Abstract
This study aimed at comparing the performance of horizontal, vertical and hybrid subsurface flow system in polishing wastewater effluent from the maturation pond at Gusii wastewater treatment plant, Kenya. The treatments were monitored for six weeks duration for chemical oxygen demand, total suspended solids, total nitrogen and total phosphorous against Kenya’s National Environmental Management Authority standards for effluent discharge. Among the systems planted with Vetiver grass, the hybrid subsurface flow system significantly removed the pollutants more efficiently than the single operated systems. The Vetiver planted hybrid subsurface flow wetland systems achieved the highest removal of COD, TN, TP and TSS at 82.4, 87.9, 65 and 94.6%, respectively as compared to other wetland systems. The planted vertical subsurface flow removed COD, TN and TP at 72.9, 75.7, and 50.7%, respectively more efficiently than the horizontal subsurface flow system that achieved removal of COD, TN and TP at 65.3, 70.0 and 43.8%, respectively. The planted horizontal subsurface flow wetland however showed better TSS removal at 89.9% compared to 83.2% achieved by vertical subsurface flow system. The unplanted systems exhibited a similar trend whereby the hybrid subsurface flow systems achieved better performance than the single systems though with significantly (P≤0.05) lower organics and nutrients removal efficiencies compared to the planted systems.
Highlights
Demand for fresh water resources is expected to rise with the growing global population yet this precious resource is under constant threat of pollution
Among the subsurface flow wetland systems planted with Vetiver grass, the hybrid system achieved significantly (p≤0.05) the lowest mean effluent COD of 20.19 mg/L followed by the vertical system at 31.06 mg/L
Among the subsurface flow wetland systems planted with Vetiver grass, the hybrid system achieved significantly (p≤0.05) the lowest mean effluent of total nitrogen (TN) at 4.23 mg/L followed by the vertical system at 8.51 mg/L
Summary
Demand for fresh water resources is expected to rise with the growing global population yet this precious resource is under constant threat of pollution. Adequate treatment of wastewater for reuse will be a viable option in ameliorating the challenge of water scarcity and environmental degradation. Many industries in developing countries use conventional wastewater treatment systems to treat their wastewater before release into the environment (Konnerup et al, 2011; Zhang et al, 2014). These conventional treatment technologies have been found to be either ineffective, wasteful and costly (Nhapi, 2004). Adoption of low cost and effective technologies such as phyto-remediation will be a suitable option for many industries and households involved in wastewater treatment
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