Oznaczanie powierzchni właściwej osadu czynnego

Powierzchnia właściwa osadu czynnego odgrywa istotną rolę w procesie biodegradacji zanieczyszczeń ściekowych. W pracy przedstawiono historyczne aspekty rozwoju metod pomiaru powierzchni właściwej osadu czynnego. Obecnie za najbardziej dokładne i jednocześnie proste można uznać metody adsorpcji barwnikowej. Opisano metodykę oznaczania powierzchni właściwej osadu czynnego z wykorzystaniem Lissamine Scarlet 4R, rodaminy B oraz p-nitrofenolu (PNP). Metoda z użyciem PNP (stosowana dla materiałów innych niż biologiczne) została przystosowana do oznaczania powierzchni właściwej osadu czynnego przez autorów. Na podstawie badań własnych dokonano także porównania otrzymywanych wyników z zastosowaniem przedstawionych trzech metod. Najbardziej zbliżone wartości uzyskano dla metody z Lissamine Scarlet 4R (55,9 ÷ 112 m2/g s.m.) i rodaminą B (62,4 ÷ 127 m2/g s.m.). Wartości powierzchni właściwej dla metody z PNP były znacznie większe (151,6 ÷ 254,7 m2/g s.m.), co prawdopodobnie wynika z małej wartości pola powierzchni siadania cząsteczki p-nitrofenolu. Stwierdzono, że porównywać można jedynie powierzchnie osadu czynnego oznaczone taką samą metodą. Wartości powierzchni właściwej dla konkretnego osadu określone różnymi metodami mogą między sobą znacznie się różnić.

Activated sludge process is the most common method for effective treatment of municipal as well as industrial wastewater. The effectiveness of the activated sludge process is related to the physical properties of the flocs. One of the very important properties of the activated sludge is specific surface area, which influences both the mass transfer into floc and the effectiveness of sludge flocculation. In this paper, the methods of measurement of activated sludge specific surface based on dye adsorption were shortly reviewed. At present, these methods can be stated as the most precise and simple to use. The methods using Lissamine Scarlet 4R, p-nitrophenol (PNP) and Rhodamine B were detailed described. The PNP method (used early for non-biological materials) was adapted for measurement of activated sludge specific surface by authors. Literature review shows clearly the advantages of the use of PNP, Lissamine Scarlet 4R and Rhodamine B for measurement of specific surface of activated sludge. The advantages of the use of PNP for this purpose are as follows: it is a small molecule with a known cross-sectional area, it shows affinity for a great variety of solids, it can be used in aqueous or non-aqueous solutions, it is stable, easily purified, and readily analysed. Lissamine Scarlet 4R is suitable for the measuring specific surface of activated sludge for the following reasons: it is stable, its solubility in water is neither too high (competition with solvent) nor too low (micelle formation), it can be efficiently purified and staining of glass tubes is negligible. However, the adsorption on activated sludge was taking place only under acidic conditions. Rhodamine B can be also use to measurement the specific surface area of activated sludge. The cross-sectional area occupied by molecule was dependent on pH and conductivity of the solution. The essential advantage of the use of Rhodamine B is possibility of surface area measurement without acidification of solution. However, its disadvantage is intensity of colour. Rhodamine B stains glass and other materials. Based on the results obtained in this study, the surface area measured by Lissamine Scarlet 4R was compared with a surface area calculated with PNP and Rhodamine B methods. The most close-up values were observed for Lissamine Scarlet 4R (55.9 ÷ 112 m2/g) and Rhodamine B (62.4 ÷ 127 m2/g). The values obtained for PNP were considerably higher (151.6 ÷ 254.7 m2/g), probably as a result of small cross-sectional area of PNP molecule. It has been concluded that values of activated sludge specific surface, measured by means of various methods can substantially differ. Therefore, only values obtained by means of the same method can be compared.