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

Part 2. Characteristics of sludges from two-stage pretreatment

The need for two-stage physicochemical pretereatment of post-processing wastewaters from construction chemicals manufacturing results from the need of preliminary preparation of wastewaters before the stage of their final biological treatment. After elimination, mainly dispersed phases at the first stage, the second stage consists in processing of the soluble load, most frequently with the use of oxidation or deep oxidation in order to regulate the basic BOD5/COD, COD(BOD5)/N, COD(BOD5)/P and N/P ratios towards the values conditioning their biological decomposition, for example with the use of active sludge methods in different variants of technical solutions. This part presents the assessment results for sludges generated in full technological scale at two installations based on two-stage physicochemical pretreatment of process wastewaters from the selected products of construction chemicals manufacturing. Pretreatment at the second stage was carried out with the use of oxidation or deep oxidation methods, which was reflected in the composition of sludges being subject to assessment in this part of research. At the first stage, coagulation methods based on the application of iron coagulants of PIX® category or the alkine ones of PAX® category were used, and at the second one – oxidation with the use of KMnO4 or Fenton’s system were applied. For generated in this way, mixed in the thickening tank sludges before pressing, the risk assessment with the use of RAC code was made on the basis of the analysis of fractional composition of selected heavy metals. It was found that dewatered by pressure mixed sludges present low risk (LR) in case of Cd, Cr, Cu, Ni, Pb and Zn and the moderate risk (MR) concerning Mn, in case of application of potassium permanganate at the second stage of pretreatment. In case of application of Fenton’s system at the second stage of pretreatment, the subject sludges presented low risk (LR) concerning all analysed heavy metals. In accordance with TCLP criteria, mixed sludges from two – stage physicochemical pretreatment of process wastewaters from manufacturing of the selected products of construction chemicals were classed as non-toxic wastes.

Keywords: process wastewaters from construction chemicals manufacturing, sludges from two-stage physicochemical pretreatment, TCLP procedure, fractional composition of heavy metals in sludges, risk assessment code (RAC).