LOCAL WATER TREATMENT FACILITIES FOR UP TO 32 POPULATION EQUIVALENTS
Local waste water treatment plants ensure high efficiency of treatment, at an acceptable cost and insignificant operation cost. These are applicable in areas where central sewerage system is missing and are designed to service single-family houses and small public sites.
The main facility is a septic vessel with integrated filter and a filter-drain system for final treatment. During their passage through the septic vessel the waste water is subjected to the following technological processes: deposition of the easily sinking fractions (sedimentation); gravity flotation of floating pollutants, mainly of kitchen origin; oxygen sludge stabilisation (psichrophilic fermentation) and their biological purification.
The efficiency of treatment in the local treatment plants becomes clear upon comparison of the parameters, characterising the pollution of the waste water at the entry and exit points of the septic vessel.
TECHNO-PLAST manufactures two types of septic tanks: 2000 litres, up to 4 residents and 3200 litres, 6-8 residents
The septic tanks are complete with PVC elements, filter manhole, filter vessel, tank cover, distribution well with cover and levelling ring.
Up to 3 containers can be connected in series, aiming at servicing more users.
The passing water retention time in the septic vessel is from 2 to 4 hours, and the time for fermentation of the sludge – not less than 180 days. The maximum admissible filling up of the vessel with sludge is up to 50% of its capacity, and the emptying frequency of the vessel should be once every 2-3 years. Bacterial activators (through the toilets) are constantly added to the septic vessel to assist the natural biological processes, to eliminate the malodours, to destroy the pathogenic bacteria and to assist in decomposition of fats and liquefying the solid deposits.
The waste waters coming out of a correctly selected and run septic vessel are clean and their quality permits their further treatment in the soil, within the filter-drainage network.
OPERATION OF THE SYSTEM
The domestic waste waters are supplied into the septic vessel along the sewer pipe. Inside the vessel, an oxygen-free bacterial processing is going on. The end product is a decontaminated filtrated liquid, which overflows towards the underground drainage network and is soaked away into the soil, irrigating and fertilising it. The drainage network is constructed of perforated PVC pipes, which are installed within drainage branches, distanced at ~2 m between each other. In the beginning of the drainage network there is a distribution manhole made of polyethylene with capacity ~80 l, to which are connected the main pipes (PVC ø110mm). The drainage pipes are installed into trenches with depth dependent on the specifics of the topology and the level of the underground waters. Around 20 cm of sand bed is laid on the bottom of the trench, then around 30 cm of gravel and upon it are installed the pre-drilled PVC pipes. These are covered by about 10 cm of gravel, on which a geotextile cloth is laid, to preserve the drainage system against contamination. On top of the cloth the trench is filled with soil until reaching the terrain level, and finally the area is grassed.
GENERIC RULES FOR THE SYSTEM CONSTRUCTION
The building, which will be served by the treatment plant, must have vent pipes, taken up on the roof, using chimney unit.
When installing drainage system, we should take into account the level of the underground waters and the soil permeability. The system’s installation must be at depth of not more than 2 m.
The drainage system must have a slope of 1,5% (1,5 cm per 1 m length).
The drainage branches must end into vent stacks.