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A laboratory study of struvite precipitation after anaerobic digestion of piggery wastes

Wrigley, T.J., Webb, K.M. and Venkitachalm, H. (1992) A laboratory study of struvite precipitation after anaerobic digestion of piggery wastes. Bioresource Technology, 41 (2). pp. 117-121.

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A dilute (0·3% TS) but relatively strong (COD 10 000 mg litre-1) piggery wastewater was used as feed in 1·6-litre laboratory anaerobic digesters. During batch digestion (56 days), NH3-N increased from 500 to 800 mg litre-1 and PO4-P from 21 to 30 mg litre-1 while Mg concentrations decreased from 32 to 20 mg litre-1. A continuously fed digester (mean residence time of 64 days) produced similar increases in NH3-N concentrations and reductions in concentrations of PO4-P (22 to 10 mg litre-1) and Mg from 32 to 20 mg litre-1. X-ray diffraction of the digester sludge indicated that langbeinite (K2Mg(SO4)3) was precipitated whilst it appeared that very fine crystals of Ca, Mg and PO4 compounds remained in suspension. The addition of MgSO4 to the batch supernate raised to a pH of 9 led to a reduction in PO4-P concentrations from 33 to 7 mg litre-1 and the supernate from the continuous digester at a pH of 9 from 10 to 0·1 mg litre-1. The precipitate formed by this reaction was comprised of struvite (MgNH4PO4.6H2O), apthitatite (K3Na(SO4)2) and thermarite (Na3SO4). The reduction of PO4-P concentrations to less than 1 mg litre-1, a significant water quality criterion in the management of eutrophication, is of importance. The production of struvite as a valuable fertilizer may offset much of the cost of this form of wastewater treatment.

Item Type: Journal Article
Murdoch Affiliation(s): School of Biological and Environmental Sciences
Publisher: Elsevier BV
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