SE--Structures and Environment Effect of Batch Aeration-Treatment on the Solubility of Phosphorus in Pig Manure

Experiments were conducted to investigate the effect of temperature on phosphorus removal from pig manure during batch aeration and the mechanism(s) involved in its removal. Five temperature regimes, 5, 10, 15, 20 and 25°C, were investigated. The resulting effects on pH, volatile fatty acids levels (VFAs), and ortho-phosphate (ortho-P) in the manure were investigated. Results indicated that manure pH was the dominant factor influencing the levels of soluble ortho-P in the manure. Two different mechanisms that effected pH change were identified. Immediately after initiating aeration (i.e. during the first 1·5 days--phase I), a rapid rise in pH caused a rapid decline in manure-soluble ortho-P (coefficient of determination R2of 0·90). The manure pH beyond the first 1·5 days (phase II aeration) seemed to depend more on the VFAs levels. It was concluded that besides any phosphorus immobilization/release by the microbial biomass in phase II, the VFAs levels in the manure significantly explained (R2of 0·83) most of the biologically mediated chemical precipitation/dissolution of ortho-P. Temperature affected soluble ortho-P status only in phase II of aeration. High manure temperatures reduced aeration efficiency but promoted the production of VFAs. The resulting low pH led to the redissolving of ortho-P previously precipitated in the higher pH-regime in phase I; this may potentially reduce the efficiency of removing orthophosphates by subsequent solid-liquid separation treatments.