Investigation of removal of nutrients from wastewaters with the denitrifying biological phosphorus removal process

Aim of project
This research project aims to evaluate the possibility of application of the process of denitrifying phosphorus removal to increase the effi ciency of integrated nitrogen and phosphorus removal from wastewater in biological reactors. Discovery of new strains of bacteria which are capable of excess phosphorus removal not only in aerobic conditions (Phosphorus Removing Organisms — PAO) but also in anoxic conditions (Denitrifying Phosphorus Removing Organisms — DPAO) with simultaneous reduction of nitrates to nitrites or gaseous nitrogen created an opportunity to utilize this process for synergic removal of nitrogen and phosphorus from wastewater at signifi cantly lower demand for organic carbon. Previous research conducted mainly on the laboratory scale has shown that full-scale application of this technology has two constraints. Firstly, the efficiency of phosphorus removal in anoxic conditions is lower than in aerobic conditions. Secondly, the composition of wastewater entering biological reactors rarely guarantees an N/P ratio of at least 7, which is required for complete nitrogen and phosphorus removal by DPAO. Despite the aforementioned drawbacks, the advantages resulting from exploiting the DPAO in the activated sludge biocenosis justify the need for further experiments which will aim at the selection of such operational conditions in the bioreactor, for which the rate of denitrifying phosphorus removal would comprise the highest possible ratio in all phosphorus and nitrogen removal processes occurring in the bioreactor.

Due to the easiness and flexibility in the configuration of operational conditions for wastewater treatment in batch reactors, all the investigations in this project will be conducted in a lab scale model of a sequencing batch reactor (SBR).

Expected results
The main advantage of the application of the technology that will guarantee a synergic occurrence of biological phosphorus removal and denitrification processes is the feasibility of carrying a nutrient removal process with limited availability of organic carbon and the reduction of energy consumption for aeration. The treatment technology which will utilize the process under investigation is particularly competitive with other treatment technologies in case where wastewaters to be treated are characterised with low COD/N and COD/P ratios. Treatment of these wastewaters in currently applied treatment systems requires addition of external carbon source in order to achieve the required concentrations of N and P in the effluent.

This entails additional costs for the treatment plant operators associated with the purchase of chemicals or additional capital costs for additional treatment units to be used for carbon source generation (i.e. volatile fatty acids (VFA)). Thus, the application of the treatment technology under investigation with all its advantages can significantly reduce the operational costs of the biological treatment stage of a wastewater treatment plant and this justifies its practical implementation.

Original and thorough technological and microbiological investigation that will be conducted will allow assessing the influence of the most relevant operational parameters on the overall effect of denitrifying phosphorus removal, which will allow in the future the full-scale implementation of this process.