## 1 Introduction
Furthermore, one cannot remove the P below a particular concentration through biological processes. Of all the methods of P removal, adsorption/ion exchange strategies are promising because they are simple and economical, result in less sludge production and therefore experience minimal disposal problems [15]. The ion exchange method provides a more selective means of separating ions from solution. In fact the ion exchange process using selective ion exchange materials is ideal for reducing phosphate to near-zero levels provided that the ion exchange resin is phosphate selective, cost-effective and amenable to efficient regeneration and reuse [16]. Different ion exchange resins have been employed to remove P from wastewater such as Purolite A500P, Purolite A520E, Purolite FerrIX A33E, Amberlite IRA910 Cl and Amberjet 1200 Na [17; 18; 19]. Ion exchange resins are used as filter media in filter-based systems and after a period of usage they become saturated with P, leading to a decline in their removal efficiency. The exhausted resins can be regenerated using different regeneration reagents or a mixture of regeneration reagents such as NaCl, NaOH, CaCl\({}_{2}\), HCl, and Na\({}_{2}\)CO\({}_{3}\)[15]. Phosphorus so removed can be recovered by precipitation with calcium/or magnesium salts and employed as phosphorus fertiliser [20; 21]. Alternatively, it can be diluted with irrigation water for fertilising irrigated crops [15]. Very few studies have been reported on this method of P recovery from real wastewater or MBR treated water although such studies have been conducted on synthetic water [18]. [PERSON] _et al._[21] used a phosphate adsorbent to recover P from municipal wastewater and successfully produced calcium phosphate fertiliser by adding calcium chloride to the solution containing the recovered P.  
In this research, MBR effluent from a water reclamation plant in Gordon, Sydney, Australia was used for the removal and recovery of P using Dowex 21K XLT ion exchange resin. The basis for selecting Dowex 21K XLT resin is that it is a strong base resin and in our previous study, we found that it had a high adsorption capacity for phosphate [22]. This resin was also used to selectively adsorb gold-cyanide complex in a previous study [23]. The objectives of this study were to: (i) determine the adsorption capacity of Dowex 21K XLT for P from the MBR treated water using batch and column modes of adsorption experiments; (ii) investigate the feasibility of struvite and hydroxyapatite production from the desorbed P and (iii) characterise the struvite and hydroxyapatite products using chemical analysis. Nitrate and sulphate concentrations in the MBR treated water were also high as phosphate concentration but no attempt was made to recover them as fertilisers because no shortage of fertilisers containing these nutrients is expected in the near future unlike in the case of phosphate fertilisers. The novel feature of the study is the removal of phosphate from wastewater containing a range of phosphate-competitive co-ions under dynamic condition. This is followed by an experimental investigation on desorption and recovery of phosphate as fertilisers for beneficial use. The study conducted on MBR treated water at the Gordon plant is expected to help other plants in Australia and other countries recover P from wastewaters and produce beneficial P fertilisers.