REMOVAL OF ORGANIC AND BIOGENIC COMPOUNDS FROM REJECT WATER WITH CONSTRUCTED WETLANDS

There are 16 dairy processing plants operating in Podlasie region, including 9 that use individual systems for sewage treatment, while others dispose wastewaters to municipal wastewater treatment plants. Personal Equivalent (P.E.) for individual objects ranges from 7000 to almost 240000 at the flow rate from 500 up to 5240 m(3) of sewage daily. Most of objects were built in 70's of the 20th century; they are overloaded due to the increase of production in factories and works observed for over 20 years. The increase of sewage load made also the increase of sewage sludge and reject water amounts. Reject water is in general directed to the beginning of the treatment process, which is a considerable load, namely due to ammonium nitrogen form. Applying the separate reject water treatment using constructed wetland is one of the possibilities to lower the dairy sewage treatment plant loads. The method can be an alternative for advanced and expensive technologies for purifying the reject waters from treatment plants that use anaerobic sludge stabilization. Studies were carried out in August-October 2008 in research installation designed by the author and operating in dairy sewage treatment plant in Bielsk Podlaski. Reject waters generated in sewage sludge thickening chamber were subject to purification. Mean pollutants concentrations in reject water were: BOD5 - 118.6 mg O-2 . dm(-3), COD - 242.1 mg O-2 . dm(-3), Kjeldahl's nitrogen - 17.2 mg N-TKN . dm(-3), ammonium nitrogen - 10.4 mg N . dm(-3), and total phosphorus - 7.2 mg P-T . dm(-3). BOD5 removal efficiency was 69.4 %, COD 53.7 %, Kjeldahl's nitrogen 55.8 %, ammonium nitrogen 72.1 %, and total phosphorus 19.4 %, on average. Mean effect of organic substance removal measured as BOD5 was achieved at the level of 20.6 g BOD5 . m(-2) . d(-1), while ammonium nitrogen 1.87 g N-NH4 . m(-2) . d(-1). The study confirmed the usefulness of constructed wetland method application for separate treatment the reject waters from aerobic sewage sludge stabilization. At present, studies on the object designed for reject waters purification for a real scale, were begun. It is the first object of that type, installed in dairy sewage treatment plant in Poland, and it was designed as a result of the research work realized by the author in 2007-2009.