Handling of released P from digesters loaded with Bio-P sludge
Phosphates are fixed in the enhanced biological phosphorus removal process and released from the Bio-P sludge in the digesters. The supernatant from digesters with large quantities of phosphate should be treated before it is recirculated to the treatment system to prevent phosphorus over-load in the system. Brackish seawater is concentrated to bittern for struvite precipitation; crystal pellets from drinking water treatment plant is generated to Grey and Yellow Powder for hydroxylapatite precipitation and adsorption. The laboratory results illustrate the bittern has an efficiency of over 90 % for phosphate precipitation in the reject water without optimization at room temperature, pH 9.5, with the ratio of 1:1:1 between Mg, N and P. The Yellow Powder failed in the reject water as a phosphate precipitant. The Grey Powder as a phosphate adsorbent has been optimized in different ranges of pH from 4.4 to 9.5, powder amount from 5 to 10g, adsorption time from 0 to 7h, and temperatures from 20 to 60°C, which achieves 90 % phosphate removal after 5h of adsorption with a capacity of 10mg/g, at room temperature and between pH 4.3~4.8. The bittern and Grey Powder are applicable to remove and recover phosphorus from the reject water, and potential to apply in wastewater treatment plants for practical purposes.