Phytoremediation Potential of Cocoyam (Colocasia esculenta), Tropical Spiderwort (Commelina benghalensis), and Water Mint (Mentha aquatica) for Soil Salinity Reduction

Abstract

Salt-rich wastewater has a variety of adverse effects on the ecological environment but very difficult to treat than other industrial wastewater. The aim of this work is to monitor the growth performance of cocoyam plant, tropical spiderwort and water mint under salty conditions, then evaluate their efficiencies in the removal of the salt from the soil. The experiments were conducted using 3 liters buckets for each plant, filled with soil and placed in a shady area free from rain. Each plant had three buckets, one for each salt concentration used (300 mg/L, 1000 mg/L and 5000 mg/L). The growth performance of the plants were monitored for 4 weeks by checking the plants every after one week for new shoots as well as whether they withered or not. At the end of the 4th week (30 days) the plants were separated from the soil and the electrical conductivity (EC), total dissolved solids (TDS) and salinity of the wet soil determined, and the percentage salt removal by each plant was calculated. The results showed that, for the last week, it was observed that though water mint and tropical spiderwort had initially produced new shoots between week two and three at all the tested concentrations, they were all drying out in the fourth week. However, for the cocoyam, there were no new shoots on the fourth week but the plant was growing perfectly at all the tested concentrations. All the plants significantly reduced salt concentration with values reaching 99 % for cocoyam at 5000 mg/L compared to 32 % for spider wort, 47 % for water mint and 34 % in 30 days.  These results show that cocoyam can be very effective in removing salt from the soil at all concentration ranges without affecting its growth performance. It is recommended the experimental period be extended for cocoyam so as confirm its long term phytoremediation potentials.