Polyphosphate salt and organic acid in deliming to reduce nitrogenous compounds in tannery wastewater

Abstract

Deliming is a process in leather manufacturing to remove lime from the limed pelt. In conventional deliming, nitrogenous pollutants (ammonia-nitrogen, NH₃-N, and Total Kjeldahl Nitrogen, TKN) are released, creating unfavorable conditions for aquatic life. In this study, a combination of pyruvic acid (PA) and polyphosphate salt (PPS) is used in deliming instead of ammonium sulfate to reduce NH₃-N and TKN in tannery wastewater. Results revealed that deliming with PA (0.5 %) + PPS (1.0 %) for 90 min showed superior reduction of TKN (86.68 %), NH₃-N (97.56 %), electrical conductivity (57.68 %), salinity (66.73 %), total dissolved solids (63.3 %), chemical oxygen demand (83.61 %), and biochemical oxygen demand (15.9 %) in the discharged wastewater. The hydroxyproline released in the experimental deliming (PA + PPS) wastewater was much lower than that of the conventional technique. The combination of PA + PPS deliming agent removed calcium to an acceptable level of chelation. The physical and organoleptic properties, shrinkage temperature, and thickness variation were comparable to the standard requirements. SEM photographs of delimed pelt and crust leather illustrated a similar fiber orientation, whereas the Pseudo-Second-Order (PSO) kinetics revealed an impressive reaction for the deliming effect compared to Pseudo-First-Order (PFO). Hence, this study provided a new pathway in leather making to reduce pollution, maintaining an environmentally friendly approach.