Abstract
High-rate activated sludge (HRAS) systems are designed to shift the energy-intensive processes to energy-saving and sustainable technologies for wastewater treatment. The high food-to-microorganism (F/M) ratios and low solid retention times (SRTs) and hydraulic retention times (HRTs) applied in HRAS systems result in the maximization of organic matter diversion to the sludge which can produce large amounts of biogas during anaerobic digestion, thus moving toward energy-neutral (or positive) treatment processes. However, in addition to the energy optimization, the removal of emerging contaminants (ECs) is the new challenge in wastewater treatment. In the context of this study, the removal efficiencies and the fates of selected ECs (three endocrine disruptors (endocrine disrupting chemicals (EDCs))—nonylphenol, bisphenol A and triclosan, and four pharmaceuticals (PhACs)—ibuprofen, naproxen, diclofenac and ketoprofen) in HRAS systems have been studied. According to the results, EDCs occurred in raw wastewater and secondary sludge at higher concentrations compared to PhACs. In HRAS operating schemes, all compounds were poorly (<40%) to moderately (<60%) removed. Regarding removal mechanisms, biotransformation was found to be the dominant process for PhACs, while for EDCs sorption onto sludge is the most significant removal mechanism affecting their fates and their presence in excess sludge.
Highlights
Until recently, scientific interest in wastewater treatment focused on the impact and removal of conventional pollutants, especially in terms of macropollutants
Among endocrine disrupting chemicals (EDCs) and PhACs, the lowest mean concentrations were observed for TCS and KFN (866 ± 164 ng/L and 822 ± 336 ng/L, respectively), while the highest concentrations were observed for NP and IBF (10,896 ± 1051 ng/L and 5085 ± 1247 ng/L, respectively)
Tran et al [29] found, from worldwide monitoring data, that IBF and NPX appear to be the most abundant nonsteroidal anti-inflammatory drugs (NSAIDs) detected in influents while they stated that distribution tendencies in influents seem to be associated with their consumption patterns, climate conditions and population size/density
Summary
Scientific interest in wastewater treatment focused on the impact and removal of conventional pollutants, especially in terms of macropollutants (i.e., suspended solids, organic carbon, nitrogen, phosphorus). The removal of these pollutants has been based on well-known biochemical reactions, such as aerobic biodegradation of organic carbon by heterotrophic bacteria, nitrification/denitrification for nitrogen removal through the combination of heterotrophic bacteria (for denitrification) and nitrifiers (for nitrification) and dephosphatation for phosphorus removal by phosphorus-accumulating organisms which can absorb dissolved phosphorus from wastewater and store it in granules within their cells.
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