Inhibition of biological nutrients removal processes in activated sludge systems with regeneration
Prof. Ing. Jiří Wanner, DrSc.
The PhD thesis comprises two independent studies. First, intensification of the wastewater treatment plant (WWTP) and evaluating of the wastewater toxicity were the main tasks of the case study in a tar processing company DEZA a.s. Valasske Mezirici, Czech Republic. Second, evaluation of biological treatability and impacts of an industrial wastewater discharged into the municipal WWTP in Usti nad Labem were the main tasks of the study ordered by Spolek pro chemickou a hutni vyrobu a.s., Usti nad Labem.
An optimum biological WWTP (in DEZA) configuration consisted of two-sludge system, where the first system served as the protection barrier against sudden toxic leakage and second (R-D-N) for the biological nitrogen removal. However, experimental evidence and mathematical simulations showed that continual external substrate dosing must follow the change of configuration. It is possible to use an alternative non-toxic wastewater side-stream (with high COD and low total nitrogen content), originated in some part of DEZA production, instead of e.g. methanol dosing. It is also possible to make a partial influent bypass, directed to the denitrification zone, but this variant requires on-line respirometer installation on this line to avoid, in case of toxic signal, deterioration of the biological nitrogen removal efficiency in R-D-N system. Furthermore, the toxicity of several wastewater streams was evaluated and optimal influent diluting ratios for the tested streams were in interval of 1:99 to 1:199.
The tested industrial wastewater streams from Spolek pro chemickou a hutni vyrobu a.s., Usti nad Labem, are biologically treatable using combination of anaerobic, anoxic and oxic conditions. Regarding the intention to discharge these wastewater streams into the municipal WWTP in Usti nad Labem, a possible impact of the discharge on the WWTP performance was also evaluated. Experimental evidence showed: 1) discharge of any tested wastewater stream into the WWTP influent will likely result in increased COD concentration on the effluent, 2) two of three tested streams have no negative impact on the biological nutrient removal efficiency. Considering these facts, those two streams can be biologically treated in the municipal WWTP in Usti nad Labem together with sewage, but extent of the effluent COD deterioration will be apparent just from the full-scale experiments.