Palm oil mill effluent (POME) treatment using a combined anaerobic-microalgae down-flow hanging sponge (DHS) reactor

Abstract

Abstract Palm oil mill effluent (POME) generated from the production of palm oil contains organic and inorganic contaminants that can be a nutrient source for microorganisms such as bacteria, fungi, and microalgae. In this study, POME was treated using a combined anaerobic (R1) and microalgae (R2) in down-flow hanging sponge (DHS) reactor. Chlorella pyrenoidosa was immobilized in sponge carriers of R2 and LED lights were used for 12 hours per day to support microalgae growth. The DHS reactors were continuously operated for 165 days in three phases with different COD loading rates, namely 3, 6, and 12 kg-COD/m³·day in Phase 1, Phase 2, and Phase 3, respectively. The hydraulic retention time (HRT) was set at 46 min and 52 min in R1 and R2, respectively. The highest COD removal rate was achieved at 6.93 kg-COD/m³·day and 4.85 kg-COD/m³·day in R1 and R2, respectively. In addition, maximum phosphate removal was 68% in both reactors. Increased concentration of nitrate in R-2 indicated that nitrification may occur in the reactor. The pH of R1 effluent was relatively stable at neutral conditions, while the pH value of R2 effluent slightly increased. Based on visual observation, bacteria biofilm also grew in the microalgae reactor (R2). Synergistic bacteria-microalgae may play an important role in pollutant removal. The results of this study show that a combined anaerobic and microalgae DHS reactor can be used as an alternative for POME treatment because they have a shorter HRT and can be applied in a small area.