Reverse osmosis brine for phosphorus recovery from source separated urine

• RO brine from a power plant could be used as a precipitant to recover P from urine.
• More than 90% P could be removed at RO brine/urine of 1:1 (v/v) at pH ≥ 9.0.
• The precipitates contain 16–39% of P2O5 and could be used in fertilizer industry.
• RO brine is a low cost and widely available precipitant for P recovery.

Phosphorus (P) recovery from waste streams has recently been recognized as a key step in the sustainable supply of this indispensable and non-renewable resource. The feasibility of using brine from a reverse osmosis (RO) membrane unit treating cooling water as a precipitant for P recovery from source separated urine was evaluated in the present study. P removal efficiency, process parameters and precipitate properties were investigated in batch and continuous flow experiments. More than 90% of P removal was obtained from both undiluted fresh and hydrolyzed urines by mixing with RO brine (1:1, v/v) at a pH over 9.0. Around 2.58 and 1.24 Kg of precipitates could be recovered from 1 m3 hydrolyzed and fresh urine, respectively, and the precipitated solids contain 8.1–19.0% of P, 10.3–15.2% of Ca, 3.7–5.0% of Mg and 0.1–3.5% of ammonium nitrogen. Satisfactory P removal performance was also achieved in a continuous flow precipitation reactor with a hydraulic retention time of 3–6 h. RO brine could be considered as urinal and toilet flush water despite of a marginally higher precipitation tendency than tap water. This study provides a widely available, low - cost and efficient precipitant for P recovery in urban areas, which will make P recovery from urine more economically attractive.

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