No abstract

The perchlorate anion (ClO4–) has been found in potentially harmful concentrations in numerous water sources. Because perchlorate is not removed by conventional water treatment processes, new treatment processes are needed. Biological perchlorate reduction is a promising alternative. The authors investigated a hydrogen‐oxidizing hollow‐fiber membrane–biofilm reactor system for perchlorate removal. Hydrogen is an ideal electron donor for biological drinking water treatment because it presents no toxicity, is inexpensive, and is unlikely to persist as a source of biological instability in distributions systems. The reactor delivers hydrogen in an efficient and safe manner. Results showed that biological perchlorate reduction takes place concurrently with nitrate reduction, no specialized inoculation is required, and perchlorate can be removed to below the preliminary regulatory standards with no chemical addition other than hydrogen gas. The optimal pH is 8, and the accumulation of intermediates is unlikely. Full denitrification and pH control may be required for excellent perchlorate removal.

Microbial biofilms can be both cause and cure to a range of emerging societal problems including antimicrobial tolerance, water sanitation, water scarcity and pollution. The identities of extracellular polymeric substances (EPS) responsible for the establishment and function of biofilms are poorly understood. The lack of information on the chemical and physical identities of EPS limits the potential to rationally engineer biofilm processes, and impedes progress within the water and wastewater sector towards a circular economy and resource recovery. Here, a multidisciplinary roadmap for addressing this EPS identity crisis is proposed. This involves improved EPS extraction and characterization methodologies, crossreferencing between model biofilms and full-scale biofilm systems, and functional description of isolated EPS with in situ techniques (e.g. microscopy) coupled with genomics, proteomics and glycomics. The current extraction and spectrophotometric characterization methods, often based on the principle not to compromise the integrity of the microbial cells, should be critically assessed, and more comprehensive methods for recovery and characterization of EPS need to be developed.

The membrane-biofilm reactor (MBfR), sometimes known as the membrane-aerated biofilm reactor (MABR), is an emerging treatment technology based on gas-transferring membranes. The membranes typically supply a gaseous electron donor or acceptor substrate, such as oxygen, hydrogen, and methane. The substrate diffuses through the membrane to a biofilm naturally forming on the membrane outer surface. The complementary substrate (electron donor or acceptor) typically diffuses from the bulk liquid into the biofilm, making MBfR counter diffusional. This paper reviews the unique behavior of counter-diffusional biofilms and highlights recent research on the MBfR. Key advances include insights into the microbial community structure of MBfRs, applying the MBfR to novel contaminants, providing a better understanding of biofilm morphology and its effects on MBfR behavior, and the development of methane-based MBfR applications. These advances are likely to further the development of the MBfR for environmental applications, such as energy-efficient wastewater treatment and advanced water treatment.

Bacteria have their own form of "twitter" communication, described as quorum sensing (QS), where bacteria emit and sense chemical signal molecules as a means to gauge population density and control gene expression. Many QS-controlled genes relate to biofilm formation and function and may be important for some water and wastewater treatment biofilms. There is a need to better understand bacterial QS, the bacteria biofilm aspects influenced by QS in engineered reactors, and to assess how designs and operations might be improved by taking this signaling into account. This paper provides a critical review of QS and how it relates to biofilms in engineered water and wastewater treatment systems and identifies needs for future research.