Filter Media Depth Research Articles

Occurrence, Concentration, and Distribution of 35 PFASs and Their Precursors Retained in 20 Stormwater Biofilters.

Current knowledge about the fate and transport behaviors of per- and polyfluoroalkyl substances (PFASs) in urban stormwater biofilter facilities is very limited. C5-14,16 perfluoroalkyl carboxylic acids [perfluorinated carboxylic acids (PFCAs)], C4,8,10 perfluoroalkanesulfonic acids (PFSAs), methyl-perfluorooctane sulfonamide acetic acid (MeFOSAA, a PFSA precursor), and unknown C6-8 PFCA and perfluorooctanesulfonic acid precursors were frequently found in bioretention media and forebay sediments at Σ35PFAS concentrations of <0.03-19 and 0.064-16 μg/kg-DW, respectively. Unknown C6-8 PFCA precursor concentrations were up to ten times higher than the corresponding PFCAs, especially at forebays and biofilters' top layer. No significant trend could be attributed to PFAS and precursor concentrations versus depth of filter media, though PFAS concentrations were 2-3 times higher in the upper layers on average (significant difference between the upper (0-5 cm) and deepest (35-50 cm) layer). PFASs had a similar spatial concentration distribution in each filter media (no clear difference between short- and long-chain PFASs). Commercial land use and organic matter were important factors explaining the concentration variations among the biofilters and between the sampling depths, respectively. Given the comparable PFAS accumulations in deeper and superficial layers and possible increased mobility after precursor biotransformation, designing shallow-depth, nonamended sand biofilters or maintaining only the top layer may be insufficient for stormwater PFAS management.

Partially saturated vertical flow constructed wetland for urban wastewater treatment

Partially saturated vertical flow constructed wetland (SVF) emerge as an alternative to classical vertical flow due to improved carbonaceous organic matter removal and nitrogen transformations without of the need for external energy source. In this context, the main objective of this study was to show the long-term evaluation of a SVF wetland with 7.5 m2 of surface area (filter media depth of 0.75 m where 53% of total depth was saturated) and planted with Typha domingensis macrophyte, operated as secondary/advanced treatment unit of urban wastewater under subtropical climate conditions. Sampling and analysis of conventional wastewater quality parameters, oxygen consumption rate estimation, and assessment of bacterial dynamics were conducted over 6 years, which allowed inferring that operating the SVF wetland with a specific hydraulic load around 4 L∙m-2∙min-1 and hydraulic regime with feeding and resting cycles of 3.5 d, all wastewater quality parameters met local legislation release standards in river water bodies. Saturated zone of the wetland favors the presence of denitrifying bacteria representing a potential of 44% of TN removal due to simultaneous nitrification-denitrification.

Nitrification potential of daily-watered biofiltration designs for high ammonium wastewater treatment

The vegetated biofiltration systems (VBS), also known as bioretentions or rain gardens, are well-established technology for treatment of urban stormwater and recently greywater, offering multiple benefits to urban environments. However, the impact of high ammonium strength wastewater (60 mg/L) on the nitrification process in these systems is not well understood. Hence, a laboratory-based column study was conducted to uncover dominant nitrification mechanisms, based on the learnings from similar onsite wastewater treatment systems. The experimental columns tested the effect of contact time (filter media depth, 150 mm, 300 mm and 700 mm), media oxygenation (active and passive) and alkalinity/pH (marble chips 5 % weight), as well as optimal operational conditions (inflow loading, concentrations, and dissolved oxygen (DO)). All nitrogen species (NH4+, NO3−, NO2−), chemical oxygen demand (COD) and physical parameters (DO, pH, electrical conductivity) were monitored across seven events over thirteen weeks. The results show that dosing with 30 and 60 mg/L of NH4+ resulted in 700 mm sand column depth to perform almost complete nitrification of NH4+ to NO3− (< 90 %), while 300 mm designs achieved partial nitrification of NH4+ to NO2−, likely due to limited contact time and inefficient nitrite oxidizing bacteria activity. Nitrification potential of all designs further supported that appropriate aerobic contact time is necessary for effective nitrification. Inflow concentration of NH4+ and DO did not significantly impact nitrification performance, while reducing daily volume loading reduced NO3− and NO2− leaching. Active and passive aeration and alkalinity buffering did not positively affect ammonium removal. While there is a potential to apply both nitrification-denitrification and anammox processes to future VBS design, further understanding of aeration and alkalinity on microbially driven nitrification processes is needed.

A Systematic Review of the Scientific Literature on Pollutant Removal from Stormwater Runoff from Vacant Urban Lands

Even though the common acknowledgment that vacant urban lands (VUL) can play a positive role in improving stormwater management, little synthesized literature is focused on understanding how VUL can take advantage of different stormwater control measures (SCMs) to advance urban water quality. The project aims to provide urban planners with information on the remediation of vacant lands using urban runoff pollutant removal techniques. To find the most effective removal method, relevant scholarly papers and case studies are reviewed to see what types of vacant land have many urban runoff pollutants and how to effectively remove contaminants from stormwater runoff in the city by SCMs. The results show that previously developed/used land (but now vacant) has been identified as contaminated sites, including prior residential, commercial, industrial, and parking lot land use from urban areas. SCMs are effective management approaches to reduce nonpoint source pollution problems runoff. It is an umbrella concept that can be used to capture nature-based, cost-effective, and eco-friendly treatment technologies and redevelopment strategies that are socially inclusive, economically viable, and with good public acceptance. Among these removal techniques, a bioretention system tends to be effective for removing dissolved and particulate components of heavy metals and phosphorus. Using different plant species and increasing filter media depth has identified the effectiveness of eliminating nitrate nitrogen (NO3-N). A medium with a high hydraulic conductivity covers an existing medium with low hydraulic conductivity, and the result will be a higher and more effective decrease for phosphorus (P) pollutants. In addition, wet ponds were found to be highly effective at removing polycyclic aromatic hydrocarbons, with removal rates as high as 99%. For the removal of perfluoroalkyl acid (PFAA) pollutants, despite the implementation of SCMs in urban areas to remove PFAAs and particulate-related contaminants in stormwater runoff, the current literature has little information on SCMs’ removal of PFAAs. Studies have also found that VUL’s size, shape, and connectivity are significantly inversely correlated with the reduction in stormwater runoff. This paper will help planners and landscape designers make efficient decisions around removing pollutants from VUL stormwater runoff, leading to better use of these spaces.

Filter media depth and its effect on the efficiency of Household Slow Sand Filter in continuous flow

This study evaluated the impact of a 50% reduction of filter media depth in Household Slow Sand Filters (HSSFs) on continuous flow to remove physicochemical and microbiological parameters from river water. Furthermore, simple pre-treatment and disinfection processes were evaluated as additional treatments. Two filter models with different filtration layer depths were evaluated: a traditional one with 50 cm media depth (T-HSSF) and a compact one (C-HSSF) with 25 cm. HSSFs were fed with pre-treated river water (24-h water sedimentation followed by synthetic fabric filtration) for 436 days at a constant filtration rate of 0.90 m3 m−2 day−1 with a daily production of 48 L day−1. Sodium hypochlorite (2.0 mg L−1 of NaOCl 2.5% for 30 min) was used to disinfect the filtered water. Water samples were analysed weekly for parameters such as turbidity, organic matter, colour and E. coli, among others. Removal of protozoan cysts and oocysts by the HSSFs were also evaluated. After pretreatment, turbidity from the HSSF river water was reduced to 13.2 ± 14.6 NTU, allowing the filters to operate. Statistical analysis indicated no significant difference (p > 0.05) between T-HSSF and C-HSSF efficiencies in all evaluated parameters throughout operation time. Hence, media depth reduction did not hinder continuous HSSF performance for almost all the evaluated parameters. However, it may have affected Giardia cysts retaining, which passed through the thinner media on one evaluation day. Disinfection was effective in reducing remaining bacteria from filtered water; however, it was ineffective to inactivate protozoa. The reduction in the filtration layer did not affect the overall filtered water quality or quantity showing that a compact HSSF model may be a viable option for decentralized water treatment.

Influence of slow sand filter cleaning process type on filter media biomass: backwashing versus scraping

Biomass was assessed as a new approach for evaluating backwashed slow sand filters (BSF). Slow sand filtration (SSF) is a simple technology for water treatment, where biological mechanisms play a key role in filtration efficiency. Backwashed slow sand filters were previously recommended for small-scale filters (~1 m² of filtration area) as an alternative to conventional filters that are usually cleaned by scraping (ScSF). Biomass was never evaluated in BSF, which is a gap in the knowledge of this technology, considering the importance of its biological mechanisms. Therefore, for the first time, two filters operating under the same conditions were used to compare the influence of backwashing on biomass; one filter was cleaned by backwashing and the other by scraping. Biomass along the filter media depth (40 cm) was assessed by different techniques and compared in terms of cellular biomass (by chloroform fumigation), volatile solids, bacterial community (by 16S rRNA gene sequencing), and observations by scanning electron and fluorescence microscopy. Filters were also monitored and compared regarding filtered water quality and headloss; their differences were related to the different cleaning processes. Overall, filtered water quality was acceptable for slow sand filter standards (turbidity < 1 NTU and total coliform removal > 1 log). However, headloss developed faster on scraped filters, and biomass was different between the two filters. Backwashing did not significantly disturb biomass while scraping changed its surface sand layers. Cell biomass was more abundant and spread across the filtration depth, related to lower headloss, turbidity, and cyanobacterial breakthrough. These results agreed with the water quality and microscopy observations. The bacterial community was also less stratified in the backwashed filter media. These results expand the knowledge of backwashing use in slow sand filters, demonstrating that this process preserves more biomass than scraping. In addition, biomass preservation can lead to bacterial selectivity and faster filter ripening. Considering the importance of biomass preservation on slow sand filtration and its biological filtration mechanisms, the results presented in this paper are promising. The novel insight that BSF can preserve biomass after backwashing may contribute to increasing its application in small communities.

The impact of stormwater biofilter design and operational variables on nutrient removal - a statistical modelling approach

Biofiltration systems can help mitigate the impact of urban runoff as they can treat, retain and attenuate stormwater. It is important to select the optimal design characteristics of biofilters (e.g., vegetation, filter media depth) to ensure high treatment performance. Operational conditions (e.g., infiltration rate) can also lead to significant changes in biofilter treatment performance over time. The impact of specific operational conditions on water quality treatment performance of stormwater biofilters is still not well understood. Furthermore, despite the importance of design characteristics and operational conditions on biofilter treatment performance, there is a lack of models that can be used to determine the optimal design and operation. In this paper, we developed a series of statistical models to predict the Total Phosphorus (TP) and Total Nitrogen (TN) removal performance of stormwater biofilters using various numbers of design characteristics and operational conditions. These statistical models were tested using data collected from four extensive laboratory-scale biofilter column studies. It was found that all models performed relatively well with a Nash-Sutcliffe Efficiency (NSE) of 0.42 - 0.61 for TP and 0.37 - 0.63 for TN. The most important design characteristics were filter media type and depth for TP treatment, and vegetation type and submerged zone depth for TN treatment. In addition, infiltration rate and inflow concentrations were the operational conditions that greatly influence outflow TP and TN concentrations from stormwater biofilters. As such, these variables need to be carefully considered when designing and operating stormwater biofilters. Sensitivity analysis results indicate that the model was quite sensitive to all regression coefficients and intercepts. Additional modelling exercises show that the model could be further simplified by reducing the number of cross-correlated parameters. These models can be used by practitioners for not just optimising the design, but also operating biofilters using real-time monitoring and control to achieve optimum performance.

Feeding mode influence on treatment performance of unsaturated and partially saturated vertical flow constructed wetland

This study aimed to evaluate the influence of two different feeding modes on wastewater treatment performance and oxygen consumption rate (OCR) of the unsaturated (UVF wetland) and partially saturated (SVF wetland) vertical flow constructed wetlands operated in parallel under subtropical climate for four years. Each wetland had a superficial area of 7.5 m2 and was planted with Typha domingensis. Both units have a filter media depth of 0.75 m, composed by sand (effective diameter of 0.29 mm and uniformity of 4). UVF wetland operated typically unsaturated, while SVF wetland had the bottom part saturated (57% of total depth). Two feeding modes were evaluated for both wetlands. The feeding mode was operated within the limits recommended by the German standard, with a hydraulic loading rate (HLR) of 75 mm d−1 and specific pulse volume (SPV) of 19 L m−2 for both wetlands and a specific hydraulic loading rate (SHLR) of 8 and 9 L m−2 min−1 for UVF and SVF wetlands, respectively. Meanwhile, the second feeding mode was applied for both wetlands, being an HLR of 103 mm d−1, 26 L m−2 of SPV, and 4 L m−2 min−1 of SHLR. The load removal efficiency of SVF wetland was higher than the UVF wetland for all parameters and feeding modes. No statistical difference was identified for OCR values between wetlands and feeding mode. The results showed that operating UVF and SVF wetlands with a SHLR around 4 L m−2 min−1 and SPV equal of 26 L m−2 is preferable. This fact could represent a significant reduction in inlet pumping power requirements and also less superficial area requirements.

Influence of filter media depth and vegetation on Faecal Coliform removal by stormwater biofilters

AbstractBiofilters are promising technologies that widely applied in the treatment of urban stormwater. However, the microbial removal capacity performance depends greatly on the design of biofilters. Hence, this laboratory study attempts to investigate the influence of filter media depths (i.e. 150, 250, 350 and 450 mm) and the variation of native plants, that is, Cow Grass (Axonopus compressus) and Pearl Grass (Axonopus compressus, dwarf) in removing stormwater microorganism particularly Faecal Coliform (FC). Findings showed that a minimum media depth of 300 mm was required to achieve &gt;1 log FC removal. The mean removal of FC at 450 mm depth filter exceeded 2 log for both Cow and Pearl grass biofilter columns. Results showed that there was no statistically significant difference in vegetation type on the performance of FC removal, however, Cow grass biofilter column revealed higher FC mean log removal compared to Pearl grass biofilter column.

Consequences of fluctuating depth of filter media on coliform removal performance and effluent reuse opportunities of a bio-sand filter in municipal wastewater treatment

Abstract Due to the rapid urbanization attaining full coverage of proper wastewater treatment is a challenge in several developing nations. The conventional sanitattion approachpracticed in different countries does not satisfy the current wastewater treatment need of fastly growing cities. Also, the decentralized technologies practiced so far is interrupted by technical issues that ends in an extensive upsurge of maintenance cost and poor effluent quality. Thus, this study focuses on the applicability of low-cost bio-sand filters as a decentralized municipal wastewater treatment technology through testing pathogen removal efficiency and effluent reuse possibilities of different media depth bio-sand filters. Three setups of bio-sand filtercolumn were established each comprised of a specific sand, fine gravel and coarse gravel with different filter depths. The results orevealed geometric mean reductions for total coliforms of 99 %, 87 % and 30 % for a bio-sand filter with the top fine sand depth of 220 mm, 120 mm, and 20 mm, respectively. While the geometric mean for the reduction of fecal coliform was 99.9 %, 99.6 %, and 99 %. The effluent from three of the bio-sand filters does not achieve the requirements for unrestricted irrigation according to WHO and US-EPA guidelines. Whereas the quality of effluent from the first scenario of the bio-sand filter can meet WHO and US-EPA guidelines for restricted irrigation reuse option. Likewise, the effluent from the second scenario of the bio-sand filter achieves the US-EPA reuse standard for restricted irrigation.

Application of Bottom Ash as Filter Media for Construction Site Runoff Control

The potential application of bottom ash (BA) for construction site runoff control as an alternative filter media with high removal efficiency of total suspended solids (TSS) and longer operation period were evaluated. Both lab-scale single-layer and pilot-scale multi-layer filtration experiments were performed using BA filter media with different particle sizes and various volumetric flow rates. Due to the mesoporous, irregular, and spherical shape of gravel-size BA filter media used in this study, relatively low surface area, negligible pore volume, and greater pore size were observed. Both TSS removal efficiencies and clogging of BA filter media were a complex function of particle size of BA filter media and loading rate of TSS. Incoming TSS particles did not significantly penetrate beyond 46-cm BA filter media depth, accumulating on the upper layers and gradually forming a clogging layer to critical thickness, and finally the clogging filtration mechanism dominated the overall removal efficiency of TSS. Accumulation of TSS on BA filter media can be explained by the lumped sigmoidal empirical model, and an exponential decline in accumulation of TSS with depth results in minimal accumulation beneath the clogging layer. As practical implications, BA filter media depth of less than 46 cm is recommended with dual- or multi-media filters using mixtures of gravel-size BA and silt-size fine media, and a combination of detention basins can reduce frequent periodic de-clogging operation and management.

Colour and E. Coli Removals by Riverbed Filtration – A Physical Modelling Study at Different Filter Bed Depths and Inflow Rates

Riverbed filtration system (RBeF) is a simple, efficient and cost-effective alternative method of extracting water for drinking water purpose. The contaminants present in the surface water were attenuated biochemically where the aquifer acts as a natural filter. This study involved a physical model work for riverbed filtration (RBeF), where the depth of filter media and the flow rate of surface water were manipulated to improve the removal percentage of true colour and E. Coli (media depth: 60 and 90 cm, flow rate: 1, 3 and 5 L/min). River water samples from Lubok Buntar, Kedah were used to simulate the effectiveness of RBeF for colour and E. Coli removal. Readings were tested at the inlet and outlet of the filter with specified flow rates. Results from the physical model study showed the colour and E. Coli removal increased as the media depth increased from 60 to 90 cm, from 23-57.28% to 14.82-78.45% (p-value 0.008) and 69.45-98.34% to 76.15-99.69% (p-value 0.027), respectively. Besides that, from the study, results showed that the colour and E. Coli removal were not significantly affected by the flow rate.

Potential of Biofilters for Treatment of De-Icing Chemicals

Organic de-icing chemicals, such as propylene glycol and potassium formate, cause environmental degradation in receiving water if left untreated, due to the high organic load resulting in oxygen depletion. Biofilters are commonly used for the treatment of biodegradable organic carbon in water treatment. This study investigated the potential for using biofilters for treating organic de-icing compounds. Lab-scale adsorption tests using filter media made of crushed clay (Filtralite) and granular activated carbon were conducted. Further, a column filtration experiment testing two different crushed clay size ranges was carried out investigating the effect of filter media depth, nutrient addition, and filtration rate. The surrogate parameter used to monitor the removal of de-icing chemicals was dissolved organic carbon (DOC). The adsorption test showed no significant adsorption of DOC was observed. The column test showed that the most active separation occurred in the first ~20 cm of the filter depth. This was confirmed by results from (1) water quality analysis (i.e., DOC removal and adenosine tri-phosphate (ATP) measurement); and (2) calculations based on a filtration performance analysis (Iwasaki model) and filter hydraulic evaluation (Lindquist diagram). The results showed that, for the highest C:N:P ratio tested (molar ratio of 24:7:1), 50–60% DOC removal was achieved. The addition of nutrients was found to be important for determining the biofilter performance.

Environmental benefits and recycling options for wood chips from furniture industries

Wood chips are generated from wood industries, particularly from furniture manufacturing. The general reuse options are, however, currently limited to low-value applications. Driven by the adverse impacts of climate change, with the aim of achieving more environmental sustainability through reducing waste and increasing reuse/recycle options, this study investigated the feasibility of using wood chips as a pipe backfilling and embankment fill material. A laboratory assessment undertaken in this research shows that wood chips are suitable as a non-structural embankment fill material, but not as a pipe backfilling material. This research also presents the environmental benefits of using wood chips in natural landscaping and the effects of filter depth in such applications. It is found that wood chips significantly trap total suspended solids (TSS) and total nitrogen (TN), contributing to increased total phosphorus (TP) concentration. As such the use of such material in urban landscaping should be subjective depending on the level of concerns for specific pollutant(s) (TSS, TN and TP). With regard to the effect of filter media depth on pollutants' removal efficiencies, it is found that the pollutants' removal efficiencies linearly vary with filter media depth.

강우유출수 모래 필터의 여과기능 및 폐색 현상에 대한 필터 여재 깊이의 영향 평가

강우유출수 모래 필터의 여과기능 및 폐색 현상에 대한 필터 여재 깊이의 영향 평가

Characterization of soluble microbial products in a drinking water biological aerated filter.

Utilization-associated products (UAPs) and biomass-associated products (BAPs) were quantified separately in this study to characterize soluble microbial products (SMPs) in a drinking water lab-scale biological aerated filter (BAF), and their basic characteristics were explored using gel filtration chromatography and three-dimensional excitation-emission matrix (3D-EEM) spectrophotometry with fluorescence regional integration analysis and parallel factor model. UAPs were observed increased with the increase of filter media depth and accumulated after BAF treatment, whereas BAPs were basically constant. 3D-EEM spectroscopy analysis result showed that tryptophan and protein-like compounds were the main components of UAPs and BAPs, and fulvic-acid-like substance was a major component of BAPs, rather than UAPs. In terms of molecular weight (MW) distribution, UAP MW presented a bimodal distribution in the range of 1-5 and >10kDa, while BAP MW exhibited unimodal distribution with MW >20kDa fraction accounting for more than 90%. The macromolecules of UAPs accumulated after BAF treatment. This study provides theoretical support for in-depth study of SMP characteristics.

Recycling of Waste Water Collected from Automobile Service Station

This paper compares the effectiveness of chemical and physical methods in treating the wash water collected from automobile service stations. Wash water was collected from two service stations in the city of Bangalore, and the effluent was characterised for different parameters such as pH, turbidity, conductivity, total solids, oil and grease, COD (chemical oxygen demand), BOD (biological oxygen demand), chlorides, sulphate and total hardness. For chemical treatment, alum was used and locally available natural materials such as saw dust and sugarcane bagasse were used for physical treatment. Alum at different concentrations was agitated with the effluent for a prescribed contact period which led to the formation of flocs. The filtered samples were tested for COD and oil & grease. in the form of filter columns of three different heights. The percentage reduction in COD and oil and grease was correlated with the depth and type of filter media. A comparison of physical and chemical methods of treatment revealed that natural materials are effective in removing oil & grease and COD from the automobile effluent and hence provide a viable solution because of its eco-friendliness. From the experimental studies it is observed that in physical treatment, the sorption capacity of any material is dependent on its porosity, surface area and height of filter bed.

Hydraulic Performance and Pollutant Concentration Profile in a Stormwater Runoff Filtration Systems

Stormwater filtration system has proven to be effective for the removal of dissolved and particulate pollutants from roadways and car parking areas. However, the long-term treatment performance of filtration systems strongly depends on the hydraulic conductivity and sorption capacity of the filter media. This paper sought to provide information regarding the hydraulic performance, characteristics and metal concentration profiles in sediments accumulated at the surface of filtration systems (SDPL) and core filter media (FMC). The lifespan of the filter media was used to estimate the lifespan of the filter media. The results showed that saturated hydraulic conductivity of the filtration systems have significantly reduced over the operational time, yet acceptable (Kf = 5.9 × 10−5 to 1.4 × 10−4 m/s). The accumulated sediments (SDPL) were predominantly composed of fine particles with 70 % < 63 μm but the heavy metals were rather uniformly distributed in the different size fractions. The concentrations of heavy metals, particularly Cu, Pb and Zn were significantly higher in the SDPL and decreased with depth of the filter bed. However, Cr and Ni increased with depth of filter media demonstrating their removal was mainly by adsorption. Concentrations of Ba, Mn, Ti and V were comparable to Zn levels indicating comparable concentrations in roadway runoff. Simultaneous adsorption of multiple heavy metals in a column experiment demonstrated that the filter media could remain operational for over 34 years. However, there is a significant concern about their lifespan, particularly due to significant reduction in the hydraulic performance and the possibility of clogging of the systems over time. Therefore, to minimize hydraulic failure, the accumulated sediment be scraped off every 7 years.

Effect of oxygen deprivation on treatment processes in a full-scale drinking water biofilter

Dissolved oxygen is critical for proper operation of waterworks that utilize anaerobic groundwater and rely on biofilters to remove iron, manganese and ammonium. In these biofilters, planned or inadvertent oxygen deprivation may occur for a variety of reasons. The water quality effects of oxygen deprivation on the function of drinking water biofilters, however, have not previously been reported. In this study, a 5-day oxygen deprivation period in full-scale biofilters was found to affect iron, manganese and ammonium concentrations differently. During the oxygen deprivation period, iron continued to be removed, although a greater depth of filter media was required to carry out the removal. Manganese oxide in filter media was mobilized, causing manganese water concentrations to increase well above raw water levels. The ammonium in the raw water passed through the biofilters unchanged, indicating the dependence of nitrification microorganisms on oxygen as their sole electron acceptor. Stringent national drinking water criteria were exceeded during the deprivation period but were once again met within hours after oxygenation was recommenced. Manganese and nitrite recovery to pre-deprivation concentrations, however, required days. The results illustrate the interdependence of treatment parameters and provide valuable practical information to waterworks that experience or plan oxygen stoppage.

Comparison of filter media materials for heavy metal removal from urban stormwater runoff using biofiltration systems

The filter media in biofiltration systems play an important role in removing potentially harmful pollutants from urban stormwater runoff. This study compares the heavy metal removal potential (Cu, Zn, Cd, Pb) of five materials (potting soil, compost, coconut coir, sludge and a commercial mix) using laboratory columns. Total/dissolved organic carbon (TOC/DOC) was also analysed because some of the test materials had high carbon content which affects heavy metal uptake/release. Potting soil and the commercial mix offered the best metal uptake when dosed with low (Cu: 44.78 μg/L, Zn: 436.4 μg/L, Cd, 1.82 μg/L, Pb: 51.32 μg/L) and high concentrations of heavy metals (Cu: 241 μg/L, Zn: 1127 μg/L, Cd: 4.57 μg/L, Pb: 90.25 μg/L). Compost and sludge also had high removal efficiencies (>90%). Heavy metal leaching from these materials was negligible. A one-month dry period between dosing experiments did not affect metal removal efficiencies. TOC concentrations from all materials increased after the dry period. Heavy metal removal was not affected by filter media depth (600 mm vs. 300 mm). Heavy metals tended to accumulate at the upper 5 cm of the filter media although potting soil showed bottom-enriched concentrations. We recommend using potting soil as the principal media mixed with compost or sludge since these materials perform well and are readily available. The use of renewable materials commonly found in Singapore supports a sustainable approach to urban water management.