Phosphorous Precipitation in Source Separated Greywater for Direct Environmental Release.

Sammanfattning: As our understanding of the impact humans have on the environment changes, so too do the mitigation strategies we employ to prevent it. One major source of anthropogenic pollution is wastewater effluent. A shift towards source separation of wastewater into different streams in recent years has opened a door to tailor treatment to specific types of water. The largest propor- tion of domestic wastewater is classified as greywater, accounting for 70% of the volume but containing roughly 30% of the contamination. Low influent concentrations of nutrients, like phosphorus, can result in lower effluent concentrations with similar amounts of chemical addi- tion. While biological and physical treatments are possible, chemical precipitation remains a simple way of achieving extremely low phosphorous concentrations. Chemical precipitation also has the ability to remove nonreactive phosphorous through sweep coagulation. Because of the relative novelty of source separation on a larger scale, not much literature exists on the use of phosphorous precipitation in greywater. The placement, dosing, chemicals, and limits of re- moval of total phosphorous were tested using greywater from RecoLab in Helsingborg, Swe- den. Greywater exiting the biological stage of treatment required lower doses of coagulant and was capable of reaching lower residual total phosphorous concentrations, chemical oxygen de- mand, and turbidity compared to influent greywater. Depending on treatment plant layout, pre- cipitation within the biological stage can remove or diminish the risk of precipitating too much phosphorous, which can lower the efficacy of the biological step. Of the two compounds con- sidered, the aluminum-based coagulant (PAX-XL60, Kemira) achieved better removal rates than the iron based one (PIX-111, Kemira) in the ranges of concentrations most commonly used at traditional wastewater treatment plants. Removal of phosphorous below a detection limit of 0.05 mg P/L was achieved with 15 mg Al3+ /L or 45 mg Fetot /L in biologically treated greywater while minimum concentrations of 0.16 mg P/L and 0.14 mg P/L were achieved in influent grey- water by adding 17 mg Al3+ /L and 36 mg Fetot /L, respectively.