Operational impacts of heavy metals on activated sludge systems: the need for improved monitoring
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Operational impacts of heavy metals on activated sludge systems: the need for improved monitoring Rasha Maal-Bared
Received: 5 August 2019 / Accepted: 28 July 2020 # Springer Nature Switzerland AG 2020
Abstract Biological nutrient removal is highly reliant on maintaining a heterogeneous, balanced, and metabolically active microbial community that can adapt to the fluctuating composition of influent wastewater and encompassing environmental conditions. Maintaining this balance can be challenging in municipal wastewater systems that sporadically receive wastewater from industrial facilities due to the impact of heavy metals and other contaminants on the microbial ecology of the activated sludge. A thorough understanding of the impacts of heavy metals on activated sludge and of practical monitoring options is needed to support decisionmaking at the wastewater utility level. This paper is divided into two parts. In the first part, the review explains what happens when heavy metals interact with activated sludge systems by highlighting biosorption and bioaccumulation processes, and when an activated sludge system switches from bioaccumulation to toxic shock. Here, it also summarizes the impacts of heavy metal exposure on plant performance. In the second part, the review summarizes practical approaches that can be used at the plant outside the realm of traditional toxicological bioassays testing to determine the possible impacts of influent heavy metal concentrations on the BNR process. These approaches include the following: monitoring operational parameters for major shifts;
R. Maal-Bared (*) Scientific Services, Quality Assurance and Environment, EPCOR Water Canada, EPCOR Tower, 2000 10423 101 Street, Edmonton, AB T5H 0E8, Canada e-mail: [email protected]
respirometry; microscopy; ATP; chemical analyses of heavy metals with a focus on synergistic impacts and inhibitory limits; and other novel approaches, such as EPS chemical analyses, molecular techniques, and quorum sensing. Keywords Heavy metals . Monitoring . Biosorption . Bioaccumulation . Toxicity . Operational parameters
Introduction Biological nutrient removal (BNR) is a secondary wastewater treatment process that reduces nitrogen and phosphorus concentrations in wastewater effluent. After playing a central role in wastewater treatment in the developed world for over a century, BNR remains one of the most environmentally and economically sustainable options to meet regulatory effluent targets for modern wastewater treatment plants (WWTP) (Gujer 2010; Xiao et al. 2015). Biological nutrient removal is primarily carried out by activated sludge processes and their variants (e.g., biofilm reactors, membrane bioreactors, sequencing batch reactors). Regardless of the process variant, BNR is highly reliant on maintaining a heterogeneous, balanced, and metabolically active microbial community that can adapt to the fluctuating composition of influent wastewater and encompassing environmental conditions (Nielsen 2009; Shahzad et al. 2015). Maintaining this balance c
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