The research progress, hotspots, challenges and outlooks of solid-phase denitrification process.

Nitrogen pollution is one of the main reasons for water eutrophication. The difficulty of nitrogen removal in low-carbon wastewater poses a huge potential threat to the ecological environment and human health. As a clean biological nitrogen removal process, solid-phase denitrification (SPD) was proposed for long-term operation of low-carbon wastewater. In this paper, the progress, hotspots, and challenges of the SPD process based on different solid carbon sources (SCSs) are reviewed. Compared with synthetic SCS and natural SCS, blended SCSs have more application potential and have achieved pilot-scale application. Differences in SCSs will lead to changes in the enrichment of hydrolytic microorganisms and hydrolytic genes, which indirectly affect denitrification performance. Moreover, the denitrification performance of the SPD process is also affected by the physical and chemical properties of SCSs, pH of wastewater, hydraulic retention time, filling ratio, and temperature. In addition, the strengthening of the SPD process is an inevitable trend. The strengthening measures including SCSs modification and coupled electrochemical technology are regarded as the current research hotspots. It is worth noting that the outbreak of the COVID-19 epidemic has led to the increase of disinfection by-products and antibiotics in wastewater, which makes the SPD process face challenges. Finally, this review proposes prospects to provide a theoretical basis for promoting the efficient application of the SPD process and coping with the challenge of the COVID-19 epidemic.

The potential of decentralised wastewater treatment in urban and rural sanitation in South Africa: lessons learnt from a demonstration-scale DEWATS within the eThekwini Municipality

The design principles of decentralised wastewater treatment systems (DEWATS) make them a practical sanitation option for municipalities to adopt in fast-growing cities in South Africa. Since 2014, a demonstration-scale DEWATS with a modular design consisting of a settler, anaerobic baffled reactor (ABR), anaerobic filter (AF), vertical down-flow constructed wetland (VFCW) and horizontal flow constructed wetland (HFCW) has been in operation in eThekwini. A performance evaluation after the long-term operation was undertaken in 2019 by comparing the final effluent with national regulatory requirements. Despite limitations in characterising the raw wastewater, a comparison of the settler and final effluent quality indicated high (≥ 85%) removal efficiencies of total chemical oxygen demand (CODt), ammonium-N (NH4-N) and orthophosphate-P (PO4-P), 75% removal of total suspended solids (TSS) and 83.3% log10 removal of Escherichia coli. Lack of exogenous and endogenous carbon and high dissolved oxygen (DO) concentrations (> 0.5 mg·L−1) inhibited denitrification in the HFCW, resulting in 12.5% of the effluent samples achieving compliance for nitrate-N (NO3-N). Moreover, mixed aggregate media and low residence times in the HFCW may have also contributed to poor NO3-N removal. During the COVID-19 lockdown, an unexpected shutdown and subsequent resumption of flow to the DEWATS indicated a 16-week recovery time based on achieving full nitrification in the HFCW. Although design modifications are necessary for the HFCW, the installation of urine diversion flushing toilets at the household level will reduce the nutrient loading to the DEWATS and potentially achieve fully compliant effluent. Alternatively, the application of two-stage vertical flow constructed wetlands to improve denitrification should also be explored in the South African context. With an improved design, DEWATS has the potential to fill the gap in both urban and rural sanitation in South Africa, where waterborne sanitation is still desired but connections to conventional wastewater treatment works (WWTWs) are not possible. © The Author(s) Published under a Creative Commons Attribution 4.0 International Licence (CC BY 4.0).

A Review and Discussion of Wastewater Process Inhibitions Observed in the U.S. as a Result of COVID-19 Countermeasures

This paper provides a summary of case studies from water resource recovery facilities (WRRFs) in the United States that have experienced wastewater process inhibitions as a result of COVID-19 countermeasures. Anecdotal feedback from staff operating impacted WRRFs and preliminary influent toxicity screening data point to quaternary ammonium compounds (QAC) in the influent as the possible cause for the inhibition events. As such, a high-level overview of QACs, and a synopsis of their fate and potential impacts in WRRFs, are summarized in this paper. Empirical evidence from full-scale facilities is presented, demonstrating that high concentrations of disinfectants used during the pandemic caused nitrification inhibition. This paper also highlights the potential of disinfectants to inhibit enhanced biological phosphorus removal (EBPR), a treatment phenomenon not yet reported on in literature to our knowledge. Finally, the authors provide recommendations for best management operational practices to mitigate inhibitory impacts at WRRFs in the future. Copyright © 2021 Water Environment Federation

Family Sphingomonadaceae as the key executor of triclosan degradation in both nitrification and denitrification systems

The usage of triclosan (TCS) has increased with the COVID-19 virus outbreak, causing more TCS were released into wastewater treatment systems. However, the difference in TCS removal pathway and TCS degrading bacteria between nitrification and denitrification systems was still unknown. In this study, batch tests of TCS biodegradation mechanism and DNA stable isotope probing (DNA-SIP) technique were applied to decrypt the different TCS removal pathway and the corresponding degrading taxon between two nitrification and two denitrification systems. The main TCS degradation pathway in both nitrification and denitrification systems were the metabolism of heterotrophic bacteria, only a little TCS was degraded by the co-metabolism of heterotrophic or nitrifying bacteria, and higher NH4+-N or NO3--N concentration contributed to more TCS degradation. Moreover, denitrification system had stronger TCS removal capacity (0.11 and 0.65 mg TCS/g SS) than nitrification system (0.83 and 1.12 mg TCS/g SS). DNA-SIP assay further revealed that active TCS degrading bacteria in both systems belonged to Sphingomonadaceae family. Furthermore, the oligotype TATGCC, TAATCA and GCCCCG of Sphingomonadaceae played important roles in degrading TCS in both systems. Moreover, reactor performance and mixed liquor suspended solids might play important roles in shaping the ecotypes of Sphingomonadaceae, which caused the difference in degrading TCS between nitrification and denitrification systems. This lab-scale research might provide meaningful opportunities for evaluating the scale-up applications, and the TCS degrading bacteria identified in present study might be recommended to be used as bioaugmentation strains in practical engineering.