Evaluation of the bio-kinetics of cement kiln dust in an upflow anaerobic sludge blanket reactor for treatment of palm oil mill effluent as a function of hydraulic retention time

Abstract

In this paper we operated an upflow anaerobic sludge blanket reactor (UASBR) continuously at 35°C in order to observe the effects of varying the hydraulic retention time (HRT) from 3.5 to 34.5d and varying the organic loading rate (OLR) from 1.5 to 46kgCODm−3d−1. The pH of the digester improved, which we varied from 1.5 to 14.5gL−1 CaO-CKD, a range pH 7.5. A high COD degradation rate of 97% and mixed liquor suspended solids (MLVSS) of 99,000 mgL−1 were achieved at an HRT of 24.5d. The maximum methane yield was 0.346lCH4/g CODremoved. A CO2 reduction of 87% was obtained at an OLR of 26.5 (r=0.99). The optimum conditions for digestion of the palm oil mill effluent were determined by studying the bio-kinetics of granulation. The growth yield (YG) was 1.45g VSS/g CODremoved day; the specific biomass decay (b) was 0.056; the specific biomass growth rate (μmax) was 0.988d−1; the saturation constant (Ks) was 460; and the critical retention time (Θc) was 2.464d−1. With a feed flow rate (QF) of 1.65l/d, the upflow velocity (Vup) was 0.6m/h, and for a QF of 2.45l/d, Vup was 0.75m/h.