A prototype single-stage anaerobic digester for co-digestion of food waste and sewage sludge from high-rise building for on-site biogas production

• A prototype single-stage anaerobic digester for co-digestion of food waste and sewage sludge was newly designed and built.
• Effects of hydraulic retention time (HRT) and the mixed waste ratio on biogas production were investigated.
• Anaerobic co-digestion can enhance methane yield by mixing food waste with sewage sludge at the ratio of 10:1.
• The methane content of biogas is significantly affected by HRT in operating the single-stage co-digestion system.
• At present, the biogas has been utilized for cooking as a model case study for high-rise building application.

At present, there has been less results from pilot-scale experiments on anaerobic co-digestion system, especially as an on-site system for high-rise building application. The objective of this study was to develop a prototype single-stage anaerobic digester for the co-digestion of food waste (FW) and sewage sludge (SWS) from high-rise building for on-site biogas production. Here, the prototype system was operated at different hydraulic retention times (HRTs) of 27, 22 and 19 days, corresponding to organic loading rates of 7.9, 10.8 and 14.0 kgCOD/m3 d. The feed mixed waste ratio (FW/SWS) of 10:1 by weight was selected from the previous laboratory-scale experiment. The results of this study indicate that higher gas production rate was obtained at shorter hydraulic retention time (HRT) of 19 days; however, higher methane content of the biogas was obtained at longer HRT of 27 days. Therefore, enhancement of methane production from the co-digestion could be achieved with sufficient operating HRT. Moreover, the proposed prototype system could reduce total volatile solid up to 70 percent at HRT of 27 days. Up to now, the biogas from on-site production has been utilized for cooking at Chulalongkorn University as a model case study for high-rise building application.