Until recently, snow collected from streets, squares and roads in Russia was discharged into the nearest water bodies without treatment, because it was treated not as waste of a settlement, as it is done in most countries of the world, but as conditionally clean natural precipitation. Nowadays, with the ever-increasing number of cars and emissions from industrial enterprises, snow adsorbs from the air and accumulates petroleum products, heavy metals, household waste, anti-icing materials, etc. from road surfaces (up to 60 pollutants). Dumping of snow mass into the dump without cleaning and disinfection causes contamination of soil, surface and underground water sources, and eventually deterioration of human health, flora and fauna.

Snow mass from road surfaces of the city is very specific in terms of the composition of contaminants. Quality indicators of melted snow are not constant and vary depending on the place of its collection and decade of the winter period. Melt water inflow to the city’s treatment facilities will inevitably increase, as the number of stationary snow melting points (SMP) in Russia is increasing every year [1]. It is prohibited to transport snow outside the city limits and dump it into the river or the nearest ravine. Therefore, it is either transported to specially equipped landfills or utilized at snow melting stations.

St. Petersburg, like any other northern city, faces the problem of snow removal every year. Given the mild climate and high humidity, snow in the city often turns into mud and slush, which hinders traffic and creates problems for residents.

The way out of this situation until recently was the removal of precipitation outside the city, to specially equipped landfills. The disadvantages of this method include:

— participation of a large number of snow removal vehicles;

— increased traffic congestion;

— considerable financial costs.

While residents of private homes cope with snow piles on their territory with the help of snow blowers (gasoline and electric), or with the help of shovels (both conventional and mechanical), the issue of snow disposal is more acute for public utilities — they need to clear huge areas in a short period of time without harming the environment.

Utilization of snow masses, which according to the federal classification catalog are included in the list of snowmelt waste, refers to measures to ensure environmental safety of the environment, as they contain not only suspended solids, but also chlorides, sulfates and other pollutants.

Thus, snow utilization can significantly reduce the negative impact on the environment.  To combat this problem, special snow melting points and facilities are used (Fig.1). These facilities are special apparatuses that allow to quickly and efficiently melt snow and ice, converting them into water [2]. The resulting water is then released into the sewer system and the clean snow is freed from debris and waste. Thus, the formation of slush and dirt on the city streets can be avoided.

Figure 1. Stationary snow melting point

There are four types of mobile and stationary snow mass processing stations.

1. Single corridor.

Most often these are stationary points for the reception of solid precipitation, placed near sewage collectors. The main condition for the organization of such points is a high speed of water flow. This show should be at least 0.5 cubic meters per second.

Near the collector, an intermediate settling tank with a large grid is installed. On it the snow mass brought from the city streets is dumped and squeezed through large cells. The snow melts under the influence of wastewater heat and flows into the collector via a bypass line.

While this method of disposal is cheap, it has two major disadvantages:

— Difficulty in squeezing the snow (sometimes tracked vehicles are used);

— the need to clean the bottom of the sump with the help of sludge collectors or slurry trucks.

2. Point with a sand trap.

A modernized version of the single-corridor one. The improvement consists in placing a specialized filter unit between the collector and the sump. This serves as a barrier to sand and fine gravel entering the collector.

3. Points with immersion burners.

A specialized unit is used for disposal, in which snow is forced to melt. Its tank is divided into 2 compartments: accumulation and auxiliary. In the second one there are gas-diesel burners, which melt solid precipitation with their heat [3].

Thanks to the design of the equipment, the melted water enters the sewer or drain.

The advantage of this recycling process is its continuity. The volume of snow masses is limited only by the individual characteristics of the snow melter.

When equipping a mobile station, no large snow storage area is required. Therefore, such stations are convenient for snow removal inside residential areas.

As negative points act as:

— noise;

— exhaust from diesel fuel processing;

— the need for frequent cleaning of the receiving hopper from associated debris.

4. Snow melting complex with crushing plant.

At stationary stations, a crushing plant is installed above the settling tank instead of a coarse-mesh grid (Fig. 2). Such replacement allows not to involve additional tracked machinery for softening of snow masses. In addition, additional snow melting takes place in the process of crushing. At such a station, the daily rate of snow and ice formations processing can reach 2400 tons.

Figure 2. Snow melting complex with crushing plant

In the future, the development of technologies in the field of thermal power engineering will make it possible to create more advanced and efficient snow melting plants that will operate faster and more economically. It is also possible to use alternative energy sources for the operation of such plants, which will reduce the negative impact on the environment.

In order to be able to justify the use of a snow melting system, it is crucial to consider a number of factors. These factors range from the pros and cons of such a system, its cost and benefits, space availability and the like.

After all, snow removal equipment is not universal, different equipment is selected for certain natural conditions, levels of snow contamination. Calculations are made, on the basis of which the type of equipment is selected, as well as its quantity.

For example, many countries use a system of dividing the city into sectors to optimize the process of snow removal. The systems distribute the collected snow from which area of the city and to which snow melting facilities. The scheme can be adjusted depending on the traffic congestion of a particular point, as well as on the situation on the roads [4]. The automated method of snowfall distribution has not yet found wide application, but soon it will become common for large megacities, and not only for small European cities.

In order for the system of snow removal in residential neighborhoods to function properly, it is first of all necessary to ensure timely cleaning and maintenance of roads in proper condition in winter.

Winter road maintenance is a set of measures including:

— protection of roads from snow drifts;

— cleaning of roads from snow;

— combating winter slippery conditions;

— protection of roads from avalanches;

— ice control.

The main peculiarity of the winter period is the formation of snow and ice deposits on roads, resulting in a sharp deterioration of vehicle traction.

The whole system of winter road maintenance activities should be designed in such a way that, on the one hand, to provide the best conditions for the movement of vehicles, on the other hand, to maximize the ease, speed and cost of winter maintenance. In order to ensure that this task is accomplished, winter maintenance activities are carried out [5]:

— preventive, the purpose of which is to prevent or minimize the formation of snow and ice deposits on roads; such measures include reducing the snow carrying capacity of roads, preventive treatment of pavements with chemical anti-icing agents, etc.;

— protective measures, which prevent access and inspection of snow and ice coming from the adjacent area; they include application of protection against meteoric transport, snow avalanches, fallen ice. The main criterion for the quality of snow protection should be the complete exclusion of snow deposits on the roadway and the fact that only the removal of short-term snow during snowfalls remains for patrol snow clearing;

— to remove snow and ice deposits that have already occurred (e.g., clearing roads of snow and ice) and to reduce their impact on car traffic (treatment of icy road surfaces with materials that increase the tire grip coefficient).

Many interesting and non-standard methods of winter maintenance of roads and pedestrian zones are used abroad [6]. One of the most unusual approaches is the use of heated inclined sidewalk (Fig.3).

Figure 3. Design of heated bridge

However, this method has many disadvantages, such as high energy consumption, which is inexpedient due to the impossibility of determining the temperature that would allow to melt the fallen snow without residue, secondly, this technology requires a global reconstruction of existing roads, which is impossible in old cities, and of course one of the big disadvantages of this method is the high cost.

Basically, the principles of snow removal in all countries are the same. According to the regulations, snow should be removed during the first hours of snowfall, not allowing its fulfillment, first of all the central streets and streets with the highest capacity are removed.

In Sweden the following method of snow clearing is used: fine sand is mixed with 90-95°C hot water and sprayed on the streets, the hot sand is absorbed into the snow, for a given surface this treatment is sufficient for 3-5 days on roads with medium capacity. The roads are subsequently cleared as the tires do not destroy the asphalt pavement of the roads.

In Japan, there are two methods of snow removal: in places where conditions allow, the snow is watered with hot water, causing it to melt, or it is moved off the road, forming a slope, and then compacted with an excavator. As a result, on some highways a kind of snow canyons are formed, which does not affect the environment.

In Germany, only the central streets are cleaned, snow is removed from the streets. Sand and peat cleanings of the owners of nearby houses or offices are used to combat ice.

In Finland: central streets must be cleared by the beginning of the working day, while residential areas are cleared throughout the working day. The granite chips that are sprinkled on the ice give it a strong shine, which does not get dusty or get the summer technician off the road. All snow is usually dumped into the Baltic Sea, which is possible because it forms ice piles, which are then taken to the sea.

In Finland there is a strict division of the areas to be cleaned. Each territory is cleaned by a separate company, with which a contract is signed. In addition, almost the whole country is covered with a network of web cameras, which show the roads and transmit information about the air temperature and traffic situation. Thanks to the data from these cameras it is possible to quickly respond to road services.

In Canada, the climate is very similar to that of Russia, the population density is less, but the specific number of motor vehicles is much higher. Therefore, the problem of street cleaning in winter is as acute there as in Russia. Disposal of snow masses caused from the territory in Canada is carried out in “dry” snow dumps (Fig. 4).

Figure 4. Dry snow dump

These dumps are fenced areas where snow is piled and shifted by bulldozers and powerful snowmaking devices to a height of 20-30m. Snow melting takes place under the action of natural heat until August. The main sites are made of surplus waste generated during the repair of road surfaces. They will also be collected in settling ponds and then subject to disposal. In Canada, neither stationary units, nor heat carriers, nor specialized machinery, nor active-passive snowplows are used for disposal.

Assuming that future developments in urban snow removal will involve the use of modern technologies such as robots and autonomous vehicles. Robots will be able to efficiently and quickly remove snow from streets and sidewalks without requiring human participation. They will be equipped with special sensors that will allow them to determine snow density, thickness and other characteristics to optimize the removal process [7].

In addition, the development of new infrastructure in cities will also contribute to more efficient snow removal. For example, special heating and drainage systems on roads and sidewalks will help prevent the formation of snow and ice. Special snow elimination systems will also be introduced that will automatically remove snow from the surface.

Thus, modern technology and infrastructure will help make snow removal more efficient, safe and environmentally friendly. This will help cities cope with winter conditions quickly and without unnecessary labor and resources.