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IntroductionAccording to the Polish Standard PN-EN 12566, household wastewater treatment plants (WWTPs) are defi ned as those serving up to 50 inhabitants. According to the Water Law (Prawo wodne 2001), the maximum throughput of objects of the type is 5 m 3 ·day -1 , and according to the Building Law (Prawo budowlane 2003) -7.5 m 3 ·day -1 . Objects of this type, in Poland and worldwide, are installed primarily in areas with scattered housing, where the construction of a sewerage system and a collective wastewater treatment plant is not economically viable.Data from the Central Statistical Offi ce (GUS 2014) indicate that by the year 2013 in Poland 154,944 household wastewater treatment plants were built. Current estimates and projections (Jóźwiakowski 2012a) indicate that in the coming years over 555 thousand new household wastewater treatment plants can be built in Poland. In the case of building such a great number of objects it is necessary to use technologies that have been tested in practice and that are characterised by a high effi ciency of operation, and that are easy to build and to operate.Household wastewater treatment plants are characterised by specifi c features that set them apart from large collective wastewater treatment plants (Lundin et al. 1999, Mucha and Mikosz 2009, Roeleveld et al. 1997 Abstract: This paper presents the use of multi-criteria analysis as a tool that helps choosing an adequate technology for a household wastewater treatment plant. In the process of selection the criteria of sustainable development were taken into account. Five municipal mechanical-biological treatment plants were chosen for the comparative multi--criteria analysis. Different treatment technologies, such as sand fi lter, activated sludge, trickling fi lter, a hybrid system -activated sludge/trickling fi lter and a hybrid constructed wetland system VF-HF type (vertical and horizontal fl ow) were taken into account. The plants' capacities were 1 m 3 •d -1 (PE=8) and they all meet the environmental regulations. Additionally, a solution with a drainage system was included into the analysis. On the basis of multi-criteria analysis it was found that the preferred wastewater treatment technologies, consistent with the principles of sustainable development, were a sand fi lter and a hybrid constructed wetland type VF-HF. A drainage system was chosen as the best solution due to the economic criteria, however, taking into consideration the primary (ecological) criterion, employment of such systems on a larger scale disagree with the principles of sustainable development. It was found that activated sludge is the least favourable technology. The analysis showed that this technology is not compatible with the principles of sustainable development, due to a lack of proper technological stability and low reliability.

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The purpose of this paper is to discuss the problem of changes of effectiveness of Kickuth-type constructed wetland with subsurface flow applied to domestic wastewater treatment. This study is based on an example of a wetland 3000 m in surface, serving 800 inhabitants, located in Poland. The results of chemical analysis showed that after an initial year of 'start-up time', the efficiency of pollutant removal gradually increased to reach an apex in the 6th year of operation. Such maximum efficiency continued up to the 10th year of operation; afterwards it gradually dropped. Moreover, after 12 years of operation, a serious problem with overland flow was observed, which indicated the porous media clogging processes.