Sewage Treatment Plant Assembly Instructions
After unpacking the set you should carry out a dry assembly in order to check and plan all the elements according to the executive design. It is very important to maintain the distance in compliance with the binding regulations. The maximum depth of the septic tank foundation counting from the bottom level equals 2,20m while the maximum thickness of backfilling over the tank equals 1m.
The bottom of the excavation is filled with a 10 -15cm sand bed. Next, you position the tank in such a way as to make it stabile on the horizontal level (the verification is done by using the level liner). You fill the tank with water up to 2/3 of the total capacity, checking its tightness. Subsequently you backfill the excavation evenly around the settling tank with 30 cm layers, gradually compacting the soil.
In the case of loose soils, the lateral backfilling should be executed of the virgin soil, whereas in cohesive soils, it should be done with medium or coarse sand without pebbles or sharp-edged elements. In fenlands and with the high water table, the settling tank should be protected against water uplift pressure during the periodic removal of sediments. For this purpose it is recommended that the settling tank be positioned on a 10-15cm sand bed executed on a concrete slab placed at the bottom of the excavations. The settling tank is fastened to the concrete slab with iron holders by means of anchoring belts.
In all the assembly works, one should take into account soil settling.
In the event of a deeper founding of the settling tank and the distribution chamber, in the inspection manholes one should apply structural extending PP pipes with the external diameter of 400mm. Each manhole is covered with a cover screwed to the body with two bolts.
Assembly of the service lines
The pipes of 110mm or 160mm in sections are connected at the gradient from 1,5% to 2,5%. If the system is to be used more rarely, we apply a higher gradient. The depth of foundation of the drain at the inlet to the settling tank should equal from 0,30 to 0,40m. In order to prevent the cooling of the wastes, it is recommended that the septic tank should be installed as close as possible to the place where the wastes flow our from the building, i.e. from 3 to 8m. With a distance longer than the recommended one, the pipe should be insulated thermally and the gradient should be increased to 3%-4%.
The settling tank should be connected to the plumb-line finished with the ventilation pipe or a separate ventilation duct of the diameter min. 110 mm protruding above the roof.
Distribution chamber
is connected with the sceptic tank with a sewer of 110mm in diameter. The tightness of the connection with the duct is ensured with gaskets placed in the openings of the chamber. The height difference between the axis of the inlet opening to the chamber and its outlet is 10cm.
The chamber is the beginning of the leach field and is designed for even distribution of the pre-treated household effluent to particular leach field strings. Its level of foundation is conditioned by the ordinate of the effluent outlet from the settling tank. The depth of the foundation equals usually about 60cm. The chamber is positioned on a 10 cm bed too. While backfilling and covering the chamber you apply the same rules as for the septic tank. An important element is the assembly of a gate in the chamber to adjust the flow to particular manifold headers for the effluent. Their assembly will allow you later to check the flow. When the sewage treatment plant is in operation, before rinsing of a duct it will be possible to close one of the leach lines and direct its flow to another line.
Assembly of manifold headers
Ducts of 2,5 m in length, green colour, are positioned at a gradient from 0,5% to 1% on the compacted sand bed and backfilled with sand, fine gravel or keramzyt. After connecting the manifold headers with the chamber, the distance between the leach lines equals about 4,5 m. The distance may be reduced to min. 2 m by respective shortening of manifold headers.
Assembly of the leach field
Pipes of 2,5 m in length, blue colour, are positioned at a gradient from 0,5% to 1% on a 10-15 cm layer of rinsed gravel of 12-24/16-32 mm in granulation or a substitute gravel of 20-40 mm in granulation. It is admissible to use a different filtering material of a similar granulation; however, it must be rinsed – it may not contain dust fractions and it must be resistant to wastes. The pipes are connected with one another by means of pipe connectors, whereas with manifold headers by means of elastic elbows. It needs to be remembered that the pipes have openings through which the treated effluent penetrates to soil. We place them with the openings facing down.
The width of the gravel layer should equal: in soils of very good permeability 0,5 m, in soils of medium permeability 0,6 m, while in soils of little permeability 0,8 m (the smaller permeability, the wider the layer).
The best depth to position the drainage is 0,5 to 0, 60 m, because the processes taking place in soil are aerobic processes. Hence, the best conditions for the development of the biological film are to the maximum depth of 1m. When the depth is increased, there is a danger of flooding with underground waters and a threat to the treatment quality due to the deteriorated aerobic conditions.
On the other hand, a shallower depth does not allow the maintenance of a sufficient layer of cultivable soil for which the required minimum equals 20cm. Around the drainage at the distance of 3,0 m one may not plant trees or bushes with a developed root system.
The manifold headers are finished with the vertically led ventilation pipe protruding min. 0,5 m above the land surface, connected by means of an arch with leach pipes. On top of the ventilation pipe, ventilation exhausts are mounted. The tightness of the connections of the treatment plant is tested by letting the water flow into it and by observing the way it distributes to particular leach strings.
The leach pipes are backfilled with a filtration material with a min. 5 cm layer over the top of the pipe. The layer is covered with geotextile, which is to protect the drainage against the pollution of the filter bed. The geotextile lets water pass, and holds small mineral fractions of the sand and other fines washed out of the virgin soil.
The treatment plant is backfilled, the upper layer of the settling tank is backfilled with crop soil and after the area levelling grass is seeded.