The focus of our work is on anaerobic digestion of locally available agro wastes like coconut oil cake, cashew apple waste, and grass from lawn cuttings. The most productive agro waste, in terms of methane yield, was coconut oil cake and grass. The results showed that the initial volatile solids concentration significantly affected the biogas production. The methane yield from coconut oil cake was found to be 383 ml CH4/g VS and 277 ml CH4/g VS added at 4 and 4.5 g VS/l. In case of grass the biogas production increased with increasing VS concentrations with methane yield of 199, 250, 256, 284, and 332 ml CH4/g VS at 3, 3.5, 4, 4.5, and 5.0 g VS/l. For cashew apple waste single-stage fermentation inhibited biogas production. However, phase separation showed methane yield of 60.7 ml CH4/g VS and 64.6 ml CH4/g VS at 3.5 and 4.0 g VS/l, respectively. The anaerobic biodegradability of coconut oil cake was evaluated in fed batch mode in a 5 L anaerobic reactor at 4 g VS/L per batch, and the maximum methane yield was found to be 320 ml CH4/g VS.
Food waste is the single largest component of the waste stream by weight. In the present work, we attempted to study the effect of caffeine and saponin on anaerobic fermentation of food waste to examine their potential influence on biogas production at 8% total solids (TS) content. Addition of caffeine at 50, 100, and 150 ppm to the food waste on the first day resulted in biogas production in 24 hours which normally comes on 4 th day. The maximum biogas production of 408.5 ml/g TS was found at 100 ppm caffeine whereas 50 ppm and 150 ppm caffeine produced 359 ml and 336 ml in comparison with the control which showed 182 ml/g TS. This is the first study of effect of caffeine as stimulants in anaerobic environments. Addition of saponin had no beneficial effect; on the other hand, it inhibited the biogas production at 50, 100 and 150 ppm.
This study evaluated the possibility of pretreating selected solid fraction of an anaerobic digester treating food waste to lower the hydraulic retention time and increase the methane production. The study investigated the effect of different pretreatments (thermal, chemical, thermochemical and enzymatic) for enhanced methane production from cottage cheese. The most effective pretreatments were thermal and enzymatic. Highest solubilisation of COD was observed in thermal pretreatment, followed by thermochemical. In single enzyme systems, lipase at low concentration gave significantly higher methane yield than for the experiments without enzyme additions. The highest lipase dosages decreased methane yield from cottage cheese. However, in case of protease enzyme an increase in concentration of the enzyme showed higher methane yield. In the case of mixed enzyme systems, pretreatment at 1 : 2 ratio of lipase : protease showed higher methane production in comparison with 1 : 1 and 2 : 1 ratios. Methane production potentials for different pretreatments were as follows: thermal 357 mL/g VS, chemical 293 mL/g VS, and thermochemical 441 mL/g VS. The average methane yield from single enzyme systems was 335 mL/g VS for lipase and 328 mL/g VS for protease. Methane potentials for mixed enzyme ratios were 330, 360, and 339 mL/g VS for 1 : 1, 1 : 2, and 2 : 1 lipase : protease, respectively.
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