A constructed wetland system for bio-polishing palm oil mill effluent and its future research opportunities

This study was carried out to investigate the potential of Scirpus grossus in polishing final discharge of palm oil mill effluent (POME). The removal of total suspended solids (TSS) and chemical oxygen demand (COD) from POME by S. grossus was conducted in two different flow systems: a sub-surface (SS) and a free-surface (FS) batch constructed wetland (CW) systems. S. grossus was exposed to POME for 30 days. It was found that S. grossus plants performed better in TSS removal from POME in both systems (98 %) as compared with unplanted treatments (85 %). Plants developed root mats, which increased the filtration efficiency, leading to a reduction of TSS during the treatment period. Additionally, on day 7, the TSS removal by the FS system was higher than that by the SS system, with concentrations of 8 and 99 mg/L, respectively, on that day. The content of suspended solids in POME was believed to help this happen, as a system with more suspended solids will sediment faster than a system with less suspended solids. The removal of COD, on the other hand, did not differ between the two flow systems or between treatments with and without plants (96-97 %), indicating that sand medium played a significant role in COD removal from POME. It can be concluded that treatment combining sand medium, S. grossus, and the FS system is highly capable of polishing TSS and COD in final discharged POME. CW could be a promising green solution to improve the environmental ecosystem and ensure sustainability.

Automated summary

The study showed that Scirpus grossus plants were effective in removing TSS from palm oil mill effluent, with a higher removal rate in the free-surface system compared to the sub-surface system on day 7. The presence of suspended solids in the effluent influenced the sedimentation rate, impacting TSS removal efficiency. COD removal was not significantly different between systems or with or without plants, indicating the importance of the sand medium in COD removal.