Evaluating Wastewater Treatment Efficiency of Two Field Scale Subsurface Flow Constructed Wetlands

Abstract

Constructed wetlands (CWs) are human-made systems designed to treat a variety of industrial, domestic and agricultural wastewaters. We study here the efficiency of domestic wastewater treatment by two field scale subsurface flow CWs under different hydraulic loading rates (HLRs). Each CW had inlet and outlet chamber for wastewater collection with Pistia stratiotes (water lettuce), two treatment sections consisting of sand and gravel media and four plant species Typha latifolia (Broadleaf cattail) and Cymbopogon citratus (lemon grass - first CW) and ( Pennisetum purpureum schum and Pennisetum americanum L (Hybrid napier) and Urochloa mutica (Paragrass - second CW). The wastewater source was from a residential urban colony. The HLRs for the first and second CW for a three-month period averaged 4.45 cm/day and 5.77 cm/day respectively. The CW was monitored for quality of wastewater inflows and outflows and nutrient accumulation in plants and sand media. Results showed that the chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen and total phosphate removals in the first and second CW over a three-month period averaged 42%, 74%, 39% and 41% and 34%, 82%, 14% and 35% respectively. Both the CWs showed similar rates of TSS removal irrespective of the type of wetland plant species. Over the three-month period, average COD, total nitrogen and the phosphate removals were greater in the first CW compared to the second CW. These results confirm the efficacy of field scale subsurface flow CWs to improve the quality of domestic wastewater in rural communities of developing countries like India.