Potential phosphorus recovery by struvite formation.
Formation of struvite (MgNH4PO4 x 6H2O) at sewage treatment works can cause operational problems and decrease efficiency. Struvite has a commercial value and the controlled formation and recovery of it would be beneficial. A mass balance was conducted at full scale across the whole sewage treatment plant in order to identify a stream to conduct bench-scale struvite crystallisation studies. The most suitable stream was identified as the centrifuge liquors. The average flow of the liquor stream was 393 m3 d(-1) and the composition was as follows: 167 mg L(-1) phosphorus, 44 mg L(-1) magnesium, 615 mg L(-1) ammonium, 56 mg L(-1) calcium and 2580 mg L(-1) of alkalinity. The pH averaged at 7.6 and the stream had a predicted struvite precipitation potential of 140 mg L(-1). Struvite crystallisation occurred quickly during the trials, by raising the pH of the centrifuge liquors to 9.0 and dosing with magnesium. Up to 97% phosphorus removal as struvite was achieved. Struvite formation occurred when the molar ratio of magnesium:phosphorus was at least 1.05:1. Below this ratio phosphorus removals of 72% were observed, but not exclusively as struvite. Annual yields of struvite were calculated to be 42-100 tonnes a year, depending on the dose regime. Revenue from the sale of produced struvite could be between Pound Sterling8400 and Pound Sterling20,000 a year.
Jaffer
Y
Y
School of Water Sciences, Cranfield University, Bedfordshire, UK.
Clark
T A
TA
Pearce
P
P
Parsons
S A
SA
D003365:Costs and Cost Analysis; D003460:Crystallization; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000737:chemistry; D017616:Magnesium Compounds / Q000737:chemistry* / Q000191:economics / Q000302:isolation & purification*; D010710:Phosphates / Q000737:chemistry* / Q000191:economics / Q000302:isolation & purification*; D010758:Phosphorus / Q000302:isolation & purification*; D010865:Pilot Projects; D012722:Sewage / Q000737:chemistry; D000069877:Struvite; D018508:Water Purification / Q000191:economics
D017616:Magnesium Compounds; D010710:Phosphates; D012722:Sewage; D010758:Phosphorus; D000069877:Struvite; D008274:Magnesium