Digester unit performance of biogas power system at Baiturrahman Boarding School, West Java, Indonesia

Study concerning the digester unit of biogas power system at Baiturrahman Boarding School is highly needed to understand the performance and function of each digester in producing biogas. There are six digesters, named as Digester 1, Digester 2, Digester 3, Digester 4, Digester 5, and Digester 6. However, Digester 2 which was purposed for food waste feed has not been operated. The fifth functioning digesters are operated with cow manure and human faeces as raw materials. This research was conducted by analyzing the process parameters, i.e., TS concentration, VFA concentration, slurry pH and thickness, and methane content of biogas produced. The result showed that based on feeding rate of cow manure and human faeces, the retention times of the slurry were significantly longer, more than 25 days for each digester and more than 100 days after the total process in all digesters. This long retention time implied the complete process after two series step in Digester 1, Digester 3, and Digester 4, that was identified by the fact that the degradation process in Digester 5 and Digester 6 did not significantly decrease TS and VFA concentrations. The methane content obtained was lower than previously researches, this might cause due to air entrainment that happens in biogas compression process. It can be concluded that many serial digesters (more than 2) are not necessarily needed if the retention time of the slurry in each digester had been significantly longer.