Fig.2.37. Scheme of septics location:

a,б,в – single-chamber; г,е – double-chamber; д – triple-chamber: 1-supplying of sewer water; 2-ventilation pipe; 3-plate of the bottom; 4-orifice; 5-outtaking of sewer water; 6-walls of septic from prefabricated reinforced concrete rings; 7,8,10,12-plate of bottom; 9-separating well; 11-dosaging chamber.

Double raw settling tanks also serve for clearing up of sewer water and sediment fermentation that already fell out. Double raw settling tank has at the top part the flowing trays, and in the lower one - septic chamber (fig.2.31). Time of sediment fermentation in double row settling tanks – 2-6 months. By this period 40-50% of organic substances are fermented.

Methane tank is a round or rectangular by the plan reservoir, in which the sediment from the settling tanks or surplus active mule is fermented. The process of organic substance disintegration in methane tank goes like in septic chamber of double row settling tank, but with more intensity due to heating and mixing.

Methane fermentation of sewer water can be in mesofilic conditions, if the temperature of fermented mass doesn’t exceed 35^oC, or in hemophilic conditions, if the temperature of fermented sediment is supported in the range 45-65^oC. Each of these types of fermentation is provided by the activity of correspondent anaerobic bacteria – methofilic and hemophilic. For methofilic fermentation the optimal temperature is 33^oC, for thermophilic -53^oC.

In methane tanks the degree of organic substance fermentation accounts in average 40%, that is enough. Sediment during this looses rotten smell, achieves uniform porous structure, in a good way gives the moisture during the drying. Fermented sediment contains nitrogen, phosphorus, calium, which are well digested by plants and that’s why the sediment is used in agriculture as fertilizer.

Fig.2.38. Scheme of methane tank

During fermentation in methane tanks the gas is emitted. This gas is removed to gas-holders for storage and than burn in boiler installations. The most rational is the exploitation of methane tanks by straight-flowing scheme at which the loading and unloading of sediment

is conducted uninterruptedly (fig.2.38).

In some cases for treatment of sediment are proposed the aerobic stabilizators or combined technologies that contain anaerobic and aerobic fermentation.

It is sufficient to mark that future usage of damp sediment is low-efficient and that’s why it’s dried (dehydrated). The most often for dehydration of sediment are used mule sites on the natural of artificial base (fig.2.39). Sediment that rotted through in methane tank has humidity in average 94-97%. At mule sites it dries to the humidity 75-80%. During this the volume of sediment considerably decreases, and it is become able to transport it.

Fig.2.39.Mule sites:

1-bounding wall; 2-tray for mule supply; 3-pneumatic panels; 4-drenaige; 5-collecting well; 6-separating partitions; 7-working cards.

Sizes of mule sites are determined depending on amount of sediment, its characteristic (fermented or raw) and climatic conditions. In winter period the sediment freezes. Mule water that was separated from sediment is pumped onto the water purifying structures.

For mechanical collection, loading and transportation of dried sediment at mule sites are protected roads for cars and means of mechanization.

At big stations instead of drying of sediment at mule sites are used mechanical drying of sediment in vacuum-filters, centrifuges, filter-presses or thermal drying. Vacuum filter (fig.2.40) – are the horizontal cylindrical drum covered by filtrating cloth.

Drum is divided into the sectors, partially deepened into launder with sediment, is slowly rotating. In sectors that are deepened into sediment, by vacuum-pump the vacuum is created. Sediments stick to the cloth and water percolates inside the drum and is removed. Sediment separates from the cloth by knife. Dehydrated sediment has the humidity 78-80%.

In continuously acting horizontal centrifuges with screw unloading of dehydrated sediment it I possible to achieve the humidity 50-80%.

Thermal drying and burning of sediment need considerable expends and that’s why they are used rarely.

Fig.2.40. Scheme of vacuum-filter: 1-roller, that rotates; 2-knife; 3-drum; 4-sediment.	Fig.2.41. Scheme of centrifuge of НОГШ type: 1-supply of sediment; 2-removing of fugate; 3-bunker for fugate; 4-holles of sediment serving to the rotor; 5-bunker for unloading of cake; 6-rotor; 7-screw; 8-holles for unloading of cake.