Recovery of organic nitrogen from beamhouse wastewater in a hair recovery process

Abstract

In the leather industry, in addition to the extrinsic contamination attributable to chemical products not absorbed by the hides, there is intrinsic contamination produced by the hides themselves. From each 100kg of raw material, 15kg of solubilised protein will end up in wastewater in the early stages of the process of transforming hides into leather. These proteins contain nearly 18% of nitrogen. In this study it is proposed to recover organic nitrogen from the proteins present in the effluents of the beamhouse operations of hides and the subsequent revalorization of the protein fraction obtained. This work seeks to characterize (the chemical oxygen demand (COD), total nitrogen, ammonium nitrogen, total soluble nitrogen, particulate nitrogen, organic nitrogen and protein) the wastewaters, individually or in groups, of the various beamhouse operations (soaking, unhairing-liming, washing, conditioning, deliming, bating, washing and pickling) with hair recovery. The studies are presented of the determination of the pH value (adjusted by means of buffers of acetic acid/sodium acetate) at which the greatest precipitate of the protein fraction is produced. In addition, the following tests were performed to characterize these precipitates: determination of the quantitative composition of the main components of the protein fraction (humidity, proteins, free amino acids, fats and other matter soluble in dichloromethane and ash); heavy metals content, calcium, magnesium, potassium and sodium and the composition in total amino acids with prior acid hydrolysis of the protein fraction with 6N hydrochloric acid.