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Biological treatment is applied for treatment of most industrial and domestic waste water before discharging it into waters.

Biological methods of waste water treatment can be divided into two types (according to types of microorganisms taking part in treatment of sewage contaminants):

  1. Aerobic biological treatment (microorganisms need oxygen to maintain their vital functions).
  2. Sewage treatment with anaerobic microorganisms (that can exist without oxygen).

Anaerobic process is applied for treatment of industrial waste water with COD higher than 1200.0 mg/l. Treatment efficiency by COD is 70.0 – 80.0% depending on waste water origin.


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Figure. Process flow diagram of anaerobic waste water treatment

A special feature of the microbiological process of anaerobic degradation of organic substances is production of biogas that can be used in-house as an energy source. This biogas consists of: methane (60.0 – 90.0 % CH4) and carbonic acid (10.0 – 40.0 % CO2).

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Depending on raw waste water quality, two types of anaerobic bioreactors can be used: UASB-reactor and EGSB-reactor.

Aerobic process is applied for treatment of domestic and industrial waste water (after local treatment) with COD not higher than 1200.0 mg/l.

Depending on waste water amount, it is possible to apply sequential-batch reactors (SBR) or classical aeration systems (aerotank-final settling tank), as well as modern MBR systems.

Sequential-batch reactors are the most effective (from an economic point of view) for waste treatment plants of 1000 m3/day capacity. A SBR can consist of one or several cyclic operation tanks:

  • phase A – waste water is supplied to the tank and is aerated (accumulation phase)
  • phase B – aerobic treatment phase. Waste water supply stops
  • phase C – aeration stops. Mixed liquor settles. At the same time, clarified waste water is disposed for further treatment, and surplus activated sludge is pumped out and supplied for mechanical dewatering.


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Figure. Process flow diagram of waste water treatment in SBR

Classical system of aerobic waste water treatment (aerotank-final settling tank):

  • Phase A – anaerobic zone (waste water mixing zone)
  • Phase B – aerobic zone (aeration zone)
  • Phase C – settling (mixed liquor gravity separation)


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Figure. Waste water treatment classical flow diagram (phase A is used when nitrogen amount must be reduced)

Membrane bioreactor (MBR) is applied for ultrafine waste water treatment with no need of advanced treatment and disinfection. The main difference of MBR from traditional systems of biological treatment in aerotanks is availability of a membrane module used for separation of mixed liquor. At the same time, mixed liquor separation is carried out automatically at molecular level by means of ultrafiltration membranes.

Membrane bioreactors of ICB Group can be designed in “external” version or with submersible modules. Selection of one or another installation method of membrane modules depends on specific tasks.

  • Phase A – anaerobic zone (waste water mixing zone)
  • Phase B – aerobic zone (aeration zone)
  • Phase C – ultrafine mechanical mixed liquor separation

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Figure. Process flow diagram of waste water treatment in MBR (with "external" version of membrane modules)



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Figure. Process flow diagram of waste water treatment in MBR (with submersible membrane modules)

 

Advantages of MBR application

1. Reaching of high efficiency indicators of waste water treatment:

  • COD: more than 98%;
  • Suspended material: less than 1.0 mg/l;
  • Ammonium nitrogen: more than 98%;
  • Removal of heavy metals: up to 80.0%;
  • Removal of bacteria: more than 99.999%;
  • Removal of viruses: more than 99.9%.

2. Compactness as it enables to:

  • refuse from mixed liquor gravity separation method which makes it possible to increase activated sludge concentration in the bioreactor to 10-20 g/l (in a classical aerotank up to 3.0 g/l) and to reduce the aerotank volume.
  • get rid of the necessity of advanced treatment and disinfection.

3. Possibility to treat highly concentrated waste water.

4. High concentrations of activated sludge enables to operate the bioreactor at low loads which provides an oxidizing ability reserve. Prevalence of a slow-growing microflora enables to significantly reduce the increase of activated sludge and therefore the required equipment capacity for dewatering of surplus activated sludge.

5. The size of activated sludge flocks is 5-10 times smaller than in widespread aerotank constructions.  This activated sludge dispersion results in the increase of contact area of microorganisms with waste water which improves the efficiency of sorption of inert substances, heavy metals and microcontaminants by the activated sludge.

6. Due to the fact that the membranes’ pores are larger than microorganisms’ cells, in particular in bacteria, partial water disinfection takes place in MBR. Bacteria removal efficiency is 99.999%, and viruses – 99.9%. Water purified in MBR can be immediately used for non-potable purposes.

7. As necessary, the membrane module can be designed inside a container which will reduce capital construction costs.

For industrial waste water treatment (with a high COD and low fat and suspended material content) so that is reaches the norms of waters for fishing, anaerobic-aerobic treatment is the most efficient method. Through anaerobic-aerobic waste water treatment, the treatment efficiency by COD reaches 99.5%. The advantage of this method is that a much smaller amount of activated sludge is produced which reduces costs for its utilization significantly.


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Aerobic fermentation is applied for biological treatment of waste water with a high COD and is an alternative solution for treatment of treatment by-products (fat wastes, sediment).

Industrial waste with a high level of fat (1g of fat = 3 g of COD) causes serious inconvenience in operation of treatment plants – clogging, foaming, odour, low settlement effect, low sediment dehydration, etc.

Flotation is a traditional method of fat removal from waste water through which flotosludge, flotofoam and sediment are produced. To reduce the amount of sediment (by about 50%), ICB Group specialists apply aerobic fermentation.

Depending on the amount of sediment, we offer two types of aerobic bioreactors made of composite materials or stainless steel and reinforced concrete.


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ADVANTAGES:

1. Compactness (reactors of composite material fit for small areas and building structures).  
2. Energy usage reducing (energy usage reduces by 3 - 4 times during treatment of fat wastes)
3. Foaming total control (foam is absorbed by a water cascade)
4. High degree of treatment (COD > 80 %, fats >90 %)
5. Clogging exclusion (a wide pass, absence of membrane air diffusers)
6. Combined treatment of fat wastes and sewage
7. Possibility to move the reactor (reactors are made of composite materials or stainless steel)
8. Reduction of costs for equipment upgrade (1 gear reducer, absence of membrane air diffusers, etc.)
9. Simple maintenance (necessity of repair can arise only for a motor rotor; safe service bridge, simple lifting device)
10. No odours (odour absorption and inflow of offensive odour take place inside the reactor)
11. Range of standardized packages (reduction of costs for design, wide range of installations)
12. Numerous customers (more than 120 reactors installed in Europe and all over the world).

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