Rotating Biologycal Contactor (RBC)

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:
1. Oxidation
2. Nitrifikasi
3. Denitrifikasi

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

Industrial Waste

Industrial waste is the waste produced by industrial activity which includes any material that is rendered useless during a manufacturing process such as that of factories, mills, and mining operations. Types of industrial waste include dirt and gravel, masonry and concrete, scrap metal, oil, solvents, chemicals, scrap lumber, even vegetable matter from restaurants. Industrial waste may be solid, semi-solid or liquid in form. It may be hazardous waste (some types of which are toxic) or non-hazardous waste. Industrial waste may pollute the nearby soil or adjacent water bodies, and can contaminate groundwater, lakes, streams, rivers or coastal waters. Industrial waste is often mixed into municipal waste, making accurate assessments difficult. Most countries have enacted legislation to deal with the problem of industrial waste, but strictness and compliance regimes vary. Enforcement is always an issue.

Industrial waste is defined as waste generated by manufacturing or industrial processes. There are many sectors of industrial manufacturing that produce waste, including:

  • Various types of factories
  • Mining
  • Textile mills
  • Food manufacturing
  • Consumer goods
  • Industrial chemicals
  • Printing and publishing

Below we’ll explore different types of industrial waste, as well as what you should know about properly disposing of it to ensure you meet all federal and state regulations.

Types of Industrial Waste

Industrial waste can be hazardous or non-hazardous. Both, however, can cause substantial damage to the environment if not properly managed. Below are some common types of industrial waste that can be hazardous to human life and the environment.

Solid Waste

Though the term “industrial waste” includes several different types, one of the most common is industrial solid waste. Solid waste can be generated by manufacturing processes such as:

  • Electric power generation
  • The use of agricultural chemicals and inorganic chemicals
  • Iron and steel manufacturing
  • Water treatment
  • Plastics and resins manufacturing
  • Many of the other manufacturing processes outlined above

 Toxic Waste

Industrial waste can also be toxic or hazardous waste. If not managed properly, this type of industrial waste can cause harm to humans, animals and the environment by contaminating waterways, such as rivers and lakes.

This type of industrial waste is generally a byproduct of other materials generated at factories, hospitals and manufacturing facilities. It’s important to note that waste laws can vary from state to state. For example, in many states, asbestos is not considered a hazardous waste.

Chemical Waste

Chemical waste mostly contains harmful chemicals. This does not mean, however, that it is classified as hazardous. For it to be considered hazardous, it must have an ignitability, corrosivity, reactivity or toxicity characteristic.

Secondary Waste

Emphasis on reusing secondary materials that are considered to be non-hazardous, such as scraps and residuals that result from the production process. Examples of secondary types of waste include:

  • Coal combustion
  • Spent foundry sand
  • Construction materials when infrastructure is demolished

How To Dispose Of Industrial Waste

Improperly handling industrial waste can have harmful consequences to both your company and the community. If not properly disposed of, harmful waste can be released into the air, soil and water. This carelessness can also pose a threat to your company’s reputation and bottom line, and expose you to costly fines and publicity that your company may struggle to recover from for years to come.

Hazardous waste disposal companies offer a safer and more convenient option, and they can help with the process of disposing of industrial waste. If you generator hazardous waste, you are legally and financially responsible for it from the time it is created to the time it is disposed of, whether it is on your property or not. This is why many industrial waste generators work with a reputable disposal company to help them manage this process and alleviate any issues that may arise from the transportation and disposal of their waste – especially once it leaves your facility.

Final Note

Industrial waste is defined as unwanted or residual materials that result from industrial operations. There are several types of industrial waste, and while some is considered non-hazardous, some types are classified as hazardous. No matter, all types of industrial waste have the potential to be harmful if improperly managed.

That’s why if you generate industrial waste, it is imperative that you understand your responsibility when it comes to management and disposal. A certified waste disposal company can assist you with declassifying your industrial waste through proper sampling so you can ensure you follow proper procedures for handling the waste.





Hazardous Waste

There are several ways of classifying waste: by its nature (dry and wet), by its chemical composition (organic matter and inorganic matter), etc.

Hazardous wastes are part of class 1 and are those types of material that pose risks to public health and the environment, requiring special treatment and disposal based on their characteristics of flammability, corrosivity, reactivity, among others.

Hazardous waste is accumulated daily in homes and businesses and, unfortunately, its disposal is still carried out irregularly. Improper disposal of hazardous waste can lead to contamination of soil and groundwater. This ends up putting the health of people and the environment at risk, taking into account that a large part of this type of waste contains very dangerous chemical substances in its composition, such as heavy metals.

To reverse the problems caused by incorrect disposal, it is necessary to begin to encourage the education of the population, as well as the adequate punishment of those who break the law and put the health of the population and the environment at risk.

Waste is regulated as hazardous if it meets any of the following characteristic:

1. Hazardous Ignitable

  • A liquid with a flash point less than 60 degrees Centigrade
  • A solid capable under normal conditions of causing fire through friction, absorption of moisture or spontaneous chemical changes
  • A flammable compressed gas
  • An oxidizer

2. Hazardous Corrosive

  • An aqueous with pH less than or equal to 2, or greater than or equal to 12.5
  • A liquid that corrodes steel at a rate greater than 0.250 inches per year at 55 degrees Centigrade

3. Hazardous Reactive

  • Is unstable and readily undergoes violent change without detonating
  • Reacts violently with water
  • Forms potentially explosive mixtures with water
  • Upon mixture with water generates toxic gases, vapors or fumes
  • Generates toxic gases, vapors or fumes at pH conditions between 2 and 12.5
  • Capable of detonation or explosive decomposition
  • Classified as a Department of Transportation explosive

4. Hazardous Toxicity Characteristic

  • The waste contains certain metals, pesticides or selected organics above specified levels.
  • if it is otherwise capable of causing environmental or health damage if improperly disposed (this judgment is based on knowledge of the material).

Are considered hazardous waste:

  • Traces of paint (they are flammable, can be toxic);
  • Hospital material (they are pathogenic, they have genetic material from another person and it is not possible to know if any bacteria present or a virus can contaminate it);
  • Chemicals (they can be toxic, they can be reactive, that is, they can react with some other substance and cause a fire or be corrosive as well);
  • Radioactive products;
  • Fluorescent lamps (they contain mercury inside the glass, which is considered a heavy metal and bioaccumulates, contaminating the environment in which it is thrown, since the mercury found loose in nature contaminates other organisms causing problems for the metabolism of the that absorb it);
  • Batteries and batteries (they have several metals in their composition that can be corrosive, reactive and toxic depending on the environment)

This type of waste requires special treatment and proper management is the first step for companies to contribute to a healthier environment. Therefore, hazardous waste must not only be stored separately, but must also be transported in different vehicles, which must have an identification plate and receive a specific and adequate final disposal.

It is of utmost importance to treat hazardous waste carefully and with great attention to the special storage and disposal needs that they require. Like public and private power, each individual in society must be aware of doing their part when it comes to protecting the planet from the consequences of human consumption.

Domestic Waste

Domestic waste is any waste that is produced in the home environment. Local authorities’ waste teams regularly collect the bulk of this, and additional household waste can be collected via one-off waste collections or skip hire. Larger or extra domestic waste can also be taken to a local recycling centre for disposal.

Household waste, otherwise known as domestic waste can be divided into many waste categories.These categories include all of the below.

Food Waste

Some local councils collect food waste from homes but, if yours doesn’t, consider setting up a compost bin or worm farm to save your fruit and vegetable scraps from ending up in landfill.

While this type of waste can rot down well in the right environment, it struggles to do so in landfill.



Recyclable Waste

Recyclable waste includes plastics, paper, cardboard, aluminium, and glass bottles.

Most UK households have council collections for recyclables, although which recyclables can vary between authorities.

Always check what you can and cannot place inside your domestic recycling bin, as incorrect items can ruin entire loads of recycling.


General waste

All households have a general waste collection, and this bin collects non-recyclable domestic waste.

If you have an excess of general waste, larger items, or rubble from renovation work, then you can take it to your local recycling centre, organise a waste collection, or hire a skip.




Garden waste

Most local authorities offer a garden waste collection service throughout the summer months, but a charge is often involved.

If you require a garden waste collection, check your council’s website for more information. Alternatively, get in touch with a waste management company that can arrange a one-off waste collection.



Domestic Hazardous waste

You may be wondering, ‘what is domestic hazardous waste?’ as most hazardous waste is commercial. Domestic hazardous waste is anything that is considered harmful to humans or the environment, including medical waste, batteries, chemicals, pesticides, and refrigerators.

Most council-run recycling centres accept many types of hazardous waste, so get in touch with your local council if you have some hazardous waste to shift.

What happens to household waste?

Once general household waste leaves your home or the recycling centre on behalf of your local authority, it is either burnt to produce energy or sent to a landfill site.

The contents of your recycling bins and recyclables from the recycling centre are taken to a processing facility where they are sorted and then recycled into new products.

If you book a waste collection or hire a skip from a waste management company, then you can ask them what happens to your waste — every company is different.

Forge Recycling is proud to send zero waste to landfill.

Liquid Waste

Water quality management and water pollution control, explain the meaning of the waste that remains of a results business and or activities that are in liquid form. Understanding liquid waste other is the rest of the exiles the process of production or domestic activity in the form of liquid. Waste liquid can be either water and material waste another mixed (suspended) or dissolved in water. Liquid waste can be classified in four groups namely:

  • Domestic wastewater (domestic wastewater), namely the waste liquid waste from the residential (household), building, trading and office. Examples are: water, soap water, detergent rest of the laundry, and fecal water.
  • Industrial liquid waste (industrial wastewater), namely the waste liquid waste industry. Examples are: the rest of the coloring of the fabric/material of the textile industry, the water from the food processing industry, the rest of the laundry meat, fruit, or vegetable.
  • Seepage and overflow (infiltration and inflow), namely liquid waste derived from various sources that enter the sewer waste liquid through seepage into the ground or through the overflow from the surface. Waste water can seep into the sewer through a pipe that is broken, damaged, or leaking while the overflow can be through the channels that open or connected to the surface. Examples are: the waste water from the roof gutters, air conditioner (AC), building trade and industry, as well as the farm or plantation.
  • Rain water (storm water), that is the liquid waste that comes from the flow of rain water over the surface of the ground. The flow of rain water on the surface of the ground can pass through and brings the particles of solid waste or liquid so that it can be called liquid waste.

Liquid waste is sourced from factories that typically use a lot of water in the system process. In addition, there is also a raw material containing water so that in the process of processing water must be disposed of. The water entrained in the process of processing and then discarded for example when used to wash the material before being processed further. Water plus certain chemicals are then processed and after it is removed. All types of this treatment resulted in the waste water.

The liquid waste is not handled or processed, may cause a great impact on environmental pollution and can be a source of disease for the community. Industry primary processing of forest products is one of the contributors of the liquid waste which is harmful to the environment. For major industries, such as pulp and paper industry, the technology of processing of liquid waste that it generates may already adequate, but not so for the industry of small or medium. In addition, domestic wastewater is usually not too concerned with whether whereas if allowed to continue in the long term can be a problem for the environment and public health. For example, waste water detergent rest of the laundry when left in the long term will be a source of environmental pollution and become a source of disease for the community. Given the importance and magnitude of impact caused by liquid waste to the environment, so it is important for the industrial sector and domestic to understand the basics of technology of processing of liquid waste.

Wastewater treatment technology is key in preserving the environment. Any kinds of processing technology of domestic waste water and industrial built to be operated and maintained by the local community. Processing technology selected must comply with the technological capabilities of the community concerned. Liquid waste processing can be grouped into three, namely: processing in biology, processing in physics, and processing chemicals.

How To Handling Liquid Waste?

Technical Visit

Meets the objective prior to the operation of formulating our economic proposal in addition to evaluating the conditions and/or volumes of liquid waste to be transported, which may be in grease traps, treatment plants, septic tanks, tanks or silos.


Once the service is accepted, the operation proceeds, for the suction the work space is verified and secured. The transfer of industrial liquid waste from the well or tank to the interior of the tank is through hoses with a suction system with a vacuum pump.


Transportation is carried out with modern tank vehicles with satellite tracking whose variety and cargo volumes depend on the customer’s transportation needs. Vehicle units have the technical characteristics and appropriate equipment to carry out transportation under special conditions and with a Rigorous control from the customer or generator facilities to the destinations or final disposal.

Final Disposal

Liquid waste according to its nature will be disposed of in authorized entities for its confinement, recycling or treatment.

Documentary Management

The entire process is accredited with the documentation that guarantees compliance with regulations and correct waste management, which are consolidated in a solid waste management report that is presented to the client.


Solid Waste

In a general sense of waste, solid waste and garbage is as follows.

  1. Waste is the material remaining on an activity and / or production process. Type of waste in the hospital is composed of solid waste, liquid waste, radioactive waste and waste gas.
  2. Solid waste (solid waste or refuse commonly called garbage. Solid waste does not include human waste.
  3. Garbage is all of the substance of objects arising from the actions of man which is discarded because it is not used or desired by the owner.

What is a Solid Waste?

Solid waste is defined as the rest of the activities of human and/or natural processes that shaped solid. Or, solid waste is the waste that is solid composed of organic material and inorganic material that is considered no longer useful and should be managed so as not to harm the environment and protect the investment of development.

Then based on the Term Environment for the Management, solid waste is a material which is wasted or thrown away from the source of the result of human activity and natural processes that do not yet have economic value. Thus, the solid waste is the rest of the/a result of human activity, which is shaped organic and inorganic substances that can harm the environment so that the necessary management and processing. Solid waste can be generated from different types of activities such as residential, office, industrial, schools, markets and other public facilities.

Type-The Type Of Solid Waste

Solid waste management is a series of activities which include storage, collection, transport, waste treatment and final disposal or hoarding basil to such processing.

Based on its composition, the solid waste can be divided into two, namely:

1. Solid Waste Wet

Solid waste damp is a solid waste that is shaped organic ingredients that are easily decomposed by microorganisms. The process of decomposition will occur when solid waste is left in a wet state and is at the optimum temperature of about 200-300C. In general solid waste wet utilized as compost. Examples of solid waste is wet, the rest of the foods, the vegetables, the skin soft fruit, and leaves.


2. Solid Waste Dry

 Solid waste dry waste solid-shaped organic and inorganic materials. In general solid waste dry do not quickly decompose microorganisms so that it is difficult in a state of decay. Solid waste dry inorganic can be upcycled into other products that are useful. Examples of solid waste is dry, like paper, plastic, containers of food or drink, cans, wood, metal, and glass or a glass.


But, solid waste can be classified into six groups as follows:

  • Organic waste easily rot (garbage), namely solid waste semi-wet, in the form of organic ingredients that is easy to rot or decompose microorganisms. Examples are: the rest of the food, the rest of the kitchen, vegetable waste, fruit peels fruits
  • Waste inorganic and organic’t rot (rubbish), namely solid waste inorganic or organic dry enough that it is difficult to decompose by microorganisms, so it is difficult to decompose. Examples are: cellulose, paper, plastic, glass, metal.
  • Trash the ashes (ashes), namely solid waste in the form of ashes, usually the result of combustion. Trash is easily carried by the wind because it is lightweight and not easy to rot.
  • Waste animal carcasses (dead animal), like all waste in the form of dead animals, such as rats, fish and livestock to die.
  • Trash sweep (street sweeping), namely solid waste results of the sweep of the street containing a variety of trash scattered in the streets, just as the foliage, paper and plastic.
  • Industrial waste (industrial waste), like all the solid waste that originate from industry. The composition of the waste depends on the type of industry.

The handling of solid waste can be distinguished from the usefulness or function of the solid waste itself. Solid waste there can be recycled or used again as well as having economic value such as plastic, textile, metal scraps, but there are also that cannot be used again. Solid waste that can not be used again usually thrown away, burned, or dumped unceremoniously. Some of the specific industry of solid waste that is produced sometimes create new problems associated with the place or the broad areas that needed to accommodate the waste.

Wastewater Treatment Processes

The modern technological chain of wastewater treatment plants includes a set of equipment for mechanical, chemical and biological wastewater treatment, as well as, in many cases, equipment for high-tech water recovery before reuse.

A. Mechanical (preliminary) Treatment Equipment

For this stage performs simple mechanical operations (eg filtration and aeration) and enables highly efficient physical processes (sedimentation, flotation) to remove large particles of contaminants from wastewater. The main contaminants that are removed during the mechanical cleaning stage are:

  • Large floating particles of solid waste.
  • Granular particles (sand) with a size of 0.1 mm or more.
  • Easily settling suspensions, the so-called primary sludge.
  • Oils and fats that float to the surface.

Removal of other contaminants from wastewater at this stage of treatment is considered less important. It is also possible at this stage to treat the waste water by aeration or possibly chlorination.

For mechanical wastewater treatment the following devices are used :

  • Sand traps: vertical, horizontal.
  • Sieves of various types, sizes and designs.
  • Sedimentation tanks of various types.

Using modern mechanical treatment, in addition to separating large particles of garbage, sludge and sand from wastewater, enterprises can reduce the suspended solids content by 50-80%, as well as reduce BOD 5 and COD by 30-50% or more. After separation from wastewater, the sludge is washed and compressed, collected in containers and sent to a landfill or special processing. The sand to be separated from the wastewater in the form of a sand slurry is washed and separated to remove organic matter.

B. Biological or Chemical Treatment

Biological wastewater treatment is based on the decomposition of pollutants in biological oxidation processes, which means the use of microorganisms. Almost all biological wastewater treatment processes are aerobic. Wastewater must contain oxygen, which is consumed by bacteria and protozoa in their life processes, and therefore the oxygen concentration must be constantly maintained. During the construction of modern wastewater treatment plants, engineering companies make extensive use of biological treatment equipment such as bioreactors. This technological process takes place under artificial conditions that intensify natural biochemical processes. The intensification of biological processes is achieved by maintaining an optimal amount of active mass of microorganisms and ensuring a constant supply of oxygen. Wastewater treatment is carried out in installations with activated sludge (biological reactors), the configuration of which depends on the type of wastewater and the substances removed from them. During aerobic biodegradation, organic compounds are degraded by enzymes and then used to grow new microorganisms (increase biomass) and are oxidized to simple inorganic compounds such as carbon dioxide, water, nitrates, sulfates or phosphates. A feature of the technology of aerobic decomposition is the release of a significant amount of energy, which contributes to the growth of biomass and a faster course of the process. Excess biomass is removed from the system in the form of sludge, which is sent for further processing.

Biological nitrogen removal includes the following processes:

  • Ammonification.
  • Nitrification under aerobic conditions.
  • Denitrification under anaerobic conditions.

The selection of the most suitable process and equipment for the construction of wastewater treatment plants depends on the initial composition of the wastewater.

Wastewater chemical treatment technology

Chemical wastewater treatment consists in the addition of coagulants, iron compounds (for example, ferrous sulfate) or aluminum (for example, aluminum sulfate), and sometimes flocculants (anionic polymers). In some cases (at low pH) calcium compounds are added to the water. The main purpose of chemical cleaning is additional phosphorus removal. It should be borne in mind that the addition of chemicals to wastewater will not only reduce the concentration of total phosphorus, but also significantly reduce the concentration of BOD5 and COD, the concentration of suspended solids and total nitrogen.

Depending on the order of adding the coagulant to the wastewater treatment process, there are three methods of chemical precipitation:

  • Pre-sedimentation with the introduction of a coagulant into untreated wastewater (before primary sedimentation tanks). This is a typical process that requires rapid mixing, flocculation and settling. Pre-sedimentation can significantly reduce the load on biological reactors and reduce the cost of treatment.
  • Simultaneous sedimentation. The introduction of the coagulant can be carried out directly into the biological reactor, as a result of which the phosphorus is precipitated during the biological wastewater treatment. At the same time, flocculation occurs and the resulting sludge is separated from the wastewater by sedimentation in secondary sedimentation tanks.
  • Final sedimentation. Phosphorus is separated from wastewater after biological treatment in a separate process, including rapid mixing, flocculation and sedimentation (as separate operations). This method makes it possible to reduce the phosphorus concentration in the treated wastewater to a level below 0.1 g / m³ (in the case of filtration instead of sedimentation).

C. Water Recovery For Reuse

Highly efficient wastewater treatment processes are designed to ensure that the resulting water can be reused for domestic or industrial purposes. This is called water regeneration. Water regeneration technologies complement existing wastewater treatment methods. They are based on processes well known in chemical engineering and commonly used in groundwater and surface water treatment. These are processes such as filtration, coagulation, adsorption and disinfection (chlorination, UV lamps).

Chemical Oxygen Demand (COD)

Chemical Oxygen Demand (COD)

Chemical Oxygen Demand (COD) is an important measurement for the treatment of waste in many industrial sectors, from municipal systems to the waste stream feed mills.

Correct COD testing is important in determining the effectiveness of your water treatment, and can help diagnose any treatment problems that may arise. In this blog we will explain what chemical oxygen demand is, how to analyze it and how to know which is the best equipment to carry out your analyzes.

  • What is COD?
  • Importance of COD
  • How is COD measured?
  • “So what do I need to start the analysis?”

What is Chemical Oxygen Demand?

Chemical oxygen demand (COD) is an indirect measurement of the amount of organic matter in a sample. With this test, you can measure virtually all organic compounds that require a reagent to go through the digestion process.

COD differs from Biochemical Oxygen Demand (BOD), which is based on the use of microorganisms that break down organic material in the sample through aerobic respiration during a specified incubation period (usually 5 days).

COD and BOD have a correlation in practically all samples, but BOD is always lower than COD, since the biochemical decomposition of organisms is often not as complete as with the chemical method.

Importance of Chemical Oxygen Demand

When evaluating organic matter in a wastewater sample, both BOD and COD are of great importance in determining the amount present. Waste with a high organic content requires a treatment that reduces its quantity before being discharged into receiving waters.

If the water treatment facilities do not reduce the organic content of the wastewater before entering the natural waters, the microbes in the receiving water will consume this organic matter.

Consequently, these microbes will also consume the oxygen in the receiving water as part of the decomposition of organic waste. The depletion of oxygen, along with nutrient-rich conditions, is called eutrophication, which is a natural water condition that can lead to the death of animal life.

Wastewater facilities reduce COD and BOD using these same microbes under controlled conditions. These facilities aerate chambers injected with a special bacteria that can decompose organic matter in an environment that does not harm natural waters. In these facilities, the reduction in BOD is used as a benchmark to determine the effectiveness of the treatment.

Because the BOD analysis takes 5 days to complete, COD is used to monitor the treatment process in daily operations. The COD analysis only takes a few hours to complete.

If BOD was always used, the wastewater treatment would have to stop and any problems in the treatment process would not be discovered until 5 days later. This means that the wastewater would have to be held until the results are verified.

Hanna’s Tip: Due to the speed of the analyzes, facilities usually establish a correlation between BOD and COD, so they only run the BOD analysis occasionally; however, be sure to get detailed advice from your local regulatory agency on BOD and COD testing regimes.

How to Measure Chemical Oxygen Demand

As mentioned above, COD measures organic matter using a chemical oxidant. It is critical that an oxidant strong enough to react with virtually all organic material in the sample is used. Traditionally, potassium permanganate has served this role, but its ability to oxidize all organic matter in a wide variety of waste samples was found to be inconsistent.

Currently, most COD tests use potassium dichromate as the oxidant. This is a bright orange hexavalent chromium salt and a very strong oxidant. Between 95% to 100% of the organic material can be oxidized with dichromate. Once it oxidizes a substance, it is converted to a trivalent form of chromium, which is a dull green color.

The digestion process is carried out on the samples with a certain amount of the oxidant, sulfuric acid and heat (150 ° C). Generally, metal salts are incorporated to suppress any interference and catalyze the digestion process, which usually takes 2 hours.

During the digestion process it is necessary to have an excess of oxidant; this ensures complete oxidation of the sample. Therefore, it is important to determine the amount of excess oxidant. The two most common methods for this are titration and colorimetry.

COD Titration

In the titration method for determining COD, the surplus dichromate reacts with a reducing agent, ferrous ammonium sulfate (FAS); By adding the sulfate slowly, the excess dichromate is converted to its trivalent form.

When all the excess dichromate reacts, an equivalence point is reached. This point indicates that the amount of ferrous ammonium sulfate you added equals the amount of excess dichromate. Colored indicators can also signal this end point, but the process can be automated with a potentiometer indicator, such as an electrode.

You can then calculate how much dichromate went into oxidation of the organic material based on how much was added at the beginning and how much was left.

COD Colorimetric Method You can also tell the consumption of dichromate by observing the change in absorbance of the sample. Samples are absorbed at certain wavelengths due to the color of trivalent chromium (Cr3+) and hexavalent chromium (Cr6+).

This is why you can quantify the amount of trivalent chromium in a sample after the digestion process, by measuring the absorbance of the sample at a wavelength of 600 nm in a photometer or spectrophotometer. As an alternative to determining COD values, the absorbance of hexavalent chromium at 420 nm can be used to establish the amount of excess chromium at the end of the digestion process.


This is an easy method that requires only a few steps.

  • Perform the digestion process on samples and on a reagent blank. The reagent blank is just a sample of deionized water that is handled in the same way as your actual samples. You can even reuse the reagent blank for the life of your reagent lot.
  • Allow the digestion process and blank samples to cool.
  • Zero the instrument using a blank vial.
  • Read the sample results.

What is the Best Method

The titration is less intensive for the equipment, since all you need is a buret, a thermoreactor and digestion vials; however, the procedure is a bit more time consuming. An automatic titration can reduce the amount of user input data and can be used for other wastewater applications such as alkalinity and volatile acidity.

Although colorimetry requires a spectrophotometer or photometer, it is convenient as most manufacturers offer premixed reagents, so all you have to do is run your samples with the digestion chemicals and have minimal contact.

Colorimetry also makes measurement easy as all the analyst has to do is go through the sample digestion process and let the team do the work. For this reason, colorimetry is the most common method for measuring COD.

“So what do I need to start the Measurements?”

Only a few pieces of equipment are required to get started with chemical oxygen demand. Because it is the most common method, we will focus on the colorimetric method for COD.

Here are the basics you need:

1. Thermal Block

Both methods for COD analysis require the step of the digestion process, so a heat block is essential to ensure that your samples give accurate and repeatable results. To improve these results, look for a thermal block that covers different temperatures, with this you will have the opportunity to use it for other analyzes, such as total phosphorus. Most thermoblocks have timers, which are critical for keeping digestion times consistent across different runs.

For added safety look for models that have an optional protective safety cover that covers the thermoblock in the event of an accident.

2. Spectrofotometer or Colorimeter

The Spectrofotometer  or Colorimeter is the device that will read the absorbance of the samples after the digestion process to correlate it with the COD. Both pieces of equipment can be used to perform COD measurements, but the two devices are slightly different from each other.

Colorimeters use filters for measurements of light with specific wavelengths, while spectrophotometers use a device that allows measurements across a broad spectrum. Regardless of which equipment you choose, look for models with pre-programmed COD methods for ease of use

3. Reagent

Reagents are one of the most important components of the COD test system. These chemicals are responsible for oxidizing organic material. It is possible to prepare internal reagents, but it is easier to buy them, which reduces contact with hexavalent chromium and strong acids. These COD vials come pre-mixed and ready to use.

Biologycal Oxygen Demand (BOD)

Biologycal Oxygen Demand (BOD)

What is BOD?

Biological oxygen demand (BOD), also called biochemical oxygen demand, The BOD5 value indicates the amount of oxygen that bacteria and other tiny living beings consume for 5 days at a temperature of 20 ° C in a water sample for the aerobic degradation of the substances contained in the water. The value BOD is thus an indirect measure of the sum of all the biodegradable organic substances in the water. The value BOD indicates the amount of dissolved oxygen (mg / l) that is required during a certain time for the biological degradation of the organic substances contained in the wastewater. This value is an important parameter to assess the degree of load that residual water represents for the environment (receiving channel). As the substances contained in the wastewater are degraded in the receiving channel by the bacteria present there, the oxygen is partially or totally eliminated from the water. When these limit values ​​are exceeded, it can cause the death of living beings that breathe oxygen (crabs, fish, etc.).

The BOD is a pollution parameter to evaluate the quality of effluent or wastewater.
Drinking water is also evaluated for organic matter, this is measured through Total Organic Carbon (TOC or TOC) instead of BOD.

The biochemical decomposition of organic substrates is carried out by microorganisms. In this case we are talking about aerobic bacteria, which need energy that they produce from oxygen to complete decomposition. The oxygen is consumed and as a result the level of oxygen dissolved in the water is reduced. If there is a large amount of organic matter in the water, the oxygen demand is also higher for decomposition to take place.

The quality of the water is controlled by the authorities to protect the health of the users and other effects of poor water quality. A high BOD level may indicate fecal contamination or dissolved organic carbon particles from different sources other than humans or animals. This kind of pollution can seriously affect human health and cause problems in industry.

It is of great importance that governments ensure a low level of BOD in the effluent water coming out of sewage plants, because it is in the public interest to have rivers, lakes and seas with a high level of dissolved oxygen.

How to measure the level of BOD?

There are two methods to measure the BOD level, both are empirical tests.

  • Method I: It is the most common method. A special bottle for BOD is filled to the brim with the water test. The test is left for 5 days at a constant temperature of 20 ° C in the dark. After 5 days the oxygen content is measured compared to the original value, the oxygen consumption during this period indicates the oxygen demand of the water.
  • Method II: If a very high BOD is expected or if other toxic or inhibitory substances are present in the water, the sample can be diluted at first. In this way you can avoid having too little oxygen present to break down organic substances. This would falsify the measurement result. As with Method I, a comparison of before and after values ​​now serves as a measure of oxygen consumption during the measurement period.

After 5 days the dissolved oxygen is measured, with which the BOD level can be calculated. Drinking water should have a concentration of less than 1mg / l after 5 days. The wastewater concentration is accepted around 20mg / l.

As the methods are empirical, the BOD indicator does not give absolute results. What the indicator provides is a good test comparison but does not give an exact measure of contamination. An alternative to BOD is COD – Chemical Oxygen Demand.

Anaerobic bacteria like SRB do not need oxygen in the water to survive. These microorganisms live on sulfur, so they cannot be detected by measuring the biochemical oxygen demand.


Physical Chemical Treatment

Mechanical separation of solid substances by filtration

Filtration separates solid substances from liquids. To do this, the mixture to be separated passes through a filter; in the simplest case, it can be made of paper. For technical applications, filters made of textile or metal fabric are mostly used. Sand filters, rotary sieves and cloth filters are also frequently used.

With the aid of filter systems, suspended organic and inorganic substances, sand and dust can be removed from the water. In wastewater technology, this mechanical separation process is used, among other things, for the dewatering of sludge in filter presses. In the treatment of water for industrial use and drinking water from surface waters, filtration is also applied; generally in a multi-stage process.

Membrane filtration is also a mechanical separation process. In this case, a membrane serves as the filter medium. This method is typically used to separate very small components.

Industrial massive water filtering mechanism.

Cleaning wastewater with membrane technology

With membrane filtration, dissolved and undissolved substances can be separated from waste water and concentrated. Thus, the separation is carried out under pressure; the membrane, with a given pore width, retains particles (eg molecules) from a certain size. The different processes are used for water treatment, for the cleaning of waste water, for the recycling of process water and for the concentration of recyclable materials for their recovery.

The micro filtration is used to separate particles, bacteria and yeast. It is used, among other things, for cold sterilization and the separation of oil and water emulsions.

The ultra filtration is an important process for treating drinking water and wastewater. It is used to separate particles, microorganisms, proteins and turbidity from water, among others, in the membrane bioreactor (MBR).

Ultrafiltration is used for example for cleaning recirculating water in swimming pools. Since the formation of clogging layers adhering to the membrane can be avoided quite well, existing sewage treatment facilities are increasingly being supplemented with an ultrafiltration called “polishing step”. In retrofitting older classic treatment plants, ultrafiltration can be inserted directly into or after the bioventilation tank to replace subsequent treatment steps or to increase the performance of biological wastewater treatment.

The nano filtration can separate viruses, heavy metal ions, large molecules and very small particles. This process is used in the softening of water and in the treatment of drinking water.

The osmosis inversa is an important step process the concentration of landfill leachate, in the treatment of drinking water in rural regions that are not connected to the mains, in seawater desalination or descaling water boilers in power plants. To do this, the concentration of dissolved substances in liquids is increased through a semi-permeable membrane, reversing the osmosis process with pressure: if the pressure is higher than the respective osmotic pressure, the solvent molecules diffuse on the side of the membrane on which the dissolved and less concentrated substances are found. This process is also used to obtain ultrapure water.

New carbon filter cartridge for house water filtration system isolated on white background.

Wastewater treatment by flotation

In flotation, substances dispersed or suspended in liquids are transported to the surface with the help of small gas bubbles, where they are removed with a removal device. Flotation processes are used in wastewater treatment to separate suspended oils, fats and fine solids.

The smaller the microbubbles, the better the particles or droplets settle. For this reason, dissolved air flotation (DAF) is frequently used in wastewater treatment technology. This has been noted for its proven efficiency and cost effectiveness. Flotation processes can be further enhanced by employing auxiliary means, such as manifolds, skimmers, regulators or pressure devices.

Close-up film of green algae on the surface of the water, preventing the flow of oxygen

Separation of solid substances by sedimentation

Sedimentation uses the force of gravity in sedimentation tanks to separate solid particles. A sedimentation tank is a flat tank with almost no current flow, especially for sedimentation processes. Solid particles settle to the bottom.

Sedimentation processes are used in multiple ways in wastewater treatment: undissolved substances are deposited in the primary settling tank. These form the primary sludge, which then thickens and becomes anaerobic in the digester. This generates digested sludge and digestion gas, which in its already clean form as biogas can be used to produce electricity and meet energy demand. Aerobically generated sewage sludge can also be introduced into the digester, after it has been separated by sedimentation from the residual water in the settling tank. Particles that are heavier than water can be separated from the liquid with the help of grit traps or sludge collectors.