The influence of percentage share of municipal landfil leachates in a mixture with synthetic wastewater on the effectiveness of a treatment process with use of membrane bioreactor

The investigations were focused on the determination of the most favorable amount of leachates treated along with a synthetic sewage in a membrane bioreactor. The leachates percentage share was changed over a range of 3-40 vol%. COD and BOD₅ of the leachates varied from 3,000 to 3,500 mg/dm³ and from 170 to 280 mg/dm³ respectively. The leachates were characterized by a high concentration of ammonia nitrogen (over 1,000 mg/dm³) and low BOD₅/COD ratio (0.06 in average), which indicated their negligible susceptibility to biodegradation. The concentration of activated sludge in the membrane bioreactor was maintained within 3.5-4.0 g/dm³, the sludge load with contaminants reached the level of 0.1 gCOD/gDMd while the oxygen concentration in the aeration tank was 4.0 mgO₂/dm³. The system operated in a 12-h cycle. The degree of impurities removal was assessed analyzing changes in the following indicators: COD, BOD5, TOC, N-NO^-₃, N-NH⁺₄, Ptot. The results revealed that the volume of leachates in the treated mixture of sewage should not exceed 10 vol%. All the tests showed a decrease in COD and BOD₅ of around 90%. The only indicator which exceeded the permissible value was nitrate nitrogen. Thus, the leachates purified by activated sludge were additionally treated by reverse osmosis