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Wastewater treatment in semi-natural systems, such as a hydroponic lagoon operating as the third stage of treatment, is becoming more and more popular because of the efficiency of organic matter and nutrient removal. The article presents an analysis of the efficiency of pollutant removal at the mechanical-biological wastewater treatment plant in Gronów with a capacity of Qd = 1125m3/day and a load of 9375 PE. The wastewater treatment plant operates on the basis of activated sludge and biomass settling technology on submerged flow beds. The treatment plant is characterized by a very high variability of wastewater inflow during the year due to periodic inflow of wastewater from tourist resorts in Łagów. The average efficiency of removing pollutants from wastewater was: BOD5 - 98.5%, COD - 92.8%, total suspended solids - 93.2%, total nitrogen - 86.1% and total phosphorus - 69.5%. The study showed that the use of a hydroponic lagoon in the technological system improved the efficiency of wastewater treatment by 1.7% for BOD5, 0.9% - COD, total suspended solids by 4.3%, 6.4% for total nitrogen and total phosphorus- 3.3%.

The article assesses the efficiency of pollutant removal at the sewage treatment plant in Goleniów after modernization of the technological system. The extension and modernization of the existing installation resulted from the need to adapt the treatment plant to accept larger loads of pollutants, improve the parameters of treated sewage discharged to the receiver, and the poor technical condition of the equipment. Before the modernization of the treatment plant, an increase in the loads of COD, BOD5, and periodic total suspended solids in raw sewage was observed as well as a reduction in the efficiency of removing pollutants from the sewage. The efficiency of removing pollutants after modernization was in the range of BOD5 - 94.4 ÷ 99.8%, COD - 89.3 ÷ 98.9%, total suspended solids TSS - 95.3 ÷ 99.7%, total nitrogen - 64.1 ÷ 95.4%, and total phosphorus - 75.4 ÷ 99.4%.

High effectiveness of organic pollutants and nutrients removal is achieved in biological wastewater treatments plants – in case of proper exploitation of these objects. Nitrogen and phosphorus transformation or removal depends on many physic – chemical and biochemical conditions, deposit and environmental factors. A rule for treating wastewater consists in decomposition of organic compounds included in wastewater in water-soil environment. Removing contaminations is performed as a result of sorption of contaminations, bio-chemical oxidation-reduction reactions and biological activity of soil microorganisms and hydrophyte flora. The research has been carried out in the constructed wetland in Małyszyn (1300 EP). The treatment plant operates in horizontal system, with under-surface flow of wastewater.

The article assesses the physical and chemical parameters of drinking water before and after the modernization of the technological system of water treatment station in Drzenin, Poland. The extension and modernization of the existing installation was necessary due to the poor technical condition of the devices, increasing demand for water in recent years and the periodic exceeding of the permissible values of water quality indicators. Analysis of physical and chemical properties of drinking water after the modernization of the system showed the effectiveness of the water purification processes used and the correct selection of the technological line. The obtained water quality parameters were in accordance with the Regulation of the Minister of Health on the quality of water intended for human consumption (Journal of Laws of 2017, item 2294).

The article presents physiochemical parameter changes in water supply network of Zielona Góra. On the basis of the obtained test results, the impact of prolonged retention of water in the network on its quality was determined, at the measuring points located on the territory of Zielona Góra. It was shown that together with an increase in distance of measuring points from Water Treatment Plant, content of mainly iron, turbidity and colour increased too. In the results analysis, it was determined that retention time and water distribution are the most significant factors in the network contributing to deterioration of water quality at measuring points.

The article analyzes the effectiveness of individual Actibloc wastewater treatment plants (produced by Sotralentz) working in the technology of low-rate activated sludge in the Sequential Batch Reactor (SBR) system. The assessment of the effectiveness of household wastewater treatment plants was made on the basis of pollutants: BOD5, COD, total suspended solids, total nitrogen and total phosphorus. The research objects were four household sewage treatment plants located in: Lubań, Kłębanowice, Stara Rzeka and Kościan. The efficiency of removing pollutants in the examined facilities was in the range of: BOD5 92.2 ÷ 97.2%, COD 82.6 ÷ 89.9%, total suspended solids 90.2 ÷ 96.2%, total nitrogen 50.8 ÷ 83.1%, total phosphorus 46.5 ÷ 73.6%. The treated wastewater met the requirements set out in the Regulation of the Minister of the Environment on the conditions to be met when discharging sewage into water or soil, and on substances particularly harmful to the aquatic environment (Journal of Laws 2014, item 1800) in terms of indicators such as BOD5, COD, total suspended solids and total nitrogen. The effectiveness of phosphorus removal in the studied treatment plants was much lower.

The 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.

The article presents the results of the basic physical and chemical indicators of water quality in the upper and lower reaches of the river Obrzyca. Assessment of water quality is important because of located at the estuary part of the river water intake surface for Zielona Góra . The water from the initial reaches has been qualified to III class of water quality based on the achieved results. According to the Regulation of the Minister of Environment from 22 October 2014 on the classification of surface water bodies and environmental quality standards for priority substances (OJ 2014 pos. 1482), samples of water taken from Obrzyca classify this part of river to II class of quality. According to the Regulation of the Minister of Environment of 27 November 2002 on the requirements to be met by surface water used for public supply of water intended for human consumption (OJ 2002 No. 204, item. 1728), Obrzyca’s water belong to A3 category of water taken to consume by people.

The paper presents results of studies concerning the designation of COD fraction in the raw, mechanically treated and biologically treated wastewater. The test object was a wastewater treatment plant with the output of over 20,000 PE. The results were compared with data received in the ASM models. During investigation following fractions of COD were determined: dissolved non-biodegradable SI, dissolved easily biodegradable SS, in organic suspension slowly degradable XS and in organic suspension non-biodegradable XI. Methodology for determining the COD fraction was based on the guidelines ATV-A 131. The real percentage of each fraction in total COD in raw wastewater are different from data received in ASM models.

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.

This paper presents the results of the research work related to the removal efficiency from wastewater organic pollutants and suspended solids at HSSF (horizontal subsurface flow) constructed wetland. The average effectiveness defined as loss of value COD in wastewater has reached 77%, for BOD5 - 80% and TOC - 82%. The effect of seasonal temperature changes and the period of plant vegetation and rest on the effectiveness of wastewater treatment were also analyzed. The results of the presented research showed a decrease in the efficiency of removing organic pollutants from wastewater and suspended solids in the autumn and winter. During the vegetation the object in Małyszyn has been characterized by the effectiveness of wastewater treatment at the level of 78% for COD, 82% for BOD5, and in the non-vegetation period the effectiveness has decreased up to 75% for COD and 74% for BOD5. During the plants growth the total suspension was removed in 88%, whereas during the plants rest efficiency of removing lowered to 69%.

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.