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Mechanisms of pathogen removal by macrophytes in constructed wetlands

ABSTRACT Developing countries are faced with a serious challenge of wastewater management that has resulted in large volumes of partially, or untreated wastewater being released into the environment. In Southern Africa, the wastewater challenge is exacerbated by the dramatic rate of urbanisation which has placed unprecedented pressure on the installed wastewater treatment services in many urban areas. Contamination of water bodies by urban wastewaters is frequently implicated in the high incidences of diarrheal diseases that have affected most developing countries. Phytoremediation, using constructed wetlands, has emerged as a promising alternative or additional treatment measure to conventional methods. Despite the promise offered by phytoremediation, the exact mechanisms of pathogen removal by the macrophytes are still being debated. Frequent and validated mechanisms include: (i) attachment, adsorption, sedimentation and mechanical filtration by plant roots, (ii) plant microbe interaction within biofilms and (iii) oxidation, UV radiation and exposure to biocides. However, research has remained silent about the possibility of pathogen removal through uptake of-, and inhibition of, pathogens in the plant body, and inhibition of the microorganisms by plant exudates. Research is therefore needed to bridge the knowledge gap and to customise phytoremediation technologies to the wastewater treatment challenges that developing countries continue to face.