Abstract:
The objectives of this research were to investigate the feasibility and effectiveness
of two-phase mesophilic anaerobic digestion of organic fraction of municipal solid waste
(OFMSW). A study of two-phase anaerobic digestion was carried out in laboratory-scale,
under mesophilic (35ºC) condition. The experiments were divided into two major parts.
The first part, was conducted to find out the optimum ratio of organic fraction of
municipal solid waste (OFMSW) and waste activated sludge (WAS) by using two-phase
anaerobic co-digestion. The co-digestion was conducted with the mixture of 100:0, 50:50 and
25:75 of OFMSW (%) and WAS (%). At all experiments, the following data were
determined as total solids (TS) and volatile solids (VS) removal efficiency and specific gas
production (SGP). It was found that the averages TS and VS removal efficiency and SGP
with 100% OFMSW obtained the significantly highest removal efficiency and SGP (p <
0.05), with the average of 72.2 %, 85.1 % and 0.72 m3 biogas STP/ kg VS added,
respectively.
The experimental second part, was assigned to be as 32 factorial design with 9
running conditions at various hydraulic retention times (HRTs) (20, 25 and 30 days) and TS
concentration (8, 12 and 15%). At all experiments, the following data were determined: TS
and VS removal efficiency and SGP. Results indicated that TS and VS removal efficiencies
in the average of 77.1%and 88.5% were achieved in the reactor with TS concentration of 8%
and HRTs of 30 days. Furthermore, the SGP varied between 0.37-0.77 m3 biogas STP/ kg VS
added, depending on the substrate added and HRTs applied to the reactor. The SGP with TS
concentration of 8% and HRTs of 30 days obtained the significantly highest SGP (p < 0.05),
with the average of 0.70 m3 biogas STP/ kg VS added.
It could be concluded that the two-phase mesophilic anaerobic digestion was
suitable for the 100% OFMSW with the optimum running condition at the HRTs of 30 days
and the total solids concentration of 8% with TS and VS removal efficiency and SGP of
77.1%, 88.5% and 0.77 m3 biogas STP/ kg VS added, respectively.