Bioaugmented anaerobic degradation of produced water

Abstract

In this study, the continuous bioaugmented degradation of a simulated oil field produced water (PW) in a 3 L submerged anaerobic membrane bioreactor (SAMBR), and the bioaugmented batch degradation of polycyclic aromatic hydrocarbons (PAH), and naphthenic acid (NA) which are commonly found in PW were investigated. The aim was to develop and optimize the bioaugmentation process where the use of a membrane in the SAMBR to uncouple the solid and liquid retention times, may improve the current biological treatment performance, retain the bioaugmented biomass, and investigate the fate of both the bioaugmented and indigenous microbial community. The next generation 16S metagenomic MiSeq sequencing technique was used to generate V4 amplicons to monitor the microbial population in the reactors, and obtain a better understanding of the archaeal and bacterial populations. Experiments developing enrichment cultures to select for microbial communities capable of efficiently degrading recalcitrant hydrocarbons revealed that although PAHs, NAs, and PW can all rapidly shape the methanogenic microbiomes from exotic sources in as quickly as 14 days, the dominant phyla varied depending on the biomass source, feed type, and variation in nutrients. The dominant methanogens identified were Methanoregula, Methanosarcina, Methanosaeta, and Methanobacterium, and clearly played important roles in the syntrophic degradation of PAHs, NAs, and PW, along with saccharolytic fermenters such as Kosmotoga, Clostridium, and Syntrophobacter. Experiments on the degradation of PAHs whilst increasing the concentration of nutrients in the media, found that increasing the nutrient concentration had no adverse effect on the degradation of PAHs as single compounds but reduced the rate of degradation of PAHs in mixed cultures, both via co-metabolism, and in the presence of increasing salinity. Furthermore, when the biomass was “primed” by prior exposure to PAHs, COD removal was achieved in 1/8th of the time that it took with pristine biomass. The bioaugmented degradation of the PAH mix showed cumulative methane produced by the bioaugmented assay was 219% more than that produced by the non-bioaugmented assay cultures. Experiments on the degradation of NAs whilst increasing nutrient concentrations found that the cumulative methane produced from the anaerobic degradation of surrogate NAs as single compounds, and as a mix without co-metabolism increased with increasing nutrient concentration up to but not exceeding 200% BMP media. However, when a mix of NAs were degraded, then methane production is enhanced with increasing nutrient concentration up to but not exceeding 100% BMP. The average cumulative methane produced in the bioaugmented assay was at least 230% more than that of the non-bioaugmented assay. Experiments on PW degradation with a bioaugmented SAMBR which was bioaugmented with Methanothrix soehngenii, Methanothrix thermoacetophila, Kosmotoga shengliensis, Kosmotoga olearia, Thauera butanivorans, and Desulfovibrio capillatus, revealed that the methane produced by the bioaugmented SAMBR was more than 600% that of the control SAMBR. The feed chemical oxygen demand (COD) ranged from 2.7 to 4.5 g.L-1, and bioaugmented SAMBR COD removal rate was statistically significant at 88%, while the control was 61%. The maximum oil and grease (O & G) removal in bioaugmented SAMBR, was ~94%; with an average of 86%, while O & G removal in the control SAMBR was on average 79% mark. 16S metagenomic MiSeq sequencing on both bioaugmented and non-bioaugmented SAMBRs, and batch reactors revealed the most dominant archaea genera as Methanobacterium, and Methanosaeta, and the most dominant bacteria genus was Kosmotoga.