Thermo-chemical pretreatment of the organic fraction of municipal solid waste for improved anaerobic digestion

The hydrolysis of organic waste in anaerobic digestion is slow and time-consuming. Pretreatment of the waste can potentially improve hydrolysis and decomposition of the waste, increase biogas production, and shorten the required digestion time. In the present study, the effects of thermal, chemical, and combined thermochemical pretreatment of the organic fraction of municipal solid waste have been investigated. Treatment temperatures ranged from 25 to 120 degrees C, with a lime concentration of 0-4%, and a treatment duration of 30 or 60 min. A full factorial DOE was used and the soluble chemical oxygen demand (SCOD), electrical conductivity (EC), pH, and NH4+ concentration of the waste were chosen as indicators to explore the suitability of the treatments. Chemical pretreatment with lime caused unwanted side effects and decreased the SCOD and soluble solids. This finding, coupled with the fact that chemicals would increase the process's operational costs, are why the results do not support the use of lime. Since thermo-chemical pretreatment was observed to have comparable effectiveness with thermal pretreatment alone, thermal treatment appears to be the most suitable option. Finally, preliminary energy consumption calculations showed that heat treatment at 90 degrees C uses a fraction of the energy compared to treatment at 120 degrees C while providing similar benefits. Therefore, pretreatment of the waste at 90 degrees C was chosen as the most suitable option for improving anaerobic digestion. As per the calculations, the methane generated from about 12 g of COD would ideally be enough to pretreat about 100 g of the digester feed at 90 degrees C.