Identifying and Overcoming Hindrance to Struvite Recovery from Filtrate of Anaerobically Digested Dairy Manure
Abstract:Struvite recovery has been demonstrated at pilot and full scales for phosphorus removal from municipal wastewater, swine wastewater, and industrial wastewater at elevated pH and high Mg2+:NH4 +:PO4 3− ratios. Anaerobically digested dairy manure is rich in magnesium, ammonium, and phosphate. However, struvite recovery from anaerobically digested dairy manure has been challenging. This study examined struvite recovery from the filtrate of anaerobically digested dairy manure, which was separated from manure solids in a pebble filter – vertical flow subsurface wetland series. Unlike mechanically separated dairy manure liquid, the filtrate had little particulate phosphorus and magnesium and substantial particulate calcium. Water extraction and acid extraction increased Ca2+ by 112% and 28% respectively. Batch precipitation tests showed linear decreases of orthophosphate concentration reduction and precipitate mass as more real manure filtrate was mixed with artificial manure filtrate, indicating hindrance to struvite precipitation from the manure filtrate. Energy dispersive X-ray analysis confirmed that the precipitates from 100% artificial manure filtrate were struvite. The hindrance could be attributed to high ionic strength, Ca2+ concentration, Ca2+:Mg2+ ratio, alkalinity, or Cl−. It was found that the manure filtrate could be pretreated via chemical precipitation at pH 9–10 for Ca removal while retaining Mg2+ and PO4 3−. The Ca precipitates were identified by energy dispersive X–ray analysis to be likely CaCO3.
Document Type: Research Article
Publication date: January 1, 2011
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