Investigating the efficiency of constructed wetlands in the removal of heavy metals and enteric pathogens from wastewater

Abstract

Constructed wetlands (CWs) are low-cost, eco-technologically engineered systems, used for sustainable and efficient treatment of wastewater. These systems are popular due to their high pollutant removal efficiencies and low-management costs. CWs reduce pollution loads by removing suspended matter, organic material, heavy metals and enteric pathogens from wastewater through their expansive rhizosphere and the filtration matrix. Previous reports indicate reductions by 71.2% for biochemical oxygen demand, 75.1% chemical oxygen demand, 24.5% total phosphates, 87.3% suspended solids and 23.5% total nitrogen. Heavy metals removal has been reported at 42% for manganese, 75–99% for cadmium, 26% for lead, 75.9% for silver and 66.7% for zinc. Heavy metals are removed by adsorption and absorption into the filtration matrix and the leaves, shoots and rhizomes of the wetland plants. CWs are also able to remove 97.6% of protozoan pathogens such as Cryptosporidium parvum 94.8% of Giardia lamblia and 52% and 99.9% of Escherichia coli. In order to appreciate the current intense research on the use and management of CWs for wastewater treatment, a detailed review of previous work on these systems was done. The focus was on the different design techniques, choice of macrophytes, treatment efficiencies, applications and models applied to the technology.