Local sewage treatment facilities: description, design and calculation

Wastewater treatment plants are used for cleaning industrial, surface and waste water. According to the regulations prescribed in the legislation of the Russian Federation, a number of special measures need to be taken before discharging rainwater or city sewage into the water bodies of spent and polluted water. Their ultimate goal is to bring the quality of the purified liquid to the specified values.

Application area

Local sewage treatment plants for storm sewage are used in industrial plants, various industrial sites, filling stations, warehouses, etc., in settlements in places with residential buildings. In addition, such systems are also used on roads for pumping water from their surface. Depending on the type of wastewater pollution, different requirements are imposed on their quality of cleaning. The greatest degree of pollution of waste water is considered to be oil products and various suspended substances.

No one doubts that sewage treatment facilities are very important. In particular, this applies to areas where wells are located, as these systems not only treat water in a special way and make it safe for the environment, but also prepare it for reuse.

The selection of such systems is determined by several factors:

• Depth of occurrence of pipelines;
• The concentration in the water of any contaminants at the entrance to the system itself;
• Productivity of treatment facilities;
• The established degree of purification, which corresponds to the norms for discharging such waters into the municipal sewage system or into any other water body.

Types and size of systems

Conventionally, stormwater treatment facilities can be divided into two categories:

• Closed systems. This means that the water through the pipes and catchers goes directly to the rainwater inlet and is piped to the places where either the discharge occurs or its storage.
• Open systems. In this case, the water accumulates and flows down the surface of the channels and gutters to the places where it is discharged.

Such systems of treatment plants are most often produced in the form of horizontal tanks using various materials, such as concrete, fiberglass, low-density polyethylene or metal. As for their size, they directly depend on the area with which run-offs run in, as well as on the weather conditions of a particular region, the places of discharge of treated waters and the type of the facility itself.

Usually a combination of a gas trap and sand trap is installed. Their sizes can be very different and for the convenience of their installation and delivery they are often placed in one housing. If discharge of effluents occurs in open reservoirs, then in addition to sand controllers, additional blocks of coal treatment, that is, sorption filters, are also used.

Systems and their passport

Block-modular treatment facilities for storm sewage are made in the form of a special installation - a sand trap. Through the hatches made in these tanks, their maintenance is carried out. Passing through modular cleaners, surface waters get rid of petroleum products and various kinds of mechanical impurities. The first of the above types of pollution include sediment conglomerates, film, primary and secondary emulsions, and to the second - hard-to-precipitate particles, silt and sand with a density of more than 1500 kg / m, as well as debris that floats on the surface.

It should be noted that factory production systems always have a passport for sewage treatment facilities, certificates of compliance and sanitary and epidemiological conclusions. In addition, the manufacturer must give a guarantee on the tightness of the case. Usually it is 10 years.

What is a sand trap and how does it work?

This product is a cylinder, often made of low pressure polyethylene. This gives it extraordinary strength, resistance to unfavorable external conditions and the ability to easily tolerate the influence of various aggressive environments.

The operation of the sand trap consists of five stages of wastewater treatment:

1. Sump. At this stage, primary rejection of large particles occurs, which under the influence of gravity fall to the bottom.
2. Thin layer module. It separates the suspended substances, as well as their oil conglomerates, into a sediment, and the surface emits a primary emulsion, merging into droplets and collecting on hydrophobic plates.
3. Sorption filter. Its task is to catch particles of oil products that do not hit the hydrophobic plates located on the thin-layer module. Sorption fiber filler, which is located in the filter housing, is housed in a high capacity and has a significant selectivity to heavy, medium and light petroleum products.
4. Coalescent module. It facilitates the separation of particles of oil products that float to the surface, the size of which is greater than 0.2 mm.
5. Carbon filter after-treatment. It is filled with a special sorbent, selective for all petroleum products.

Designing

As you know, in the territories of enterprises and stand-alone gas stations, there is a constant accumulation of rain and meltwater, which must be taken out and dropped to the ground or into any water body.
To determine which wastewater treatment plants are necessary, you need to know the following data:

• Uniformity and volume of wastewater;
• Composition of impurities and effluents;
• Parameters of groundwater and land.

The design of sewage treatment facilities for production sites requires, first of all, to determine to which group the given object belongs. There is a specially developed classification of the VODGEO Research Institute, which divides them into two groups. The first include the surface and the enterprise, the sewage from which are similar in composition to the waters of residential areas. This means that they contain toxic and other specific elements.

The second group includes those territories of enterprises from which surface runoff with similar harmful impurities can occur. After that, choose the type of the technological scheme itself, and at the end make calculations and determine the appropriate sewage treatment facilities.

Necessary calculations

The calculations differ from each other depending on the specific selection of the component parts. When using a flow diagram without the use of an averager, the construction is selected by determining the flow of storm drains. For this, it is necessary to know the statistical characteristics of the rain in a certain locality, and also the SNiP coefficient determining the water surface. When the calculation of sewage treatment facilities is ready, the appropriate model of the system is finally chosen.

Performance

It is worth noting that the efficiency of the work of the structures is very important, since untreated thawed and storm water can be extremely dangerous both for buildings and structures, and for the whole territory of the enterprise. Harmful chemical impurities, which are contained in sewage, can damage waterproofing, and this is fraught with the destruction of foundations and engineering underground communications. Moisture, accumulating on the elements of structures, contributes to the appearance of fungus, which in turn can cause them irreparable harm. Therefore, the efficiency and productivity of sewage treatment facilities is very important, not only because environmental authorities require it, but also, for the most part, based on practical considerations.

Installation of systems

There is a certain order in which the treatment facilities are installed. First of all, with the help of technology or manually tear out several trenches and excavations of the required size. Sometimes, if necessary, their bottom is concreted. After this, all cleaning components are installed on pre-prepared places, and then the structural elements are insulated and waterproofed. The last stage of the work is to backfill the soil.

It is worth noting that the successful design of treatment facilities depends to a large extent on the correctness of the necessary analyzes, studies and calculations, since even a small error can contribute to flooding the site and breaking the purification system itself.