The Performance of Anaerobic Co-digester of Swine Slurry and Food Waste

Abstract

In order to assess the performance of co-digester using pig slurry and food waste at the farm scale biogas production facility, the anaerobic facility that adopts the one-stage CSTR of 5 <TEX>$m^3\;day^{-1}$</TEX> input scale was designed and installed under the conditions of the OLR of 2.33 kg <TEX>$m^3\;day^{-1}$</TEX> and HRT of 30 days in an pig farmhouse. Several operation parameters were monitored for assessment of the process performance. The anaerobic facility was operated in three stages to compare the performance of the anaerobic co-digester. In the Stage I, that was fed with a mix of pig slurry to food waste ratio of 7:3 in the input volume, where input TS content was 4.7 (<TEX>${\pm}0.8$</TEX>) %, and OLR was 0.837-1.668 kg-VS <TEX>$m^3\;day^{-1}$</TEX>. An average biogas yield observed was 252 <TEX>$Nm^3\;day^{-1}$</TEX> with methane content 67.9%. This facility was capable of producing an electricity of 626 kWh <TEX>$day^{-1}$</TEX> and a heat recovery of 689 Mcal day-1. In Stage II, that was fed with a mixture of pig slurry and food waste at the ratio of 6:4 in the input volume, where input TS content was 6.9 (<TEX>${\pm}1.9$</TEX>) %, and OLR was 1.220-3.524 kg-VS <TEX>$m^3\;day^{-1}$</TEX>. The TS content of digestate was increased to 3.0 (<TEX>${\pm}0.3$</TEX>) %. In Stage III, that was fed with only pig slurry, input TS content was 3.6 (<TEX>${\pm}2.0$</TEX>) %, and OLR was 0.182-2.187 kg-VS <TEX>$m^3\;day^{-1}$</TEX>. In stage III, TS and volatile solid contents in the input pig slurry were highly variable, and input VFAs and alkalinity values that affect the performance of anaerobic digester were also more variable and sensitive to the variation of input organic loading during the digester operation. The biogas produced in the stage III, ranged from 11.3 to 170.0 <TEX>$m^3\;day^{-1}$</TEX>, which was lower than 222.5-330.2 <TEX>$m^3\;day^{-1}$</TEX> produced in the stage II.