RBC or Rotating Biological Contactor is a liquid waste treatment process using a method in which this wastewater treatment unit rotates with a center on an axis or axle which is driven by a motor drive system and/or air blowing (air drive system) from a diffuser immersed in wastewater. , under media. Made of plastic, the media for attachment of microbes is installed in such a way that there is the widest possible contact with waste water and oxygen that occurs alternately. Where the method involves contact with biological elements in rotation or rotation.
RBC is like a collection of discs where on the surface there is a disk media as a place for microorganisms to eat the organic matter content in the waste, it is cultivated that the disk media can be provided as widely as possible so that microorganisms can easily take pollutants in the flowing waste. The RBC operating system uses microorganisms to eat organic matter. Microorganisms need food and O2 to survive. So that the RBC is set like a spinning wheel so that when it is below the microorganism can take food while it can process it by taking oxygen first when it is above. However, it should also be noted that if RBC has been used for a long time on the surface of the disk media, large piles of microorganisms will form due to the growth of MO (microorganisms). if this MO continues to pile up, then the MO in the lowest pile that lives is only an aerobic MO because it is covered by the MO above it. so sometimes it forms like a crust.
RBC Working Principles
The working principle of wastewater treatment with RBC is that wastewater containing organic pollutants is contacted with a layer of micro-organisms (microbial film) attached to the surface of the media in a reactor. The media where the biological film is attached is in the form of a disk (disk) made of lightweight polymer or plastic and arranged in a row on an axis to form a module or package, then the module is rotated slowly in a state partially immersed in flowing wastewater. continuously into the reactor.
In this way micro-organisms such as bacteria, algae, protozoa, fungi, and others grow attached to the surface of the rotating medium forming a layer consisting of micro-organisms called biofilm (biological layer). Micro-organisms will decompose or take organic compounds in water and take oxygen dissolved in water or from the air for their metabolic processes, so that the content of organic compounds in wastewater is reduced.
When the biofilm attached to the medium in the form of a thin disc is immersed in wastewater, micro-organisms absorb organic compounds present in the wastewater flowing on the surface of the biofilm, and when the biofilm is above the water surface, the micro-organisms absorb oxygen from the surface of the biofilm. air or oxygen dissolved in water to decompose organic compounds. The energy resulting from the decomposition of organic compounds is used by micro-organisms for the process of reproduction or metabolism.
Compounds resulting from the metabolic processes of these micro-organisms will come out of the biofilm and be carried away by the flow of water or in the form of gas and will be dispersed into the air through the cavities in the medium, while suspended solids (SS) will be retained on the surface of the biological layer (biofilm). ) and will decompose into water-soluble forms.
The growth of these micro-organisms or biofilms is getting thicker and thicker, until finally due to gravity some of it will peel off from the medium and be carried out by the water flow. Furthermore, micro-organisms on the surface of the medium will grow again by itself until an equilibrium occurs according to the content of organic compounds present in the wastewater.
Aplication of Rotating Biological Contactor (RBC)
The performance of the RBC depends also on the number of compartments. One module can contain four or five compartments. In the first compartment, backflow can be added to the initial settling unit so that the conditions are not too anaerobic so that the bad smell is reduced while helping the dynamics of microbial growth. Likewise, in the final compartment a backflow to the initial settling unit may be installed for the same purpose. Generally, the RBC contact medium is submerged in wastewater as high as 40% of its diameter. The rotation speed is between 1 – 3 revolutions per minute. This rotation provides sufficient energy for the hydraulic force to dislodge the biofilm and the water flow is turbulent so that the solid remains suspended (does not settle). The hydraulic residence time in each module is relatively short, ie 20 minutes at normal load. Each stage or module tends to operate as a completely stirred reactor.
Regarding the microbial adhesive media, there are several materials that can be used. What is often chosen is HDPE (high-density polyethylene) plastic media with a diameter of 2-4 m, with a thickness of up to 10 mm. The form of media can be in the form of plates but can also be in the form of pipes or tubes mounted on an iron shaft with a span of up to 8 m. The media along with the shaft and the motor is called a module that keeps on rotating in the tub. Several modules can be installed in series or parallel according to the discharge requirements of the treated wastewater. Usually the modules are separated by a baffle to avoid short circuiting in the tank. RBC performance is also influenced by wastewater temperature, influent substrate concentration, hydraulic residence time, ratio of tank volume to media surface area, media rotation speed, and dissolved oxygen.
Generally, to treat RBC domestic wastewater, it does not require microbial seeding. This is because the microbes are already available in sufficient quantities to start the process. Approximately a week to two weeks after starting the processing, on the surface of the media will stick biomass with a thickness of 1-4 mm. This thickness depends on the strength of the wastewater and the rotational speed of the adhesive medium. According to Antonie, 1978, the concentration of these microbes reached 50,000 – 100,000 mg/l, a very high amount so that quite a lot of organic pollutants and nitrogen were removed with the help of dissolved oxygen.
Waste Treatment Process with RBC
In general, the wastewater treatment process with the RBC system consists of a sand separator, initial settling basin, flow control tank, rotary biological reactor/contactor (RBC), final settling basin, chlorination tank, and a sludge treatment unit.
Sand Separator Tub. Wastewater flows quietly into a sand separator, so that dirt in the form of sand or coarse silt can be deposited. Meanwhile, floating dirt such as garbage, plastic, cloth waste and others are stuck in the screen installed at the inlet of the sand separator pool.
Early Sediment Tub. From the separator/sand settler tank, wastewater is drained to the initial sealing tank. In this initial settling tank mud or suspended solids mostly settle. The residence time in the initial sealing tank is 2 – 4 hours, and the sediment that has settled is collected and pumped into the sludge deposition tank.
Flow Control Body. If the wastewater flow rate exceeds the planning capacity, the excess wastewater discharge is channeled to a flow control tank for temporary storage. When the flow rate is low, the wastewater in the control tank is pumped into the initial settling basin together with the new wastewater according to the desired discharge.
Biological contactor (reactor) Swivel. In this contactor bath, the medium is a thin disk (disk) of polymer or plastic material in large quantities, which is attached or assembled on a shaft, rotated slowly in a state partially immersed in the wastewater. The residence time in the contactor bath is approximately 2.5 hours. Under such conditions, micro-organisms will grow on the surface of the rotating medium, forming a biological film. The biological film consists of various types/spicies of micro-organisms such as bacteria, protozoa, fungi, and others. Micro-organisms that grow on the surface of this media will decompose organic compounds in the wastewater. The biological layer is getting thicker and thicker because of the gravity it will peel off by itself and the organic mud will be carried away by the water flow out. Furthermore, the biological layer will grow and develop again on the surface of the media by itself.
Final Precipitation Tub. The wastewater that comes out of the contactor (reactor) tank is then channeled to the final settling basin, with a settling time of about 3 hours. Compared to the activated sludge process, the sludge from RBC is easier to settle, because it is larger in size and heavier. The runoff water (over flow) from the final settling basin is relatively clear, then it is flowed into the chlorination tank. Meanwhile, the sludge that settles at the bottom of the tank is pumped to the sludge concentration tank together with the mud from the initial settling basin.
Chlorination tub. Treated water or runoff water from the final settling basin still contains coli bacteria, pathogenic bacteria, or viruses that have the potential to infect the surrounding community. To overcome this, the wastewater that comes out of the final settling basin is channeled into a chlorination tank to kill pathogenic micro-organisms present in the water. In the chlorination tank, the wastewater is spiked with chlorine compounds with a certain dose and contact time so that all pathogenic micro-organisms can be killed. Furthermore, from the chlorination tank, wastewater can be discharged into water bodies.
Mud Concentration Tub. Sludge from the initial settling basin and the final settling basin is collected in a sludge concentration basin. In the tank, the mud is stirred slowly and then concentrated by allowing it to stand for about 25 hours so that the mud settles, then the supernatant water at the top is flowed into the initial settling basin, while the concentrated mud is pumped into the mud dryer or accommodated in the tank. separately and periodically sent to a sludge treatment center elsewhere.
Reaction on RBC
In the RBC process, there are several reactions that occur, namely:
This is described as follows. Organic material contained in the waste then takes oxygen so that there is a reaction between organic matter, O2 and nutrients (usually already contained in the waste) in the metabolic process and then NH3, CO2, C5H7HO2 (new cells) are released into the air.
In addition to the above process, there is endogenous respiration to obtain energy, namely:
C5H7HO2 + O2 –>> 5CO2 + H2O + Energy
in the nitrification of waste has a pollutant containing ammonia NH4 which smells very pungent. with the following reaction:
2NH4 + O2 (with the help of nitrosomonas) —>> 2NO2 + 4H + 2H2O