Application of hybrid systems to the treatment of meat industry wastewater

The study aimed to assess the effectiveness of meat industry wastewater treatment applying two hybrid systems of activated sludge and ultrafiltration in: (1) an aerobic bioreactor in combination with ultrafiltration and (2) a bioreactor equipped with separate denitrification and nitrification tanks in combination with ultrafiltration. It was found that it is feasible to treat this wastewater in both systems; however, the aerobic bioreactor necessitated the use of a very low activated sludge loading of 0.017 gCOD/gTS×d. Consequently, the bioreactor equipped with separate denitrification and nitrification tanks proved to be more favourable. The substrate loading of 0.15 gCOD/gTS×d, aeration intensity of 800 dm3 and constant activated sludge loading of 4 g/dm3 were used in this system. The wastewater treated under these conditions satisfied the requirements of the Regulation of the Minister of the Environment of 8 July 2004 and could be discharged into receiving water.

The most favourable substrate loading of activated sludge in the aerobic membrane bioreactor was 0.017 gCOD/gTS×d. Despite being low, this loading enabled a satisfactory removal of total nitrogen (and other contaminants as well) from the treated wastewater. It was found that the bioreactor equipped with separate denitrification and nitrification tanks yielded similar results as the aerobic bioreactor when applying a tenfold activated sludge loading. Thus, this solution has been considered as more favourable. In previous research the purification of wastewater coming from the meat industry was undertaken but in a different hybrid systems: (1) activated sludge (SBR) with reverse osmosis [10,11]; (2) activated sludge (SBR) with coagulation [12]; (3) ultrafiltration with reverse osmosis [13]; (4) coagulation with reverse osmosis [13]; and (5) coagulation with ultrafiltration and reverse osmosis [14]. It was proved that there was the possibility of effective purification of wastewater coming from the meat industry in all analysed processes. Depending on the method of purification, the cleaned wastewater could be drained away to receiving water or turned back to the production cycle. However, the most profitable system from all those analyzed during the entire research period was the bioreactor equipped with separate denitrification and nitrification tanks. The results obtained during wastewater treatment in this system are discussed in a subsequent article. The membrane bioreactor has an advantage in comparison to conventional wastewater treatment (e.g., SBR), as it does not only serve as a secondary settling tank but also removes macromolecular contaminants. The activated sludge contact period is extended; however, the hydraulic retention time of treated wastewater in the aerobic tank is reduced. As the research shows, it is possible to use higher concentrations of suspensions in the activated sludge tank (up to 30 kg/m3, while it is only 1.5–3.0 kg/m3 in conventional treatment plants), which enables the sludge to operate at lower substrate loadings. When the wastewater needs to be recirculated to the production cycle, an additional treatment using reverse osmosis is recommended.