Application of Phytoremediation Techniques to Treat Reverse Osmosis Concentrate using Wetlands

Abstract

Reverse Osmosis (RO) plants have been introduced by many organizations to Chronic Kidney Disease of Unknown Etiology (CKDu) affected areas as an effective drinking water treatment method. The liquid byproduct of RO system known as RO concentrate or reject is considered as the major environmental and economic drawback of RO process and normally released to the environment without any treatment. Main objective of this study was to investigate the potential of phytoremediation techniques in treating RO concentrate through pilot scale constructed wetlands (CWs). Four plant species; Vetiver (Vertiveria zizanioides), Cattail (Typha augustifolia), Cannas (Canna indica) and Bulrush (Scirpus californicus) were planted in small plastic containers (60 x30 x 30 cm) and soil without amendments was served as the control. There were 3 replicates for each treatment. The experimental units were treated with continuous flow of concentrates obtained from RO plant installed in Faculty of Agriculture, Rajarata University of Sri Lanka at a rate of 2.3 ml s-1 for three months period. The hydraulic retention time was 52 h. Water samples were collected from inlets and outlets of each experimental unit by two weeks interval and analyzed for pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), concentration of Na+, K+, Ca2+, Mg2+, NO3--N, PO43--P and NH4+-N. The results revealed that removal efficiencies (RE) of all pollutants were increasing with time. Cattail plants showed highest removal efficiencies for PO4--P, NO3--N and NH4+-N by 45%, 30% and 39% respectively. Sodium Adsorption Ratio of all treatment plants were within the irrigation water quality standards. Therefore, it can be concluded that the quality of RO concentrate can be improved using phytoremediation techniques.