Removal and recovery of nutrients by ion exchange from water and wastewater
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In this study, a fixed bed ion exchange system for nutrient removal and recovery for water and waste water was developed and tested for nitrate and phosphate. A post-treatment consisting of a fixed bed bed ion-exchange system with a Purolite and an HFO column in series and individually was used to remove and recover nitrate and phosphate from synthetic water and wastewater. The efficiency of the ion exchange materials incorporated into the anthracite matrix at 1, 3, 5 and 10%, in their ability to remove and recover these nutrients was investigated. Another ion exchange material, HAIX, was also investigated for the removal and recovery of nitrate and phosphate. Also, the study considered regeneration and reuse of the ion exchange media in order to see how long the system can effectively remove and recover nitrate and phosphate before saturation. Purolite was found to exhibit a higher capacity for the removal of nitrate than for phosphate. HFO was found to exhibit a higher capacity for the removal of phosphate than for nitrate. Both these media were required in series to remove both nitrate and phosphate. Increase in dose of the two ion exchange materials incurred an increased in removal efficiency of nitrate and phosphate. However, the selectivity of Purolite for nitrate and HFO for phosphate decreased with increase percentage by mass of the ion exchanger in the anthracite matrix. Regeneration was undertaken using a distilled water wash as well as 3% NaC1 wash. It was found that NaC1 successfully regenerated the exhausted media for reuse. Distilled water wash was not a successful medium for regeneration. A column experiment was also conducted with MBR effluent to investigate the possibility of removing the nitrate and phosphate. Both N and P in the MBR effluent were found in different forms (as NH₄ – N, organic N, inorganic and organic phosphorus). Other competing anions like C1⁻ and SO₄²⁻ were also present in the feed. Despite the different forms of N and P as well as competing anions, the Purolite and HFO in series system still had a removal efficiency of 87-100%. The column was able to remove almost 100% of nitrate and phosphate in the effluent. The Langmuir, Freundlich and Sips isotherm models were used to model the equilibrium isotherm of nitrate and phosphate removal by Purolite (A500PS), HAIX and HFO. The results show that the experimental data satisfactorily fitted to all three models. The kinetic data for the adsorption of both nitrate and phosphate were satisfactorily described by the Ho model. The fit for phosphate on HFO was less satisfactory than the other adsorbents.
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