Operation of the Nowa Sarzyna sewage treatment plant (processing both municipal and industrial wastewaters) in 2003 was analyzed and math. modeled. The sewage treatment consisted of mech. and biolog. purith. of wastewaters and mechn. dewatering of the sludge. The crude and treated sewages were analyzed for pH, suspensions, BOD, COD, as well as for Cl-, SO4-2, volatile phenols, total N and P contents. The treatment resulted in decrease in BOD from 160250 mg/L down to 1.1-4.5 mg/L and in COD from 328-669 mg/L down to 28-106 mg/L. Four math. linear models were used to correlate exptl. data.