature of the column, the injection port and the detector were 60˚ C, 60˚ C and 90˚ C respectively. Nitrogen was used as carrier gas at a flow rate of 30 ml min-1. Gas samples (500µl) in the head space were collected using a pressure-lock gas syringe and injected into GC. The results were interpreted using the Clarity Lite software. 2.4. Batch Kinetic models. The pseudo-first and pseudo-second order kinetic studies on VS degradation rates were performed for the anaerobic co-digestion of IWS, FW individually and different mixing ratios of IWS and FW using the following kinetic equations of (Eq 4 and 5). [‫ݐ]ܥ‬ ൰ = −‫ܭ‬1 [‫]ܥ‬0

(4)

1 1 =൬ ൰ + K2 t [C]t [C]0

(5)

ln ൬

Where, [C]0 is the concentration of VS at time t=0; [C]t is the concentration VS at time “t”; t is time in days; k1 and k2 are the pseudo first order and second order rate constants respectively. The first-order model based on the availability of substrate as the limiting factor was used3436

to evaluate the performance of biogas production in the current study.

From the basic equation: dB/dt=-kB

(6)


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Where “k” is the first-order substrate utilization rate constant (time-1) and B (mg/L) represents the biodegradable substrate concentration. On integration, Eq 6 becomes: B = e−kt B0

(7)

Where, B0 (mg/L) represents initial substrate concentration. Substrate concentration can be correlated with biogas production (Y) as mentioned below:

ሺY∞ − Yሻ B = Y∞ B0

(8)

Where, Y∞ is the maximum biogas production at infinite digestion time. From the above two equations Eq 7&8, the integrated equation for the first-order model, which provides the analytical relation between the volume of biogas produced and digestion time was obtained and used to quantify the extent of biogas production as follows: 37

Y = Y∞ [ 1 − e−kt ]

(9)

Where, k (time-1) is the first-order biogas production rate constant. Taking Napierian logarithms in the above equation and ordering the terms, the following equation is obtained:

Y∞ ln ൤ ൨ = kt ሺY∞ − Yሻ

(10)

3. RESULTS AND DISCUSSIONS 3.1. Characteristics of substrates and inoculum. The characteristics of anaerobic sludge (inoculum), IWS and FW are given in Table 1. The pH of anaerobic sludge and IWS were observed


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to be 7±0.4 and 7.8 ± 0.2 respectively which is the suitable and optimal pH range for AD process and for the methane-producing microbes (6.5-7.8).38-40 From the Table 1, it is observed that the total solids (TS), volatile solids (VS) and VS/TS ratio of IWS and FW were found to be higher indicating that the substrates are more suitable for AD process. Similarly, the presence of higher protein and lipids concentrations in IWS (35.38 ± 0.01 & 14.0 ± 0.05 % w/w basis) than FW (18.54 ± 0.06 & 6.42 ± 0.06 % w/w basis), which is also represented by lower and higher C/N ratio of 3.4 and 38.5 in IWS and FW respectively. From results of elemental analysis, it is found that the nitrogen content in IWS is 14.9 % while for FW it is only 2.1%. AD of wastes with higher nitrogen content leads to ammonia toxicity in the reactor and affects the methanogenic activities which in turn affects biogas production.41-43 The mixing of IWS and FW based on VS content and wet weight basis with different ratios of 1:1, 1:2, 1:3, 1:4 and 1:5 resulted in the C/N ratios of 19.2, 26.4, 29.7, 34.1, and 36.8 respectively, which resulted in improvement of C/N ratio and also found to be more suitable for AD.

3.2. Effect of mixing ratio of IWS and FW on biogas production. The cumulative biogas productions from experimental reactors for IWS, FW and various mixing ratios of IWS & FW (1:1, 1:2, 1:3, 1:4 and 1:5) are shown in Figure 1. In the batch study, the digested samples were collected at different time intervals for estimation of pH, VFA, alkalinity, TAN, TS and VS content at the end of 10th, 20th and 30th days. The biogas production (L/g of VS added) and VS removal efficiency were estimated at the end 10th, 20th and 30th days for IWS, FW and various mixing ratios of IWS & FW and the results are depicted in Figure 2a&b. Similarly, the profile of pH, VFA, alkalinity, TAN and free ammonia were estimated and shown in Figure 3 a-e. Based on the results obtained at the end of 10th day, biogas production of IWS and FW were found to be 0.08 and 0.24 L/g of VS added


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and the VS removal efficiency were found to be 23.51 and 49.29 % respectively (Figure 2b). Similarly, the results of different mixing ratio of 1:1, 1:2, 1:3, 1:4 and 1:5 (IWS: FW), the VS removal efficiencies were found to be 51.84, 52.60, 49.01 48.23 and 47.97% respectively. The biogas production from the batch experiments for different mixing ratios were 0.26 (1:1), 0.32 (1:2), 0.27 (1:3), 0.27 (1:4) and 0.25 (1:5) L/g of VS added. Lesser biogas production of 0.08 L/g of VS added was observed in IWS alone reactor due to presence of high protein and lipid content, which is reflected in low C/N ratio of 3.4, whereas, in FW alone with C/N ratio of 38.7, higher biogas production of 0.24 L/g of VS added was observed compared with IWS. However, in mixing ratio 1:2, the maximum biogas production of 4 and 1.3 times higher than the individual biogas production of IWS and FW at the end of 10th day was observed. In case of other mixing ratios of 1:1, 1:3, 1:4 and 1:5 (IWS:FW), considerable increase in biogas production was observed when compared with individual biogas production from IWS while compared with FW, slight increase in biogas production was observed. Biogas production was found to vary depending upon mixing ratios, as the mixing ratio has an influence on initial C/N ratio of the mixed feed substrate. It is observed that, the higher biogas productions were obtained in the mixing ratios of 1:2, 1:3 and 1:4, which showed C/N ratio which is reported to be in the optimum range of 25 – 35 for AD. While, other mixing ratios of 1:1 and 1:5 showed C/N ratio slightly away from the optimum range which resulted in lesser biogas production. VFA/Alkalinity ratio was found to be less than acceptable value of 0.4 in all mixing ratios except for FW and IWS where it was 0.67 and 0.53 respectively.44 Presence of higher VFA concentrations (1587 mg/L in FW and 1264 mg/L in IWS) and lower buffer capacity was observed at the end of 10th day indicating the accumulation of VFA in the reactor.16,45 Higher VFA accumulation was observed in FW due to presence of higher carbonaceous and easily degradable organics with C/N ratio of 38.7. But in the case of IWS alone, maximum


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TAN concentration of 1728 mg/L was observed, among other experimental reactors, resulting in the formation of 261 mg/L free ammonia at the end of 10th day which is higher than the optimum level (higher than 1500 mg/L of TAN and 90 mg/L of FA) reported to have higher inhibitory effect on methanogen.46 It is also reported that the presence of free ammonia in the reactor ruptures the cell wall of methanogen and reduces the methanogen activity resulting in accumulation of VFA which was indicated by higher VFA/ alkalinity ratio of 0.53. At the end of 20th day, VS removal efficiencies were found to be 41.14 %, 57.13 %, 55.62%,

57.70 %, 57.51%,

55.68 and 54.58% for IWS , FW, 1:1, 1:2, 1:3, 1:4 and 1:5

respectively. The biogas production (L/g of VS added) at the end of 20th day was observed in the order of 0.39 (1:2) > 0.35 (1:3) > 0.34 (1:1) > 0.33 (1:4) 0.32 (FW) = 0.32 (1:5) > 0.15 (IWS). The maximum biogas production of 0.39 L/g of VS added was observed in the same mixing ratio of 1:2 (IWS: FW). Between the 10th and 20th day, the increase in biogas production showed the following order: 0.08 (FW, 1:1 & 1:3) > 0.07 (IWS, 1:2 & 1:5) > 0.06 (1:4) L/g of VS added. Buffering capacity of the reactor in terms of VFA/alkalinity ratio were found to be 0.54, 0.67, 0.42, 0.4, 0.48, 0.53 and 0.55 for IWS, FW, 1:1, 1:2, 1:3, 1:4 and 1:5 respectively. The IWS and FW showed higher VFA/alkalinity ratio, which indicates some instability of the reactor performance and it confirmed by pH increased from 8.2 to 8.4 in IWS and decrease in FW from 5.8 to 5.5. In addition, the TAN concentration was found to be 1736 mg/L in IWS reactor and the free ammonia concentration was estimated to be 307 mg/L which is found to be higher than the acceptable limit and results in VFA accumulation of 1387 mg/L inside the reactor. This high free ammonia concentration inside the reactor affects the more sensitive acetoclastic methanogens which converts the acetate to methane and carbon dioxide.47 similar trend was observed in the mixing ratio of 1:4 and 1:5 which is reflected in pH of 5.8 and 5.5 respectively.


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At the end of 30th day, the third set reactors were collected and analyzed for the performance of the reactors with respect to VS removal and biogas production and the results are shown in Figure 2a&b. The biogas production of IWS, FW, mixing ratios of 1:1, 1:2, 1:3, 1:4 and 1:5 were found to be 0.18, 0.36, 0.38, 0.43, 0.39, 0.35 and 0.35 L/g of VS added respectively. Similarly, VS removal efficiency at the end of 30th day were found to the following order of 64.02 %( 1:2) > 61.28 % (1:3) > 60.91 % (FW) > 60.34 % (1:4) 60.21 % > (1:2) > 60.15 % (1:5) > 47.69 % (IWS). From the results of 30th day of batch reactor studies, the mixing ratio of 1:1, 1:2 and 1:3 have shown an increase in biogas production of 0.04 L/g of VS added when compared with biogas production of 20th day, while, the increase in biogas productions from IWS, FW, 1:4 and 1:5 were found to be insignificant. In the mixing ratio of 1:4 and 1:5, the high VFA/ Alkalinity ratio of 0.55 & 0.57 and lower pH of 5.6 & 5.4 and accumulation of TAN upto 1262 & 1278 mg/L respectively were observed, which leads to less biogas production during this period. Whereas in IWS, TAN concentration of 1756 mg/L was higher than all other reactors (between 1200 – 1400 mg/L) and also higher than the optimum value of 1500mg/L.46 Similarly, the accumulation of higher free ammonia concentration upto 407 mg/L was observed in IWS reactor at the end of the 30th day, which increased the VFA accumulation inside the reactor and also affected the methanogenic activity resulting in lesser biogas production. The free ammonia concentrations estimated in FW, 1:3, 1:4 and 1:5 were found to be 0.18, 2.3, 0.56 and 0.36 mg/L respectively, which were less than the reported value of 9 mg/L for better performance of the reactor and biogas production. In the case of 1:1 and 1:2 FA concentration estimated were 24 & 17 mg/L which were higher than the reported value of 9 mg/L indicated by higher biogas productions. Biogas compositions were estimated by gas chromatography (Figure S2) and the methane content were found to be in the range of 55.7 to 60.2 % (Figure 4).


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Theoretical retention time defined as 80% of total biogas production for IWS,FW, different of IWS and FW were estimated to be 20, 14, 16, 13, 14, 12 and 13th days

ratio

for

IWS,FW,1:1,1:2, 1:3, 1:4 and 1:5 respectively. It was observed that the lowest theoretical retention time of 12 days was observed for mixing ratio of 1:4 with biogas production of 0.28 L/g of VS added while in the mixing ratio of 1:2, the biogas production of 0.35 L/g of VS added was achieved in 13 days, which is more than 17% the biogas production from 1:4. Theoretical retention time was significantly reduced to less than 15 days (1:2 ratio) from 20 days (for IWS alone) which helps to optimize and reduce the capital investment of full biogas plant significantly. Hence, the co-digestion of IWS with FW can be an alternative solution to the current practice of disposal of IWS in open dumping and costly treatment method of rendering system. 3.3. Batch kinetic study. The pseudo first and seconds order kinetics for the degradation rate of VS were fitted and the corresponding rate constants were calculated as shown in Table 2 for the mixing ratio of 1:1 to 1:5 (IWS : FW). It is observed that, VS reduction in the different mixing ratios of IWS: FW during the AD, the results best fitted with pseudo second order kinetic model based on the regression coefficient (R2). From the analysis of data, it is observed that rate constant of 1:2 mixing ratio of the second order kinetics was found to be effective to get higher than individual and other mixing ratios of 1:1, 1:3, 1:4 and 1:5. Based on the biogas production from IWS, FW and different mixing ratios, the first order batch kinetics was used to fit the experimental data on biogas production as given in Eq 10. The plot between ln[Y∞/(Y∞-Y)] versus ‘t’ has been made and a straight line with slope equal to k with intercept zero confirmed the best fitting of pseudo first order for biogas production. Y∞ is the maximum volume of biogas accumulated at the end of each experiment and Y is the actual biogas


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production at time‘t’. Representation of the experimental data in the above equation gives straight lines with intercept practically zero and slope equal to k (d-1). The value of “k” was obtained from a linear regression analysis. The values of first-order rate constant (k) are in the order of 0.145 (1:4) > 0.136 (1:5) > 0.120 (FW) > 0.113 (1:1) > 0.106 (1:3) > 0.101 (1:2) > 0.099 (IWS) d-1.

4. CONCLUSION It is concluded from the overall batch study results that, the mixing of IWS and FW has improved the C/N ratio of the feed substrate to the acceptable range for AD. This improvement of C/N ratio is also reflected in the enhancement of biogas production in different mixing ratio studied. The maximum biogas production was observed in the mixing ratio of 1:2 when compared with other mixing ratios 1:1, 1:3, 1:4 &1:5 of at the end of the 30th day which had the C/N ratio between the optimal ranges of 25-30. The maximum biogas production of 0.43 L/g of VS added was observed in 1:2 at the end of the 30th day, which is 57% and 17% higher than the biogas production from IWS and FW respectively. In addition, it is concluded that, the mixing ratio of 1:2 has resulted in higher the methane content of biogas of 65.3 % when compared with individual and other mixing ratios. Theoretical retention time of 80% of total biogas production for IWS,FW, different ratio of IWS and FW were estimated to be 20, 14, 16, 13, 14, 12 and 13th days for IWS,FW,1:1,1:2, 1:3, 1:4 and 1:5 respectively. It is concluded that, the reduction in theoretical retention time significantly to less than 15 days (1:2 ratio) from 20 days (for IWS alone) ACKNOWLEDGEMENT The Authors thank the Director, CLRI, Chennai for his support in research work. Authors wish to thank the staff and research scholars in Environmental Science and Engineering Division, CLRI,


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Chennai. Sincere and Special thanks Prime minster PhD fellowship and our industry mentor M/s Envion Engineers Pvt. Ltd., Chennai. CORRESPONDING AUTHOR Dr. S.V. Srinivasan, Senior Scientist, Environmental Science and Engineering Division CSIR-Central Leather Research Institute, Adyar, Chennai – 600 020, Tami Nadu, India Tel: +91-44-24916351, Email: [email protected] REFERENCES: (1)

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List of Tables Table 1

Initial characteristics of anaerobic sludge, slaughterhouse and food wastes

Table 2

Pseudo first and second order kinetics evaluation of VS degradation List of Figures

Figure 1.

Cumulative gas productions of 1:1,

Figure 2.

1:2,

1:3,

IWS &

1:4 and

FW alone, IWS: FW mixing ratios of

1:5 reactors

Performance of the reactor in terms of (a) biogas production (b) VS removal efficiency

10th

20th and

30thday 30th day

of IWS & FW alone, IWS: FW mixing

ratios of 1:1, 1:2, 1:3, 1:4 and 1:5 Figure 3.

Profile of (a) pH, (b) VFA, (c) Alkalinity (d) total ammonia nitrogen (e) free ammonia concentration for IWS & FW alone, IWS :FW mixing ratios of 1:1, 1:2, 1:3 1:4 and 1:5 reactors on 10th, 20th and 30th day

Figure 4.

Methane content of IWS, FW and 1:2 mixing ratio List of supporting informations

Figure S1.

VDI Experimental set-up and measurement of biogas production using pressure method

Figure S2

Biogas composition of (a) IWS (b) FW and (c) 1:2 mixing ratio using gas chromatography


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Table 1 Initial characteristics of anaerobic sludge, slaughterhouse and food wastes S. No

Parameter

Unit

Sludge

IWS

FW

Physico-chemical 1 pH 2 Total Solids

mg/g on wet weight

7±0.4

7.8 ± 0.2

5.5 ± 0.5

64.7 ± 2.3

278.7 ± 5.6

193.9 ± 5.2

35.3 ± 1.2

231.2 ± 2.6

173.8 ± 2.3

93.5

72.1

80.6

basis 3 Volatile Solids

mg/g on dry weight basis

4 Moisture

%

Biochemical 6 Proteins

% w/w basis

35.38 ± 0.01

18.54 ± 0.06

7 Lipids

% w/w basis

14.0 ± 0.05

6.42 ± 0.06

8 Carbohydrates

% w/w basis

0.050 ± 0.02

12.5 ± 0.02

9 C

% on dry weight basis

30.6

52.1

81.4

10 H


3.9

7.4

7.1

11 N


3.3

14.9

2.1

12 S


2

0.4

0.2

9.2

3.4

38.7

13 C/N Ratio


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Table 2. Pseudo first and second order kinetics evaluation of VS degradation Pseudo first order

Second order

Rate constant (k)

R2

Rate constant (k)

R2

IWS

0.0241

0.9736

0.0021

0.9823

FW

0.0385

0.7186

0.0032

0.9085

IWS:FW (1:1)

0.0378

0.6451

0.003

0.8481

IWS:FW (1:2)

0.0407

0.704

0.0035

0.9038

IWS:FW (1:3)

0.039

0.7349

0.0033

0.9093

IWS:FW (1:4)

0.0383

0.7132

0.0032

0.0767

IWS:FW (1:5)

0.0376

0.7253

0.0031

0.9066

Reactor details


Page 25 of 28

6,000

IWS IWS:FW (1:2) IWS:FW (1:5)

5,000

Biogas production (ml)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

FW IWS:FW (1:3)

IWS:FW (1:1) IWS:FW (1:4)

4,000

3,000

2,000

1,000

0 0

5

10

15

20

25

30

35

Days

Figure 1. Cumulative gas productions of 1:1,

1:2,

IWS & 1:3,

FW alone, IWS: FW mixing ratios of

1:4 and

1:5 reactors


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

10th day

20thday

Page 26 of 28

30thday

(a)

IWS 0.50

0.40

IWS:FW (1:5)

FW

0.30 0.35 0.20

0.36

0.18

0.32

0.32

0.25

0.10

0.15

0.24

0.08 0.00 0.35

IWS:FW (1:4)

0.330.27

0.26 0.34

0.38

IWS:FW (1:1)

0.27 0.32 0.35

0.39 0.43

0.39

IWS:FW (1:3)

IWS:FW (1:2)

10th day

20thday

30thday

(b)

IWS 100.00

80.00

IWS:FW (1:5)

FW

60.00 47.69 60.21

40.00

54.55

41.14

47.94 20.00 23.51

57.13

60.91

49.26

0.00 60.34

IWS:FW (1:4)

55.62 51.84 60.15

48.76 55.68

IWS:FW (1:1) 49.01 57.51

61.28

IWS:FW (1:3)

52.60 57.70 64.05

IWS:FW (1:2)

Figure 2. Performance of the reactor in terms of (a) biogas production (b) VS removal efficiency 10th

20th and

30thday 30th day

of IWS & FW alone, IWS: FW mixing ratios of 1:1, 1:2, 1:3, 1:4

and 1:5


Page 27 of 28

14

1800 10thday

20th day

(a)

30thday

10thday

20th day

30thday

1600 1400

10

VFA (mg/L)

pH (mg/L)

12

(b )

1200

8

1000

6

800 600

4

400 2

200

0

0 IWS

FW

IWS:FW (1:1)

IWS:FW IWS:FW (1:2) (1:3) Substrate

IWS:FW (1:4)

IWS:FW (1:5)

IWS

4000 20th day

30thday

(c)

Ammonia nitrogen (mg/L)

10thday

3500

Alkalinity (mg/L)

3000 2500 2000 1500 1000 500 0 IWS

FW

IWS:FW (1:1)

IWS:FW IWS:FW (1:2) (1:3) Substrate

IWS:FW (1:4)

IWS:FW (1:5)

2000 1800 1600 1400 1200

FW

IWS:FW IWS:FW IWS:FW IWS:FW IWS:FW (1:1) (1:2) (1:3) (1:4) (1:5) Substrate

10thday

20th day

30thday

(d)

1000 800 600 400 200 0 IWS

FW


450

Free Ammonia (mg/L)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

10thday

400

20th day

30thday

(e)

350 300 250 200 150 100 50 0 IWS

FW


Figure 3. Profile of (a) pH, (b) VFA, (c) Alkalinity (d) total ammonia nitrogen (e) free ammonia concentration for IWS & FW alone, IWS :FW mixing ratios of 1:1, 1:2, 1:3 1:4 and 1:5 reactors on 10th, 20th and 30th day


Energy & Fuels

100 90

Biogas composition (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 28 of 28

CH4

80 70

55.72

57.15

IWS

FW

60.22

60 50 40 30 20 10 0 IWS: FW (1:2)

Figure 4 Methane content of IWS, FW and 1:2 mixing ratio

27


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