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Incorporation of a carbon-based nutrient enhancement strategy for drinking water biofiltration is an attractive option, especially for source waters which contain recalcitrant organics. This study compared biofilters that were operated in parallel and individually enhanced with amino acids (including alanine, phenylalanine, and tryptophan), inulin, and sucrose to increase biomass concentration and promote biodegradation of dissolved organic carbon (DOC) in the source water, including disinfection by-product (DBP) precursors. Biomass activity was characterized by measuring adenosine tri-phosphate (ATP), dissolved oxygen (DO) consumption, and through the use of laccase and esterase enzyme assays. Performance was evaluated in terms of headloss, turbidity, pH, DOC, UV 254 , and DBP formation potential (DBP FP). The introduction of carbon-based nutrients significantly increased biomass activity, where ATP values peaked at 976 ng/g of filter media, 853 ng/g, and 513 ng/g for amino acids, inulin, and sucrose-spiked biofilters, respectively, while a non-spiked control only reached 104 ng/g. DO utilization by the enhanced biofilters was significantly higher than the control, with a strong correlation between ATP and DO uptake observed for all filters (R 2  > 0.74). Laccase and esterase enzyme activities of enhanced biofilters were also elevated (p > 0.05), suggesting greater biodegradation potential. Operational parameters such as headloss development and turbidity control were not impaired by carbon supplementation strategies or an increase in biomass concentration and activity. However, the enhancement strategy did not provide improvement in terms of source water carbon removal (DOC and UV 254 ) or DBP FP when treated filters were compared to a control., (Copyright © 2019. Published by Elsevier B.V.)

The evolving demands of drinking water treatment necessitate processes capable of removing a diverse suite of contaminants. Biofiltration can employ biotransformation and sorption to remove various classes of chemicals from water. Here, pilot-scale virgin anthracite-sand and previously used biological activated carbon (BAC)-sand dual media filters were operated for ∼250 days to assess removals of 0.4 mg/L ammonia as nitrogen, 50-140 μg/L manganese, and ∼100 ng/L each of trace organic compounds (TOrCs) spiked into pre-ozonated Colorado River water. Anthracite achieved complete nitrification within 200 days and started removing ibuprofen at 85 days. Limited manganese (10%) removal occurred. In contrast, BAC completely nitrified ammonia within 113 days, removed all manganese at 43 days, and exhibited steady state removal of most TOrCs by 140 days. However, during the first 140 days, removal of caffeine, DEET, gemfibrozil, naproxen, and trimethoprim decreased, suggesting a shift from sorption to biotransformation. Acetaminophen and sulfamethoxazole were removed at consistent levels, with complete removal of acetaminophen achieved throughout the study; ibuprofen removal increased with time. When subjected to elevated (1 μg/L) concentrations of TOrCs, BAC removed larger masses of chemicals; with a subsequent decrease and ultimate cease in the TOrCs spike, caffeine, DEET, gemfibrozil, and trimethoprim notably desorbed. By the end of operation, anthracite and BAC exhibited equivalent quantities of biomass measured as adenosine triphosphate, but BAC harbored greater microbial diversity (examined with 16S rRNA sequencing). Improved insight was gained regarding concurrent biotransformation, sorption, and desorption of multiple organic and inorganic contaminants in pilot-scale drinking water biofilters., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Incomplete nitrification in biological filters during drinking water treatment is problematic, as it compromises drinking water quality. Nitrification problems can be caused by a lack of nutrients for the nitrifying microorganisms. Since copper is an important element in one of the essential enzymes in nitrification, we investigated the effect of copper dosing on nitrification in different biological rapid sand filters treating groundwater. A lab-scale column assay with filter material from a water works demonstrated that addition of a trace metal mixture, including copper, increased ammonium removal compared to a control without addition. Subsequently, another water works was investigated in full-scale, where copper influent concentrations were below 0.05 μg Cu L(-1) and nitrification was incomplete. Copper dosing of less than 5 μg Cu L(-1) to a full-scale filter stimulated ammonium removal within one day, and doubled the filter's removal from 0.22 to 0.46 g NH4-N m(-3) filter material h(-1) within 20 days. The location of ammonium and nitrite oxidation shifted upwards in the filter, with an almost 14-fold increase in ammonium removal rate in the filter's top 10 cm, within 57 days of dosing. To study the persistence of the stimulation, copper was dosed to another filter at the water works for 42 days. After dosing was stopped, nitrification remained complete for at least 238 days. Filter effluent concentrations of up to 1.3 μg Cu L(-1) confirmed that copper fully penetrated the filters, and determination of copper content on filter media revealed a buildup of copper during dosing. The amount of copper stored on filter material gradually decreased after dosing stopped; however at a slower rate than it accumulated. Continuous detection of copper in the filter effluent confirmed a release of copper to the bulk phase. Overall, copper dosing to poorly performing biological rapid sand filters increased ammonium removal rates significantly, achieving effluent concentrations of below 0.01 mg NH4-N L(-1), and had a long-term effect on nitrification performance., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Invertebrate colonization of granular activated carbon (GAC) filters in the waterworks is one of the most frequently occurring and least studied biological problems of water processing in China. A survey of invertebrate colonization of GAC filters was carried out weekly from October 2010 to December 2011 at a reservoir water treatment works in South China. Twenty-six kinds of invertebrates were observed. The abundance was as high as 5600ind.m(-3) with a mean of 860ind.m(-3). Large variations in abundance were observed among different seasons and before and after GAC filtration. The dominant organisms were rotifers and copepods. The average invertebrate abundance in the filtrate was 12-18.7 times of that in the pre-filtered water. Results showed that the GAC filters were colonized by invertebrates which may lead to a higher output of organisms in the filtrate than in the pre-filtered water. The invertebrate abundance in the GAC filters was statistically correlated with the water temperature. Seasonal patterns were observed. The invertebrate abundance grew faster in the spring and summer. Copepods were dominant in the summer while rotifers dominated in all other seasons of the year. There was a transition of small invertebrates (rotifers) gradually being substituted by larger invertebrates (copepods) from spring to summer. Control measures such as backwashing with chloric water, drying filter beds and soaking with saliferous water were implemented in the waterworks to reduce invertebrate abundances in the GAC filters. The results showed that soaking with saliferous water (99%, reduction in percent) was best but drying the filter beds (84%) was more economical. Soaking filter beds with 20g/L saliferous water for one day can be implemented in case of emergency. In order to keep invertebrate abundance in the acceptable range, some of these measures should be adopted., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Abstract Biological drinking water treatment technologies offer a cost-effective and sustainable approach to mitigate microcystin (MC) toxins from harmful algal blooms. To effectively engineer these systems, an improved predictive understanding of the bacteria degrading these toxins is required. This study reports an initial comparison of several unstructured kinetic models to describe MC microbial metabolism by isolated degrading populations. Experimental data was acquired from the literature describing both MC removal and cell growth kinetics when MC was utilized as the primary carbon and energy source. A novel model-data calibration approach melding global single-objective, multi-objective, and Bayesian optimization in addition to a fully Bayesian approach to model selection and hypothesis testing were applied to identify and compare parameter and predictive uncertainties associated with each model structure. The results indicated that models incorporating mechanisms of enzyme-MC saturation, affinity, and cooperative binding interactions of a theoretical single, rate limiting reaction accurately and reliably predicted MC degradation and bacterial growth kinetics. Diverse growth characteristics were observed among MC degraders, including moderate to high maximum specific growth rates, very low to substantial affinities for MC, high yield of new biomass, and varying degrees of cooperative enzyme-MC binding. Model predictions suggest that low specific growth rates and MC removal rates of degraders are expected in practice, as MC concentrations in the environment are well below saturating levels for optimal growth. Overall, this study represents an initial step towards the development of a practical and comprehensive kinetic model to describe MC biodegradation in the environment. Graphical abstract Image 1 Highlights • Unstructured kinetic models were applied to predict microcystin (MC) biodegradation. • Moser and Heijnen models reliably predicted MC removal kinetics across experiments. • Diverse growth characteristics were observed when comparing MC degrading bacteria. • Model predictions suggest MC removal kinetics are suboptimal in the environment. [ABSTRACT FROM AUTHOR]

The removal of biodegradable ozonation by-products was evaluated at pilot-scale using one conventional biofilter containing sand and anthracite and five fixed bed biofilm reactors (FBBRs) containing plastic media. Four of the FBBRs incorporated chemical or environmental optimization strategies (light restriction, chloramine, hydrogen peroxide, and nutrients) to either promote healthy biomass or minimize macrofauna proliferation. Conventional media biofiltration consistently removed assimilable organic carbon (AOC) by a maximum of 70% and was not susceptible to snail grazing. The control FBBR reduced AOC by a maximum of 60%, but dropped to zero following snail grazing on established biomass. Adenosine triphosphate (ATP) was used to quantify viable biomass attached to plastic media (tATP) and aqueous biomass in the column effluent (cATP). The control FBBR averaged 61 ng tATP/cm3of attached biomass compared to chloramine (7 ng tATP/cm3), hydrogen peroxide (21 ng tATP/cm3), dark conditions (45 ng tATP/cm3), and nutrients (61 ng tATP/cm3). Hydrogen peroxide (1.8 mg/L) and light restriction strategies precluded dark algae and chironomids, but allowed snail development. None of this biota was observed in the presence of chloramine (0.20 mg/L). While the conventional biofilter and control FBBR produced similar AOC removals, FBBRs were sensitive to hydraulic disruptions and susceptible to grazer organisms. [ABSTRACT FROM PUBLISHER]

Biofilters have gained in popularity for drinking water treatment for reasons that include reducing disinfectant demand, disinfection by-product formation, and regrowth in distribution systems. Adenosine triphosphate (ATP) detection is being used more frequently as an easy and rapid method to quantify viable biomass in biofilters; however, there is little information on the relationship of ATP levels to biofiltration parameters and performance. In this study, a comprehensive comparison of published ATP data was conducted, which found that concentrations at the top of active, acclimated biofilters typically were in the range of 102 to 103 ng ATP/cm3 media. The effect of various biofilter parameters (source water characteristics and quality, pretreatment, hydraulic loading rate, temperature, and sampling depth) on ATP levels is discussed and evaluated using published ATP data. The authors also assess the relationship between ATP and biofilter performance in terms of carbon removal and identify a need for further research in this area. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

The article discusses a study on the fate of saxitoxins in biologically active water treatment plant (WTP) filters. The saxitoxins, a group of potent alkaloid neurotoxins produced by cyanobacteria and dinoflagellates in freshwater and marine environments, block nerve cell sodium channels and can cause death if consumed in sufficient quantity. Findings revealed that decreases in the concentration of the less toxic variants coincided with increases in the concentrations of the more toxic variants through the filters containing anthracite sourced from two different WTPs. According to the study, organisms within the biofilm of the anthracite filters possessed the ability to biotransform the saxitoxins variants, which has important implications for the treatment of drinking water.

Nitrification was developed within a biological filter to simultaneously remove biodegradable organic matter (BOM) and residual ammonia added to control bromate formation during the ozonation of drinking water. Testing was performed at pilot-scale using three filters containing sand and anthracite filter media. BOM formed during ozonation (e.g., assimilable organic carbon (396–572μg/L), formaldehyde (11–20μg/L), and oxalate (83–145μg/L)) was up to 70% removed through biofiltration. Dechlorinated backwash water was required to develop the nitrifying bacteria needed to convert the residual ammonia (0.1–0.5mg/L NH3-N) to nitrite and then to nitrate. Chlorinated backwash water resulted in biofiltration without nitrification. Deep-bed filtration (empty-bed contact time (EBCT)=8.3min) did not enhance the development of nitrification when compared with shallow-bed filtration (EBCT=3.2min). Variable filtration rates between 4.8 and 14.6m/h (2 and 6gpm/sf) had minimal impact on BOM removal. However, conversion of ammonia to nitrite was reduced by 60% when increasing the filtration rate from 4.8 to 14.6m/h. The results provide drinking water utilities practicing ozonation with a cost-effective alternative to remove the residual ammonia added for bromate control. [Copyright &y& Elsevier]

The quality of drinking water is sometimes diminished by the presence of certain compounds that can impart particular tastes or odours. One of the most common and problematic types of taste and odour is the earthy/musty odour produced by geosmin (trans-1, 10-dimethyl-trans-9-decalol) and MIB (2-methylisoborneol). Taste and odour treatment processes including powdered activated carbon, and oxidation using chlorine, chloramines, potassium permanganate, and sometimes even ozone are largely ineffective for reducing these compounds to below their odour threshold concentration levels. Ozonation followed by biological filtration, however, has the potential to provide effective treatment. Ozone provides partial removal of geosmin and MIB but also creates other compounds more amenable to biodegradation and potentially undesirable biological instability. Subsequent biofiltration can remove residual geosmin and MIB in addition to removing these other biodegradable compounds. Bench scale experiments were conducted using two parallel filter columns containing fresh and exhausted granular activated carbon (GAC) media and sand. Source water consisted of dechlorinated tap water to which geosmin and MIB were added, as well as, a cocktail of easily biodegradable organic matter (i.e. typical ozonation by-products) in order to simulate water that had been subjected to ozonation prior to filtration. Using fresh GAC, total removals of geosmin ranged from 76 to 100% and total MIB removals ranged from 47% to 100%. The exhausted GAC initially removed less geosmin and MIB but removals increased over time. Overall the results of these experiments are encouraging for the use of biofiltration following ozonation as a means of geosmin and MIB removal. These results provide important information with respect to the role biofilters play during their startup phase in the reduction of these particular compounds. In addition, the results demonstrate the potential biofilters have in responding to transient geosmin and MIB episodes. [ABSTRACT FROM AUTHOR]

Nitrification during biological filtration is currently used in drinking water production to remove ammonia, which is the source of several water quality problems during treatment and distribution. We evaluated here the impact of backwashing on nitrification efficiency in filters used for drinking water treatment. Two different granular activated carbon (one open and one closed carbon superstructure) were tested. Ammonia removal and fixed nitrifying bacterial biomass before and after backwashing were compared in first-stage pilot filters and full-scale second-stage filters. Backwashing has a greater impact on nitrification on first-stage than on second-stage filters. Backwashing improved the ammonia removal in warm (≥ 18°C) water in a first-stage filter containing an open-superstructure granular activated carbon, whereas a closed-superstructure support showed a removal capacity that is less after a regular backwashing than before, or similar to it. In cold water (≤ 4°C), backwashing had a negative impact on nitrification capacity in an open-superstructure medium first-stage filter. In full-scale second-stage filters, backwashing had a slight negative impact on filter performances for both open- and closed-superstructure media at temperatures between 8°C and 12°C. In colder waters (≤ 3°C), nitrification was very poor both before and after backwashing. Sampling of fixed, nitrifying biomass in the pilot filter columns showed that in all cases (low and high expansion backwash; both media tested) and at 20±3°C, the overall biomass levels remained unchanged before and after backwash. In the full-scale second-stage filters, nitrifying biomass was similar before and after backwashing for both types of media tested. [ABSTRACT FROM AUTHOR]