Biotesting – the modern criterion of evaluating the efficiency of UV-systems for water disinfection

Summary

Nowadays ultraviolet irradiation increasingly becomes an actual method of water disinfection. Herewith units with amalgam and mercury low pressure lamps are mostly used. In the radiation spectrum of these lamps the mercury resonance line is dominating with 253.7 nm wave length on which up to 40% of the lamp power can fall. Radiation with this wave length has a powerful disinfection effect. The impact of UV-irradiation results in irreversible DNA and RNA damage in microorganisms so that the latter lose their reproductive capacity (become inactivated). The main parameter that characterizes the efficiency of these installations is UV-irradiation dose. It is a calculated value, therefore to obtain the maximum information on the operation of a UV-disinfection unit it is advisable to carry out biotesting with the help of live microorganisms. Besides, in some countries (Germany, France, Austria, USA) biotesting of UV-systems is obligatory. In Russia bio-validation is not obligatory; therefore real biological tests are often substituted with computer simulation. Process simulation carried out for a seven-lamp unit manufactured by «LIT» Scientific-Production Association produces the results close to the results obtained during biotesting. This confirms the range of use of disinfection UV-unit claimed by the manufacturer. However, the absolute guarantee of the UV-unit efficiency is bio-validation only since it supposes the use of live water and microorganisms. The data obtained in the process of biotesting allow describing the specific features of the disinfection unit operation to the fullest extent possible. The certificate verifying biotesting is a credible guarantee that the unit will provide for the required level of water disinfection.

Key words

microorganisms , inactivation , biotesting , amalgam lamp , ultraviolet irradiation , UV disinfection , UV-unit , irradiation dose

UDC 628.166.085
DOI 10.35776/VST.2023.03.06

Bogun P. V.

Effect of the reflection from the reactor walls
on the energy efficiency of UV water disinfection units

Summary

The results of a theoretical study of possible improving the effective dose of irradiation in a water disinfection unit with ultraviolet (UV) radiation without increasing the lamp power, as well as studying the effect of the radiation reflection from the reactor inner surface on the operation of the disinfection units are presented. The calculations were carried out for the most popular design with one lamp and a cylindrical reactor with specular reflection from the walls. The calculations have shown that at a high reflection coefficient of radiation and at certain ratios of the effective length of the propagation of UV radiation in water and the dimensions of the reactor, the energy efficiency, i. e., the plant capacity per unit of power consumed, can be increased by 35–40 % compared to the already known designs.

Key words

energy efficiency , water disinfection , ultraviolet irradiation , effective length of radiation propagation

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UDC 628.166.085

Kostyuchenko S. V., SMIRNOV A. D., Pokhil Yu. N., Bagaev Iurii

Introduction of UV-disinfection at the Novosibirsk wastewater treatment facilities

Summary

Water recycling in the modern municipal services is a comprehensive task. On one hand the city inhabitants should be supplied with high-quality drinking water meeting all the sanitary and hygienic requirements; on the other hand the discharged municipal effluents shall not produce any adverse effect on the environment. To fulfil these tasks the most advanced disinfection technologies that ensured meeting all the microbiological requirements to the drinking water and effluents were introduced at the Novosibirsk water and wastewater treatment facilities. The use of ultraviolet irradiation provided for the efficient multi-barrier protection in drinking water purification and environmentally safe disinfection of wastewater.

Key words

chlorination , disinfection , wastewater , water supply , water disposal , ultraviolet irradiation

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UDC 628.1/.2(98)

Kofman V. Ya.

Water supply and wastewater disposal in the Arctic Region:
advanced technical soltions (a review)

Summary

In Canada wastewater treatment technology has been developed for small isolated arctic communities based on the effective biodegradation of organic carbon using a combination of anaerobic methanogenic and microbial bioelectrochemical processes that provide for biomethane generation. Microbial electrochemical degradation is executed in a membrane-free flow-type reactor with a bioanode and a biocathode operating at a voltage below the threshold of water electrolysis. In laboratory-based experiments in a wide range of mesophilic and psychrophilic temperatures (5–23 °C) a high efficiency of reducing BOD₅ (90–97%) was achieved with a residual content of less than 7 mg/l. Energy consumption is 0.6 kWh/kg COD. Low energy consumption along with the production of biomethane ensures the operation of the reactor in the mode of power generation. For the conditions of Greenland a scheme of wastewater disinfection involving chemical coagulation and addition of peracetic acid, and/or ultraviolet irradiation was developed. Complete inactivation of Escherichia coli is achieved with the combined use of ultraviolet radiation (2.1 kWh/m³) and peracetic acid. Preliminary coagulation is an essential prerequisite for the effective inactivation of microorganisms. In the United States a closed water treatment scheme based on the peroxone process with reuse of water for drinking purposes has been proposed for the city of Fairbanks (Alaska). The big advantage of the closed-loop scheme is 85% conservation of the water in the system while preserving the thermal energy obtained from different water heaters. As a result the purified warm water is returned to the consumer; while less energy is required for its additional heating. In addition, the mineralization of organic substances in the oxidation process ensures the achievement of 0.7 mg/l residual COD.

Key words

wastewater , water disinfection , water treatment , ultraviolet irradiation , water reuse , the Arctic Region , preliminary coagulation , peracetic acid , peroxone process , heat energy of water , anaerobic methanogenic process , microbial electrochemical process

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UDC 628.166.085

SMIRNOV A. D., Strelkov A. K., Tkachev Andrei

Revisiting the selection of wastewater disinfection technology

Summary

Environmental law enforcement in relation to discharging chlorine and organochlorine contaminants induces the use of advanced safe and efficient chlorine free methods of wastewater disinfection. The use of ultraviolet irradiation provides for meeting all the requirements imposed on the technology of wastewater disinfection eliminating any adverse impact on the environment. The use of this technology eliminates possible penalty charges for polluting the environment with chlorine and organochlorine contaminants. The economic comparison of two disinfection methods (the application of sodium hypochlorite and UV-irradiation) reveals significant operational benefit when introducing UV-disinfection. Annual savings of operational expenditures is 50% and more at the comparable capital expenditures. The advantages of UV-disinfection are as follows: efficiency in relation to all types of indicator and pathogenic microorganisms, whereas chlorine-containing chemicals do not often ensure fair efficiency in viruses and protozoa elimination; no by-products are generated; no adverse impact on the water bodies is produced (consequently, no penalties); no threat of overdosing; easy and simple control over the disinfection process; no need in dosing system and additional control systems; disinfection effect independence from fluctuations of effluents quality within the limits of the design parameters; minimum footprint; no additional facilities are needed (e. g., contact tank for dechlorination); possible retrofitting into the existing buildings or facilities, for example, in the process of wastewater treatment facilities upgrade and chlorination replacement; low operational expenditures (lamp replacing once in a year and a half – two years and energy saving). In this context switching to chlorine free disinfection technologies that eliminate the formation of organochlorine contaminants is a correct solution.

Key words

chlorination , disinfection , wastewater , dechlorination , ultraviolet irradiation , effluents charge

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UDC 628.166.085

Bogun P. V.

On increasing the capacity of UV-units for liquid disinfection

Summary

The results of theoretical studies of the possible capacity improvement of units for disinfecting liquids including water by ultraviolet irradiation eliminating any increase in energy consumption are presented. Capacity improvement is possible at the fixed reactor geometry and source strength owing to the redistribution of liquid flows in the reactor. It is shown that the maximum possible efficient radiation dose is equal to the mean by reactor volume radiation intensity multiplied by the mean time of liquid residence in the reactor. The necessary and sufficient condition for obtaining this dose is the availability of liquid flow in every point of the reactor volume and equal radiation dose for every microvolume of liquid. By way of example the calculations of the maximum possible radiation dose for a spherical reactor with a point source of radiation and for a cylindrical reactor with a linear radiation source are presented. It is noted that widely manufactured at present UV water disinfection unit designs with a single source (a lamp) use only 30% of the source capacity. The design with a cylindrical reactor and spiral downward liquid flow distributed along the reactor length provides for the maximum possible radiation dose and/or capacity of the installation.

Key words

water disinfection , ultraviolet irradiation , irradiation dose , reactor , installation capacity

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