Biological Sand Filters Research Articles

Study on mechanism of removal of sudden Tetracycline by compound modified biological sand filtration process

The removal of tetracycline from the sewage plant effluents through advanced treatment methods is key to controlling tetracycline levels in the water environment. In this study, modified quartz sands (QS) were used in a biological sand filter to remove tetracycline. The modified QS, with different surface characteristics, were prepared using glass etching technology combined with subsequent chemical modification methods, including hydroxylation treatment, metal ion modification, and amino modification. The adsorption efficiency of hydroxylated QS was higher than that of metal ion modified and amino modified QS, with adsorption efficiencies of 20.4331 mg/kg, 12.8736 mg/kg, and 10.1737 mg/kg, respectively. Results indicated that QS primarily reduce tetracycline through adsorption. Adsorption on ordinary QS fit the pseudo-first-order kinetic model, while adsorption on other modified QS and biofilm-coated QS fit the pseudo-second-order kinetics model. Biodegradation was identified as another mechanism for tetracycline reduction, which fit the zero-order kinetic model. Pseudomonas alcaligenes and unclassified Pseudomonas accounted for 96.6% of the total tetracycline-degrading bacteria. This study elucidates the effectiveness and mechanisms of five types of QS in treating tetracycline from sewage plant effluents. It provides a novel method for tetracycline reduction in real-world wastewater scenarios.

Biosand Reactors for Municipal and Industrial Wastewater Treatment: Status Quo, Challenges and Opportunities

Biosand reactors (BSRs), alternatively known as slow or biological sand filters, are passive systems that are used to remove contaminants from domestic wastewater, industrial wastewater and drinking water. This review focuses specifically on their application for remediation of industrial effluent and sewage-containing municipal and household effluent. The relationships between the physicochemical characteristics of the sand grains (size, size distribution, shape, chemical composition) and the hydraulic conductivity of the sand employed in BSFs are critically discussed in relationship to the achievable loading rates and hydraulic retention times. The modes of operation and influence of the functional microbial biomass as well as biodegradable and recalcitrant particulates on these parameters is comprehensively reviewed. Finally, the bioremediation of sewage-based and industrial wastewater is examined. This includes an account of the biotic and abiotic removal mechanisms and the limitations of BSRs for removal of pollutants such as phosphorus/phosphate and nitrates/nitrites. The removal mechanisms and removal efficiencies of macronutrients, micropollutants, fecal indicators and other microorganisms such as antibiotic-resistant bacteria in BSRs are discussed.

Study on Plugging Material and Plugging Mechanism of Crude Oil Sand Water Filter Pipe

In order to develop the biological self-cleaning anti-clogging high-permeability sand filter tube, it is very important to analyze the plugging material and plugging mechanism of crude oil sand water filter. Under laboratory conditions, based on vacuum drying, condensation reflux, chromatographic separation, and other technologies, the plugging components were preliminarily analyzed. The plugging components were analyzed via XRD, infrared analysis, 1H NMR, and 13C NMR. Through analysis and testing, XRD results showed that the solid compositions were clay and sand grains. Meanwhile, the infrared analysis, 1H NMR, and 13C NMR demonstrated that the main components of the plug are asphaltene crude oil, and the proportion of aromatic components and saturated components is close.

Does Methane Contribute to Growth of Invertebrate Communities in Drinking Water?

Methane is a potential source of carbon in drinking water. Typically, it is removed at waterworks during an initial treatment step such as aeration or stripping. Remaining methane may be converted by methane-oxidizing bacteria to organic carbon, which is then available for heterotrophic growth and may ultimately contribute to invertebrate growth. We investigated the presence of invertebrates at a waterworks with incomplete methane removal and at a waterworks without methane. Microscopy and analyses of 16S and 18S ribosomal genes were conducted on filter sand from full-scale biological rapid sand filters. Primary filters with methane were dominated by methane- and ammonia-oxidizing bacteria. Upper layers of secondary filters were dominated by heterotrophic bacteria, while the deepest layer contained 92% eukaryote DNA. Rotifers, nematodes, platyhelminths and annelids constituted 22% of the DNA in the secondary filters. Filters with methane contained higher shares of invertebrates (13%) than the filter without methane (7%). Furthermore, pilot studies were conducted to estimate suitable levels of methane when implementing methane removal technologies. Methane concentrations of 0.24 mg/L caused rapid visible growth. Vacuum stripping and nitrogen addition removed methane to 0.018–0.03 mg/L and prevented growth of methane-oxidizing bacteria.

Formation of carbonyl compounds during ozonation of lake water and wastewater: Development of a non-target screening method and quantification of target compounds

Ozonation of natural waters is typically associated with the formation of carbonyl compounds (aldehydes, ketones and ketoacids), a main class of organic disinfection byproducts (DBPs). However, the detection of carbonyl compounds in water and wastewater is challenged by multiple difficulties inherent to their physicochemical properties. A non-target screening method involving the derivatisation of carbonyl compounds with p-toluenesulfonylhydrazine (TSH) followed by their analysis using liquid chromatography coupled to electrospray ionisation high-resolution mass spectrometry (LC-ESI-HRMS) and an advanced non-target screening and data processing workflow was developed. The workflow was applied to investigate the formation of carbonyl compounds during ozonation of different water types including lake water, aqueous solutions containing Suwannee River Fulvic acid (SRFA), and wastewater. A higher sensitivity for most target carbonyl compounds was achieved compared to previous derivatisation methods. Moreover, the method allowed the identification of known and unknown carbonyl compounds. 8 out of 17 target carbonyl compounds were consistently detected above limits of quantification (LOQs) in most ozonated samples. Generally, the concentrations of the 8 detected target compounds decreased in the order: formaldehyde > acetaldehyde > glyoxylic acid > pyruvic acid > glutaraldehyde > 2,3-butanedione > glyoxal > 1-acetyl-1-cyclohexene. The DOC concentration-normalised formation of carbonyl compounds during ozonation was higher in wastewater and SRFA-containing water than in lake water. The specific ozone doses and the type of the dissolved organic matter (DOM) played a predominant role for the extent of formation of carbonyl compounds. Five formation trends were distinguished for different carbonyl compounds. Some compounds were produced continuously upon ozonation even at high ozone doses, while others reached a maximum concentration at a certain ozone dose above which they decreased. Concentrations of target and peak areas of non-target carbonyl compounds during full-scale ozonation at a wastewater treatment plant showed an increase as a function of the specific ozone dose (sum of 8 target compounds ∼ 280 µg/L at 1 mgO3/mgC), followed by a significant decrease after biological sand filtration (> 64–94% abatement for the different compounds). This highlights the biodegradability of target and non-target carbonyl compounds and the importance of biological post-treatment.

Backwashing of granular media filters and membranes for water treatment: a review

AbstractFilter backwashing is a supplemental part of a drinking water treatment (DWT) facility to wash the filter bed at regular intervals using water or air scour/water by fluidizing the filter bed. Deposited material induces clogging the filter pores and enhances head loss in the bed. Biofiltration has been extensively utilized to decrease organic matter and manage the occurrence of disinfection by-products within drinking water sources. Biological rapid sand filters are frequently utilized to eliminate ammonium from groundwater provinces with the purpose of meeting drinking water requirements. Biological activated carbon (BAC) filters need to be backwashed to wash and enhance the treatment capability by detaching both restrained materials and residual biomass. The reclamation of activated carbon-used backwash water (UBW) was managed by exercising an ultrafiltration (UF) procedure.

Slow Sand Filters for the 21st Century: A Review.

Safe drinking water remains a major global challenge, especially in rural areas where, according to UNICEF, 80% of those without access to improved water systems reside. While water, sanitation, and hygiene (WASH)-related diseases and deaths are common outcomes of unsafe water, there is also an economic burden associated with unsafe water. These burdens are most prominent in rural areas in less-developed nations. Slow sand filters (SSFs), or biological sand filters (BSFs), are ideal water treatment solutions for these low-resource regions. SSFs are the oldest municipal drinking water treatment systems and improve water quality by removing suspended particles, dissolved organic chemicals, and other contaminants, effectively reducing turbidity and associated taste and odor problems. The removal of turbidity and dissolved organic compounds from the water enables the use of low-cost disinfection methods, such as chlorination. While the working principles of slow sand filtration have remained the same for over two centuries, the design, sizes, and application of slow sand filters have been customized over the years. This paper reviews these adaptations and recent reports on performance regarding contaminant removal. We specifically address the removal of turbidity and microbial contaminants, which are of great concern to rural populations in developing countries.

Manganese oxidation counteracts the deleterious effect of low temperatures on biofilm formation in Pseudomonas sp. MOB-449.

Mn removal from groundwater by biological sand filter technology is negatively impacted by low temperatures in winter periods. Therefore, the need to study Mn(II)-oxidizing bacteria (MOB) having the potential to oxidize Mn(II) and form biofilms at low temperatures is imperative. These MOB can have potential as inocula for sand filter bioaugmentation strategies to optimize Mn removal during winter periods. We previously showed that a Pseudomonas sp. MOB-449 (MOB-449), isolated from a Mn biofilter, oxidizes Mn(II) in a biofilm-dependent way at low temperatures. In this work, MOB-449 Mn(II) oxidation and growth capacities were evaluated under planktonic and biofilm conditions at different temperatures. At 18°C, MOB-449 showed enhanced biofilm formation due to the addition of Mn(II) to the medium correlating with Mn(II) oxidation, compared to biofilms grown in control medium. Moreover, this enhancement on biofilm formation due to the addition of Mn(II) was only observed at 18°C. At this temperature, Mn(II) oxidation in membrane fractions collected from biofilms was induced by uncoupling oxidative phosphorylation from the electron transport chain with 2,4-Dinitrophenol. In Pseudomonas, a role for c-type cytochrome in Mn(II) oxidation has been demonstrated. Accordingly, transcriptional profiles of all terminal oxidases genes found in MOB-449 showed an induction of cytochrome c terminal oxidases expression mediated by Mn(II) oxidation at 18°C. Finally, heme peroxidase activity assays and MS analysis revealed that PetC, a cytochrome c5, and also CcmE, involved in the cytochrome c biogenesis machinery, are induced at 18°C only in the presence of Mn(II). These results present evidence supporting that cytochromes c and also the cytochrome c terminal oxidases are activated at low temperatures in the presence of Mn(II). Overall, this work demonstrate that in MOB-449 Mn(II) oxidation is activated at low temperatures to gain energy, suggesting that this process is important for survival under adverse environmental conditions and contributing to the understanding of the physiological role of bacterial Mn(II) oxidation.

Effect of Particle Character and Calcite Dissolution on the Hydraulic Conductivity and Longevity of Biosand Filters Treating Winery and Other Acidic Effluents

Acidic effluent such as winery wastewater is challenging to remediate. Biological sand reactors can simultaneously remove organics and neutralize winery wastewater via biotic and abiotic mechanisms. The systems have been shown to be suitable for treating the intermittent flow of wastewater at small wineries. It has been shown that dissolution of calcite is the most important abiotic mechanism for increasing the pH of the influent. In this study, sand column experiments were used to determine the effects of (i) sand particle size distribution on calcite dissolution kinetics, and (ii) the effects of calcite particle dissolution on the hydraulic conductivity. The results were then used to calculate the theoretical temporal abiotic neutralization capacity of biological sand reactors with differently sized sand fractions, including unfractionated (raw) sand. The results were compared with those determined from a pilot system treating winery wastewater over a period of 3 years. Sand fractions with larger particles contained lower amounts of calcite (using Ca as a proxy), but exhibited higher hydraulic conductivities (3.0 ± 0.05 %Ca and 2.57 to 2.75 mm·s−1, respectively) than those containing smaller particles and/or raw sand (4.8 ± 0.04 to 6.8 ± 0.03 %Ca and 0.19 to 1.25 mm·s−1, respectively). The theoretical abiotic neutralization capacity of biological sand reactors was compared with a pilot system with the same flow rates, and a temporal abiotic neutralization capacity of 37 years was calculated for biological sand reactors, which compared favorably with the theoretical results obtained for wastewater with pH values between 2 (8.2 years) and 3 (82 years). It was concluded that biological sand filters with around 10% calcite will be able to abiotically neutralize winery wastewater and other wastewaters with similar acidities for the projected life span of the system. Future work should focus on determining the effect of sand grain size on the bioremediation capacity, as well as the use of biological sand reactors for treating other acidic organic wastewaters such as fruit processing, food production and distillery wastewater.

Removal of Escherichia coli from domestic sewage using biological sand filters: Reduction effect and microbial community analysis

The recycling of sewage is an economical option to solve the water resource pressure. However, to avoid health risks to humans, pathogens in sewage must be removed before reuse. In this study, a biological sand filter (BSF) was used to remove pathogen indicator Escherichia coli (E. coli) from sewage. The biolayer (schmutzdecke layer) formation process of BSFs, operation performance, factors affecting E. coli removal and microbial community structure were evaluated. The results of schmutzdecke layer culture showed that a large number of microorganisms were attached to the upper medium of BSFs. At the same time, the BSFs could reduce both conventional contaminants and E. coli. The E. coli removal experiments revealed that the removal rate of E. coli was about 96.1% at higher effective medium depth (50 cm), the removal rate was about 95% when set hydraulic loading rate (HLR) to 0.16 m3/m2/h and the removal efficiency reached 93.6% at lower influent bacteria concentration. Finally, the microbial community analysis indicated that different BSFs had similar microbial structure, and the microbial abundance in the schmutzdecke layer was higher than that in the bottom layer in the same BSFs. Besides, Biological action played a significant role in the removal of E. coli, including the bacteriolysis of Bdellovibrio and the competition between other bacteria and E. coli. In summary, BSF was a promising technology for removing E. coli from sewage.

Oxidation of 51 micropollutants during drinking water ozonation: Formation of transformation products and their fate during biological post-filtration

Micropollutants (MP) with varying ozone-reactive moieties were spiked to lake water in the influent of a drinking water pilot plant consisting of an ozonation followed by a biological sand filtration. During ozonation, 227 transformation products (OTPs) from 39 of the spiked 51 MPs were detected after solid phase extraction by liquid chromatography high-resolution mass spectrometry (LC-HRMS/MS). Based on the MS/MS data, tentative molecular structures are proposed. Reaction mechanisms for the formation of a large number of OTPs are suggested by combination of the kinetics of formation and abatement and state-of-the-art knowledge on ozone and hydroxyl radical chemistry. OTPs forming as primary or higher generation products from the oxidation of MPs could be differentiated. However, some expected products from the reactions of ozone with activated aromatic compounds and olefins were not detected with the applied analytical procedure. 187 OTPs were present in the sand filtration in sufficiently high concentrations to elucidate their fate in this treatment step. 35 of these OTPs (19%) were abated in the sand filtration step, most likely due to biodegradation. Only 24 (13%) of the OTPs were abated more efficiently than the parent compounds, with a dependency on the functional group of the parent MPs and OTPs. Overall, this study provides evidence, that the common assumption that OTPs are easily abated in biological post-treatment is not generally valid. Nevertheless, it is unknown how the OTPs, which escaped detection, would have behaved in the biological post-treatment.

Start-up strategies for nitrification and manganese oxidation on a single stage RSF for drinking water production

Abstract In drinking water production from groundwaters, biological rapid sand filters (RSFs) can be used for ammonium and manganese removal in aerobic conditions. However, in some boreholes, a start-up duration of several months is required to reach the required removal capacity, leading to significant water losses. Moreover, in specific industrial cases, no exogenous biomass under the form of backwash water or activated sludge can be added to accelerate the process, and different approaches are seldom considered in the literature. With the aim of saving water, start-up strategies coupling water temperature increase and substrate dosing were studied to accelerate the installation of biological activities in a pilot plant fed with borehole water. These set-ups enabled a substantial acceleration of nitrification but no improvement of manganese oxidation in the experimental conditions, although the experiments showed no clear negative influence of nitrification, through nitrite accumulation, on biological manganese oxidation. To further save energy and reduce water loss, outlet water recirculation at a rate of 75% during the start-up phase was validated. The proposed start-up strategy enabled the complete installation of active biofilms with a mean start-up time reduction of 36% and water use reduction of 84% compared to the reference natural conditions.

Removal of phytotoxins in filter sand used for drinking water treatment

Phytotoxins - toxins produced by plants – are contaminants with the potential to impair drinking water quality. They encompass a large group of toxic, partially persistent compounds that have been detected in seepage waters and in shallow wells used for drinking water production. If phytotoxins enter wells used for drinking water production, it is essential to know if the drinking water treatment processes will remove them from the water phase. However, it is currently unknown whether phytotoxins remain stable during traditional groundwater treatment using sand filters as the main treatment process. The objective of this study is to investigate removal potential of phytotoxins in biological sand filters and to asses if the removal potential is similar at different waterworks.Microcosms were set up with filter sand and drinking water collected at different groundwater-based waterworks. To be able to monitor phytotoxin removal ptaquiloside, caudatoside, gramine, sparteine, jacobine N-oxide, senecionine N-oxide and caffeine were applied at initial concentrations of 300 µg L-1, which is approx. two orders of magnitude higher than currently detected in environment, but expected to cover extreme environmental conditions. Removal was monitored over a period of 14 days. Despite the high initial concentration, all filter sands removed ptaquiloside and caudatoside completely from the water phase and at waterworks where pellet softening was implemented (pH 8.4) prior to rapid sand filtration, complete removal occurred within the first 30 min. All filter sands removed gramine and sparteine, primarily by a biological process, while jacobine N-oxide, senecionine N-oxide and caffeine were recalcitrant in the filter sands. During degradation of ptaquiloside and caudatoside we observed formation and subsequent removal of degradation products pterosin B and A. Filter sands with the highest removal potential were characterised by high contents of deposited iron and manganese oxides and hence large specific surface areas. Difference between bacterial communities investigated by 16S rRNA gene analyses did not explain different removal in the filter sands.All five investigated filter sands showed similar degradation patterns regardless of water chemistry and waterworks of origin. In drinking water treatment systems biological sand filters might therefore remove phytotoxin contaminants such as ptaquiloside, caudatoside, gramine, sparteine, while for other compounds e.g. jacobine N-oxide, senecionine N-oxide further investigations involving more advanced treatment options are needed.

Designing the Next Generation of Fe0-Based Filters for Decentralized Safe Drinking Water Treatment: A Conceptual Framework

The ambitious United Nations Sustainable Development Goal for 2030 to “leave no one behind” concerning safe drinking water calls for the development of universally applicable and affordable decentralized treatment systems to provide safe drinking water. Published results suggest that well-designed biological sand filters (BSFs) amended with metallic iron (Fe0-BSFs) have the potential to achieve this goal. Fe0-BSFs quantitatively remove pathogens and a myriad of chemical pollutants. The available data were achieved under various operating conditions. A comparison of independent research results is almost impossible, especially because the used Fe0 materials are not characterized for their intrinsic reactivity. This communication summarizes the state-of-the-art knowledge on designing Fe0-BSFs for households and small communities. The results show that significant research progress has been made on Fe0-BSFs. However, well-designed laboratory and field experiments are required to improve the available knowledge in order to develop the next generation of adaptable and scalable designs of Fe0-BSFs in only two years. Tools to alleviate the permeability loss, the preferential flow, and the use of exhausted filters are presented.

Manganese removal efficiencies and bacterial community profiles in non-bioaugmented and in bioaugmented sand filters exposed to different temperatures

Biological sand filtration systems are widely used to remove Manganese (Mn) from groundwater. Different experiences have demonstrated that low environmental temperatures decrease the performance of these systems. In order to overcome this problem, in a previous work, a Pseudomonas sagittaria strain named MOB-181, that showed high Mn(II) oxidation and biofilm formation capacities when grown at low temperatures, was isolated. Here, the impact of summer and winter temperatures on Mn removal efficiencies and on bacterial community profiles of both, non-bioaugmented and MOB-181 bioaugmented sand filters, was analyzed. Under summer conditions, MOB-181 inoculated columns showed the best Mn removal performance, removing Mn from the first day of system operation with an efficiency of 27%; also these columns reached an optimum Mn removal efficiency (95%) earlier than control columns (23 days and 29 days, respectively). Under winter conditions, the 27% efficiency was reached earlier for the inoculated columns than for control columns (20 days and 42 days, respectively); and the maximum efficiency (95%) was also reached faster than for the controls (39 days and 54 days, respectively). Bacterial communities profiles were more influenced by temperature changes than by the bioaugmentation process. This work demonstrated the importance of bioaugmentation with the MOB-181 strain to improve Mn removal, by shortening start-up periods, mainly at lower temperatures. Moreover, the obtained data will improve the knowledge on bacterial communities ecosystem involved in Mn removal at different temperatures and should help in developing novel bioaugmentation strategies for the optimization of biological groundwater treatment plants.

Impact of influent ammonia concentration on partial nitrification of biological sand filter and kinetics

The impact of influent NH4 +/-N concentration on partial nitrification performance was investigated in a biological sand filter. The removal kinetics model of NH4 +-N in partial nitrification-sand filter was established and its accuracy was verified. The results showed that the NH4 +-N removal rates and NO2 −-N accumulation rates stabled at about 60% and 94% respectively and the effluent NO2 −-N/NH4 +-N ratios were 1.20~1.39 when the hydraulic load was 1.0 m/d and the influent NH4 +-N concentration was 45~50 mg/L, indicating that the sand filter had good partial nitrification effect, and the effluent quality basically met the theoretical influent demand of anaerobic ammonia oxidation. The kinetic model of NH4 +/-N removal in sand filter could be described as Sh /S 0=exp(-1.0033S 0 −1.1337 h) when the influent NH4 +-N concentration was 10.2~61.3 mg/L. The model had high accuracy and could provide scientific guidance for effluent quality prediction and optimization design.

Peat swamp groundwater treatment: efficiency of mixed citrus peel and kernel activated carbon layer

One of the natural water resources is groundwater. Groundwater is another alternative to meet the increasing water demand in Malaysia. Then, the decrease in supplying raw groundwater which may due to depletion of groundwater and hence it is important to maintain the availability of water supply locally and even establish new water source such as from peat swamp to overcome future water crisis. Activated carbon is famous for its characteristic in eliminating various organic contaminants. In this investigation, low cost mixed activated carbon of food waste (citrus peel) and agricultural waste (palm kernel shell) are used as adsorbents in biological sand filter to treat peat swamp groundwater whereby the overall aim of study to evaluate the performance of mixed activated carbon layer of citrus peel and kernel in biological sand filter for peat swamp groundwater treatment. The mixed activated carbon with 1:1 ratio is filled into the biological sand filter. The efficiency of the mixed activated carbon layered biological sand water treatment system is evaluated using parameters pH, Turbidity, Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Suspended Solids (TSS) and E. coli and removal of heavy metal ions of peat swamp groundwater. All these parameters follow the Standard Methods for Examination of Water and Wastewater 2005. The implementation of investigation improved the water quality of the peat swamp groundwater, the water treatment technology using combination of activated carbon and biosand filter, human living standards by providing safe and clean water supply.

Challenges and Opportunities in implementing leachate recirculation in Indonesia: technical aspects

Sanitary landfill is the most commonly used way to process municipal solid waste (MSW) in most countries including Indonesia. Sanitary landfill system produces leachate which contains a lot of inorganic pollutants, heavy metals, dissolved organic matter, and xenobiotics. Most leachate treatment plants in Indonesia consist of stabilization ponds, aeration ponds, anaerobic ponds, maturation ponds, and tertiary treatment such as wetlands. A small part of waste water treatment plant (WWTP) consists of equalization tanks, facultative bodies, aeration tanks, polishing pools, sedimentation tanks, chemical and biological processing tanks, mud ponds and sand filters. In fact, leachate was found at depths of 4, 9, 15, 20, 30 m in final processing site in the Gampong Jawa, Banda Aceh. Real conditions, some WWTPs do not function properly, buildings are damaged, and effluent quality exceeds the standard. Leachate needs to be managed properly, so as not to cause pollution to ground water and surface water. Although, there are many negative problems related to leachate management, but there are many opportunities that can be developed. These opportunities not only reduce their negative impacts but also help meet energy needs and improve environmental health in the long run. This review article aims to discuss the opportunities and challenges of leachate recirculation in Indonesia in terms of technical aspects.

Characterizing a Newly Designed Steel-Wool-Based Household Filter for Safe Drinking Water Provision: Hydraulic Conductivity and Efficiency for Pathogen Removal

This study characterizes the decrease of the hydraulic conductivity (permeability loss) of a metallic iron-based household water filter (Fe0 filter) for a duration of 12 months. A commercial steel wool (SW) is used as Fe0 source. The Fe0 unit containing 300 g of SW was sandwiched between two conventional biological sand filters (BSFs). The working solution was slightly turbid natural well water polluted with pathogens (total coliform = 1950 UFC mL−1) and contaminated with nitrate ([NO3−] = 24.0 mg L−1). The system was monitored twice per month for pH value, removal of nitrate, coliforms, and turbidity, the iron concentration, as well as the permeability loss. Results revealed a quantitative removal of coliform (>99%), nitrate (>99%) and turbidity (>96%). The whole column effluent depicted drinking water quality. The permeability loss after one year of operation was about 40%, and the filter was still producing 200 L of drinking water per day at a flow velocity of 12.5 L h−1. A progressive increase of the effluent pH value was also recorded from about 5.0 (influent) to 8.4 at the end of the experiment. The effluent iron concentration was constantly lower than 0.2 mg L−1, which is within the drinking-water quality standards. This study presents an affordable design that can be one-to-one translated into the real world to accelerate the achievement of the UN Sustainable Development Goals for safe drinking water.

Copper-Induced Stimulation of Nitrification in Biological Rapid Sand Filters for Drinking Water Production by Proliferation of Nitrosomonas spp.

Copper is a cofactor of the ammonia monooxygenase, an essential enzyme for the activity of ammonia oxidizing prokaryotes (AOP). Copper dosing at less than 1 μg/L stimulated ammonium removal in the poorly nitrifying biological filters of three full-scale drinking water treatment plants. Upon copper dosing, the ammonium concentration in the effluent decreased from up to 0.18 to less than 0.01 mg NH4+-N/L. To investigate how copper dosing affected the filter microbial community, we applied amplicon sequencing and qPCR targeting key nitrifying groups, including complete ammonia oxidizing (comammox) Nitrospira. Copper dosing increased the abundance of different nitrifiers. Multiple Nitrosomonas variants (betaproteobacterial ammonia oxidizers), which initially collectively represented 1% or less of the total community, increased almost 10-fold. Comammox Nitrospira were abundant and increased too, but their relative abundance within the AOP decreased because of Nitrosomonas proliferation. No other consistent change in the filter communities was detected, as well as no adverse effect of copper on the filters functionality. Our results show that copper dosing in three independent treatmentplants was associated with consistent growth of AOP and that efficient nitrification was achieved through the joint contribution of comammox Nitrospira and an increasing fraction of betaproteobacterial ammonia oxidizers.