Abstracts

Brown, R. R. and M. Farrelly (2007). Barriers to advancing sustainable urban water management: A typology. 13th International Rainwater Catchment Systems Conference and 5th International Water Sensitive Urban Design Conference. Sydney, Australia.

Sustainable urban water management (SUWM) requires an integrated, adaptive, coordinated and participatory approach. Current urban water policies are beginning to reflect this understanding yet the rhetoric is often not translated to implementation. Despite the 'new' philosophy, urban water management remains a complex and fragmented area relying on traditional, technical, linear management approaches. Despite widespread acknowledgement of the barriers to change, there has been little systematic review of what constitutes the scope of such barriers and how these should be addressed to advance SUWM. To better understand why implementation fails to occur beyond ad hoc project interventions, a meta-analysis of observed and studied barriers was conducted. Drawing on local, national and international literature from the field of integrated urban water management and other similar fields, 53 studies were assessed, resulting in a typology of 12 barrier types. The analysis revealed the barriers are largely socio-institutional rather than technical, reflecting issues related to community, resources, responsibility, knowledge, vision, commitment and coordination. Furthermore, the meta-analysis demonstrated a paucity of targeted strategies for overcoming the stated institutional barriers. Evaluation of the typology in relation to capacity building, suggests that these systemic issues require a sophisticated program of change, that focus on fostering social capital, inter-sectoral professional development, and inter-organisational coordination.

Brown, R. R. and J. M. Clarke (2007). The transition towards water sensitive urban design: a socio:technical analysis of Melbourne, Australia. Novatech 2007. 6th International Conference on Sustainable Techniques and Strategies in Urban Water Management. Lyon, France. 1: 349-356.

This research is focused on determining the social-technical transition qualities that need to be enabled to mainstream 'water sensitive urban design' (WSUD) across urban regions.  Reported in this paper are the outcomes of qualitative social research that attempts to map the institutionalisation of WSUD, so far, across Metropolitan Melbourne, Australia.  The results reveal that fostering the development of local champions across the science, policy and private domains are essential for enabling'Niche' transition processes.  The 'Niche' needs to be supported by mechanisms including the establishment of bridging organisations, scientifically informed policy targets, strategic funding opportunities, and the demonstration of a business case for WSUD.

Hatt, B. E., T. D. Fletcher and A. Deletic (2007). Stormwater reuse: designing biofiltration systems for reliable treatment. Water Science and Technology 55(4): 201-209.

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.

Hatt, B. E., T. D. Fletcher and A. Deletic (2007). The effects of drying and wetting on pollutant removal by stormwater filters. Novatech 2007. 6th International Conference on Sustainable Techniques and Strategies in Urban Water Management, Lyon, France.

Biofiltration systems experience high levels of variability in the frequency and period of inundation and intervening dry period. The effect of alternate wetting and drying on the treatment performance of five different non-vegetated, soil-based filters was tested in the laboratory, where they were exposed to varying periods of inundation and drying. The wetting and drying regime did not influence the treatment of sediment, heavy metals and phosphorus. However, it did have a marked influence on nitrogen, with significantly higher outflow concentrations observed upon re-wetting following extended dry periods compared with wet periods. This result has implications for current design practices, since these nitrogen pulses could have detrimental ecological consequences for downstream receiving waters.

Hatt, B. E., T. D. Fletcher and A. Deletic (2007). Hydraulic and pollutant removal performance of stormwater filters under variable wetting and drying regimes. Water Science & Technology 56(12): 11-19.

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.

Hatt, B. E., T. D. Fletcher and A. Deletic (2008). Hydraulic and pollutant removal performance of fine media stormwater filtration systems. Environmental Science & Technology 42(7): 2535-2541.

Stormwater runoff from urban areas has multiple negative hydrologic and ecological impacts for receiving waters. Fine media stormwater filtration systems have the potential to mitigate these effects, through flow attenuation and pollutant removal. This work provides an overall assessment of the hydraulic andpollutantremovalbehavior ofsand-andsoil-basedstormwater filters at the laboratory scale. The influence of time, cumulative inflow sediment, cumulative water volume, wetting and drying, and compaction on hydraulic capacity was investigated. The results suggested that the primary cause of hydraulic failure was formation of a clogging layer at the filter surface. Loads of sediment and heavy metals were effectively retained; however, the soil-based filters leached nitrogenandphosphorus for the duration of the experimental period. Media pollutant profiles revealed significant accumulation of all pollutants in the top 20% of the filter profile, suggesting that elevated discharges of nutrients was due to leaching of native material, rather than failure to remove incoming pollutants. It is recommended that the top 2-5 cm of the filter surface be scraped off every two years to prevent hydraulic failure; this will also avoid excessive accumulation of heavy metals, which may otherwise have been of concern.

Read, J., T. Wevill, T. D. Fletcher and A. Deletic (2008). Variation among plant species in pollutant removal from stormwater in biofiltration systems. Water Research 42(4-5): 893-902.

Biofiltration systems use vegetation to improve efficiency of pollutant removal from stormwater, but little is known of how plants vary in their capacity to improve biofilter effectiveness.We used a pot trial of 20 Australian species to investigate how species vary in the removal of pollutants from semisynthetic stormwater passing through a soil filter medium. Effluent levels of total suspended solids (TSS), Al, Cr, Cu, Pb and Zn were similarly low for vegetated and non-vegetated soils, with reduction to <1-12% of levels in the stormwater input. N and P effluent concentrations were generally lower from vegetated than non-vegetated soils, but total N increased on average in effluent of both vegetated and non-vegetated soils relative to stormwater input. Effluent concentrations varied 2-4-fold among species for TSS, total N and P, total dissolved N (TDN), organic nitrogen and Cu, to more than 20-fold for NO_x, NH₄⁺, Mn, Pb and Fe. Species also varied markedly in pollutant removal per root mass (a means of standardising for plant size), with 18-50-fold variation among species in effluent concentrations of total P and N, TDN and organic N, to >150-fold variation in NO_x and NH₄⁺. Hence, choice of plant species may have marked effects on biofilter effectiveness.

Fletcher, T. D., Y. Zinger and A. Deletic (2007). Treatment efficiency of biofilters: results of a large scale biofilter column study. 13th International Rainwater Catchment Systems Conference and 5th International Water Sensitive Urban Design Conference, Sydney, Australia.

In order to evaluate the optimal design of biofilters for treatment of sediment, nitrogen and phosphorus, 140 biofilter columns were constructed, using different plant species, different depths and types of filter media, along with different storm volumes and input concentrations. All biofilters tested were found to be highly effective for removal of TSS, reducing inflow concentrations by an average of 98%. Total phosphorus was reduced by an average of 80%, whilst nitrogen removal was much more variable, including some configurations which yielded a net increase in nitrogen concentration. However, careful selection of plants and media type was able to achieve a simultaneous reduction of 50-70% of nitrogen and 90% of phosphorus. Carex appressa and to a lesser extent Melaleuca ericifolia performed very well in nutrient removal, whilst Dianella revoluta, Leucophyta brownii and Microlaena stipoides did not, within the nine months of testing, effective in facilitating nitrogen removal. Appropriate sizing of biofilters relative to their catchment area, as well as careful selection of plants for climate condition may be critical for biofilter performance. Further research will be undertaken to determine whether relatively poorly performing biofilter designs can be improved by retrofitting a saturated anaerobic zone, to promote denitrification and enhance drought tolerance.

Bratieres, K., T. D. Fletcher, A. Deletic and Y. Zinger (in press). Optimisation of the treatment efficiency of biofilters; results of a large-scale laboratory study. Water Research.

A large scale column study was conducted in Melbourne, Australia, to test the performance of stormwater biofilters for the removal of sediment, nitrogen and phosphorus. The aim of the study was to provide guidance on the optimal design for reliable treatment performance. A variety of factors were tested, using 125 large columns: plant species, filter media, filter depth, filter area and pollutant inflow concentration. The results demonstrate that vegetation selection is critical to performance for nitrogen removal (e.g. Carex appressa and Melaleuca ericifolia performed significantly better than other tested species). Whilst phosphorus removal was consistently very high (typically around 85%), biofilter soil media with added organic matter reduced the phosphorus treatment effectiveness. Biofilters built according to observed 'optimal specifications' can reliably remove both nutrients (up to 70% for nitrogen and 85% for phosphorus) and suspended solids (consistently over 95%). The optimally designed biofilter is at least 2% of its catchment area and possesses a sandy loam filter media, planted with Carex appressa or Melaleuca ericifolia. Further trials will be required to test a wider range of vegetation, and to examine performance over the longer term. Future work will also examine biofilter effectiveness for treatment of heavy metals and pathogens.

Blecken, G.-T., Y. Zinger, A. Deletic, T. D. Fletcher and M. Viklander (under review). Impact of a submerged anoxic zone and a cellulose based carbon source on heavy metal removal in stormwater biofiltration systems. Ecological Engineering.

Given the substantial pollutant loads in urban stormwater, biofilters are a potentially effective treatment option, particularly for heavy metals. However, to increase their nitrogen treatment efficacy, the introduction of a submerged (anoxic) zone (SZ) and a cellulose based carbon source (C) has been recommended because it has been shown to enhance denitrification, thus increasing overall nitrogen removal. To examine the impact of this design modification on the removal of heavy metals, a laboratory study using biofilter mesocosms with different levels of SZ with and without added C was conducted. The results show that SZ and C have a significant impact on metal treatment. In particular, the removal of Cu was improved significantly. The presence of SZ and C allows outflow Cu concentrations to meet Swedish and Australian water quality target values, which are not met with a biofilter without SZ or C. Even the already high Zn and Pb removal was enhanced slightly by the presence of a SZ. However, since removal of these metals is already very high (>95%), this improvement is of less practical importance. The best metal treatment was achieved with 450 mm and 600 mm SZ. Based on these results, the incorporation of SZ with C in stormwater biofilters is recommended.

Zinger, Y., T. D. Fletcher, A. Deletic, G. T. Blecken and M. Viklander (2007). Optimisation of the nitrogen retention capacity of stormwater biofiltration systems. Novatech 2007, 6th International Conference on Sustainable Techniques and Strategies in Urban Water Management, Lyon, France.

Excess nitrogen in stormwater is a principal cause for eutrophication of many water bodies in the world. Biofilters, which used a vegetated soil media, have been shown to reduce nitrogen concentrations in stormwater, although there is substantial scope to improve their current nitrogen removal performance. This paper explores the nitrogen transformations in biofilters and optimised theirs design to maximise removal. To achieve this, 20 columns were constructed to test a range of submerged anoxic zone (SAZ) depths, to maximise denitrification. The effect of adding a carbon source to act as an electron donor supplement in the filter media was also tested. Nitrate removal of up to 99% was achieved, with removal by columns with added carbon significantly greater, with a mean removal of greater than 90%, whilst the non-carbon columns showed an average 50% nitrate removal. Depth profiles revealed that mineralization is the limiting step of nitrogen removal in the biofilter columns. The results will contribute to guidelines for optimal biofilter design.

Zinger, Y., A. Deletic and T. D. Fletcher (2007). The effect of various intermittent wet-dry cycles on nitrogen removal capacity in biofilters systems. 13th International Rainwater Catchment Systems Conference and 5th International Water Sensitive Urban Design Conference, Sydney, Australia.

Stormwater biofilter systems have the potential to remove nutrients from urban runoff.  These systems operate in unique intermittent dry-wet cycles that may affect their performance. Current consensus suggests that sediment drying promotes the release of potentially significant amounts of bio-available nitrogen and phosphorus upon re-wetting. We sought to investigate the impact of drying/wetting cycles on biofilter performance. Eighteen columns were planted with Carex appressa which reached maturity after eight months. The recovery of biofilter systems was tested in a range of drying periods from one to eight weeks with and without a Submerged Anoxic Zone (SAZ) and carbon supplement in the filter media. In all experiments, moisture content, adjacent soil and ambient temperature were logged in parallel to record the drawdown profile behaviour. A freely drained biofilter configuration was used as a control. The results indicated that having a submerged anoxic zone is critical for nitrogen removal at dry periods greater than two weeks. In addition, the anoxic zone was able to enhance biofilter nitrogen removal recovery and make it less dependent on drying/wetting.

Le Coustumer, S. and S. Barraud (2007). Long-term hydraulic and pollution retention performance of infiltration systems. Water Science and Technology 55(4): 235-243.

Infiltration techniques are now widely used to manage stormwater in urban areas. These techniques are used and recognized around the world for their many advantages, such as decreasing stormwater flow in sewer systems and recharging groundwater. But numerous cases of infiltration devices that failed after a few years of operation are still being reported. This study, which is based on sitemonitoring of operational infiltration systems, is part of the Field Observatory for Urban Water Management (OTHU). The main goals of this study are to improve knowledge of long-term hydraulic behaviour, especially as concerns the clogging speed and the quality of the runoff. This article will present the site, the monitoring process and the model that will be used to assess the hydraulic behaviour. First results of the calibration of the model show that the model is able to assess the hydraulic behaviour of the basin when it is clogged (average value of hydraulic resistance 17.1 h) and when it has been scraped (hydraulic resistance less than 3.8 h). However, further data are needed in order to validate the model. We also show that the experimental setup is well designed to assess the water volume and the sediment brought to the basin with low uncertainties.

Le Coustumer, S., T. D. Fletcher, A. Deletic and S. Barraud (2007). Hydraulic performance of biofilters: first lessons from both laboratory and field studies. Novatech 2007. 6th International Conference on Sustainable Techniques and Strategies in Urban Water Management, Lyon, France.

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 the influence hydraulic behaviour 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 (&micro;
=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.

Le Coustumer, S., T. D. Fletcher, A. Deletic and S. Barraud (2007). Hydraulic performance of biofilters for stormwater management: first lessons from both laboratory and field studies. Water Science and Technology 56(10): 93-100.

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 (µ= 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.

Hatt, B. E., J. Lewis, A. Deletic and T. D. Fletcher (2007). Insights from the design, construction and operation of an experimental stormwater biofiltration system. 13th International Rainwater Catchment Systems Conference and 5th International Water Sensitive Urban Design Conference, Sydney, Australia.

Biofiltration systems are being installed on an ever-increasing scale, both for stormwater quality improvement and as a component of stormwater reuse systems.  However, there is currently a general lack of knowledge regarding their design, implementation and performance.  This paper reports on the issues encountered and lessons learnt during the installation and operation of an experimental biofiltration system.  While the water industry familiarizes itself with biofiltration technologies, effective communication and clear guidance is required to ensure successful construction and operation of biofilters.  The studied biofiltration system consisted of three separate cells, each containing a different, soil-based media type.  Compaction of filter media, organic matter and moss growth significantly reduce hydraulic conductivity, however root penetration and the addition of vermiculite and perlite appear to assist in maintaining porosity.  Preliminary treatment performance results indicate that all three cells effectively remove sediment and heavy metals (lead, copper and zinc), however they are all net producers of nitrogen and phosphorus.  However, biofiltration systems appear to be promising technologies for treatment of stormwater, both for reuse and aquatic ecosystem protection.

Smith, N., R. Allen, A. McKenzie-McHarg, A. Deletic, T. D. Fletcher and B. Hatt (2007). Retrofitting functioning stormwater gardens into existing urban landscapes. Cairns International Public Works Conference, Cairns.

Urban stormwater runoff has a major impact on waterway health in South East Queensland. Over the next 20 years an additional one million people are expected to move to the region, further increasing pressure on waterways. In line with growth in South East Queensland, Brisbane's population is expected to expand by 15%, most of which will be accommodated through infill and redevelopment of existing urban land.  Stormwater gardens (street-scale biofiltration systems) are one of a number of devices currently being investigated by Brisbane City Council to improve urban stormwater quality. These systems provide an opportunity for Water Sensitive Urban Design (WSUD) to be retrofitted in existing urban areas as well as implemented as part of infill and redevelopment of appropriate sites.  The constraints that existing urban infrastructure places on the design and construction of WSUD measures presents a considerable challenge to the retrofit potential of these systems in Brisbane. This paper documents the design, construction and maintenance of a retrofit stormwater garden in the northern suburbs of Brisbane.  Ongoing simulated and actual storm-event monitoring of these stormwater gardens presents a unique opportunity to gain a greater understanding of the treatment processes and performance of these systems under Brisbane's climatic conditions.

Hatt, B. E., T. D. Fletcher and A. Deletic (in press). Hydrologic and pollutant removal performance of stormwater biofiltration systems at the field scale. Journal of Hydrology.

Biofiltration systems are a recommended and increasingly popular technology for stormwater management, however there is a general lack of performance data for these systems, particularly at the field scale.  The objective of this study was to investigate the hydrologic and pollutant removal performance of three field-scale biofiltration systems in two different climates.  Biofilters were shown to effectively attenuate peak runoff flow rates by at least 80%.  Performance assessment of a lined biofilter demonstrated that retention of inflow volumes by the filter media, for subsequent loss via evapotranspiration, reduced runoff volumes by 33% on average.  Retention of water was found to be most influenced by inflow volumes, although only small to medium storms could be assessed.  Vegetation was shown to be important for maintaining hydraulic capacity, because root growth and senescence countered compaction and clogging.  Suspended solids and heavy metals were effectively removed, irrespective of the design configuration, with load reductions generally in excess of 90%.  In contrast, nutrient retention was variable, and ranged from consistent leaching to effective and reliable removal, depending on the design.  To ensure effective removal of phosphorus, a filter medium with a low phosphorus content should be selected.  Nitrogen is more difficult to remove because it is highly soluble and strongly influenced by the variable wetting and drying regime that is inherent in biofilter operation.  The results of this research suggest that reconfiguration of biofilter design to manage the deleterious effects of drying on biological activity is necessary to ensure long term nitrogen removal.

Hatt, B. E., T. D. Fletcher and A. Deletic (2008). Improving stormwater quality through biofiltration: Lessons from field studies. 11th International Conference on Urban Drainage. Edinburgh, UK.

Biofiltration systems are an increasingly popular low-energy treatment technology for improved stormwater management.  However, while extensive laboratory testing has demonstrated their capacity for effective removal of a wide range of stormwater pollutants, field-scale performance data is limited.  Three stormwater biofiltration systems of varying size, age and catchment characteristics, and in two different climates, were monitored to evaluate their pollutant removal performance.  Concentrations of suspended solids and heavy metals were effectively and reliably reduced at all three sites.  Effluent nutrient concentrations, on the other hand, were more variable and ranged from being substantially lower, through to considerably higher, than influent stormwater concentrations.  These results are essentially consistent with related laboratory studies.  Suspended solids and heavy metals will be reliably removed by a wide range of soil-based filter media and phosphorus also, provided the filter media has a low phosphorus content.  Retention of nitrogen remains a challenge because it is easily transformed to soluble forms and is influenced by the variable wetting and drying that is inherent in biofilter function.  However, a related laboratory study of biofiltration systems that incorporate a permanent pool of water at the bottom of the systems has demonstrated the potential for buffering against desiccation. 

Lewis, J. F., B. E. Hatt, S. Le Coustumer, A. Deletic and T. D. Fletcher (2008). The impact of vegetation on the hydraulic conductivity of stormwater biofiltration systems. 11th International Conference on Urban Drainage. Edinburgh, UK.

Stormwater biofiltration systems are an increasingly popular treatment technology and are being installed in all major cities in Australia. Their concept is very simple and easily implemented in all urban forms. Unfortunately, we know very little about the performance of biofiltration systems, particularly with respect to their long-term hydraulic performance. There is some concern regarding the ability of biofiltration systems to treat the design volume of stormwater for the duration of their intended lifespan, or whether factors such as compaction of the filter media and surface clogging will impede their infiltration performance. To address this knowledge gap, the Facility for Advancing Water Biofiltration has been monitoring the hydraulic capacity of field-scale biofiltration systems. Vegetation was shown to be critical in maintaining the infiltration capacity of biofiltration systems, helping them to recover from the inevitable reduction in hydraulic conductivity due to initial compaction of the filter media under hydraulic loading. The creation of macropores due to root growth and senescence is thought to contribute to this behaviour. Biofiltration systems were shown to attenuate mean peak flows by 80% (range 45 - 96%). A performance analysis of a lined biofiltration system demonstrated that, on average, 42% of an event volume (range: 15 - 83%) was retained by the filter media and subsequently lost via evapotranspiration. This high level of losses is mainly due to the fact that the monitored events were largely small to medium in their size (monitoring of large events was not conducted).

Blecken, G.-T., Y. Zinger, T. M. Muthanna, A. Deletic, T. D. Fletcher and M. Viklander (2007). The influence of temperature on nutrient treatment efficiency in stormwater biofilter systems. Water Science and Technology 56(10): 83-91.

Nutrients can cause eutrophication of natural water bodies. Thus, urban stormwater which is an important nutrient source in urbanised areas has to be treated in order to reduce its nutrient loads. Biofilters which use soil filter media, biofilms and plants, are a good treatment option for nutrients. This paper presents the results of a biofilter column study in cold temperatures (+2°C, +8°C, control at +20°C) which may cause special problems regarding biofilter performance. It was shown that particle-bound pollutants as TSS and a high fraction of phosphorus were reduced well without being negatively influenced by cold temperatures. Nitrogen, however, was not reduced; especially NOx was produced in the columns. This behaviour can be explained with both insufficient denitrification and high leaching from the columns.