S. I. Klochkov, head; Y. N. MАKHINYA, chief engineer (Small Enterprise "Gprvodokanal", city of Zheleznogorsk of the Kursk region)

OPERATION EXPERIENCE OF WASTEWATER TREATMENT STATION OF THE CITY OF ZHELEZNOGORSK

The municipal treatment facilities in Zheleznogorsk (two lines) have been working in their full capacity since 1988, their design productivity being 67,7 ths. m 3per day and night, actual sewage disposal makes up around 45 ths. m 3per day and night. Domestic sewage with the dredge content of 200-250 mg/l and biochemical oxygen demand5 150-200 mg/l make up 87 % of the sewage purified at the treatment facilities.

To the mechanical treatment of water belong the inlet box, grid structure with three mechanized rakers, two horizontal sand catchers with water circulation and four primary settlers.

The biological treatment is carried out by the three four-corridor aerotanks with concentrated water-in and possibility to change the reactivation tank volume from 0 to 50 %. Originally aeration was carried out through the filtering plates. The air is fed to the aerotanks by the turboblowers and the recirculating sludge is fed by the pumps. Six secondary radial settlers with the diameter of 24 m belong to the treatment facilities as well.

After the biological treatment the sewage is polished at the polishing station by eight sand-gravel filters with the upper water supply by pumps for filtration.

For sewage disinfecting there is a chlorinating plant with separate storage and chlorine preparation in evaporators and filters of primary and secondary purification. The contact of the purified water and chlorine is carried out in the mixer, sewage transmission reservoir and in the 17-km long delivery conduit. A water-metering chute and aerator before dumping the treated sewage into the river were built at the sewage treatment facilities.

Apart from the system of full sewage treatment there has been planned the system of constructs of fresh sediment and excessive sludge with its salinity in two two-corridor mineralizers, concentration in two concentration-tanks and centrifuge treatment with separate fresh sediment and compacted sludge delivery. The capacity of the planned and built sludge beds reached only 20 % of the productive capacity of sediment and sludge treatment facilities.

During the treatment facilities construction and introduction into service there had been exposed a large number of defects, there turned out to be even more numerous in the process of functioning.

Firstly, the reliability of sediment and excessive sludge treatment system functioning either in dewatering body (due to a quick centrifuge auger depreciation) or at the sludge beds (due to virtually out-of-operation drainage and their low productive capacity) had not been provided.

Parsimony as to the new sludge beds throughout the country has resulted and keeps resulting in environment pollution.

Thus, there are no resources and means in the city of Zheleznogorsk for the sediment and sludge treatment by press-filters or highly efficient centrifuges with addition of flocculating agents the way this problem has been settled abroad and at isolated facilities of our country – the sludge beds are to be designed at least for 200 % of the treating facility capacity. Virtually none of the cities of such and even larger scale has such planned functioning system.

Another problem concerns the economical part of the project. The designers pay most attention to means saving for construction and little attention is paid to exploitation costs, system, construct and machine functioning reliability. Thus, at our municipal sewage treatment facilities around 50 % of power inputs are consumed by the work of polishing stations because the sewage is supplied to the filters by pumps though it might have been self-flowing. A separate reservoir with installed polishing filters with the required pressure of 6-7 standard atmospheres was constructed, though there are treated sewage transfer pumps to the river Svapa with the collector pressure of 10 standard atmospheres. The auxiliary water supply was projected by the three pumps with the required pressure of 6 standard atmospheres though there is a discharge header with the pressure of 10 standard atmospheres.

Understanding that the main thing in treatment facilities functioning is the aerotank functioning, the throughput capacity of each filtering plate had been checked by a special facility before bringing the facilities into service and the plates had been installed in the channels according to their throughput capacity. It took the desired effect during the first years. However, in the process of exploitation the filtering plates often break down, which puts the aerotank out of action and consequently the quality of treatment deteriorates drastically.

Cooperation with the “Ekopolimer” firm has produced the desired effect. The developed by the “Ekopolimer” tubular aerators have proven to be effective and allowed shutting down one blower of the system. Tubular aerators are easy and economical to mount in the filtering channels. One aerotank reconstruction by the team of 4 men took about 7-8 working days.

Circular aerators (the city of Kostroma) are no worse as to aeration effect but the aerotank with circular aerators stopped twice a year for short repair works, part of the aerators was torn off due to ineffective attachment point construction.

A small proportion of sludge gathers at the aerotank bottom, the water in the aerotanks “boils” moving through the corridors; when using tubular aerators, the water, being dressed by oxygen, gyrates through the corridors. The circular aerators are much more complicated as to their construction and mounting.

The aerotank reconstruction has let considerably increase the sewage treatment effect at municipal facilities in the ammonium group (see the table).

After the aerotank replacement such a mode of aerotank functioning had been adjusted that during 7 months in the autumn-winter season the treatment facilities had been working virtually with no excess sludge dumping, wherein the sludge dosage during this period had increased from 2 to 3 g/l.

Nitrification in the facilities of biological purification (aerotanks) under regular aeration passes well, the ammonia nitrogen decreases to decimal figures of mg/l, and the nitrite nitrogen decreases to millesimal figures of mg/l, at that the nitrate nitrogen increases to 7-10 mg/l. Besides, the phosphates had decreased from 10 to 1 mg/l and lower in the process of exploitation (including March-April) at the treatment facilities.

Conclusions

The “Ekopolimer” aerators not only possess design merits but due to their high mass transfer characteristics allow transferring the biological purification facilities to the mode of ammonia nitrogen disposal and considerable decrease of excessive sludge volume.