Wojciech Dąbrowski, Józefa Wiater
The paper presents author's experience related to reject water produced during aerobic sludge treatment in dairy waste water treatment plant. Problem of reject water relates to almost every biological sewage treatment plant that applies aerobic or anaerobic stabilization of sewage sludge. Reject water is a byproduct like sewage sludge. It is usually returned to the beginning of purification line. Dairy WWTP belonging to Bielmlek Bielsk Podlaski was modernized in 2011 after 30 years exploitation with “Promlecz” system. Flotation process was implemented as high efficiency biological treatment witch SBR system too. The main aim of investigation was to find out the quantity and quality of reject water and raw sewage after modernization. Author presents results obtained between September and November 2012. Mean pollution concentration in reject water and sewage from Bielmlek dairy W.W.T.P. after modernization were: BOD5 -114 mg O2/l in reject water and 1520 mg O2/l in sewage, COD-290 mg O2/l in reject water and 1890 mg O2/l in sewage, TKN-2.4 mg N/l in reject water and 65,0 mg N/l in sewage, ammonia nitrogen 19.8 mg N-NH4/l in reject water and 1.8 mg N-NH4/l, in sewage and total phosphorus -7.5 mg P/l in reject water and 9.8 mg P/l in sewage. The mean quantity of reject water was 45 m3/day while raw sewage 780 m3/day. The share of reject water load in row dairy sewage load was counted and it was only 0.7% for BOD5, 8% for TKN and 38% for ammonia nitrogen. Due to high load of ammonia nitrogen in reject water it is justified to implement separate treatment to decrease it. In 2010 in Bielmlek dairy WWTP was started full scale installation to treat reject water with constructed wetland. It was implementation of his research project “Evaluation of constructed wetlands usefulness to purify reject water from sludge aerobic processing in dairy wastewater treatment plants”. Due to composition of reject water after modernization of dairy WWTP. It was counted that the share ammonia nitrogen load in row wastewater can be decreased from 38.6% without treatment to 12.4% after treatment with constructed wetland.
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