Escherichia coli in urban stormwater: explaining their variability.

The development of a model that predicts the levels of microorganisms in urban stormwater will aid in the assessment of health risks when using stormwater for both recreational uses and as an alternate water resource. However, the development of such a model requires an understanding of the dominant processes that influence the behaviour of microorganisms in urban systems. Using simple and multiple regression analyses this paper determines the dominant processes which affect the inter-event variability of the microbial indicator Escherichia coli (E. coli ) in four urbanised catchments. The results reveal that a number of antecedent climatic conditions, together with rainfall intensity, can significantly explain the inter-event variation in wet weather E. coli levels.     

Hydraulic performance of biofilters for stormwater management: first lessons from both laboratory and field studies.

In order to improve knowledge on stormwater biofiltration systems, the Facility for Advancing Water Biofiltration (FAWB) was created at Monash University in Melbourne, Australia. One of the aims of FAWB is to improve hydraulic performance of biofilters, given that there are numerous cases of infiltration devices failing after a few years of operation. Experiments were conducted in the field to evaluate the performance of existing systems, and in the lab to understand the factors that influence hydraulic behavior over time. The field experiments show that 43% of tested systems are below nominal Australian guidelines for hydraulic conductivity. The preliminary lab results show a decrease in hydraulic conductivity during the first weeks of operation (mu=66% reduction), although most remain within acceptable limits. Influences of the size of the biofilter relative to its catchment and the importance of the type of media, on the evolution of hydraulic conductivity, are examined.     

Escherichia coli removal in waste stabilization ponds: a comparison of modern and classical designs.

Two PC-based waste stabilization pond design procedures, based on parameter uncertainty and 10,000-trial Monte Carlo simulations, were developed for a series of anaerobic, facultative and maturation ponds to produce < or = 1000 E. coli per 100 ml for both 50% and 95% compliance. One procedure was based on the classical Marais equations and the other on the modern von Sperling equations. For the range of parameter variations selected the classical design procedure required less land area and had a shorter hydraulic retention time than the modern design procedure. For both procedures the design for 90% compliance required substantially more land and a longer retention time than the design for 50% compliance. Regulators and designers should seek a balance between system reliability (as set by the percentage compliance specified or adopted) and system costs, especially (but not only) in developing countries. It is recommended that new waste stabilization pond (WSP) systems be designed for compliance with a given E. coli effluent requirement by the classical procedure and that existing overloaded WSP systems be upgraded using the modern procedure.     

Laboratory study on factors influencing nitrogen removal in marble chip biofilters incorporating nitritation and anammox

It remains challenging to integrate nitritation and anammox in ecologically engineered treatment systems such as passive biofilters that are packed with natural materials and have low energy inputs. This study explored the factors influencing nitritation-anammox through parallel operation of two laboratory-scale biofilters packed with large and small marble chips respectively. Clean marble chips (mainly CaCO3) had an alkalinity dissolution rate of 130 mg CaCO3/kg marble d when water pH approached 6.5. Marble chips effectively increased water pH and provided sufficient alkalinity to support nitritation-anammox in the biofilters. Ammonium and total nitrogen removal decreased by 47 and 26%, respectively, when nutrients were not amended to influent. An influent nitrite concentration above 8.9 mg N/L could inhibit anammox in thin biofilms of biofilters. Nitritation-anammox was enhanced with a hydraulic retention time of 2 d relative to 7 d, likely due to enhanced air entrainment. Size of marble chips rarely made a significant difference in nitrogen removal, possibly due to sufficient surface area available for bacterial attachment and alkalinity dissolution.     

Hydraulic and pollutant removal performance of stormwater filters under variable wetting and drying regimes.

Biofiltration systems are an effective stormwater treatment technology. However, their robustness is yet to be tested, particularly their performance following extended dry periods. The hydraulic and treatment performance of five different non-vegetated, soil-based filters under varying periods of inundation and drying was assessed. The infiltration capacity of the filters decreased during wet periods and increased following dry periods, most probably due to swelling and shrinkage of the filter media. Treatment of sediment, heavy metals and phosphorus was not influenced by the wetting and drying regime. However, outflow concentrations of nitrogen were significantly higher upon re-wetting following extended dry periods compared with wet periods. This result has implications for current design practices, as these nitrogen pulses could negatively impact the ecological health of downstream receiving waters.     

Pollutant removal efficiency of alternative filtration media in stormwater treatment.

Sorption experiments were used to assess the ability of various materials (sand, compost, packing wood, ash, zeolite, recycled glass and Enviro-media) to remove heavy metal contaminants typically found in stormwater. Compost was found to have the best physicochemical properties for sorption of metal ions (Cu, Zn and Pb) compared with sand, packing wood, ash, zeolite and Enviro-media. The compost sorption of these metal ions conformed to the linear form of the Langmuir adsorption equation with the Langmuir constants (q,) for Zn(ll) being 11.2 mg/g at pH 5. However, compost was also found to leach a high concentration of dissolved organic carbon (DOC, 4.31 mg/g), compared with the other tested materials. Various combinations of sand, compost and other materials were observed to have excellent heavy metal removal (75-96% of Zn and 90-93% of Cu), with minimal DOC leaching (0.0013-2.43 mg/g). The sorption efficiency of the different Enviro-media mixes showed that a combination of traditional (sand) and alternative materials can be used as an effective medium for the treatment of dissolved metal contaminants commonly found in stormwater. The application of using recycled organic materials and other waste materials (such as recycled glass) also provides added value to the products life cycle.     

中国海绵城市开发与加拿大综合雨洪管理对比研究:以多伦多为例

介绍了加拿大城市流域雨洪规划管理的发展进程以及加拿大最大城市——多伦多市雨洪管理的政策、原则和标准,与中国的海绵城市建设技术指南进行对比,对指南中存在的一些问题,如指南未给出LID设计的检验和校核方案,也未充分考虑降雨等问题进行讨论,旨在为中国的雨洪管理提供新的研究思路和参考。     

Effect of external organic matter on nutrient removal and growth of Phragmites australis in a laboratory-scale subsurface-flow treatment wetland.

Coconut dust, which is used intensively in horticultural applications, was tested as an external organic additive in a series of laboratory-scale subsurface-flow constructed wetlands planted with Phragmites australis. The systems were fed with a mixture of NO3(-)-N, NH4+-N, and SRP in tap water to simulate high nutrient loads. In the absence of plants, TN removal efficiency was 66%, and the efficiency increased to > 80% in the microcosm wetlands. TN and NO3- removal efficiencies were marginally increased by coconut-dust treatment in comparison with sand-bed microcosms. Analysis by ANOVA showed that the TN removal from a coconut dust-supplemented sand-bed microcosm was significantly different from a sand-bed microcosm (0.0437 < p < 0.05). All the systems showed an equal capacity to treat NH4+ nitrogen under low influent concentration levels. Phosphorus removal efficiencies were > 98% in all three systems, and a difference between planted and unplanted systems was not observed. Shoot height and shoot densities of P. australis grown in the coconut dust-supplemented medium were significantly higher than those grown in the sand-bed medium. The difference in P. australis growth in response to the coconut dust addition revealed that the added material has the potential to create favourable conditions for plant growth.     

Restoration of a constructed stormwater wetland to improve its ecological and hydrological performance.

Although the vegetation within constructed stormwater wetlands plays an important role in the treatment processes taking place, its density and distribution depends on the wetland bathymetry and the imposed hydrologic regime. This paper describes an ecological and hydrological assessment of a constructed stormwater treatment wetland over a 5 year period. This assessment included the use of a continuous simulation hydrologic model combined with a Digital Elevation Model of the wetland bathymetry, plus a time series of vegetation maps. The combined spatial and temporal analysis indicates that both the frequency and duration of inundation has affected the fate of vegetation throughout the wetland. Restoration strategies have also been investigated to improve the survival of vegetation within the wetland.     

水合氧化锆吸附剂除氟性能的试验研究

通过静态和动态试验研究了水合氧化锆吸附剂的适宜的pH值、剂量效应、动力学性能、重复利用性能.试验表明,该吸附剂在pH值为2.0～4.0范围内时吸附性能较佳;原水氟化物含量为3.72 mg/L时,吸附剂添加量为0.5g/100mL即可将氟化物浓度降至1.0 mg/L以下.试验中调节原水pH值至3.0,控制柱内停留时间为3 min,连续进行了3个周期的吸附-脱附试验,证明水合氧化锆吸附剂具有良好的洗脱性能,可多次重复利用.     

Evaluating ozone dose for AOC removal in two-step GAC filters

Upgrading an existing post-ozonation plant with two-step granular activated carbon (GAC) filtration for assimilable organic carbon (AOC) removal was studied. The effects of ozone dose on AOC formation and its removal in the subsequent two-step GAC filtration was studied using chemically pretreated 2 to 14° C humic lake water. Two parallel pilot-plant trains with different ozone doses (0 to 1.2 mgO₃/mgTOC) and a shortterm ozonation study were performed. The optimum ozone dose for maximum AOC formation was 0.4–0.5 mgO₃/mgTOC. The AOC-P17 of ozonated water was three-fold higher and AOC-NOX over ten-fold higher than in non-ozonated water, while the following biofiltration (first step) removed 51 % and 72 % of AOC-P17 and AOC-NOX, respectively. The adsorber (second step) contributed to less than 10% of the overall AOC reduction. It appeared that biofiltration is a feasible method in upgrading water treatment plants for AOC removal even when treating cold humic waters, while the subsequent adsorber seems to have less significance for AOC removal.     

Implications to stormwater management as a result of lot scale rainwater tank systems: a case study in Western Sydney, Australia

Rainwater tanks are increasingly adopted in Australia to reduce potable water demand and are perceived to reduce the volume of stormwater discharge from developments. This paper investigates the water balance of rainwater tanks, in particular the possible impacts these tanks could have in controlling the stormwater discharge volume. The study collected water quantity data from two sites in the Hawkesbury City Council area, New South Wales, Australia and utilised the collected data in a simple water balance model to assess the effectiveness of rainwater tanks in reducing the stormwater discharge volume. The results indicate that a significant reduction in discharge volume from a lot scale development can be achieved if the rainwater tank is connected to multiple end-uses, but is minimal when using irrigation alone. In addition, the commonly used volumetric runoff coefficient of 0.9 was found to over-estimate the runoff from the roof areas and to thereby under-estimate the available volume within the rainwater tanks for retention or detention. Also, sole reliance on the water in the rainwater tanks can make the users aware of their water use pattern and water availability, resulting in significant reductions in water use as the supply dwindles, through self-imposed water restrictions.     

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.     

Exploring fecal indicator bacteria in a constructed stormwater wetland

Microbial pollution in surface waters is a concern throughout the world, with both public health and economic implications. One contributing source to such pollution is stormwater runoff, often treated using various types of stormwater control measures. However, relatively little is known regarding microbe sequestration in constructed stormwater wetlands (CSWs), one type of commonly installed stormwater control measure. In this study, indicator bacteria concentrations in both the water and sediment of a CSW were evaluated at multiple locations. Results suggested that fecal coliform concentrations in stormwater runoff decrease through the system, with relatively consistent concentrations noted throughout the second half of the wetland. This potentially indicates a baseline concentration of fecal coliform is present due to internal processes such as animal activity and microbial persistence. However, wetland sediments showed little E. coli present during most sampling events, with minimal patterns existing with respect to sediment sampling location. CSW designs should promote optimization of hydraulic retention time and minimization of stormwater velocities to promote sedimentation and degradation of microbes by way of wetland treatment functions.     

Conventional and holistic urban stormwater management in coastal cities: a case study of the practice in Hong Kong and Singapore

This study compares stormwater management in two coastal cities: Hong Kong and Singapore. Hong Kong adopted conventional urban stormwater management for flood control and embraced hard-engineering infrastructure in the scheme. In contrast, Singapore has put in place a series of holistic management practices to manage urban runoff. By comparing the stormwater management practices in these two cities, the differences in approaches to non-structural and structural practices were elucidated. Life cycle costing and environmental benefit analysis indicate that holistic urban stormwater management can lead to higher economic efficiency, sustainability and environmental friendliness, compared to conventional urban stormwater management.     

Macrophyte zonation in stormwater wetlands: getting it right! A case study from subtropical Australia.

In Australia stormwater wetlands are becoming an increasingly popular component of water sensitive urban design. However, they must be designed to cope with the dynamic nature of urban hydrology, in particular, fluctuations in water level. The concept of macrophyte zonation relies on a thorough understanding of the water regimes of different plant species. Water depth is crucial and the hydroperiod, i.e. duration and frequency of inundation, has a significant impact on the survival of wetland vegetation. The aim of this study was to investigate plant establishment in a newly constructed stormwater wetland in Brisbane, subtropical Australia. Changes in plant distribution and density have been monitored since 2001. Rainfall and water depth data enabled us to use a hydrologic model to predict the extent of inundation of the different macrophytes zones. The field survey showed macrophyte survival was poor with the complete loss of several species in marsh and ephemeral zones. The main reason for the lack of macrophyte establishment and survival was the extended periods of inundation (supported by the hydrologic model) and deeper water levels. Stormwater wetlands must be designed to ensure that ephemeral species are not permanently inundated or the preferred water depths in marsh zones are not exceeded for extended periods.     

Denitrification with polycaprolactone as solid substrate in a laboratory-scale recirculated aquaculture system.

A denitrification system based on the biodegradable polymer Poly-epsilon-Caprolactone (PCL) was tested in a laboratory-scale recirculated aquaculture system with eels in comparison to a reference system without denitrification. The experiments were conducted with fluidized bed reactors in two parallel systems to examine the feasibility and performance of the process and to observe the condition of fishes by measuring weight gain during the test-period. The most evident effect of the system with denitrification was the low nitrate concentration compared with the untreated reference system. A further advantage was the stability of the pH in the systems with denitrification whereas pH of the untreated water decreased due to nitrification. All over the test-period the eels showed a similar weight gain in both systems.     

Escherichia coli survival and transfer in estuarine bed sediments

Bed sediment resuspension is a potential source of faecal microorganisms in the water column of estuaries. As such, it is important to identify the survival of faecal microorganisms in these bed sediments and understand how bed sediment resuspension impacts the quality of estuarine waters. This study explores the effect of bed sediment resuspension on Escherichia coli concentrations in the water column and the persistence of E. coli in the water column and bed sediments of the Yarra River estuary in South‐Eastern Australia. Using sediment cores, we identified that the resuspension of both surficial sediments (e.g., by tidal movements) and deeper bed sediments (e.g., by large storm events) can increase E. coli concentrations in the water column by up to 20 times in estuaries in oceanic climates. Bed sediment resuspension can result in increased E. coli concentrations in the water column even up to 24 days after E. coli first enters the estuarine water. This study demonstrates that faecal microorganisms, such as E. coli, can persist for extended periods in estuarine bed sediments, which may then be re‐entrained into the water column via recreational activities, high flow events, or tidal fluctuations. If the survival and resuspension processes observed here hold true for pathogenic microorganisms, the resuspension of bed sediments may indeed represent an increased public health risk.     

Significance of denitrifying enzyme dynamics in biological nitrogen removal processes: a simulation study.

Activated Sludge Model No. 1 (ASM1) was extended to include the enzyme kinetics of denitrifying bacteria switching between oxygen and nitrate as electron acceptors. The extended ASM1 (eASM1) model was applied to two different periodic process configurations, fed-batch and Biodenipho, commonly used for nitrogen removal from wastewater. Predictions of optimal unaerated volume fraction (UVF) by eASM1 were similar to those by ASM1 for both the fed-batch and Biodenipho processes. However, eASM1 predicted substantially longer optimal cycle lengths than ASM1 for both processes. Predictions of optimal UVF and cycle length for the Biodenipho process by eASM1 were closer to current operational values for the University of Florida Biodenipho process than predictions by ASM1.     

Evaluating the economic viability of solar-powered desalination: Saudi Arabia as a case study

Abstract

This article constructs a cost calculator to estimate the economic competitiveness of solar-powered desalination in Saudi Arabia. Solar desalination is defined as a plant that obtains solar energy from a closed system. This is done to focus the investigation on desalination technologies, rather than the efficacy of replacing conventional energy sources with renewables in an integrated electricity grid. The results suggest that current options for solar-powered desalination are not cost-competitive compared to incumbent technologies in Saudi Arabia. The article offers insight into where costs must decrease before solar technologies are economically competitive in the country.