The Legionella genus houses several opportunistic pathogens that cause legionellosis, which ranges from mild (Pontiac Fever) to severe (Legionnaires' disease). Legionella pneumophila (Lp), the leading observed cause of legionellosis, persists in drinking water distribution systems (DWDSs) and building plumbing systems due to factors such as intrinsic disinfectant resistance and shielding by biofilms and free-living amoebae. Remediation efforts, therefore, might be hindered if Lp is primarily associated with biofilms, free-living amoebae, or other particles. However, the extent to which Lp and other Legionella spp. in drinking water occur as free-living organisms versus associated with free-living amoebae or other particles is unclear. In this study, we quantified free-living and particle-associated Lp and Legionella spp. in first-draw and flushed drinking water samples. Citizen scientists collected 1-L cold tap samples (first-draw and flushed) at 19 sites across the U.S. and across three seasons. Free-living and particle-associated microorganisms were size fractionated via membrane filtration, and Legionella spp. and Lp were quantified by digital polymerase chain reaction. Further, amplicon sequencing targeting the Legionella genus was used to explore the diversity of Legionella spp. at each site. The concentration of free-living Legionella spp. was significantly higher than that of particle-associated Legionella spp. (p=2.86×10-9) in paired samples at each site, and significantly higher concentrations of total Legionella spp. were found in surface water than in groundwater systems (p=0.020). Lp detection was geographically and temporally sporadic, with detections occurring at seven sites. Sequencing results showed that the site strongly influenced the specific Legionella spp. present. These results emphasize the influence of source water type and site on Legionella spp. in DWDSs and building plumbing. Further, this study suggests that consumers are more frequently exposed to free-living than to particle-associated Legionella spp. at the tap.

The occurrence of harmful algal blooms (HABs) in freshwater environments has been expanded worldwide with growing frequency and severity. HABs can pose a threat to public water supplies, raising concerns about safety of treated water. Many studies have provided valuable information about the impacts of HABs and management strategies on the early-stage treatment processes (e.g., pre-oxidation and coagulation/flocculation) in conventional drinking water treatment plants (DWTPs). However, the potential effect of HAB-impacted water in the granular media filtration has not been well studied. Biologically-active filters (BAFs), which are used in drinking water treatment and rely largely on bacterial community interactions, have not been examined during HABs in full-scale DWTPs. In this study, we assessed the bacterial community structure of BAFs, functional profiles, assembly processes, and bio-interactions in the community during both severe and mild HABs. Our findings indicate that bacterial diversity in BAFs significantly decreases during severe HABs due to the predominance of bloom-associated bacteria (e.g., Spingopyxis, Porphyrobacter, and Sphingomonas). The excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) confirmed that filter influent affected by the severe HAB contained a higher portion of protein-like substances than filter influent samples during a mild bloom. In addition, BAF community functions showed increases in metabolisms associated with intracellular algal organic matter (AOM), such as lipids and amino acids, during severe HABs. Further ecological process and network analyses revealed that severe HAB, accompanied by the abundance of bloom-associated taxa and increased nutrient availability, led to not only strong stochastic processes in the assembly process, but also a bacterial community with lower complexity in BAFs. Overall, this study provides deeper insights into BAF bacterial community structure, function, and assembly in response to HABs.

Nitrate and arsenic often co‐exist in groundwater sources. Reverse osmosis, electrodialysis, and ion exchange are the commonly implemented technologies for nitrate removal. Compared to these technologies that generate high‐strength waste streams, biological treatment converts nitrate to innocuous nitrogen gas without producing a concentrated waste. When nitrate and arsenic co‐exist in a water source, combining a biotic process for nitrate removal with an abiotic process (i.e., chemical–physical process such as coagulation/flocculation) for arsenic removal may provide an effective approach for simultaneous removal of these contaminants. A 12‐month pilot study was conducted with a two‐stage, fixed‐bed biotreatment system, originally developed for nitrate removal, for simultaneous removal of nitrate and arsenic. With an empty bed contact time as low as 10 min in the bioreactor, nitrate was consistently lowered from ~35 mg/L N to <0.1 mg/L N (treatment target was <1 mg/L N), whereas arsenic was effectively lowered from ~14 μg/L to <5 μg/L. Overall, the results demonstrated efficient and resilient simultaneous removal of nitrate and arsenic using a two‐stage biotic‐abiotic treatment system.

Key TakeawaysThe Water Research Foundation (WRF) Research Priority Program identifies industry challenges and helps address them through targeted, multiyear research projects.WRF's biofiltration research area was designed to provide drinking water utilities with tools to improve biofiltration's effectiveness and maximize its reliability.Research area objectives were to provide guidance documents for implementing, enhancing, monitoring, and optimizing biofiltration, and to communicate biofiltration's attributes.

The occurrence of harmful algal blooms dominated by toxic cyanobacteria has induced continuous loadings of algal organic matter (AOM) and toxins in drinking water treatment plants. However, the impact of AOM on the active biofilms and microbial community structures of biologically-active filtration (BAF), which directly affects the contaminant removal, is not well understood. In this study, we systematically examined the effects of AOM on BAF performance and bacterial biofilm formation over 240 days, tracing the removal of specific AOM components, a cyanotoxin [microcystin-LR (MC-LR)], and microbial community responses. The component analysis (excitation and emission matrix analysis) results for AOM revealed that terrestrial humic-like substances showed the highest removal among all the identified components and were strongly correlated to MC-LR removal. In addition, reduced empty bed contact time and deactivation of biofilms significantly decreased BAF performances for both AOM and MC-LR. The active biofilm, bacterial community structure, and mlrA gene (involved in microcystin degradation) abundance demonstrated that bacterial biofilm composition responded to AOM and MC-LR, in which Rhodocyclaceae, Saprospiraceae, and Comamonadaceae were dominant. In addition, MC-LR biodegradation appeared to be more active at the top than at the bottom layer in BAF. Overall, this study provides deeper insights into the role of biofilms and filter operation on the fate of AOM and MC-LR in BAF.

The presence of objectionable taste-and-odor (T&O) compounds in surface water supplies is a common problem facing drinking water utilities across the country and worldwide. While there are several viable T&O treatment options, including adsorption, biotransformation, and advanced oxidation, no single option fits all applications or is without potential limitations. Through bench- and pilot-scale testing, this work developed and evaluated high-rate biological roughing filtration as a promising alternative for geosmin and 2-methylisoborneol abatement to help utilities minimize T&O complaints without straining their annual operating budgets. Testing showed that biological roughing filtration can effectively treat a wide range of raw water T&O levels using short contact times, and the intermittent presence of T&O compounds did not appear to appreciably affect removal efficacy. Pilot-testing results were used to develop the design criteria for a full-scale 54-mgd biological roughing filter that is currently treating surface water in Manatee County, Florida.

Biological filtration (biofiltration) is the operational practice of managing, maintaining, and promoting biological activity on granular media in a filter to enhance the removal of organic and inorganic constituents before treated water is introduced into the distribution system. A major barrier to more widespread acceptance of biofiltration is the lack of recognized full‐scale experience available to utilities. To overcome this barrier, the Biofiltration Knowledge Base was developed (Water Research Foundation Project 4459). The Biofiltration Knowledge Base is a compendium of planning, design, operation, and monitoring experiences of 45 biofiltration facilities across North America with over 420 combined years of operational experience. This resource facilitates the exchange of knowledge, communicates the benefits of biofiltration, documents lessons learned, provides optimization strategies, and identifies needs for future research. Data demonstrate that biofiltration is widely used throughout North America and has been successful over a range of water qualities, design configurations, and operating conditions.

Hexavalent chromium (Cr(VI)) can be biologically reduced to nontoxic and easily separable trivalent chromium (Cr(III)) without generating concentrated wastes. Using a 6–25 gpm pilot-scale two-stage, fixed-bed (FXB), biologically active carbon (BAC) treatment system, approximately 75 μg/L Cr(VI) was consistently removed to less than 7 μg/L with a 10-min empty-bed contact time. Potential Cr(VI)-reducing bacteria, including members from the Dechloromonas and Acinetobacter genera, were present in the system. The system was resilient, and 91% Cr removal was observed when the system was challenged with a 24-h phosphoric acid feed shutdown, a 3-day system shutdown, spiking Cr(VI) to 100 μg/L, or operating intermittently with regular shutdown periods of hours to days. The system recovered within 6 h after a 26-h acetic acid feed shutdown. Readily settling backwash wastewater was generated with characteristics similar to municipal wastewater. Overall, the results indicated that a two-stage, FXB BAC system can provide an effective and robust option for Cr(VI) removal.

The Water Research Foundation published a user‐friendly tool that allows utilities to organize and interpret biofilter monitoring data to understand performance trends, actively monitor for changes that can indicate potential problems, and evaluate control changes or enhancement strategies.

While disinfection provides hygienically safe drinking water, the disinfectants react with inorganic or organic precursors, leading to the formation of harmful disinfection byproducts (DBPs). Biological filtration is a process in which an otherwise conventional granular filter is designed to remove not only fine particulates but also dissolved organic matters (e.g., DBP precursors) through microbially mediated degradation. Recently, applications of biofiltration in drinking water treatment have increased significantly. This review summarizes the effectiveness of biofiltration in removing DBPs and their precursors and identifies potential factors in biofilters that may control the removal or contribute to formation of DBP and their precursors during drinking water treatment. Biofiltration can remove a fraction of the precursors of halogenated DBPs (trihalomethanes, haloacetic acids, haloketones, haloaldehydes, haloacetonitriles, haloacetamides, and halonitromethanes), while also demonstrating capability in removing bromate and halogenated DBPs, except for trihalomethanes. However, the effectiveness of biofiltration mediated removal of nitrosamine and its precursors appears to be variable. An increase in nitrosamine precursors after biofiltration was ascribed to the biomass sloughing off from media or direct nitrosamine formation in the biofilter under certain denitrifying conditions. Operating parameters, such as pre-ozonation, media type, empty bed contact time, backwashing, temperature, and nutrient addition may be optimized to control the regulated DBPs in the biofilter effluent while minimizing the formation of unregulated emerging DBPs. While summarizing the state of knowledge of biofiltration mediated control of DBPs, this review also identifies several knowledge gaps to highlight future research topics of interest.

The performance of four pilot‐ and full‐scale biologically active filters (biofilters) was evaluated in terms of change in water quality parameters and removal of disinfection by‐product (DBP) precursors. Biologically active filtration successfully decreased dissolved organic carbon (DOC) by 5–25% and dissolved organic nitrogen (DON) by 5–38%. The removal of these parameters corresponded to some decreases in carbonaceous and nitrogenous DBP formation. Formation potential tests showed 13–45% and 18–57% reduction in the formation of trihalomethanes and haloacetic acids, respectively. Bromine incorporation factors of trihalomethanes and haloacetic acids increased across the biofilters. Biofilters also showed 25–48%, 15–20%, and 34–50% removal of halonitromethane, haloacetonitrile, and N‐nitrosodimethylamine precursors, respectively. The effects of filter media and phosphate amendment were also evaluated in full‐ and pilot‐scale systems. Results showed that replacing the anthracite layer with granular activated carbon increased the removal of DOC, DON, and DBP precursors. Phosphate amendment had no distinct effect on the removal of DOC, DON, or DBP precursors.

At a 2013 AWWA symposium on biological treatment of drinking water, presentations covered a full spectrum of topics; speakers outlined different processes, dispelled misconceptions, introduced new research, and summarized the regulatory aspect of biotreatment.

Biofiltration, a reliable process that has been used to purify water for hundreds of years, can address a wide array of regulated and emerging contaminants of concern. However, the water industry lacks a comprehensive set of best practices for biofiltration use. To address this knowledge gap, the Water Research Foundation (WRF) launched Project 4459, Development of a Biofiltration Knowledge Base (http://bit.ly/OsQUdy), to catalog information from high‐rate biofiltration facilities across North America.

The use of biological drinking water treatment processes for the treatment of surface water and groundwater has recently been increasing in North America. Biofiltration can simultaneously remove a wide range of dissolved organic and inorganic contaminants, while achieving particle removal goals. Organic compounds, including color and taste and odor (T&O)-causing compounds, are not only removed but also destroyed in this process. This can limit the formation of disinfection byproducts (DBPs) and lower regrowth potential in the distribution system. Operation of biofilters requires low energy input, minimal chemicals, and little waste production. Although biofiltration can provide numerous benefits, biofilter systems can be susceptible to hydraulic and water quality challenges, such as shortened runtimes, biological clogging, and breakthrough of contaminants such as T&O, manganese (Mn), and organic carbon. Drinking water biofilters are often de

Removal of dissolved organic and inorganic contaminants is an anticipated benefit of the biofiltration of drinking water; however, common biofiltration design and operational practices do not seek to enhance the biological activities associated with those removals. A pilot‐scale study identified two enhancement strategies—nutrient and peroxide dosing—that improved both water quality and hydraulic performance of a biofilter. These strategies control the formation of extracellular polymeric substances (a potential foulant of biological filters) while maintaining or increasing microbial activity. Biofilter nutrient enhancement was found to decrease terminal head loss by ~ 15% relative to a control filter with no nutrient enhancement. Nutrient enhancement also sustainably decreased breakthrough of 2‐methylisoborneol (MIB), manganese (Mn), and dissolved organic carbon (DOC). Peroxide enhancement was performed to increase oxidative action of biofilter microorganisms and promote the oxidation of inactive biomass. Peroxide enhancement decreased terminal head loss up to ~ 60% relative to the control filter, while maintaining MIB, Mn, and DOC treatment performance. This case study is an important step in moving the practice of biofiltration from a passive process to a purposefully operated biological system, i.e., engineered biofiltration.

Contaminant removal from drinking water sources under reducing conditions conducive for the growth of denitrifying, arsenate reducing, and sulfate reducing microbes using a fixed-bed bioreactor may require oxygen-free gas (e.g., N-2 gas) during backwashing. However, the use of air-assisted backwashing has practical advantages, including simpler operation, improved safety, and lower cost. A study was conducted to evaluate whether replacing N-2 gas with air during backwashing would impact performance in a nitrate and arsenic removing anaerobic bioreactor system that consisted of two biologically active carbon reactors in series. Gas-assisted backwashing, comprised of 2 min of gas injection to fluidize the bed and dislodge biomass and solid phase products, was performed in the first reactor (reactor A) every two days. The second reactor (reactor B) was subjected to N-2 gas-assisted backwashing every 3-4 months. Complete removal of 50 mg/L NO3- was achieved in reactor A before and after the switch from N-2-assisted backwashing (NAB) to air-assisted backwashing (AAB). Substantial sulfate removal was achieved with both backwashing strategies. Prolonged practice of AAB (more than two months), however, diminished sulfate reduction in reactor B somewhat. Arsenic removal in reactor A was impacted slightly by long-term use of AAB, but arsenic removals achieved by the entire system during NAB and AAB periods were not significantly different (p > 0.05) and arsenic concentrations were reduced from approximately 200 mu g/L to below 20 mu g/L. These results indicate that AAB can be implemented in anaerobic nitrate and arsenic removal systems. (C) 2011 Elsevier Ltd. All rights reserved.

Using microbial biomass to treat groundwater provides new opportunities for U.S. utilities to address widespread nitrate contamination, eliminate traditional waste streams, achieve greater water recovery, and save money.

Terminal electron accepting process (TEAP) zones developed when a simulated groundwater containing dissolved oxygen (DO), nitrate, arsenate, and sulfate was treated in a fixed-bed bioreactor system consisting of two reactors (reactors A and B) in series. When the reactors were operated with an empty bed contact time (EBCT) of 20 min each, DO-, nitrate-, sulfate-, and arsenate-reducing TEAP zones were located within reactor A. As a consequence, sulfate reduction and subsequent arsenic removal through arsenic sulfide precipitation and/or arsenic adsorption on or coprecipitation with iron sulfides occurred in reactor A. This resulted in the removal of arsenic-laden solids during backwashing of reactor A. To minimize this by shifting the sulfate-reducing zone to reactor B, the EBCT of reactor A was sequentially lowered from 20 min to 15, 10, and 7 min. While 50 mg/L (0.81 mM) nitrate was completely removed at all EBCTs, more than 90% of 300 μg/L (4 μM) arsenic was removed with the total EBCT as low as 27 min. Sulfate- and arsenate-reducing bacteria were identified throughout the system through clone libraries and quantitative PCR targeting the 16S rRNA, dissimilatory (bi)sulfite reductase (dsrAB), and dissimilatory arsenate reductase (arrA) genes. Results of reverse transcriptase (RT) qPCR of partial dsrAB (i.e., dsrA) and arrA transcripts corresponded with system performance. The RT qPCR results indicated colocation of sulfate- and arsenate-reducing activities, in the presence of iron(II), suggesting their importance in arsenic removal.