Crystal seed-enhanced ammonia nitrogen and phosphate recovery from landfill leachate using struvite precipitation technique

Nitrogen and phosphorous are limiting and crucial elements for all living organisms. The recovery of nitrogen and phosphorous as struvite gained attention due to its ecofriendly fertilizer application. In the present study, feasible recovery of NH4+ -N available in the landfill leachate with addition of economically viable waste resources like sewage sludge and Mg2+ source as struvite is investigated. However, the fertilizer application of struvite depends upon its purity, which in turn is influenced by pH, molar ratio, and presence of other ions. Laboratory scale studies are conducted to find optimum pH and molar ratio. The results of the studies demonstrated the optimum pH being 9.5 along with PO43- -P: Mg2+: NH4+ -N molar ratio of 1:1.3:1 is the best condition for struvite formation. To further augment the struvite precipitation kaolinite seed is added to the solution and optimized seed dose is 20 g/L. Existence of Ca2+ and Na+ ions in the solution exhibits a negative impact on struvite precipitation. Response surface methodology is employed to understand the interactive influence of parameters on recovery efficiency. The recovered precipitate consists of 82.5% struvite with PO43- -P: Mg2+: NH4+ -N ratio 1:1.1:0.9. Also, bioavailability of PO43- -P in the recovered precipitate is 89.3%; this signifies high performance of precipitate as fertilizer. Economic assessment highlights that the struvite production is profitable and the profit gained is 159.5$/m(3).