The aim of the study was to determine the influence of the percentage of sewage from septic tanks to the variability of pollutant concentrations in the mixture of sewage undergoing treatment process in the collective sewage treatment plant. The study involved measuring the daily amount of wastewater influent and from septic tanks and determined the percentage of the amount of sewage from septic tanks in relation to the total wastewater being purified. During the 5-year study collected and analyzed 20 samples of sewage, which were made markings indicators: BOD5, COD and total suspension. After the statistical analysis, it was found that with the increase of the share of sewage from septic tanks by 1% increased the value of BOD5 14.6 mgO2•dm-3, increases the value of COD 40.2 mgO2•dm-3 and increases the concentration of total suspension of 21,4 mg•dm-3 in the total mixture of the waste water being purified.
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