Anaerobic Digestion Of Food Waste For Bio-hydrogen Production

Hydrogen is the cleanest source of energy as it produces water when combusted as by-product instead of greenhouse gases. Although, it can be produced from fossil fuels through thermo-chemical processes, but biological production processes are found more attractive as they are environment friendly and less energy intensive as compared to other conventional processes. Among all biological processes for bio-hydrogen production, anaerobic digestion has the lowest operational cost, because mix consortia of Clostridia in the form of sludge can be used as an inoculum. Along with inoculum,anaerobic fermentation also requires feedstock to produce bio-hydrogen. For this purpose, the organic fraction of municipal solid waste or food waste (FW) is getting more attraction due to its high content of volatile solids and organic matter. In 2013,172.39 Mt of FW was produced in China where restaurants were the major contributors.The major components of FW were rice and noodle, as 40% of FW is consisted of rice waste (RW) and noodle waste (NW).Keeping in view all these facts, this research work was designed to produce bio-hydrogen from food waste co-digested with heat shocked sludge in equal proportion under different pH and temperature control conditions by using 550mL lab scale digesters. The bio-hydrogen production, chemical oxygen demand (COD), volatile solids (VS), drop in pH, glucose consumption and production of volatile fatty acids were studied during the incubation period. The modified Gompertz equation was used to study the kinetic parameters of bio-hydrogen production. Response surface methodology was opted through quadratic modeling for better representation of the results. The results are generalized as following;1. Food waste, noodle waste and rice waste were tested for bio-hydrogen production by using sludge as a source of mix consortia of Clostridium under different physical conditions (pH 5, 6 and 7, temperature 37? and 55?). The pH was maintained manually to the initial value after every 12h. It was observed that the increase in pH from pH 5 to pH 7 increased the bio-hydrogen yield for all tested wastes,whereas; increase in temperature increased the bio-hydrogen yield just for food waste.The highest experimental yield of 115.76mL/VSremoved was produced in the mesophilic noodle waste reactor at pH 7. The drop in pH from 7 to 4.8±0.2 was found optimum for bio-hydrogen production for all tested wastes under mesophilic as well as thermophilic conditions. Most of the hydrogen production was observed within 72 hours of incubation that can be used as optimum bio-hydrogen production period for food waste.2. The impact of increasing temperature from mesophilic to thermophilic on bio-hydrogen production from food waste, noodle waste and rice waste with an initial pH of 7 were studied under no pH control conditions. Experimental results showed that an increase in temperature from mesophilic (37?) to thermophilic (55?) effectively increased the bio-hydrogen production from food waste and noodle waste, but it caused a negative impact on bio-hydrogen production from rice waste. Most of the production was observed during 48 hours of incubation, that continued till 72 hours of incubation and decline in pH during that interval was 4.3 and 4.4 from a starting value of 7 under mesophilic and thermophilic conditions, respectively. The maximum bio-hydrogen yields of 82.47 mL/VS,131.38 mL/COD,and 44.90 mL/glucose were obtained from thermophilic food waste, thermophilic noodle waste and mesophilic rice waste,respectively.3. The bio-hydrogen production from food waste along with its two component was studied under pH management intervals of 12h (PM 12) and 24h (PM24) for temperature 37±0.1? and 55±0.1?. The bio-hydrogen production was higher in all reactors under PM 12 as compared to PM24. The drop in pH from 7 to 5.3 was observed to be appropriate for bio-hydrogen production via mesophilic co-digestion of noodle waste with the highest bio-hydrogen yield of 145.93 mL/g CODremo,ved under PM12.When the temperature was increased from 37? to 55? and pH management interval was reduced from 24h to 12h, the bio-hydrogen yields were also changed from 39.21 mL/g CODremoved to 89.67 mL/g CODremoved, 91.77 mL/g CODremoved to 145.93 mL/g CODremoved and 15.36 mL/g CODremoved to 117.62 mL/g CODremoved for FW, NW and RW, respectively. Overall, PM12 was found to be an effective mean for bio-hydrogen production through anaerobic digestion of food waste.4. Food waste and its two major derivatives were used for bio-hydrogen production under mesophilic and thermophilic conditions to study the impact of heating 12h/day (HI 12) and 24h/day (HI24). The highest experimental bio-hydrogen yield of 104.08 mL/VSremoved and 85.14 mL/VSremoved was achieved from thermophilic noodle waste under HI24 and mesophilic rice waste under HI 12 respectively. The decrease in heating interval from HI24 to HI 12 decreased the bio-hydrogen yield by 28.19% and 27.11% of thermophilic noodle waste and mesophilic food waste, respectively. The same change in heating interval increased the bio-hydrogen yield by 17.24% of mesophilic rice waste. As a whole, thermophilic HI12 treatment resulted higher bio-hydrogen yield as compared to mesophilic HI24 treatment, whereas the theoretical energy requirement of both were almost the same.5. The impact of heating interval on volatile solids removal efficiency was studied and it was observed that the HI12 as compared to HI24 reduced the volatile solids removal efficiency of mesophilic food waste by 22.66%, which make HI12 a suitable energy conservation option for wastewater treatment plants. The interval heating was also found helpful for decreasing the average drop in pH and decreased VFA production, which provide better control of pH and VFA.