Anerobic Treatment in Novel Contact Digester

Laboratory studies are presented on a combined jet gas mixed and sludge blanket anaerobic contact digester with continuous sludge recycle. Raw piggery waste substrate is used as feed with a COD_nf contents of 13-14 g/L. The aims of the study are to establish lower limits of hydraulic retention and upper limits of COD loading, in conditions of continuous sludge recycle without intentional sludge wasting, in order to formulate design criteria for the process operated either as a roughing treatment or a combined primary-secondary treatment of strong industrial wastewaters. The studies show the feasibility of obtaining methanogenic conditions at hydraulic retention (HRT) as low as 0.5 d and corresponding organic load of 28 kg COD/m³d. Satisfactory secondary treatment is attained at HRT = 3.5d and a load of 4 kg COD_nf/m³d, yielding steady state COD_nf removals in excess of 85% and filtered effluent COD_f and BOD_5f of 1,200 and 500 mg O₂/^L³, respectively. The biogas production at that loading is 3.15 m³/m³d (75% CH₄) which corresponds to 0.17 m³/kg COD_nf removed.