Biochemical treatment of water in closed circulation systems
Vital activity of microorganisms deranges the water pipelines, stimulates corrosion of steel, aluminium, and brass, and decreases the quality of water.
Wastewaters discharged by various branches of industry have different chemical compositions. However, all the sewage types can be successfully treated with PHMG hydrochloride.
Application of PHMG hydrochloride in all these cases decontaminates wastewater, suppresses fermentation, putrefaction, biofouling, and corrosion.
Even small concentrations of surfactants in water basins cause high foam formation, disturb the oxygen exchange, and have a negative impact on animals and plants.
The technology with closed water cycle is one of the types of zero-discharge production systems used in various industries. Appropriate degree of sewage treatment is necessary for the normal functioning of such systems, as well as for the prevention of biofouling, corrosion, and scale build-up.
Industrial wastewater is usually treated with mineral coagulants and organic flocculants before recirculation. However, such treatment leaves a large concentration of microorganisms in the recycled water, which can lead to biofouling and corrosion of water pipelines.
Chlorination of water for microorganism elimination and water treatment with copper sulphate for algae growth suppression is widely used in Russia. Application of these chemicals has a number of essential drawbacks: high toxicity, low duration of after-effect in water, enhancement of scale build-up, increased corrosion activity of water.
All this is a serious threat for the functioning of a closed water cycle system.
High-molecular biocides polyalkylene guanidines (polyhexamethylene guanidine hydrochloride, PHMG hydrochloride) – Biopag and Phosphopag, developed by the Institute of Ecotechnologies are very perspective chemicals for sewage purification and decontamination.
These water-soluble solid polymers have antiseptic properties with a wide range of biocide activity, as well as cationic flocculant properties. In contrast to chlorine, they are low toxic, non-volatile, stable in storage, impart neither smell nor taste to the water. Preparation of working solutions and dosage of PHMG hydrochloride does not require special equipment and safety measures.
PHMG hydrochloride have a prolonged bactericidal activity in water, they kill gram-positive and gram-negative bacteria, fungi, and algae. Complete water decontamination occurs within 30 60 minutes after the chemical’s application.
New nidus of infection introduced into water two or three days after the first water treatment with PAG is eliminated within 20-30 minutes without an additional application of the chemical.
PHMG hydrochloride also have flocculating properties, apart from the biocide action. Their flocculating action is due to the cationic activity of the guanidine group that has a positive charge.
PHMG hydrochloride can be applied both independently, and in combination with coagulants.
One of the research laboratories of the Moscow water supply Company “Mosvodokanal” performed extensive experiments both in laboratory conditions, and at the production facilities of Moscow automobile plant “ZIL”.
Perspectives of substituting the traditional flocculant - polyacrylamide - with PHMG salts were studied in these experiments.
Technological scheme with closed water cycle was developed for the “ZIL” plant. This scheme includes industrial sewage treatment, makeup water preparation, and local purification of lubrication-cooling liquids.
PHMG salts are applied in all the stages as biocides, flocculants, and deemulsifying agents. This allowed reducing the necessary quantity of aluminium sulphate coagulant by a factor of 2-3 in some of the water treatment stages.
This also leads to the decrease of oil product concentration in the treated wastewater from 180 mg/l to approximately 2 mg/l, and of suspended particle concentration – from 200 to 3 4 mg / l.
Note that the polymers used for water treatment are almost completely involved into the flocculation process and precipitate to the bottom together with the impurities the water contains.
The residual concentration of PHMG hydrochloride in settled treated sewage is very low. Application of PHMG hydrochloride in the system for treatment of makeup water taken from the river reliably protects the river water intake system, purification facilities and supply pipelines.
This also ensures the necessary water quality according to the complete set of requirements, including sanitary and hygienic norms.
Lubricating and cooling liquids are used in engineering plants for a number of manufacturing operations (cutting, polishing, pressing, etc.). The cooling liquids are polluted with dust particles of micron sizes, soot, lubricating oils, and putrefaction process begins due to the activity of microorganisms.
Discharge of such contaminated oil-water emulsions into drainage inadmissible, because it could disrupt the process of wastewater treatment with activated sludge. Separation of true emulsions and decontamination of the precipitates and clarified wastewater is the most difficult task in treatment of cutting liquids.
Polyethyleneimine and quaternary ammonium salts are widely used as flocculants and deemulsifiers for this purpose. This allows reaching 96-98% degree of lubricating liquid decomposition, but it cannot ensure the sanitary safety of the wastewater.
Therefore application PHMG hydrochloride as biocidal cationic flocculant appears very perspective. E.g., phase separation degree can increase by a factor of 2-3, and complete antiseptisation of water can be achieved via introduction of a PHMG salt into spent emulsion containing «Óêðèíîë-1Ì».
The water produced by cutting emulsion decomposition in this case is almost clear, has a light yellow colour, and does not derange the operation of the factory sewage treatment facilities. Such wastewater can be safely discharged into the factory sewage system.
Almost any closed-cycle system of industrial water supply provides conditions for biocenosis development. The activity of such biocenoses deranges water pipeline operation, enhances corrosion of steel, aluminium, and brass, and has a negative effect on water composition.
Water contamination with microorganisms from air and from the make-up river water is the principal source of biological pollution of the industrial water circulation systems.
PHMG hydrochloride have a high biocide activity against such biocenosis components as chlorella, cyanobacteria, fungi of the Aspergillus, Cladosporium, Mucor types that form clusters in recirculating water systems.
This allows using these polymers to fight biofouling of technological equipment.
Biofouling is easiest to counter before mechanical admixtures and microorganism clusters are formed in the circulation system. Periodical treatment of the system with water containing PHMG salt is recommended to prevent biofouling.
Such treatment reduces the total microbe concentration in the circulation system from 8*109 to 102 CFU / ml, and no biofouling occurs for at least 36 days. For comparison, biofouling in the recycling water supply systems becomes obvious already 8-9 days after the treatment with chlorine.
To remove the existing biofouling build-up it is necessary to substantially increase the PHMG salt concentration or its operation time.
PHMG hydrochloride are successfully applied for purification of sewage discharged in the process of cinema and photo film production.
Wastewater containing precious silver salts is treated first with a cationic flocculant (polydimethyl ammonium hydrophosphate, ÂÏÊ-phosphate), and then with an anionic flocculant (carboxymethylcellulose).
The cationic flocculant neutralises the negative charge of superfine silver particles and forms small aggregates, and the anionic flocculant binds these aggregates into easily precipitating particles and large flakes.
PHMG salt is introduced into the wastewater after settling, and then the mixture is filtered. Degree of silver recovery from the sewage reaches practically 100% with this technology. Integrated treatment of wastewater occurs at the same: 70 % of dispersed particles are removed; coloration is reduced by 70 % and chemical oxygen demand (COD) decreases by 65-70 %.
Waste waters of tanning and fur branches of light industry as well as those of dyeing and decorating factories of textile industry contain high concentration of various pollutants. Large suspended particles (scrapings, wool, fibres, semi-product shreds, etc.) are removed with mechanical filters.
According to the sanitary and technological requirements for the treated industrial sewage in tanning, fur, and textile industries and due to the large amount of sewage, coagulation, flocculation, and floatation techniques are widely used. Aluminium sulphate or aluminium oxychloride is usually applied as coagulant. Cationic polymer ÂÏÊ-402 (poly-N’N-dimethyl-N’N-diallyl ammonium chloride) is used as flocculant. Polyacrylamide and partially hydrolysed polyacrylamide (Hypan) are among the most effective non-ionic and anionic flocculants.
The Chair for technology and equipment of the Academy of light industry has developed the methods for the sewage treatment in tanning and textile industry with BioPAG (polyhexamethylene guanidine chloride, PHMG chloride).
Concentration of surfactants, sulphides, chromates, phenol, and dyes in wastewater of such industries can reach 250-300 mg / l, whereas the maximum permissible concentration limit for these pollutants in sewage discharged into the natural water basins is as low as 0.5-1.0 mg / litre.
The presence of sulphides in wastewater causes sewer and pipeline corrosion, hydrogen sulphide release, and development of thionic bacteria that produce sulphuric acid. Application of PHMG chloride to the wastewater reduces the sulphide content by a factor of 3-6.
Combined application of a coagulant (aluminium sulphate) and PHMG chloride reduces the sulphide concentration by a factor of 24-110 (depending on the reagent concentration). Optimal consumption of reagents allows reducing sulphide concentration in wastewater down to 5-10 mg / l.
Application of PHMG chloride also disinfects the sewage, prevents protein putrefaction in the settling vats, and therefore reduces hydrogen sulphide release.
High concentration of surfactants is also present in the tanning industry wastewater, as well as those of the dyeing and decorating industry. Even low concentration of surfactants in water basins causes excessive foam formation, disrupts the oxygen exchange, and has a negative impact on the water animals and plants; this can even cause fish death.
Combined application of PHMG chloride and aluminium sulphate allows reducing surfactant concentration in wastewater from 270 330 mg / l to 3-5 mg / l.
The existing technology of dyeing in textile industry discharges wastewater with concentration of various types of dye up to 1000 mg / l. Some of these dyes are toxic with local impact, besides that they have a toxic and inhibiting action on the microorganisms, and therefore they are not easily oxidised with biochemical technique.
Application of PHMG chloride as flocculant allows reducing the dye concentration: down to 6-10 mg/l for the direct black, down to 0.4-1.0 mg / l for the chrome green, and down to 0.2-0.3 mg / l for the âîôàëàíà áîðäîâîãî (???).
Concentration of phenols in tanning industry wastewater can be reduced from 270-330 mg / l down to the values below the maximum permissible value.
High toxicity of the galvanic industry sewage poses a danger for the natural water basins. Such wastewater discharged into the municipal sewage system can also disrupt the biochemical process of the residential wastewater treatment.
Existing multi-stage techniques for the treatment of galvanic industry sewage are very expensive, because they require a lot of reagents. Non-cyanic galvanic technology developed by the Institute of ecotechnologies for zinc and cadmium plating uses GEK additive instead of the highly toxic cyanides.
This improves the working environment and the ecological safety of the production. This also allows excluding high-toxic phenol from the technological process. GEK additives have the properties of cationic polyelectrolyte, that facilitates effective purification of spent electrolytes and rinsing water contaminated with heavy metal salts in galvanic industry.
Application of Biopag in paper production reduces the loss of raw materials and ensures a substantial (fivefold) decrease of industrial sewage pollution. This effect is due to the interaction of the Biopag cations with negatively charged cellulose particles.
This interaction is stronger for the smaller particles that have greater specific surface. Biopag induces conglomeration of smaller particles with larger ones by reducing the negative charge of the former. Thus large flakes are formed that precipitate rapidly to the net of paper-making machine.
The examples show that the wastewater discharged by various industries and varying in their chemical composition can be effectively treated with PHMG hydrochloride. In all the cases application of PHMG hydrochloride decontaminates the wastewater, suppresses the fermentation, putrefaction, biofouling, and corrosion processes.
Problems connected with the microorganism activity appear often in the cooling systems of electronic devices that use ordinary distilled water as heat carrier.
A cooling system with water circulation often includes aluminium pipes and rubber tubing. These systems interact with the atmosphere that is the principal source of the system contamination with microorganisms. Microorganism development in such cooling systems leads to the decrease of pipe throughput due to the biofouling of the pipe inner surface. This disrupts the functioning of the cooling system and causes damage to the pipe material. This damage is due to the action of microorganism metabolism products and it can have the form of pittings (deep local cavities in the metal surface).
Electron microscope studies of the inner and outer surface of the cooling system aluminium pipes found evidence of biocorrosion. Forty-five types of microorganisms (bacteria, micromycetes, and yeast – see Table) causing biodestruction were found and identified in the cooling systems.
Electron microscope studies of the inner and outer surface of the aluminium pipes of a cooling system found evidence of biocorrosion. Forty-five types of microorganisms (bacteria, micromycetes, and yeasts – see Table) causing biodestruction were found and identified in the cooling systems.
The direct evidence of aggressivity of microflora association towards aluminium was obtained in the following experiment. Aluminium plates were exposed for ten days in a retort with microorganisms found in cooling systems.
Coral-shaped fungus colonies were observed under a microscope on the metal surface. Pigmentation and gas release were also observed in the vicinity of these colonies. After the mechanical removal of the colonies round shell-like defects in the metal surface were found with microfissures at their bottom going into the sample bulk.
The diversity of the microorganism contaminating the cooling systems requires application of biocides with a wide spectrum of action. Besides, the biocides should not cause corrosion of the structural materials of the cooling system. Yet another requirement is the long-term preservation of biocide activity at low temperature.
The existing chemicals inhibiting metal corrosion have a number of drawbacks. They are either effective only within a narrow concentration range, or they are toxic for animals and humans, or favour biofouling in the water circulation systems. Twenty biocides for protection of cooling systems were studied, including “Progress”, Twin-40, Triton X-100, Syntanol ÄÑ-10, sodium dodecylsulphate, glutaric aldehyde, dichlor glyoxime, N cetyl pyridine chloride, catamine AB, etc.). PHMG chloride proved to be one of the three most perspective biocides for the protection of cooling systems. PHMG phosphate was recommended for the complete protection of water circulation systems from corrosion, biofouling, and scale deposition.
Microorganisms found in the coolant and the decayed parts of the cooling system
|Bacteria||Number of strains||Micromycetes and yeasts||Number of strains|
|Pseudomonas aeruginosa||4||Penicillium chrysogen||1|
|Pseudomonas lemoignei||1||Penicillium sp||6|
|Pseudomonas ruhlandii||1||Aspergillus sp||2|
|Proteus mirabilis||1||Cladosporium sp||1|
|Proteus inconstans||2||Aureobasidium sp||1|