Unification of requirements for the use of reagents for the treatment of sewage sludge from urban sewage treatment plants

. This paper describes the experience of unification of requirements for the use of natural and synthetic reagents at all stages of wastewater sludge treatment. The practical necessity of this study is due to the tightening of environmental requirements around the world and the increasingly active introduction of closed-loop technologies of the economy. To date, products from sewage sludge are unclaimed not only by construction and road enterprises, but also by municipalities, which could more actively use the soil for landscaping urban areas. The most promising in terms of results and costs is the use of reagents at all stages of wastewater sludge treatment. Their use makes it possible to significantly reduce the costs of such technological processes as dehydration and stabilization. Reagents are an indispensable component in modern approaches to composting and disinfection.


Introduction
The current stage of development of urban sewerage treatment facilities is characterized by a focus on long-term sustainable development, which, in addition to the total cost, requires taking into account such parameters as the maximum possible involvement of waste in the circular economy, increasing resource and energy efficiency.
Treatment plants, whatever their size, technological lines and quality standards for purified water produce sediment, the amount of which is related to the type of technological process itself (primary treatment, physico-chemical treatment, biological treatment) [1].
Until now, the main method of disposal of sewage sludge remains its mechanical dewatering and storage on sludge ponds or in technological earthen barns, where disinfection takes place for a long time.
Sludge beds are one of the first sewage sludge treatment facilities.They are designed for natural dewatering of sludge generated at biological wastewater treatment plants.They are the most common method of sludge dewatering.Currently, 90% of all sludge is processed at sludge beds.This method does not meet modern environmental and technical requirements, leads to long-term and often irrevocable alienation of significant land resources, is accompanied by emissions of pollutants into the atmosphere, environmental risks of groundwater pollution in the zone of influence of waste storage sites, as well as an increase in the financial costs of enterprises due to environmental payments [1].
Modern technologies for recycling sewage sludge use detoxification, stabilization, composting and thermal processes.The high content of the organic component in sludge, as well as the presence of biogenic elements, suggests that the most rational and economically feasible way to dispose of sewage sludge is a method based on their processing to obtain a product based on sludge [1][2][3][4].
Sewage sludge contains heavy metals, which leads to pollution of water bodies and atmospheric air during their disposal, and also significantly limits the reuse of neutralized sludge.This problem can be solved by detoxifying and treating waste with the following reagents:  quicklime;  humic preparations,  complexing reagents based on copper compounds etc. [2] Quicklime, humic and complexing preparations provide detoxification of sewage sludge by different mechanisms.In the case of quicklime, the formation of insoluble compounds of heavy metals occurs; for other reagents, it is possible to bind heavy metal ions into poorly soluble metal humates or form stable complex compounds that actually fix heavy metals [2].

Materials and methods
Wastewater treatment (and water supply) operations make extensive use of chemicals.Water treatment plant operators add chemicals in a variety of processes to control corrosion, eliminate odors, remove grease, reduce BOD, pH-control and biosolids, ammonia oxidation, bacterial reduction, and more.
For the purposes of the study, the functional tasks of using reagents were formulated:  ensuring effective treatment of municipal and industrial wastewater;  stimulation of the work of biological treatment facilities;  increasing the degree of dewatering of sewage sludge at the stages of mechanical dewatering (newly formed sludge);  increasing the water-yielding properties of sediment placed on silt pads (accumulated sediment);  disinfection and deworming of sewage sludge;  elimination of unpleasant odors when treating sewage sludge;  stabilization and provision of fermentation/composting processes of sewage sludge.To use any chemicals correctly, it is important to calculate their dosage.One of the most commonly used mathematical calculations in wastewater treatment and water supply operations is the determination of dosages and loads.Chemical dosage is measured by the amount of chemical added to the wastewater.The amount of chemicals needed depends on their type, the purpose of their use and the size of the stream being treated.
The study examined the characteristics and features of the use of natural and synthetic reagents (Table 1).The practical basis for the study was 60 municipalities with the status of "municipal (city) district", which are responsible for organizing wastewater disposal within the district's boundaries.The study examined the water supply and sanitation schemes of these municipalities.Of the 60 municipalities, 45 have water supply and sanitation schemes published in accordance with legislation.
Of the 45 municipalities that have placed Schemes in accordance with the legislation, 7 do not have their own treatment facilities.The wastewater of these urban districts is passed through the treatment facilities of Mosvodokanal, the Energetik municipal unitary enterprise in Pavlovsky Posad, at the Shchelkovo interdistrict treatment plants and through the water treatment system of Lyuberetsky Vodokanal.
The urban districts of Pushkinsky and Dolgoprudny have sewage treatment plants of insufficient capacity and additionally use wastewater treatment facilities of other municipalities.
Having analyzed the water supply and sanitation schemes, the following conclusions can be drawn:  wastewater treatment plants in 28 municipalities use sludge banks to dewater sludge;  in 9 urban districts, sludge is transported to a landfill under an agreement with a specialized organization;  the urban districts of Dubna and Shakhovskaya use the composting method to process sludge;  in the urban districts of Podolsk and Kolomna, treated sludge is used as a component for the production of soil.

Results and discussion
Based on the results of the study, they were systematized, which made it possible to identify and confirm the capabilities of reagent technologies in order to optimize the treatment of wastewater sludge at wastewater treatment plants (Table 2).The use of reagents is not within the scope of BAT.The introduction of reagents allows you to optimize work and reclaim existing sludge beds.Accordingly, it is possible to eliminate/reduce the volume of previously accumulated sediment.

Reducing the volume of sludge generated by optimizing the operation of biological treatment facilities
Biological products, effective microorganisms, aqueous solutions This task does not optimize the operation of treatment facilities, but gives a temporary effect until reconstruction.A decrease in the volume of sediment generated leads to a change in the technological process in aeration tanks and, accordingly, to the dependence of structures on the constant dosing of reagents.Does not comply with NDT.This is not a solution that can be recommended, except in the case of very old treatment facilities where reconstruction is not possible [ Based on the study, a standard regulation was proposed for carrying out work on the disposal of sewage sludge from biological treatment plants using reagents that can be used when working with sludge formed at sewage treatment plants.
The use of reagents for neutralization, disinfection and stabilization of sewage sludge is used in the following areas:  disinfection and stabilization of raw sewage sludge that has not undergone preliminary mechanical dewatering  disinfection and stabilization of mechanically dewatered sewage sludge  disinfection of household wastewater  disinfection from pathogenic and conditionally pathogenic microorganisms, viruses, bacteria, fungi and mold.

Conclusion
The technological regulations developed as a result of the study regulate the procedure for the disposal of wastewater sludge from sewage treatment plants using reagents and biological additives, including: quicklime, humic preparations, complexing reagents based on copper compounds, etc. followed by processing of the mixture.The developed document is intended for organizations providing services for wastewater treatment of centralized sewerage systems and disposal of wastewater sludge from sewage treatment plants.
The result of the work is the possibility of justifying the rules and stages of the processes of neutralization and disposal of newly formed and accumulated wastewater sludge using reagents and subsequently obtaining products.

Table 1 .
Analyzed types of reagents.

Table 2 .
Possibilities for justifying the introduction of reagents when treating wastewater sludge.