Effluent contains substances of organic and inorganic origin, and much more organic. And if it is easiest to get rid of inorganic inclusions mechanically, then other methods are needed to remove organic impurities. One of the main ones is biological wastewater treatment. You will learn about its features, varieties and technologies in this article.
Water is life, but we consume it clean and return it dirty. If the drains are not cleaned, then the time of “precious moisture”, described by many science fiction writers, will come very soon. Nature can purify water on its own, but these processes are very slow. The number of people is increasing, the volume of water consumption is also increasing, so the problem of organized and thorough wastewater treatment is particularly acute. The most effective water purification technology is biological. But, before considering the basic principles of its work, you need to understand the composition of water.
Composition of domestic wastewater
In any house with running water there is also a sewerage system. It provides normal processes for transporting wastewater from apartments and houses to treatment plants. Ordinary water flows in sewer pipes, but polluted. Impurities in it are only 1%, but it is he who makes the effluent unsuitable for further use. Only after purification, the water can be reused for drinking and at home.
The exact composition of wastewater cannot be named, since it depends on the place where a special sample was taken, but even in the same place, the amount and set of impurities may vary. Most often, water contains solid particles, biological impurities, inorganic inclusions. Everything is simple with inorganic matter - even the simplest filter removes it, but you will have to fight with organic matter. If nothing is done, these substances begin to decompose and form a rotting sediment (hence the unpleasant characteristic “sewage smell”). Moreover, not only decomposed organic matter begins to rot, but also water.
In a nutshell, the composition of wastewater includes fats, surfactants, phosphates, chloride and nitrogen compounds, petroleum products, sulfates. They cannot disappear from the water on their own - complex cleaning is needed. The problem is especially acute in those houses in which an autonomous drainage and water supply system has been installed, because each site has a cesspool and a well for water. If the drains are not cleaned, they can get into the faucet - and the situation will become life-threatening.
Methods for the treatment of domestic and industrial wastewater
Wastewater can self-purify under natural conditions, but only if its volume is small. Since the industrial sector is highly developed today, the volumes of effluents at the outlet are significant. And in order to get clean water, a person must solve the issue of sewage - that is, their purification. In total, there are several methods for purifying wastewater - these are mechanical, chemical, physico-chemical and biological. Let's take a closer look at the features of each of them.
Mechanical cleaning involves the use of techniques such as filtration and settling. The main tools are gratings, sieves, filters, traps and traps. When the water undergoes primary treatment, it enters the sump - a container designed to settle wastewater with the formation of sediment. Mechanical cleaning is used in most modern systems, but rarely as an independent method. And the thing is that it is not suitable for removing chemical components and organic impurities.
Chemical cleaning is carried out using reagents - special chemicals that react with impurities contained in water and form an insoluble precipitate. As a result, the content of soluble suspensions is reduced by 25%, and insoluble by 95%.
Physico-chemical purification involves the use of techniques such as oxidation, coagulation, extraction, and so on. These processes make it possible to remove inorganic inclusions from water and destroy poorly oxidized organic impurities. The most popular physical and chemical cleaning method is electrolysis.
Biological purification is a process based on the use of specific microorganisms and the principles of their vital activity. Bacteria target specific organic pollutants, and water is purified.
Methods of biological wastewater treatment and its benefits. Stations and facilities for biological wastewater treatment
The methods of biological wastewater treatment include aerotanks, biological filters and the so-called bioponds. Each method has its own characteristics, which we will tell you about below.
Aerotanks
This biological treatment method involves the interaction of previously mechanically cleaned wastewater and activated sludge. The interaction takes place in special containers - they consist of at least two sections and are equipped with aeration systems. Activated sludge contains a large number of aerobic microorganisms, which, under appropriate conditions, remove various pollutants from wastewater. Silt is a complex system of biocenosis in which bacteria, subject to regular oxygen supply, begin to absorb organic impurities. Biological purification occurs constantly under one main condition - air must enter the water. When organic processing is completed, the level of oxygen demand (BOD) drops, and water is supplied to the next sections.
In other sections, nitrifying bacteria are included in the work, which process such an element as nitrogen of ammonium salts with the formation of nitrites. These processes are carried out by one part of the microorganisms, while the other part eats nitrites with the formation of nitrates. Upon completion of this process, the treated effluents are fed into the secondary clarifier. Here activated sludge precipitates, and purified water is sent to reservoirs.
Biofilter is a biological treatment station popular among owners of country houses. It is a compact device, which includes a reservoir with feed material. In the form of an active film in the biofilter, there are microorganisms that carry out the same processes as in the first case.
Installation types:
- two-stage;
- drip filtration.
The performance of devices with a drip type of filtration is low, but they guarantee the maximum degree of wastewater treatment. The second type is more productive, but the cleaning quality will be about the same as in the first case. Both filters consist of the so-called "body", distributor, drainage and air distribution systems. The principle of operation of biofilters is similar to the principle of operation of aerotanks.
biological ponds
To carry out wastewater treatment by this method, there must be an open artificial reservoir in which self-cleaning processes will take place. This method is the most effective, even shallow ponds up to one meter deep are suitable. A significant surface area allows the water to warm up well, which also has the necessary effect on the vital processes of the microorganisms involved in the purification. This method is most effective in the warm season - at a temperature of about 6 degrees and below, the oxidation processes stop. In winter, cleaning does not occur at all.
Types of ponds:
- fish breeding (with dilution);
- multi-stage (without dilution);
- post-treatment ponds.
In the first case, effluents are mixed with river water, after which they are sent to ponds. In the second, water is sent to the reservoir without dilution immediately after settling. The first method requires about two weeks of time, and the second month. The advantage of multistage systems is a relatively low price.
What are the advantages of biological wastewater treatment?
Biological wastewater treatment guarantees almost 100% clean water. However, please note that the biostation is not used as an independent method. You can get crystal clear water only if you first remove inorganic impurities in other ways, and then remove organics by biological methods.
Aerobic and anaerobic bacteria - what is it?
Microorganisms used in the process of wastewater treatment are divided into aerobic and anaerobic. Aerobic exist only in an oxygen-containing environment and completely break down organic matter to CO2 and H2O, while simultaneously synthesizing their own biomass. The formula for this process is as follows:
CxHyOz + O2 -> CO2 + H2O + bacterial biomass,
where CxHyOz is organic matter.
Anaerobic microorganisms normally do without oxygen, but their biomass growth is also small. Bacteria of this type are needed for oxygen-free fermentation of organic compounds with the formation of methane. Formula:
CxHyOz -> CH4 + CO2 + bacterial biomass
Anaerobic techniques are indispensable at high concentrations of organics - which exceed the maximum allowable for aerobic microorganisms. At a low content of organic matter, anaerobic microorganisms, on the contrary, are ineffective.
Appointment of biological methods of water purification
Most of the wastewater pollutants are substances of organic origin. The main sources of pollution data and consumers of treated effluents:
- Housing and communal services, food industry enterprises and livestock complexes.
- Enterprises of the chemical, oil refining, pulp and paper, and leather industries.
The composition of effluents in these cases will be different. One thing is for sure - only under the condition of complex cleaning with the obligatory use of biological methods can ideal results be achieved.
Principles of biological treatment and a list of necessary equipment
Taking into account the current principles of biological treatment, equipment is being selected for organizing a biological treatment plant. Main options:
- biological ponds;
- filtering fields;
- biofilters;
- aeration tanks;
- metatanks;
- filter wells;
- sand and gravel filters;
- circulating oxidation channels;
- bioreactors.
Please note that different methods can be used for artificial and natural wastewater treatment.
Wastewater treatment by biological methods: advantages and disadvantages
Biological methods are effective for cleaning wastewater from organic matter, but really high results can be achieved only if different methods are used in an integrated manner. In addition, the possibilities of bacteria are not unlimited - microorganisms remove minor organic impurities. The cost of biological treatment plants is relatively low.
All methods of wastewater treatment
Before entering the biological treatment system, wastewater must be subjected to mechanical cleaning, and after it - disinfection (chlorination, exposure to ultrasound, electrolysis, ozonation, etc.) and disinfection. Therefore, within the framework of complex wastewater treatment, chemical, mechanical, membrane, reagent methods are also used.
