Drinking Water Biofilters Research Articles

Microbial stratification and DOM removal in drinking water biofilters: Implications for enhanced performance

Biofiltration is a low-cost, low-energy technology that employs a biologically activated bed of porous medium to reduce the biodegradable fraction of the dissolved organic matter (DOM) pool in source water, resulting in the production of drinking water. Microbial communities at different bed depths within the biofilter play crucial roles in the degradation and removal of dissolved organic carbon (DOC), ultimately impacting its performance. However, the relationships between the composition of microbial communities inhabiting different biofilter depths and their utilisation of various DOC fractions remain poorly understood. To address this knowledge gap, we conducted an experimental study where microbial communities from the upper (i.e., top 10 cm) and lower (i.e., bottom 10 cm) sections of a 30-cm long laboratory-scale biofilter were recovered. These communities were then individually incubated for 10 days using the same source water as the biofilter influent. Our study revealed that the bottom microbial community exhibited lower diversity yet had a co-occurrence network with a higher degree of interconnections among its members compared to the top microbial community. Moreover, we established a direct correlation between the composition and network structure of the microbial communities and their ability to utilise various DOM compounds within a DOM pool. Interestingly, although the bottom microbial community had only 20 % of the total cell abundance compared to the top community at the beginning of the incubation, it utilised and hence removed approximately 60 % more total DOC from the DOM pool than the top community. While both communities rapidly utilised labile carbon fractions, such as low-molecular-weight neutrals, the utilisation of more refractory carbon fractions, like high-molecular-weight humic substances with an average molecular weight of more than ca. 1451 g/mol, was exclusive to the bottom microbial community. By employing techniques that capture microbial diversity (i.e., flow cytometry and 16S rRNA amplicon sequencing) and considering the complexities of DOM (i.e., LCOCD), our study provides novel insights into how microbial community structure could influence the microbial-mediated processes of engineering significance in drinking water production. Finally, our findings could offer the opportunity to improve biofilter performances via engineering interventions that shape the compositions of biofilter microbial communities and enhance their utilisation and removal of DOM, most notably the more classically humified and refractory DOM compound groups.

Accelerated startup of full-scale drinking water biofilters using mature media: Insights into microbial communities and manganese oxide coating

This study addressed the critical challenge of expediting biofilter commencement in groundwater treatment. By incorporating 8 cm-thick mature media, the start-up period was reduced to approximately 7 days. Significantly, NH4+-N and Mn2+ removal efficiencies reached 96.5% and 95.7%, with effluent concentrations at 0.07 mg/L and 0.04 mg/L, respectively. The loose and porous manganese oxide coating (MnOx) emerged as a pivotal factor in facilitating rapid biofilter maturation, providing attachment points for microorganisms. Analysis revealed variations in microbial communities associated with Fe2+ and Mn2+ removal between primary and secondary filters. The convergence of microbial communities in the mature and original medium of the secondary filter highlights the critical role of MnOx. Bacteria's essential contribution during the startup phase, driving MnOx formation, proves crucial for contaminant removal in the stable phase. This research provides concise insights into improving groundwater treatment system efficiency.

The application of different methods for indirect microbial development assessment in pilot scale drinking water biofilters

The application of different methods for indirect microbial development assessment in pilot scale drinking water biofilters

Antibiotic resistance genes and the association with bacterial community in biofilms occurring during the drinking water granular activated carbon (GAC) sandwich biofiltration

The granular activated carbon (GAC) sandwich modification to slow sand filtration could be considered as a promising technology for improved drinking water quality. Biofilms developed on sand and GAC surfaces are expected to show a functional diversity during the biofiltration. Bench-scale GAC sandwich biofilters were set-up and run continuously with and without antibiotic exposure. Surface sand (the schmutzdecke) and GAC biofilms were sampled and subject to high-throughput qPCR for antibiotic resistance gene (ARG) analysis and 16 S rRNA amplicon sequencing. Similar diversity of ARG profile was found in both types of biofilms, suggesting that all ARG categories decreased in richness along the filter bed. In general, surface sand biofilm remained the most active layer with regards to the richness and abundance of ARGs, where GAC biofilms showed slightly lower ARG risks. Network analysis suggested that 10 taxonomic genera were implicated as possible ARG hosts, among which Nitrospira, Methyloversatilis and Methylotenera showed the highest correlation. Overall, this study was the first attempt to consider the whole structure of the GAC sandwich biofilter and results from this study could help to further understand the persistence of ARGs and their association with the microbial community in drinking water biofiltration system.

Acclimation, manganese removal, and backwash impact on full‐scale drinking water biofilter microbiome

AbstractBiofiltration for drinking water treatment has several water quality benefits but questions remain about biofilter start‐up in temperate climates where temperature and water quality changes can impact performance. A year‐long full‐scale demonstration was performed with biofilters operated in parallel to chlorinated filters to (O1) monitor the development of the biofilter microbiota across the acclimation period with respect to removal of Mn and total organic carbon, and (O2) determine the impact of depth and backwash events on the microbial community composition and function. Biofilter media biomass increased for the first 6 months of operation and after about 9 months the biofilters achieved comparable Mn removal to the chlorinated filters. Prokaryotic diversity decreased when the water temperature dropped. Backwash resulted in an increase in microbial diversity deeper in the biofilter. By the next sampling (30 h post backwash), 16S rRNA gene copies were again more abundant in the upper layers. Metagenomic sequencing confirmed the presence of moxA and mofA, Mn oxidizing genes. The results presented can help inform expected performance of full‐scale biofilters in temperate climates.

Field evaluation of phosphorus limitation in drinking water biofilters

AbstractHydraulic performance issues in drinking‐water biofilters have sometimes been associated with phosphorus limitation and increased production of extracellular polymeric substances in previous bench‐scale studies. However, field studies utilizing phosphorus supplementation to improve biofilter hydraulic performance have produced mixed results. Here, we determined the ratio of activities for phosphatase to glycosidase (PHO:GLY), which are enzymes involved in acquiring orthophosphate and biodegradable organic carbon from complex organic substrates, to assess phosphorus limitation in 21 pilot‐ and full‐scale biofilters. Supplementation of the pilot‐scale biofilter influents with 37 μg/L orthophosphate‐P reduced the PHO:GLY from 1.8–40.3 (mean 14.8) to 0.3–15.9 (mean 5.3), demonstrating that increased orthophosphate availability decreases PHO:GLY. In the absence of phosphorus supplementation, the PHO:GLY of the pilot‐ and full‐scale biofilters ranged from 0.3 to 40.3 (mean 10.1), and no hydraulic performance issues were noted. Thus, severe phosphorus limitation appears uncommon in the field, suggesting that phosphorus supplementation is unlikely to improve hydraulic performance in typical drinking water biofilters.

Microbiome and hydraulic performance changes of drinking water biofilters during disruptive events-media replacement, lake diatom bloom, and chlorination

Little is known about filter media microbiome and characteristics during disruptive events and drastic hydraulic performance decline in drinking water biofilters.

AWWA Water Science Author Spotlight

Having recently published an article in AWWA Water Science, Martin Earle answered questions from the publication's editor-in-chief, Kenneth L. Mercer, about the research. Predicting Manganese and Iron Precipitation in Drinking Water Biofilters Martin R. Earle, Inês L. Breda, Amina K. Stoddart, and Graham A. Gagnon On a recent trip to Hawaii, Martin relaxes during a sunset sail. I went into civil engineering expecting to specialize in infrastructure, without knowing that water treatment fell under the civil engineering umbrella at Dalhousie. My first exposure to water treatment was in my third year, when I took Dr. Graham Gagnon's water quality class. The first assignment for that class was a literature review, which opened my eyes to both water treatment and graduate studies. I found that assignment and the class in general fascinating, and I quickly realized that water science was something important and worth committing my efforts to. I have had many mentors already in my career and have been fortunate to get a lot of great advice. However, I want to highlight my coauthor, Dr. Inês Breda, who was generous enough to share her data with me and help me write this paper at a time when I had no access to research facilities because of COVID-19. She helped me understand that failure is a normal part of graduate school, and that the key to producing quality research is to not let those failures derail you. Martin and his fiancée, Genevieve, enjoy kayaking on Kejimkujik Lake, the largest lake in Nova Scotia's Kejimkujik National Park. I believe that the future of manganese control is biological treatment; however, our understanding of how manganese is removed across biological systems is limited, which has prevented widespread adoption of the technology in North America. To improve our understanding of these systems, we focused on one potential removal mechanism that is often ignored by researchers: homogeneous oxidation. The article investigates this mechanism using full-scale data and generates a framework for future investigations into manganese removal. I grew up enjoying the beautiful lakes, parks, and campgrounds in Nova Scotia, especially Kejimkujik National Park, which I still visit every year. It is very important to me that we protect the natural environment so that future generations can continue to enjoy it. After seeing the destruction left by Hurricane Fiona, which tore through the Atlantic provinces in late September 2022, it has never been clearer that we need to push everything we do to be sustainable, especially water treatment. Replacing the chemical treatments typically used to control manganese with sustainable biological treatments will be a great step toward a cleaner future. Climate change is going to cause more and more problems for the water industry, especially in Canada, where we tend to rely on surface waters. Even if we could stop polluting today, we will still face the consequences of what has already happened. The wilderness of Nova Scotia has always been an integral part of Martin's life and pastimes. Biological manganese treatments have been shown to be robust and sustainable. By continuing to develop this technology, we can help protect the public from health risks associated with manganese and the environmental pollution resulting from chemical treatments. Martin and Genevieve's cat, Apollo, helps bring balance to the stresses of Martin's PhD work. Hiking in Diamond Head State Monument, Hawaii.

Predicting manganese and iron precipitation in drinking water biofilters

Predicting manganese and iron precipitation in drinking water biofilters

Comammox Nitrospira bacteria outnumber canonical nitrifiers irrespective of electron donor mode and availability in biofiltration systems.

Complete ammonia oxidizing bacteria coexist with canonical ammonia and nitrite oxidizing bacteria in a wide range of environments. Whether this is due to competitive or cooperative interactions, or a result of niche separation is not yet clear. Understanding the factors driving coexistence of nitrifiers is critical to manage nitrification processes occurring in engineered and natural ecosystems. In this study, microcosm-based experiments were used to investigate the impact of nitrogen source and loading on the population dynamics of nitrifiers in drinking water biofilter media. Shotgun sequencing of DNA followed by co-assembly and reconstruction of metagenome assembled genomes revealed clade A2 comammox bacteria were likely the primary nitrifiers within microcosms and increased in abundance over Nitrosomonas-like ammonia and Nitrospira-like nitrite oxidizing bacteria irrespective of nitrogen source type or loading. Changes in comammox bacterial abundance did not correlate with either ammonia or nitrite oxidizing bacterial abundance in urea-amended systems, where metabolic reconstruction indicated potential for cross-feeding between strict ammonia and nitrite oxidizers. In contrast, comammox bacterial abundance demonstrated a negative correlation with nitrite oxidizers in ammonia-amended systems. This suggests potentially weaker synergistic relationships between strict ammonia and nitrite oxidizers might enable comammox bacteria to displace strict nitrite oxidizers from complex nitrifying communities.

Mixed Calcinated Oyster Shell and Granular Activated Carbon for Drinking Water Biofiltration Can Effectively Remove Antibiotic Resistance Genes

Mixed Calcinated Oyster Shell and Granular Activated Carbon for Drinking Water Biofiltration Can Effectively Remove Antibiotic Resistance Genes

Mixed Calcinated Oyster Shell and Granular Activated Carbon for Drinking Water Biofiltration Can Effectively Remove Antibiotic Resistance Genes

Mixed Calcinated Oyster Shell and Granular Activated Carbon for Drinking Water Biofiltration Can Effectively Remove Antibiotic Resistance Genes

Genomic Analysis and Stability Evaluation of the Phenol-Degrading Bacterium Acinetobacter sp. DW-1 During Water Treatment.

Phenol is a toxic organic molecule that is widely detected in the natural environment, even in drinking water sources. Biological methods were considered to be a good tool for phenol removal, especially microbial immobilized technology. However, research on the “seed” bacteria along with microbial community analysis in oligotrophic environment such as drinking water system has not been addressed. In this study, Acinetobacter sp. DW-1 with high phenol degradation ability had been isolated from a drinking water biofilter was used as seeded bacteria to treat phenol micro-polluted drinking water source. Meanwhile, the whole genome of strain DW-1 was sequenced using nanopore technology. The genomic analysis suggests that Acinetobacter sp. DW-1 could utilize phenol via the β-ketoadipate pathway, including the catechol and protocatechuate branches. Subsequently, a bio-enhanced polyhedral hollow polypropylene sphere (BEPHPS) filter was constructed to investigate the stability of the seeded bacteria during the water treatment process. The denatured gradient gel electrophoresis (DGGE) profile and the quantification of phenol hydroxylase gene results indicate that when the BEPHPS filter was operated for 56 days, Acinetobacter sp. was still a persistent and competitive bacterium in the treatment group. In addition, 16S rRNA gene amplicon sequencing results indicate that Acinetobacter sp., as well as Pseudomonas sp., Nitrospira sp., Rubrivivax sp. were the predominant bacteria in the treatment group, which were different from that in the CK group. This study provides a better understanding of the mechanisms of phenol degradation by Acinetobacter sp. DW-1 at the gene level, and provides new insights into the stability of seeded bacteria and its effects on microbial ecology during drinking water treatment.

Biodegradation of salicylic acid, acetaminophen and ibuprofen by bacteria collected from a full-scale drinking water biofilter

This study examined the biodegradation of two pharmaceuticals-acetaminophen, and ibuprofen, and one natural organic surrogate-salicylic acid, by bacteria seeded from backwash water collected from a full-scale biofiltration plant. The degradation was studied in the presence of oxygen. Complete removal of salicylic acid was observed in 27–66 h depending on the seasonality of the collected backwash water, while 90–92% acetaminophen removal was observed in more than 225 h. Ibuprofen demonstrated poor removal efficiencies with only 50% biodegradation after 230 h. Adenosine tri phosphate (ATP) in the reactor was found to be linked with the biodegradation rate. ATP was found to be correlated with oxygen uptake rate (OUR). ATP also had a correlation with each of extracellular polymeric substances (EPS), protein and polysaccharides. These results highlight the potential for increasing the biodegradation rates to achieve enhanced contaminant removal.

Full-Scale Manipulation of the Empty Bed Contact Time to Optimize Dissolved Organic Matter Removal by Drinking Water Biofilters

A study was conducted at a water treatment plant to optimize parallel rapid gravity biofilters for dissolved organic matter (DOM) removal. The biofilters treat urban and agriculturally impacted river water using a commercial non-adsorptive, expanded-clay filter medium. The study aimed to locate the optimal operating conditions via experimental manipulation of the biofilter empty bed contact time (EBCT) during full-scale operation at the plant. During a two-month experiment, contact times in four parallel biofilters were switched to and maintained at 15, 30, 50, and 80 min by manipulating the hydraulic loading on each filter. The removal efficiency of organic matter fractions increased with EBCT for dissolved organic carbon (DOC) and microbial humic-like (F290/420) and protein-like (F280/340) fluorescent organic matter. Other DOM fractions were largely unaffected by biofiltration, or at slightly higher concentrations in the effluent. Protein-like fluorescence is associated with labile organic matter fractions, which are known to be removed poorly by drinking water treatment barriers apart from biological filters. The results suggest that long contact times (>30 min) have advantages for the operation of some biological filters, especially if placed ahead of barriers that are sensitive to biofouling, e.g., membranes.

Removal of antibiotics in sand, GAC, GAC sandwich and anthracite/sand biofiltration systems

Drinking water biofiltration offers the possibility of the removal of trace level micropollutants from source water. Sand, granular activated carbon (GAC), GAC sandwich (a layer of GAC loaded in the middle of sand bed), and anthracite-sand dual biofilters were set-up in duplicate at bench-scale to mimic the filtration process in real drinking water treatment works. During the 3-month system operation, removal of five antibiotics (amoxicillin, clarithromycin, oxytetracycline, sulfamethoxazole, and trimethoprim) and overall biofilter performance were evaluated. Natural surface water spiked with a mixture of the target antibiotics was used as feedwater to the biofilters. Results showed that the target antibiotics were substantially removed (>90%) by GAC-associated biofilters and partially removed (≤20%) by sand alone and anthracite-sand biofilters. In particular, the GAC sandwich biofilter exhibited superior performance compared to sand/anthracite biofilter, and the comparisons among all biofilters indicated that both adsorption and biodegradation contributed to the removal of the target antibiotics in the GAC-associated biofilters. Adsorption kinetics showed that sulfamethoxazole fitted with pseudo-first-order adsorption model, while trimethoprim, amoxicillin, oxytetracycline and clarithromycin fitted the pseudo-second-order model. All antibiotics fitted the Langmuir model according to the isotherm experiment. To date, this is the first study evaluating the removal of antibiotics by GAC sandwich biofilters. Overall, this research will provide useful information which can be used for optimising or updating existing biofiltration processes in industry to reduce antibiotic residues from source water.

Predicting manganese and iron precipitation in drinking water biofilters

AbstractManganese is removed from drinking water because of aesthetic, health, and corrosion concerns. Like iron, manganese removal in biofilters depends on homogeneous, heterogeneous, and biological processes. This study aims to add further understanding to the importance of homogeneous processes for manganese removal in drinking water biofilters. Data collected from 10 groundwater biofilters across filter depth were analyzed using Pourbaix diagrams and thermodynamic modelling software (PHREEQC). Both methods predicted that iron would precipitate in all samples, but the predictions differed for manganese. The software approach provided a more precise look into the minerals predicted to form by homogeneous oxidation, allowing for deeper interpretation of biofilter oxidation–reduction (redox) conditions. Results suggest that multiple manganese removal mechanisms occur across biofilters, but homogeneous manganese oxidation may be essential to meet new Canadian guidelines. Utilities operating manganese removing biofilters should measure redox conditions to determine if changing biofilter pretreatment could decrease effluent manganese concentrations.Article Impact StatementResults of this study suggest that homogeneous manganese oxidation may be important for achieving the low effluent concentrations required by Canadian guidelines.

Removal of organic matter through full-scale drinking water biofilters

Removal of organic matter through full-scale drinking water biofilters

Microbiome of Drinking Water Biofilters is Influenced by Environmental Factors and Engineering Decisions but has Little Influence on the Microbiome of the Filtrate.

Bacterial communities in biofilters can improve drinking water quality through the biodegradation of dissolved contaminants but also pose potential risks by harboring and shedding microbes into the drinking water distribution system. In this study, pilot-scale granular activated carbon (GAC)-sand and anthracite-sand pilot-scale biofilters were investigated to determine the effects of filter design and operation on the microbiome of the filter media and its relationship to the microbiome in the filter effluent water. Bacterial abundance in the biofilters was relatively stable over time. Bacterial community composition exhibited spatial variation (i.e., with bed depth) and temporal variation linked to water quality changes. Bacterial community composition was significantly affected by the media type (GAC vs anthracite) and backwashing strategy (chloraminated water vs nonchloraminated water). The biofilters reduced bacterial abundance in the water (∼70%) but had only a minor effect on the bacterial community composition in the filtrate. Overall, our results suggest that the bacterial communities growing on biofilters affect filtered water quality primarily through the biotransformation of pollutants and nutrients rather than by altering the microbial community composition of the water as it passes through the filter.

Simultaneous TOC and Ammonia Removal in Drinking-Water Biofilters: Influence of pH and Alkalinity

AbstractA bench-scale biofiltration study was conducted to investigate the potential benefits of adjusting water pH and alkalinity as a simple water quality control on biofilter efficacy in terms o...