Environmental Influences on Pollutants Removal in Modular Bioretention Swale

Abstract – The change in land use due to industrialization and urbanization has resulted in an increase in percentage perviousness in urban landscape. Nutrients and suspended solids accumulated on surfaces of urban cities are often washed into stormwater runoff receiving waterbodies causing eutrophic and unattractive waterbodies. As such, there is a pressing need to mitigate the impact of urbanization and industrialization by shifting towards the use of bioretention systems as a sustainable urban stormwater management system. Despite the large numbers of studies conducted to understand the influences and optimize the performance of bioretention systems; many of these studies were conducted on laboratory or pilot scale, which may not be applicable in field-based studies. Furthermore, many of the researches were done in Australia where there is seasonal changes thus may not be applicable to a tropical country like Singapore. In this study, a modular bioretention swale was constructed and monitored for its performance to improve the quality of urban stormwater runoff. Effluent quality from the bioretention system was observed to meet stormwater treatment guideline set by local government agency, with average removal efficiency of 50.7, 52.6 and 83.8% for total nitrogen, total phosphorus and total suspended solids respectively. It was observed that removal efficiencies of pollutants were affected by influent concentrations and their dissolved (soluble) percentages. Environmental influences such as soil moisture and air temperature also played a part in the performance of the bioretention system. However, due to different nature and removal pathway of the pollutants, the extent in which performance was impacted varied among the pollutants monitored in the project.


Nitrogen and phosphorus are macronutrients essential for plant growth. However, high concentration of these nutrients in waterbodies can lead to eutrophication. Anthropogenic eutrophication can be detrimental to the health of natural waterbodies as the increase in nutrients encourages algal growth (algae bloom). When the algae dies or respire at night, dissolved oxygen (DO) is used causing a drop in DO concentration in the waterbodies. This could result in the death of aquatic organism due to the lack of oxygen content for respiration. Eutrophication can also cause a drop in biodiversity due to increased competition and change dominating biota in waterbodies. Furthermore, it affects the amenity value of the water, increases downstream water treatment cost and may cause water to be injurious to health.

Growing population, industrialization and urbanization has resulted in the replacement of green areas like forests and natural wetlands with impervious surfaces for various urban land uses. Such developments alter stormwater runoff hydrology as well as water quality and the use of traditional stormwater management systems to divert stormwater runoff bypasses treatment of runoff through the infiltration of soil and vegetation. Pollutants accumulated on urban surfaces are washed into receiving waterbodies by stormwater runoff as they are not retained by the natural treatment processes causing elevated nutrients concentration and eutrophication in receiving waterbodies [1].

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