Septic tank

The sump is a tank consisting of a single sealed enclosure (concrete or plastic), usually divided into two or three sections (A, B, C), a pipe for supplying the original sewage sewage water (E), and drainage of treated water (F) , blockers between sections.

SNiP 2.04.03-85, depending on the flow of wastewater emits:

• single chamber septic tanks - at a wastewater flow rate of up to 1 m³ / day;
• two-chamber - up to 10 m³ / day;
• three-chamber - over 10 m³ / day.

The first section (zone A) of the septic tank is directly connected to the inlet sewer line on the one hand, and on the other, through a blocking system (water trap) with the second section (zone B). Then through the blocker with the third section (zone C). Zone A acts as the primary septic sedimentation tank for coarse sediment. In this chamber, the primary, rough cleaning of household wastewater entering the septic tank from suspended small and large particles is naturally carried out. At the bottom of the cell, sand settles, small potato peelings, etc. (everything that can pass through the sink in the kitchen or in the bathroom). The second section of the treatment plant (zone B), the methantank, serves as an anaerobic reactor. Here, the decomposition of chemical compounds resulting from the use of various detergents, personal care products and the decomposition of organic compounds of natural origin. The third part of the treatment plant (zone C) serves as the final clarifier of domestic sewage. By final settling of suspended particles, clarified effluents reach a degree of purification of up to 65% of the initial level of contamination.

After passing the septic part of the treatment plant, the wastewater is directed to soil post-treatment. In cases where soil post-treatment cannot be performed: the groundwater level is too high (less than 0.4 m from the ground surface) or if an improved quality of wastewater treatment is required, a drip biofilter (bioseptic) is used.

SNiP 2.04.03-85 recommends taking the total estimated volume of the septic tank equal to:

• at a wastewater flow rate of up to 5 m³ / day - at least 3 times the daily inflow;
• at a flow rate of more than 5 m³ / day - at least 2.5 times.

Domestic household wastewater from a house (structure) through a sewer pipe flows by gravity to the receiving chamber of the septic tank - zone A of coarse sediment, where floating films, fats, surfactants and non-precipitated particles are retained. Non-settling substances floating on the surface of the water form a film over time. Larger or harder substances that enter household waste water and are able to settle, are screened out and accumulate at the bottom of the septic tank in the form of silt sediment. From the receiving chamber, so-called septic zone, domestic wastewater through the blocker system enters the anaerobic fermentation chamber - zone B (methantank).

For proper operation of the cleaning system in the septic tank, the vias of the blocker should be located below the level of the floating film, but above the level of incoming sludge. The construction of the structure should have a sufficiently sealed enclosure. The presence of hydraulic locks and blockers at the inlet and outlet of the methantank allows maintaining a deficiency of free oxygen in the septic tank, thereby providing an anaerobic process for cleaning domestic wastewater.

In the methane tank, in the reaction zone, facultative microorganisms primarily work, then methanogenic bacteria. The anaerobic process itself takes place in two stages:

• acid fermentation stage: carbohydrates, proteins and fats break down to a number of lower fatty acids: acetic, butyric, formic and propinic acids; carbon dioxide, hydrogen sulfide, ammonium, various alcohols and other organic compounds.
• methane fermentation stage: fatty acids, alcohols, various organic compounds formed at the acid fermentation stage decompose to hydrogen, carbon dioxide and methane.

After purification in the methane tank, domestic wastewater flows through the bypass into the third section of the septic tank - into zone C, where organic compounds from anaerobic processes (processes of processing organic and inorganic waste by bacteria into sludge) go from a dissolved state to a suspended one, and then precipitate. Then, from the zone C ', domestic wastewater enters the filtering soil layers for subsequent, final post-treatment.

The most important factors affecting the activity of microorganisms are: the presence of organic matter in household waste; domestic waste water temperature (optimally 10–35 ° С); access to the oxygen installation; runoff acidity; lack of toxic substances. The septic tank carries out the purification of domestic wastewater both with the use of bioenzymes and without the use of these drugs. The use of bioenzymes can sufficiently accelerate the decay of organic substances and increase the quality of wastewater treatment.

Mandatory when using a septic tank as an element of a sewage treatment plant. The design of the soil treatment facility is determined by the working draft and depends on the type of soil, the conditions for the discharge of domestic wastewater (the required quality of treatment), the level of groundwater, the climate zone, the topography, and the site plan. The location of the treatment plant is determined at the design stage with an individual reference in plan and height to the building, subject to the following information and characteristics of the site: the hydrogeological situation at the location of the proposed treatment plant, the filtering ability of the soil, the presence of karst rocks, the protection of the underground aquifer, groundwater standing height.

In areas where the discharge of clarified wastewater without additional treatment is prohibited by sanitary standards, the installation of a filtration field is required. The filtration field is a pipeline made of drainage pipes laid over a layer of crushed stone in the thickness of the sandy base. Water is filtered through sand and enters the layers of filtering crushed stone, and then absorbed into the soil. There is also the use of such post-treatment systems as: a filter well, a filtering trench, a filter using activated materials, as well as ultraviolet disinfection lamps.

With soil post-treatment, the following structures can be used:

• filtering well (FC);
• absorbent trench (platform) (VT);
• sand and gravel filter or filtering trench (FT);
• underground filtering field (PPF).

They are arranged on filtering soils - sandy loam, sandy soils (FC, PPF) and non-filtering (FT) soils with a groundwater level of more than 1 m lower than the base of the well (FC), irrigation pipe tray (PPF) or drainage pipe tray (FT) ) The structure is equipped with a ventilation pipe D = 100 mm, which is discharged above the soil surface above the expected level of snow cover (usually 0.7 m). Ventilation is placed on each irrigation (at the end of the line) and drainage (at the beginning) pipe.

The dimensions of the well and the length of the sprinklers are determined by the permissible hydraulic load - water flow per 1 m² of filtered surface (bottom and walls of the FC) or 1 m of the length of the irrigation pipe (PPF, FT).

The drainage device, depending on the available soil characteristics on the site, is divided into two main types of execution: filtering soil (sandy loam, sand, peat) or non-filtering soil (clay).

Filter Well

On the filtering soil a filter well is organized, the filtration area for sandy loam is 3 m², for sand - 1.5 m², (calculated per person living in the house). The larger the filtration area, the longer the life of the well will be. For the system to work correctly, groundwater must lie below the level of crushed stone laying by 500 mm, and it is necessary that the base of the well be higher than the groundwater level by more than 1 m.

The filter well is installed in sand and sandy loam from monolithic reinforced concrete, or prefabricated reinforced concrete structures or from brick. The bottom of the walls is poured with crushed stone, inside the well is filled with a layer of crushed stone up to 1 m high. The efficiency of treatment of domestic wastewater according to the indicators of suspended solids can reach 100%.

Absorbent Trench (Playground)

Where the discharge of domestic clarified effluents after passing through a septic tank without the installation of a post-treatment system according to construction and sanitary standards is not allowed, an additional installation of an absorbent trench or site is possible. An absorbent pad is a pipe made of perforated material. Water passing through it enters the soil, then, passing through a layer of porous filtering soil, it contributes to the ideal development of natural bacteria.

The absorbent trench is used in sand and sandy loams and is a system of perforated, irrigation pipes made at a depth of 0.9 m and more than 1 m above the groundwater level. An irrigation system is a system of perforated pipe laid with a slope of 0.001-0.003. To ensure rigidity in the base of the pipes, under them it is necessary to lay a bed of crushed stone, broken brick, gravel or slag of a fine fraction (20-40 mm). At the end of the irrigation system, it is necessary to carry out a ventilation riser (air flow) with a total length of at least 0.7 m. The effect of possible cleaning according to the indicators of suspended solids in the filtration fields is up to 98%.

Filter Trench

The filtering trench is performed in soils with low filtering characteristics (loams and clays), forming artificially formed soil layers, in the layers of which drainage and irrigation networks are made. It is recommended to place these trenches close to trenches, inclined recesses, where purified household wastewater flows by gravity, or arrange for pumping incoming clarified wastewater through a water well. The space between the drainage and irrigation network is filled with rubble and sand. The difference between a sand and gravel filter from a filtering trench is that drainage and irrigation pipes placed in the pit are made in parallel lines.

The field of underground filtration filtering trench placed on the slope of the terrain. The length of one line of the irrigation and drainage network is recommended to take no more than 12 m; bias in the direction of movement of water 0,01. The configuration in the plan (beam, linear, parallel) depends on the general layout and topography of the site, its size, existing and planned landscaping and landscaping. With the number of lines of the irrigation network, more than one arrange a distribution well, which ensures uniform distribution of wastewater along the lines. Parallel trenches are made separate (usually PPF in sandy loamy soil) or combine two or three lines of irrigation pipes in one wide trench, observing the distance between the axes. Under the irrigation pipes, in a wide trench, one or two drainage pipes are laid in the gap. Then the filtered water flows into drainage pipes and enters a ditch or ravine.

Post-filter

With special requirements for the quality of clarified domestic wastewater, additional biological treatment is used in the biofilter tank. Filtration materials: granite crushed stone , gravel , sand , anthracite , granulated blast furnace slag , polymers, etc. The use of polymer filters that have a good three-dimensional distribution and a large free volume of up to 90% (crushed stone is only 25%) allows you to clean drains better quality.

Septic tank is a sealed container. The material can be used in a variety of ways: composite fiberglass, polyethylene, polypropylene, reinforced concrete, however, you need to choose the material, considering all its technical characteristics: tightness (reinforced concrete septic tanks have insufficient tightness, so that this disadvantage does not cause inconvenience, use waterproofing with internal and external parties), susceptibility to corrosion (metal and reinforced concrete tanks have this drawback), mechanical resistance to soil pressure, or strength ( polypropylene containers have a lack of strength, despite the stiffening ribs on the body). It should also be noted the advantage of sectional septic tanks over ordinary (hollow): to create a full-scale treatment plant for ordinary tanks, a larger amount will be required. The most common are septic tanks made of reinforced concrete structures, as they are considered durable and reliable.

• SP 32.13330.2012 “Updated version of SNiP 2.04.03-85“ Sewerage. External networks and constructions ""