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Dariusz Zdebik*, Piotr Zawadzki*, Michał Pieczonka**
*Central Mining Institute, Katowice, Poland; **Żory Water Supply and Sewage Company, Poland
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Abstract
The purpose of this work was to analyze work of the sludge part of the wastewater treatment plant in Żory. During the analysed period (years 2015-2017) the wastewater treatment plant in Żory worked in conditions typical for the municipal facilities. The characterization of the sludge generated in the wastewater treatment process has also shown that the sludge properties are typical for the municipal wastewater treatment plants. Based on the data provided by the PWiK Sp. z o. o. in Żory. the characteristics of the technological process were made. This characteristics in a detailed way includes the sludge part of the treatment plant. The analysis of the functioning of the sludge part was performed and the influence of the pollutants load in leachates on the effectiveness of work in the main technological line was characterized. Studies on the functioning of the sludge part showed discrepancies between the design status of the wastewater treatment plant and the real state. This is due to the increasing amount of the wastewater flowing into the treatment plant and the associated increase in the amount of the occurring sludge. The belt press and the digested sludge tank are particularly loaded. The belt press works for about 11.9 h/d with assumed 4.1 h/d. In turn. the residence time of the sludge in the digested sludge tank is about 3 times shorter than assumed. Despite the observed. increasing concentrations of pollutants and the amount of treated wastewater. the plant meets the legal requirements regarding the quality of the wastewater discharged to the receiver by the water-legal permit and the Regulation of the Minister of the Environment. Based on the results of laboratory tests of the wastewater and leachates generated in the process of dewatering on the filter presses. their impact on the efficiency of treatment in the main technological line was characterized. The amount of leachates in relation to the amount of the wastewater flowing into the treatment plant was 1.8%. The leachates had high content of ammonium nitrogen. total phosphorus and total suspended solids. The average concentrations of these parameters were: SNNH4 = 592.6 mg/dm3, SNog = 664.8 mg/dm3, SPog = 197.7 mg/dm3 and SZog = 1100.9 mg/dm3. The average values of BOD5 and COD indices were SBOD5 = 66.4 mg/dm3, and SCOD = 386.9 mg/dm3. The leachates coming from the filter presses carried a significant load of total phosphorus. which constituted on average 27.3% of the total load flowing into the treatment plant. as well as the total suspension and total nitrogen. which maximum load constituted 7.3% (Zog) and 11.8% (Nog) of the total load flowing into the treatment plant. The ratio of COD/BOD5 indices of pollutants of the leachates from the presses was 5.83. which indicated the introduction of hardly biodegradable compounds into the main technological line. In order to increase the efficiency of nitrogen removal in the main technological line it was proposed the implementation of deammonification process of the leachates from the sludge dewatering. aiming to reduce the ammonium nitrogen load. introduced to the biological part of the treatment plant.

Keywords 
wastewater treatment plant, activated sludge, sewage sludges, quality of the wastewater, leachate, sewage sludge management

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