Efficacy of Hydroponic and Soil-Based Vetiver Systems in the Treatment of Domestic Wastewater

摘要

Conventional wastewater treatment technologies are deemed to be either ineffective or costly for developing countries such as Kenya. This has led to extensive research in phyto-remediation; the use of aquatic plants such as vetiver grass to reduce pollutant levels in wastewaters. This paper describes the comparative performance of vetiver grass systems in the treatment of domestic wastewater when the plant is established using three different techniques: in a soil medium (soil-based system), with roots suspended in water (hydroponic system) and as a hybrid of these two. Three experimental units of dimensions 1.0 x 0.6 x 0.4m (length x width x depth) fabricated from sheet metal and established with 120 vetiver plants using the three techniques were involved. They were administered with post-septic tank domestic wastewater whose levels of BOD 5 , TSS, TN and TP were measured prior to application, and five days after. The results indicated that generally, the soil- based vetiver system achieved the highest reduction in pollutant levels, followed by the hybrid and the hydroponic systems. For instance, in case of BOD 5, the soil-based, the hybrid, the hydroponic and the control units achieved 75.12, 68.44, 65.64 and 37.66 percentage reduction rates respectively. Analysis of variance at 5% significant level and the comparison of means by the least significance difference (LSD) test at P 0.05 consistently indicated the existence of significant differences between the vetiver treatments and the control, and between the soil-based vetiver system and the others. The major findings were that both the soil medium and the vetiver plants play a major role in wastewater remediation. Based on these findings, it was concluded that constructed wetland vetiver systems should preferably involve a suitable solid growth medium.