Czestochowa University of Technology, Faculty of Infrastructure and Environment, Department of Chemistry, Water and Wastewater Technology, Częstochowa, PL
THE INFLUENCE OF CONDITIONING METHODS ON THE QUALITY OF SLUDGE LIQUIDS AFTER SEWAGE SLUDGE MECHANICAL DEWATERING
As a result of the thickening of sewage sludge, its biological stabilization and dewatering sludge liquids are formed. Quantitatively sludge liquids represent only a few percent of the total volume of wastewater. However, the load of pollutants, including biogenic compounds, which is recycled into sewage path can be up to several dozen percent of the total charge flowing into the wastewater treatment plant (WWTP). For the proper functioning of the WWTP such a large load can pose a threat. The problem of the return of sludge loads is increasingly recognized and being under examination. Considering the importance of the quality of sludge liquids, the influence of selected means and conditioning methods such as PIX 113, PIX 123, polyelectrolyte Zetag 8160, ultrasound field and their effect on the properties of sediment liquids are presented in the publication. The sewage sludge after the anaerobic digestion process was used in experiment. The sewage sludge was taken from a communal wastewater treatment plant, where RLM is bigger than 100 000. The WWTP uses a mechanical and biological methods with the removal of nitrogen and phosphorus compounds. The tests included: pH, suspension, COD, ammonium nitrogen and phosphate in sludge liquids. Raw sludge liquid was characterized by very high concentrations of ammonium nitrogen (931.5 - 1508.9 mg N-NH4+/dm3), phosphates (24.3-89.4 mg PO43-/dm3) and organic compounds as COD (784.0–1856.4 mg O2/dm3). It was found that the combined action of the inorganic coagulant PIX 123 and polyelectrolyte reduced the suspensions and COD in sludge liquids. In case of suspension the best reduction was achieved when PIX 123 was applied and it was 53.8%. By analyzing COD changes similar effects were observed for PIX 123 (43.1%) and for combined method (43.5%). On the other hand, the combined use of coagulant PIX 113 and polyelectrolyte Zetag 8160 resulted in increased suspension in the sludge liquor in comparison to raw sludge liquor. The combined effect of PIX 113 and Zetag 8160 resulted in a decrease of COD (90%), ammonium nitrogen (43.1%) and phosphates (97.1%) in comparison to raw sludge liquids. The least effective in the experiments was Zetag 8160.
Keywords: sludge liquids, conditioning, sewage sludge, coagulants, polyelectrolytes