G. P. Verbitsky, O. B. Kurnilovich “Krivbassvodokanal” Municipal Enterprise, city of Krivoy Rog, Ukraine

CONDITIONS OF RELIABLE OPERATION OF THE EKOPOLIMER DIFFUSERS

Specific features of the Ecopolimer aerators operation were studied at the premises of Krivoy Rog aeration station during seven years; factors guaranteeing its absolute reliability have been determined.

The Ekopolimer polyethylene tubular aerators have been used at aeration station of “Krivbassvodokanal” Municipal Enterprise since 1993.

Initially, two two-corridor aeration tanks (100 x 18 x 4.5 m) and one four-corridor aeration tank (120 x 36 x 5.2 m) of the Central aeration station were equipped with aerators of this type; additionally, these aerators were installed at four-corridor aeration tanks (48 x 18 x 3.2 m) at the North aeration station and one aeration accelerator of 20 m diameter at the South station.

According to the current situation, during several years different types of aerators have been used at the Central station at the same time – diffusing plates, steel perforated pipes and the Ekopolimer polyethylene piped aerators. It gave an opportunity to comprehensively and thoroughly compare technical and technological capabilities of different types of aerators in operating environment.

Special attention was paid to investigation of reliability of various types of aerators.

Comparative analysis revealed that diffusing plates can be described as the least reliable. They hold water hammers poorly. In the situations when frequent electricity cutoffs result in interrupted air supply to the aeration station, filtering plates are destroyed in multiple places. There were cases reported when layers consisting of ten to twelve or more plates were broken. Dead spaces appear in aeration tanks. Oxidizing process deteriorates. Restoration work with cement or epoxide filling can be performed in the summer time only.

Perforated aerators made of steel tubes are more resistant to water hammers, but the holes in them (0.4 mm) are soon clogged with fibrous substances and covered with ferro-bacteria. The material the tubes are made of is subject to corrosion. Besides, oxygen usage coefficient for this type of aerators is approximately twice less and required air consumption, consequently, twice as much as for the milli-bubble aerators.

Due to the flexibility of polyethylene carcass, dispersing layer elasticity and reliability of constructions used for aerators interconnection, the Ekopolimer aerators are practically indestructible. There was not a single case reported of aerators being destroyed.

For that reason, reliability and regularity of the Ekopolimer aerators operation is determined exclusively by the qualification and quality of aerators fastening to the aeration tanks bottom as well as aerators assembling.

Aerators design allows their assembly in the shortest terms possible. Two types of connections are employed: - aerator tube is threaded on both ends, and tubes are interconnected by means of threaded polyethylene couplings (The Aqua-Pro aerators);
- aerator tube has internal thread on one end and external thread on the other (The Aqua-Line aerators). Aerators of this type are interconnected without using couplings, they are simply screwed into each other.

Aerators connection assembly design is extremely simple, requires no sealing materials, nor welding or additional arresting elements.

Aerators are assembled using special devices (belt wrenches and other similar instruments), which provide the required torque without damaging aerator dispersing layer.

Such industrially manufactured instruments are rarely found. Workers responsible for aerators assembly often fail to meet the requirements using primitive self-made devices, which negatively affects the quality of assembling. For this reason, there are cases of low-quality assembling: outer layers of certain aerators are damaged, and connections are sometimes loosened during testing.

Though such cases are not frequent, we should exclude them absolutely. It would be advisable for the “Ekopolimer” research and production firm to supply each stock of aerators with industrially manufactured instruments for their assembly. In this case the assembly workers will have no questions regarding technical aspect of assembly and installation.

This was the way the Ekopolimer used to solve the problem of reliable fastening of aerators to aeration tank bottom.

This work, basically not very complicated, requires time, attention and accuracy, especially with regard to two factors:
- usually quite a large number of fastening elements are necessary to install aerators. For instance, to fasten aerators of 1950 mm length in a four-corridor aeration tank with 50% regeneration (with dimensions 100 x 32 x 4 m), 490 fastening elements are to be installed;
- fastening elements must guarantee strictly horizontal aerator position along the whole length of the corridor; otherwise, no uniform distribution of air in the aeration tank space or efficient oxygen usage can be provided.

When aerators of this type were first installed, assembly workers used random design fastening elements, mostly clamps made of reinforcing wire, which were fixed to the armature of diffusing channels. However, such fixtures turned out not to be reliable enough, in particular in cases when aerators were installed into aeration tanks of 20-25 years old or more.

The Ekopolimer specialists have worked out fastening rings of special design as well as drawings for aerators fastening in diffusing channels or directly to aeration tank bottoms for cases when for some reason it is not recommended to use diffusing channels as a foundation for fixing aerators.

During aerators installation on diffusing channels according to the Ekopolimer drawings, primary fixing parts in the form of vertical armature rods are first installed inside the channel for each securing element; for this purpose, one diffusing plate in the place of installation has to be removed. Primary fixing parts are then secured with concrete and fastening rings are welded to them. Ekopolimer fastening rings are included into the aerator supply set.

Ordinarily, aerators manufacturing and supply are performed within a certain period after signing a contract with the customer and initial payment for the order (not more than a month). If it is quite necessary to shorten aeration installation terms, it is advisable to arrange for securing elements supply immediately after the payment for the order. In this case, securing elements can be installed without haste by the time aerators are manufactured and supplied, thus providing required reliability and aerators horizontal position.

It is easy to guarantee necessary horizontal position without substantial time expenditure. For this purpose, fixing beacon rings are first installed in appropriate places at the two ends of the aeration section and a steel string is stretched between them. All the rest of the fixing elements are then installed level to this string.

High costs of the Ekopolimer aerators is often mentioned, and this is true when it is compared to the cost of aerators of traditional design. Nevertheless, these costs are paid back manifold due to substantial saving of labor, material and financial resources. A major part of these savings is determined by high reliability of operation both of the aerators themselves and the aeration systems in which they are used. Still, considering absolute reliability of aerators design, special attention should be paid to the quality of their assembly and securing to the aeration tank bottom. One more interesting aspect is worth mentioning. As analysis performed by the “Krivorozhindusstroy” Public Joint-Stock Company revealed, reconstruction of aeration system in aeration tanks with the term or operation of over 20-25 years using the Ekopolimer aerators instead of worn-down diffusing plates is comparable to the cost of capital repairs of existing aeration systems.

The thing is, after a long term of operation not only diffusing plates but also underlying constructive elements of diffusing channels become inoperable. The whole aeration system needs replacement, including several kilometers of diffusing channels; the length of these channels at the Central aeration station alone is 9.8 km. Under these circumstances, aerators reconstruction using the Ekopolimer aerators becomes not only technically and technologically, but also financially efficient with respect to the capital investment to the aeration tanks reconstruction.