The Hydro International Downstream Defender® is an advanced hydrodynamic separator designed to remove sediment, floatables and associated pollutants from stormwater. The trial installation was conducted in a roadside drain adjacent to a busy street-side market area with residential and light industrial areas upstream. Prior to installation, floatables, oils and grease and sediments were trapped and sampled at a specific point in the drain.
The Downstream Defender was installed offline above the sampling point, with stormwater diverted through it and gross pollutants measured both at the sampling point and extracted from the device itself. After installation, no floatables or sediments were measured at the sampling point, and hydrocarbon concentrations were also very much lower.
Infrastructure and hydrological engineers Weida (M) Bhd conducted the trials and concluded that the separator is an effective gross pollutant trap which captured and stored nearly all gross pollutants carried in the storm drain over the trial period.
“[The Downsteam Defender’s] main strength is the ability to retain pollutants and prevent re-entrainment even at maximum flow volumes; this is better than other designs of gross pollutant traps,” said Calista Kim Kher San, project engineer for Weida. “The Downstream Defender is also very effective in trapping the large amounts of big floatables, such as litre plastic bottles and polystyrene foam blocks. These large items have to be manually scooped out of the drains, but with the Downstream Defender this is achieved through standard maintenance using a suction truck.”
“These trials are encouraging because they are helping to test the Downstream Defender’s ability to provide ‘first flush’ treatment in intense storm conditions, even though the device was originally developed for more temperate US and UK climates,” said Hydro export manager Graeme Fenton.
The National Hydraulic Research Institute of Malaysia (NAHRIM) commissioned the trials and the results will be passed to the United Nations South East (UNSEA) for consideration as a solution in Malaysia and neighbouring countries with similar conditions. “We are very hopeful that the trials will help this promising technology to gain acceptance as a much-needed answer to a problem not only in Malaysia, but throughout the region, where conditions are similar,” said Fenton.
The onset of rapid urban development in parts of Malaysia has increased areas of impervious surfaces which deliver high flash flow conditions under intense rain storms. Urbanisation also increases the amounts of discarded waste such as polystyrene food trays and other packaging, organic pollutants such as food and cooking oil, as well as hydrocarbons. Rainfall is also a major factor in transporting pollution to storm drains, with Kuala Lumpur, for example, having an annual rainfall of nearly 2400 mm with peaks up to 280 mm in April and November. Short duration showers can realise 100mm or more in an hour. Urban Malaysia’s typical storm drainage comprises deep road side drains which discharge into high volume monsoon drains, and eventually into the river. After storm events, the heavy load of silt and trash is visually evident in the rivers.