Bacterial and methanogenic archaeal community changes during treatment of palm oil mill effluent and biological indicators for final discharge

The sustainable practice in the palm oil industry which supplies the most demanded edible oil in the world, has a long way to be well developed. One of the most challenging problems is the management of wastewater generated from the oil palm processing, known as palm oil mill effluent (POME). The most popular treatment method applied to treat POME in the palm oil mills is anaerobic ponding system. Bioconversion of POME to generate methane gas via anaerobic digestion involves a consortium of microbes which are responsible in several steps of the biodegradation process. However, the biodegradation potential of the microorganisms in the full-scale treatment system in the palm oil mill is yet to be explored. POME is also known to have the adverse environmental effects if it is not properly treated, including contamination of land and aquatic ecosystem and the loss of biodiversity. A proper treatment is needed to ensure POME can be discharged into the nearby river water or land according to the requirement set by the authority. However, the current monitoring system using physicochemical characterisation is not sensitive enough to indicate the actual source of contamination in the water bodies. In general, a detailed evaluation of the compositions of the bacterial communities in the POME final discharges obtained from four different palm oil mills and composition of bacterial community during the anaerobic treatment of POME were elucidated in this study using PCR-denaturing gradient gel electrophoresis (DGGE) and high-throughput MiSeq approaches, aided by advanced bioinformatics analysis in analysing the bacterial community structures. The correlation relationships were also carried out which allow deeper understanding of the interactions between the shift of bacterial community compositions and the changes of physicochemical properties of POME, including pH, temperature, biochemical oxygen demand (BOD5) and chemical oxygen demand (COD). The compounds analyses were also done to correlate the biodegradation potential of bacteria during the treatment of POME. The findings demonstrated a significant difference of bacterial species richness and evenness among the four POME final discharges. However, the bacterial community compositions in the different final discharges exhibited almost similar patterns in that the phylum Proteobacteria was dominant in all the samples. Interestingly, the proposed bioindicators to indicate the river water contamination due to POME final discharge, the Alcaligenaceae and Chromatiaceae families, were found to be present in all the four final discharges despite the different characteristics of the mills and the different biotreatment processes used by them. In addition, both bioindicators were also shown to be strongly and positively correlated with the concentration of BOD5, hence make them reliable bioindicators to indicate the river water contamination due to POME final discharge. Furthermore, in order to elucidate the biodegradation potential of microorganisms in the POME treatment, a thorough analysis of bacterial and archaeal communities in different stages of POME treatment was carried out which comprised of anaerobic, facultative anaerobic and aerobic processes, including the mixed raw effluent (MRE), mixing pond, holding tank and final discharge phases. The bacterial and archaeal communities were shown to be shifted according to their biodegradation potential and the changes of physicochemical properties of POME. Based on the data obtained, the following biodegradation processes were suggested to take place in the different treatment stages: (1) Lactobacillaceae (35.9%) dominated the first stage that contributed to high lactic acid production; (2) higher population of Clostridiaceae in the mixing pond (47.7%) and Prevotellaceae in the holding tank (49.7%) contributed to the higher acetic acid production; (3) the aceticlastic methanogen Methanosaetaceae (0.6–0.8%) played a role in acetic acid degradation in the open digester and closed reactor for methane generation; (4) Syntrophomonas (21.5–29.2%) might be involved in fatty acids and acetic acid degradations by syntrophic cooperation with hydrogenotrophic methanogen, Methanobacteriaceae (0.6–1.3%); (5) phenols and alcohols detected in the early phases but not in the final discharge indicated the successful degradation of lignocellulosic materials. A sustainable palm oil industry could be developed with better POME pollution management by adopting a reliable and accurate monitoring system. To our knowledge, this is the first study reported on the biodegradation mechanisms involved in the different stages of the full-scale nt of POME.

Text FBSB 2019 7 - ir.pdf Download (1MB)

Actions (login required)

View Item