Methodological approaches to the design of acidifiers for primary sludge to enhance the processes of nitrogen and phosphorus removal from municipal wastewater

Summary

The experience of introducing the process of raw sludge acidification at the Moscow wastewater treatment facilities is summarized. Two types of acidifiers have been operated at the Kuryanovskie and Lyuberetskie Wastewater Treatment Facilities in Moscow: acidifiers-thickeners and acidification reactors (mixers) with subsequent rinsing and thickening in a separate thickener. The main indicator for the acidification process is the solids retention time (SRT, solids retention time). At Moscow wastewater treatment plants, it was 3.5 days, that was the optimal value. Extra formation of BOD₅ (an increase in acidificate-enriched primary water compared to primary water) from 17.8 ± 9.1 to 31 ± 17.5 mg/l and specific BOD₅ formation of 0.1 mg/mg of suspended solids, or 0.15 mg/mg of ashless matter (an increase in acidificate-enriched primary water compared to primary water in specific formation of BOD₅ from 1 mg of suspended or ash-free matter settled in primary settlers and sent to the acidifier) was shown. Formulas are derived for calculating the basic process indicators: hydraulic retention time, retention time as dry matter, the rate of formation of volatile fatty acids. An algorithm of process calculations for designing sludge acidifiers of primary settling tanks in order to enhance the processes of removing nitrogen and phosphorus from municipal wastewater is presented.

Key words

wastewater treatment , acidification , readily available organic matter , prefermentation , process parameters of the acidifiers’ operation , acidifier designing