The paper presents the results of studies concerning the designation of COD fraction in raw wastewater. The research was conducted in four municipal mechanical-biological sewage treatment plants and one industrial sewage treatment plant. The following fractions of COD were determined: non-biodegradable (inert) soluble SI, biodegradable soluble fraction SS, particulate slowly degradable XS and particulate non-biodegradable XI. The methodology for determining the COD fraction was based on the ATV-A131 guidelines and Łomotowski-Szpindor methodology. The real concentration of fractions in raw wastewater and the percentage of each fraction in total COD are different from data reported in the literature.

The removal of nitrogen compounds in constructed wetlands depends on various physical, chemical and biomechanical factors as well as on conditions of the environment. The paper presents the results of a statistical analysis of the depositing of nitrogen at HSSF (horizontal subsurface flow) construcred wetland. The results of the substrate showed that the highest contents of nitrogen existed in the surface soil layer up to 20 cm of the depth. Nitrogen accumulation decreased in the deposit with depth, and in the direction of the wastewater flow.

Abs tra ctThe article characterises most frequently selected by investors individual mechanical and biological sewage treatment systems. On the basis of gathered information and technical documentation, technical and technological analysis of the devices was conducted. Assess factors include technology, structure, workflow, control, exploitation conditions, and sewage treatment system effectiveness. On the basis of conducted analysis, limited possibility of using activated sludge wastewater treatment in a flow system was established due to the difficulty of stabilizing the whole system. An optimal solution for individual wastewater treatment system are solutions of activated sludge technology in SBR system and hybrid technologies.does not have access to a sewage system. Situation in the city stands decidedly better, with only 10% of inhabitants not using sewage system [3,7,13]. Habitants of non-canalised areas use onsite sewage collection systems: holding tanks and onsite wastewater treatment systems. 2 333 thousands of the devices functioned in Poland in 2016, ca. 91% of which were holding tanks. For the last few years, a systematic decrease of holding tanks number has been noted, with simultaneous increase of onsite wastewater treatment systems number. Number of holding tanks decreased from about 2 136 thousands in 2015 to 2 117 thousands in 2016 (by 0.9%), while number of onsite wastewater treatment systems increased from about 203 thousands in 2015 to about 217 thousands in 2016 [3]. Amount of wastewater production in the country will be increasing due to easier access to water systems, building of new houses, and higher standard of resident buildings equipment. Thus, investing in individual wastewater treatment systems in areas of scattered housing, where common sewage systems are most frequently absent, becomes necessary [1,4,5,6]. In the last few years, onsite sewage collection systems have been gaining more and more popularity. It is connected primarily to decidedly lower cost of system purchase and relatively low exploitation costs. The basis of onsite wastewater treatment system selection should be not only the economic criterium, but also technological and environmental aspects. The best solutions should be technologically effective, environmentally friendly, and acceptable in economic and exploitative aspects [4,5,8,10].