Abstract
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 (Y1), fresh biomass growth (Y2), COD (Y3), BOD (Y4) and TSS (Y5). 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.
Highlights
Semiconductor industry is recognized as one of the fastest growing industries due to the high global demand of electronic products (Huang et al 2017)
Face-centered central composite design (CCD) was employed as the design of experiment (DoE), in which the design consisted of 30 runs, with 6 center points and 24 axial points, and α = 1
The two-factor interaction (2FI) model was successfully developed for the response of ammoniacal nitrogen (AN) removal efficiency
Summary
Semiconductor industry is recognized as one of the fastest growing industries due to the high global demand of electronic products (Huang et al 2017). Semiconductor manufacturing processes are complex which include silicon growth, oxidation, doping, photolithography, etching, stripping, dicing, metallization, planarization, cleaning (Wong et al 2013). The high efficiency of phytoremediation to remove a wide range of pollutants, which include heavy metals, radioactive materials, petroleum hydrocarbon, nutrients, organic contaminants and suspended substances, had been reported by many researchers (Rezania et al 2015; Rai and Singh 2016; Mishra and Maiti 2017; Nayanathara and Bindu 2017). Eichhornia crasssipes, commonly known as water hyacinth, is recommended as the AN phytoremediating candidate due to its characteristics such as fast growth rate, high nitrogen uptake capacity, easy to control and great adaptability to various wastewater environments (Ting et al 2018). Apart from the efficiency in AN removal, floating species such as E. crasssipes is more convenient and less expensive to be harvested compared to small plants (e.g., phytoplankton) or submerged plants (Valipour et al 2015)
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