Waste lime as a potential cation source in the phosphate crystallization process

In this study, the feasibility of waste lime as a potential cation source in phosphate crystallization process was investigated using laboratory scale upflow reactors, adopting sequencing batch type configuration. This research focused on its successful application in a novel sludge treatment process, which is comprised of a high performance fermenter (operating conditions: 55 degrees C and pH 9) followed by a crystallization reactor. In the struvite precipitation test using synthetic wastewater, considerable nutrient removal (about 60%) in the form of ammonia and phosphate was observed within 0.5 - I hr of retention time, and only small amounts (< 5%) of ammonia stripping occurred naturally due to the alkaline (pH 9) characteristic of the feed substrate. By replacing the synthetic wastewater with the fermentation effluent, the optimal dosage of magnesium salt for struvite precipitation was 0.86 g Mg g(-1) P, similar to the mass ratio of the struvite. The optimal dosage of waste lime was 0.3 g l(-1), resulting in 80% of NH4-N and 41% of PO4-P removal, at about 3 hrs of retention time. Microscopic analysis showed that amorphous crystals were mainly observed in the settled solids with waste lime addition whereas prism-like crystals were found in the system with magnesium salt added. Mass balance analysis in full-scale model plants (Q=158,880 m(3)d(-1)) based on the present experimental results revealed that nutrient recycle loading from side stream to main liquid stream would be significantly reduced. The results of the experiment reveal that reuse of industrial waste lime in a nutrient recovery system has the various advantages such as higher economical benefits and sustainable treatment of the industrial waste.