Domestic waste water treatment plants
The treatment of the waste water takes place in two phases : the physical-chemical one – for the separation of the solid matters in suspension and for the diminishment of the excessive phosphorus – and the biological one – for the elimination of the dissolved organic substances, of nitrogen and of phosphorus. Optionally, the purged water may be disinfected by ozone or chlorine.
Subject to the quality of the water upon entrance and to the efficiency of the mechanical phase, the biological purification is designed and executed according to different flows.
I. TYPES OF BIOLOGICAL TREATMENT FLOWS
a) Compact treatment plants with a biological stage
Compact waste water treatment plants with a biological stage, with flow rates ranging between 10 and 400 m3/day. The plant provides the advanced treatment of the waste waters charged according to NTPA002. According to the flow rate, it can have one or several treatment modules. The plant can be placed in the close vicinity of the waste water source and it is operable even at low flow rates. The production of excessive sludge is relatively low and dehydration takes place in filters endowed with big bags.
The biological step operates according to the following technological flow :
b) compact treatment plants, with two successive biological purification stages, for waste waters highly charged with nitrogen and phosphorus
Compact waste water treatment plants, with flow rates ranging between 10 and 400 m3/day
The plant provides the advanced treatment of the waste waters with charges far exceeding the values of the relevant standards, notably in case of the ammonia nitrogen indicator. The treatment flow includes : an anoxic tank, two successive aerobic tanks and one secondary decanter. In the aerobic tanks there are two types of biological purification : high charge aeration in the firs tank and full mixture in the second tank. This takes place by an external recirculation of the active sludge from the secondary decanter into each aerobic tank, in various proportions, so that the concentration of the sludge in the tank corresponds to the kind of purification selected. In the former tank there is a dominant reduction of the organic carbon and less for the nitrogen, whereas in the latter tank there will mainly be the completion of the nitrification process. The reduction of the nitrogen is made by the internal recirculation from the last aerobic tank into the anoxic tank.
The purification efficiency is higher than for the plants with one aerobic stage.
II. CONSTRUCTIVE VARIANTS
According to the beneficiary’s request and to the locating conditions, the waste water treatment plants built by our company can be :
- compact, underground or aboveground, in a concrete construction ;
- modular, from aboveground composite materials, with rectangular tanks ;
- modular, from aboveground composite materials, with vertical cylindrical tanks.
Fig. 1 Waste water treatment plant
Fig.2. Treatment module with rectangular tanks
1 – Guiding groove ; 2 – Primary decanter ; 3 – Sludge thickener ; 4 – Sludge pump ; 5 – Anoxic tank ; 6 – Mixer ; 7 – Aerobic biological tank ; 8 – Aeration network ; 9 – Secondary decanter ; 10 – Discharge joint.
Fig. 3. Treatment module with vertical cylindrical tanks
1. Vertical primary decanter, 2. Anoxic biological stage, 3. Aerobic biological stage, 4. Vertical secondary decanter, 5. Sludge dehydration plant, 6. Access ladder, 7. Sludge thickener, 8. Module container