Charakterystyki reologiczne osadów ściekowych kondycjonowanych polielektrolitami

Przedstawiono badania dotyczące charakterystyk Teologicznych osadów przefermentowanych (pobranych za otwartymi komorami fermentacyjnymi) kondycjonowanych polielektrolitami: Praestol 630 BC, Zetag 92 i Renfloc 28486. Na podstawie testu CSK dobrano optymalne dawki polielektrolitów, dla których wykonano badania reologiczne. Próbki kondycjonowanych osadów poddawano w reometrze prędkościom ścinania w zakresie (0-2000 s-1 w ciągu 120 s i mierzono odpowiadające im naprężenia styczne. Analiza pozornych krzywych płynięcia pozwala na stwierdzenie, że w porównaniu z osadem niepreparowanym osady kondycjonowane polielektrolitami charakteryzują się większymi naprężeniami stycznymi. Wartość granicy płynięcia dla osadów niepreparowanych wynosi 3,750 Pa. Natomiast granica płynięcia dla osadów kondycjonowanych Praestolem 630 BC mieści się w zakresie od 3,625 do 15,636 Pa, dla osadów kondycjonowanych Zetagiem 92 od 2,673 do 4,912 Pa oraz dla osadów kondycjonowanych poli-elektrolitem Renfloc 28486 od 2,332 do 6,036 Pa.

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The application of rheology in water and wastewater treatment is related to non-Newtonian character of sludge flow. The sewage sludge is formed mainly after coagulation and sedimentation processes in wastewater treatment plants. The practical application of the rheological experiment is related to the relationship between sludge structure and its rheological features, as well as sludge structure and ways of its treatment. The treatment of sludge is connected with dewatering processes which lead to the reduction of water volume. The process of sludge conditioning has an impact on the changes of sludge structure and properties and allows for more effective water removal. Practically the following conditioning methods are used: - chemical conditioning, - mechanical conditioning, - thermal conditioning. Among them the chemical method is commonly used for sludge conditioning. The added organic or non-organic substances build up floc strength, increase the floc volume through agglomeration of colloidal solids and create resistance to shearing and compression. The rheological tests were carried out for sewage sludge after the digestion process in open digesters. The samples of sludge were conditioned by means of different polyelectrolytes: Praestol 630 BC, Zetag 92, Renfloc 28486. Based on the CST test the optimum doses of polyelectrolytes were determined and added to sludge prior to rheological measurements. The samples of conditioned sludge were analyzed in a rheometer RC20 at the controlled shear rates from 0 to 2000 s-1 during 120 s, and the responding shear stresses were measured. The samples were analyzed at a constant temperature of 20°C kept using the ultra-thermostat. The physicochemical characteristics of sludge were following: pH = 7.5; total solids 20 g/dm3, organic matter content 61%, mineral fraction content 39%, initial hydration 97.9%, CST 1803 s, electro kinetic potential - 8.79 mV. Microscopic pictures of sludge structure allow for easier observation of sludge changes during conditioning process. The effect of increased polymer dose on the size of flocs was observed. The rheological experiments show the impact of shear stress on flocs in process of conditioning. The analysis of rheological curves allows to find that conditioned sludge has the higher value of shear stress than unprepared sludge. The yield stress for digested non-prepared sludge was of 3.750 Pa. For sludge conditioned with Praestol 630 BC, Zetag 92 and Renfloc 28486 the yield stresses varied within the range of 3.625 - 15.636 Pa, 2.673 - 4.912 Pa and 2.332 - 6.036 Pa, respectively. Bigger yield stress at increased polyelectrolyte dose indicates that flocs are stronger. The higher is value of initial shear stresses the stronger are the flocs. This was confirmed by examining the photographs of sludge structure. Preliminary studies confirmed the feasbility of application of rheological parameters for determination of optimum dose of polyelectrolyte for conditioning processes prior to sewage sludge dewatering.