Nature is a constantly evolving, wise, unique, self-healing organism. However, a certain amount of time must pass for such recovery. In conditions of constant anthropogenic attack, nature does not have enough strength and resources to restore itself. Because of this, global environmental problems arise. One of them is pollution of the oceans and, as a result, the lack of clean drinking water in many regions of the world. Due to the pollution of water bodies, their inhabitants also suffer. In this article, we will discuss the wastewater of industrial enterprises, methods for their rationing and purification.
Ecological problems of big cities
It is difficult to imagine a city that does not affect the environment. The first and main thing that needs to be done to establish a settlement is the alienation of a large territory and its transformation from a forest or field into a reinforced concrete jungle. This does not end there. Human waste products pollute nature and often cause irreparable damage to the animal and plant world.
Among the main environmental problems of industrial cities can be identified:
- pollution of rivers, seas and lakes due to wastewater discharges from industrial enterprises containing toxic pollutants;
- air pollution due to emissions from enterprises;
- pollution of soil, water bodies and air (smell) with hazardous industrial waste;
- destruction of green spaces and their inhabitants;
- lack of clean drinking water;
- climate change and ozone depletion.
All these processes occur under the influence of an anthropogenic factor, and therefore it is in human power to change the situation for the better. Wastewater of industrial enterprises and their treatment should be a priority in the domestic policy of cities and support for enterprises engaged in this type of activity.
Types of Wastewater
In this case, the classification is based on the chemical composition in order to select disposal methods. Wastewater of industrial enterprises are divided into three types:
- household wastewater;
- industrial effluents;
- surface and infiltration effluents.
Each type of discharge normally has its own sewage system, although sometimes in some cities everything is mixed together. This only exacerbates the problem of subsequent cleaning.
Domestic wastewater
This type of discharges is typical for any building and structure equipped with a bathroom, and therefore the composition of such discharges, as a rule, is always the same. Domestic wastewater has a high organic content, the presence of nitrogen, phosphorus and coarse impurities. Purification of this type of pollution is usually biological and does not cause difficulties, high energy costs, and therefore is carried out by public utilities.
The composition of the wastewater of industrial enterprises of this type differs only in that workers can drain liquids into the toilet and sink that cannot be drained there. This is very characteristic of laboratories, chemical plants, galvanic industries, pharmaceutical plants.
Surface wastewater
All precipitation in cities through the storm sewer system goes to the accumulation tanks, and then to the sewage treatment plant. This type of effluent, in fact, is polluted only with suspended solids and oil products, and therefore all city storm drains are cleaned according to the principle of sedimentation and removal of oil products.
It is important to understand that these discharges from the roof, asphalt pavement are collected, and even drains from the soil and grass are taken into account. The main difference between the wastewater of industrial enterprises of this type is that during unscrupulous gas cleaning and spills (accidents), they can be contaminated with specific substances characteristic of this type of production. Therefore, this type of discharges must also be pre-treated.
Industrial wastewater
There are no completely waste-free technologies. Even the smallest company that uses water in its production process forms wastewater. The nature of the pollution of such discharges varies from the plant industry.
- The pulp and paper industry is characterized by very polluted effluents. Therefore, cleaning in this case is assumed to be multi-stage and high-quality. The main pollutants are fiber, selenium, chlorine, turpentine, SO 2 .
- Motor transport enterprises generate wastewater during washing, painting, repair, and therefore they are heavily contaminated with oil products, phenols, and suspended solids.
- Oil refineries use water recycling systems. Wastewater of some industrial enterprises contains hardness salts, oil products, sulfates, suspended solids, and chlorides.
- Poultry farms and meat processing plants form discharges polluting reservoirs and sewage systems with nitrogen, phosphorus, potassium, viruses and bacteria.
As can be seen from the list, wastewater treatment of industrial enterprises strictly depends on the scope of the plant and the component composition of pollutants.
Environmental regulation system
To avoid accidents and negative consequences, it is necessary to exercise control over any industry. In order to protect the environment, wastewater treatment of industrial enterprises and methods for their regulation are laid down in the environmental legislation of the Russian Federation. It is based on the principles of rational use of natural resources, on the right of every person to a healthy environment and on the principle of sustainable development.
The basis for environmental regulation is the concept of maximum permissible concentration (MPC), as well as maximum permissible emissions (MPE) and discharges (MPC). Such regulation allows you to set maximum values for pollutants that can be discharged into a reservoir or sewage system. It is important to understand that the maximum permissible concentration for discharge into the reservoir will be much stricter than the maximum permissible concentration for discharge into the city sewer, since in the latter case, sewage will first accumulate and be treated at the municipal sewage treatment plants, and then only enter the reservoir.
Legal regulation in the field of water resources protection is based on Federal Law 416- "On Water Supply and Sanitation" dated 11/29/2011, by-laws and state standards, joint ventures, SanPiNakh. Acceptable concentrations are given in the latter and specific recommendations are given.
SanPiN for MPC of wastewater of industrial enterprises of the Russian Federation establishes standards for the qualitative composition of wastewater for discharge into water bodies and requirements for sanitary protection of wastewater. This document is practical in nature, and therefore impurities, color, temperature, pH, mineralization, BOD5, and infectious pathogens are normalized in it. Sanitary rules and norms 2.1.5.980-00 "Sanitation of populated areas, sanitary protection of water bodies. Hygienic requirements for the protection of surface water" adopted 01.01.2001. They are based on the principles of resource conservation, that is, they do not allow discharges if there is the possibility of reuse of water with preliminary treatment.
If we are talking about specific MPC for pollutants, then SanPiN for wastewater of industrial enterprises is not valid here. For such cases, Government Decision No. 644, adopted on July 29, 2013, sets out the basic principles for using sewage systems. The document developed a list of substances prohibited for discharge, as well as the maximum permissible concentration of wastewater from industrial enterprises for discharge into the sewer. If we are talking about general-alloy and domestic wastewater systems, the concentration of some pollutants should not exceed the following marks (mg / dm 3 ):
- suspended solids ≤ 300;
- sulfides ≤ 1.5;
- sulfates ≤ 1000;
- chlorides ≤ 1000;
- total phosphorus ≤ 12;
- total nitrogen ≤ 50;
- oil products ≤ 10;
- chloramines and chlorine ≤ 5;
- phenols (total) ≤ 5;
- iron and aluminum ≤ 5;
- zinc, copper, manganese ≤ 1;
- hexavalent chromium ≤ 0.05;
- lead, nickel ≤ 0.25;
- cadmium ≤ 0.015;
- arsenic ≤ 0.05;
- mercury ≤ 0.005;
- SAS (nonionic, anionic) ≤ 10;
- volatile organic compounds ≤ 20;
- fats ≤ 50.
At the same time, the temperature of the wastewater should not exceed + 40 ° C. If we are talking about discharges into stormwater drainage systems, then the MPC of some substances become noticeably stricter:
- sulfates ≤ 500;
- petroleum products ≤ 8.
Cleaning methods
Technique and technology of wastewater is a rather extensive and constantly developing discipline. All cleaning methods are based on the separation and separation of contaminants into the solid phase and the formation of clean water. There are the following methods for this:
- upholding;
- mechanical filtration;
- physical and chemical (flotation, flocculation, coagulation, reagent treatment);
- sorption;
- reverse osmosis and ultrafiltration;
- disinfection (UV, ozonation, chlorination).
It is important to understand that all these methods are not used separately, but in combination. The classical technological scheme includes sedimentation, mechanical filtration, physicochemical method, sorption and disinfection. Each of them will be briefly described below.
Upholding
The fundamentally important and first stage of wastewater treatment of industrial enterprises is sedimentation (clarification). At this stage, equipment called settlers is used. They are a reinforced concrete (sometimes fiberglass) tank, with a slight slope of the bottom towards the pit. At this stage, water literally settles (stays in the sump) for at least 3 days. During this time, all undissolved impurities are released: heavy suspended solids settle to the bottom and slide into the sump, and oil products float up and are removed by a special device (skimmer) or a mechanical scraper.
This stage of cleaning is really the most important, since all further equipment will not be able to work if coarse-dispersed impurities (sand, rust), which are trapped in the sump, get into it.
Physicochemical Methods
Wastewater treatment technologies of industrial enterprises always provide for the main processing module, on which the substances dissolved in water are released and converted to insoluble form. The physicochemical method of wastewater treatment usually acts in its quality. This is carried out in flotators and coagulators.
Flotators
To isolate insoluble substances, air bubbles are used in these units. Flotators are containers in which water accumulates, and a mixture of water and air is supplied from below with a special device for sparging. Bubbles of air capture contaminants due to their stickiness and are carried up to form a foam called a flotation sludge. Obviously, this method is suitable for light dissolved impurities. Coagulants can be added to this, which enlarge the particles of pollutants, if they are very small. The dose of reagents is optimally selected so that they do not destroy the air bubble.
Coagulators
In order to isolate insoluble substances, these units use the principles of adhesion and coagulation, that is, adhesion and coagulation of impurities. A coagulator (or electrocoagulator) is a container with coalescent baffles, into which a coagulant-flocculant is fed in order to enlarge the impurities. Heavy particles of contaminants eventually settle into the conical bottom and are removed. Reagents are not added to the electrocoagulator; their action is replaced by aluminum or iron electrodes.
These methods provide the maximum cleaning effect and are used in almost all treatment facilities.
Filtration
This cleaning method is used to capture residual impurities in water. Filtration is conditionally divided into two types: mechanical and sorption.
A mechanical filter is a container filled with gravel loading or filter woven material. In this case, mechanical cleaning of the contaminants and their retention in the pores of the material occurs. At this time, water flows through the pores and is purified.
The sorption filter is filled with activated carbon, silica gel, schungite and any other sorbent that absorbs pollution. This download either changes completely or is flushed and used again.
Disinfection
This cleaning method is installed at the end of each technological scheme. Disinfection is carried out using ultraviolet lamps, hypochlorite or an ozonizer. This type of treatment is necessary to remove residual viruses and bacteria in the wastewater of industrial enterprises.
Cleaning “at the beginning of the pipe”
The main principle of ecology is preventiveness and says that if pollution can be prevented, the accident should not be allowed, and the resource should be reused, then the nature user must do it. Cleaning “at the beginning of the pipe” regarding wastewater involves the following set of measures:
- circulating and closed water supply systems with reuse of water for household needs;
- drawing up a water balance and a water footprint showing the specific consumption of water in order to reduce them as much as possible;
- the study of advanced methods of wastewater treatment;
- the establishment of industrial equipment in order to reduce water consumption.
Today, the problem of providing the population with clean water is one of the priority areas of the policy of many countries. Water is the source of life.