Draining sludge pits using sawdust. Design of sludge beds. Stormwater treatment plants
The simplest and most widespread structures for dewatering sludge generated at treatment plants of relatively low capacity are sludge platforms on a natural basis (with and without drainage) and compaction platforms.
2.9.1 Natural sludge beds
These sites are planned plots of land, divided into separate maps and fenced on all sides with earthen ridges. They can be installed in well-filtering soils and burial depths groundwater at least 1.5 m from the surface of the cards. A diagram of the construction of sludge pads on a natural foundation without drainage is shown in Figure 9. If the depth of groundwater is less than 1.5 m from the surface of the pads, drainage should be installed.
Rice. 9. Scheme of sludge beds on a natural basis
It is recommended to calculate sludge beds on a natural basis in the following sequence.
Initially, the daily volume of digested sludge entering the sludge beds is established W sbr, m 3 /day. For two-tier settling tanks W sbr is calculated using formulas (43) or (44), and with clarifiers-decayers W sbr = W day – according to formulas (56) or (57).
Useful area of sludge beds F n, m 2, determined by the formula
, (106)
Where h – sediment load on sludge beds; m 3 / m 2 per year; magnitude h in areas with an average annual air temperature of 3 - 6 0 C and an average annual precipitation of up to 500 mm is given in Table 12;
TO– climatic coefficient; magnitude TO varies depending on the climate zone (from 0.6 in the north to 1.2 in the south of the Russian Federation); TO is taken from the isoline map given in.
Area of one map of sludge beds f k, m2, it is recommended to take equal to the area simultaneously filled with sludge f e, m 2, and determined by the formula
, (107)
Where W sbr. unit – volume of sludge supplied to sludge beds at a time, m3. From two-tier settling tanks, sludge is usually supplied to the sites once every 10 days, that is W sbr. units = 10 W sbr – formula (45); with clarifiers and rotators, sludge is usually unloaded daily, that is W sbr. unit = W day – formulas (56) or (57);
h unit – height of the sediment layer supplied to the sites at a time, m; h unit = 0.25 – 0.3 m.
Required number of sludge bed maps n determined by the formula
. (108)
The number of cards should be at least four, that is n≥ 4 . In cases where a large number of small-sized maps are obtained, for economic and technical reasons it is advisable to accept a smaller number of larger-sized maps (but not less than four), and to fence the area simultaneously filled with silt with portable shields.
, m 3 / m 2 per year.|
Sediment characteristics |
Type of sludge beds |
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On a natural basis |
On a natural base with drainage |
On an artificial base with drainage |
Cascade with settling and surface removal of sludge water |
Platforms-seal- |
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Digested mixture of sludge from primary settling tanks and activated sludge under conditions: mesophilic | |||||
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thermophilic | |||||
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Digested sludge from primary settling tanks, two-tier settling tanks and clarifiers-digesters | |||||
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Aerobically stabilized mixture of activated sludge and sludge from primary settling tanks or stabilized activated sludge | |||||
, (109)
Where T– duration of the period of sediment freezing on the sites in days; T should be taken equal to the number of days with an average daily air temperature below minus 10 0 C either according to the isoline map given or according to;
0.75 – coefficient taking into account winter filtration and freezing of moisture;
h n – height of the sediment freezing layer on the sites, m; h n = h c – 0.1; Here h c – the height of the earthen ridge enclosing the maps of the silt areas; h in = 1 – 1.3 m.
The area of the sites occupied for winter freezing of sediment should not exceed 80% of the useful one, that is F h. n ≤ 0.8 F P; the remaining 20% of the area is intended for use during the spring melting of frozen sediment on the sites.
Dimensions of site maps, that is, width b and length l, are assigned based on the accepted map area f k. Length l, m, is determined by the formula
. (110)
For ease of use of the sites, the width of the cards at small treatment plants with one-sided influx of sludge is usually set to no more than b= 10 – 20 m, and at medium and large stations with double-sided influx of sediment – b= 40 – 50 m.
One of the oldest and most proven methods for recycling sediments formed in primary settling tanks, digesters, two-tier settling tanks is sludge pads, and it is also the simplest and cheap method. The sites are also used for other types of precipitation, the main thing is that their humidity is greater than 90%.
Sludge beds can be designed:
- With natural base;
- With drainage system;
- Without drainage system;
- With surface water drainage;
- As compaction pads.
Mud pads on a natural basis are a piece of land specially planned in the form of several areas, which are called maps. Each site is fenced with an earthen berm on all sides (but an entrance for vehicles can be arranged on one side). A system of supply pipes is organized at the site, through which raw sludge or activated sludge is periodically supplied evenly over the area. It is dried to a humidity of about 75-80%. After which the “dry sludge” is loaded onto a vehicle or trolley and transported to landfills or for further processing. Silt water seeps through the ground. There are two options for collecting sludge water:
- If the soil under the sludge beds does not have sufficient filtering properties, then a drainage system is installed. It consists of pipes located in ditches, covered with gravel or crushed stone. Such ditches are installed at a depth of more than 0.6 m. Silt water is most often sent to the beginning of the treatment plant.
- If the soil under the sludge beds has good filtering abilities (sand, loam, sandy loam), then drainage may not be necessary. But only if the sludge water is not dangerous from a sanitary point of view and the groundwater is located at a depth of 1.5 m, otherwise a decrease in its level is required.
Types of sludge beds
It is recommended to design sludge platforms with surface water drainage in areas with an average annual temperature of 3-6 0C and precipitation up to 500 mm/year. Such sludge platforms are made in the form of a cascade of maps located at different height levels. The sludge is fed to the most high card, as it dries, it is diverted down through bypass-wells. Sludge water is discharged from the bottom card into the primary settling tank.
Sludge compaction platforms are reservoirs (usually reinforced concrete with a monolithic bottom), with a depth of 2 m.
Calculation of sludge beds
Calculation of sludge beds involves determining the dimensions of the maps, rollers, slopes and pipeline diameters.
The area of silt maps depends on the volume, structure of sediment, climatic conditions and the type of soil that serves as the foundation. IN general view it is calculated by the formula:
S = (Vο 365)÷(a b C)
Where, Vo– sediment volume, t/day; a– coefficient adopted to take into account the reduction in sludge volume due to its disintegration during fermentation (reference value and depends on the type of structure from which the sludge is received); b– coefficient adopted to take into account the decrease in volume due to loss of moisture; WITH– load on sludge beds (reference value and depends on the design of the sludge bed, climatic conditions, type of sediment), m³/m².
The sufficiency of the area obtained by calculation is checked by the freezing condition in winter period. To do this, calculate the height of the frost layer:
Hus = (W t K2)÷(S K1)
Where, W– volume of sediment per day, m³; t– freezing period, days; S– useful area of cards, m²; K1- Part usable area sludge area allocated for freezing, m²; K2– coefficient taking into account filtration and evaporation.
The dimensions of the map are taken based on the aspect ratio of 1:2 or 1:2.5. Number of cards – at least 2.
The height of the rollers is taken from 0.3 m, their slope depends on the soil.
The slope of the drainage network is assumed to be 0.003, and that of the supply network is 0.01-0.03.
Operation of sludge beds
Operation of sludge sites involves monitoring the condition of distribution, outlet, supply, drainage pipes, the condition of rollers (for collapses and other types of deformation), humidity and chemical composition sludge (supplied and discharged) and its timely removal. Dried sludge is collected manually with shovels into trolleys that move along rollers (for small stations), manual loading, peat and manure loaders onto vehicles, scrapers, bulldozers (for medium and large stations).
→ Cleaning Wastewater
Sludge beds and silt ponds
Sludge beds are one of the first sewage sludge treatment facilities. Sludge beds are designed for natural dewatering of sediments generated at stations biological treatment waste water. However, even in the era of intensive implementation of mechanical sludge dewatering facilities, sludge beds are the most common method of sludge dewatering in Russia. Currently, 90% of all sludge generated in Russia is processed at sludge sites. The attractiveness of these structures is explained by the simplicity engineering support and ease of operation compared to filter presses, vacuum filters, and drying units.
Sludge beds, to a greater extent than other wastewater treatment and sludge treatment facilities and systems, depend on climatic and natural factors.
Rice. 16.1. Sand playground:
1 – sand pipeline with a diameter of 200 mm from sand traps; 2 – distribution tray with a cross-section of 200×200 mm (i = 0.01); 3 – pipeline with a diameter of 200 mm for drainage water
Depending on the extent to which natural processes are used, sites can be divided into two main categories: natural dewatering and drying and intensive dewatering and drying.
The first category includes sites that use natural processes evaporation and decantation without significant changes compared to the same processes occurring in the natural environment. As a rule, these are sites on a natural foundation with surface water drainage and compaction sites.
The second category includes sites in which certain factors of the natural cycle are modified and intensified. As a rule, these are sites with artificial drainage, heating, creation of a vacuum in the drainage system, and artificial waterproof coating. The use of one or another type of site depends on local conditions: climate specifics, availability additional sources energy, free space.
Natural dehydration and drying areas. At natural cycle sites, sludge is dewatered through the process of compaction and subsequent removal of sludge water, as well as drying.
Silt beds consist of maps surrounded on all sides by ridges (Fig. 16.2). The size of the cards and the number of issues are determined based on the moisture content of the sediment, the range of its spillage and the method of cleaning after drying.
Rice. 16.2. Silt pads on a natural basis with drainage:
1 – ditch of a protective ditch; 2 – road; 3 – drain tray; 4 – shield under drain tray; 5- distributing tray; 6 – drainage well; 7 – prefabricated drainage pipe; 8 - drainage layer; 9 – drainage pipes; 10 – exit to the map; 11 – drainage ditch; 12 – gates; K1-K5 – wells
Silt pads on a natural basis are designed on well-filtering soils when groundwater occurs at a depth of at least 1.5 m from the surface of the maps and only when filtration of silt water into the soil is allowed. If the depth of groundwater is less than 1.5 m, then it is necessary to lower its level.
The spill range of sludge with a humidity of about 97% can be 75-100 m. In this case, it is advisable to build areas measuring 100x100 m. The spill range of sludge with a humidity of 93-95% can be 20-25 m, in this case the width of the maps will be limited to 40 -50 m with double-sided inlet. Narrow areas are preferable when planning on an area that has a well-defined slope.
The dried sludge is raked by bulldozers or scrapers and transported by truck. The humidity of the dried sludge is 75%.
Roads with ramps for access to the maps of vehicles and mechanization equipment are constructed on the sludge sites.
In dense and waterproof soils, sludge platforms are constructed on a natural foundation with tubular drainage laid in drainage ditches. The artificial drainage base of sludge beds must be at least 10% of their area.
The following should be taken: working depth of cards - 0.7-1 m; the height of the barrier rollers is 0.3 m above the working sediment level on the map; the slope of distribution pipes or trays is not less than 0.01; the number of cards is at least four.
The most widespread are sludge platforms on natural foundations of the cascade type with settling and surface removal of sludge water. After filling the sludge platform cards with sediment and draining the separated sludge water, further dewatering of the sludge is carried out by evaporation of the remaining moisture from the surface.
An improved version of cascade-type platforms are compaction platforms. Sludge compaction platforms are rectangular reinforced concrete tanks (cards) with holes located in the longitudinal wall at different depths and covered with gates. To release silt water released when sediment settles, holes are made along the height of the longitudinal walls of the reservoir tanks, blocked by gates. Sludge water is sent for cleaning to the head of structures, similar to sludge platforms, with settling and surface removal of water. The distance between sludge water outlets is set to no more than 18 m. For mechanized collection of dried sludge, ramps with a slope of up to 12% are installed.
One of the possible methods that accelerates the natural drying of sludge on sludge beds is the turning process. At the same time, the vegetation cover is removed and the surface crust is destroyed, which promotes accelerated drying of the sediment in warm, dry times and deeper freezing in winter.
Characteristic feature natural cycle sites is their complete dependence on climatic factors. When designing and operating such sites, it is especially necessary to take these factors into account in order to obtain the desired result - dewatered sludge of a certain moisture content.
Sludge sites for intensive dewatering and drying can be divided into traditional and improved. The first category includes sludge platforms with vertical and horizontal drainage, the second category includes sites with the creation of a vacuum in the drainage system, an artificial waterproof coating with air blowing, and heating.
Cascade type sludge beds with a natural base and surface water drainage through monk wells installed at the ends of the pads are transitional type sludge beds. The walls of the monk wells on the card side are drainage walls made of double reinforcing mesh with gravel loading with a particle size of 15-20 mm.
Sludge beds with artificial drainage are designed to obtain clean filtrate and increase the rate of dewatering.
Filtering through horizontal drainage system can be carried out by filter panels with special holes or drainage pipes.
A filter platform with horizontal drainage (Fig. 16.3) is a shallow rectangular tank with waterproof walls and a false bottom made of special panels. These panels have wedge-shaped holes measuring 1-4 mm. The border of the false bottom is made waterproof, and the joints between the panels and the walls are sealed.
Rice. 16.3. Layout of the filter sludge platform:
1 – compaction zone; 2 – partition with wedge-shaped slots; 3 – filtrate level control chamber; 4 – outlet valve that regulates the filtration rate
An outlet valve is provided on one of the walls of the platform, connected to the space under the false bottom. A controlled drainage rate is ensured by introducing a layer of water into the system to a certain level above the false bottom. The sediment is then slowly introduced and, under appropriate conditions, maintained on a layer of water. After supplying the required amount of sludge, the initially introduced water and silt water from the sludge seeps through the false bottom. The filtration rate is maintained constant by a constant pressure in front of the outlet valve. For a successful dewatering process, it is necessary that the sediment and the original aqueous layer do not mix. The sludge dewatering technique at such sites involves the controlled formation of a cake layer at the interface between the sludge and the filter medium before any significant amount of tiny particles will fall onto this surface or into the holes of the false bottom and end up in the filtrate. The productivity of the filter platform in terms of dry matter is usually from 2.4 to 4.8 kg/m2 per load.
The drainage system of traditional sludge filter beds with drainage pipes usually includes: – upper layer sand 15-25 cm high, with an effective diameter of 0.3-1.2 mm and a heterogeneity coefficient of less than 5; – a layer of gravel 20-45 cm high, with a grain size of 0.3-2.3 cm; – drainage pipes, often made of ceramic, minimum diameter 10 cm, with open ends, located at a distance of 2-6 cm from each other.
IN Lately began to be used plastic pipes, since ceramic ones are quickly destroyed during mechanized sediment removal.
The sediment is fed onto the filter cards either at one or several points in a layer of 250-450 mm and remains on the cards until it dries. Under favorable weather conditions, well-fermented sludge dries within 2 weeks, reaching a humidity of 60-70%
To reconstruct existing sites, a drainage system containing vertical filter elements and pipes for draining sludge water can be used. Such a drainage system is made in the form of sectional pipes distributed over the surface of the site and a common one, having seats with mesh bottoms into which vertical filter elements are installed.
The common pipe is connected to the sludge water drainage pipe.
Filter fiberglass pipes can be used as filter elements of drainage systems. Such filter pipes are used for well construction. The design of the horizontal drainage system consists of a fiberglass plastic pipe. The vertical filter element is made from a similar pipe, but of a larger diameter, coated with filter material. It is connected to horizontal drainage pipelines using steel tees and flange connections.
Visual observations of the operation of the drainage system during various types loadings showed that a layer with high filtration resistance is formed at the sediment-drainage loading boundary.
It was noted that in the initial period the specific filtration rates through the vertical drainage system are higher than through the horizontal one, then they level out. At the final stage of drying, only horizontal drainage works. When re-pouring sediment onto an already dried layer, the filtration rate is significantly reduced.
A study of the composition and properties of urban wastewater sludge, carried out by I.S. Turovsky, showed that the load on sludge beds largely depends on the type and water yield of sludge. Analysis of operating data for a number of treatment plants showed that there is a certain relationship between the values resistivity sedimentation and operation of sludge beds. Thus, at the aeration station of Kaliningrad (Moscow region), with a humidity of the fermented mixture of 94.8% and its specific resistance of 25800-1010 cm/g, the load per 1 m2 of sludge beds was 0.35 m3 per year. The drainage quickly became clogged, and the platforms worked only to evaporate the liquid.
The clogging of the base occurs the faster, the worse the sediments are filtered, which is due to the high content of fine and colloidal particles in them. The layer of simultaneous influx of sediment onto sludge beds can be greater, the lower the value of the sediment resistivity. At high values of sediment resistivity, most of the moisture is removed by evaporation.
Improved sites for intensive sludge dewatering and drying. To intensify the sludge drying process, it is proposed to blow it with air directly on the site.
The sludge platform contains a waterproof bottom, side walls, drainage loading, perforated pipes placed on the bottom, air duct and pipelines for washing and filtered water. Air purging is carried out to the required degree of dehydration.
The use of capillary suction effect accelerates the process of sludge dewatering on sludge beds. A sludge pad using this effect (Fig. 16.4) works as follows. When the cards 1 are filled with sediment, thanks to the forces of capillary suction, water from the sediment is absorbed through the edges of the sheets 4 placed in the corridor 3, evaporating into the environment.
The walls of adjacent cards are installed to form corridors, in which sheets of capillary fiber are also placed - porous material. The sludge beds are equipped with blowers connected to the corridors by air ducts.
Abroad, sludge beds are often protected from precipitation with a glass coating. This coating can significantly improve the performance of sites, especially in cold and humid climates. Experience has shown that in some cases, the coating device can reduce the area required for drying sludge by 33%.
The degree to which the required area is reduced and the load on sludge beds increased as a result of the use of transparent or translucent coatings depends on local conditions, such as the amount of precipitation, temperature, and solar radiation.
Rice. 16.4. Sludge bed using capillary suction effect:
1 – silt maps; 2 – enclosing walls; 3 – corridor; 4 – sheets of capillary-porous material; 5 – blower; 6 – air duct
In our country, closed areas, glazed like greenhouses, are recommended to be used in resort areas to save space and reduce the intensity of odors. The load on digested sludge from digesters is assumed to be 10 m3/(m2year).
Asphalted sludge beds with central drainage and heating are used in Dunedin (USA, Florida). These sites are of interest due to the use of a heating system on them. Thermal energy, obtained by burning biogas from wastewater treatment plants, is used to heat water, which circulates in pipes located in the asphalt part of the sites. The sludge beds are heated, but not closed. Polyelectrolytes are used to condition sediments. The drying time for sediment is on average 5 days and increases to 12 days during the rainy season. The annual load on sludge beds in terms of dry matter ranges from 87.9 to 209.9 kg/(m2.year).
Conditioning the sludge before dewatering sludge on sludge beds significantly reduces the duration of the dewatering process and improves the performance of the dried sludge. The method of conditioning sludge with organic flocculants before feeding it to sludge beds is currently widely used in Germany. The humidity of flocculated and untreated fermented sludge from one of the stations after dewatering it on sludge beds was respectively: after 2 days 76 and 87%, after 5 days 73 and 86%, after 10 days 72 and 83%, after 15 days 71 and 80% , after 20-25 days approximately 70-77%). Under normal atmospheric conditions (Germany), the conditioned sludge is dried on sludge beds after 3-4 weeks to a humidity of approximately 75%> and can be removed without difficulty using machinery. Thanks to the coagulation of colloids and tiny particles, the phenomenon of silting of drainage is reduced. Dehydrated sludge has a “permeable hydrophobic structure” and even when it rains it does not absorb water, its humidity does not increase.
Studies of the use of domestic flocculants to intensify the work of sludge beds were carried out on a fermented mixture of sediments and aerobically stabilized activated sludge on laboratory models and in pilot industrial conditions on a sludge bed measuring 600 m2, equipped with vertical and horizontal drainage systems made of fiberglass filters. The best results were obtained when using flocculant brands KNF and K-100. At the same time, sludge humidity of 78-81% was achieved approximately twice as quickly as when drying sludge not treated with flocculants. The specific productivity of the site during dewatering of sludge treated with flocculants was 4.5-6 m3/(m2-year). The drainage load consisted of a layer of sand 50-150 mm with fraction sizes of 1-3 mm and 3 layers of crushed stone with fraction sizes from top to bottom of 5-3 mm, 10-5 mm, 15-10 mm. Studies have shown that the load on sludge beds when drying stabilized activated sludge and digested sludge for conditions middle zone In Russia, respectively, 4.5 and 5 m3/(m2-year).
To intensify the work of sludge beds, in addition to treatment with flocculants, it is possible to carry out preliminary washing of difficult-to-filter sediments with purified waste liquid, coagulation of sediments with chemical reagents, as well as freezing and subsequent thawing of sediments. All these types of treatment reduce the resistivity of sediment filtration. Preliminary washing of sludge allows you to increase the load on sludge beds by 70%, and the use of chemical reagents or additive materials when drying sediments increases the load on sludge beds by 2-3 times. The resistivity of aerobically stabilized sludge is significantly lower than that of fermented sludge. In sludge beds on an artificial base with drainage and surface water removal at an average annual air temperature of 3-6°C and an average annual precipitation of up to 500 mm after aerobic stabilizers, according to the Federal State Unitary Enterprise Research Institute VODGEO, the load is 3-5 m3/(m2year) with the humidity of the incoming sediment 96.5-97%. In this case, the drainage area is 8-10% of the site area. The size of the card is based on filling it to a working depth of 1-2 m for no more than 3 days. An additional increase in the productivity of the sludge bed can be achieved by subjecting aerobically stabilized sewage sludge to treatment with ammonium nitrate in an amount of 100-150 mg/l. Ammonium nitrate is introduced into the aerobically stabilized sludge (at the outlet of the aerobic stabilizer) and fed to the sludge bed. In the filled sludge bed, the biological process of denitrification of the nitrate compound occurs, i.e. ammonium nitrate introduced into the sediment. The process is spontaneously carried out by denitrifying bacteria, which are part of the bacterial flora of sediment, and is accompanied by intense gas release of nitrogen, ensuring flotation and thickening of sediment particles. The volume of sediment decreases by 5-6 times, its concentration is approximately 50 g/l. Under the compacted layer of sediment there is silt water containing 6-10 mg/l of suspended solids. After the sediment compaction process is completed (4-7 hours), the drainage is opened and the sludge water is released. The condensed sediment sinks to the bottom and quickly dries, because has a good structure due to the presence large number pores formed by gas bubbles. One cycle of operation of the site from the moment of loading to unloading of dry sludge is no more than 1 month. The load reaches 8-10 m3/m2 per year with a site depth of 1.0-1.5 m.
Principles for calculating sludge beds. The method for calculating sludge beds was developed in the twenties by Imgoff and has existed virtually unchanged to this day. The calculation is based on the load Kf> m3/(m2year), which establishes the permissible volume of precipitation placed on a unit surface of the sludge platform per year.
The total area of sludge beds should be increased by 20-40% for the construction of fencing ridges and access roads.
During periods of negative temperatures, the supplied sludge freezes. 80% of the area of sludge beds is allocated for winter freezing, and 20% is intended to accommodate sediment during the period of melting of previously frozen sediment.
Recent studies of the operation of sludge beds have shown that the dewatering process must be considered as complex, consisting of several elementary processes.
The rate of moisture removal as a result of drying, according to research, depends on the wind speed and the lack of humidity in the air above the sites.
The filtration stage is determined by the properties of the sediment and the characteristics of the drainage system, and the decantation rate is determined by the ability of the sediment to compact.
Intensification of the work of sludge beds. Increasing the productivity of sites is possible through the following measures: – compaction of sludge supplied to the sites; – ensuring mechanical tedding and removal of dried sludge from the site; – conditioning of sludge before delivering it to the site; – blowing the sediment with air directly on the site; – devices above the platform of a translucent coating or general coverage greenhouse type with appropriate ventilation systems; – use of vacuum systems to speed up filtration; – installation of sludge heating systems directly on sludge beds.
The turning process significantly accelerates the natural drying of sludge on sludge beds. The wind speed over the surface of sediment overgrown with vegetation is practically zero, the deficit of water vapor elasticity is characterized by a decrease from the upper tier of leaves to lower tier virtually to zero, therefore, the rate of evaporation of water from sediment, densely overgrown with vegetation, is zero. The formation of a crust of overdried sediment on the surface of the sediment reduces the drying rate by 4 times.
When turning, the plant cover is removed and the surface crust is destroyed, which contributes to accelerated drying of the sediment in warm, dry times and deeper freezing in winter.
The properties of the processed sludge, especially the ability to compact and specific filtration resistance, influence the choice of sludge platform design: at g 4000 -1010 cm/g - with settling and surface water removal.
Dehydration of fermented sludge, which has a specific filtration resistance of the order of 4000 -1010 cm/g, on maps with horizontal drainage has low efficiency. Filtration rates do not exceed 0.48 kg/(m day), which is 1.5 times less than the evaporation rate with a moisture deficit of 6 mbar. The site drainage quickly becomes clogged and stops passing filtrate. The amount of water released during filtration through drainage is insignificant.
The specific filtration resistance of aerobically stabilized activated sludge is 20-100 times less than the specific filtration resistance of digested sludge, therefore, it is rational to use areas with drainage for dewatering aerobically stabilized activated sludge.
Choice optimal technology sludge dewatering can significantly improve the productivity of sludge beds. The filling mode, primarily the height and frequency of filling, depend on the type of sediment, its concentration, the characteristics of preparation and the time of year. When supplying stabilized activated sludge with an initial humidity of up to 98% to the site, the filling height should be 0.8-1 m. In this case, a significant volume of drainage water is discharged through a vertical drainage system.
For fermented sediments the most effective method dewatering on sludge beds is a technology of separate compaction, drying and freezing. As the depth of the compacted sediment layer increases, the compaction speed increases and the likelihood of sediment stratification decreases. It is recommended to compact the sludge at a filling height of at least 2.5 m, and drying and freezing in layers of no more than 0.3 m.
Silt ponds. In developing countries, silt ponds (lagoons), made in the form of ditches or by damming natural depressions or ravines, have become widespread. The cost of constructing sludge ponds is less than that of sludge platforms, primarily due to the use of natural excavations and simplicity of design. A necessary condition in all cases, the occurrence of groundwater below the silt ponds is evident. After filling, the lagoons are covered with a layer of local soil up to 40 cm thick. The sediments rot over several years, after which they are used as fertilizer.
Multi-stage sludge ponds are used, in which liquid sediment and water are transferred to subsequent ponds, and drying and unloading are carried out in the previous ponds. In Daugavpils (Latvia), periodic silt ponds with an area of 12.0 ha were built with filtration of silt water into the ground.
A design has been developed for silt ponds 6 m deep with screening of the bottom and slopes with a polymer film. In such ponds, the furrows (ditches) are filled with sediment layer by layer, and a layer of soil 0.7 m thick is poured on top. After a year or two, trees for forest protection or forest park purposes are planted in this place.
6.387. Sludge pads can be designed on a natural foundation with or without drainage, on an artificial asphalt concrete base with drainage, cascade with settling and surface removal of silt water, and compaction pads.
6.388. The sediment load on sludge beds, m 3 /m 2 per year, in areas with an average annual air temperature of 3-6 ° C and an average annual precipitation of up to 500 mm should be taken according to table. 64.
6.389. On sludge sites, roads should be provided with exits to the maps for vehicles and mechanization equipment with a chain for ensuring mechanized cleaning, loading and transportation of dried sludge.
For cleaning and removal of dried sludge, mechanisms used in excavation work should be provided.
6.390. Silt pads on a natural foundation can be designed provided that groundwater occurs at a depth of at least 1.5 m from the surface of the maps and only in cases where filtration of silt water into the ground is allowed.
At a shallower depth of groundwater, it is necessary to lower its level or use sludge beds on an artificial asphalt concrete base with drainage.
6.391. When designing sludge beds, the following should be taken into account: working depth of the cards - 0.7-1 m; the height of the protective rollers is 0.3 m above the working level; the width of the rollers at the top is at least 0.7 m, when using mechanisms for repairing earthen rollers 1.8 - 2 m; the slope of the bottom of distribution pipes or trays is calculated, but not less than 0.01; the number of cards is not less than four.
6.392. When designing sludge beds with settling and surface drainage of sludge water, the following must be taken into account:
number of cascades - 4-7; number of cards in each cascade - 4-8;
useful area of one card - from 0.25 to 2 hectares; map width - 30-100m (for terrain slopes of 0.004-0.08), 50-100m (for slopes of 0.01-0.04), 60-100m (for slopes of 0.01 or less); map length for slopes over 0 .04 - 80-100m, with slopes of 0.01 and less - 100-250m, width to length ratio 1:2 - 1:2.5; height of fencing rollers and embankments for roads - up to 2.5m; the working depth of the cards is 0.3 m less than the height of the protective rollers; deposits of sediment: with 4 cards in a cascade - on the first 2 cards, with 7-8 cards in a cascade - on 3-4 first cards; silt water transfers between cards - in a checkerboard pattern: the amount of silt water is 30-50% of the amount of dewatered sludge.
6.393. It is allowed to provide sludge compaction platforms with a working depth of up to 2 m in the form of rectangular reservoirs with waterproof bottoms and walls. To release silt water released when sediment settles, holes should be provided along the longitudinal walls, blocked by gates.
6.394. When designing compaction platforms, the following should be taken into account:
card width - 9-18m;
the distance between silt water discharges is no more than 18 m;
installation of ramps for the possibility of mechanized collection of dried sludge.
6.395. The area of sludge beds should be checked for freezing. To freeze sediment, it is allowed to use 80% of the area of sludge beds (the remaining 20% of the area is intended for use during the spring melting of frozen sediment).
Duration of freezing period should be taken equal to the number days with an average daily air temperature below minus 10°C (see Figure 3).
The amount of frozen sludge may be taken equal to 75% of that supplied to the sludge beds during the freezing period.
The height of the frozen sediment layer should be 0.1 m less than the height of the roller. The bottom of distribution trays or pipes must be above the frost horizon.
6.396. The artificial drainage base of sludge pads must be at least 10% of the map area. The design and placement of drainage devices and the dimensions of the sites should be taken into account with regard to mechanized sludge removal.
6.397. The hard covering of sludge areas must be made of two layers of asphalt 0.015-0.025 m thick and crushed stone-sand preparation 0.1 m thick, asphalt concrete or concrete, depending on the type of mechanisms used for sludge removal.
6.398. The supply of sludge water from sludge sites should be provided to treatment facilities, and the facilities are designed taking into account additional pollutants and the amount of sludge water. Additional amounts of pollutants from sludge water should be taken: when drying fermented sludge - for suspended solids - 1000-2000 mg/l, for total BOD -1000-2000 mg/l (larger values for compaction sites, smaller values for other types of sludge sites) , for aerobically stabilized sediments - according to clause 6.367.
6.399. When justified, sludge platforms may be constructed on alluvial (bulk) soil.
6.400. When locating sludge sites outside the territory of treatment stations, service and household premises should be provided for service personnel, as well as a storage room in accordance with clause 5.26 and a telephone connection.
INVENTION
Patent Russian Federation RU2079453
Inventor's name:
Akchurin B.K.
Patent owner's name:
Joint-Stock Company"Nizhny Novgorod Santekhproekt"
Correspondence address:
Patent start date:
12.01.1995
Use: dewatering of municipal wastewater sludge on sludge beds. The essence of the invention: the sludge platform contains a waterproof base 1, drainage filter devices with filters 2 and drainage pipes 3 equipped with removable plugs, water receiving trays 4, a pipeline 5 for supplying liquid sediment, drainage wells 6 and an enclosing dam 7 made of horizontal layers of filter material. The base of the dam is located on the waterproof base of the site, and the layers are laid offset to the central vertical axis and form a container in the shape of a truncated pyramid. The drainage wells are made of composite ring elements 14, 15, 16 installed on top of each other. Dewatered municipal wastewater sludge is used as a filter material for the dam. The method of operating a sludge platform includes filling it with liquid sludge, filtering through drainage filter devices and a dam, discharging silt water through drainage wells, holding and removing the dewatered sludge. Before filling, the site is fenced off with the lower layer of the dam and the drainage pipes of 3 drainage devices are blocked with removable plugs. During the filling process, as sediment accumulates, the next layers of the dam and the height of the drainage wells are periodically increased. After filling the sludge platform to the top of the dam, holding is carried out. In this case, the drainage pipes 3 are freed from plugs and dewatered by filtration through drainage filter devices and a dam. During the holding process, complete stabilization and disinfection of municipal wastewater sludge also occurs.
DESCRIPTION OF THE INVENTION
The invention relates to municipal services, in particular to the dewatering of sewage sludge in natural conditions on sludge beds and can be used in municipal wastewater treatment plants.
The simplest and most common method of dewatering liquid sewage sludge is to dry it on sludge beds. The latter are planned drained areas on a natural or artificial foundation, surrounded on all sides by earthen ridges up to 1.5 m high, a top width of at least 0.7 m and a drainage system
With relatively simple technology and low operating costs, sludge beds provide an extremely low dewatering effect, especially in areas with large amounts of precipitation. Such areas include most of the territory of Russia, where sludge sites are forced to turn into sludge reservoirs for long-term storage liquid sediment.
After filling the sites, dehydration of the sludge mixture to 80% lasts practically from 3 to 10 years, depending on the specific climatic and hydrogeological conditions, constructive solutions for the removal of nadil and drainage waters. Currently, the problem of sludge dewatering in natural conditions is being solved by allocating additional areas for sludge beds. At wastewater treatment plants in large cities, hundreds of hectares are occupied by sludge beds, so the improvement of their design is in the direction of intensifying dewatering. A number of inventions provide for the use of vertical filter devices for this purpose.
A sludge platform is known that contains a waterproof base with enclosing walls, a pressure sludge pipeline, a collection manifold, and a drainage system with vertical filter elements.
The walls of the platform have windows with stepped gate devices. Vertical cassette-filtering devices are mounted on the opposite side of the walls, providing additional filtration and water removal. The design of this sludge platform is complicated and not effective enough, since filtration is carried out on the entire surface of the enclosing walls, but only through its individual sections. Maintenance of this site also becomes more complicated, since due to calmatization, the filter media requires frequent regeneration or replacement.
They are used as filter materials for drainages and vertical filters. various materials, including dewatered, stabilized sewage sludge. The invention protects the dewatering of sewage sludge, in which a layer of dry sludge with a humidity of 65-70%, 15-20 cm thick, is laid on a sludge platform with an asphalt concrete coating and with a drainage device in the form of trays filled with gravel. During operation, the liquid sludge is fed onto the site with periodic inflows, alternating them with breaks, during which filtering occurs through a layer of sediment and drainage gravel backfill. After a period of filling, which lasts several months, a period of sludge drying follows, and then mechanical cleaning takes place and the site is prepared for the next cycle. This method is also not effective enough, because... The dehydration process is carried out only through filtration and natural drying; it does not use the process of natural phase separation of the liquid sludge mixture. The method does not reduce the volume of loading and unloading operations, nor does it contribute to the reduction of occupied territories for sludge beds.
The sludge platform and its method of operation are closest to the claimed technical solution. The site contains a waterproof base, a drainage system of vertical filter elements and a pipeline for supplying sludge. When dewatering municipal wastewater sludge necessary element The sites are also drainage wells for removing excess water. The filter elements of this platform are made of porous concrete with through slotted holes.
They are installed along the perimeter of the sludge platform and perpendicular to the movement of sludge water, forming maps.
The lower mark of the slot holes is recessed under the waterproof base, and the sediment supply pipelines are perforated and installed on the filter elements. With this design of the sludge platform, the sediment is gradually poured from the edge of the map to its middle, and under the influence of gravity, hydroclassification of the sediment occurs, a return filter is formed from it, which helps to retain particles that have not yet settled in the sediment.
The dewatering technology at this site boils down to the fact that sludge is filled continuously to the entire working depth of the site, along the entire height of the layer. Water is drained through the sediment layer and moves along the waterproof base to the filter elements. After the site is filled, a period of time is taken to dehydrate and dry the sludge.
Then the vertical filter elements are removed and the site is cleared of dried sediment using mechanization.
Warehousing and storage of dewatered sludge is carried out in warehouses-landfills at wastewater treatment plants. Before a new cycle and supply of the next portion of liquid sludge, vertical filter elements are reinstalled on the site. The disadvantages of this design are: high labor intensity in maintenance, insufficient capacity of the site, limited by the height of the enclosing walls and vertical filter elements, a large volume of unproductive preparatory and loading and unloading work, frequent repetition of work cycles.
In addition, the dehydration process is carried out only through filtration through vertical filter elements. The required intensity of dewatering is achieved by an increased number of these elements, which become clogged during operation and require frequent regeneration and replacement, which also complicates the operation of the sludge site.
The purpose of the present invention is intensification of the dewatering processor, increasing site capacity and simplifying maintenance.
This goal is achieved by the design of the inventive sludge platform containing a waterproof base, drainage filter devices, drainage wells, water intake trays and a pipeline for supplying liquid sludge, in that, according to the invention, the site is additionally equipped with an enclosing dam made of horizontal layers of filter material, and the base of the dam is placed on the waterproof base of the site, the layers are laid offset to the vertical axis and form a container in the shape of a truncated pyramid, and the drainage wells are made of composite ring elements installed on top of each other to the level of the top of the dam. To achieve this goal, the most appropriate option is to make a containment dam from dewatered municipal wastewater sludge.
This goal is also achieved by the method of operating the proposed sludge platform, including filling it with liquid sediment, filtering through drainage filter devices and a dam, draining nadil waters through drainage wells, holding and removing dehydrated sludge, in that, according to the invention, before filling the site, it is fenced with a lower layer of the dam, during the filling process, periodically, as sediment accumulates, the next layers of the dam and the height of the water intake wells are increased, and filtering through drainage filter devices is carried out after completion of filling, during the holding period.
The proposed sludge platform with an enclosing dam made of filter material has a greatly increased capacity due to an increase in height, without expanding the occupied territory. The design makes it possible to intensify the dehydration process by increasing the hydrostatic pressure of the liquid phase, and to organize filtration not only through bottom drainage, but also through the dam itself. Dewatering is also intensified by the removal of nadil waters from various levels along the height of the dam through the expanding elements of composite drainage wells. The use of dewatered municipal wastewater sludge as a filter material is most appropriate, since this ensures the homogeneity of the composition of the dewatered sludge, which is important for its subsequent use for economic purposes. The presence of a dam provides not only dewatering, but also storage of multi-year volumes of sewage sludge, eliminates loading and unloading operations for transferring dried sludge to landfills for its storage and greatly simplifies the maintenance of the sludge site.
The proposed sequence of operations during the operation of a sludge platform makes it possible to improve the conditions for sludge dewatering both at the first stage when filling the sludge platform to the level of the top of the dam, when dewatering occurs mainly due to sedimentation, and at the second stage during the holding period, when the dewatering process occurs due to filtration .
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The essence of the invention is illustrated by drawings, which show: FIG. 1 - the proposed sludge platform in plan at the time of construction of the 1st layer of the dam (view along arrows 1-1 in Fig. 2); in fig. 2 vertical section of the site with a diagram of building up 5 layers of the dam and, accordingly, the height of the drainage wells; in fig. 3 drainage well in section. The proposed sludge platform contains a waterproof base 1, made, for example, from several layers of polyethylene film or from a layer of crumpled clay, drainage filter devices 2 of the “return filter” type and perforated drainage pipes 3, equipped with removable plugs at the ends (not shown in the figure) , water intake trays 4 located along the perimeter of the site, a pipeline 5 for supplying liquid sediment, drainage wells 6 for discharging nadil waters and an enclosing dam 7 made of layers 8, 9, 10, 11, 12 of filter material stacked on top of each other. The base of the dam is located directly on the waterproof base of platform 1. Layers of filter material 8-12 are located offset to the vertical axis of the platform, and form a container in the shape of a truncated pyramid. Dried sludge from city wastewater treatment plants is used as the dam's filter material. In the absence of sediment, for example, when commissioning new treatment facilities, sand or other similar filter material acceptable for dam construction can be temporarily used as a filter material. Drainage wells 6 are made of composite concrete base 13 and ring elements 14, 15, 16 installed on top of each other. Wells 6 and dam 7 always have the same height, increasing in parallel during the period of filling the sludge platform. The bases of the wells 6 are connected to the outlet pipeline 17. At the level of the inlet 18 of the wells 6, a “floating” water seal 20 with foam padding 21 is placed in the guides 19. The inlet 18 height is adjusted by a set of bars 22 covering its flow area, placed in grooves 23. |
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The sludge platform works as follows:
Before putting it into operation, the site is fenced with the bottom layer 8 of the dam. In this case, the drainage wells 6 also have a minimum height and consist of a concrete base 13 and one lower annular element 14, the “floating” water seal 20 is in the lower position. Liquid sediment is fed through pipeline 5 continuously. It gradually fills the entire site to the level of the top of the lower layer of the dam. In this case, the pipes of 3 drainage filter devices are blocked with plugs and there is no filtering process through them. In the volume of the sludge platform, sedimentation occurs with the separation of the liquid and solid phases, with the formation of a bottom layer of sediment, a “pond” and a crust-like layer of sediment floating on its surface. Nadil water from the “pond” is drained through the holes of 18 drainage wells 6. In this case, the water seal 20 is always in the liquid phase and prevents a floating crust-like layer of sediment from entering the wells 6. Since the height of the lower layer of the dam is significantly (2-3 times) higher than the height of the enclosing ridges of well-known sludge platforms, their capacity and filling time increase.
The duration of filling the site can last a season, a year or more. During this time, the sediment thickens. When the site is filled to top level From the bottom layer of the dam, the second layer is built up, shifting it to the central vertical axis of the site. At the same time, the height of the drainage wells 6 is increased to the level of the top of the second layer of the dam. This is achieved by installing the next ring element 15 drainage wells. Extension is carried out using construction equipment(bulldozers, excavators, etc.). This is facilitated by the pyramidal shape of the dam with a natural outer slope, which ensures the movement and lifting of equipment along a serpentine-type road.
As the site is further filled, the layer of sediment at its bottom increases and becomes compacted, the liquid phase of the “pond” moves upward, the floating hydraulic valves 20 on the drainage wells also move up along the guides 19. Nadil water is removed through the wells 6 and is discharged through the pipeline 17 outside the area. Surface and melt water flowing from the slopes of the dam during rains and snow melting are discharged into water intake trays 4. During the period of filling the site, all subsequent layers of the dam are periodically built up, and at the same time the height of the drainage wells is increased to the level of the top of the dam. The period of filling the sludge site can be 10-20 years or more.
Due to the fact that the outlet openings of the pipes of 3 drainage filter devices are closed with plugs during the entire period of filling the site, calmatization and clogging of the drainage filters during this period are excluded.
Dewatering at this first stage occurs mainly due to the process of sedimentation with the separation of liquid and solid phases and the removal of nadil waters through drainage wells.
After the end of the period of filling the sludge platform to the upper level of the last layer of the dam and draining the nadil water from the “pond”, the plugs are removed from the pipelines of 3 drainage filter devices.
The next technological holding period begins, during which further dewatering by filtration and stabilization of the sediment occurs. After opening the plugs, the filters of 2 drainage filter devices begin to work.
Filtration also occurs through the entire side surface of the dam with water being discharged into the site’s drainage system and water intake trays 4. At this stage, dehydration occurs under natural conditions and lasts several years. At the same time, the process of deeper stabilization and disinfection of the sediment continues. After curing, the sludge bed is ready for sediment unloading, which is done using mechanization. Dewatered stabilized sludge can be used for economic purposes, for example, as fertilizer for farmland, for filling low-lying areas, and for leveling work. It makes most sense to use dewatered, stabilized sludge as a filter material for dam barriers on adjacent sludge beds. At urban wastewater treatment plants, it is advisable to have at least two identical sludge beds of the proposed design, operating in different modes: filling, holding and unloading. At the same time, the sludge beds completely provide each other with filtering material for the construction of the dam.
The proposed design of the sludge platform and the method of its operation provide the following advantages compared to the prototype.
Occupied sites are reduced many times by increasing site capacity. The height of the loaded site can be 10-20 m or more.
Operating costs are reduced, including the cost of preparing and restoring the waterproof base and drainage devices, because their service life is increased many times over, and loading and unloading operations for transferring sludge from sludge sites to storage sites are eliminated.
During the entire period of filling the sludge platform with liquid sludge, optimal conditions are provided for the separation of solid and liquid phases and the introduction of the settling process.
Due to the development of the sludge platform in height, conditions are created for the pressure mode of filtration of the liquid phase through the enclosing dam, which increases the efficiency of natural dewatering.
CLAIM
1. A sludge platform containing a waterproof base, drainage filter devices, drainage wells, water intake trays and a liquid sludge supply pipeline, characterized in that it is additionally equipped with a boundary dam made of horizontal layers of filter material, and the base of the dam is placed on the waterproof base of the site, the layers are laid offset to the vertical axis and form a container in the shape of a truncated pyramid, and the drainage wells are made of composite ring elements installed on top of each other to the level of the top of the dam.
2. The site according to claim 1, characterized in that the enclosing dam is made of dewatered municipal wastewater sludge.
3. The method of operating a sludge platform according to claim 1, including filling it with liquid sediment, filtering through drainage filter devices and a dam, discharging nadil waters through drainage wells, holding and removing dehydrated sludge, characterized in that before filling the site, it is fenced with a lower layer dams, during the filling process, as sediment accumulates, the next layers of the dam and the height of the drainage wells are periodically increased, and filtering through drainage filter devices is carried out after completion of filling during the holding period.
