Underground wastewater treatment plant Crystall BIO-P

Crystall-BIO-P is meant for domestic or similar industrial wastewater biological treatment. The technology is based on the method of extended aeration, which allows to simplify plant operation and, consequently, minimize operating costs. The entire complex of units is made in underground (buried) design that allows to locate the units in any suitable place (from hydraulic point of view) and include them in any landscape design.

For maximum effect, it is recommended to discharge treated water to subsurface discharge or filtration trenches.


Specifications
Capacity
from 5 to 100 m3/day
Treatment effects
SS (Suspended Solids) - 92 - 95%
BOD 5 (Biological Oxygen Demand) - 93 - 95%
COD (Chemical Oxygen Demand) - 87 - 93%

The plant is designed for treatment of domestic wastewater from autonomous facilities.

The complex includes the units of mechanical, chemical and natural biological treatment, as well as of sludge digestion. The technological scheme considers the features of wastewater composition and inflow mode, the possible operation level of the units. They are manufactured individually according to Customer's specifications with regard to their capacity, terrain relief, hydrogeological, geological and other conditions.    

Technological scheme of the plant Crystall-BIO-P    

Taking into account high concentration of organic pollutants, hourly, daily and seasonal non-uniformity of their income, the following units are included in the technological scheme:

Septic tank is meant for mechanical wastewater treatment, densification and anaerobic digestion of generated sludge. Wastewater treatment efficiency in the septic tank is as follows:    

  • suspended solids - 70-90%
  • BOD5 - 35-50%

Sludge is removed from the septic tank by a portable pumping plant or special-purpose machinery. Frequency of sludge removal is every 6 months (twice a year), humidity of removed sludge is about 90%. Approximately 20-25% of sludge should be left in the septic tank for generation of anaerobic microorganisms in incoming sludge; it speeds up the decomposition process.

To intensify the processes of biological treatment and sludge digestion in the septic tank, the bioreactor "Klinblok", developed by the Institute of Microbiology, the National Academy of Sciences of Belarus, or its analogues can be used.

Aerotank of extended aeration (total oxidation) is meant for complete biological treatment of wastewater. Its distinctive feature is that wastewater treatment and activated sludge mineralization take place in the aeration zone simultaneously, what significantly reduces its growth. Surplus activated sludge is periodically (once every 2-4 months) pumped from the secondary clarifier into the septic tank. In the aerotank of extended aeration (here wastewater should be stored for not less than 24 hours), according to BOD5, organic pollutants are reduced up to 20-25 mg/liter, ammonia nitrogen is reduced by 30-50%.

The technological process in the aerotank is provided by aeration by means of air blowers and constant recirculation of activated sludge from the secondary clarifier. Relative air rate is 30-35 m3/m3 of wastewater.

The aerotank operates at variable concentration of activated sludge (2-6 g/liter); the average value is 3-4 g/liter. When sludge concentration increases up to 6-7 g/liter, surplus sludge is pumped to the septic tank.

For the period of possible prolonged stoppage of wastewater income (for more than 2 days), aerotank operation is transferred to the recirculation mode, at which a part of activated sludge is supplied to the septic tank. In this case, the products of sludge decomposition in the form of volatile fatty acids (VFA) that are a good substrate for life support of activated sludge biocenosis, come from the septic tank to the aerotank.

Secondary clarifier is meant for separation of activated sludge from treated water and flow formation of circulating activated sludge.

Clarified water is collected in a water collecting tray and discharged from the clarifier, and sludge in the form of circulating activated sludge is continuously pumped by a submersible pump into the aerotank. There is the possibility to supply a part of sludge to the septic tank (for surplus sludge densification).

At normal operation of the secondary clarifier, suspended solids, which concentration does not exceed 25-30 mg/liter, are discharged to subsurface discharge, filtration trenches and sand-gravel filters.

The choice of such type of units depends on their capacity, hydrological conditions of their location, terrain relief, etc.

Subsurface discharge should be used in well-filterable sandy and sandy loam soils with a low level of groundwater.

Irrigation pipes 100-150 mm in diameter are laid at a depth of 0.6-1.8 m on the underlying layer 0.3-0.5 m thick from fine gravel, crushed stone or well- sintered slag. Vent stacks 100 mm in diameter, rising to 0.5 m above the ground level, are mounted at the ends of the irrigation pipes for aeration of filtration zones.

Wastewater coming to subsurface discharge is filtered through the soil. The bulk of pollutants stay in the soil layer (0.3-0.5 m thick) adjacent to irrigation pipes. Physicochemical and biological processes that occur in this layer lead to mineralization of coming organic substances and nitrification of ammonium-nitrogen compounds. Denitrification processes (decomposition of nitrates) occur in deeper layers.

Construction of the plant Crystall-BIO-P

In order to minimize general construction works and reduce construction time, the basic units are manufactured as a complex of units of full factory readiness.

The septic tank and the aerotank Crystall Bio-P manufactured as a single cylindrical unit are determined by their capacity, concentration of wastewater pollutants and local conditions. Maximum total volume of the unit amounts to 60 m3 (diameter - 2.4 m, length - 13.5 m). Its body and all elements are made of constructional polymer materials.

The section of the aerotank is equipped with a pneumatic aeration system. Compressed air is supplied by air blowers (1 operating, 1 reserve) that are placed in a free-standing ground unit. It is equipped with a pipeline system and valves and piping for air supply, circulating sludge and activated sludge supply.

The secondary clarifier Crystall Bio-P-D(O) is a vertical cylinder tank with a conical bottom and a supply/discharge system of treated water. A submersible pump for constant sludge supply to the aerotank (a reserve pump is kept at stock) is placed at the bottom of the clarifier. Height and diameter of the clarifier are determined by the capacity of the units. The body and all elements of the clarifier are made of constructional polymer materials.

The treatment units are fully automated. Periodic maintenance is necessary for control of the surplus sludge level and its pumping.

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