Control of natural water purification processes. Sewage sludge treatment methods, applied facilities

largest ecological problem CIS countries - contamination of their territory with waste. Of particular concern are wastes generated in the process of urban wastewater treatment - sewer sludge and sewage sludge (hereinafter referred to as SS).

The main specificity of such wastes is their two-component nature: the system consists of organic and mineral components (80 and 20%, respectively, in fresh wastes and up to 20 and 80% in wastes after long-term storage). The presence of heavy metals in the composition of waste determines their IV hazard class. Most often, these types of waste are stored in the open air and are not subject to further processing.

For example, By now, more than 0.5 billion tons of WWS have been accumulated in Ukraine, the total area for storage of which is approximately 50 km 2 in suburban and urban areas.

The absence in world practice of effective methods for the disposal of this type of waste and the resulting aggravation of the environmental situation (pollution of the atmosphere and hydrosphere, rejection of land areas for landfills for storing WWS) indicate the relevance of finding new approaches and technologies for involving WWS in economic circulation.

In accordance with Council Directive 86/278/EEC of 06/12/1986 "On the protection of the environment and in particular soils when using sewage sludge in agriculture" in the countries of the European Union in 2005, WWS were used as follows: 52% - in agriculture, 38% - burned, 10% - stockpiled.

Russia's attempt to transfer the foreign experience of WWS combustion to domestic soil (construction of waste incineration plants) turned out to be ineffective: the volume of the solid phase decreased by only 20% while simultaneously releasing a large amount of gaseous toxic substances and combustion products into the atmospheric air. In this regard, in Russia, as in all other CIS countries, their storage remains the main way of handling WWS.

PERSPECTIVE SOLUTIONS

In the process of searching alternative ways disposal of WWS by carrying out theoretical and experimental studies and pilot testing, we have proved that the solution of the environmental problem - the elimination of accumulated waste volumes - is possible through their active involvement in economic circulation in the following industries:

• road construction(production of organo-mineral powder instead of mineral powder for asphalt concrete);
• construction(production of expanded clay insulation and effective ceramic bricks);
• agricultural sector(production of high-humus organic fertilizer) .

Experimental implementation of the results of the work was carried out at a number of enterprises in Ukraine:

• pavement of the heavy equipment storage area MD PMK-34 (Lugansk, 2005), section of the bypass road around Lugansk (at pickets PK220-PK221+50, 2009), pavement of the street. Malyutin in Anthracite (2011);

BY THE WAY

The results of observations of the condition and quality of the road surface indicate its good performance, exceeding traditional analogues in a number of indicators.

• production of a pilot batch of effective lightweight ceramic bricks at the Lugansk brick factory No. 33 (2005);
• production of biohumus based on WWS at the treatment facilities of Luganskvoda LLC.

COMMENTS ON THE INNOVATION OF THE USE OF WWS IN ROAD CONSTRUCTION

Analyzing our accumulated experience of waste disposal in the field of road construction, we can highlight the following: positive points:

• The proposed recycling method allows involving large-tonnage waste in the sphere of large-tonnage industrial production;
• the transfer of WWS from the category of waste to the category of raw materials determines their consumer value - the waste acquires a certain value;
• in ecological terms, waste of hazard class IV is placed in the roadbed, the asphalt concrete surface of which corresponds to hazard class IV;
• for the production of 1 m 3 of asphalt concrete mix, up to 200 kg of dry WWS can be disposed of as an analogue of mineral powder to obtain a quality material corresponding to regulatory requirements to asphalt concrete;
• the economic effect of the adopted method of disposal takes place both in the field of road construction (reducing the cost of asphalt concrete) and for Vodokanal enterprises (preventing payments for waste disposal, etc.);
• in the considered method of waste disposal, the technical, environmental and economic aspects are consistent.

Problem moments related to the need:

• cooperation and coordination of various departments;
• wide discussion and approval by specialists of the chosen method of waste disposal;
• development and implementation national standards;
• amendments to the Law of Ukraine dated 05.03.1998 No. 187/98-ВР “On Waste”;
• development of technical specifications for products and certification;
• amendments to building codes and regulations;
• preparation of an appeal to the Cabinet of Ministers and the Ministry of Environmental Protection with a request to develop effective mechanisms for the implementation of waste disposal projects.

And finally, one more problematic point - can't solve this problem alone.

HOW TO SIMPLIFY ORGANIZATIONAL POINTS

On the way to the widespread use of the considered method of waste disposal, organizational difficulties arise: cooperation is necessary between various departments with different visions of their production tasks - public utilities (in this case, Vodokanal - the owner of the waste) and a road construction organization. At the same time, they inevitably have a number of questions, incl. economic and legal ones, such as “Do we need it?”, “Is it a costly mechanism or profitable?”, “Who should bear the risks and responsibility?”

Unfortunately, there is no common understanding that the general environmental problem - the disposal of WWS (essentially waste from society accumulated by public utilities) - can be solved with the help of public utilities in the road construction industry by involving such waste in the repair and construction of public roads. That is, the whole process can be carried out within one communal department.

NOTE

What is the interest of all participants in the process?
1. The road construction industry receives sediment in the form of an analogue of mineral powder (one of the components of asphalt concrete) at a price much lower than the cost of mineral powder and produces high-quality asphalt concrete pavement at a lower cost.
2. Sewage treatment companies dispose of accumulated waste.
3. The society receives high-quality and cheaper road surfaces while improving the environmental situation in the territory of its residence.

Taking into account the fact that the disposal of WWS solves an important environmental problem of national importance, in this case the state should be the most interested participant. Therefore, under the auspices of the state, it is necessary to develop an appropriate legal framework that would meet the interests of all participants in the process. However, this will require a certain time interval, which in a bureaucratic system can be quite long. At the same time, as mentioned above, the problem of precipitation accumulation and the possibility of solving it are directly related to the utility industry, therefore, it must be solved here, which will drastically reduce the time for all approvals, and the list necessary documentation narrow down to departmental standards.

VODOKANAL AS A PRODUCER AND CONSUMER OF WASTE

Is cooperation of enterprises always necessary? Let us consider the option of disposing of accumulated WWS directly by Vodokanal enterprises in their production activities.

NOTE

Vodokanal enterprises after the repair work on pipeline networks obliged to restore the damaged roadbed, which is not always done. So, according to the results of our approximate average annual assessment of the volume of such works in the Luhansk region, these volumes range from 100 to 1000 m 2 of the coverage area, depending on the locality. Considering that the structure large enterprises, such as Luganskvoda LLC, includes dozens settlements, the area of ​​restored coatings can reach tens of thousands of square meters, which requires hundreds of cubic meters of asphalt concrete.

The need to get rid of waste, the properties of which make it possible to obtain high-quality asphalt concrete as a result of its disposal, and, most importantly, the possibility of its use in the repair of disturbed road surfaces are the main reasons for the possible use of the considered method of waste disposal by Vodokanal enterprises.

It should be noted that the WWS of treatment facilities in various settlements are similar in their positive impact on asphalt concrete, despite some differences. chemical composition.

For example, Asphalt concrete modified by precipitation in Luhansk (Luganskvoda LLC), Cherkassy (Azot Production Association) and Kievvodokanal meets the requirements of DSTU B V.2.7-119-2003 “Asphalt concrete mixes and asphalt concrete for road and airfield. Specifications" (hereinafter - DSTU B V.2.7-119-2003) (Table 1).

Let's discuss. 1 m 3 of asphalt concrete has an average weight of 2.2 tons. With the introduction of 6-8% sediment as a substitute for mineral powder in 1 m 3 of asphalt concrete, 132-176 kg of waste can be disposed of. Let's take an average value of 150 kg/m 3 . So, with a layer thickness of 3-5 cm, 1 m 3 of asphalt concrete allows you to create 20-30 m 2 of the road surface.

As you know, asphalt concrete consists of crushed stone, sand, mineral powder and bitumen. Vodokanals are the owners of the first three components as artificial technogenic deposits: crushed stone - replaceable loading of biofilters; sand and deposited sediment are waste from sand and silt sites (Fig. 1). To turn this waste into asphalt concrete (useful disposal), only one additional component is needed - road bitumen, the content of which is only 6-7% of the planned output of asphalt concrete.

Existing waste (raw materials) and the need to carry out repair and restoration work with the possibility of using these wastes are the basis for creating a specialized enterprise or site within the structure of Vodokanal. The functions of this unit will be:

• preparation of asphalt concrete components from existing waste (stationary);
• production of asphalt mix (mobile);
• laying the mixture in the roadway and its compaction (mobile).

The essence of the technology for preparing the raw material component of asphalt concrete - mineral (organo-mineral) powder based on WWS - is shown in Fig. 2.

As follows from Fig. 2, feedstock (1) - sediment from dumps with a moisture content of up to 50% - is preliminarily sieved through a sieve with a mesh size of 5 mm (2) to remove foreign debris, plants and loosen lumps. The sifted mass is dried (in natural or artificial conditions) (3) to a moisture content of 10-15% and is fed for additional screening through a sieve with 1.25 mm mesh (5). If necessary, additional grinding of lumps of mass (4) can be performed. The resulting powdered product (microfiller is an analogue of mineral powder) is packed into bags and stored (6).

Similarly, crushed stone and sand are prepared (drying and fractionation). Processing can be carried out at a specialized site located on the territory of the treatment plant, using improvised or special equipment.

Consider the equipment that can be used at the stage of preparation of raw materials.

vibrating screens

Vibrating screens are used for screening WWS various manufacturers. So, vibrating screens can have the following characteristics: “The adjustable rotation speed of the vibration drive allows you to change the amplitude and frequency of vibration. Hermetic design allows the use of vibrating screens without an aspiration system and with the use of inert media. The material distribution system at the entrance to the vibrating screens allows you to use 99% of the screening surface. The vibrating screens are equipped with a split class wiring system. End replacement of screening surfaces. high reliability, easy setup and adjustment. Quick and easy deck replacement. Up to three screening surfaces .

Here are the main characteristics of the VS-3 vibrating screen (Fig. 3):

• dimensions - 1200 × 800 × 985 mm;
• installed power - 0.5 kW;
• supply voltage - 380 V;
• weight - 165 kg;
• productivity — up to 5 t/h;
• sieve mesh size - any on request;
• price - from 800 dollars.

Dryers

For drying bulk material- soil-soil (sediment) and sand - in an accelerated mode (unlike natural drying) it is proposed to use drum dryers SB-0.5 (Fig. 4), SB-1.7, etc. Consider the principle of operation of such dryers and their characteristics (Table 2).

Through the loading hopper, wet material is fed into the drum and enters the internal nozzle located along the entire length of the drum. The nozzle provides uniform distribution and good mixing of the material over the drum section, as well as its close contact with the drying agent during pouring. Continuously mixing, the material moves to the exit from the drum. The dried material is removed through the discharge chamber.

Delivery set: dryer, fan, control panel. In dryers SB-0.35 and SB-0.5, the electric heater is built into the structure. Production time - 1.5-2.5 months. The cost of such dryers is from 18.5 thousand dollars.

Moisture meters

To control the moisture content of the material, various types of moisture meters can be used, for example, VSKM-12U (Fig. 5).

Let's bring specifications such a moisture meter:

• humidity measurement range - from dry state to full moisture saturation (real ranges for specific materials are indicated in the device passport);
• relative error measurements - ± 7% of the measured value;
• depth of the control zone from the surface - up to 50 mm;
• calibration dependences for all materials controlled by the device are stored in non-volatile memory for 30 materials;
• the selected type of material and measurement results are displayed on a two-line display directly in humidity units with a resolution of 0.1%;
• the duration of a single measurement is no more than 2 s;
• duration of holding indications - not less than 15 s;
• universal power supply: autonomous from the built-in battery and from the mains ~ 220 V, 50 Hz via a network adapter (it is also a charger);
• dimensions of the electronic unit - 80 × 145 × 35 mm; sensor — Æ100×50 mm;
• total weight of the device - no more than 500 g;
• full service life - at least 6 years;
• price - from 100 dollars.

NOTE

According to our calculations, the organization of a stationary point for the preparation of asphalt concrete aggregates will require equipment in the amount of 20-25 thousand dollars.

Production of asphalt concrete with OSV filler and its laying

Consider the equipment that can be used directly in the process of manufacturing asphalt concrete with OSV filler and its laying.

Small Asphalt Mixing Plant

For the production of asphalt concrete mixtures from the production waste of Vodokanal and their use in pavement the smallest capacity of the possible complexes is proposed - a mobile asphalt concrete plant (mini-APC) (Fig. 6). The advantages of such a complex are low price, low operating and depreciation costs. The small dimensions of the plant allow not only its convenient storage, but also energy-efficient instant start-up and production of finished asphalt concrete. At the same time, the production of asphalt concrete is carried out at the place of laying, bypassing the stage of transportation, using a mixture of high temperature, which ensures a high degree of compaction of the material and excellent quality of the asphalt concrete pavement.

The cost of a mini-assembly plant with a capacity of 3-5 tons/hour is 125-500 thousand dollars, and with a capacity of up to 10 tons/hour - up to 2 million dollars.

Here are the main characteristics of mini-ABZ with a capacity of 3-5 t / h:

• outlet temperature — up to 160 °С;
• engine power - 10 kW;
• generator power - 15 kW;
• volume of bitumen tank - 700 kg;
• fuel tank volume - 50 kg;
• fuel pump power - 0.18 kW;
• bitumen pump power - 3 kW;
• power exhaust fan- 2.2 kW;
• skip hoist motor power - 0.75 kW;
• dimensions - 4000 × 1800 × 2800 mm;
• weight - 3800 kg.

In addition, to carry out a full cycle of work on the production and laying of asphalt concrete, it is necessary to purchase a container for transporting hot bitumen and a mini-skating rink for laying asphalt (Fig. 7).

Vibratory tandem road rollers weighing up to 3.5 tons cost 11-16 thousand dollars.

Thus, the entire complex of equipment required for the preparation of materials, production and placement of asphalt concrete can cost about 1.5-2.5 million dollars.

FINDINGS

1. The application of the proposed technological scheme will solve the problem of waste disposal sewer stations through their involvement in economic circulation at the local level.

2. The implementation of the method of waste disposal considered in the article will make it possible to bring water utilities into the category of low-waste enterprises.

3. Through the use of WWS in the production of asphalt concrete, the list of services provided by Vodokanal can be expanded (the possibility of repairing intra-quarter roads and driveways).

Literature

1. Drozd G.Ya. Utilization of mineralized sewage sludge: problems and solutions // Ecologist's Handbook. 2014. No. 4. S. 84-96.
2. Drozd G.Ya. Problems in the sphere of treatment with deposited sewage sludge and methods for their solution // Water Supply and Water Supply. 2014. No. 2. S. 20-30.
3. Drozd G.Ya. New technologies for sludge disposal - a way to low-waste sewage treatment facilities // Vodoochistka. Water treatment. Water supply. 2014. No. 3. S. 20-29.
4. Drozd G.Ya., Breus R.V., Bizirka I.I. Deposited sludge from urban sewage. Recycling Concept // Lambert Academic Publishing. 2013. 153 p.
5. Drozd G.Ya. Proposals for the involvement of deposited sewage sludge in the economic turnover // Mater. International Congress "ETEVK-2009". Yalta, 2009. C. 230-242.
6. Breus R.V., Drozd G.Ya. A method for utilizing sediments from local sewage waters: Patent for the core model No. 26095. Ukraine. IPC CO2F1 / 52, CO2F1 / 56, CO4B 26/26 - No. U200612901. Appl. 12/06/2006. Published 09/10/2007. Bull. No. 14.
7. Breus R.V., Drozd G.Ya., Gusentsova E.S. Asphalt-concrete sumish: Patent for coris model No. 17974. Ukraine. IPC CO4B 26/26 - No. U200604831. Appl. 05/03/2006. Published 10/16/2006. Bull. No. 10.

• Sewage treatment facilities: issues of operation, economics, reconstruction

• Decree of the Government of the Russian Federation of 01/05/2015 No. 3 "On Amendments to Certain Acts of the Government of the Russian Federation in the Sphere of Water Disposal": what's new?

The textbook highlights ways to determine the efficiency of water treatment and water treatment facilities, as well as sludge treatment plants. The methods and technologies of laboratory and production control over the quality of natural, tap and waste waters are considered. The third edition of the textbook under the same name was published in 2004.
For students of construction technical schools studying in the specialty 2912 "Water supply and sanitation".

QUALITY ASSESSMENT OF NATURAL, DRINKING AND TECHNICAL WATER.
The sources of water supply in most regions of the Russian Federation are surface water rivers (reservoirs) and lakes, which account for 65-68% of the total water intake. Below is an assessment of the quality of water in them, depending on some characteristic indicators of the composition: pH, salinity (salt content), hardness, content of suspended and organic substances, as well as the phase-dispersed state.

Comparing the estimated and actual indicators of the composition of water in sources Russian Federation, one can note the predominance of soft and very soft, as well as low- and medium-mineralized waters in its Asian part and northern regions, i.e. over most of the country. Pervasive pollution water bodies impurities of anthropogenic and technogenic origin, observed in recent years, is due to the inflow of untreated and insufficiently treated wastewater, domestic and industrial, melt and storm water from catchment areas.

CONTENT
INTRODUCTION
CHAPTER 1. TECHNOLOGICAL CONTROL OF NATURAL AND INDUSTRIAL WATER TREATMENT PROCESSES.»
1.1. Assessment of the quality of natural, drinking and technical water
1.2. Laboratory and production control of water quality in systems of domestic drinking and industrial water supply
1.3. Control of water pre-treatment, coagulation, settling, filtering processes
1.4. Control of water disinfection processes
1.5. Control of processes of fluorination, defluorination, deferrization of water, removal of manganese
1.6. Control of processes of stabilization water treatment. Gas removal: oxygen, hydrogen sulfide
1.7. Control of water softening, desalination and desalination processes
1.8. Control of the hydrochemical mode of operation of circulating cooling water supply systems
1.9. Control of the water cooling process
1.10. Exercises and tasks
SECTION 2. TECHNOLOGICAL CONTROL OF WASTEWATER TREATMENT PROCESSES
2.1. General provisions
2.2. Wastewater classification. Types of contaminants and methods for their removal
2.3. Control of mechanical wastewater treatment processes
2.4. Monitoring the operation of aerobic biological wastewater treatment facilities
2.5. Control of the processes of post-treatment and disinfection of wastewater
2.6. Control of sludge treatment processes. Methane fermentation processes and control of digester operation
2.7. Monitoring the operation of sludge dewatering and drying facilities
2.8. Control of industrial wastewater treatment processes and methods for extracting harmful substances from them
2.9. Control of destructive methods Industrial wastewater treatment
2.10. Exercises and tasks
CONCLUSION
LITERATURE.

Free download e-book in a convenient format, watch and read:
Download the book Water quality control, Alekseev L.S., 2009 - fileskachat.com, fast and free download.

Download djvu
You can buy this book below best price at a discount with delivery throughout Russia.

The treatment and disposal of sewage sludge is a very acute problem for large cities in all highly developed countries. During the purification process, suspended solids contained in wastewater precipitate in mechanical treatment facilities.

The amount of raw sediment directly depends on the content of suspended particles in the water and the quality of cleaning: the higher the quality of cleaning, the more sediment is formed.

At treatment plants with biological treatment, in addition to raw sludge, activated sludge is formed, the amount of which in terms of dry matter can reach 50% of the total sludge volume.

Sludge must be pre-treated before disposal.

Purpose of processing- reduction of humidity and sediment volume, unpleasant odor, the number of pathogenic microorganisms (viruses, bacteria, etc.) and harmful substances; reducing transportation costs and ensuring an environmentally friendly end use.

For the treatment of precipitation, special facilities are built:

metatanks;

aerobic stabilizers,

various installations for dewatering and drying,

silt sites.

Metatenki - these are hermetically sealed tanks, where anaerobic bacteria in thermophilic conditions (t o \u003d 30 - 43 o C) ferment the raw residue in primary and secondary clarifiers. During fermentation, gases are released: CH 4 , hydrogenH 2 , carbon dioxideCO 2 , ammoniaNH 3 etc., which can then be used for various purposes.

Aerobic Stabilizers - these are reservoirs where the organic part is mineralized by aerobic microorganisms for a long time with constant air purge. The treated sludge is stored in sludge beds and then used as fertilizer.

The stored sediments containing salts of heavy metals, contaminated with pathogenic microflora, helminth eggs, viruses, pose an environmental hazard and require an extraordinary approach to the mode of placement and disposal.

A certain danger is also represented by the migration of harmful substances into ground water. Sludge beds and landfills themselves can be sources of harmful emissions into the atmosphere. Emission of gases also occurs from the soils of former landfills, landfills and during the transportation of waste.

The volume and nature of atmospheric pollution depend on the parameters of the technological process of processing precipitation and on the temperature regime.

For large volumes of precipitation, two categories of methods are used: thermal drying and incineration. Thermal drying preserves organic matter used as fertilizer. When sediments are burned, organic substances are converted into gaseous products.

In most countries, there is an upward trend in the amount of sludge burned. The main driver is rising land prices, which makes the development of new technologies more cost-effective and environmentally more efficient than landfill expansion.

Burning precipitation

Burning precipitation applies if they are not subject to other types of processing and disposal. 25% sludge generated at wastewater treatment plants is used in agriculture, 50% placed on landfills and near 25% is burned.

Currently, wastewater treatment is carried out at treatment plants according to the classical scheme of complete biological treatment, in which a mixture of raw sludge from primary clarifiers and excess activated sludge is formed.

Precipitation- this is a non-disinfected wet (up to 99.7%) mass containing up to 70% organic substances.

The sequence of operations for sludge treatment is as follows:

pretreatment on gratings;

mixing sludge from primary settling tanks with activated sludge and straining the mixture on thin grates;

treatment with a reagent - flocculant and dehydration on center presses;

transportation of dehydrated sludge to incinerators;

combustion in furnaces "Pyrofluid" with a fluidized layer of sand.

Wastewater

Wastewater treatment plant

sediment

ash

Suspensions released from waste and waste water in the course of their mechanical, biological and physico-chemical (reagent) treatment are sediments.

It is advisable to divide the properties of sediments into those that characterize their nature and structure, as well as those that determine their behavior in the process of dehydration.

Influence of initial water quality on disinfection effect	The growth of turbidity, color and pH worsens	In the presence of organic substances in water, the bactericidal effect does not change.	As the concentration of suspended solids increases, the bactericidal activity decreases.	With an increase in the concentration of suspended solids, temperature, and salt composition, the	The presence of suspended solids dramatically reduces the disinfection effect.	Does not affect
Influence on the organoleptic properties of water	Improves: oxidizes phenols to products that do not have chlorophenolic odors	Aggravates: smell of iodine, which disappears after 40-50 minutes	Improves: Eliminates odors	Does not affect	Does not affect	Improves: eliminates odor
Period after action	A day or more depending on the dose			90-150 days depending on the dose		Doesn't work on Escherichia coli
Decontamination time, min					Instantly
Method	Chlorination	iodination	Ozonation	Silver ion treatment	UV treatment	Gamma irradiation

constant mass. In liquid sediments, it is approximately close to the concentration of suspended solids determined by filtration or centrifugation.

In hydrophilic organic sediments, this indicator is often close to the content of organic substances and characterizes the content of nitrogenous substances.

The elemental composition is especially important for organic sediments, primarily in terms of such indicators as the content of: carbon and hydrogen to determine the degree of stabilization or establish the total acidity; nitrogen and phosphorus to assess the fertilizer value of the sediment; heavy metals, etc.

For inorganic sediments, it is often useful to determine the content of Fe, Mg, Al, Cr, Ca salts (carbonates and sulfates), and Si.

Toxicity. Metals contained in industrial sewage sludge (copper, chromium, cadmium, nickel, zinc, tin) are toxic. They have the ability to cause various types of biological effects in the human body - general toxic, mutagenic and embryotoxic. The degree of toxicity and danger of various metals is not the same and can be assessed by Mean lethal doses for laboratory animals. Experimental results show that chromium and cadmium are the most toxic for animals.

According to the currently accepted maximum permissible concentrations, which take into account, along with toxicity, the cumulative properties of substances, cadmium, chromium, and nickel pose the greatest danger to public health; less dangerous are copper and zinc.

Sediments from wastewater treatment plants of galvanic industries containing oxides of heavy metals belong to the fourth hazard class, i.e., to low-hazard substances.

The formation of sludge with desired properties begins with the choice of those cleaning methods that provide the possibility of recycling or safe storage of sludge, reducing the cost of their dehydration and drying.

The possibility of safe storage of sewage sludge is determined by the following characteristics and properties of the sludge: the apparent viscosity and associated fluidity of the sludge, as well as the nature of the water contained in the sludge.

The apparent viscosity and the associated fluidity of sediments can be considered as a measure of the intensity of the forces of the relationship between particles. It also makes it possible to evaluate the thixotropic character of the precipitate (the ability of the precipitate to form a gel at rest and return to fluidity even with slight agitation). This property is very important for assessing the ability of the sludge to collect, transport and pump.

The sludge slurry is not a Newtonian fluid because the viscosity found is very relative and depends on the applied shear stress.

The nature of the water contained in the sediment. This water is the sum of free water, which can be easily removed, and bound water, including colloidal water of hydration, capillary water, cellular water, and chemically bound water. The isolation of bound water requires considerable effort. For example, cellular water is separated only by heat treatment (drying or burning).

An approximate value of this ratio can be obtained thermogravimetrically, i.e., by plotting the mass loss curve of a sample of compacted sediment at a constant temperature and processing in relevant conditions. The point at which the thermogram has a break can be determined by constructing the dependence K = f (5"), where V- drying speed, g/min; S - The content of dry matter in the sample,% (Fig. 2.6).

The ratio between free and bound water is a decisive factor in assessing the dewaterability of a sludge.

From fig. 2.6 it can be seen that the first critical current determines the amount of water that can be removed from the sludge at a constant drying rate (phase 1), and represents the dry matter content in the sludge after the loss of free water. Next, bound water is removed: first, to the point S2 with a linear relationship between a decrease in the drying rate and an increase in the dry matter content (phase 2), and then with a sharper decrease in the rate of decrease in the drying rate (phase 3).

These factors include: the ability to seal; resistivity; numerical characteristics of sludge compressibility under the influence of increasing pressure (sludge compressibility); determination of the maximum percentage of dry matter in the sludge at a given pressure.

The ability to compact is determined from the analysis of the sedimentation curve for sediment. This curve is drawn based on laboratory research in a vessel equipped with a slow-acting stirrer. The curve characterizes the degree of separation of the sediment mass in the vessel depending on the residence time in it.

The most important indicator of the ability of sewage sludge to yield moisture is the resistivity. The value of resistivity (g) is a generalizing parameter and is determined by the formula

Where P is the pressure (vacuum) at which the sediment is filtered; F- filtering surface area; ri is the viscosity of the filtrate; WITH - the mass of the solid phase of the precipitate deposited on the filter upon receipt of a unit volume of the filtrate;

Here t is the duration of filtration; V- the amount of precipitated.

Humidity. This parameter takes into account changes in the composition and properties of sludge during their processing and storage.

Sediment compressibility. As the pressure drop increases, the cake pores disappear and the resistance to filtration increases. Sludge compressibility factor (S) determined by the formula

gr2 -gr{

Lgp2-lgi?" (2-5)

Where r, and r2 are the resistivity of the sediment, calculated by formula (2.3), respectively, at a pressure />, and P2.

The water filtration rate will increase, remain constant, or decrease as P increases, according to whether the value of S is less than, equal to, or greater than one.

Insoluble crystalline substances are usually difficult to compress (5 close to 0 or< 0,3). Суспензии с гидрофильны­ми частицами имеют высокую сжимаемость (5>0.5, reaching and sometimes exceeding 1.0).

For many types of organic sludge, there is even a "critical pressure" above which the pores of the cake close to such an extent that drainage becomes impossible. For example, for urban sewage sludge, pressure filtration above 1.5 MPa is almost ineffective. This is why a gradual increase in pressure is believed to have some advantage in delaying cake compaction.

The maximum dry matter content of the sludge at a given pressure. Moisture in precipitation can be in chemical, physico-chemical and physico-mechanical bonds with solid particles, as well as in the form of free moisture. The more bound moisture in the sediment, the more energy must be expended to remove it. An increase in the water yield of precipitation is achieved by redistributing the forms of moisture bonding with solid particles towards an increase in free moisture and a decrease in bound moisture by various processing methods.

Studies of the dependence of the filtration coefficient of precipitation on their humidity have shown that with a decrease in the humidity of precipitation, the values ​​of the filtration coefficient also decrease. At the same time, certain values ​​of precipitation humidity can be noted, below which the filtration coefficient depends little on humidity. For hydroxide sludge of wastewater from electroplating plants, it
lies in the region of 67-70%, and for sediments after galvanic coagulation treatment of wastewater - in the region of 50-55%.

Strength. Using a single moisture criterion to predict the storage capacity of wastewater sludge is not enough. Therefore, to assess the possibility of storing sediments, their strength characteristics are used - shear strength and load bearing capacity, toxicity, leaching, moisture, stability (strength) and filterability.

Washability. Heavy metals are contained in sediments in the form of hydroxides or sparingly soluble salts, such as carbonates, phosphates, chromates, sulfides, etc. -chemical processes occurring during the storage of sediments. More reliable data can be obtained by testing sewage sludge for leaching.

The amount of pollution washed out depends on many factors. In terms of phase composition, sewage sludge can be characterized as crystal cell with soluble and semi-soluble constituents and pores filled with liquid. The liquid phase of sediments contains sedimentary amounts of heavy metals and dissolved salts in the form of anions SO4, SG, CO2 ", etc. During the storage of sediments, physical and chemical aging of metal hydroxides occurs, as a result of which desorbed cations and anions pass into the liquid phase, the pH value decreases and salt content increases, contributing to the reduction of hydroxide solubility products.When exposed to the sediment of the leaching liquid, semi-soluble compounds, such as gypsum, are dissolved, which also leads to an increase in the salinity of the liquid phase.If the leaching liquid contains anhydrides of acids (sulphuric, carbonic, nitric), the pH value also decreases.

Experimental determination of sediment washout is carried out under static and dynamic conditions. The essence of the static study is the soaking of sediment samples in distilled water without mixing and changing the water, followed by monitoring the content of the leachable component in the water for 6-12 months. A dynamic experiment provides for the storage of samples in natural conditions on specially equipped sites, where they are exposed to all types of external atmospheric influences (rain, freezing, etc.). The washout of the element is controlled both in water samples taken from the site and by its loss in the sediment during the experiment (6-12 months or more).

The water yield of sediments largely depends on the size of their solid phase. The smaller the particles, the worse the water yield of precipitation. The organic part of the sediment quickly rots, while the number of colloidal and fine particles increases, resulting in a decrease in water loss.

On fig. Figure 2.7 shows a typical process flow used to treat sewage sludge.

Modern technical means any degree of moisture reduction can be achieved.

Currently, four methods of compaction and thickening of sediments are used (see Fig. 2.7): gravity, flotation, thickening in a centrifugal field and filtration.

Gravity compaction is the most common method of sediment compaction. It is easy to use and relatively inexpensive. The compaction time is set experimentally and can be very different - from 2 to 24 hours or more.

In order to reduce the duration of compaction, obtain a sediment with lower moisture content and reduce the removal of suspended solids from the compactor, various methods are used: mixing during compaction, cyclic thickening, coagulation, joint compaction various kinds precipitation and thermogravitational method.

When the sludge is stirred during compaction, a partial destruction of the continuous spatial structure of the sludge occurs. The blades of the agitator, moving apart the parts of the structured sludge torn apart from each other, create conditions for the unimpeded release of free moisture, previously captured and retained by the spatial structure of the sludge. Slow mixing contributes to the convergence of individual sediment particles, which leads to their coagulation with the formation of large aggregates, which are more intensively compacted under the action of their own mass.

On fig. 2.8 shows the dependence of the degree of sediment thickening on the duration and speed of mixing in a rod mixer.

The maximum compaction effect was achieved at mixing speeds of the end of the mixer blades of 0.04 m/s, the content of suspended solids in the clarified water did not exceed 50 mg/dm3.

Cyclic thickening is carried out by successively accumulating the thickened sludge from several thickening cycles with slow stirring with a rod agitator and pumping out clarified water after each thickening cycle. The efficiency of the cyclic thickening process can be explained by the fact that with an increase in hydrostatic pressure, determined by the number of successive sludge thickening cycles, and slow mechanical mixing more intensively than with a single filling, secondary flocculation is observed in the previously coagulated sludge, which leads to weighting of the flakes and acceleration of compaction draft.

An increase in the hydrostatic pressure of the overlying layers of the thickened sediment to the underlying ones leads to deformation of the sediment structure, accompanied by the transition of part of the water bound in the flocculent structures of the sediment into free water, which is removed by filtration through the pore space of the thickened sediment layer.

Various mineral and organic compounds are used as coagulants. In the reagent management system, the quality of reagent solutions (ferric chloride and lime) is controlled by the concentration of the active agent in them. Careful control of reagent solutions is necessary, since their excess does not improve the filterability of sediments, while at the same time, excessive consumption of scarce substances entails an unreasonable increase in the cost of operation.

In the thermographic compaction method, the precipitate is subjected to heating. During heating, the hydration shell around the sediment particle is destroyed, part of the bound water passes into free water, and therefore the compaction process improves. The optimal temperature for heating the activated sludge of wastewater from hydrolysis plants is 80-90°C. After heating for 20-30 minutes, followed by sludge holding and compaction, its moisture content decreases from 99.5 to 96-95%. The total processing time is 50-80 minutes.

Flotation. The advantage of this method is that it can be controlled by changing the parameters on the fly. The disadvantages of the method include higher operating costs and the impossibility of accumulating a large amount of sediment in the compactor.

Typically, impeller, electric and pressure flotation is used. The latter is the most widespread.

When designing a flotation compactor, a specific dry matter load of 5-13 kg / (m2 x h) and a hydraulic load of less than 5 m3 / (m2 x h) are prescribed; the concentration of the compacted sediment is taken: without polyelectrolytes 3-4.5% by dry matter, with the use of polyelectrolytes 3.5-6% in accordance with the dose of the polyelectrolyte and the load.

The volume of the sludge accumulator should be designed for several hours, since after this time the air bubbles leave the sludge and it regains its normal specific gravity.

Filtration seal. Filtration is most often used as a method of mechanical dehydration of sludge, and is rarely used for thickening them. The following types of modern sealing filters are common: drum filter, drum strainer and filter container.

For anaerobic digestion, two temperature regimes are usually used: mesophilic at a temperature of 30-35°C and thermophilic at a temperature of 52-55°C.

Control of methane fermentation processes includes a system of measurements and analyzes of solid, liquid and gaseous phases. Measuring the amount of incoming precipitation and activated sludge by volume makes it possible to calculate the daily dose of loading the digester by volume D in%. The total volume of the digester is taken as 100%. The volume of incoming precipitation per day, expressed as a percentage of the total volume of the digester, is the volumetric dose of loading the structure. This value can be expressed either as a percentage of the total volume of the digester, or in fractions of a unit of its volume, i.e., in m3 of sediment per 1 m3 of volume per day. For example, if the dose D \u003d 8%, then the second version of the expression for this value is 0.08 m3 / (m3 x day).

It is assumed that during the fermentation process, the volume of sediment and the total amount of water entering the digester do not change. Thus, in accounting, the amount of moisture that enters with superheated steam (used to heat the fermented mass) and is also lost with the removed fermentation gases is neglected.

At least 1-2 times a week for incoming and digested sludge, analyzes are performed to determine their moisture content and ash content. Knowing the humidity and ash content of the initial sediments, as well as D, it is not difficult to calculate the dose of loading the digester using the ashless substance Dbz. This value, measured in kilograms of ash-free substance per 1 m3 of structure volume per day, is similar to the load per volume unit determined for aerotanks. Depending on the type of sediments loaded and their characteristics in terms of moisture and ash content, the value of D63 varies widely: for the mesophilic mode of fermentation from 1.5 to 6 kg / (m3 x day), and for the thermophilic mode - from 2.5 to 12 kg / (m3 x day).

During the operation of digesters, chemical analysis of sediments for the content of gas-forming components, as well as phosphates, surfactants, and total nitrogen is usually performed once a quarter (less than once a month). The analysis is made from average samples collected over the study period. The dried precipitates remaining after the determination of the moisture content are used.

Accounting for the amount of fermentation gases is carried out continuously using automatic registration devices. Chemical analysis of the composition of gases is performed once a decade or a month. CH4, H2, CO2, N2 and 02 are determined. If the process is stable, then the content of H2 - the product of the first phase of fermentation - should not exceed 2%, the content of CO2 should not exceed 30-35%. In this case, oxygen should be absent, since this process is strictly anaerobic. The presence of oxygen is detected only due to non-compliance with complete isolation from atmospheric air of the instruments used for analysis. The amount of methane is usually 60-65%, nitrogen - no more than 1-2%. If the usual ratios in the composition of gases change, then the reasons should be sought in violation of the fermentation regime.

Deep and long-term changes in the composition of gases, expressed in a decrease in the percentage of methane and an increase in the content of carbon dioxide, may be evidence of the souring of the digester, which will necessarily affect the chemical composition of the interstitial water. Acid phase products, in particular lower fatty acids (LFAs), will appear in it in large quantities, while the alkalinity of interstitial water will decrease, which is determined, in addition to NFAs, by the content of carbonate and hydrocarbonate compounds.

In this case, there is a sharp drop in the gas yield per unit volume of the loaded sediment and a decrease in the pH value to 5.0. Hydrogen sulfide H2S appears in the gases of acid fermentation, methane CH4 decreases, and the concentration of carbon dioxide CO2 increases greatly. All this is accompanied by the formation of foam and the accumulation of a dense crust inside the digester.

Under a stable fermentation regime, the content of SFA in interstitial water is at the level of 5-15 mg-eq/dm3, and the alkalinity is 70-90 mg-eq/dm3. The sum of all organic acids is determined through the equivalent of acetic acid, and alkalinity is determined through the equivalent of the bicarbonate ion.

The chemical composition of interstitial water is determined 1-3 times a week (according to the schedule for determining the moisture content of sediments). In interstitial water, in addition, determine the nitrogen content of ammonium salts, which appears as a result of the breakdown of protein components. During normal operation of the digester, the concentration of nitrogen of ammonium salts in interstitial water is from 500 to 800 mg/dm3.

According to the analysis and measurements, a number of calculations are made, as a result of which D and D63 are determined, the percentage of decomposition of the ash-free substance of the precipitation P63 (accounted for by changes in humidity and ash content), as well as the gas output Рg, the gas output from 1 kg of loaded dry matter and 1 kg fermented ashless substance and steam consumption per 1 m3 of sediment.

The reasons for violations of normal fermentation can be: a high dose of loading the digester with fresh sludge, a sharp fluctuation in temperature and loading into the digester of impurities that cannot be digested. As a result of the impact of these causes, the activity of methane-producing microorganisms is inhibited and the intensity of the sludge fermentation process decreases.

Accounting for the operation of the digester is carried out in the form given in Table. 2.17.

During commissioning, first of all, the tightness of the digesters is checked, the presence of safety valves, as well as the presence and performance of mixing devices; Attention is drawn to the possibility of sparks due to possible grazing of steel rotating parts on stationary parts of structures.

Table 2.17 Statement of monthly accounting of the work of digesters

The following devices are used for automated control of technological parameters of operating digesters.

1. Devices for monitoring gas contamination of premises and signaling explosion-proof (up to 2%) gas content in the air. The sensor of the signaling device is installed on the wall in the injection room, and the indicating device is installed on the control panel, which can be removed from the sensor at a distance of up to 500 m. When the emergency concentration of methane in the air is reached, the emergency fan and the sound (light) signal of the emergency are automatically turned on.

2. Sludge temperature control device. It includes a primary device - a copper or platinum thermal resistance in a sleeve embedded in the digester tank, and a secondary device on the control panel.

3. To measure the gas flow from the digesters, a membrane or bell differential pressure gauge is used as a primary converter, and a recorder is used as a secondary one. The amount of gas released is recorded daily.

In addition, typical designs of digesters provide for measuring the gas temperature in gas pipelines from each digester and measuring the gas pressure.

The control of methane fermentation processes is carried out to achieve the following goals:

Reducing the duration of digestion when a given degree of decay is reached to reduce the volume of structures, and, consequently, capital costs;

Increasing the amount of biogas released during the fermentation process in order to use it to reduce the cost of heating the digesters themselves and additionally obtain other types of energy;

Increasing the content of methane in biogas to increase its calorific value and utilization efficiency;

Achieving good compaction and water-releasing properties of the digested sludge to reduce the cost of facilities for its dewatering.

The main task of sewage sludge treatment is to obtain the final product, the properties of which make it possible to utilize it in the interests of National economy or minimize the damage caused by environment. The technological schemes used to implement this task are very diverse.

Technological processes for the treatment of sewage sludge at all treatment plants for mechanical, physical, chemical and biological treatment can be divided into the following main stages: compaction (thickening), stabilization of the organic part, conditioning, dehydration, heat treatment, recycling of valuable products or elimination of sediments (scheme 2) .

Figure 5 - Stages and methods of sewage sludge treatment

Precipitation compaction

Sludge compaction is associated with the removal of free moisture and is a necessary stage in all technological schemes for sludge treatment. During compaction, on average, 60% of moisture is removed and the sediment mass is reduced by 2.5 times.

For compaction, gravity, filtration, centrifugal and vibration methods are used. Gravity compaction is the most common. It is based on the settling of particles of the dispersed phase. Vertical or radial settling tanks are used as sludge thickeners.

The compaction of activated sludge, in contrast to the compaction of raw sludge, is accompanied by a change in the properties of the sludge. Activated sludge as a colloidal system has a high structure-forming ability, as a result of which its compaction leads to the transition of part of the free water into bound state, and an increase in the content of bound water in the sludge leads to a deterioration in water loss.

By applying special treatment methods, for example, treatment with chemical reagents, it is possible to achieve the transfer of part of the bound water to a free state. However, a significant part of the bound water can only be removed by evaporation.

Sludge stabilization

Anaerobic stabilization

Anaerobic digestion is the main method of disposal of urban sewage sludge. Fermentation is called methane fermentation, because as a result of the decomposition of organic matter in sediments, methane is formed as one of the main products.

The biochemical process of methane fermentation is based on the ability of microorganism communities to oxidize organic substances of sewage sludge during their life activity.

Industrial methane fermentation is carried out by a wide range of bacterial cultures. Theoretically, the fermentation of sediments is considered, consisting of two phases: acidic and alkaline.

In the first phase of acid or hydrogen fermentation, complex organic substances of sediment and sludge are first hydrolyzed to simpler ones under the action of extracellular bacterial enzymes: proteins to peptides and amino acids, fats to glycerol and fatty acids, carbohydrates - to simple sugars. Further transformations of these substances in bacterial cells lead to the formation of end products of the first phase, mainly organic acids. More than 90% of the formed acids are butyric, propionic and acetic acids. Other relatively simple organic substances (aldehydes, alcohols) and inorganic substances (ammonia, hydrogen sulfide, carbon dioxide, hydrogen) are also formed.

The acid phase of fermentation is carried out by ordinary saprophytes: facultative anaerobes such as lactic acid, propionic acid bacteria and strict (obligate) anaerobes such as butyric, acetonobutyl, cellulose bacteria. Most of the bacterial species responsible for the first phase of fermentation are spore-forming. In the second phase of alkaline or methane fermentation, methane and carbonic acid are formed from the end products of the first phase as a result of the vital activity of methane-forming bacteria - non-spore-bearing obligate anaerobes, very sensitive to environmental conditions.

Methane is formed as a result of the reduction of CO 2 or the methyl group of acetic acid:

where AH 2 is an organic substance that serves as a hydrogen donor for methane-forming bacteria; usually these are fatty acids (except acetic) and alcohols (except methyl).

Many types of methane-forming bacteria oxidize the molecular hydrogen formed in the acid phase. Then the reaction of methane formation has the form:

Microorganisms using acetic acid and methyl alcohol carry out the following reactions:

All of these reactions are sources of energy for methane-producing bacteria, and each of them is a series of successive enzymatic transformations of the starting material. It has now been established that vitamin B 12 takes part in the process of methane formation, which is credited with the main role in the transfer of hydrogen in the energy redox reactions in methane-forming bacteria.

It is believed that the rates of transformation of substances in the acidic and methane phases are the same, therefore, with a stable fermentation process, there is no accumulation of acids - products of the first phase.

The fermentation process is characterized by the composition and volume of the released gas, the quality of the interstitial water, and the chemical composition of the digested sludge.

The resulting gas consists mainly of methane and carbon dioxide. During normal (alkaline) fermentation, hydrogen as a product of the first phase can remain in the gas in a volume of no more than 1–2%, since it is used by methane-forming bacteria in redox reactions of energy metabolism.

The hydrogen sulfide H 2 S released during the breakdown of the protein practically does not enter the gas, since in the presence of ammonia it easily binds with the available iron ions into colloidal iron sulfide.

The end product of ammonification of protein substances, ammonia, binds with carbonic acid to form carbonates and bicarbonates, which cause high alkalinity of interstitial water.

Depending on the chemical composition of sediments during fermentation, from 5 to 15 m 3 of gas is released per 1 m 3 of sediment.

The speed of the fermentation process depends on the temperature. So, at a sediment temperature of 25 - 27 ° C, the process lasts 25 - 30 days; at 10°C, its duration increases to 4 months or more. To accelerate fermentation and reduce the volume of facilities required for this, artificial heating of the sludge to a temperature of 30 -35 ° C or 50 - 55 ° C is used.

A normally occurring process of methane fermentation is characterized by a slightly alkaline reaction of the medium (pH? 7.b), high alkalinity of interstitial water (65–90 mg-eq/l) and a low content of fatty acids (up to 5–12 mg-eq/l). The concentration of ammonium nitrogen in the interstitial water reaches 500 - 800 mg/l.

Process disruption can result from overloading a facility, changing temperature regime, intake of toxic substances with sediment, etc. The disturbance manifests itself in the accumulation of fatty acids, a decrease in the alkalinity of interstitial water, and a drop in pH. The volume of the resulting gas sharply decreases, the content of carbonic acid and hydrogen, the products of the acid phase of fermentation, increases in the gas.

Acid-forming bacteria responsible for the first phase of fermentation are more resistant to any kind of adverse conditions, including overload. Sediments entering for fermentation are largely seeded with them. Rapidly multiplying, acid-forming bacteria increase the assimilation capacity of the bacterial mass and thus adapt to increased loads. In this case, the rate of the first phase increases, and a large amount of fatty acids appears in the medium.

Methane bacteria multiply very slowly. The generation time for some species is several days, so they are not able to quickly increase the number of cultures, and their content in the raw sediment is insignificant. As soon as the neutralizing ability of the fermenting mass (alkalinity reserve) is exhausted, the pH drops sharply, which leads to the death of methane-forming bacteria.

Of great importance for normal sludge fermentation is the composition of wastewater, in particular the presence in them of such substances that inhibit or paralyze the vital activity of microorganisms that carry out the sludge fermentation process. Therefore, the question of the possibility of joint treatment of industrial and domestic wastewater should be resolved in each individual case, depending on their nature and physico-chemical composition.

When mixing domestic wastewater with industrial wastewater, it is necessary that the wastewater mixture has a pH = 7 - 8 and a temperature not lower than 6 ° C and not higher

30°C. The content of toxic or harmful substances should not exceed the limit allowable concentration for microorganisms growing under anaerobic conditions. For example, when the content of copper in the sediment is more than 0.5% of the dry matter of the sludge, the biochemical reactions of the second phase of the fermentation process slow down and the reactions of the acidic phase accelerate. At a dose of sodium hydroarsenite of 0.037% by weight of the ash-free substance of fresh sediment, the process of decomposition of organic matter slows down.

Three types of structures are used for processing and fermentation of raw sludge: 1) septic tanks (septic tanks); 2) two-tier settling tanks; 3) digesters.

In septic tanks, water is clarified and the sediment that has fallen out of it is rotting at the same time. Septic tanks are currently used at stations with a small throughput.

In two-tier settling tanks, the settling part is separated from the putrefactive (septic) chamber located in the lower part. The development of the design of a two-tier settling tank is a clarifier-decomposer.

For sludge treatment, digesters are currently most widely used, serving only for sludge fermentation with artificial heating and stirring.

The digested sludge has high humidity(95 - 98%), which makes it difficult to use it in agriculture for fertilizer (due to the difficulty of moving with conventional vehicles without pressure distribution networks). Humidity is the main factor that determines the amount of sediment. Therefore, the main task of sludge treatment is to reduce its volume by separating water and obtaining a transportable product.