Innovative approach for recycling phosphorous from agro-wastewaters using water treatment residuals (WTR)

Phosphorus capture from polluting streams and its re-use using industrial byproducts has the potential to also reduce environmental threats. An innovative approach was developed for P removal from soil leachate and dairy wastewater using Al-based water treatment residuals (Al-WTR) to create an organic-Al-WTR composite (Al/O-WTR), potentially capable of serving as a P fertilizer source. Al-WTR was mixed with either soil leachate, or with dairy wastewater, both of which contained elevated P concentrations (e.g., 7.6-43.5 mg SRP L^-1). The Al-WTR removed ∼95% inorganic P, above 80% organic P, and over 60% dissolved organic carbon (DOC) from the waste streams. P removal was correlated with P concentration in the waste streams and was consistent with an increase in Al/O-WTR P content as determined by X-ray fluorescence (XRF) and surface analysis using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Organic C was a major constituent in the original Al-WTR (31.4%) and increased by 1% in the Al/O-WTRs. Organic C accumulation on particles surfaces possibly enhanced weak P bonding. Desorption experiments indicated an initial and substantial P release (30 mg SRP kg^-1 Al/O-WTR), followed by relatively constant low P solubility (ca. 10 mg kg^-1). Organic C was continuously released to the solution (over 8000 mg kg^-1), concomitantly with Ca and other electrolytes, possibly indicating dissolution from inner pores, accounting for the highly porous nature of the Al-WTR, evident by SEM images. The potential of P-loading on Al/O-WTR to promote P recycling should be further studied.