Evaluation of surfactant removal efficiency in selected domestic wastewater treatment plants in Poland

The aim of this study was to evaluate the work of a two types of household sewage treatment plant: wetland wastewater treatment plant (ORS type) and treatment plant of SBR type (SBR-K-6 type). Physicochemical analyses of selected pollution indices (BOD5, COD, total suspension, total phosphorus) and surfactants were carried out and compared with currently applicable values of such indexes according to the Regulation of the Minister of the Environment in Poland on the conditions to be met when discharging sewage into water or soil, and on the substances particularly harmful to the aquatic environment. The removal efficiency of organic compounds, expressed as COD and BOD5, reached the threshold of 90%, which is required in regulations. In contrast, the effects of removal of biogenic compounds were low - in case of total nitrogen the removal rate reached approx. 40% and the desired admissible concentration of 30 mg N/L was not achieved. The reduction efficiency of total suspended solids reached 57.0 and 59.6% for the ORS and SBR-K-6 type objects, respectively, and therefore the required threshold of minimum 90% was not reached. Anionic surfactants were removed by up to 98 and 88% in the ORS and SBR-K-6 type wastewater treatment plants, respectively. Lower removal efficiency was achieved in case on non-ionic surfactants, which reached 76% for the ORS type object and 56% for the SBR-K-6 type object. This article proven high wastewater treatment efficiency and lower than necessary concentrations in the effluent from domestic wastewater treatment plants may be achieved mainly by proper exploitation of the devices and appropriately selected vegetation.