The role of salvinia rotundifolia in scavenging aquatic Pb (II) pollution: a case study

Bio-surveillance of environmental pollution is increasingly gaining ground, as it is felt that if and when standardized, it might prove to be a long term cost-effective alternative technology. In aquatic media, for monitoring heavy metal pollutants, which are mostly xenobiotic, a number of hydrophytes have been tried by earlier researchers. These hydrophytes have shown to have varying degree of accumulation capacities, which could be preferably utilized in scavenging the toxicants such as Pb(II) among others. The screening criteria of such a suitable scavenger also take into account the ease of harvesting and handling the biomass on a large scale. Here comes the use of a macrophyte, and its potentiality of forming metallo-protein complexes (phytochelatin) to hold back the diffused metal, Pb(II), ions. In the present investigation, the experimental test system was the common tropical aquatic weed, Salvinia rotundifolia, Willd. It has shown a high promise for Pb(II) removal from synthetic as well as industrial (battery producing unit) wastewater. Within a span of 4 days, 50?gm (wet weight) of the plant was capable of removing about 85–95% of Pb(II) from 1.50 litres of both kinds of wastewaters containing 0.65–1.8?ppm of the metal at an optimum pH of 5.5. The uptake potentials were examined under various combinations of pH, plant weight, and metal concentration. It is suggested that the high uptake and recovery of Pb(II) by Salvinia Rotundifolia can be efficiently used as a possible future biotechnological solution for industrial wastewater treatment in a tropical and developing country like India. In the present study, a reduction of biomass weight from 80 to 72.3 (in mg dry wt/g of fresh wt.) was noted, while an increase of tissue conductivity from 161 to 181.5 in micro-mhos/cm was observed. This reflects the potential injurious effect of heavy metals to the cell membrane of the biomass. These changes, when standardized, are likely to serve as a suitable `biomonitoring' device for aquatic metal pollution. In the present case, effluent quality of a battery manufacturing unit, India was evaluated. Even though there is an existing effluent treatment plant (ETP) of the industry, the effluent from the balancing tank (discharge point) was found to contain high concentrations of lead (0.657–1.021?mg/l), BOD (470?mg/l) and COD (680?mg/l) as against State Pollution Control Board's standards of 0.1?mg/l, 30?mg/l, and 250?mg/l respectively. In the present investigation, an attempt has also been made to treat wastewater from the balancing tank of the existing effluent treatment plant (ETP) of the above-stated industrial unit to bring down the concentrations of Pb(II), BOD (5 days), and COD within the permissible limits prescribed by the regulatory board. The treatment was done in a laboratory-scale oxidation pond, cultured with Salvinia rotundifolia, of 85 litres capacity using a hydraulic retention period of about 10 days.