Anaerobic storage of commercial pig manures to dissolve phosphorus forstruvite precipitation

摘要

Removal of excess P from pig manure is a practical goal to recycle waste P back into the supply stream. The precipitation reaction to form struvite (MgNH_4PO_4 -6 H_2O) from liquid manure is limited however by the concentration of phosphorus in dissolved form (P-PO_4). P-PO_4 makes up about ten percent of total phosphate in typical pig manure, the remainder is in either organic or inorganic solid form. To increase P recovery from this resource, manure can be stored anaerobically (fermented) to increase acidity, which has been to shown to produce higher concentrations of PO_4 in a week of storage. However, manures from different farms can vary significantly in chemical properties and this technique may only be effective to varying degrees. This experiment investigated chemical changes from anaerobic fermentation of manures collected from several commercial pig operations in Manitoba.Fresh manures were placed in triplicate stirred anaerobic digesters and monitored daily for pH and analyzed for total solids (TS), volatile solids (VS), alkalinity, VFA, dissolved and total nutrients P, Mg, Ca, NH_4 initially and at 4, 8, and 12 day intervals. Under identical storage conditions manures displayed different phi and PO_4 responses, varying from almost no response to a significant drop in pH and corresponding increase in PO_4 and Mg. Manure pH and PO_4 concentration were negatively correlated in all manures (-0.63 to -0.98). VFA concentration was 9,000 mg/L in manures that had little pH change and 800 mg/L in the manure with the greatest pH shift, eliminating VFA as a driver in pH shift. Through comparison with these and other manures, a relationship was found between manure alkalinity buffering and the acid forming effects of VS as expressed as to mg/L of total alkalinity to g/L VS. A low ratio between the two chemical features enabled reliable prediction of both pH decrease and P-PO_4 and Mg increase in fresh manures. When manures were ranked using this ratio, other parameters such as pH change, P-PO_4, and Mg increase generally corresponded. Thus, manures with low alkalinityA/S ratios became acidic during anaerobic fermentation and consequently increased in P-PO_4 concentration. Both VS and alkalinity are easily performed analysis and the ratio could be used to predict the suitability of a manure to release PO_4 during anaerobic storage. The increase of manure PO_4 increases the total recoverable P by struvite precipitation.The abstract is often the only part of the paper to be read, so include your major findings in a useful and concise manner. Include a problem statement, objectives, brief methods, quantitative results, and the significance of your findings. The abstractshould be no more than 250 words long.