| Abstract [eng] |
Biological methods are the most widely used strategies to treat wastewater. In order to maintain the efficiency of this process, it is important to evaluate the toxicity of potentially hazardous chemicals in influents to wastewater treatment plants. Previous studies described in literature mainly focus on determining the toxicity of chemicals to activated sludge either from municipal or industrial wastewater plants. Most researchers use shock loads of toxicants, rather than repeatedly adding the chemical of interest to the test system. Moreover, only short-term response to the toxicant is investigated. In this study the effect of 3,5-dichlorophenol was assessed and compared between different activated sludge systems. Activated sludge used in this study was obtained from KN (AB Klaipėdos nafta) sequencing batch reactors, as well as from an aerobic basin from a local municipal wastewater treatment plant at UAB Kauno vandenys. Some of the used laboratory scale bioreactors were supplied with biologically activated carbon. The effect of 3,5-dichlorophenol to dissolved organic carbon removal and activated sludge dehydrogenase activity was assessed. Ethanol was selected as a suitable substrate for dissolved organic carbon removal assay. EC50 values for 3,5-dichlorophenol obtained in this study showed that a higher sludge system is less sensitive to the effect of this toxicant, compared with the activated sludge from a municipal wastewater treatment plant. The EC50 values in these systems were 21,78 and 11,33 mg/l, respectively. Continuous tests conducted for five days showed that higher age activated sludge is capable of adapting to 15 mg/l 3,5-dichlorpohenol concentration more rapidly. Inhibition of dissolved organic carbon removal in this system decreased 2,89 fold in five days, whereas the inhibition of this parameter decreased only 1,26 fold in a system utilising activated sludge from a municipal wastewater treatment plant, when compared with control. Inhibition of sludge dehydrogenase activity in these two systems decreased to 18,7 and 25,5 % on the fifth day of testing, respectively. The ability of activated carbon to improve resistance to toxic upsets was confirmed. It was shown that a 10,75 g/l biologically activated carbon supplement is capable of completely overcoming the inhibitory effect of 3,5-dichlorophenol, when this toxicant is added to test system repeatedly at a concentration of 20 mg/l. |
