Abstract:
Wastewater treatment is extremely important and mandatory in the modern world. For many developing countries, conventional wastewater treatment technologies urban centers are increasingly becoming impractical or expensive, being dependent on land availability, electrical energy and skilled personnel. They are also being seen as wasteful, since their designs are based on aspects of disposal. Phyto-remediation, which involves the use of aquatic plants to absorb pollutants fi'om wastewater, has the potential to improve on these technologies. Vetiver grass is one of the most promising plants for use in these aspects. This particular study was aimed at comparing the performance of vetiver grass in the reduction of the levels of BOD, COD, total nitrogen (TN), total phosphorous (TP) and total suspended solids (TSS) from wastewater when the vetiver is established using three different techniques: in a soil medium (soil-based system), with roots suspended in water (hydroponic system) and finally, a hybrid of these two. It comprised of three distinct experimental units made using metal boxes of dimensions 1.0 x 0.6 x 0.4m (length x width x depth), established with 120 vetiver plants using the three techniques. The treatments, together with a control were replicated thrice. They were administered with 40 litres of post-septic ta.nk wastewater and their pollutant reduction abilities determined over three, five and seven day contact periods. The data was analyzed by the Statistical Analysis Software (SAS 2008) at 0t=5%, revealing significant difierences between them. For instance, over the 5- day contact time, the soil-based, the hybrid and the hydroponic systems achieved TN reduction rates of 57.1, 49.8 and 49.4% respectively against the control wifli 26.14%. For BOD, the systems achieved rates of 75.1, 68.4, and 65.4% against the control’s 37.7%. When their abilities were evaluated over different contact times, all the three treatments including the control achieved significantly different reduction rates. For TN the soil-based system achieved the rates of33.6, 56.1 and 67.4% compared with the control’s 16.5, 25.6 and 31.1% for the 3, 5 and 7- day contact periods respectively. For BOD, these rates were 49.8, 75.5 and 80.8 against 14.9, 38.7 and 43.4% respectively. For the duration of the experiment, plant age had a significant effect on the vetiver systems’ performance after the sixth week. It was concluded that wastewater treatment systems that contain vetiver grass perform best if the plants are established in a soil medium than hydroponically or by the hybrid technique, and are therefore recommended.
