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Biostable drinking water, which limits bacterial growth and community changes, is obtained by removing bacterial growth-promoting nutrients, such as assimilable organic carbon (AOC), through a range of treatment processes. To date, various controlled laboratory bacterial growth tests have been developed using different inoculum types to study the growth-promoting nutrients in water. However, many countries have not considered limiting bacterial growth by reducing the growth-promoting nutrients in drinking water, because they primarily use chlorine in their distribution systems. This review provides an overview of the available methods to analyze dissolved growth-promoting nutrients in water and summarizes the current knowledge on nutrient characteristics and concentrations in water from source to tap, through various treatment processes. Bacterial growth-promoting nutrients in surface water are affected by seasonal variables, such as water temperature, precipitation, and algal blooms. The use of groundwater, bank filtration, and artificial recharge of water sources provide low bacterial growth-promoting nutrient concentrations in drinking water. The treatment type as well as operational conditions significantly affect biostable drinking water production. To achieve water biostability, it is important to understand not only the water treatment process but also the distribution conditions, including the impact of pipe materials on the nutrient levels in water. The impact of climate change on biostability as well as the role of complex and particle bound nutrients on microbial growth in drinking water distribution systems should be investigated in future studies.

In this study, the effects of algal organic matter (AOM) from Microcystis aeruginosa on the attenuation of selected trace organic contaminants (TrOCs) were observed in managed aquifer recharge using laboratory scale soil columns. Changes in dissolved organic matter and bacteriological characteristics were also investigated to elucidate the performance of managed aquifer recharge during algal bloom. AOM exhibited a high ratio of biopolymers and low molecular weight neutrals in dissolved organic matter. Dissolved organic matter was effectively removed even after the addition of AOM (4 mg L−1) in the feed water during soil passage; however, the removal rate was significantly reduced under abiotic conditions, confirming that the main removal mechanisms of dissolved organic matter involve biodegradation. AOM exhibited a much higher ratio of assimilable organic carbon/dissolved organic carbon than river water. Attenuation of four hydrophilic acid TrOCs (diclofenac, bezafibrate, ibuprofen, and ketoprofen) was significantly reduced in the presence of AOM during soil passage, but neutral TrOCs were not affected by AOM. It was difficult to remove carbamazepine using managed aquifer recharge. AOM influenced the attenuation of gemfibrozil, diclofenac, bezafibrate, ibuprofen, ketoprofen, carbamazepine, pentoxifylline, and phenacetin even after ozonation, followed by soil passage. Thus, it is important to monitor the removal of some TrOCs in managed aquifer recharge during algal blooms.

A hybrid process of managed aquifer recharge with pre-oxidation was investigated as part of a multiple-barrier approach for safe water production. This study evaluated O3 and O3/H2O2 for the pre-oxidation of urban surface water prior to managed aquifer recharge (MAR) and compared their effectiveness with respect to trace organic contaminants (TrOCs), biostability, and trihalomethane formation potential. The combination of pre-oxidation and MAR was performed using long-term column studies, and the results confirmed the removal of 64 and 56% dissolved organic carbon by using O3 and O3/H2O2, respectively. MAR combined with O3 and O3/H2O2 achieved >50% removal of dissolved organic carbon with the first 5 days of residence time. O3 alone showed better performance in alleviating trihalomethane formation potential during chlorination compared to using O3/H2O2. The pre-oxidation of urban surface water was effective in attenuating selected TrOCs (35 - >99% removal), and subsequent MAR achieved >99% removal of selected TrOCs within the first 5 days, regardless of pretreatment methods examined in this study. The results of this study provide an understanding of the effects of O3 and O3/H2O2 as pre-oxidation processes on urban surface water prior to MAR, as well as the resulting impact on MAR.

Bacterial aerosols resulting from membrane bioreactor (MBR) processes, which require excessive aeration in a confined space, are important to investigate because of their possible adverse effects on human health. This study investigated the influence of solid retention time (SRT) on bacterial aerosols from MBRs. Moreover, powdered activated carbon (PAC) and calcium were used to attenuate bacterial aerosol emissions from MBRs. The particulate matter (PM) emitted from the MBRs was reduced by 30.5 and 25.2% at SRTs of 20 and 80 d, respectively, compared to the level emitted at an SRT of 10 d. Total cell counts were similarly reduced at SRTs of 20 and 80 d. Longer SRTs also led to greater reductions in the particle size distribution of the sludge within 10 μm. Several factors in the MBR influenced the behavior of the bacterial aerosol emissions from the MBRs. This study showed that changes in viscosity and particle size induced by the SRT influenced the bacterial aerosol emissions in MBRs. Therefore, SRT was identified as an important design parameter affecting bacterial aerosol emissions in MBR processes. The amounts of particulate matter and bacterial aerosols were reduced in MBRs using PAC and calcium, both of which exerted an immediate effect on the bacterial aerosol emissions in MBRs by increasing the aerosol-particle size.

This study investigated the role of soil mixture blocks (SMBs) in the removal of trace organic contaminants and the changes in dissolved organic matter characteristics in a laboratory-scale multi-soil-layering (MSL) system. The experimental setup included three soil-based water treatment systems, namely MSL, MSL without SMBs (zeolite/slag), and a sand filter. The effect of SMBs in the removal of dissolved organic matter in MSL was not significant, but the use of zeolite/slag in MSL enhanced the removal of humic substances and building blocks. Through membrane fractionation, the size distribution of dissolved organic matter in the MSL system was not changed, and the majority of the dissolved organic matter is below 1 kDa. Ten pharmaceutically active compounds and three endocrine-disrupting compounds were used to investigate the removal of selected trace organic contaminants in the MSL system, zeolite/slag, and sand filter. The attenuation of pentoxifylline, caffeine, 17α-ethinylestradiol, estrone, and 17β-estradiol in the MSL system was similar to that for zeolite/slag, and the removal efficiency was greater than 80%. However, pentoxifylline, caffeine, 17α-ethinylestradiol, estrone, and 17β-estradiol exhibited relatively low removal efficiencies in the sand filter compared to those in the MSL system and zeolite/slag. Results from this study provide insight into the removal of selected trace organic contaminants in MSL system, which could be considered as one of the series of barriers to remove trace organic contaminants in wastewater.

This study investigated the effect of powdered activated carbon and calcium on trihalomethane toxicity in zebrafish embryos and larvae in hybrid membrane bioreactors. Two hybrid membrane bioreactors were configured with the addition of powdered activated carbon or calcium to reduce the trihalomethane formation potential. Trihalomethane formation decreased by approximately 37.2% and 30.3% in membrane bioreactor-powdered activated carbon and membrane bioreactor-calcium, respectively. Additionally, the toxic effect of trihalomethane formation was examined on zebrafish embryos and larvae. About 35% of the embryos exposed to trihalomethanes (800 ppb) showed signs of deformation, with the majority displaying coagulation within 24 h after exposure. Color preference tests, which were conducted to identify any abnormal activities of the embryos, showed an increase in preference from short to longer wavelengths upon exposure to high levels of trihalomethanes. This may indicate damage to the optical organs in zebrafish when exposed to trihalomethanes. Behavioral analysis showed reduced mobility of zebrafish larvae under different trihalomethane concentrations, indicating a decrease in the average activity time with an increasing trihalomethane concentration. The membrane bioreactor effluents were toxic to zebrafish embryos and larvae in the presence of high trihalomethane concentrations. To understand the mechanism behind trihalomethane toxicity, further studies are needed.

Biofilm formation on biofilters can influence their hydraulic performance, thereby leading to head loss and an increase in energy use and costs for water utilities. The effects of a range of factors, including hydrogen peroxide and phosphate, on the performance of biological activated carbon (BAC) and biofilm formation were investigated using laboratory-scale columns. Head loss, total carbohydrates, and proteins were reduced in the nutrient-enhanced, oxidant-enhanced, and nutrient + oxidant-enhanced BAC filters. However, there were no changes in the removal of dissolved organic matter, trihalomethane formation potential, or selected trace organic contaminants. The biofilm formation on polyvinyl chloride and stainless steel coupons using the laboratory biofilm reactor system was lower when the effluent from a nutrient-enhanced column was used, which indicated that there was less biofilm formation in the distribution systems. This may have been because the effluent from the nutrient-enhanced column was more biologically stable. Therefore, enhanced biofiltration could be used not only to reduce head loss in biofilters, but also to delay biofilm formation in distribution systems.

Soil column (SC) experiments were conducted to investigate the feasibility of using silver nanoparticles (AgNPs) as microbial inhibitors; the microbial viability affecting the degradation of pharmaceutically active compounds (PhACs) and the characteristics of organic matter during managed aquifer recharge were specifically evaluated. Natural surface water samples treated with AgNPs (0, 2.5, 5, and 10 mg L − 1 ) were continually fed into the soil columns for 2 years. The adverse impact of AgNPs on the cell membrane integrity and microbial enzymatic activity was quantitatively determined using flow cytometry and adenosine triphosphate analysis. The increase in AgNP concentration in the feed water (up to 10 mg L − 1 ) resulted in a corresponding deterioration in the performance of the managed aquifer recharge (MAR), with respect to the removal of organic carbon, oxidation of nitrogenous compounds, and PhAC attenuation. The fluorescence excitation–emission matrices of feed water and treated water showed the favorable removal of protein-like substances compared to humic-like substances regardless of the AgNP concentrations; however, the extent of removed fractions decreased noticeably when the microbial viability was lowered via AgNP treatment. The biological oxidation of organic nitrogen was almost completely inhibited when 10 mg L − 1 AgNP was added during soil passage. The attenuation of bezafibrate, ketoprofen, diclofenac, clofibric acid, and gemfibrozil was strongly associated with the significant deterioration in biodegradation as a result of AgNP activity.