The Feasibility Evaluation of Nitrogen Recovery from Tannery Sludge Leachate Combined with Phosphogypsum Leachate by the Struvite Precipitation

The use of struvite (MgNH4PO4 center dot 6H(2)O) to precipitate nutrients from tannery sludge leachate is an attractive option. However, the limited phosphorus content in TSL makes it necessary to add a phosphorus source to increase nitrogen removal, resulting in higher reaction costs. This study investigates the optimal conditions for nitrogen removal from tannery sludge leachate using disodium hydrogen phosphate and phosphogypsum leachate as phosphorus sources and compares the costs of both methods with an economic analysis. The results show that phosphogypsum leachate is a feasible alternative phosphorus source, both technically and economically. Under the conditions of pH= 8.5, a tannery sludge leachate/phosphogypsum leachate volume ratio of 1:6, and a Mg/N molar ratio of 1.2:1, the removal rates of NH4+-N and PO43- were 56.5% and 85.1%, respectively. Although the ammonia nitrogen removal rate was reduced by 14.9 compared to the use of a chemical phosphorus source, the treatment cost was only 2.46 $/m(3). X-ray diffraction and scanning electron microscopy-energy dispersive X-ray spectroscopy results confirmed that the precipitates produced were struvite. The harvested struvite had a precipitation content of 51.3%, with low content of heavy metal impurities, making it suitable for use as fertilizer. Furthermore, the toxicity of the treated leachate to Vibrio qinghaiensis sp.-Q67 was reduced by 30.2%. The recovery of nutrient elements from tannery sludge leachate promotes the utilization of waste resources and holds promising applications.

Automated summary

The use of struvite as a precipitation method for removing nutrients from tannery sludge leachate is an attractive option, but additional phosphorus sources are needed to increase nitrogen removal. This study explores the optimal conditions for nitrogen removal using different phosphorus sources and compares the costs. The results show that phosphogypsum leachate is a technically and economically feasible alternative phosphorus source, and can significantly reduce treatment costs.