A series anaerobic-aerobic down-flow hanging sponge (DHS) reactor for the treatment of palm oil mill effluent (POME)

Abstract

Abstract Palm oil mill effluent (POME) contains very high organic compounds that must be treated before being discharged into the environment. Pond technology has been widely used for the treatment of POME; however, it requires a huge area of land. Down-flow hanging sponge (DHS) reactor has shown a high pollutant removal efficiency, less energy, and land area requirement. This study aimed to investigate the performance of a series of anaerobic (R3) and aerobic (R4) DHS reactors in treating POME. The reactor was continuously supplied with POME in three different phases for 165 days. The COD loading rate was set at 3.06, 6.12, and 12.24 kg-COD/m³·day in Phase 1, Phase 2, and Phase 3, respectively. Hydraulic retention time (HRT) was set at 47 min and 50 min, in R3 and R4, respectively. The reactors showed good performance for pollutant removal efficiency, especially COD. In Phase 1, the average COD removal rate was 2.68 and 0.27 kg-COD/m³·d in R3 and R4, respectively. In Phase 2, when the COD loading rate was increased, the average COD removal rate achieved 4.12 and 1.53 kg-COD/m³·d in R3 and R4, respectively. In Phase 3, the COD loading rate was doubled to 12.24 kg-COD/m³·day and the average COD removal rate of 5.81 and 2.90 kg-COD/m³·d was achieved in R3 and R4, respectively. During operation, the concentration of nitrate fluctuated in R4, which indicated that nitrification had occurred. Phosphate could be reduced in R3, but only a small portion could be removed in R4. Total suspended solids (TSS) could be effectively removed in R4. These results revealed that a combination of anaerobic-aerobic DHS reactors showed good performance in removing pollutants such as COD and TSS. Therefore, DHS technology can be used as a polishing treatment for treated POME.