Biological Sand Filters Research Articles

Development of an integrated wetland microbial fuel cell and sand filtration system for greywater treatment

This research focused on the design and operation of a system combining a constructed wetland microbial fuel cell (CW-MFC) and a biological sand filter (BSF) for the continuous treatment and recycling of handwashing greywater. The technology was assessed both in terms of its ability to treat the greywater and to generate bioelectricity. The performance was evaluated by regularly monitoring the organic material, nutrient and E. coli removal efficiencies as well as the power generation. The system was observed to achieve a complete bacterial removal for a 4-log E. coli influent load and a 99% COD removal was achieved with a 432 mg L−1 organic load. The final effluent quality was found to comply with South African standards for drinking water quality, illustrating the potential for reuse. Moreover, a maximum power density of 4.33 mW m-3 was achieved by the system thus demonstrating the ability of the process to recover power from handwashing greywater. It was recommended that future investigations focus on determining the performance and maintenance requirements of a pilot-scale system operated using real handwashing greywater, appropriate methods for disinfection of the effluent, improved power generation and the expected life-cycle behaviour of the greywater treatment system.

Biological Sand Filter Performance Test Using Multiple Methods for Pathogen Detection: a Longitudinal Field Study in Kenya

Fifty biological sand filters (BSFs) housed in 70-L plastic containers were built and installed in the West Pokot County of Kenya. Half of the BSFs were installed in June 2010; the remainder were installed in June 2012. BSF performance was analyzed during June 2012 and 2015. Performance indicators included the removal of turbidity and fecal and total coliforms. In 2012, 17 of the original 25 BSFs installed were operational, and their performance was evaluated. In 2015, 15 of the BSFs were operational. BSF performance during 2015 showed an average fecal coliform removal of 98.9%. The most common reasons provided to explain why the BSF installed was no longer in use included the family moved and the BSF was too heavy to carry, and the effluent pipe broke. Relative affluence was observed using the Progress out of Poverty Index (PPI)™. With an increase in elevation, we noted a decrease in PPI. The average PPI for homesteads with operation BSFs was 10 points higher than homes where the BSFs were in disrepair. An assay to estimate Escherichia coli presence and concentration was modified, and the results were compared with more traditional field enumeration methods. The field assay used a five-compartment bag to quantify the most probable number (MPN) of E. coli to provide a low-tech option to field workers in developing country to test the viability of drinking water sources. We used a Hach medium, varying from that prescribed by Aquagenx. Results from using the modified method compared well with the more traditional field assay.

Environmental Bacteria Involved in Manganese(II) Oxidation and Removal From Groundwater.

The presence of iron (Fe) and manganese (Mn) in groundwater is an important concern in populations that use it as source of drinking water. The ingestion of high concentrations of these metals may affect human health. In addition, these metals cause aesthetic and organoleptic problems that affect water quality and also induce corrosion in distribution networks, generating operational and system maintenance problems. Biological sand filter systems are widely used to remove Fe and Mn from groundwater since they are a cost-effective technology and minimize the use of chemical oxidants. In this work, the bacterial communities of two biological water treatment plants from Argentina, exposed to long term presence of Mn(II) and with a high Mn(II) removal efficiency, were characterized using 16S rRNA gene Illumina sequencing. Several selective media were used to culture Mn-oxidizing bacteria (MOB) and a large number of known MOB and several isolates that have never been reported before as MOB were cultivated. These bacteria were characterized to select those with the highest Mn(II) oxidation and biofilm formation capacities and also those that can oxidize Mn(II) at different environmental growth conditions. In addition, studies were performed to determine if the selected MOB were able to oxidize Mn(II) present in groundwater while immobilized on sand. This work allowed the isolation of several bacterial strains adequate to develop an inoculum applicable to improve Mn(II) removal efficiency of sand filter water treatment plants.

Effect of supernatant water level on As removal in biological rapid sand filters

Current groundwater treatment facilities, mostly relying on aeration-filtration configurations, aim at the removal of iron (Fe), ammonia (NH4+) and manganese (Mn). However, recently water companies expressed the ambition to also reduce arsenic (As) concentrations in these rapid sand filters. The aim of this study was to investigate the effect of the Fe oxidation state entering a biological filter bed on As removal. By varying supernatant water level, either Fe(II) or Fe(III) in the form of hydrous ferric oxides (HFO) could be stimulated to enter the filter bed at alkaline groundwater pH (7.6). The experimental pilot column filters showed that once the As(III) oxidation stabilised in the top layer of the filter sand, As removal reached its maximum (±75% at 120 cm supernatant level and 1.5 m/h filtration velocity). The increase in supernatant level from 5 to 120 cm resulted in additional HFO production prior to rapid filtration (1.5, 5 and 10 m/h), i.e. homogeneous Fe(II) oxidation and flocculation, and subsequently, HFO ending up deeper into the filter bed (120 cm filter depth). At a low supernatant water level of 5 cm, Fe(II) oxidised heterogeneously and was removed within the top 20 cm of the filter bed. Consequently, filters with high supernatant levels removed As to lower levels (by 20%) than in filters with low supernatant water levels. The benefits of Fe(II) oxidation prior to filtration for As removal was confirmed by comparing Fe(III) to Fe(II) additions in the supernatant water or in the filter bed. Overall it is concluded that in biological groundwater filters, the combination of a higher supernatant level and/or Fe(III) addition with biological As(III) oxidation in the top of the filter bed promotes As removal.

Comparison of removal efficiency of pathogenic microbes in four types of wastewater treatment systems in Denmark

The aim of the present work was to evaluate and compare the performance in the removal of pathogenic microbes in four different types of decentralized wastewater treatment systems, namely: horizontal flow constructed wetlands (HFCW), vertical flow constructed wetlands (VFCW), biological sand filters (BSF) and biofilters (BF). All the systems analyzed are located in Jutland, Denmark. Water sampling took place during a three months period that covered from winter to spring. Conventional microbial indicators such as Escherichia coli, total coliforms (TC), intestinal enterococci and sulphite-reducing clostridia were quantified using traditional microbiological culture methods, whereas Bacteroides spp. determination was performed by quantitative PCR (qPCR). Other water quality parameters such as dissolved oxygen, biological oxygen demand (BOD5), total suspended solids (TSS), pH, temperature, ammonium concentration and conductivity of influent and effluent water samples were also analyzed. The results showed that bacterial indicators significantly reduced in all the systems analyzed. In general, BF showed the best performance in the removal of microbes for all bacteria studied, while BSF demonstrated an improved capacity to eliminate E. coli and TC. Contrarily, VFCW seems to be more effective reducing the amount of intestinal enterococci, sulphite-reducing clostridia, and Bacteroides spp. In the present study, HFCW were the less efficient wastewater treatment system for the elimination of the evaluated pathogens. However, the performance in the removal of microbes was still significant considering that such systems were the oldest under operation (with over 20 years of continuous task).

Biological sand filter system treating winery effluent for effective reduction in organic load and pH neutralisation

Wineries generate 0.2–14 L of wastewater per litre of wine produced, which is often used for irrigation or discharged into aquatic systems. To mitigate adverse environmental impacts, there is a need for low cost wastewater treatment options. The novel biological sand filtration system described in this pilot study is a sustainable off-grid modular system which can be easily retrofitted to current infrastructure. The system was operated with average hydraulic and organic loading rates of 150 L m−3 sand.day-1 and 152 gCOD.m−3 of sand.day−1, respectively. Over 762 days of operation, average removal efficiencies of 79% and 77% in terms of chemical oxygen demand and total phenolic concentrations were achieved. In addition, an average 1.8-fold increase in the calcium concentration was achieved, with a concomitant reduction in the sodium adsorption ratio and similar indices. This pilot study also confirmed in a ‘real world’ setting the results of laboratory-based studies where biological sand filters neutralised acidic synthetic winery wastewater and reduced the organic load.

Bacterial nitrogen fixation in sand bioreactors treating winery wastewater with a high carbon to nitrogen ratio

Heterotrophic bacteria proliferate in organic-rich environments and systems containing sufficient essential nutrients. Nitrogen, phosphorus and potassium are the nutrients required in the highest concentrations. The ratio of carbon to nitrogen is an important consideration for wastewater bioremediation because insufficient nitrogen may result in decreased treatment efficiency. It has been shown that during the treatment of effluent from the pulp and paper industry, bacterial nitrogen fixation can supplement the nitrogen requirements of suspended growth systems. This study was conducted using physicochemical analyses and culture-dependent and -independent techniques to ascertain whether nitrogen-fixing bacteria were selected in biological sand filters used to treat synthetic winery wastewater with a high carbon to nitrogen ratio (193:1). The systems performed well, with the influent COD of 1351 mg/L being reduced by 84–89%. It was shown that the nitrogen fixing bacterial population was influenced by the presence of synthetic winery effluent in the surface layers of the biological sand filters, but not in the deeper layers. It was hypothesised that this was due to the greater availability of atmospheric nitrogen at the surface. The numbers of culture-able nitrogen-fixing bacteria, including presumptive Azotobacter spp. exhibited 1–2 log increases at the surface. The results of this study confirm that nitrogen fixation is an important mechanism to be considered during treatment of high carbon to nitrogen wastewater. If biological treatment systems can be operated to stimulate this phenomenon, it may obviate the need for nitrogen addition.

Challenges in using allylthiourea and chlorate as specific nitrification inhibitors

Allylthiourea (ATU) and chlorate (ClO3−) are often used to selectively inhibit nitritation and nitratation. In this work we identified challenges with use of these compounds in inhibitory assays with filter material from a biological rapid sand filter for groundwater treatment. Inhibition was investigated in continuous-flow lab-scale columns, packed with filter material from a full-scale filter and supplied with NH4+ or NO2−. ATU concentrations of 0.1–0.5 mM interfered with the indophenol blue method for NH4+ quantification leading to underestimation of the measured NH4+ concentration. Interference was stronger at higher ATU levels and resulted in no NH4+ detection at 0.5 mM ATU. ClO3− at typical concentrations for inhibition assays (1–10 mM) inhibited nitratation by less than 6%, while nitritation was instead inhibited by 91% when NH4+ was supplied. On the other hand, nitratation was inhibited by 67–71% at 10–20 mM ClO3− when NO2− was supplied, suggesting significant nitratation inhibition at higher NO2− concentrations. No chlorite (ClO2−) was detected in the effluent, and thus we could not confirm that nitritation inhibition was caused by ClO3− reduction to ClO2−. In conclusion, ATU and ClO3− should be used with caution in inhibition assays, because analytical interference and poor selectivity for the targeted process may affect the experimental outcome and compromise result interpretation.

Copper deficiency can limit nitrification in biological rapid sand filters for drinking water production

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.

Efficiency of new Miswak, titanium dioxide and sand filters in reducing pollutants from wastewater

In this work, I tried to improve the efficiency and performance of the sand filter with a simple low cost method. This work successfully reported an alternative for the traditional biological sand filter which was considered as a time consuming filter. Miswak and TiO2 were added to the filter and their effects were observed. Three filters were designed (SF-1, SF-2, and SF-3). The results of this work indicated that chemical oxygen demand (COD) was reduced by 47.54%, 90.94%, and 95.47% in case of SF-1, SF-2, and SF-3, respectively. Moreover, the total suspended solids (TSS) removal % reached to 98.05% for both SF-1 and SF-2. Also, the total organic carbon (TOC), surfactants (SUR), biochemical oxygen demand (BOD), and total bacterial count were reduced when SF-1, SF-2, and SF-3 were used.

An improved method to set significance thresholds for β diversity testing in microbial community comparisons.

Exploring the variation in microbial community diversity between locations (β diversity) is a central topic in microbial ecology. Currently, there is no consensus on how to set the significance threshold for β diversity. Here, we describe and quantify the technical components of β diversity, including those associated with the process of subsampling. These components exist for any proposed β diversity measurement procedure. Further, we introduce a strategy to set significance thresholds for β diversity of any group of microbial samples using rarefaction, invoking the notion of a meta-community. The proposed technique was applied to several in silico generated operational taxonomic unit (OTU) libraries and experimental 16S rRNA pyrosequencing libraries. The latter represented microbial communities from different biological rapid sand filters at a full-scale waterworks. We observe that β diversity, after subsampling, is inflated by intra-sample differences; this inflation is avoided in the proposed method. In addition, microbial community evenness (Gini > 0.08) strongly affects all β diversity estimations due to bias associated with rarefaction. Where published methods to test β significance often fail, the proposed meta-community-based estimator is more successful at rejecting insignificant β diversity values. Applying our approach, we reveal the heterogeneous microbial structure of biological rapid sand filters both within and across filters.

Biodegradation of organics and accumulation of metabolites in experimental biological sand filters used for the treatment of synthetic winery wastewater: A mesocosm study

Winery effluent is characterized by the presence of high concentrations of organic molecules. Biological sand filters are ideal systems for the bioremediation of this waste at small wineries. In this study, synthetic winery wastewater, consisting of phenolics and high concentrations of ethanol and acetate was treated in experimental biological sand filters operated in batch mode. The organic substrates and metabolites in effluent and pore water samples, taken from four niches (superficial and deep; inlet and outlet), were identified and quantified. The highest COD concentrations were measured at the deep inlet and the lowest at the deep outlet, reflecting the establishment of degradation gradients from inlet to outlet due to plug flow. Ethanol was the preferred substrate in all niches but contrary to expectations, the biodegradation of ethanol and phenolics took place preferentially under lower redox conditions, in the deep niches. There was an accumulation of acetate and propionate, with propionate being found in notably higher ratios in the deep niches. The acidic influent (pH 3.5) was neutralized.

Effects of dynamic operating conditions on nitrification in biological rapid sand filters for drinking water treatment

Biological rapid sand filters are often used to remove ammonium from groundwater for drinking water supply. They often operate under dynamic substrate and hydraulic loading conditions, which can lead to increased levels of ammonium and nitrite in the effluent. To determine the maximum nitrification rates and safe operating windows of rapid sand filters, a pilot scale rapid sand filter was used to test short-term increased ammonium loads, set by varying either influent ammonium concentrations or hydraulic loading rates. Ammonium and iron (flock) removal were consistent between the pilot and the full-scale filter. Nitrification rates and ammonia-oxidizing bacteria and archaea were quantified throughout the depth of the filter. The ammonium removal capacity of the filter was determined to be 3.4 g NH4–N m−3 h−1, which was 5 times greater than the average ammonium loading rate under reference operating conditions. The ammonium removal rate of the filter was determined by the ammonium loading rate, but was independent of both the flow and influent ammonium concentration individually. Ammonia-oxidizing bacteria and archaea were almost equally abundant in the filter. Both ammonium removal and ammonia-oxidizing bacteria density were strongly stratified, with the highest removal and ammonia-oxidizing bacteria densities at the top of the filter. Cell specific ammonium oxidation rates were on average 0.6 × 102 ± 0.2 × 102 fg NH4–N h−1 cell−1. Our findings indicate that these rapid sand filters can safely remove both nitrite and ammonium over a larger range of loading rates than previously assumed.

Biological sand filters: low-cost bioremediation technique for production of clean drinking water.

Approximately 1.1 billion people in rural and peri-urban communities of developing countries do not have access to safe drinking water. The mortality from diarrheal-related diseases amounts to ∼2.2 million people each year from the consumption of unsafe water. Most of them are children under 5 years of age--250 deaths an hour from microbiologically contaminated water. There is conclusive evidence that one low-cost household bioremediation intervention, use of biological sand filters, is capable of dramatically improving the microbiological quality of drinking water. This unit will describe this relatively new and proven bioremediation technology's ability to empower at-risk populations to use naturally occurring biological principles and readily available materials as a sustainable way to achieve the health benefits of safe drinking water.

Biodegradation of the cyanobacterial hepatotoxin [Dha7] microcystin-LR within a biologically active sand filter

Cyanobacterial blooms in Thailand waters contain microcystin (MC) hepatotoxins that are a risk to animal and human health. The biodegradation of MCs is a safe and natural method of removal from water. The [Dha7] MC-LR was purified by chromatography, identified by liquid chromatography–tandem mass spectrometry (LC-MS) and used for examining the biodegradation of MCs. Analysis of MC levels revealed degradation of the [Dha7] MC-LR by the bacterium Novosphingobium sp. KKU15, with complete degradation occurring within 3 days under conditions in batches of a flask experiment. The ability of the bacterium to degrade the MCs through a slow sand filter was also investigated. Removal of the [Dha7] MC-LR by biological sand filtration was assessed using a polyvinyl chloride column experiment. In MC-dosed water, degradation of the MC was observed specifically in the inoculated samples (bacterial concentration of 1.6 × 107CFU/cm3 of sand), with complete degradation occurring within 7 days compared to the uninoculated controls. A polymerase chain reaction (PCR) specifically targeting the 16S rRNA gene of Novosphingobium sp. KKU15 was used to monitor the presence of the bacterium in the experimental trials. PCR products indicative of a bacterial population were observed at all of the sample sites in the column where the degradation of the MCs was observed, indicating that this bacterial isolate was active in the degradation of MCs.

The effect of increasing grain size in biosand water filters in combination with ultraviolet disinfection

With sand less than 0.70 mm often difficult to source in the field, it is of interest to study larger grained sand for use in biosand water filters (BSF). This study examined how sand grain size affects biological sand water filtration and how the combination of biological sand filtration and ultraviolet (UV) disinfection affects drinking water quality. Two BSFs were built: a control with maximum grain size, dmax = 0.70 mm and an experimental with grain sizes ranging from 0.70 mm to dmax = 2.0 mm. Untreated water was passed through each BSF daily. Results show Escherichia coli and turbidity removal characteristics of the control and experimental BSFs were not significantly different from one another. Both BSFs produced water that met World Health Organization (WHO) drinking water guidelines for turbidity, and although E. coli reduction was over 98% for each BSF, a high initial bacteria concentration resulted in effluent levels above WHO guidelines. Subsequently, effluent from each BSF was placed in clear plastic bottles under UV light, after which water from each BSF met E. coli guidelines. The data yielded promising results for using larger sand in BSFs, but longer duration studies with more data points are needed.

Selection ofClostridiumspp. in biological sand filters neutralizing synthetic acid mine drainage

In this study, three biological sand filter (BSF) were contaminated with a synthetic iron- [1500 mg L⁻¹ Fe(II), 500 mg L⁻¹ Fe(III)] and sulphate-rich (6000 mg L⁻¹ SO₄²⁻) acid mine drainage (AMD) (pH = 2), for 24 days, to assess the remediation capacity and the evolution of autochthonous bacterial communities (monitored by T-RFLP and 16S rRNA gene clone libraries). To stimulate BSF bioremediation involving sulphate-reducing bacteria, a readily degradable carbon source (glucose, 8000 mg L⁻¹) was incorporated into the influent AMD. Complete neutralization and average removal efficiencies of 81.5 (±5.6)%, 95.8 (±1.2)% and 32.8 (±14.0)% for Fe(II), Fe(III) and sulphate were observed, respectively. Our results suggest that microbial iron reduction and sulphate reduction associated with iron precipitation were the main processes contributing to AMD neutralization. The effect of AMD on BSF sediment bacterial communities was highly reproducible. There was a decrease in diversity, and notably a single dominant operational taxonomic unit (OTU), closely related to Clostridium beijerinckii, which represented up to 65% of the total community at the end of the study period.

A novel bench-scale column assay to investigate site-specific nitrification biokinetics in biological rapid sand filters

A bench-scale assay was developed to obtain site-specific nitrification biokinetic information from biological rapid sand filters employed in groundwater treatment. The experimental set-up uses granular material subsampled from a full-scale filter, packed in a column, and operated with controlled and continuous hydraulic and ammonium loading. Flowrates and flow recirculation around the column are chosen to mimic full-scale hydrodynamic conditions, and minimize axial gradients. A reference ammonium loading rate is calculated based on the average loading experienced in the active zone of the full-scale filter. Effluent concentrations of ammonium are analyzed when the bench-scale column is subject to reference loading, from which removal rates are calculated. Subsequently, removal rates above the reference loading are measured by imposing short-term loading variations. A critical loading rate corresponding to the maximum removal rate can be inferred. The assay was successfully applied to characterize biokinetic behavior from a test rapid sand filter; removal rates at reference loading matched those observed from full-scale observations, while a maximum removal capacity of 6.9 g NH4+–N/m3 packed sand/h could easily be determined at 7.5 g NH4+–N/m3 packed sand/h. This assay, with conditions reflecting full-scale observations, and where the biological activity is subject to minimal physical disturbance, provides a simple and fast, yet powerful tool to gain insight in nitrification kinetics in rapid sand filters.

Selection of Diazotrophic Bacterial Communities in Biological Sand Filter Mesocosms Used for the Treatment of Phenolic-Laden Wastewater

Agri effluents such as winery or olive mill wastewaters are characterized by high phenolic concentrations. These compounds are highly toxic and generally refractory to biodegradation. Biological sand filters (BSFs) represent inexpensive, environmentally friendly, and sustainable wastewater treatment systems which rely vastly on microbial catabolic processes. Using denaturing gradient gel electrophoresis and terminal-restriction fragment length polymorphism, this study aimed to assess the impact of increasing concentrations of synthetic phenolic-rich wastewater, ranging from 96 mg L(-1) gallic acid and 138 mg L(-1) vanillin (i.e., a total chemical oxygen demand (COD) of 234 mg L(-1)) to 2,400 mg L(-1) gallic acid and 3,442 mg L(-1) vanillin (5,842 mg COD L(-1)), on bacterial communities and the specific functional diazotrophic community from BSF mesocosms. This amendment procedure instigated efficient BSF phenolic removal, significant modifications of the bacterial communities, and notably led to the selection of a phenolic-resistant and less diverse diazotrophic community. This suggests that bioavailable N is crucial in the functioning of biological treatment processes involving microbial communities, and thus that functional alterations in the bacterial communities in BSFs ensure provision of sufficient bioavailable nitrogen for the degradation of wastewater with a high C/N ratio.

Assessment of temporal and spatial evolution of bacterial communities in a biological sand filter mesocosm treating winery wastewater

To assess the impact of winery wastewater (WW) on biological sand filter (BSF) bacterial community structures, and to evaluate whether BSFs can constitute alternative and valuable treatment- processes to remediate WW. During 112days, WW was used to contaminate a BSF mesocosm (length 173cm/width 106cm/depth 30cm). The effect of WW on bacterial communities of four BSF microenvironments (surface/deep, inlet/outlet) was investigated using terminal-restriction fragment length polymorphism (T-RFLP). BSF achieved high Na (95·1%), complete Cl and almost complete chemical oxygen demand (COD) (98·0%) and phenolic (99·2%) removals. T-RFLP analysis combined with anosim revealed that WW significantly modified the surface and deep BSF bacterial communities. BSF provided high COD, phenolic and salt removals throughout the experiment. WW-selected bacterial communities were thus able to tolerate and/or degrade WW, suggesting that community composition does not alter BSF performances. However, biomass increased significantly in the WW-impacted surface sediments, which could later lead to system clogging and should thus be monitored. BSFs constitute alternatives to constructed wetlands to treat agri effluents such as WW. To our knowledge, this study is the first unravelling the responses of BSF bacterial communities to contamination and suggests that WW-selected BSF communities maintained high removal performances.