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INTRODUCTION

Under conditions of anthropogenic impact factor determining the magnitude of the negative impact on water bodies is the insufficient level of wastewater and recycled water treatment. The relevant problem is the reduction of natural water consumption for production needs, replacement of natural water for recharge of circulating water systems with alternative sources of water supply surface rivers and groundwater.

The relevant problem is the reduction of natural water consumption for production needs, replacement of natural water for recharge of circulating water systems with alternative sources of water supply. According to data [1] at many enterprises of chemical and petrochemical industries in biologically treated wastewater COD value reaches 150-200 gO/m³ and salt content exceeds 2500 g/m^З. The most common and effective coagulants for water treatment from salts and pollutants are aluminum polyoxychlorides (PAC). The theoretical basis for the production of PAC is discussed in detail in papers [2-4]. Mechanism of coagulation water purification in works [5-7].

Earlier [8, 9] we developed a fundamentally new technology of PAС production on the basis of multicomponent active aluminum alloys as metals-activators, we used (Ga, In, Sn) 5 wt.% of each.

The purpose of this work is to study physicochemical and microbiological parameters of natural, industrial recycled water and their treatment by new generation coagulants based on activated aluminum alloys with the content of metal-activators from 1.5 to 3.0%, which will significantly reduce prices.

MATERIALS AND METHODS

Materials

As natural waters were analyzed: natural waters from water intake "Almaty SU", tract "Medeu", from the well of pilot metallurgical production (EMP) of the Institute of Metallurgy and Ore Beneficiation (IMOB), the river Zhaiyk (Ural). As recycled water was analyzed water sampled from the water treatment unit of deep oil refining production (WTU of PDOR)

Activated aluminum alloys Rau-97, Rau-98, Rau-98.5, containing metals-activators: gallium, indium, tin (from 0.5 to 1 wt%) were obtained by the method described in works [9, 11].

Aluminum polyoxychlorides (PAC) were obtained by interaction of aluminum activated by metal-activators (indium, gallium, tin) in the amount of 0.5-1.0 weight % each with 3% hydrochloric acid.  Quality parameters - mass fraction of AI in terms of Al2O3 33,2-36,9%, basicity 56-67%, corresponded to GB 15892-2009 standard

Water Analysis and Treatment Methods

As natural waters were analyzed: the water of the Zhaiyk River was analyzed as natural water for water supply to industrial enterprises in Atyrau and irrigation (transboundary water artery of Kazakhstan and Russia) [12] Water samples were taken from the main collector of "ANPZ" LLP, as well as water intake "Almaty SU", tracts "Medeu", from the well. The water sample taken from the water treatment unit of deep oil refining production (WTP) was analyzed as recycled water.

Water samples were taken according to state standard No59024-2020, were evaluated by organoleptic (smell, taste, color), physical (turbidity, pH, conductivity, permanganate oxidation), chemical parameters (total salt content, the content of anions-hydrocarbonates, sulfates, chlorides) in accordance with the sanitary rules Order of the Minister of Health of the Republic of Kazakhstan February 20, 2023 № 26 [13-15].

Water treatment methodology: a certain amount of PAC was injected into 500 ml of test water while intensely stirring, after 3 minutes the speed was reduced to 50 rpm for 15 minutes, and was allowed to stand for 30 minutes afterwards.

Turbidity before and after treatment of natural and recycled water was measured directly with a turbidity meter HACH 2100Q Turbidimeter (USA).

Permanganate index (PI) was determined according to ISO 8467:1993.

Bacteriological analysis was carried out on water samples taken from the "Medeu" tract. The number of microbes and microbial composition were determined by sowing on selective nutrient media. The number of bacteria using organic nitrogen and some groups of microorganisms using mineral nitrogen were counted on Tryptone soya agar (TSA) and Meat infusion agar (MIA), enterobacteria on Endo differential diagnostic medium, all species of Pseudomonas group on Pseudomonas isolation agar (PIA). The number of fungi and yeasts was counted on selective medium Sabouraud dextrose agar (SDA). The seeded cups were incubated at 30ºC and 37ºC. Cell morphology of microbial cultures was studied by light microscopy using a MicroOptix MX-1150 stereoscopic-trinocular microscope.  Bacterial colonies were counted on day 2-3, yeasts and fungi on day 5-7. In the inoculations, dilutions of 1:102 and 1:104 were used [13].

RESULTS AND DISCUSSION

Natural Water Analysis

In order to evaluate the coagulation efficiency of reagents created based on activated aluminum alloys their tests were carried out on different types of natural and recycled water. The assessment of quality of the tested water consisted in its analysis and in comparison, with the sanitary and epidemiological standards established for drinking water supply, recycled and wastewater intended for discharge into water bodies.

Physico-chemical parameters of the investigated natural waters are presented in Table 1.

Analysis showed that natural waters, in general, are slightly alkaline, low-mineralized fresh, moderately hard (Table 5). Alkalinity and turbidity increase in the samples taken in autumn compared with spring. The content of salts in the water of the river Zhayyk (Atyrau) exceeds, allowable by regulations upper levels, not more than 1000 mg/cm³. The main cations are sodium, potassium, calcium, magnesium, in concentrations below the maximum permissible concentration, iron less than 0.1%.  All investigated natural surface waters by turbidity exceed the allowable standards (not more than 2.6 FNU).

Microbiological Composition

Table 2 shows the taxonomic groups of microorganisms detected in water samples from the "Medeu" tract. The level of microbial infestation reached 12.8x10² CFU/ml.

Presence of aerobic Gram-negative, facultatively anaerobic microorganisms, Gram-positive cocci; Gram-positive bacilli and endospore-forming cocci (genera Bacillus; Bacillus spp. cocci; Gram-positive bacilli and cocci forming endospores (genera Bacillus; Clostridium), and also the presence of Escherichia coli bacteria, Proteus bacteria and saprophytic bacteria of the genera Aeromonas and Pseudomonas [16-18]. The presence of saprophytic bacteria from 1x10¹ to 13x10² CFU/ml in water indicates the pollution of the water body with by organic substances.  In addition, a comparative study was conducted on the number of representatives of the genus Pseudomonas. It was found that the total number of bacteria in 1 ml, according to the method of serial dilutions, is 2.4x10²

 

Coagulant Analysis

In order to treat natural water as well as industrial recycled water, samples of aluminum alloys with the content of activating additives from 0.5 to 1 wt% were prepared and PACs were synthesized on their basis.

PAC synthesis was carried out by dissolution in 3% hydrochloric acid, activated alloy with aluminum content from 97% to 98.5% at an initial process temperature of 25ºC without heat supply from the outside. The reaction is accompanied by emission of heat and hydrogen and temperature rise to 65-70ºC, which is maintained by the heat of exothermic reaction. The process is completed in 2-4.5 hours (Table 2). In contrast to the known methods of obtaining PAC [2-4], the process temperature is 30-40 ºC lower, more than three times lower in concentration of hydrochloric acid applied and 1.5 times faster in implementation time. Depending on the composition of the activated alloy used and reaction conditions, the mass fraction of aluminum in terms of aluminum oxide (Al₂O₃) in PAC varies from 33.2 to 41.0%, basicity from 55.1 to 66.5%.

The characteristics of PACs synthesized using activated aluminum alloys are shown in Table 3.

Natural Water Treatment

The results of evaluation of PAC efficiency for natural water treatment are presented in Tables 4, 5. Turbidity reduction efficiency reaches 99.8%. The treated water complies with the normative requirements for hydrogen index, chemical oxygen demand, turbidity, cations and anions content. The effectiveness of reducing permanganate oxidation of the water sample from the "Medeu" tract reaches 90.7% (Table 6). Also found that in the water after treatment with coagulants aluminum content is 0.03 mg/l which corresponds to Sanitary and epidemiological requirements for sources of water supply, places of water intake for domestic drinking purposes, domestic drinking water supply [14].

The number of bacteria in 1 ml, and the species composition of microorganisms after treatment of water "Medeu" in two concentrations were studied. In water samples "Medeu" before treatment, the total number of microorganisms reached 12.8x10² CFU/mL, whereas after treatment with coagulant № 20 (0.1% solution in terms of Al₂O₃) 0.1 ml/L (0.3 g/t of dry) (dose, this figure was 0.3x10² CFU/mL. At a concentration of 5 ml/L (15.1 g/t of dry), the total number of saprophytic microorganisms did not exceed 0.1x10² CFU/mL.

Total number of bacteria in 1 ml according to the serial dilution method before treatment with 2.4х10² cells/mL in the samples after the treatment with the dose (0.1ml/L,) 0.2х10² cells/ml, in the concentration of 5 ml/L no representatives of this genus were found.

Microbial diversity in natural water of Medeu tract before and after treatment with 0.1% coagulant solution №20 in terms of Al₂O₃ is illustrated in Fig.1.

In the water sample before coagulant treatment the number of Gram-negative bacteria (Enterobacter, Proteus, Aeromonas, Chromobacterium, Flavobacterium, Alcaligenes) was ~ 7.3 CFU/mL. Gram-positive bacteria (Bacillus, Bacillus, Clostridium, Micrococcus, Enterococcus cocci and endospores) was ~ 4.2 CFU/mL, other groups of microorganisms were about ~ 1.3 CFU/mL,

After RAS treatment at a concentration of 0.1 ml/L: Gram-negative bacteria decreased to ~ 5.1 CFU/mL (by 30.1%), Gram-positive bacteria decreased to ~ 2.2 CFU/mL (by 48%), other groups of microorganisms decreased to 0.1 CFU/mL ~ (by 92%).  After treatment at a concentration of 5 mL/L, the number of gram-negative bacteria decreased to ~ 2.0 CFU/mL (73%), gram-positive bacteria to ~ 0.7 CFU/mL (84%). other groups of microorganisms decreased from 1.3 to - 0.05 CFU/mL ~ 96%.  Up to 16.0% of Gram-positive bacteria and up to 27% of Gram-negative bacteria were retained in the treated water at a concentration of 5ml/L. Fungi and yeasts (Mucor, Fusarium), their number was 8x10² CFU/mL, after treatment representatives of this genus were not detected in both concentrations.

Recycled Water Treatment

The results of assessing the effectiveness of treatment of recycled water, selected from the WTU of PDOR are shown in Table 7. Table 7 shows the results of assessing the effectiveness of reducing turbidity of recycled water samples taken from the WTU of PDOR when treated with PAC solutions based on activated aluminum alloys in comparison with the industrial Aqua-Aurat. Water turbidity for sample №1 was 94.9 FNU, for sample №2 -182 FNU. Optimization experiments on coagulants doses were conducted to determine an acceptable and sufficient dose of coagulant. The coagulant dose is an important technological parameter in reagent water treatment. If the coagulant dose is insufficient, the required degree of purification is not achieved while consumption in excess can affect water quality (change the aluminum content in the treated water).

Analysis of the data in Table 7 indicates that the required coagulant dose to achieve the highest degree of purification (99%) depends on the mass fraction of aluminum in terms of Al₂O₃ in the PAC. As the mass fraction of aluminum in PAC increases, the sufficient coagulant dosage to the required effect decreases. Therefore, for Akva-Aurat (mass fraction of Al₂O₃ is 30%) the dose of coagulant is 233 g/t. For coagulant №25, (mass fraction is 37.9 %) it is 184 g/t. For coagulant №20, (mass fraction is 33.2%) a sufficient dose is 210 g/t. Turbidity is reduced for sample №1 from 94.8 FNU to 1 FNU, for sample №2 from 182 to 1.8 FNU.  In the pH range of 6-8.5, coagulants are effective for high turbidity water treatment. The pH values at which the appropriate coagulant acts most effectively were determined. Figure 2 shows curves of the degree of decrease in the turbidity of raw water with pH of 8.5, compared with water acidified to pH 6.0 depending on the dose of coagulant №20. Sedimentation of suspended solids is more effective for water with pH 6.

Consequently, PACs synthesized using activated aluminum alloys are effective coagulants for natural water and recycled water treatment and exhibit bactericidal properties.

CONCLUSION

Chemical and microbiological composition of natural and industrial recycled water has been studied. Unique alloys with high energy characteristics based on aluminum activated by metal-activators: indium, gallium and tin have been created. The content of each additive is 0.5 to 1.0 wt.%. Alloy with such additions possesses high activity in different oxidizing environments (water, hydrochloric acid). Coagulants PAC synthesized using them are efficient in processes of water conditioning and physical-chemical treatment of recycled and wastewater from toxic compounds of natural and anthropogenic origin. In addition, coagulants possess bactericidal activity.  The use of coagulants allows to avoid primary chlorination, the level of Gram-negative bacteria in treated water is reduced to 73%, Gram-positive bacteria to 84% and up to 96% of other groups of microorganisms. Fungi and yeasts (Mucor, Fusarium), their number was 8x102 CFU/mL, after treatment of representatives of this genus were not found in both concentrations. Coagulants are effective in a wide pH range from 6 to 8.5.

The results of analysis of treated water comply with the requirements for drinking water supply and wastewater disposal Order of the Minister of Health Republic of Kazakhstan dated February 20, 2023 № 26 and ISO5667.

About the authors

Галина Бойко

Satbayev University

Author for correspondence.
Email: galina.boyko.kaznitu@gmail.com
ORCID iD: 0000-0002-2912-3384

Doctor of Chemical Sciences, Professor of the Department of Chemical and Biochemical Engineering

Kazakhstan

Raushan G. Sarmurzina

KAZENERGY

Email: sarmurzina_r@mail.ru
ORCID iD: 0000-0002-9572-9712

D. Sc. (Chemistry), professor

Kazakhstan, Astana

Nina P. Lyubchenko

Satbayev University

Email: amtek@bk.ru
ORCID iD: 0000-0002-7133-808X

Chemical Sciences, Associate Professor

Kazakhstan

Жазира Балтабекова

Email: jazira001@mail.com
ORCID iD: 0000-0003-3076-0652

Куаныш Талгатович Тастамбек

КазНИТУ им. Сатпаева

Email: tastambeku@gmail.com
ORCID iD: 0000-0002-2338-8816

Ph.D, ведущий научный сотрудник

Kazakhstan, Алматы

Pavel V. Kenyaikin

Satbayev University

Email: kenyaikin.p@gmail.com
ORCID iD: 0000-0002-4360-1573
Kazakhstan, Almaty

Anel Taubatyrova

Satbayev University

Email: gggnika465@gmail.com
ORCID iD: 0009-0001-1329-0372
Almaty

References

Supplementary files