Investigation on the performance evaluation of vertical subsurface flow constructed wetland for the treatment of rural wastewater.

Abstract

In a rural country like India, low cost and decentralized treatment units like the vertical subsurface flow constructed wetland (VSSF CW) can be reflected as a novel wastewater system. In this concern, a pilot-scale VSSF CW unit of size 0.92 m × 0.92 m × 0.85 m bed planted with Typha latifolia and Phragmites australis was operated for a 12-month duration to treat simulated rural wastewater. During the operation, a constant head arrangement was made to maintain a continuous flow to achieve 5 different Hydraulic Retention Times (HRTs) of 2, 4, 6, 8 and 10 days in each season, such as winter, summer and rainy, to investigate the performance of the unit under different retention times. The reactor showed optimum removal efficiency at 6 days HRT at 12.5 cm/day Hydraulic Loading Rate (HLR) for organic matter removal. Both macrophytes and the microbial biomass of filter media effectively treated the rural wastewater. Average removal efficiency of the reactor during the entire study was 64.73%-88.80% for Chemical Oxygen Demand, 74.96%-95.34% for Biochemical Oxygen Demand, 40.13%-79.45% for Ammonia Nitrogen, 25.36%-65.65% for Total Kjeldahl Nitrogen, 22.86%-58.48% for Phosphate phosphorus, 23.50%-55.45% for Total phosphorous, 74.91%-98.59% for Faecal Coliforms and 71.14%-95.31% for Total Coliforms respectively. Two-way ANOVA followed by post-hoc Tukey's test showed that HRT had a significant impact on removal efficiency but not the season. Overall performance of the unit was good and study suggested that VSSF CW can be a smart alternative technology to treat rural wastewater before final disposal.