S. Żak, T. Rauckyte-Żak
University of Science and Technology, Faculty of Chemical Technology and Engineering, Bydgoszcz, PL


Building own plant for physicochemical pretreatment of process wastewaters is inextricably linked with considerable financial outlays. It is often connected with the lack of ready-made solutions concerning significantly effective pretreatment methods and suitable apparatus configuration enabling to obtain the so called ecological effect. Recently, new economic entities appeared in our country, the core of which business activity consists in providing services related to collection and neutralization of liquid wastewaters after their processing which are process wastewaters originating from various branches of industry. This paper presents the results of assessment regarding sludges originating from the processes of physicochemical pretreatment of process wastewaters from low-tonnage productions carried out on autonomous installations used for neutalization of such wastes. Two independent installations for physicochemical pretreatment where sludges were generated were subjected to assessment. They consisted of flow storage and averaging tanks, where separators for light liquid fractions (scoop conveyors), process reactors, dosing stations and sludge dewatering units were installed. Neutralization, chemical precipitation, coagulation and sorption on bentonites were used at these installations for pretreatment and sludge thickening was carried out with the use of floculation in conditions which required slow-moving mixing or streams of fine bubble air. Dewatering of generated sludges was carried with the use of chamber pressure presses. Due to significant diversity of wastewaters and charges contained in them which are directed to pretreatment installations, the obtained sludges could also be described as significantly heterogeneous and diversified as far as leachibility level is concerned and the participation of the individual speciation forms determined for the selected heavy metals. On the basis of the fractional composition of such heavy metals as Cd, Cr, Cu, Mn, Ni, Pb and Zn, it was found that the dewatered by pressure sludges from physicochemical pretreatment of wastewaters for example the ones after galvanization show high risk (HR) in relation to Cr, Cu and Zn, and the sludges from physicochemical pretreatment of wastewaters after passivation present moderate risk (MR) conerning Cr and Ni. In accordance with TCLP criteria, these sludges were classified in the respective categories.

Keywords: process wastewaters from the selected branches of industry, sludges from physicochemical pretreatment, TCLP test, fractional composition of heavy metals in sludges, risk assessment code (RAC).