Microbial community in biofilters for water reuse applications: A critical review

Biologically active filtration (BAF) for metabolic 1,4-dioxane removal from contaminated groundwater

1,4-Dioxane is a persistent contaminant that is not effectively removed by conventional water treatment processes. In this study, bench-scale granular activated carbon (GAC)-based biologically active filtration (BAF) systems were developed to metabolically degrade 1,4-dioxane at environmentally relevant levels (<1000 μg L-1). BAF was established using predeveloped biologically activated carbon particles by mixing a 1,4-dioxane-degrading microbial community with granular activated carbon. 1,4-Dioxane removal performance was examined at a range of 1,4-dioxane concentrations (100-1000 μg L-1), hydraulic loading rates (3.6-14 cm h-1), and with the presence of co-contaminants (natural organic matter (NOM) and 1,1-DCE). BAFs achieved 69 ± 7 % removal with an influent 1,4-dioxane concentration of 100 μg L-1 and hydraulic loading rates of 3.6-14 cm h-1, with the lowest effluent concentration of 21 μg L-1. The presence of NOM and 1,1-DCE negatively and irreversibly impacted 1,4-dioxane removal performance of BAF, and pretreatment processes to remove co-contaminants are crucial to maintain the 1,4-dioxane removal efficiency. Microbial analysis revealed the enrichment of 1,4-dioxane degrading species (CB1190-like bacteria) and functional genes responsible for 1,4-dioxane biodegradation (dxmB and aldh) at the top 12 cm of the columns, suggesting the effectiveness of biological 1,4-dioxane removal within short column lengths. This study demonstrated effective metabolic 1,4-dioxane removal at environmentally relevant concentrations by the BAFs, and can provide insights into designing better 1,4-dioxane remediation strategies.

Role of ammonia-oxidising bacteria in the removal of odorous gases by the use of plastic recycling waste as a biofilter

Ammonia gas has emerged as a major concern for many industrial facilities. With the same degree of hazard, plastic waste after mechanical processing is becoming a crucial challenge for many mechanical plastics recycling plants. In this respect, the present study explored the use of plastic waste obtained from mechanical recycling plants as an adsorbent to treat ammonia gas using a biofiltration device. The physical-chemical parameters of the adsorbent used, notably moisture, ash, organic matter, pH and elemental analysis were determined. Next-generation sequencing and scanning electron microscopy analyses were carried out to detect and identify the nature of bacterial communities in the biofilters used. The results of the chemical analysis showed that the adsorbent used is appropriate for the development of the microorganisms. X-ray fluorescence analysis showed that the adsorbent belongs to the silico-aluminous materials, proving its effectiveness as an adsorbent. The efficiency of ammonia removal was over 93% using the biofilter. Next-generation sequencing revealed that bacteria belonging to ammonia oxidizers such as Nitrosomonas and Nitrosospira are among the most abundant bacteria after the biofiltration process, which explains the efficiency of ammonia removal. Scanning electron microscopy confirmed the development of a biofilm on the surface of the biofilter after filtration. Ultimately, these results offer a promising novel approach for valorisation of the plastic waste.

Greywater Reuse: Contaminant Profile, Health Implications, and Sustainable Solutions

Global water scarcity is becoming an increasingly critical issue; greywater reuse presents a promising solution to alleviate pressure on freshwater resources, particularly in arid and water-scarce regions. Greywater typically sourced from household activities such as laundry, bathing, and dishwashing, constitutes a significant portion of domestic wastewater. However, the reuse of greywater raises concerns about the potential risks posed by its complex composition. Despite the growing body of literature on greywater reuse, most studies only focus on specific contaminants, thus there is a limited understanding of the comprehensive profile of contaminants, health, and environmental effects associated with these pollutants. This review adds new knowledge through a holistic exploration of the composition and physico-chemical characteristics of greywater, with a focus on its organic and inorganic pollutants, heavy metals, EDCs, emerging microplastics, nanoparticles, and microbial agents such as bacteria, fungi, viruses, and protozoa. This review sheds light on the current state of knowledge regarding greywater pollutants and their associated risks while highlighting the importance of safe reuse. Additionally, this review highlights the removal of contaminants from greywater and the sustainable use of grey water for addressing water scarcity in affected regions.

Exploring synergistic interactions of ethyl acetate removal and community ecology using magnetite-entrapped biofilters

Emissions of ethyl acetate (EA) exhaust from industrial sources can cause environmental and health risks. EA can be effectively removed by biological filtration with low operating costs and promising good benefits. This study demonstrated the synergistic effect of using magnetite and pebbles as bio-packing in promoting microbial activity and microbial abundance for EA degradation. The biofilter filled with magnetite and pebbles exhibits the most efficient removal of EA, average removal efficiency >90% (Inlet load: 120.19 ± 9.33 g/(m3·h), Empty bed residence time: 60s). Meanwhile, magnetite promoted the increase of Adenosine Triphosphatase (ATP) and Lactate Dehydrogenase (LDH) concentrations compared to the control group, with maximum concentrations of 1.31 μM/L and 0.024 U/104 cell, respectively. Furthermore, the presence of magnetite promoted the structural diversity of microbial community (Rhodoblastus, Xanthobacter, Saccharibacteria_genera_incertae_sedis and Acidocella. A first-attempt mechanism of ethyl acetate degradation was proposed to reveal interactions of microbial communities in magnetite biofilter columns, by stimulating microbial community diversification to promote the above-mentioned dominant species bioremediation.

Relating microbial community composition to treatment performance in an ozone-biologically active carbon filtration potable reuse treatment train

Treatment trains that couple ozone (O3) with biologically active carbon (BAC) filtration are of interest as a lower cost, more sustainable, membrane-free approach to water reuse. However, little is known about the microbial communities that are the fundamental drivers of O3-BAC treatment. The objective of this study was to demonstrate microbial community profiling as a diagnostic tool for assessing the functionality, biological stability, and resilience of coupled physical, chemical, advanced oxidative and biological processes employed in water reuse treatment. We utilized 16S rRNA gene amplicon sequencing to profile the bacterial microbiota over time throughout a potable reuse train employing coagulation, flocculation, sedimentation, ozonation, BAC filtration, granular activated carbon (GAC) adsorption, and UV disinfection. A distinct baseline microbiota was associated with each stage of treatment (ANOSIM, p < 0.05, r-stat = 0.52), each undergoing succession with time and operational shifts. Ozonation resulted in the sharpest shifts (i.e., 83.3 % average change in Genus level relative abundances, when adjusted O3:TOC ratio > 1), and also variance, in microbial community composition. Adjustment in O3:TOC ratios, temperature, filter-aid polymer, monochloramine quenching agent, and empty-bed contact time also resulted in measurable changes in the baseline microbial community composition of individual processes, but to a lesser degree. Of these, supplementation of nitrogen and phosphorus resulted in the strongest bifurcation, especially in the microbial communities inhabiting the BAC (ANOSIM: p < 0.05, BAC5 r-stat = 0.32; BAC10 r-stat = 0.54) and GAC (ANOSIM: p < 0.05, GAC10 r-stat = 0.54; GAC20 r-stat = 0.63) units. Additionally, we found that the BAC microbial community was responsive to an inoculation of microbially active media, which resulted in improved TOC removal. The findings of this study improve understanding of bacterial dynamics occurring in advanced water treatment trains and can inform improved system design and operation.

Electrocatalytic denitrification biofilter for advanced purification of chlorophenols via ceramsite-based Ti/SnO2-Sb particle electrode: Performance, microbial community structure and mechanism

In response to the demand for advanced purification of industrial secondary effluent, a new method has been developed for treating chlorophenol wastewater using the novel ceramsite-based Ti/SnO2-Sb particle electrodes (Ti/SnO2-Sb/CB) enhanced electrocatalytic denitrification biofilter (EDNBF-P) to achieve removal of chlorophenols (CPs), denitrification, and reduction of effluent toxicity. The results showed that significantly improved CPs and TN removal efficiency at low COD/N compared to conventional denitrification biofilter, with CPs removal rates increasing by 0.33%-59.27% and TN removal rates increasing by 12.53%-38.92%. Under the conditions of HRT = 2h, 3V voltage, charging times = 12h, and 25 °C, the concentrations of the CPs in the effluent of EDNBF-P were all below 1 mg/L, the TN concentration was below 15 mg/L, while the effluent toxicity reached the low toxicity level. Additionally, the Ti/SnO2-Sb/CB particle electrodes effectively alleviated the accumulation of NO2--N caused by applied voltage. The Silanimonas, Pseudomonas and Rhodobacter was identified as the core microorganism for denitrification and toxicity reduction. This study validated that EDNBF-P could achieve synergistic treatment of CPs and TN through electrocatalysis and microbial degradation, providing a methodological support for achieving advanced purification of chlorophenol wastewater with low COD/N in industrial applications.

Involvement of functional metabolism promotes the enrichment of antibiotic resistome in drinking water: Based on the PICRUSt2 functional prediction

Biofilters are the important source and sink of antibiotic resistance genes (ARGs) and antibiotic resistance bacteria (ARB) in the drinking water. Current studies generally ascribed the prevalence of BAR in biofilter from the perspective of gene behavior, i.e. horizontal gene transfer (HGT), little attentions have been paid on the ARGs carrier- ARB. In this study, we proposed the hypothesis that ARB participating in pollutant metabolism processes and becoming dominant is an important way for the enrichment of ARGs. To verify this, the antibiotic resistome and bacterial functional metabolic pathways of a sand filter was profiled using heterotrophic bacterial plate counting method (HPC), high-throughput qPCR, Illumina Hiseq sequencing and PICRUSt2 functional prediction. The results illustrated a significant leakage of ARB in the effluent of the sand filter with an average absolute abundance of approximately 102-103 CFU/mL. Further contribution analysis revealed that the dominant genera, such as Acinetobacter spp., Aeromonas spp., Elizabethkingia spp., and Bacillus spp., were primary ARGs hosts, conferring resistance to multiple antibiotics including sulfamethoxazole, tetracycline and β-lactams. Notably, these ARGs hosts were involved in nitrogen metabolism, including extracellular nitrate/nitrite transport and nitrite reduction, which are crucial in nitrification and denitrification in biofilters. For example, Acinetobacter spp., the dominant bacteria in the filter (relative abundance 69.97 %), contributed the majority of ARGs and 53.79 % of nitrite reduction function. That is, ARB can predominate by participating in the nitrogen metabolism pathways, facilitating the enrichment of ARGs. These findings provide insights into the stable presence of ARGs in biofilters from a functional metabolism perspective, offering a significant supplementary to the mechanisms of the emergence, maintenance, and transmission of BARin drinking water.

Treatment of cow manure from exercise pens: A laboratory-scale study of the effect of air injection on conventional and alternative biofilters

Woodchips in stand-off pads for wintering cows have been applied in countries like Ireland and New Zealand. Their primary role is to protect soils by effectively filtering nutrients during wet conditions, while ensuring a healthy and comfortable environment for the cows. The stand-off pad concept has the potential to be adopted in Canada to provide year-long outdoor access to tie-stall dairy cows. The objective of this study was to evaluate the effect of alternative filtering materials and bed aeration under controlled laboratory conditions. Twelve biofilter columns (0.3 m in diameter and 1-m high) were installed in 12 environmentally-controlled chambers (1.2-m wide by 2.4-m long), and divided into four treatments: a bed of conventional woodchips or an alternative mix of organic materials (sphagnum peat moss, woodchips and biochar) with and without aeration (flux rate set at 0.6 m3/min/m2). Approximately 0.6 L of semi-synthetic dairy manure and 1 L of tap water were poured on the biofilters during two experimental periods of 4 weeks, simulating the effect of either winter or summer conditions (room temperature below or over 10 °C) on the retention of nutrients and fecal bacteria. Results showed that the alternative biofilters under both summer and winter conditions were more efficient in removing COD, SS, TN, and NO3-N than conventional biofilters (maximum efficiencies of 97.6%, 99.7%, 96.4%, and 98.4%, respectively). Similarly for E. coli, they achieved a minimum concentration of 1.8 Log10 CFU/100 ml. Conventional biofilters were more efficient for PO4-P removal with a maximum efficiency of 88.2%. Aeration did not have any significant effect under the tested temperature conditions. Additional factors such as media adaptation time as well as aeration flow during this period should be considered.

How effective is biological activated carbon in removing micropollutants? A comprehensive review

Micropollutants (MPs), also called emerging contaminants, are detected in various environmental compartments. Wastewater is their main entry pathway due to the incomplete removal of MPs in wastewater treatment plants (WWTPs). These contaminants are a risk to human health and the integrity of the ecosystem because they are persistent and toxic to organisms. Complementary treatments such as adsorption are studied to increase the efficiency of existing WWTPs. However, a disadvantage of using activated carbon is its high cost of production and regeneration. Biological activated carbon (BAC) is an alternative to overpass this scenario. In BAC, biofilm development occurs on the surface of activated carbon, which enables bioregeneration of the adsorbent and extends its lifetime. This review focused on the studies that applied BAC to remove MPs in aqueous matrices. The review methodology was based on bibliometric and systematic analysis. Tables and thematic maps were presented to investigate trends and gaps in research and related themes. The study points out the leading MPs researched in adsorption in the last ten years. The systematic analysis showed that most studies bring sequential treatments with real wastewater/water, in which BAC is the final process. BAC has the potential to be a complementary treatment for removing MPs. However, there is a lack of articles investigating only BAC as the main tertiary treatment. Topics that should be further investigated in this area are the microbiological community formed in the biofilm, the column's lifetime, and the cost analysis of BAC implementation and operation.

Safe purification of rural drinking water by biological aerated filter coupled with ultrafiltration

Water resources of many rural areas are usually lakes or reservoirs, which can be easily affected by run-off, non-point source pollution and are often of poorer quality compared with urban water sources. Drinking water supply in remote rural areas usually suffers from various challenges, such as the high cost of construction and maintenance of centralized drinking water treatment plants and pipe networks, due to the dispersed nature of villages, which are often located in varied and complex topographies. In this study, a combined process comprising biological aerated filter (BAF) combined with ultrafiltration was developed to treat polluted reservoir water. Organic matter indexes, turbidity, and chroma were used as indicators for the evaluation of the system performance. In a long-term experiment lasting 260 days, the combined process was tested under different values of critical operational parameters, including filler types and empty bed contact time (EBCT). Furthermore, the microbial communities in different BAF reactors were carefully evaluated at different times, finding that microorganisms with specific functions were enriched in the various BAF reactors. The combined process reached 85.5 % removal rate of DOC with an EBCT of 45 min and using granule active carbon (GAC) as filler. Most of the effluents of BAF reactors met the requirements for drinking water in China. The combined system showed practical potential for polluted water treatment in some rural areas.

Use of wood and cork in biofilters for the simultaneous removal of nitrates and pesticides from groundwater

About 13% and 7% of monitored groundwater stations in Europe exceed the permitted levels of nitrates (50 mg NO₃^- L^-1) or pesticides (0.1 μg L^-1), respectively. Although slow sand filtration can remove nitrates via denitrification when oxygen is limited, it requires an organic carbon source. The present study evaluates the performance of the use of wood pellets and granulated cork as carbon sources in bench-scale biofilters operated under water-saturated and water-unsaturated conditions for more than 400 days. The biofilters were monitored for nitrate (200 mg L^-1) and pesticide (mecoprop, diuron, atrazine, and bromacil, each at a concentration of 5 μg L^-1) attenuation, as well as for the formation of nitrite and pesticide transformation products. Microbiological characterization of each biofilter was also performed. The water-saturated wood biofilter achieved the best nitrate removal (>99%), while the cork biofilters lost all denitrification power over time (from 38% to no removal). The unsaturated biofilter columns were not effective for removing nitrates (20-30% removal). As for pesticides, all the biofilters achieved high removal rates of mecoprop and diuron (>99% and >75%, respectively). Atrazine removal was better in the wood-pellet biofilters than the cork ones (68-96% vs. 31-38%). Bromacil was only removed in the water-unsaturated cork biofilter (67%). However, a bromacil transformation product was formed there. The water-saturated wood biofilter contained the highest number of denitrifying microorganisms, with Methyloversatilis as the characteristic genus. Microbial composition could explain the high removal of pesticides and nitrates achieved in the wood-pellet biofilter. Overall, the results indicate that wood-pellet biofilters operated under water-saturated conditions are a good solution for treating groundwater contaminated with nitrates and pesticides.

Biological filtration for wastewater treatment in the 21st century: A data-driven analysis of hotspots, challenges and prospects

Biological filtration has been widely used in wastewater treatment around the world, yet achieving satisfactory removal of pollutants remains a challenge due to the complexity of water pollution. In order to reveal the hotspots and trends of biological filtration from the perspective of research innovation, 5454 SCI papers and 14,287 patents collected from the Web of Science Core Collection and Derwent Innovation Index database were analyzed by visualization techniques. The results showed that China ranked first in the number of both papers and patents, while the USA and Japan contributed significantly in papers and patents, respectively. Co-occurrence analysis obtained the mapping knowledge domains and demonstrated distinct associations between contaminants ("nitrogen", "pharmaceuticals", "personal care products"), chemicals ("carbon", "activated carbon", "media"), process ("biodegradation", "adsorption" or "ozonation") and characteristics ("kinetics", "performance", "diversity"). Moreover, this review summarized the recent advances of biological filtration media, microorganism and combined process being applied. It was concluded that environmentally friendly biological filtration ("phytoremedi", "microalga", "recirculating aquaculture system"), bio-enhanced biological filtration ("bioaugment", "fungi", "low augment") and emerging pollutants ("emerging contamin", "antibiotic resistance gen", "organic micropollut", "trace organic chem") were the hotspots through data-driven analyses. Technology evolution path of biological filtration generally indicated the transition from conventional biological filtration for nitrogen and phosphorus removal to Fenton-biofiltration combined technology and finally to ozone-biological filtration. Furthermore, the technical innovation direction of the collaborative control of multi-media pollution, the low-carbon biological filtration and short-process technology was prospected. This work can serve as a quick reference for early-career researchers and industries working in the area of biological filtration.

Optimal integration of vacuum UV with granular biofiltration for advanced wastewater treatment: Impact of process sequence on CECs removal and microbial ecology

This study explored process synergies attainable by integrating a vacuum ultraviolet-based advanced oxidation process with biofiltration. A comparison using granular activated carbon or granular zeolite as filtration media were examined in context of advanced wastewater treatment for potable reuse. Six biofiltration columns, three with granular activated carbon and three with granular zeolite, were operated in parallel and batch-fed daily with nitrified secondary effluent. After achieving a pseudo-steady state through the filter columns, vacuum ultraviolet treatment was applied as pre-treatment or as post-treatment, at two different applied energies (i.e., VUV-E1=1 kWh/m³ and VUV-E10=10 kWh/m³). Once granular activated carbon had transitioned to biologically activated carbon, as determined based on soluble chemical oxygen demand removal, adsorption was still observed as the main mechanism for contaminants of emerging concern and nitrate removal. Vacuum ultraviolet pre-treatment markedly improved contaminants of emerging concern removal through the integrated system, achieving 40% at VUV-E1 and 90% at VUV-E10. When applied as post-treatment to zeolite column effluents, VUV-E1 and VUV-E10 further increased contaminants of emerging concern removal by 20% and 90%, respectively. In the zeolite system, vacuum ultraviolet pre-treatment also increased soluble chemical oxygen demand removal efficiency, indicating that higher energy vacuum ultraviolet increased biodegradability. Total prokaryotes were two-fold more abundant in biologically activated carbon than in zeolite, with vacuum ultraviolet pretreatment markedly affecting microbial diversity, both in terms of richness and composition. Media type only marginally affected microbial richness in the biofilters but showed a marked impact on structural composition. No clear relationship between compositional structure and depth was observed.

Removal of toxic heavy metals using genetically engineered microbes: Molecular tools, risk assessment and management strategies

The direct release of industrial effluent into the water and other anthropogenic activities causes water pollution. Heavy metal ions are the primary contaminant in the industrial effluents which are exceptionally toxic at low concentrations, terribly disturb the endurance equilibrium of activities in the eco-system and be remarkably hazardous to human health. Different conventional treatment methodologies were utilized for the removal of toxic pollutants from the contaminated water which has several drawbacks such as cost-ineffective and lower efficiency. Recently, genetically modified micro-organisms (GMMs) stand-out for the removal of toxic heavy metals are viewed as an economically plausible and environmentally safe technique. GMMs are microorganisms whose genetic material has been changed utilizing genetic engineering techniques that exhibit enhanced removal efficiency in comparison with the other treatment methodologies. The present review comments the GMMs such as bacteria, algae and fungi and their potential for the removal of toxic heavy metals. This review provides current aspects of different advanced molecular tools which have been used to manipulate micro-organisms through genetic expression for the breakdown of metal compounds in polluted areas. The strategies, major limitations and challenges for genetic engineering of micro-organisms have been reviewed. The current review investigates the approaches working on utilizing genetically modified micro-organisms and effective removal techniques.

Microbial ecology of biofiltration used for producing safe drinking water

Abstract

Biofiltration is a water purification technology playing a pivotal role in producing safe drinking water. This technology attracts many interests worldwide due to its advantages, such as no addition of chemicals, a low energy input, and a high removal efficiency of organic compounds, undesirable taste and odours, and pathogens. The current review describes the microbial ecology of three biofiltration processes that are routinely used in drinking water treatment plants, i.e. (i) rapid sand filtration (RSF), (ii) granular activated carbon filtration (GACF), and (iii) slow sand filtration (SSF). We summarised and compared the characteristics, removal performance, and corresponding (newly revealed) mechanisms of the three biofiltration processes. Specifically, the microbial ecology of the different biofilter processes and the role of microbial communities in removing nutrients, organic compounds, and pathogens were reviewed. Finally, we highlight the limitations and challenges in the study of biofiltration in drinking water production, and propose future perspectives for obtaining a comprehensive understanding of the microbial ecology of biofiltration, which is needed to promote and optimise its further application.

Key points

• Biofilters are composed of complex microbiomes, primarily shaped by water quality.

• Conventional biofilters contribute to address safety challenges in drinking water.

• Studies may underestimate the active/functional role of microbiomes in biofilters.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12013-x.

Extremophilic Exopolysaccharides: Biotechnologies and Wastewater Remediation

Various microorganisms thrive under extreme environments, like hot springs, hydrothermal vents, deep marine ecosystems, hyperacid lakes, acid mine drainage, high UV exposure, and more. To survive against the deleterious effect of these extreme circumstances, they form a network of biofilm where exopolysaccharides (EPSs) comprise a substantial part. The EPSs are often polyanionic due to different functional groups in their structural backbone, including uronic acids, sulfated units, and phosphate groups. Altogether, these chemical groups provide EPSs with a negative charge allowing them to (a) act as ligands toward dissolved cations as well as trace, and toxic metals; (b) be tolerant to the presence of salts, surfactants, and alpha-hydroxyl acids; and (c) interface the solubilization of hydrocarbons. Owing to their unique structural and functional characteristics, EPSs are anticipated to be utilized industrially to remediation of metals, crude oil, and hydrocarbons from contaminated wastewaters, mines, and oil spills. The biotechnological advantages of extremophilic EPSs are more diverse than traditional biopolymers. The present review aims at discussing the mechanisms and strategies for using EPSs from extremophiles in industries and environment bioremediation. Additionally, the potential of EPSs as fascinating biomaterials to mediate biogenic nanoparticles synthesis and treat multicomponent water contaminants is discussed.