Water Journal : Water Journal September 2011
refereed paper technical features 88 SEPTEMBER 2011 water stormwater treatment Periodic grab samples from the wet-sump indicate that most of the TN load in the standing water is present as ammonia-N at concentrations that are two orders of magnitude higher than typical influent ammonia-N concentrations. As such, ammonia-N is, possibly, generated in the wet-zones by anaerobic decomposition of organic nitrogen in the inter-storm event periods. This has two important implications: 1): the load of ammonia-N passed to the StormFilter® cartridge is significantly higher than is suggested by the influent EMC, which implies that the removal rates for ammonia-N removal may be an under-estimate; and 2): by converting organic nitrogen to ammonia-N in the wet-zones and then removing this ammonia, the system has the potential to remove soluble organic-N. Discussion The results for Storm 6 represent a snapshot of one storm, and should not be considered as comprehensive; they do suggest, however, that the main TN removal pathways for the treatment train is the efficient removal of particulate organic nitrogen, complemented by the sorptive removal of soluble ammonia-N and organic-N. Very often TN removal is treated as a key performance benchmark for stormwater treatment practices. This is potentially problematic, given the apparent variation in the nature of the TN load. In a comprehensive study of nitrogen composition in Melbourne (Taylor et al., 2005), ca. 25% of the load was present as particulate organic nitrogen. The remainder was soluble and, of these species, oxidised nitrogen predominated over dissolved organic nitrogen and ammonia-N. Taylor et al. (2005) inferred that either 'removing' the water by infiltration or denitrification (ie, in the anaerobic zone of bio-retention practices) would be necessary to achieve significant TN reduction. Fletcher et al. (2004) reported that the TN composition measured in wet weather samples for various land uses in the Sydney and Illawarra regions was extremely variable. For urban catchments, median oxidised nitrogen concentrations were in the range 0.09 to 0.42 mg/L, while the median TN concentration range was 0.65 to 2.32 mg/L. The oxidised nitrogen represents a much smaller proportion of the TN load than was observed by Taylor et al. (2005) for Melbourne data. In a study of nutrient build-up on urban roads in the Gold Coast, Miguntanna et al. (2010) found that oxidised nitrogen comprised only ca. 10% of the TN load, across three different land uses, and most of the TN load was present as TKN and a significant proportion of this was particulate in nature. Consequently, the measured TN load from the Gold Coast catchments is similar to that measured at the Streets Creek, Kuranda site, providing applicability of Nitrogen removals to various urban land uses. Conclusions The results from this field trial generally correlate well with an earlier study at this site by JCU (Munksgaard and Lottermoser, 2008). The data collection from this study has been based on a rigorous and technically demanding monitoring program, which adds further credibility of the results (Goonetilleke, 2010). From an operational perspective, the system captured an appreciably large sediment load requiring annual cleaning to maintain its operational effectiveness. The EnviroPod®/StormFilter® treatment train achieved 78% removal for suspended solids under 500 microns, which approximates the long-term environmental target recommended by NSW DECC (2007), QLD DERM (2010) for South East Queensland (SEQ) and consistent with the 80% reduction target of many consent authorities in the US. The runoff at Streets Creek contained very low levels of phosphorus and nitrogen. Total Phosphorus removal was between 45% and 70% respectively in both the Stormwater360 field trial and the JCU research project, which approximates the NSW DECC (2007) and QLD DERM (2010) SEQ long-term environmental targets of 65% and 60% respectively, and is better than expected given the low influent EMCs. Total Nitrogen removal was consistent, substantial and in agreement with the NSW DECC (2007) and QLD DERM (2010) SEQ 45% long-term environmental target, despite the proximity of the influent EMC to the irreducible concentration of the treatment train. The removal of nitrogen was particularly noteworthy, given that the debris captured and stored within the treatment train was not included in the influent load into the system, but may have been sampled as a soluble leachate by the effluent sampler. Acknowledgements The authors would like to acknowledge the support of and contributions by Professor Ashantha Goonetilleke and Geoffrey Hunter. The Authors Michael Wicks (email: michaelw@ stormwater360.com.au) is Technical Director of Stormwater360 Australia. Nick Vigar is Research Manager and Mike Hannah is Technical Director, both of Stormwater360 New Zealand. References ANZECC, 2000: Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Volume 1. The Guidelines. Tables 3.3.4-3.3.5 Tropical Australia p.3.3-12 and Table 3.3.5 p.3.3-13. National Water Quality Management Strategy, October 2000. BMP Database, 2010: International Stormwater Best Management Practices (BMP) Database Pollutant Category Summary: Nutrients. Prepared by Geosyntec Consultants Inc. and Wright Water Engineers Inc. (available from http://www.bmpdatabase.org). Duncan HP, 1999: Urban Stormwater Quality: A Statistical Overview, Report 99/3, Cooperative Research Centre for Catchment Hydrology, Melbourne, Australia. ETV (2004). Fletcher T, Duncan H, Poelsma P & Lloyd S, 2004: Stormwater Flow and Quality, and the Effectiveness of Non-Proprietary Stormwater Treatment Measures -- A Review and Gap Analysis. Cooperative Research Centre for Catchment Hydrology, Technical Report 04/8. Goonetilleke A, 2010: Letter to Author, 15 March, 2010. Livingston EH & McCarron ME, 1992: Stormwater Management: A guide for Floridians. Florida DER (71 pages). Miguntanna NP, Goonetilleke A & Egodowatta P, 2010: Understanding nutrient build-up on urban road surfaces. Journal of Environmental Sciences, Vol 22(6), pp 806--812. Munksgaard NC & Lottermoser B, 2008: Treatment of Road Runoff Waters, Kuranda Range Project. Report for Queensland Department of Main Roads, School of Earth and Environmental Sciences, James Cook University, Cairns, Queensland, Australia. NSW Department of Environment and Climate Change (DECC, 2007): Managing Urban Stormwater: Environmental Targets. Consultation Draft -- October 2007, Department of Environment and Climate Change NSW, p 4. QLD DERM, 2010: Urban Stormwater Quality Planning Guidelines 2010 -- December 2010, Department of Environment and Resource Management, Table 2.2 SEQ (2010). Taylor GD, Fletcher TD, Wong THF, Breen PF & Duncan HP, 2005: Nitrogen Composition in Urban Runoff -- Implications for Stormwater Management. Water Research, Vol 39, pp 1982--1989. White M & Pezzaniti D, 2001: Evaluation of Gully Pit Inlet Control Systems Project Number: 2368261, Urban Water Resources Centre, University of South Australia (20 pages).
Water Journal November 2011
Water Journal August 2011