High solid anaerobic co-digestion of dried food waste with different additives for Biogas production.
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Anaerobic co-digestion of food waste, parthenium weed, sugarcane bagasse and faecal sludge was tested at two different total solid (TS) concentrations. In the low-solids group with TS 10.6 %, the biogas production increased linearly as the ratio of food waste in substrate increased from 25% to 100%, but no synergetic effect was found between the two substrates. Moreover, the additive food waste resulted in the accumulation of volatile fatty acids and decelerated biogas production. Thus, the blend ratio of food waste should be lower than 50%. While in the high-solids group with TS 25%, the weak alkaline environment with pH 7.5–8.5 avoided excessive acidification but high concentration of free ammonia was a potential risk. However, good synergetic effect was found between the substrates because the added food waste improved mass transfer in sludge cake. Thus, 50% was recommended as the optimum ratio of food waste in substrate because of the best synergetic effect. System stability and performance of high-solids anaerobic co-digestion of food waste (FW), sugarcane bagasse, parthenium weed and faecal sludge in comparison with mono digestions were investigated. System stability was improved in co-digestion systems with cosubstrate acting as a diluting agent to toxic chemicals like ammonia or Na+. For high-solids digestion, the addition of NaOH not only improved system stability but also greatly enhanced volumetric biogas production. For high-solids digestion of FW, the addition of faecal sludge could reduce Na+ concentration and help maintain satisfactory stability during the conversion of FW into biogas. System performances of co-digestion systems were mainly determined by the mixing ratios of substrates. Biogas production and volatile solids (VS) reduction in digestion of the co-mixture of substrates increased linearly with higher ratios of Food waste