Comparative characteristics of the emissions control during the operation of passenger trains

. (cid:3) The trend in the development of railway transport also includes the solution of such an important environmental, technological, sanitary and, to some extent, aesthetic problem as the transfer of all operated mainline passenger trains to environmentally friendly toilet complexes (EFTC). For the disposal of EFTC waste, a system has been created for the disposal of fecal waste in parking lots, which are then transported by sewage disposal machines and dumped into general treatment facilities. At the moment, as one of the possible options for industrial waste disposal of EFTC, wastewater sludge incineration plants are being considered. The method of waste incineration reduces the time, labor and financial costs of waste turnover, and taking into account the epidemiological risks of fecal waste, it has high development prospects. This article discusses similar combustion processes using the example of technologies implemented at wastewater sludge incineration plants, emissions from enterprises and the processes of formation of pollutants. And also, within the framework of this work, a comparative analysis of the control of emissions of pollutants from the combustion of sewage sludge into the atmosphere in the Russian Federation and in the EU, countries were carried out.


Introduction
The most important role in the pollution of environmental objects, such as atmospheric air, natural waters, soils, soils, along with emissions from industrial enterprises is played by emissions and wastes from various types of transport. In particular, the problem of atmospheric air pollution by emissions from waste incineration plants is one of the leading environmental problems of recent years. Many international agreements, conventions, conferences, scientific communities, including the annual UN conferences on climate change, are devoted to the issues of atmospheric air pollution by emissions of carbon dioxide, heavy metals, polyaromatic hydrocarbons, dioxins and other pollutants.
Control of air emissions of pollutants is the most important tool for protecting the environment. Pollutants include chemicals and compounds of natural or anthropogenic origin, the content of which in the objects of the environment exceeds the background values.
In accordance with the requirements of the Federal law of the Russian Federation dated 10.01.2002 N 7-FZ (rev. dated 30.12.2021) "On environmental protection" the pollutants in relation to which the measures of state regulation in the field of environmental protection are applied are: taking into account the level of toxicity, carcinogenic and (or) mutagenic properties of chemical and other substances, including those tending to accumulate in the environment, as well as their ability to transform in the environment into compounds of greater toxicity; taking into account the data of state environmental monitoring and socio-hygienic monitoring; if there are methods (techniques) for measuring pollutants. The list of pollutants subject to state regulation measures in the field of environmental protection is established by the Government of the Russian Federation.
When developing and implementing programs to control and reduce emissions of pollutants into the air, it is noted that when calculating the annual amount of pollutants, a number of factors are not taken into account. This fact may be due to a number of reasons: 1. Every year, an amount of pollutants exceeding the annual emission is deposited from the atmosphere; 2. Difficulty of making an inventory of all sources of pollutants, control at these sources and a limited number of experimental dates; 3. Existence of potential sources of secondary emission [1] (ingress of pollutants into the atmosphere from other objects of the environment), quantitative characterization of which is practically impossible and inexpedient. Sources of secondary emission can be sublimation processes, deposition of particles from the atmosphere, adsorption, soil erosion, transfer of particles by air or water flow.
Many pollutants are highly stable in environmental objects. Such stability contributes to the accumulation, preservation and distribution of pollutants between solid, liquid, air and living organisms. Thus, the existing impact on the biosphere may be due not only to current emissions, but also to emissions that occurred several years ago. For example, studies of urban and rural soils in the United States for the content of such persistent organic pollutants (POPs) as dioxins, given the total area and distribution of pollutants depending on the topography, show rather high content: in rural soils of the USA, the dioxin content is 1530 kg I-TEQ, in urban ones -250 kg I-TEQ [1]. Studies of household waste landfills in the territory of the European Union [4] give data on the dioxin content of about 400 kg I-TEQ.
Some contaminants do not penetrate deep into soils and soils, accumulate on surface soil particles and can be transported with particles by air or water currents. A 1990-1993 study of the sources of dioxin inputs to the Hudson River Delta found that 76% came from rainfall runoff, 19% from anthropogenic runoff, 4% from atmospheric deposition, and 1% from shoreline erosion. In comparison, in the seventies, 70% came in with anthropogenic runoff, 15% with rainfall runoff, 15% was deposited from the atmosphere, and 0.1% was due to shoreline erosion [3]. With soil particles pollutants can also enter the atmosphere. The air transport of soil particles can be influenced by wind speed, topography, green mass, particle size and density, particle moisture, air humidity and many other factors. The literature [4] cites data that from 70 to 90% of pollutants contained in dust deposited in urban areas enter the air from soil. For rural areas, this value is 20-40%.
Contaminants can enter water bodies and bottom sediments by precipitation from the atmosphere, with rain and storm water runoff, and with anthropogenic waste.
According to an inventory conducted in Great Britain, the content of persistent organic pollutants in soil and in plants is correlated as 1000:1, with a small part of the total amount of POPs entering plants through the root system -less than one-tenth of one percent. Studies show [5,6] that a significant part of pollutants enters plants as a result of the equilibrium process of their absorption from atmospheric air. And further with the fallen leaves the pollutants get into the soil and ground. It is believed [7] that the transfer of pollutants from plant to plant is impossible.
In the animal world, in contrast to plants, there is a significant accumulation of pollutants in the tissues of organisms, including heavy metals -mercury, lead, cadmium, and their further transfer through the food chains. Presumably, up to 95% of pollutants enter the human body with food [8]. Fish poses the greatest danger in this respect because of the bioconcentration effect [7].
In the literature, there is information that the half-life of dioxins from the human body is about 7 years [9]. At the same time, only about 10% of dioxins are metabolized. The most rapid elimination of dioxins from the organism occurs during lactation, but during the period of breastfeeding a child receives about 4% of the total amount of dioxin absorbed by human during the whole life [10,11].

Materials and methods
The problems of waste management from various industries, railroads and other modes of transport, municipal and domestic agriculture, and in general the life activity of mankind have not lost their importance, and in recent decades they have taken on the role of a global environmental problem. This waste also includes sludge from urban wastewater treatment, which is the main type of waste from wastewater treatment plants. Modernization of old wastewater treatment plants and the construction of new ones is an urgent task, because at present, due to the development of human activities, in some regions there is a lack of production capacity for quality water treatment.
In [12] the basic methods of sewage sludge utilization in a number of Western countries, including the EU, are presented in the table (1): The given data speak about absence of "ideal", unanimously accepted decisions of the given question, testify about technological, logistical and economic problems in the sphere of waste management of the considered category. At that, the urgency in creation of some road map on waste recycling with the use of the best available technologies with scientifically grounded criteria and objective ecological and economic assessment grows every year, as well as the volumes of generated waste.
There are a large number of patents, sometimes very inventive, for the treatment of sewage sludge, but today there are mainly three main methods: aerobic and anaerobic biothermal digestion, as well as incineration.
Aerobic treatment is the most important in terms of treatment volumes and has many special solutions [13] aimed at reducing the time of use and maintaining favorable factors: the presence of oxygen in the air, optimal temperature and humidity of the mixture, optimal environmental reaction and microbiota activity. The main negative aspects of this treatment method are usually the absence of a strong high-temperature phase and, accordingly, the risk of incomplete disinfection of pathogenic microflora. For this reason, other disinfection methods are often used at different stages of the process, such as the introduction of special agents with antimicrobial action. Or the use of thermophilic digested sewage sludge from wastewater treatment plants [13]. There are well known methods of disinfection by ultraviolet and microwave radiation. [12] describes a cavitation generator with a capacity of 100 m3/h which allows the destruction of microbial cells through the mechanical action of the accumulated microbubbles.
Another way of handling sewage sludge is bioenergetic anaerobic fermentation, which involves the use of methanogenic microorganisms in bioreactors: sealed concrete or steel tanks for biogas formation. This way has long been developed in several European countries (the first biogas plant for the production of sewage sludge was built in Birmingham in 1911) and in Russia (Moscow treatment facilities, Lyubertsy treatment plants).
The use of digesters (bioreactors) in processing anaerobic waste has been thoroughly tested. In the Russian Federation standards containing general requirements for bioreactors were introduced already in 2010 [12], production technologies are being developed and improved, new bioreactors are being developed. A few years ago, the first bioreactors were successfully installed on European railroads. An example of such a system is the AKW A+V Protec Rail GmbH bioreactor. According to "Der Protec Bioreaktor" (https://www.akwauvprotec.com/Company.htm), waste water is biologically treated in the bioreactor described therein and then transferred to the railroad tracks. By early 2020, more than 2,000 railcars were equipped with such devices. It is true that the success of bioreactors in Europe is largely due to lower environmental requirements. For example, the maximum permissible concentrations of pollutants declared by the manufacturing company are significantly higher than the requirements of Russian regulations.
The technology of anaerobic fermentation of organic waste in railway toilets is also promising in railroad transport, but it should be noted that the activity of methanogenic microorganisms decreases when the processed waste contains salts of heavy metals and biocides [12].
A third option for fecal waste disposal is the incineration of sewage sludge. This method makes it possible to significantly reduce the rotation period, while taking into account the epidemiological risks of fecal waste and the significant calorific value of the final mixture, it can also have application prospects. In this case, the problems of separation of solid and liquid fractions and drying the solid mass must be solved. The unstructured mass of organic waste is very slow to release moisture, which is mainly contained in membranes and biogels. The problem has been solved by such equipment as vacuum filters, compression filters, screw dryers, and precipitation centrifuges [14], but it is very difficult to reduce the moisture to the amount necessary for efficient combustion of 5-7%.
The trend of railway transport development includes the solution of such an important environmental, technological, sanitary and, to some extent, aesthetic problem as the conversion of all operated mainline passenger trains to environmentally friendly toilet complexes (EFTC). In order to dispose of EFTC waste, a system has been created for the disposal of fecal waste at stops, which is then transported by sewage trucks and discharged into the general sewage treatment facilities. At the moment, as one of the possible options for industrial utilization of EFTC waste, sewage sludge incinerators (SSIs) are considered. The method of waste incineration reduces the time, labor and financial costs of waste turnover, and taking into account the epidemiological risks of fecal waste, has high prospects for development.
Due to production needs, the Russian Railways railway enterprise is constantly engaged in innovations, including those in the field of environmental protection. One of the most promising options for the enterprise is incineration of sewage sludge from toilet complexes of mainline passenger trains. The company is considering the option of building SS incinerators. The positive aspects of construction of such facilities are that they can bring the Russian Railways enterprise to a fundamentally new level -in particular, in compliance with international standards, which will change the approach to environmental impact. This will make it possible to profit from the waste generated in the course of operations through the production of by-products: energy and fertilizers.
Since 1996, a technology exists in St. Petersburg, Russia, to treat sewage sludge more efficiently by incineration in pyro-fluidized fluidized bed incinerators. Ash is produced by burning centrifugally dewatered sewage sludge (a mixture of primary sludge and excess concentrated activated sludge) in fluidized bed furnaces at 850 °C. Three industrial plants are currently in operation, reducing the amount of sludge by more than 10 times. However, in addition to the obvious benefits (reduced number of vehicles, reduced area of new landfills and thus reduced emissions and improved environmental conditions), new problems arise in terms of emissions of combustion products into the atmosphere and disposal of ash from sewage sludge incineration. [15].

Results
In accordance with the Order of the Ministry of Natural Resources and Environment of the Russian Federation dated 07.08.2018 № 352 "On Approval of the Procedure for Inventorying Stationary Sources and Emissions of Harmful (Polluting) Substances into Atmospheric Air, Adjusting Its Data, Documenting and Storing Data Received as a Result of Such Inventories and Adjustments" the emissions inventory is conducted by legal entities and individual entrepreneurs who carry out economic and (or) other activities using stationary In the Russian Federation the emission inventory is a mandatory procedure for the determination and systematization of data on emissions into the atmospheric air and is a basic concept of the system of state regulation in the field of environmental protection. The procedure of inventory and control of emissions is regulated by a number of normative legal acts of federal, regional, municipal importance, state standards, sanitary and epidemiological rules, hygienic norms, etc.
Inventory of emissions is carried out individually for each individual enterprise or organization, whose activities are related to the sources of emissions of pollutants into the air, subject to state accounting and rationing. The inventory takes into account the quantitative and qualitative composition of emissions into the atmosphere, technological processes at the enterprise, background values of pollutants in the place of the enterprise activity with the summation effect, maximum permissible loads on ecological systems, location of residential buildings and much more. Emissions of pollutants into the atmospheric air are monitored with a specified periodicity and are also subject to revision in case of changes in technological processes at the enterprise, change of raw materials, purification facilities, etc. and every five years.

Discussion/Analysis of Results
In comparison to Table 2 we can give the data for the plant for incineration of sewage sludge, presented in the expert conclusion of 17.08.2015 № 78.01.06-4a/920FBUZ "Center for Hygiene and Epidemiology in the city of St. Petersburg". According to the expert opinion, the sources of atmospheric pollution were tested for the content of more than 46 pollutants: diAluminum trioxide, diIron trioxide, cadmium oxide, magnesium and its compounds, copper oxide, nickel oxide, lead and its inorganic compounds, mercury compounds waterand poorly soluble, chromium, zinc oxide, cobalt oxide, antimony, nitrogen dioxide, ammonia, nitrogen (II) oxide, hydrochloride, arsenic (inorganic compounds), carbon (soot), sulfur dioxide, hydrogen sulfide, Carbon oxide, gaseous fluorides, methane, C6-C10 mixture of saturated hydrocarbons, benz(a)pyrene, butane-1-ol, phenol, ethylformate, propanal, formaldehyde, hexanoic acid, Dimethylsulfide, mixture of natural mercaptans, methylamine, microorganisms, gasoline, kerosene, mineral oil, C12-C19 limit hydrocarbons, emulsol, inorganic dust: 70-20% SiO2, fur dust, abrasive dust, calcium carbonate, dioxins. The list and frequency of control of pollutants were established during the inventory of emissions. While the European Directive 2000/76/EU regulates the list of pollutants more than two times less than that established in the territory of the Russian Federation.

Conclusion
Thus, based on the above example we can conclude that in the Russian Federation there are more stringent requirements for emissions from sewage sludge incineration plants, than for