Constructed wetlands use natural processes to treat polluted water. In many instances around the world, stormwater, municipal and industrial waste water drains into canals and rivers; causing the water to foul with excessive nutrients and other harmful pollutants.
Constructed wetlands (also called retention basins) are shallow, flat water bodies that fill and drain in rain events. They traditionally contain carefully selected and positioned plants. The plants are integral in the success of the nutrient removal as they act like a sieve to filter and capture sediment and fine particles. They also slow down the flow of the waste water. Longer residence times in the wetland assists in the uptake of nutrients.
Phoslock Environmental Technologies (PET) is building constructed wetlands to treat waste water from large Chinese canals. Canal water is diverted into the constructed wetland to significantly reduce the concentration of nutrients (phosphorus and nitrogen) and minimise the sediment load discharging back into the canal network. This process effectively provides a natural chemical and physical sieve for the canal water. Given the high level of nutrients in Chinese canals, PET is adding Phoslock and modified zeolites into the wetlands to significantly reduce the level of phosphorus and nitrogen in the water.