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hydrogen production from kitchen waste using heat treated anaerobic biogas plant slurry

Proceedings of the International Conference on Sustainable Solid Waste Management, 5 - 7 September 2007, Chennai, India. pp.356-362

Hydrogen Production from Kitchen Waste using Heat Treated Anaerobic Biogas Plant Slurry
S. Jayalakshmi1, V. Sukumaran2 and Kurian Joseph3
2

Civil Department, Periyar Maniammai College of Technology for Women, Vallam, Thanjavur. Dept. of Biotechnology, Periyar Maniammai College of Technology for Women, Vallam, Thanjavur 3 Centre for Environmental Studies, Anna University, Gundy, Chennai Email: j_lak2001@yahoo.co.in ABSTRACT Anaerobic digestion of kitchen waste for hydrogen production was performed in lab scale reactors, using heat-treated anaerobically digested biogas plant slurry. The biogas plant slurry was given heat treatment at varying temperatures ranging from 70oC to 100 oC for 15 minutes. The reactor operated with 100 oC heat-treated inoculum was efficient in hydrogen production from kitchen waste. The rate of hydrogen production was 176.2 mL/kg TS/ h. Methane was not reported in all the operated reactors except that the reactor operated with 70 oC heat-treated inoculum. The hydrogen concentration was found to be 55-60% and the remaining was CO2. Normal butyrate was the main acid product, and the percentages of butyrate, acetate and propionate at tested conditions were 45 – 50 %, 20 – 25% and 20 – 25% respectively. Keywords: Anaerobic Digestion, Kitchen Waste, Heat-treated inoculum, Hydrogen gas

1

1.0 INTRODUCTION Hydrogen is a promising alternate to fossil fuels due to its clean and high-energy potential. Anaerobic Digestion of organic waste produces various volatile fatty acids (VFA), H2, CO2 and other intermediates (Rustrian et al 1999). The reactions involved in hydrogen production are rapid and making them useful for treating large quantities of organic wastes. Hydrogen gas is not the only beneficial energy source, but also VFA can be used for methane production by methanogenes (Llabres et al, 1999). Acidification of organic wastes, however, needs hydraulic retention time (HRT) longer than 3 days in which hydrogen consumers such as methanogenes could be multiplied. Because of this reason, most researches on hydrogen production have been carried out under inhibitory condition of hydrogen consumers. In order to inactivate hydrogen consumers, inoculum was cultured with pure chemicals such as glucose or sucrose at short HRT and /or low pH (Fang et al, 2002) or preheated inoculum to harvest spore-forming anaerobic bacteria (Lay et al, 1999). Continuous production of hydrogen was also tried at short HRT to prevent the growth of hydrogen consumers (Mizuno et al, 2000). However, there have been no studies on continuous hydrogen production at enough HRT from organic solid wastes. So far, majority of research work has been directed at expensive pure substrates to a much lesser quantity of solid waste (Hawkes et al, 2002). Therefore the aim of this current work was to investigate the feasibility of hydrogen production from kitchen waste using heat-treated anaerobic biogas plant slurry. 356

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2.0 MATERIALS AND METHODS 2.1 Composition and Characterization The kitchen waste used as the feedstock was collected from the hostel kitchen of Periyar Maniammai College of Technology for Women (PMCTW) in Tamil Nadu, India. In the hostel, there are around 1000 inhabitants. The total solid waste generation from the hostel kitchen is 77 kg/day. The average composition of the kitchen waste (KW) generated is reported in Table 1. The kitchen waste was analysed for moisture content, pH, carbon, nitrogen, total solids and volatile solids as per standard methods (APHA, 1998) and the results are reported in Table.2. The kitchen waste contained around 95 % of biodegradable waste suitable for AD.
Table 1. Average Composition of Kitchen Waste

Sl.No. 1 2 3 4 5 6

Component Food Waste Vegetable Waste Ash Tea Waste Egg Shell Packing Materials Total

Quantity (kg/day) 51.40 20.10 2.80 0.75 0.85 1.10 77.0

Composition ( % by weight) 67 26 3.6 1.0 1.1 1.3 100

Table 2. Characteristics of Kitchen Waste

Sl.No 1 2 3 4. 5 6

Characteristics pH Total Solid (% dry wt.) Volatile Solids (% dry wt.) Moisture Content (%) Organic Carbon (% dry wt.) Total Kjeladal Nitrogen (% dry wt.)

value 5.5 16.14 86.0 83.86 48.1 2.26

2.2 Heat Treatment for Inoculum The biogas plant slurry obtained from the biogas plant at PMCTW campus was used as the innoculum. The slurry was heat treated at various temperatures ranging from 70oC to 100 oC for 15 minutes (Fang et al, 2002) to inactivate the non-spore forming methanogens. The heat-treated inoculum (HTI) was spore stained. The harvested spore forming acitogens are used for producing hydrogen from kitchen waste. 2.3 Experimental Setup The experiments were conducted in 500 mL serum bottles. One Serum bottle was used as digestion bottle and another as gas collection bottle as depicted in Figure1. The mouth of the digestion bottle was closed by rubber cork with proper ceiling to ensure anaerobic condition. The collection bottle was 357

Hydrogen Production from Kitchen Waste using Heat Treated Anaerobic Biogas Plant Slurry

hung in inverted position. The headspace of the reactor bottle was initially purged with nitrogen gas to maintain strict anaerobic condition. The reactors were fed with different combinations of the feedstock and inoculum as per Table 3. The experiments were conducted at ambient temperature condition (28 Ο C ± 5 ΟC).

Figure 1 Lab Scale Reactor Table 3. Feeding of Lab Scale Reactor

Sl. No 1 2 3 4 5

Sl. No. of Lab Scale Reactor 1,2,3 4,5,6 7,8,9 10,11,12 13,14,15

Ingredients in Lab Scale reactor Kitchen Waste Kitchen Waste + Innoculum with heat treatment @ 70οC for 15 minutes Kitchen Waste + Innoculum with heat treatment @ 80οC for 15 minutes Kitchen Waste + Innoculum with heat treatment @ 90οC for 15 minutes Kitchen Waste + Innoculum with heat treatment @ 100οC for 15 minutes

2.4 Analyses Volume of biogas produced in all reactors was measured daily using gas displacement method (Demeier et al, 1978). The concentration of hydrogen, CO2 and CH4 were analyzed using Chemito 1000 model gas chromatograph fitted with a thermal conductivity detector and a column packed with molecular sieve 5A. Volatile fatty acid (VFA) was quantified using gas chromatograph Chemito 1000 model fitted with a Flame Ionization detector and capillary (BP1) column 3.0 RESULTS AND DISCUSSION 3.1 Heat Treatment of Inoculum The HTI at various temperatures from 70 οC to 100 οC were shown in Figure 2 and Figure 3. Vegitative Cells were found at 70οC HTI whereas there were no symptoms of vegetative cells in the rest of the temperatures.

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Figure 2 Heat-Treated Inoculum at 70o C

Figure 3 Heat-Treated Inoculum at 100o C

3.2 Composition and Characterisation of Digested Slurry The final characteristics of the digested slurry is presented in Table.4. The VS values of the slurry from all the digesters showed a digestion of around 42% except in the reactor operated without inoculum. 3.3 Hydrogen Production The cumulative variation of hydrogen production at 25oC is depicted in Figure 4. It shows that the maximum production was achieved in the reactor operated with 100oC HTI. The reactors operated with 80 oC to 100 oC HTI consists 55 – 60% H2 concentration and the rest was CO2. A trace of methane was found in the reactor operated with 70oC HTI. The rate of hydrogen production were 54.1mL/kg TS/h, 69.2 mL/kg TS/h, 116.4 mL/kg TS/h, 167.7 mL/kg TS/h and 176.2 mL/kg TS/h in the reactors operated with 70 oC to 100 oC HTI respectively.
Table 4. Characteristics of Digested Slurry after 10th Day

Sl. No. 1 2 3 4. 5 6

Components pH Total Solid (% dry wt.) Volatile Solids (% dry wt.) Moisture Content (%) Organic Carbon (% dry wt.) Total Kjeladal Nitrogen (% dry wt.)

KW 5.4 13.23 86.77 82.52 40.8 2.58

KW+ HTI @ 70οC 5.5 12.93 64.35 87.07 39.75 2.94

Characteristics KW+ KW+ HTI @ HTI @ 80οC 90οC 5.6 5.6 10.35 9.72 63.58 62.95 89.65 90.28 39.62 39.71 3.52 3.64

KW+ HTI @ 100οC 5.6 8.84 62.18 91.16 39.72 3.92

3.4 Effect of pH and Volatile Fatty Acids on Hydrogen Production The initial pH of the kitchen waste was 5.5. The optimal pH for anaerobic hydrogen production reported in literature was essentially within the range of 5.5 – 6.7 (Hawkes et al, 2002, Fang et al, 359

Hydrogen Production from Kitchen Waste using Heat Treated Anaerobic Biogas Plant Slurry

2002). The variation in pH and TVFA are depicted in the Figures 5 to 9. The initial pH was 5.5, and subsequently the pH started decreasing. It may be because of the higher concentration of acids produced during digestion (Girija devi and Kurian Joseph, 2004). After five days of digestion there was an indigation of increase in pH value. This indicates the conversion of VFA into hydrogen (Fang and Liu, 2002). It is inferred from the Figures 5 to 9 that during the initial days, the TVFA concentration was very high and later, it started to decrease. Production of various volatile fatty acids in the acitogenic stage may be the reason for the increased TVFA concentration in the earlier days (Hang sik et al, 2004, SunKee Han, et al, 2004). The reduction in TVFA may be due to their conversion into gaseous products (Girija devi and Kurian Joseph, 2004).
1600 1400 1200 1000 800 600 400 200 0 0 2 kw 90°C 4 6 Days 70°C 100°C 8 10 80°C 12
2900 2800 2700 5.4 2600 TVFA mg/kg 2500 2400 2300 5.1 2200 2100 2000 1 4 Days 7 10 5 4.9 5.3 5.2 pH TVFA pH 5.5 5.6

Cummulative hydrogen production (mL)

Figure 4 Cumulative Hydrogen Production
TVFA pH

Figure 5 Profile of pH and Formation of TVFA – Without Inoculum
6000 TVFA pH 5000 5.7 5.6 5.5 5.4 5.3 3000 5.2 5.1 2000 5 4.9 4.8 pH

4500 4300

5.6 5.5

4100 3900 TVFA mg/kg 3700 3500 3300 3100 2900 5 2700 2500 1 4 Days 7 10 4.9 5.2 5.1 5.4

4000
5.3 pH

TVFA mg/kg

1000

0 1 4 Days 7 10

4.7

Figure 6 Profile of pH and Formation of TVFA – at 70oc Heat Treated Inoculum

Figure 7 Profile of pH and Formation of TVFA – at 80oc Heat Treated Inoculum

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Sustainable Solid Waste Management
6500 TVFA pH 6000 5.7 5.6 5.5 5.4 TVFA mg/kg 5.3 pH 5.2 5000 5.1 4500 5 4.9 4000 1 4 Days 7 10 4.8

7500 7000 6500 6000 TVFA mg/kg 5500 5000 4500 4000 3500 3000 1 4 Days

TVFA pH

5.8 5.6 5.4 5.2 5 4.8 4.6 4.4 4.2 4 pH

5500

7

10

Figure 8 Profile of pH and Formation of TVFA – at 90oc Heat Treated Inoculum

Figure 9 Profile of pH and Formation of TVFA – at 100oc Heat Treated Inoculum

Results concerning production of soluble products during hydrogen fermentation are reported in Table.5. The soluble metabolites include butyric acid (n-HBu), acetic acid (HAc), and Propoionic acid (HPr). The most abundant product was n-HBu, which accounted for 40-60% of total soluble metabolite. The production of HAc and HPr were also found to be 20 – 25% and 20 – 25% respectively.
Table 5. Production of Soluble Metabolites during Hydrogen Fermentation

Condition KW KW+ 70οC HTI KW+ 80οC HTI KW+ 90οC HTI KW+ 100οC HTI

TVFA (mg/kg) 2894.3 4291 4928.25 6225.12 7219.3

n-Hbu (mg/kg) 1075.05 2488.78 2810.56 3727.52 4115.04

Hac (mg/kg) 628.69 2521 1168.3 2121 1992.04

HPr (mg/kg) 895.7 858.2 1307.26 1418.26 1588.26

n- HBu : Butyric acid, HAc : acetic acid, HPr : Propionic acid, TVFA = HAc + HBu + HPr 4.0 CONCLUSION The hydrogen producing efficiency of the heat-treated inoculum was studied in the lab scale reactor under ambient mesophilic temperature conditions both in the presence and absence of heat-treated inoculum. Biogas plant slurry collected was heat treated at various temperatures from 70 oC to 100 oC and used as the inoculum. The maximum hydrogen production took place at the reactor operated with 100 oC HTI and the rate of hydrogen production is 176.2 mL/kg TS/h. REFERENCE APHA, Standard Methods for the Examination of Water and Wastewater. American Public Health Association, Washington, (1998).

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Demirer G.N., Speec e R.E., Anaerobic Biotransformation of Four 3 – Carbon Compounds (acrolein, acrylic acid, allyl alcohol and n-propanol) in UASB Reactors. Water Research, 32(3): pp.747759 (1998). Fang HHP, Liu H., Efect of pH on hydrogen production from glucose by amixed culture, Bioresour Technol, 82. pp.87 – 93 (2002). Girija Devi G, Kurian Joseph, 2004 Solid Phase Anaerobic Digestion of Municipal Solid Waste, Journal of IAEM, Vol.31. pp.147 – 152. Hang – Sik Shin, Jong – Ho Youn, Sang – Hyoun Kim, Hydrogen Production from Food Waste in Anaerobic Mesophilic and Thermophilic Acidogenesis. International Journal of Hydrogen Energy 29, pp.1355 – 1363 (2004). Hawkes Fr, Dinsdale R, Hawkes DL, Hussy I, Sustainable fermentative hydrogen production:challenges for process optimization. Int J Hydrogen Energy;27. pp. 1339-47 (2002). Lay JJ, Lee YJ, Noike T., Feasibility of biological hydrogen production from organic fraction of municipal solid waste, Water Res 33 (11), pp. 498-500 (1999). Llabres P, Pavan P, Battistioni P, Cecchi F, Mata-Alvarez J, The use of organic fraction of municipal solid waste hydrolysis products for biological nutrient removal in wastewater treatment plants. Water Res 33 (1), pp 214 –22 (1999). Mizuno O, Dinsdale R, Hawkes FR, Hawkes DL, Noike T. Enhancement of hydrogen production from glucose by nitrogen gas sparging. Bioresource Technol. 73. pp. 59-65 (2000). Rustrian E, Delgenes JP, Bernet N, Moletta R, Acidogenic activity: process of carbon source generation for biological nutrient removal. Water Sci Technol 40(8), pp. 25 –32 (1999).

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