The impact of nitrate dosing and semi-conductive media on anaerobic fluidised-bed treatment of low-strength wastewater
File(s)
Author(s)
Beirns, Emma
Type
Thesis
Abstract
This thesis describes the performance of two anaerobic fluidised-bed bioreactors (AFBRs) operated over 290 days and the microbial communities within. Both reactors utilised 7-channel plastic beads as the fluidised media, however, in one reactor, the media had a semi-conductive polyaniline coating to stimulate direct interspecies electron transfer (DIET). The synthetic low-strength wastewater fed into the reactors also contained a low dose of nitrate, stimulating denitrification, as well as both nitric oxide dismutation and dissimilatory nitrate reduction to ammonia (DNRA).
Although the performance data showed no significant difference to the methane production or yield between the two AFBRs, metagenomics analysis showed that the polyaniline coating did favour electroactive microbes. Furthermore, by the late stages of operation, a constant low presence of oxygen stimulated a high relative abundance of oxygen-tolerant methanogens. This demonstrates that polyaniline is successful at stimulating DIET, however, the performance of methanogenesis may have been impacted by the presence of nitrate.
The presence of oxygen in the biogases and the increased concentration of ammonia in the effluents confirmed the activation of nitric oxide dismutation and DNRA. Furthermore, genes for DNRA were detected and sequence similarity searches found genes that had some similarity to nitric oxide dismutase genes. Mass balances calculations showed that the polyaniline-containing AFBR had a higher rates of nitrous oxide production. This implies that DIET favoured conventional denitrification, albeit incomplete, over nitric oxide dismutation or DNRA.
This experiment is the first to explore any relationship between DIET and nitric oxide dismutation, ultimately finding no evidence of linkage between the two. This is likely due to nitric oxide dismutation being an electron neutral reaction, and therefore DIET does not confer any advantage. The establishment of nitric oxide dismutation in an anaerobic wastewater treatment reactor shows great potential for reducing nitrous oxide emissions if the process can be scaled.
Although the performance data showed no significant difference to the methane production or yield between the two AFBRs, metagenomics analysis showed that the polyaniline coating did favour electroactive microbes. Furthermore, by the late stages of operation, a constant low presence of oxygen stimulated a high relative abundance of oxygen-tolerant methanogens. This demonstrates that polyaniline is successful at stimulating DIET, however, the performance of methanogenesis may have been impacted by the presence of nitrate.
The presence of oxygen in the biogases and the increased concentration of ammonia in the effluents confirmed the activation of nitric oxide dismutation and DNRA. Furthermore, genes for DNRA were detected and sequence similarity searches found genes that had some similarity to nitric oxide dismutase genes. Mass balances calculations showed that the polyaniline-containing AFBR had a higher rates of nitrous oxide production. This implies that DIET favoured conventional denitrification, albeit incomplete, over nitric oxide dismutation or DNRA.
This experiment is the first to explore any relationship between DIET and nitric oxide dismutation, ultimately finding no evidence of linkage between the two. This is likely due to nitric oxide dismutation being an electron neutral reaction, and therefore DIET does not confer any advantage. The establishment of nitric oxide dismutation in an anaerobic wastewater treatment reactor shows great potential for reducing nitrous oxide emissions if the process can be scaled.
Version
Open Access
Date Issued
2024-12-16
Date Awarded
01/06/2025
License URL
Advisor
Lee, Po-Heng
Smith, Stephen
Publisher Department
Department of Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)