Abstract
Struvite production mediated by bacteria has opened up a new route for phosphorus recovery from wastewater streams but its application to digested sludge dewatering liquors is not yet well understood. This study investigates the growth and biological struvite production of selected bacteria in wastewater liquors with pHs between 5.7 to 9.1. The bacterial growth was assessed through flow cytometry. Bacillus pumilus, Halobacterium salinarum and Brevibacterium antiquum remained viable at pHs between 5.7 to 9.1 but B. antiquum was able to grow at pHs between 7.3 to 7.8. Further analysis allowed the identification of crystals as struvite in tests between pH 7.3 to 8.3. All strains were capable of producing struvite at a range of pHs, but the highest production of 135–198 mg/L was observed for pHs between 7.3 to 8.3. At pHs > 8.3, precipitation of struvite and calcium compounds was observed in inoculated and non-inoculated tests. This study demonstrates that biological struvite production can occur at a wide range of pHs, hence significantly different from chemical struvite precipitation that occurs at pH > 8.3, making it a potentially viable process for phosphorus recovery as struvite from wastewater streams and sludge liquors without strict pH control.
Highlights
Phosphorus (P) is an essential element in all organisms and a key nutrient in agriculture limiting food production
Taking advantage of the potential for high pH variability of sludge liquors and to minimise costs associated with the addition of chemicals, pH increase through CO2 stripping through increased agitation or aeration is used in full scale processes for liquors from biological nutrient removal (BNR) sites[6]
As an alternative process to chemical struvite precipitation, a recent study demonstrated the ability of selected bacteria to form bio-struvite in activated sludge liquors and in dewatering liquors, opening a completely new route for P recovery via biomineralisation[10]
Summary
Phosphorus (P) is an essential element in all organisms and a key nutrient in agriculture limiting food production. Phosphorus recovery from sludge dewatering liquors lines has been implemented in several WWTPs through chemically induced struvite precipitation[4]. Induced struvite precipitation in the liquors line has the advantage of reducing the return of P to the head of the works, as well as decreasing operational costs by minimising scale formation (calcium phosphate and struvite) in the pipelines and pumps. This process allows for the recovery of P as struvite which can be used as an agricultural fertiliser[9]. No relationship was found between the taxonomic status of a given strain and its ability to form bio-struvite[16] as this property has been reported in aerobic, chemoorganothrophic, halotolerant and halophilic bacterial strains[14]
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