Analysis of the effectiveness of coagulants in water treatment

Background. Obtaining water suitable for domestic and industrial needs and safe for the consumer is the main task of water treatment. The search for ways to improve the coagulation process and methods that allow its intensification is currently still relevant. The article presents the results of studies of coagulants at various combinations and doses in laboratory conditions. Irtysh river water intended for drinking purposes is considered as an object of research. The efficiency of using different coagulants that allow to remove pollutants such as heavy metals, organic compounds, microbiological pollutants, etc. in a more qualitative way has been studied. This is especially important for the treatment of water from surface sources, which is often characterized by a high content of impurities. Experimental studies in the shop of operation of water supply networks and facilities of Rosvodokanal Omsk were conducted with the following coagulants “Brilliant-18”, “Bopak-E”, “OHA”, “Aqua-aurat 30” and “ASA” in combination with flocculant FL 4540PWG. Coagulants were tested in the spring flood period at the source water temperature of 6-8°C. On the source water of the Irtysh River the best results were shown by coagulants such as “Bopak-E”, “OHA” and “Aqua-aurat 30”. The optimal dose for the most effective coagulants is Dk=1.5 mg/l (by Al2O3) when combined with flocculant with Df=0.1-0.13 mg/l. Coagulant “Aqua-aurate 30” shows better flaking, sedimentation and clarification, and accordingly better performance on water turbidity. To confirm the results of laboratory tests and select the most effective reagent, it is recommended to conduct production tests of coagulant “Aqua-aurat 30”.

Purpose. The main objectives of the research are to test the used reagents in laboratory conditions and compare their efficiency in different seasons of the year, as well as to improve the water treatment process by introducing new reagents.

Materials and methods. According to the results of industrial tests it was found that water after treatment with liquid aluminum sulfate meets hygienic requirements for water quality of centralized drinking water supply systems. In summer period the working dose of liquid SA 1.5 mg/l (by Al2O3) is similar to the working dose of OHA. But liquid aluminum sulfate can be used for water treatment at water treatment plants only in summer, as in winter time of the year the coagulation process is much worse. Therefore, the laboratory of the water supply networks and facilities operation shop conducted laboratory studies on the effectiveness of introduction of other coagulants based on aluminum polyoxychloride: “Brilliant”, “Bopak”, “OHA”, “Aqua-aurat 30” and “ASA”, which can be used in different seasons of the year.

Taking into account the current technology of natural water treatment at the facilities of Rosvodokanal Omsk the following methodology of trial coagulation (on automatic flocculator “Lovibond”) was adopted. Addition of reagents (coagulant and flocculant sequentially) in the source water and stirring for 3 minutes at a rotation speed of 146 rpm. Stirring is then continued for 10 minutes at a lower speed (43 rpm). This is followed by settling for 30 minutes. Trial coagulation was carried out with flocculant FL 4540PWG with a concentration of 0.1%. Samples of treated water were taken after settling from the middle layer of water. Water quality parameters were evaluated after the sedimentation process, excluding filtration.

Results. As a result of the tests, large flakes were formed only when “Aqua-aurate 30” and “ASA” were applied at a dose of (1.5/0.1 mg/l). Other coagulants formed small and medium flakes and all coagulants showed intensive sedimentation and clarification.

Tests of coagulants were carried out in the spring flood period at the source water temperature of 6-8°C On the source water of the Irtysh River the best results showed coagulants such as “Bopak-E”, “OHA” and “Aqua-aurat 30”.

The optimal dose for the most effective coagulants is Dk=1.5 mg/l (by Al2O3) when combined with flocculant with Df=0.1-0.13 mg/l.

During the laboratory tests, coagulants “Bopak-E” and “Brilliant-18” showed the same results of clarified water quality in terms of residual aluminum and water turbidity in comparison with the coagulant “OHA” used at Rosvodokanal Omsk, at doses as close as possible to those established at production (Dk=1.8 mg/l and Df=0.13mg/l).

Coagulant “Aqua-aurate 30” shows better flaking, sedimentation and clarification, and accordingly better indicators of water turbidity.

Under low alkalinity conditions, Aqua-aurat 30 coagulant increases this index, which contributes to solving the problem of poor coagulation. At optimum doses quality indicators of clarified water by residual aluminum, as well as filtered water by turbidity and residual aluminum, meet the quality assurance of drinking water in accordance with SanPiN 1.2.3485-21, GN 2.1.5.1315-03, GN 2.1.5.2280-07.

To confirm the results of laboratory tests and to select the most effective reagent, it is recommended to conduct production tests of coagulant “Aqua-aurat 30”.

Conclusion. In the process of laboratory testing, many reagents are tested. The purpose of the analysis is to find effective reagents under conditions when the water supply source changes its charge and alkalinity decreases.

Laboratory tests of coagulants based on aluminum polyoxychloride such as “Bopak-E”, “OHA” and “Aqua-aurat 30” show that the performance in conditions of low alkalinity is difficult, but the best coagulation ability is shown by the reagent “Aqua-aurat 30” because of its ability to increase alkalinity by 15-18%, which helps to improve the efficiency of coagulation.