A B S T R A C TWater eutrophication is a serious global issue that needs urgent attention. Ammoniacal nitrogen (AN) is present in both domestic and industrial wastewater which acts as one of the main contributors of eutrophication. There is a need to reduce AN to permissible levels as enforced by local authorities before final discharge. Phytoremediation has been recommended as an alternative solution to other conventional physiochemical and biological methods to treat wastewater with high AN content due to its cost-effective, environmental friendly and sustainable characteristics. Water hyacinth (Eichhornia crassipes) is a free-floating macrophyte, which is known as the most noxious weed in the world that shows characteristics of fast growth rate, adaptability to a wide range of environmental conditions and high nutrient uptake capacity. These capabilities contribute to the wide applications of water hyacinth for phytoremediation purpose. This paper provides extensive review on the technical advantages and limitations of phytoremediation as compared to other nitrogen removal technologies, as well as the insight for the development of phytoremediation technology using water hyacinth to treat wastewater with high AN content. This paper also provides fundamental knowledge on the AN removal mechanisms and necessary considerations in selecting the operating conditions of water hyacinth-based phytoremediation system, which may facilitate the design of industrial scale phytoremediation system for effluent treatment. Overall, phytoremediation technology assisted by water hyacinth has been shown to be promising for AN removal, which can be a potential solution in the future for various industries to reduce the AN level in their effluent discharge.

Eutrophication is a serious environmental issue that needs urgent concern. There is necessity to treat wastewater with high ammoniacal nitrogen (AN) concentration to the permissible standard limit to protect the aquatic ecosystem. This study investigated the optimum condition for AN removal from wastewater using Eichhornia crassipes-based phytoremediation process. Face-centered central composite design (CCD) was employed as the experimental design, in which four operational variables including pH (4-10), retention time (2-14 days), macrophyte density (5-30 g/L) and salinity (0-5 g NaCl/L) were involved in the study, while five responses were investigated, namely AN removal efficiency (Y 1), fresh biomass growth (Y 2), COD (Y 3), BOD (Y 4) and TSS (Y 5). AN removal was the main focus in this study. Through numerical optimization, the highest AN removal efficiency of 77.48% (initial AN concentration = 40 mg/L) was obtained at the following optimum condition: pH 8.51, retention time of 8.47 days, macrophyte density of 21.39 g/L and salinity of 0 g NaCl/L. The values predicted from the models agreed satisfactorily with the experimental values, which implied that response surface methodology was reliable and practical for experimental design developed using optimization of the phytoremediation process. The validation experiment using real semiconductor effluent further supported the high potential of the E. crassipes-based phytoremediation system to remove AN and other organic pollutants in this industrial effluent under optimal condition.