Effect of substrate, pH and hydraulic retention time (HRT) in tertiary treatment of POME using biogranules

Abstract

Palm oil mill effluent (POME) has high concentrated dark brown colloidal suspension. One of the alternatives in treating POME is using biological treatment via biogranulation system operated with sequential anaerobic and aerobic condition. However, many factors which are believed to influence the performance of the systems are not yet well understood especially the ones related to the treatment of POME. Experiments were conducted to investigate the removal performance of color and COD in order to assess the effectiveness and feasibility of biogranules for tertiary treatment of POME. The operating parameters such as hydraulic retention time (HRT), pH and substrates in different concentrations were evaluated. First, effects of three different pH values (5, 7 and 9) were observed on COD removal and decolorization with 24 hours HRT of sequential anaerobic and aerobic phases. pH 7 was elected for the rest of the experiments due to better color and COD removal. At second stage where pH was adjusted to pH 7 effects of three different types of carbon sources namely glucose, sodium acetate and ethanol on COD and color removal were evaluated. Each of the substrate was tested with four concentrations of 250, 500, 1000 and 2000 mg/L. From this experiment glucose concentration of 2000 mg/L showed the best removal performance. The third stage of experiments was conducted at pH 7 with glucose concentration of 2000 mg/L to investigate the effect of different HRT (24, 18, 12 and 6 hours). Based on the results, the experiment conducted with HRT of 24 hours at pH 7 and glucose concentration of 2000 mg/L showed the highest removal percentages for color (38%) and COD (84%). All of the results obtained were analyzed using analysis of variance (ANOVA).