Abstract
The ever growing demand of effluent quality standards, increasing costs of electricity consumption and carbon footprint presents a problem under current wastewater treatment (WWT) processes. This has directed interest towards more circular approaches to treating wastewater. Theoretically, anaerobic wastewater treatment (AnWWT) is a promising approach to traditional processes that could address the conflicting demands. However, there is a knowledge gap on how emerging contaminants influence AnWWT. In particular, the literature on how pharmaceutical micropollutants affect anaerobic bacteria is limited. A review of current research on the occurrence of pharmaceuticals in wastewater identified 10 compounds of interest: atenolol, bezafibrate, caffeine, carbamazepine, ciprofloxacin, clarithromycin, erythromycin, lidocaine, oxytetracycline and propranolol. All were selected to investigate the impact of environmentally relevant pharmaceutical concentrations during AnWWT.A novel technique was developed to evaluate the biochemical methane potential (BMP) of low strength wastewater substrates. This allowed for the rapid assessment of anaerobic microbes under various conditions and later the impacts of pharmaceuticals. Encouraging results showed that the anaerobic microbes were resilient to a range of substrate strengths and temperatures, but mesophilic conditions (38⁰C) were optimal.
Laboratory experiments investigated the impacts of environmentally relevant pharmaceutical concentrations on the BMP of the wastewater substrate. This was a novel aspect of this study; most studies published up to this time had only considered the influence of individual pharmaceuticals (mainly antibiotics) at concentrations much higher than the amount expected in influent. Results showed that pharmaceuticals could negatively impact the performance of anaerobic microbes. However, this was dependant on pharmaceutical concentrations and the diversity of the microbial community. Interestingly, microbes were shown to adapt to the presence of pharmaceuticals over time.
Semi-continuous experiments, using a continuously stirred tank reactor (CSTR), were designed to investigate the influence of pharmaceuticals during AnWWT. Performance of the reactor declined after pharmaceuticals were introduced and when concentrations were increased, but recovery was noted. It suggested that shock loadings of pharmaceuticals can have negative consequences on treatment. Also, removal rates varied for each compound and depended on the organic loading rate (OLR). High removals were observed for clarithromycin (>75%) during a low OLR (1.83g COD d-1 ). Ciprofloxacin, caffeine carbamazepine and lidocaine were moderately removed (36 – 60%), whilst low removals were determined for atenolol (7 – 17%). Clarithromycin and caffeine continued to be highly removed from the wastewater (> 60%) after the OLR was increased (3.66g COD d-1 ). Lidocaine and atenolol removals remained consistent but negative removals were observed for bezafibrate and carbamazepine. Adsorption and biomass washout were expected to have contributed to the concentrations found in the wastewater effluent.
Finally, recommendations on the type of wastewater suited to AnWWT were provided and it is suggested that AnWWT may be less suited to mainstream municipal wastewater due to variability of micropollutants. Instead, opportunities could include direct conversion treatment of defined (low-variation) streams such as specific industrial effluents and smaller treatment plants (including small sewage systems). Future recommendations included the impact of other emerging pollutants, the performance of AnWWT using different sources of biomass and low cost techniques for biomass retention to improve degradation of micropollutants.
| Date of Award | 2022 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Ole Pahl (Supervisor), Moyra McNaughtan (Supervisor) & Colin Hunter (Supervisor) |