Storage of urine as a pre-treatment for struvite recovery

Struvite (magnesium ammonium phosphate) is a bioavailable fertilizer that has had been successfully recovered from traditional wastewater treatment plant effluents. Since urine is a richer and more concentrated source of phosphorus, it makes sense to recover struvite from the urine collected in dry toilets. Traditional struvite recovery from wastewater effluents requires the addition of a caustic to increase pH and achieve supersaturated conditions necessary for precipitation. This work demonstrates that, by utilizing the urease-driven pH increase, the requirement for a pH modifier disappears, and thus additional cost, is removed. By removing calcium and other non-desirable compounds and allowing the pH to naturally attain an ideal working range, only magnesium needs to be added to recover a pure struvite product. It is shown then, that the storage of urine is an essential step to recovering struvite, not in fact, an obstacle to overcome.