1- Activated sludge wastewater treatment package with extensive aeration (EAAS)
Extended Aeration is the most common activated sludge treatment method in the world, which is widely used for the treatment of sewage and effluents in small communities. In this method, wastewater is aerated for 18 to 30 hours, which reduces its organic pollution load.
Because the masses of bacteria (which act as our workers in the matter of purification) are in contact with oxygen for a relatively long time, as a result, very little and digested biomass is produced, which is called excretory sludge. Therefore, in this method, sludge digestion facilities are completely removed. It is worth mentioning that the purification efficiency of this method is between 85 and 95%
2- Sewage treatment package using upward anaerobic sludge blanket method (UASB)
UASB anaerobic treatment system
The UASB anaerobic wastewater treatment system was formed in the late 1970s in the Netherlands and is considered a development in anaerobic wastewater treatment. One of the most important advantages of this system is the extraction of methane gas from the reactor, as well as the ability to purify wastewater with a high pollution load. The efficiency of this system is between 65 and 75%.
This system is usually used in the process of treating industrial wastewater with a very high organic load, usually wastewaters with an organic load above 2000 mg/liter are used in the UASB process to break down the organic load and break down hard degradable materials.
3- Rotating biological discs reactor (RBC)
Rotating biological contactor
It was made in Germany in the 1960s and was used in many refineries in a short period of time. RBC consists of several parallel plates (discs) that are connected to the motor by means of a shaft. The basis of this method is the “attached growth process” which may be operated aerobically or anaerobically. The design of RBCs is based on the organic load factor, and it is not possible to comment on the initial cost, but the operating cost is higher than other conventional systems.
Brief description of the process
The raw sewage first enters the primary sedimentation pond and then it is pumped into the reactor. Here, according to the type of system (either aerobic or anaerobic), we give the sewage a residence time so that the attached growth operation is carried out and the sewage is purified by the existing bacteria.
After the wastewater treatment operation, it is directed to the secondary sedimentation pond, and the purpose of this unit is to separate the excess sludge from the treated wastewater, this sludge is directed by pumps to the sludge digestion units.
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4- Biological membrane reactor (MBR)
This method is a combination of filtration and attached growth operations, the history of this method goes back to the 60s and simultaneously with the use of microfiltration and ultrafiltration on an industrial scale. This process is actually a type of activated sludge process where biological decomposition is carried out in a suspended growth state where a membrane system is used.
In fact, the basis of this method is based on activated sludge, but in addition to suspended growth, it uses attached growth as well as filtration operation, which removes the secondary sedimentation units and the disinfection unit. The efficiency of removing the pollution load in this method is between 90 and 98%.
Brief description of the process
After the wastewater enters the reactor, it is aerated by the diffusers installed in the floor, and the wastewater treatment is performed by bacteria. Due to the presence of membranes, the sedimentation operation changes from gravity mode to membrane mode, and filtration and disinfection operations are also performed at the same time.
The wastewater is sucked by the vacuum pump from inside the membranes and the biological mass remains in the reactor, which increases the amount of MLSS in the aeration pond, and as a result, the organic matter removal operation is performed with higher efficiency.
Sequencing Batch Reactor
It performs the purification process in successive tanks or reactors. Normally, this method consists of 5 tanks, but according to the conditions, it can be made from 2 tanks, one of which is for the sewage inlet and the other for the outlet, to its completed type, which has 6 tanks.
5-sequential batch reactor (SBR)
Brief description of the process
As you can see in the figure, in the conventional SBR system, the first tank is used to collect raw sewage, in the second tank, aeration is performed on the surface or deep, so that unstable organic materials are converted into stable minerals, and in the next tank, into minerals. (sludge) we give it time to settle and then some of the treated wastewater is transferred to the disinfection unit and some of the settled sludge is transferred to the sludge concentration units
In this way, the system has practically gone through a complete cycle and is ready to enter the raw sewage to start the process again. The important point and the main difference between this cycle and the first cycle is the amount of active biological mass in the reservoirs, which is the return sludge in The activated sludge system is considered, which makes the treatment operation with higher efficiency or the number of bacteria (more workers) to be done.
According to the instructions of Iran’s Environmental Organization, it is forbidden to dispose of any sewage and effluent into the environment without treatment.
Considering the introduction of different processes for wastewater treatment, it is worth mentioning that aerobic methods with more production sludge and the need for units to stabilize sludge have higher initial and operating costs than anaerobic systems, but they have higher treatment efficiency (85 to 95 percent). That is why we are required to use these systems in order to reach the output standard.
But anaerobic systems are more economical in terms of the proposed costs and even in some cases it is possible to extract methane gas from reactors, and this is the reason why it is very difficult to treat industrial wastewater without using anaerobic systems.
In general, in determining the type of process used, several factors such as
The amount of available space
The amount of capital required for the project
Type of incoming sewage
Expected quality for output