Analysis of the operation of acidifiers after the reconstruction of the block of the Liuberetskie Wastewater Treatment Facilities

Summary

Municipal wastewater in Moscow after primary settling contains insufficient organic matter for the sustainable removal of nitrogen and phosphorus to the standard quality during treatment. Therefore, while designing the reconstruction of the old block of the Liuberetskie Wastewater Treatment Facilities in Moscow, the acidification (prefermentation) method was chosen as the most efficient process solution for enriching wastewater with easily decomposable organic matter (obtaining organic acids during acidic fermentation of raw sludge from primary settling tanks). Upon the completion of the reconstruction of the old LWWTF block at the end of 2021, primary sludge acidifiers were put into operation. Launching acidifiers provided for enriching primary water with easily decomposable organic matter (volatile fatty acids, including acetate) resulting in the improved efficiency of denitrification and biological dephosphorization processes in the aeration tanks. Two or three weeks after the acidifiers had been put into the operation mode, the quality of effluent for nitrogen as nitrates and phosphorus as phosphates was meeting the MPC for fisheries. The process parameters of the acidifiers (hydraulic retention time, residence time for dry matter, the rate of volatile fatty acids formation, the degree of recirculation, the dry matter concentration in the incoming flow) corresponded to those recommended in the literature. Possible situations of abnormal operation of acidifiers have been analyzed and recommendations have been developed to eliminate the causes.

Key words

nitrogen removal , wastewater treatment , acidification , readily available organic matter , prefermentation , phosphorus elimination , process parameters of the acidifiers’ operation

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

Industrial tests at the Kur’ianovskie Wastewater Treatment Facilities involving the transfer of one primary settling tank into the acidification mode

Summary

In the process of Moscow wastewater treatment primary effluent is lacking enough organic substances for sustainable removal of nitrogen and phosphorus to meet the regulations. One of the methods of enriching wastewater with easily decomposable organic matter is acidification (acid fermentation) of raw sludge. At the Kur’ianovskie Wastewater Treatment Facilities in Moscow industrial testing was conducted at the first new treatment block operating according to the UCT process flow scheme with a design capacity of 600 thousand m³/day on transferring one settling tank into the acidification mode. Of the four settling tanks of the block, raw sludge from the three primary settling tanks operating in the clarification mode was fed to the fourth one operating in the acidification mode. Wastewater flow rate for the acidifier was 30–100% of the flow rate of each of the primary settling tanks, or 11–25% of the water flow rate of the block. The acidified sludge recycling was 100% with respect to the raw sludge flow, or 3% with respect to the mixture of raw sludge and wastewater entering the acidifier. The residence time of the sludge in terms of dry matter (SRT) in the acidifier changed during the experiment from 2 to 3.5 days; the highest treatment efficiency in relation to removing nitrogen and phosphorus compounds was achieved with a residence time of 3.5 days. The hydraulic residence time of wastewater in the settling tank-acidifier (HRT) ranged from 1.9 to 5.5 hours and did not have a noticeable effect on the rate of removing nitrates and phosphorus as phosphates at the next biological stage. The arrangement of the operation of the primary settling tank in the acidification mode showed the presence of the effect of this process that contributed to the additional removal of 3.5 mg/l of nitrogen as nitrate and 0.23 mg/l of phosphorus as phosphate, and provided for the treatment level up to BAT standards. The average concentration of nitrogen as nitrates in the effluent decreased from 11.6 to 8.1 mg/l. For phosphorus as phosphate, before the introduction of acidification at the facilities, the standard effluent quality was provided; however, the enrichment of wastewater in the process of acidification with easily decomposable organic matter contributed to a decrease in the concentration of phosphate phosphorus from 0.35 to 0.12 mg/l. The transfer of one primary settling tank to the acidification mode provided for implementing the acidification process eliminating the construction of acidifiers as separate tanks.

Ключевые слова

nitrogen removal , wastewater treatment , acidification , readily available organic matter , prefermentation , phosphorus elimination , process parameters of the acidifiers’ operation