Temperature effect on nitrification processes in activated sludge

Summary

Temperature has been an important factor affecting the efficiency of biological nitrogen removal by activated sludge at wastewater treatment facilities. A laboratory SBR reactor was used in the experiments; activated sludge for cultivation was obtained from aeration tanks of the municipal wastewater treatment facilities. The taxonomic composition of bacteria in activated sludge was determined by high throughput sequencing of the DNA section encoding 16S rRNA. The nitrification rate was determined at water temperatures of 1, 5, 8, 11, 17, 19 and 21°C. Nnitrifying bacteria Nitrosomonas spp. and Nitrospira spp. were found in activated sludge with the abundance of 0.07% and 0.34%, respectively. The maximum nitrification rate observed at 21 °C was 4.3 mg N–NO₃ per 1 g of ash-free substance of activated sludge per hour. The nitrification rate decreased with decreasing temperature and was 0.3 mg/(g·h) by N–NO₃ at 1°C. The results of the study can be used as a theoretical basis for optimizing the operation of the treatment facilities in areas with low temperatures to improve the efficiency of nitrogen removal from wastewater.

Key words

wastewater , nitrification , activated sludge , temperature , biological removal of nitrogen

Nitrogen removal in a circulation oxidation ditch model
under the conditions of lowered concentration of organics in wastewater

Summary

The summarized results of the third stage of an integrated study of energy efficient processes of wastewater treatment in circulation oxidation ditches are presented. The experiment was carried out in a laboratory model of a circulation oxidation ditch with horizontal directional flow of mixed liquor. The impact of low concentration of dissolved oxygen in the bioreactor volume (at 0.5 mg/l level) and low concentration of organic pollutants in the incoming model wastewater on the treatment efficiency and biomass stability was studied. The highest efficiency of total nitrogen removal was reached at the specific organics load on activated sludge (BOD) R = 0.07 g/(g∙day), average dissolved oxygen concentration 0.5 mg/l and 7.5 hours aeration time. At that the concentration of ammonium nitrogen in the effluent was about 0.6 mg/l; the concentration of nitrate nitrogen was 9.6 mg/l. The operation of the bioreactor at lowered dissolved oxygen concentrations resulted in partial biomass bulking. The sedimentation properties of activated sludge changed; however stayed at satisfactory level.

Key words

wastewater , nitrification , energy efficiency , activated sludge , denitrification , circulation oxidation ditch , biological removal of nitrogen