Water treatment for domestic and semi-industrial needs
The segment of domestic water treatment has a pronounced direction. The first direction is the post-treatment of network water offered by public utilities. The second direction is the post-treatment of water obtained from artesian sources. Of course, one more direction can be singled out – additional purification of water for domestic purposes from surface water sources. However, the latest installations on the territory of Ukraine are rare and deserve a separate discussion.
Due to the fact that centralized water supply has different sources (as a rule, these are the rivers of Ukraine, less often – artesian ones), and also due to the fact that artesian sources are highly dependent on groundwater basins, household water treatment has a pronounced regional character, which affects the technical performance of one method or another.
In household and small-scale industrial water treatment, two main intended uses of water are distinguished – for household needs and for drinking (cooking).
Domestic water is used for life support systems of a residential and / or industrial premises and may not have a regulatory binding for its qualitative composition. An exception is the case of providing such water by public utilities that are obliged to provide drinking water for household needs (for example, in the case of an apartment building). In principle, household water should ensure minimal deposits of calcium carbonate salts on heating surfaces (so-called scale), not clog household appliances with mechanical impurities (suspended solids and pipe rust), not stain plumbing surfaces (ferric iron oxide), be not hard (poor lathering of surfaces) and not very soft (poor rinsing of soap products), not have foreign odors (rotten from hydrogen sulfide or mercaptans).
Water for drinking purposes on the contrary – must comply with the state standard: STATE SANITARY STANDARDS AND RULES “Hygienic requirements for drinking water intended for human consumption” (DSanPiN 2.2.4-171-10). Here you can give a link to download on our website (the document itself is in the attachments to the letter, it can be posted in the information section) It is in it that the quality parameters are reflected – both the maximum allowable and the minimum contents of salts which distinguish drinking water from partially or completely desalinated (Appendix 4 to DSanPiN 2.2.4-171-10 “INDICATORS of physiological completeness of mineral structure of drinking water”).
Traditional technological methods for obtaining water for domestic and drinking purposes are mechanical filtration (cartridge or multilayer granular), iron removal (using external oxidizing agents or granular materials that catalyze the oxidation process with oxygen dissolved in water), softening (ion exchange using strong acid cation exchanger in Na+-form), removal of active chlorine, chlorine-organic and chlorine-volatile compounds of artificial origin (cartridge or granular activated carbons), organic impurities of natural origin (cartridge or granular activated carbons, ion exchange using a highly basic anion exchange resin in Cl—form – the so-called. absorbent, ultrafiltration), microbiological purity (disinfectants, ultraviolet radiation, ultrafiltration), partial desalination (nanofiltration or reverse osmosis).
In the case of using centralized water supply systems as a source of domestic and semi-industrial water treatment, as a rule, technological solutions are used using cartridge filter materials (softening technology is often an exception) and domestic ultrafiltration and/or nanofiltration and/or reverse osmosis units.
This is due to the fact that public water supply services have done quite a lot of work to purify water from their own water sources. Contrary to the popular belief “…utilities do nothing but demand payment of bills…” I would like to note their huge contribution to bringing water quality up to drinking standards, especially in the case of surface water sources. Those qualitative inconsistencies that are present today are the result of obsolete technological methods and / or equipment and materials used. But even in such conditions, some municipal enterprises of Ukraine are trying to optimize existing technological processes, carry out reconstruction of equipment and networks, as well as apply modern technical methods from the field of industrial water treatment. Those interested can get acquainted with the reports of utilities at the conference ETEVK-2017 (ECOLOGY-TECHNOLOGY-ECONOMY-WATER SUPPLY-SEWERAGE).
And yet, when developing a water treatment system for tap water, it is worth focusing on: mechanical pollution, residual chlorine, sometimes optimizing the hardness and mineral composition of water and, especially, organic compounds of natural and artificial origin (in the latter case, exceptional attention to chlorination products! ). Regional bindings to large cities (Kyiv, Dnipro, Lvov, Kharkiv, Odessa, Donetsk and others) should take into account in the technological solution for domestic water treatment the features of local prevailing mineral contaminants, the content of organic impurities (permangantan and / or bichromate oxidizability parameter, measured in mgO2/дм3) and especially the decontamination method adopted by the local utility company (chlorine gas, sodium hypochlorite, chlorine dioxide, ultraviolet radiation).
For example, the water of the Seversky Donets River is harder than the Dnieper River. Поэтому жесткость водопроводной воды будет колебаться между 9,0 – 11,0 мг*экв/дм3 (требует обязательного умягчения) и 2,5 – 3,5 мг*экв/дм3 (достаточно комфортно и без умягчения) соответственно (при норме по ДСанПіН 2.2.4-171-10 равной 7,0 мг*экв/дм3). Thus, when installing a domestic reverse osmosis unit in an apartment (in a washing version), it is advisable to take into account these features of tap water: in the first case, equip the unit with an ion-exchange resin cartridge (partial softening function), in the second case, you can save money and put just a mechanical cartridge or activated carbon cartridge.
Domestic and semi-industrial water treatment on artesian water has an even more pronounced regional character. This is due to the fact that even within the same region, the quality of artesian water can be different, which is associated with the depth of the well – i.e. with aquifers from which water is withdrawn. Therefore, along with the experience of a potential Contractor of a water treatment system in a given region and / or part of it, it is no less important to understand the qualitative and quantitative (!) Composition of a particular water source. Thus, the availability of qualitative indicators will allow the potential Contractor to verify the compliance (or non-compliance, which is not rare) of a typical (basic) solution for a given location, and the availability of quantitative indicators (well flow rate, static and dynamic levels) will allow choosing the right set of equipment for implementation techniques and automation of the entire process.
For example, in the same suburban village, at a distance of 100 m, there are areas with artesian wells: in the first case, the depth of the aquifer is 10 m, in the second, 50 m.
The characteristic features of the surface horizons (the first well) will be a low mineral composition, acceptable hardness, but increased contents of iron, organics and mechanical impurities (sometimes all at once, in different regions – in different ways). Содержание железа может достигать 2 – 3 мг/дм3 (при норме ДСанПіН 2.2.4-171-10 равной 0,3 мг/дм3). To avoid staining of sanitary ware, household water treatment should use equipment with the principle of industrial design – the oxidation of iron to a trivalent (insoluble) form, followed by filtration on a regenerated granular load. The technical methods of this process may be different, but neglecting them and / or calculating with large errors and / or installing equipment without calculation and / or using a simpler solution (for example, mechanical cartridges) threatens with a constant “headache” for a potential Contractor or Customer (in depending on how the contract is drawn up and what qualitative and quantitative guaranteed indicators are prescribed).
Characteristic features of deep horizons (second well) will be minimal organic and mechanical impurities, iron, odors, but high mineral composition, high hardness. The content of the same parameter (iron) may not even exceed 0.1 mg/dm3 and this parameter is not of fundamental importance for the design of domestic water treatment. However, now, during domestic water use, nozzles of automatic irrigation systems, heating elements of equipment, etc., may suffer, for example, due to high hardness and, as a result, deposits of calcium and magnesium carbonates. Thus, industrial design principles should be applied to the ion exchange plant (softener) with all the possible consequences described above.
In conclusion, I would like to note that standard (template) solutions in the field of household and semi-industrial water treatment have proven themselves well with their availability (especially in municipal waters) due to the exclusion from the cost of participation of highly qualified specialists (water treatment engineers), technological risks, technological guarantees, etc. P. However, especially at artesian water sources, it is not uncommon for technological support and adaptation of standard equipment to be almost the only opportunity for a comfortable, stable and problem-free water supply.
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