Small Concentric Constructed Wetland for Treatment of Domestic Wastewater in a Tea Estate in Sri Lanka

Water pollution due to indiscriminate discharge of domestic wastewater is one of the major issues limiting access to safe water. A study was conducted to characterize water use and effluent in communities in a tea estate in the upper watershed in Sri Lanka. A questionnaire survey, field visits and focus group discussions were conducted to quantify water consumption. At a pilot scale, concentric rings with diameters of 0.3, 0.75 and 1.5 m were used for constructed wetland. Aggregates and soil were used to fill the rings. Scirpus grossus and Nasturtium officinale were planted in the middle and outer rings respectively. Wastewater from a collection tank was fed into the inner ring and treated wastewater was discharged through the outer ring. Water was sampled at the inlet - at the inner ring, middle ring and outer ring for analysis of Biological Oxygen Demand (BOD5) and other quality parameters. Domestic water usage varied with income, education and access to water. Per capita daily water use was higher in high-income and medium-level educated people. Per capita daily water usage of stream water users and pipe-borne water users were 246 and 194 L, respectively. Major consumption was for bathing followed by laundry. BOD5 of greywater varied from 20-55 mg/L and was highly contaminated with total coliform and E coli. The pilot-scale constructed wetland showed higher removal efficiency of BOD5, SS and TDS at 85, 65 and 55%, respectively. The constructed wetlands were in concentric rings. The hydraulic retention time of 2.3 days increased the pathways and facilitated the filtration, biodegradation and plant uptake of nutrients. This system can be recommended for small communities in the upper watershed in Sri Lanka.