Abstract
Extensive applications of quaternary ammonium compounds (QACs) in household and industrial products inevitably lead to their release into wastewaters; however, little attention has been paid to the acute effects on activated sludge. In this work, we investigated the responses of microorganisms in a membrane bioreactor (MBR) to transient shock loads of QACs with different alkyl chain length and their impacts on MBR performance. Results showed that QACs affected microbial viability and caused damage to key enzymes (e.g., ammonium monooxygenase and nitrite oxidoreductase), inhibiting organic matter degradation and nitrogen removal. The presence of QACs also caused negative influences on dehydrogenase activity, catalase and superoxide dismutase, thus increasing the production of reactive oxygen species. Moreover, QACs with longer alkyl chains and/or benzyl groups bonded to the nitrogen atom could induce a more severe damage to cell integrity and microbial viability. The interaction with QACs also induced the release of organic matters and the changes of adhesion properties of microbial products, resulting in aggravated membrane fouling in MBRs. Our results demonstrate the acute negative effects of QACs on activated sludge, and special attention should be paid to the performance of biological wastewater treatment processes subject to the shock loads of QAC-bearing industrial streams.
Highlights
The growing concerns over the scarcity of freshwater sources and increasingly stringent environmental standards have incented advanced treatment and reclamation of domestic wastewater
Compared to the control experiment, it can be observed that quaternary ammonium compounds (QACs) significantly affected the microbial activity (p < 0.05); i.e., with an increase in the length of alkyl chains, the inhibition became severe, suggesting that a longer alkyl chain could result in higher toxicity to the bacteria
This finding is not surprising because it is alleged that the substitution of a methyl group with a benzyl group can increase the hydrophobicity of QACs (Garcia et al 2001; Xiao et al 2008), causing a stronger interaction of QACs with the microorganisms and likely affecting the cell membrane integrity
Summary
The growing concerns over the scarcity of freshwater sources and increasingly stringent environmental standards have incented advanced treatment and reclamation of domestic wastewater. Membrane bioreactor (MBR) has gradually gained popularity as a result of its superior solid–liquid separation performance that provides high-quality effluent suitable for the downstream polishing (e.g., deionization) While the great success in commercialization corroborates that the MBR technology has become more and more sophisticated in domestic wastewater treatment with the intensive R&D efforts (Kim et al 2011; Ma et al 2015; McCarty et al 2011), there is, surprisingly, limited consideration given to the increasing proportion of the industrial streams in domestic wastewater and its. The periodical shock loads of the chemical industry wastes are expected to cause adverse effects on the activity of microorganisms in MBRs. A comprehensive investigation on the microbial responses to the chemical shock loads and the consequent impacts on the performance of MBRs is of great importance for the optimization of the system operation and development of controlling strategies
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