11. Efficiency of Constructed Wetland Microcosms (CWMs) for the Treatment of Domestic Wastewater Using Aquatic Macrophytes

Constructed wetland microcosms (CWMs) are engineered wastewater treatment systems that are designed to treat wastewater from small communities, involving aquatic plants, a variety of substrate materials, soils and their associated microbial fauna. CWMs are considered as promising ecological technology that requires low or no energy input, low operational cost and provides more benefits and better alternative to conventional wastewater treatment systems. In CWMs dissolved oxygen (DO), pH and temperature are controlled to achieve the desirable treatment efficiency. Several other components such as plant, substrate, water depth, hydraulic loading rates (HLRs) and hydraulic retention time (HRT) are also critical to establishing viable CWMs for the better performance. The literature on CWMs suggests excellent nutrient removal performances which are achieved with low and stable effluent concentrations. Further, the choice of appropriate macrophyte species having high uptake of pollutants and high pollutant tolerance and choice of substrate materials are critical for treatment performance. CWMs can be differentiated based on existing native vegetation type (such as floating leaved macrophytes, free-floating macrophytes, emergent macrophytes and submerged macrophytes, in which emergent macrophytes are common) and, hydrology (surface flow constructed wetlands (SFCWs), subsurface flow constructed wetlands (SSFCWs) and hybrid systems). The focus of this paper is to review the state of the art in improving the overall efficiency of CWMs for wastewater treatment. The paper documents both the design and operation of CWMs which are critically dependent on environmental, operational and hydraulic factors. It further outlines key challenges and future prospects for their wider replication.