Browsing by Author "Scrimshaw, Mark"

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    Engineering biological wastewater treatment for the removal of hazardous chemicals.
    (Cranfield University, 2019-10) Mensah, Lawson; Campo Moreno, Pablo; Scrimshaw, Mark
    The European Union’s Environmental Quality Standards (EQS) continue to be stringent with regards to discharge of hazardous chemicals (HCs) (mainly organic micropollutants) from wastewater treatment plants (WWTPs). The strict limits are driven by the growing interest in wastewater reuse, evidence of feminisation of male aquatic species and bioaccumulation of HCs in water-based biota. WWTPs are the last barrier to these chemicals getting into the environment from homes, institutions and industries and therefore optimisation of existing WWTPs is critical. The operational conditions of the WWTPs such as solid retention time (SRT), hydraulic retention time (HRT), dissolved oxygen (DO) concentration and seasonal temperature variations have been proven to influence the removal of these HCs and also affect the microbial/bacterial diversity in WWTPs. This study therefore aimed to find the missing link in the literature, which is to seek the relationship between the microbial/bacterial diversity or abundance and HCs removal in WWTPs. A pilot-scale study was conducted to analyse the microbial and bacterial diversity using phospholipids fatty acid and 16S rRNA analysis respectively at 3, 10 and 27 d SRT (at constant 8 h HRT) and then repeated at a fixed 27 d SRT while HRT varied at 8, 16 and 24 h. The concentrations of nonylphenols and estrogens in the influent and effluent were also analysed using LC-MS/MS to determine the plant’s chemical removal efficiency. The results showed that raising SRT (from 3 to 27 d) and HRT (from 8 to 24 h) increased bacterial diversity by 2.7 times and increased the removal of EE2 by 11%. The pilot-scale also revealed 32 novel positive correlations between bacterial genera abundance and HCs removal. The abundances of Hyphomicrobium, Mesorhizobium, Planctomyces, and Rhizomicrobium positively correlated with the removals of estrogens (E1, E2 and E3) and with nonylphenols (NP₂ EC, NP ₅EO) at r- values >0.7. The experiment was repeated by surveying the bacterial diversity in 12 full-scale activated sludge plants (ASPs) operating at varying DO levels, SRTs (4.9 to 22.3 d), HRTs (6.2 to 26.6 h) and temperature (10.6 to 20.3 ˚C). The concentrations of 26 micropollutants (analgesics, antibiotics, anti-depressants, beta-blockers, estrogens, flame retardants etc.) were also analysed in the influent and effluent. The results showed that bacterial diversity in the full- scale reactor differed from that of the pilot-scale plant. Euclidean distance matrix shows that temperature (p<0.005) was the most influential parameter in chemical removal and bacterial diversity. SRT and HRT were also important in bacterial diversity and HC removal but not in every ASP. Removal of HC followed a pseudo first order kinetics with metformin and ibuprofen achieving >98% removals. DO concentration did not show any effect due to lack of variation across the WWTPs. Once again, some novel correlations between bacterial genera abundance and chemical removal were found. The abundances of Candidatus Accumulibacter (a phosphate accumulating bacteria capable of denitrification) and Nitrosomonas (nitrite-oxidising bacteria) correlate positively with the removal of trixylenyl phosphate (flame retardant) at R>0.7. Anaeromyxobacter dehalogenans abundance also correlates positively with the removal of erythromycin. This work has shown that process parameters do influence both bacterial diversity and hazardous chemical removal, and there are correlations between bacteria taxa abundance and HCs removal. This knowledge will be vital in the discussion on improving existing activated sludge plants achieve better chemical removal and it will also be the foundation for future research into correlations of bacterial taxa abundance with chemical removal in the ASP reactor.
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    Influence of solids and hydraulic retention times on microbial diversity and removal of estrogens and nonylphenols in a pilot-scale activated sludge plant
    (Elsevier, 2023-08-30) Mensah, Lawson; Petrie, Bruce; Scrimshaw, Mark; Cartmell, Elise; Fletton, Mandy; Campo, Pablo
    The removal of EDCs in activated sludge processes can be enhanced by increasing solid and hydraulic retention times (SRT and HRT); it has been suggested that the improvement in removal is due to changes in microbial community structure (MCS). Though the influence of SRT and HRT on chemical removal and MCS has been studied in isolation, their synergistic impact on MCS and the removal of estrogens and nonylphenols in activated sludge remains unknown. Hence, we investigated how both parameters influence MCS in activated sludge processes and their ulterior effect on EDC removal. In our study, an activated sludge pilot-plant was fed with domestic sewage fortified with 100 and 1000 ng/L nonylphenols or 2 and 15 ng/L estrogens and operated at 3, 10 and 27 d SRT (constant HRT) and at 8, 16 and 24 h HRT (constant SRT). The MCS was assessed by phospholipid fatty acids (PLFA) analysis, and the archaeal and bacterial diversities were determined by 16S rRNA analysis. From the PLFA, the microbial abundance ranked as follows: Gram-negative > fungi > Gram-positive > actinomycetes whilst 16S rRNA analysis revealed Proteobacteria > Bacteroidetes > Others. Both PLFA and 16S rRNA analysis detected changes in MCS as SRT and HRT were increased. An SRT increment from 3 to 10 d resulted in higher estrone (E1) removal from 19 to 93% and nonylphenol-4-exthoxylate (NP4EO) from 44 to 73%. These findings demonstrate that EDC-removal in activated sludge plants can be optimised where longer SRT (>10 d) and HRT (>8 h) are suitable. We have also demonstrated that PLFA can be used for routine monitoring of changes in MCS in activated sludge plants.
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    Proactive monitoring of changes in the microbial community structure in wastewater treatment bioreactors using phospholipid fatty acid analysis
    (Elsevier, 2024-12-01) Mensah, Lawson; Cartmell, Elise; Fletton, Mandy; Scrimshaw, Mark; Campo, Pablo
    Diverse microbial community structures (MCS) in wastewater treatment plants (WWTPs) are vital for effectively removing nutrients and chemicals from wastewater. However, the regular monitoring of MCS in WWTP bioreactors remains unattractive owing to the skill and cost required for deploying modern microbial molecular techniques in the routine assessment of engineered systems. In contrast, low-resolution methods for assessing broad changes in the MCS, such as phospholipid fatty acid (PLFA) analysis, have been used effectively in soil studies for decades. Despite using PLFA analysis in soil remediation studies to capture the long-term effects of environmental changes on MCS, its application in WWTPs, where the microbial mass is dynamic and operational conditions are more fluid, remains limited. In this study, microbial communities in a controlled pilot plant and 12 full-scale activated sludge plants (ASPs) were surveyed over a two-year period using PLFA analysis. This study revealed that changes in the MCS in wastewater bioreactors could be detected using PLFA analysis. The MCS comprised 59 % Gram-negative and 9 % Gram-positive bacteria, 31 % fungi, and 1 % actinomycetes. The abundances of Gram-negative bacteria and fungi were strongly inversely correlated, with an R2 = 0.93, while the fatty acids cy17:0 and 16:1ω7c positively correlated (R2 = 0.869). Variations in temperature, solid retention time, and WWTP configuration significantly influenced the MCS in activated sludge reactors. This study showed that WWTP bioreactors can be routinely monitored using PLFA analysis, and changes in the bioreactor profile that may indicate imminent bioreactor failure can be identified.