25-100 m3/day INSTALLATIONS
Combined installations (patents 1020379, 1214608, 1533239, 1761688, 2040482, 2085515) are designed for biochemical purification of the sewage produced by small settlements and small enterprises and characterized by impurity concentration BOD max. 1,000 mg/L and suspended matters amount max. 400 mg/L.
The primary sewage is first discharged to the tangencial sand trap with dirt catching gauze 1, and after that to mixing chamber 2. As the water level in 2 reaches the max. mark, automatically switches on pump 3 which is simultaneously pumping the sewage through the siphon piping from 2 and (through the suction pipe-line) the sludge mixture from settling aeration tank 4. Further on the sewage and sludge mixture is discharged to biofilter 5 for processing. The biofilter feed is made of ceramic ball-shaped elements having evenly placed recesses whose axes meet in the ball centre. Irrespective of the manner the elements are laid, some part of the recesses will be filled with the sludge mixture. A longer contact between the sewage and the immobilized microflora and availability of the active sludge help to reach an 80-85% purification effect in the biological filter. A 98% purification level may be reached with the help of the active sludge in the settling aerotank. Oxygen is driven to the aerotank due to the air oxygen dissolution during the charge irrigation and as a result of the air involvement during the liquid discharge to air-spripping towers 6. Oxygen is dissolved in the towers during the air bubble floating too. The aerotank contents is mixed thanks to definite columns placement inside the reservoir. As the sewage flow stops and water level in 2 gets down to the min. mark, the pump is switched off. However the sludge mixture from settling aerotank 4 starts to be driven to chamber 2 through the siphon piping. At night time and in a prearranged time period (40 to 60 minutes) the chamber is periodically filled with sludge mixture and the pump is again switched on. The pump switch-off periods are regulated with latch 6. While the pump is not working as a result of a long emergency shutdown, the humid regime inside the biofilter feed is maintained due to a large number of vessels filled with fluid. This permits to preserve the microflora vital functions even in case of 2-day long shutdowns. The installations provide organic impurity concentration reduction from BOD 100-1,000 mg/L to 7-20 mg/L, suspended matters amount from 100-400 mg/L to 3-15 mg/L. The total pump working time makes 16-20 hours a day, the power consumption equals 0.2-0.3 kW/h/kgBOD, and the the labour expenditure makes 2-3 man-hours/day. 25-50 m3/day biological purification stations have been designed to the order of Ministry of Agriculture of the Russian Federation (see the pictures).
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