Study of microbiological runoff water quality from a green roof and in an open storm water system

Abstract

Augustenborg is suburb city in Malmö south of Sweden. The climate is temperate with occasional snow during the winter. Open storm water is applied in Augustenborg since late 1990s and the storm water is disconnected from the combined sewer system in order to give the area a lift up value and to solve the flooding problems in basements after heavy rainfall events. The new open system consists of ponds, infiltration surfaces, canals and green roofs combined together to function as a one unit. The drainage system is designed to drain area of about 5 ha divided into four sub areas. Area representing the final part of the drainage system consists of a schoolyard, parkland, and grass swale. Upstream areas consist of buildings separated by paved yards and a council property. The storm water flows from upstream to downstream through series of BMPs (Best Management Practice) including wet ponds, garden, meandered channel, wetland and dry pond. The water in the open system is exposed and may constitute a potential health risk for public in the surrounding neighborhood, especially the children. The aim of this study is to investigate the microbiological water quality of runoff and in an open storm water system to assess the potential health risks due to contact with storm water in an open storm water system and to identify potential needs for further studies. Many microorganisms’ grubs have been commonly used in water microbiology as indicators or tracer for fecal pollution in the water. The purpose of using such indicators is either to assess the treatment efficiency of a particular water system or evaluate water quality in general. In our study, the most appropriate indicators that have been selected were E-coli, total coli forms, clostridium perfringens, and intestinal enterococci.
Grab water samples have been collected during/after three different precipitation events taking place in 6 May, 26 October and 24 November 2009. The water samples were taken at the following four locations from the Augustenborg storm water systems: green roof, pond 1, pond 2, and the ditch; one sample at each location and event. The runoff from the green roof was collected in a plastic barrel of capacity 25 l that was connected by a plastic hose with a green roof section. The plastic barrel has been emptied and cleaned with tap water after each collection event. One grab water sample was taken from the barrel after each of the sampled precipitation events. At other, three sites (two ponds and ditch), the water samples were collected manually in plastic bottles by submerging the bottles under the water surface until the sampling bottle fills up. Sampling bottles (300 ml) were sterile and they were prepared at the laboratory according to the requirements for sampling equipment for collecting water for microbiological analysis. The samples have been taken after storms, which generated enough runoff for the system to allow water sampling. The water samples were delivered to the (VA SYD) water laboratory in Malmö and analyzed immediately after collection. Concentration of E-coli, total coli forms, and intestinal enterococci have been measured by number of each individual parameter per 100 ml water sample (st/100ml) while the clostridium perfringens was measured by a colony forming unit (CFU) in 100 ml water sample. Since there are no standards for microbial quality in storm water and storm water recipients, the recreational water quality standards can be used as a reference in assessing water quality. The obtained results from each collection site are compared with recreational water quality standards for EU countries.
The results vary from point to point to point and the bacteria concentrations fluctuate with rainfall intensity. The results show that the samples taken from green roofs are least polluted. Among runoff water samples from green roofs the sample that have been collected on 6th May has the highest bacteria concentration. It is because the sample was collected after a long dry period, which resulted in accumulation of deposition material on the top of the roof. Results from the ditch sampling have the highest microbial parameters among all sampling points. Pond1 and pond2 sampling points have less microbial indicators comparing with the ditch. The water quality in the ponds is affected by the addition of drinking water from mains supply, which has been added occasionally to the ponds during dry periods. The process of adding drinking water affected the water quality in the ponds positively. Most of the collected samples did not meet the standard for bathing water quality. Around 80% of the investigated samples exceeded the standard value (1000/100 ml) for total coli form indicator while, 33 % of the samples exceeded the standard value for E. coli indicator (500st/100ml) and 66% of the samples exceeded the standard value for intestinal enterococci indicator. In general the storm water in Augustenborg open system can judged as polluted water in microbiological point of view and there a need for further research for better linkage between rainfall intensity, the length of the proceeding dry period and microbial concentration in storm water.

• author: Hussain, Ammar
• supervisor: JUSTYNA CZEMIEL BERNDTSSON
• organization: Division of Water Resources Engineering
• course: VVR820 20091
• year: 2010
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: open storm water system, Storm water microbiology
• publication/series: TVVR10/5006
• report number: 10/5006
• ISSN: 1101-9824
• language: English
• additional info: Examiner: Magnus Persson
• id: 1608096
• date added to LUP: 2010-06-11 15:05:01
• date last changed: 2019-03-27 11:51:12