Biofiltration as pre-treatment to water harvesting and recycling

This paper presents the results of the long term biofilter experiments conducted with raw stormwater collected from a canal at Carlton, in Sydney. Anthracite and granular activated carbon (GAC) were used as a single filter media in biofilter columns. Media heights of 75 and 40 cm were used. The filter columns were operated at filtration velocities of 0.12 and 0.25 m/h. The removal efficiency for turbidity and DOC for the GAC filter media were found to be 75% and almost 100% respectively. The removal efficiency for the anthracite filter was much lower. Molecular weight distribution analysis showed an almost similar trend to the DOC removal. Compared with anthracite filter media, the GAC biofilter removed a much larger range of organic compounds present in the stormwater. The GAC biofilter removes organic matter earlier as compared to anthracite. Based on a limited sample of stormwater, the removal efficiency for phosphorus was upto 74% and that of nitrogen was up to 30%. In general GAC filter shows higher heavy metal removal efficiency than anthracite. The removal of zinc, iron, lead and nickel were good. However the concentration of heavy metal in the raw surface water sample was low.     

Stormwater reuse: designing biofiltration systems for reliable treatment.

Stormwater reuse is increasing in popularity as a technique for overcoming water shortages in urban Australia. However, technology for the reliable treatment of stormwater for reuse is still not fully developed. This paper presents the first steps in refining biofilters for stormwater reuse. Six different filter media were selected, to target specific stormwater pollutants, as well as support plant growth. They were tested in the laboratory, where the filters were dosed three times per week with semi-synthetic stormwater for five weeks. Pollutant removal performance was monitored, and revealed that all soil-based filters performed similarly (while sand filters behaved somewhat differently). All filters removed more than 80% of solids and greater than 90% of lead, copper, and zinc. Three filter types were able to remove some phosphorus (particularly in the top 30 cm of the media). Apart from sand, all filter media were net producers of nitrogen, leading to an important conclusion that non-vegetated, soil-based filters are not suitable for targeting nutrients. However, since heavy metals are the primary pollutant of concern with respect to stormwater reuse for irrigation (the most popular end-use), it was concluded that biofilters may be promising technologies for treatment of stormwater for reuse.     

Development of a confined water sensitive urban design (WSUD) system using engineered soils.

Innovative Water Sensitive Urban Design (WSUD) systems are being investigated at three locations to the north and south of Sydney, Australia. These systems contain porous concrete pipes that are designed so that stormwater exfiltrates through the permeable walls of the pipes into the surrounding substrate media material. The porous pipes and media material treat the passing stormwater. The primary aim of the overall project is to develop a model to describe the treatment effectiveness of confined WSUD systems. This paper focuses on the system located at the Weathertex Industrial Site, Heatherbrae. Due to wood processing operations that occur at this site, it is recognised that the surface runoff will carry a heavy organics loading. Granulated Activated Carbon (GAC) is recognised for its ability to reduce the concentration of dissolved organics present in both wastewater and stormwater. GAC was therefore chosen as a filtration medium to be investigated at this site. To maximise the effectiveness of the GAC, extensive laboratory batch studies were undertaken prior to the field system being constructed to determine the optimum GAC/sand ratio. The purpose of the experimental work was to assess the dissolved organic removal potential through sorption of various concentrations of GAC. The aim of this paper is to describe these laboratory experiments and discuss how they related to the field system. Through these experiments it was determined that a sand/GAC ratio of 25:1 was ideal for the media material at the Heatherbrae site.     

Performance of enviss? stormwater filters: results of a laboratory trial

An experimental study was undertaken by Monash University to develop and test enviss? stormwater treatment and harvesting technologies - non-vegetated filtration systems with an extremely low footprint. This paper focuses on the water quality and hydraulic performance of two systems tested over a 'year' of operation in a Melbourne climate: (1) REUSE enviss? filters, designed for stormwater harvesting systems for non-potable supply substitution, and (2) WSUD enviss? filters, developed to treat urban stormwater prior to discharge to downstream systems. The presence of chlorine as a disinfection agent proved to be very efficient for the removal of microorganisms in REUSE enviss? filters. WSUD enviss? filters had the benefit of providing an elevated nutrient treatment performance, due to an extended depth of filter media. However, nutrient outflow concentrations (total nitrogen (TN) in particular) were found to increase during the testing period. Also, extended dry weather periods were found to have a detrimental effect on the treatment performance of almost all pollutants for both filters (nutrients, Escherichia coli and heavy metals). Although hydraulic conductivity results indicated two or three sediment trap replacements per year are required to maintain filtration rates, it is expected that the compressed loading rate schedule overestimated this maintenance frequency.     

Assessment of Impact of Filter Design Variables on Clogging in Stormwater Filters

Stormwater filters are widely used in stormwater management, sometimes as standalone structures (e.g. stormwater filter beds), or as part of porous pavements, soak ways, infiltration basins and trenches. Due to the high levels of sediment present in stormwater, clogging is the main operational issue for these systems. A laboratory-based study was conducted to investigate the effect of filter bed design variables on the clogging phenomenon in non-vegetated stormwater filters with high infiltration rates. Design parameters studied include: filter media particle sizes (0.5 mm, 2 mm, 5 mm); depth of the filter bed (100 mm, 300 mm and 500 mm); and filter media packing configurations (layered or mixed). The size of filter media particles significantly impact the clogging process, as well as the overall sediment removal performance of the filters; filters with smaller particles had better sediment removal efficiency, but subsequently shorter lifespan. Deeper systems had longer lifespan compared with shallower ones, notwithstanding deeper systems removed more sediment over their life span. Having two layers of distinct sized media in the filter bed improved performance (e.g. volume of water treated; sediment removed) over the single-layered systems. However, the three-layered systems behaved similarly to two-layered systems. Mixed systems also showed improved performance, as compared with single-layered systems, and were similar to the three-layered systems. This study therefore suggests that simple modifications to a stormwater filtration system can help improve sediment removal performance and/or reduce maintenance intervals significantly, while only slightly affecting sediment removal performance.     

Filter media for stormwater treatment and recycling: the influence of hydraulic properties of flow on pollutant removal.

Improved urban water management in Australia is of national importance. Water resources are stretched and urban runoff is a recognized leading cause of degradation of urban waterways. Stormwater recycling is an option that can contribute to easing these problems. Biofilters are effective structural stormwater pollution control measures with the potential for integration into stormwater treatment and recycling systems. However, premature clogging of biofilters is a major problem, with resulting decreased infiltration capacity (and hence the volume of stormwater the system can detain) and increased detention time. This paper presents preliminary findings with respect to the effect of clogging on pollutant removal efficiency in conventional stormwater filter media. A one-dimensional laboratory rig was used to investigate the impact of clogging on pollutant removal efficiency in a conventional biofiltration filter media (gravel over sand). Both the individual gravel layer and the overall multi-filter were highly efficient at removing suspended solids and particulate-associated pollutants. This removal efficiency was consistent, even as the filters became clogged. Removal of dissolved nutrients was more variable, with little reduction in concentrations overall. Although preliminary, these results challenge the concept that increased detention time improves the treatment performance of stormwater filtration systems.     

Photocatalytic inactivation of Flavobacterium and E. coli in water by a continuous stirred tank reactor (CSTR) fed with suspended/immobilised TiO2 medium

A photocatalytic continuous stirred tank reactor (CSTR) was built at laboratory scale to inactivate two environmental bacteria strains (Flavobacterium and E. coli) in tap water. Several parameters were found to impact reactor efficiency. Bacterial initial concentration is an important factor in inactivation rate. After 30 minutes of irradiation at 10(8)-10(9) CFU mL(-1) starting concentration, a >5 log reduction was achieved while at 10(4)-10(6) CFU mL(-1) only a 2 log reduction was observed. Water hardness and pH have an important influence on the photocatalytic inactivation process. Soft water, with low Ca(+2) and Mg(+2) at low pH approximately 5.3 resulted in increased inactivation of Flavobacterium reaching >6 orders of magnitude reduction. E. coli and Flavobacterium at pH 5 were inactivated by 3 logs more as compared to pH 7 under similar conditions. pH below TiO2 isoelectric point (approximately 5.6) supports better contact between bacteria and anatase particles resulting in superior inactivation. TiO2 powder suspension was compared with immobilised powder in sol-gel coated glass beads in order to exclude the need for particles separation from the treated water. TiO2 suspension was more effective by 3 orders of magnitude when compared to coated glass beads. An interesting observation was found between the two bacterial strains based on their hydrophobicity/hydrophilicity balance. The more hydrophobic Flavobacterium compared to E. coli was inactivated photocatalytically by >3 logs more then E. coli in the first 30 minutes of irradiation interval. The results indicate the importance of the parameters involved in the contact between TiO2 particles and microorganisms that govern the successful inactivation rate in CSTR.     

Assessment of the Impact of Stormwater Characteristics on Clogging in Stormwater Filters

Hydraulic conductivity of granular filter media and its evolution over time is a key design parameter for stormwater filtration and infiltration systems that are now widely used in management of polluted urban runoff. In fact, clogging of filter media is recognised as the main limiting factor of these stormwater treatment systems. This paper focuses on the effect of stormwater characteristics on the clogging of stormwater filters. Effect of five different operational regimes has been tested in this study of sediment concentration; pollutant concentrations; stormwater sediment size; loading rate and stormwater loading/dosing regime and compared with the Base case. For each operational condition, five column replicates were tested. Results suggest that sediment concentration in stormwater is a significant parameter affecting hydraulic and treatment performance, eventually affecting longevity of these stormwater treatment systems. Further, the size of sediments (and their relation to the size of filter media grains) in stormwater was found to be an important parameter to be considered in design of coarse filters with high infiltration rates that are used for stormwater treatment. As expected, the addition of metals and nutrients had limited or no contribution to changes in hydraulic or sediment removal performance of the studied stormwater filters. Whilst loading rate was found to be an important parameter affecting the hydraulic and treatment performance of these systems, any variation in the stormwater loading regime had a limited effect on their performance. This study therefore develops an understanding of the effect of catchment characteristics on design of filters and hence their longevity and maintenance needs.     

Four years of development and field-testing of IHE arsenic removal family filter in rural Bangladesh

UNESCO-IHE has been developing an arsenic removal family filter with a capacity of 100 L/day based on arsenic adsorption onto iron oxide coated sand, a by-product of iron removal plants. The longer term and field conditions performance of the third generation of eleven family filters prototypes were tested in rural Bangladesh for 30 months. All filters achieved initially highly effective arsenic removal irrespective of arsenic concentration and groundwater composition. Arsenic level in filtrate reached 10 mug/l after 50 days of operation at one testing site and after 18 months of continuous operation at other 3 testing sites. Arsenic level at other 7 sites remained below the WHO guideline value till the end of study. Positive correlation was found between arsenic removal capacity of the filter and iron concentration in groundwater. In addition to arsenic, iron present in groundwater at all testing sites was also removed highly effectively. Manganese removal with IHE family filter was effective only when treating groundwater with low ammonia. A simple polishing sand filter, after IHE family filter, resulted in consistent and effective removal of manganese. IHE family filters were easy to operate and were well accepted by the local population.     

Modification of granular activated carbon surface by chitosan coating for geosmin removal: sorption performances.

This study presents the results of the sorption performances for geosmin removal by sorption onto granular activated carbons (GAC) manufactured from different raw materials of coconut shell and bituminous coal. The surface of GAC was modified by chitosan coating. The 90% deacetylated chitosan flakes were used for coating on GAC with the GAC: chitosan ratio of 5:1. The surface of GAC was characterised by scanning electron microscope (SEM) analysis, Fourier transform infrared spectroscopy and measurement of the pH solution of GAC samples. The sorption of geosmin onto the chitosan for both uncoated and coated GACs could be described by the Freundlich adsorption model. Data revealed that the sequence of Freundlich constant (K(F)) was chitosan coated bitominous coal (CB) > uncoated bituminous coal (UB) > chitos approximately equal to an coated coconut shell (CC) approximately equal to uncoated coconut shell (UC). The bituminous coal based GAC with chitosan coating had a maximum capacity of 23.57 microg/g which was approximately two-fold of uncoated bituminous coal based GAC. Two simplified kinetic models, pseudo-first order and pseudo-second order, were tested to investigate the sorption mechanisms. It was found that the intraparticle diffusion was a rate controlling step for the sorption and followed the pseudo-second order equation.     

Evaluating Escherichia coli removal performance in stormwater biofilters: a laboratory-scale study

Biofilters are common, low energy technologies used for the treatment of urban stormwater. While they have shown promising results for the removal of stormwater microorganisms, certain factors affect their performance. Hence, this study investigated the effects of particle-microbial interaction, inflow concentration, antecedent microbial levels and plant species on microbial removal capacity. A biofilter column study was set up to evaluate removal performance and a sequential filtration procedure was used to estimate microbial partitioning. The columns were dosed with different concentrations of free phase Escherichia coli only and E. coli mixed with stormwater sediment. Results indicate that the microbial removal is significantly affected by inflow concentration and antecedent microbial levels. Leaching was only observed when a relatively low inflow concentration event occurred within a short period after a very high inflow concentration event. Finally, Lomandra longifolia showed better removal compared with Carex appressa.     

Elimination of viruses, bacteria and protozoan oocysts by slow sand filtration.

The decimal elimination capacity (DEC) of slow sand filters (SSF) for viruses, bacteria and oocysts of Cryptosporidium has been assessed from full-scale data and pilot plant and laboratory experiments. DEC for viruses calculated from experimental data with MS2-bacteriophages in the pilot plant filters was 1.5-2 log10. E. coli and thermotolerant coliforms (Coli44) were removed at full-scale and in the pilot plant with 2-3 log10. At full-scale, Campylobacter bacteria removal was 1 log10 more than removal of Coli44, which indicated that Coli44 was a conservative surrogate for these pathogenic bacteria. Laboratory experiments with sand columns showed 2-3 and >5-6 log10 removal of spiked spores of sulphite-reducing clostridia (SSRC; C. perfringens) and oocysts of Cryptosporidium respectively. Consequently, SSRC was not a good surrogate to quantify oocyst removal by SSF. Removal of indigenous SSRC by full-scale filters was less efficient than observed in the laboratory columns, probably due to continuous loading of these filter beds with spores, accumulation and retarded transport. It remains to be investigated if this also applies to oocyst removal by SSF. The results additionally showed that the schmutzdecke and accumulation of (in)organic charged compounds in the sand increased the elimination of microorganisms. Removal of the schmutzdecke reduced DEC for bacteria by +/-2 log10, but did not affect removal of phages. This clearly indicated that, besides biological activity, both straining and adsorption were important removal mechanisms in the filter bed for microorganisms larger than viruses.     

Seasonal variation of fecal indicator bacteria in storm events within the US stormwater database

Bacteria are one of the major causes of surface water impairments in the USA. Over the past several years, best management practices, including detention basins, manufactured devices, grass swales, filters and bioretention cells have been used to remove bacteria and other pollutants from stormwater runoff. However, there are data gaps in the comprehensive studies of bacteria concentrations in stormwater runoff. In this paper, the event mean concentration (EMC) of fecal indicator bacteria (Enterococcus, Escherichia coli, fecal Streptococcus group bacteria, and fecal coliform) across the USA was retrieved from the international stormwater best management practices database to analyze the seasonal variations of inflow and outflow event mean concentrations and removal efficiencies. The Kruskal-Wallis test was employed to determine the seasonal variations of bacteria indicator concentrations and removals, and the two-sample Kolmogorov-Smirnov test was used for comparing different seasonal outcomes. The results indicate that all the inflow EMC of FIB in stormwater runoff is above the water quality criteria. The seasonal differences of fecal Streptococcus group bacteria and fecal coliform are significant. Summer has the potential to increase the bacteria EMC and illustrate the seasonal differences.     

Characterisation of the biosand filter for E. coli reductions from household drinking water under controlled laboratory and field use conditions.

More than a billion people in the developing world lack access to safe and reliable sources of drinking water. Point of use (POU) household water treatment technology allows people to improve the quality of their water by treating it in the home. One emerging POU technology is the biosand filter (BSF), a household-scale, intermittently operated slow sand filter. Laboratory and field studies examined Escherichia coli reductions achieved by the BSF. During two laboratory studies, mean E. coli reductions were 94% and they improved over the period of filter use, reaching a maximum of 99%. Field analysis conducted on 55 household filters near Bonao, Dominican Republic averaged E. coli reductions of 93%. E. coli reductions by the BSF in laboratory and field studies were less than those typically observed for traditional slow sand filters (SSFs), although as for SSFs microbial reductions improved over the period of filter use. Further study is needed to determine the factors contributing to microbial reductions in BSFs and why reductions are lower than those of conventional SSFs.     

Virus removal in a pilot-scale 'advanced' pond system as indicated by somatic and F-RNA bacteriophages.

Advanced pond systems (APS), incorporating high-rate ponds, algal settling ponds, and maturation ponds, typically achieve better and more consistent disinfection as indicated by Escherichia coli than conventional waste stabilisation ponds. To see whether this superior disinfection extends also to enteric viruses, we studied the removal of somatic phages ('model' viruses) in a pilot-scale APS treating sewage. Measurements through the three aerobic stages of the APS showed fairly good removal of somatic phage in the summer months (2.2 log reduction), but much less effective removal in winter (0.45 log reduction), whereas E. coli was removed efficiently (> 4 logs) in both seasons. A very steep depth-gradient of sunlight inactivation of somatic phage in APS pond waters (confined in silica test tubes) is consistent with inactivation mainly by solar UVB wavelengths. Data for F-RNA phage suggests involvement of longer UV wavelengths. These findings imply that efficiency of virus removal in APS will vary seasonally with variation in solar UV radiation.     

Development and evaluation of methods to detect coliphages in large volumes of water.

New and improved methods have been developed to detect somatic and male-specific coliphages in large volumes of water by single agar layer (SAL), enrichment and membrane filter methods. Somatic coliphages were detected efficiently on E. coli hosts C and CN13, male-specific coliphages were detected more efficiently on E. coli Famp than on Salmonella typhimurium WG49 and both types of coliphages were detected simultaneously on E. coli C3000. For water volumes of up to 100 ml, the SAL method was efficient and reliable. For water volumes of <1 L and as many as 10 multiple 1 L volumes, the enrichment method was efficient in detecting very low numbers of coliphages. Membrane filter methods, in which coliphages were adsorbed to and eluted from filters, also were relatively efficient, but they were less efficient than SAL and enrichment methods and were considered to be more cumbersome. For filter adsorption-elution methods, coliphage recoveries were most efficient for cellulose ester filters, less efficient for electropositive 1 MDS filters and least efficient for a direct membrane filter method. Overall, the enrichment method was preferred because of its ability to easily and rapidly detect low levels of coliphages in large sample volumes by either presence-absence or most probable number quantification.     

Potential of organic filter materials for treating greywater to achieve irrigation quality: a review

The objectives of this literature review were to: (i) evaluate the impact of greywater generated in rural communities, with the emphasis on Jordanian conditions, on soil, plant and public health and assess the need for treatment of this greywater before it is used for irrigation, and (ii) assess the potential of different types of organic by-products as carrier material in different filter units for removal of pollutants from greywater. Greywater with high BOD5, COD, high concentrations of SS, fat, oil and grease and high levels of surfactants is commonly found in rural areas in Jordan. Oxygen depletion, odour emission, hydrophobic soil phenomena, plant toxicity, blockage of piping systems and microbiological health risks are common problems associated with greywater without previous treatment. Organic by-products such as wood chips, bark, peat, wheat straw and corncob may be used as carrier material in so-called mulch filters for treating wastewater and greywater from different sources. A down-flow-mode vertical filter is a common setup used in mulch filters. Wastewaters with a wide range of SS, cBOD5 and COD fed into different mulch filters have been studied. The different mulch materials achieved SS removal ranging between 51 and 91%, a BOD5 reduction range of 55-99.9%, and COD removal of 51-98%. Most types of mulches achieved a higher organic matter removal than that achieved by an ordinary septic tank. Bark, peat and wood chips filters removed organic matter better than sand and trickling filters, under similar conditions. Release of filter material and increase in COD in the effluent was reported using some mulch materials. In conclusion, some mulch materials such as bark, peat and woodchips seem to have a great potential for treatment of greywater in robust, low-tech systems. They can be expected to be resilient in dealing with variable low and high organic loads and shock loads.     

Pathogen removal efficiency from UASB + BF effluent using conventional and UV post-treatment systems.

The aim of this study was to verify the efficiency of removal of microorganisms in effluents of a Wastewater Treatment Plant (WWTP) comprising an association of a UASB reactor followed by three submerged aerated biofilters (BAF) and one tertiary filter. The WWTP designed to treat domestic wastewater from a population of 1,000 inhabitants showed high removal efficiency for organic matter and suspended solids. Helminth eggs were also efficiently removed from the tertiary effluent and were found in the sludge from the UASB reactor; however, removal of bacteria in this system was very low. To enhance the efficiency of the system, the effluent from tertiary filters was submitted to UV disinfection in a real scale reactor. Our results showed that UV irradiation was very effective at lowering the concentrations of E. coli, thermotolerant coliforms and coliphages to acceptable levels for agricultural reuse. Salmonella spp. and helminth eggs were seeded into the tertiary effluent before passing through the UV reactor. Salmonella was not found in the final effluent, but helminth eggs were not completely inactivated by UV irradiation and viable eggs were detected after 28 d of incubation.     

剩余臭氧影响活性炭净水效能原因分析

通过中试分析了长期运行条件下臭氧—活性炭工艺中溶解性臭氧对活性炭净水效能产生影响的原因。试验条件下活性炭对UV254的去除能力随剩余臭氧浓度的增加而下降。根据试验推测臭氧对活性炭的影响主要体现在3个方面:首先,在臭氧投加量较高时,NOM中亲水性有机物比例增加,此类物质在活性炭上的吸附性较差;其次,臭氧氧化降低了活性炭的吸附能力,同时臭氧可能与活性炭反应生成新的氧化产物;最后,臭氧可抑制活性炭上微生物的生长繁殖。因此建议在臭氧—活性炭工艺运行时严格控制进入活性炭吸附池的剩余臭氧浓度。     

Modelling pathogen fate in stormwaters by a particle-pathogen interaction model using population balances

Stormwater is polluted by various contaminants affecting the quality of receiving water bodies. Pathogens are one of these contaminants, which have a critical effect on water use in rivers. Increasing the retention time of water in stormwater basins can lead to reduced loads of pathogens released to the rivers. In this paper a model describing the behaviour of pathogens in stormwater basins is presented including different fate processes such as decay, adsorption/desorption, settling and solar disinfection. By considering the settling velocity distribution of particles and a layered approach, this model is able to create a light intensity, and particle and pathogen concentration profile along the water depth in the basin. A strong effect of solar disinfection is discerned. The model has been used to evaluate pathogen removal efficiencies in stormwater basins. It includes a population of particle classes characterized by a distribution of settling velocities in order to be able to reproduce stormwater quality and treatment in a realistic way.