Anaerobic treatment of distillery slop and landfill leachate using UASB and hybrid reactors.

A single-phase hybrid reactor treating landfill leachate was operated at a constant hydraulic retention time (HRT) of 13.5 hours. The major objective was to evaluate the treatability of landfill leachate in a hybrid reactor while increasing the organic loading rate (OLR) step wise. The treatability of landfill leachate was poor as shown by low methane production rate, poor volatile fatty acids (VFA) degradation, low Chemical Oxygen Demand (COD) removal efficiency and pH remained above $.Q. At the highest OLR of 15.4 g COD/1/d, the COD removal was 34.2 %. The highest COD removal efficiency attained was 39.8 % at an OLR of 12.3 g COD/1/d which is very low and hence leading to poor performance of the reactor. A comparison of the performance of a double-phase combining an upflow anaerobic sludge blanket (UASB) reactor with an anaerobic filter and a Hybrid reactor treating distillery slop was made. The double-phase UASB reactor showed better performance in terms of maintaining a relatively stable pH in a range which is favourable to methanogenic activity, VFA degradation, lower biomass washout and a higher COD removal efficiency. The highest COD removal efficiency attained in the double-phase UASB reactor was 92 % at an OLR of 16g COD/1/d. The Hybrid reactor showed higher methane production rate, effluent pH and biomass washout than the UASB reactor. The highest COD removal efficiency attained in the Hybrid reactor was 84 % at an OLR of 13.8 g COD/1/d. At the highest OLR of 24.9 g COD/1/d in the double-phase UASB reactor, COD removal efficiency decreased to 49 %, and at OLR of 20.77 g COD/1/d, the COD removal in Hybrid reactor decreased to 36 a. These results suggest that the doublephase UASB had better performance than the Hybrid reactor under the applied conditions. The effect of OLR on co-digestion of distillery slop and landfill leachate in a Hybrid reactor was evaluated. Step wise increase in ratio of distillery slop to leachate was carried out. The ratios of distillery slop to leachate used by volume (v/v) were : 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1. A mixture of distillery slop to leachate of 2:8 (v/v) produced a relatively more stable pH; whereas a mixture of 6:4 (v/v) corresponding to OLR of 87.1 g COD/1/d produced the highest COD removal efficiency of 81.4 % and had the highest methane production rate. Increase in the ratio of volume of distillery slop to leachate to 9:1 (v/v) lead to poor performance of the reactor. At the highest OLR of 125 g COD/1/d, there was a decrease in methane production rate, increase in biomass washout and a reduction in COD removal efficiency to 49 % which is quite low for normal digester performance. But the results have shown that co-digestion of distillery slop and landfill leachate improves the treatability of leachate. Distillery slop was treated in a UASB reactor at a constant HRT of 16.8 hours. Step wise increase in OLR was carried out until the reactor was overloaded. The overloading occurred at an OLR of 31.4 g COD/1/d and the COD removal efficiency at the same OLR was 43 %. The highest COD removal attained was 92 % at an OLR of 15.73 g COD/1/d. The distillery slap effluent from the overloaded UASB reactor caas used as a substrate in batch culture. The objective was to study the effect of ferric chloride on volatile fatty acids degradation. Different ferric chloride concentrations in the order of 5, 10, 20, 30, 50 and 100 mM were added to the batch cultures. A reduction in volatile fatty acids ie. acetate, propionate and butyrate was observed. Bottles where 100 mM of ferric chloride was added, showed the highest reduction in volatile fatty acids and maximum specific methane production. The results suggest that ferric chloride can improve on VFA degradation at higher organic loadings.