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Controlled struvite crystallisation for removing phosphorus from anaerobic digester sidestreams
1Brisbane Water, 240 Donaldson Rd, Rocklea, Brisbane, QLD 4106, Australia. ppoebw@brisbane.qld.gov.au
Water Research
|March 22, 2001
Summary
Controlled struvite crystallization effectively removes phosphorus from wastewater sidestreams. The pilot-scale magnesium ammonium phosphate (MAP) reactor achieved 94% phosphorus removal, producing a fertilizer compliant with regulations.
Area of Science:
- Environmental Engineering
- Water Treatment Technologies
- Chemical Engineering
Background:
- Enhanced biological phosphorus removal (EBPR) systems generate sidestreams with high phosphorus concentrations.
- These phosphorus-rich sidestreams originate from sludge dewatering in wastewater treatment plants with anaerobic digesters.
- Controlled struvite crystallization offers a method for phosphorus recovery from these challenging wastewater streams.
Purpose of the Study:
- To evaluate the operational performance of a pilot-scale magnesium ammonium phosphate (MAP) reactor for phosphorus removal.
- To assess the efficiency of struvite crystallization in treating centrate from dewatered anaerobically digested sludge.
- To determine the quality of the recovered MAP product for potential fertilizer reuse.
Main Methods:
- A continuously operated pilot-scale MAP reactor (143 L), based on the Phosnix process, was utilized.
- The reactor featured an air-agitated column with distinct reaction and settling zones.
- Magnesium hydroxide slurry was employed for magnesium addition and pH adjustment to approximately 8.5.
Main Results:
- The MAP process achieved a 94% removal of ortho-phosphate from an average influent concentration of 61 mg/L.
- Phosphorus removal efficiency was sensitive to magnesium dosing, with insufficient dosing negatively impacting performance.
- Hydraulic residence time (1-8 h) did not significantly influence the process efficiency.
- The recovered MAP product contained heavy metals (cadmium, lead, mercury) below regulatory limits for fertilizers.
Conclusions:
- Controlled struvite crystallization is a highly effective method for phosphorus removal from wastewater treatment plant sidestreams.
- The pilot-scale MAP reactor demonstrated robust performance, achieving high phosphorus recovery rates.
- The resulting struvite product is suitable for reuse as a slow-release fertilizer, contributing to nutrient circularity.