A comparative study on anaerobic co-digestion of kitchen waste with sewage sludge and cow manure

Abstract

A comparative study on anaerobic co-digestion of kitchen waste (KW) with sewage sludge (SS) and KW with cow manure (CM) were carried out in 1 liter batch digesters under mesophilic temperature (37°C). CM and SS both acted as seed of bacteria to produce biogas through bio-degradation of organic materials under anaerobic conditions. At first, three digesters were prepared to observe the individual degradation rate of KW, CM and co-digested KW with CM at room temperature(25°C ∼30°C) and at 37°C and observed the degradation rate for co-digested KW with CM was higher than other two components. Again, another three digesters were prepared to observe the individual degradation rate of KW, SS and co-digested KW with SS and observed that the degradation rate for co-digested KW with SS was higher than the other two. Secondly, four digesters were constructed to optimize the loading rate and result showed that the highest degradation rate was obtained from loading rate of 200 gm/L for both CM and SS. Consequently, three digesters were constructed to observe the effect of alkalinity at temperature 37°C and loading rate 200 gm/L for both cases. Three alkali (NaOH) doses 1.0%, 1.5% and 2.0% on wet matter basis of kitchen waste were applied to improve biodegradability and biogas production. The highest degradation rates were 6.8 ml/gm and 5.74 ml/gm which were obtained for 1.5% NaOH from co-digested KW with CM and co-digested KW with SS respectively. It was also observed that the biogas production was almost doubled from treated KW than untreated KW due to its high biodegradability. Finally, two portable biogas reactors were fabricated for pilot-scale biogas production which included an agitator and heating system. These reactors were operated at both 37° C and room temperature at a loading rate of 200 gm/L and observed that the digestion rates were faster at 37° C than room temperature. Anaerobic co-digestion of KW with CM produced more biogas than co-digestion of KW with SS in all cases. The prime object of this work was to compare the biogas production rate and ultimate protection of environment from the bad effect of methane gas that would be produced by uncontrolled anaerobic digestion (AD).