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. Nitrification
3. Denitrification

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

Total Suspended Solid (TSS)

Total suspended solids (TSS) are residues of total solids retained by a sieve with a maximum particle size of 2μm or larger than the colloid particle size. TSS includes mud, clay, metal oxides, sulfides, algae, bacteria and fungi. TSS is generally removed by flocculation and filtration.

TSS contributes to turbidity by limiting light penetration for photosynthesis and visibility in waters. So that the turbidity value cannot be converted to the TSS value. Turbidity is the tendency of the sample size to scatter light. While scattering is produced by the presence of suspended particles in the sample. Turbidity is purely an optical property.

The pattern and intensity of the distribution will differ due to changes in the size and shape of the particles and matter. A sample containing 1,000 mg/L of fine talcum powder will give a different turbidity reading than a sample containing 1,000 mg/L. coarsely ground talc. The two samples will also have different turbidity readings than samples containing 1,000 mg/L ground pepper. Although the three samples contain the same TSS value.

The difference between total suspended solids (TSS) and total dissolved solids (TDS) is based on the screening procedure. Solids are always measured as dry weight and the drying procedure must be observed to avoid errors caused by retained moisture or material loss due to evaporation or oxidation.

Analysis TSS is as follows the homogeneous test sample was filtered with filter paper that had been weighed. The residue retained on the filter is dried to a constant weight at a temperature of 103ºC to 105ºC. The increase in sieve weight represents the total suspended solids (TSS). If suspended solids obstruct the filter and prolong filtration, it is necessary to increase the diameter of the filter pores or reduce the volume of the test sample. To obtain the TSS estimate, the difference between total dissolved solids and total solids was calculated.

TSS (mg/L) = (A-B) X 1000 / V

With understanding

A = weight of filter paper + dry residue (mg)

B = weight of filter paper (mg)

V = volume contoh (mL)


TDS and pH in Drinking Water

Water is a very important need for life. Not only for hygiene needs, water is also consumed by the body to meet the mineral needs needed by the body. Based on the general aspect, good drinking water is colorless, odorless and tasteless. However, there are important parameters that must be measured to determine the quality of drinking water consumed.

In the process, drinking water can be produced using 2 types of water, namely surface water and subsurface water. The process carried out on water also depends on the water source used. In this case, each company must have a different water purification system, but in general the process is carried out as follows:

  1. Sedimentation/ flocculation

This stage is the stage of clumping (coagulation) of small particles contained in the water source so as to form a larger particle so that it is easy to filter later. For the formation of this coagulant / flocculant requires additional substances in the form of aluminum salts or ferric salts.

  1. Filtering

At this stage, the water that has been taken from the source is filtered using several materials and several filtering steps. This filtering step can consist of filter, pre-filter and final filter. The purpose of this stage is to remove fine impurities and harmful ions present in the source water. The materials used are sand (sand filter), ion exchange filter and activated carbon. At this stage it is possible for the processed water to be more easily disinfected.

  1. Sterilization

This process is the stage of eliminating microorganisms such as bacteria, viruses, fungi and others. At this stage, ozone is applied to treated water which is intended to kill bacteria, viruses and microbes present in the water or better known as the ozonation process. In addition, some companies still use chlorine as a disinfectant. This stage can also be done by irradiating UV lamps.

  1. Shelter

At this stage the water that has been disinfected is accommodated into the reservoir. Distribution of water into the bottle via four pumps. Inside each pump there is a 0.45µm diameter filter which functions to filter all organic matter and microorganisms present in the water after the ozonation process.

Based on SNI 01-355-2006, bottled drinking water is divided into two classes, namely mineral water and demineralized water. Several test parameters that must be carried out on bottled drinking water are shown in Table 1

Table 1. Some Test Parameters for Bottled Drinking Water





Mineral water

Air Demineral

1 Circumstances      
1.1 Construction

No smell

No smell

1.2 Flavor



1.3 Color

Unit Pt-Co

Max. 5

Max. 5

2 pH

6,0 – 8,5

5,0 – 7,5

3 turbidity



Max. 1.5

4 Solute




5 Total Organic Carbon


Max. 0.5

6 Organic Substances (KMnO4 Number)


Max. 45

Some of these parameters are very important to be tested in the manufacture of bottled drinking water, one of which is pH. From Table 1, it is stated that good drinking water has a pH that ranges from 6 to 8.5. This is disclosed by the World Health Organization (WHO) that if drinking water is consumed too alkaline (pH> 8.5) it can cause irritation to the eyes, skin and tissues and even experience gastrointestinal disorders. On the other hand, if the pH is too acidic (pH<4), the same thing will happen. This is of course dangerous, so bottled drinking water is processed in such a way that the contaminants in it can be minimized and safe for consumption.

Several ways to increase the pH value are by adding calcium or magnesium carbonate (CaCO3 or MgCO3). This addition can be done on pH monitoring before entering the disinfection stage. This is because pH has an important role in the process of disinfection of microorganisms. The use of calcium or magnesium carbonate not only to raise the pH but also to enrich the healthy minerals in the water.

In addition to pH, the parameter that must be monitored is Total Dissolved solid (TDS) or total dissolved substance. If the pH range for good drinking water is in the range of 6.0 – 8.5, it is different with the TDS parameter which should not exceed 500 ppm. This is because the TDS parameter also represents the minerals contained in the water. These minerals can be classified into 2, namely those that are harmful such as arsenic, sulfate, bromide, manganese and others and those that are good for the body such as calcium and magnesium. The TDS value must be monitored because this parameter will affect the taste of the water consumed. However, the high value of TDS will cause damage to systems such as pipes and reservoirs as well as turbines. This is because TDS can cause scale on the system.

Table 2. TDS Value on Water Quality

TDS value (ppm)

Water quality

Less than 300

Very good

300 – 600


600 – 900


900 – 1200


Above 1200

Not accepted (very bad)

In the process of monitoring these two parameters, a tool is needed that can meet the needs of the range for drinking water applications, easy to use and very flexible to be brought to the field or for laboratory checking scale.


Monitoring Total Suspended Solid (TSS) in Drinking Water Treatment

The quality of drinking water is very important to pay attention to, especially in the processing process. One of the parameters that determine the quality of drinking water treatment is Total Suspended Solid (TSS) or total suspended solids. This is because raw material water for drinking water treatment can come from various sources, namely springs, surface water (rivers, lakes, reservoirs, etc.), groundwater (dug wells, drilled wells) and rainwater which can carry solids in the form of sand, soil, and even mud which can affect the quality of treated drinking water. Almost all industry players agree that TSS measurement is time consuming and requires a lot of additional tools. however, is there an easy, practical, and accurate way that can be used to monitor this parameter.

Benefits of Drinking Water for the Human Body

All organisms need water, more than all other substances. Humans can survive several weeks without food, but only about a week without water. Most of the cells are surrounded by water, and the cells themselves are about 70 – 95% made up of water. Other scientists have also proven that water is a component that affects 60% of body weight. Every system in the body needs water to function properly.

Water in the human body comes from drinking water consumed by humans. Drinking water is defined as water that goes through a processing process or without a processing process that meets health requirements and can be drunk directly.

Water has several functions in the body, namely regulating body temperature, maintaining humidity in the mouth, eyes, and nose, protecting body organs and tissues, helping prevent constipation, helping to dissolve minerals and nutrients, being a joint lubricant, removing waste products of metabolism that are not useful. for the body, and distribute nutrients and oxygen into cells.

Several studies have concluded that everyone’s water needs are different. This depends on several factors such as health conditions, activities carried out, and the environment in which you live. While lack of water can cause dehydration which is a condition that occurs when the body does not have enough water in the body. Mild dehydration can cause a lack of energy and leave the body exhausted.

Drinking Water Treatment Process

The principle of drinking water treatment is based on physical, chemical and biological separation of water from impurities with the aim of obtaining clean and healthy water that meets drinking water quality standards. for drinking water, better known as the Water Treatment Plant (WTP) is an integrated system that functions to treat water from contaminated raw water quality to the desired water quality according to predetermined quality standards.

Each raw water contains many impurities. The following contaminants are found in raw water:

  1. Inorganic ions, such as Na + , Ca 2+ , Mg 2+ , Fe 2+ , K + , Cl , SO 42- , PO 43- , etc. Usually monitored based on the value of its conductivity or resistivity.
  2. Organic compounds, usually measured by the Total Organic Compound (TOC) content, which shows the amount of organic carbon in the water, excluding inorganic carbon such as carbonates, bicarbonates, and dissolved carbon dioxide.
  3. Bacteria, measured in number with a fluorescence microscope such as Coliform bacteria and Eschericia Coli.
  4. Endotoxins and nucleases, measured by specific enzymes.
  5. Dissolved solid particles or particulates, usually measured by filter paper.

In general, WTP consists of 5 processes, namely coagulation, flocculation, sedimentation, filtration, and disinfectant.

  1. Coagulation

In the coagulation process, there is a destabilization process of colloidal particles contained in the raw water source with the aim of separating the water from the impurities dissolved in it. The destabilization process can be carried out in several ways, such as adding a chemical coagulant (coagulant), physically with rapid mixing, or using a mechanical stirring rod.

  1. Flokulasi (Flocculation)

The flocculation process aims to form and enlarge flocs (clots of impurities) in raw water (raw water) whose impurities have been coagulated, usually slow mixing is carried out and chemicals are added flocculant to increase the coagulation efficiency.

  1. Sedimentation

In principle, the process of deposition (sedimentation) based on the specific gravity of each impurity colloidal particles. In this process, there is a deposition of colloidal particles that have been destabilized by the coagulant and a flocculation process occurs, where colloid particles that are larger in density than water will settle below the surface. Currently, the coagulation, flocculation, and sedimentation processes can be combined into one integrated system.

  1. Filtering (Filtration)

The filtration process is the main process in a water treatment plant. This process can use sand media (sand filter), activated carbon (activated carbon), and membrane technology (membrane process) such as Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) or Reverse Osmosis (RO).

  1. Disinfectant (Disinfectant)

The function of the disinfection process is to kill bacteria or viruses that are still present in the water. This process can use chemical compounds such as the addition of chlorine, the ozonation process, the emission of UV rays, or by heating.

It is not only the treatment process that must be considered, but the water quality measurement parameters during the processing also need to be considered. The summary of the stages of WTP and water quality parameters during the treatment process that must be measured and monitored

Monitoring Total Suspended Solid (TSS)

Total Suspended Solid (TSS) or suspended solids are solids that cause water turbidity, are not dissolved, and cannot settle consisting of mud and micro-organisms originating from soil erosion or erosion, and generally consist of phytoplankton, zooplankton, animal waste, waste dead plant and animal remains, human waste and industrial waste carried into the water. Suspended solids in the form of particles carried by the flow of water will affect the amount of TSS inside. The impact TSS on water quality can lead to a decrease in water quality. This condition can cause disturbance, damage and danger to humans if used as drinking water which will have an impact on health.

By taking into account the quality standards of drinking water quality, and the maximum limit of TSS in water treatment, as well as the impact of TSS on human health, it is TSS important to real time. Many methods and tools can be used to measure TSS. One way of measuring TSS in real time can be done with instrument online used is a practical, accurate, efficient and controlled way of measuring TSS in drinking water treatment.

Several factors that need to be considered in the use of online are as follows:

  1. Instruments online used are in accordance with the TSS globally recognized
  2. Easy and practical to use by operators.
  3. Measurements in real time and have data logger that is easy to access.
  4. The controller has a display with good lighting and makes it easier for the operator to read the measurement results.
  5. The controller should have a visual alarm that can alert the operator to the measured TSS threshold value.
  6. Probes Additional controller as measurement sensors should be made of materials that are not easy to corrode and are not easily scratched, such as stainless steel and titanium.
  7. Probes additional controller expected to be used at high temperatures and pressures.

Thus, TSS can be controlled using online that can monitor and maintain the quality of treated drinking water and ultimately produce drinking water that conforms to predetermined quality standards and can be consumed.



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.


Biologycal Treatment of wastewater

Anaerobic biological cleaning of wastewater with UASB process

The RAFA (upflow anaerobic sludge blanket – UASB) reactor method is frequently used for the biological treatment of industrial wastewater. With this process, large amounts of organic substances, such as dissolved sugars, proteins and fats, can also be removed from the wastewater.

These are chemically treated in a special reactor in the absence of atmospheric oxygen by microorganisms, transforming them into biogas. Biogas is a gas mixture that contains mainly methane and carbon dioxide. It can be used as an energy source in production; This generally generates power and heat in a cogeneration plant.

This special version of a biogas plant is mainly used for wastewater treatment in the food and beverage industry, citrus fruit production industry. and in the manufacture of paper and cellulose.

Aerobic biological processes for wastewater treatment

Wastewater cleaning with the MBBR process

The moving bed biofilm reactor (MBBR) process is a technology for the biological treatment of wastewater in which the necessary microorganisms grow as biofilm on a support material.

With the settlement of microorganisms on the surfaces of the filling medium, a large effective surface is generated. The aeration of the reactor ensures that the fluid is permanently mixed and thus sufficient contact of the substances in the waste water with the microorganisms is generated. It is also possible to apply the moving bed process with biofilm anaerobically; in this case, the mixing is carried out with the aid of pumps or with a stirrer.

Both the dominant transverse forces in the bioreactor and the substances in the wastewater influence the thickness and composition of the biofilm on the support material: the higher the content of organic substances in the wastewater, the faster the biofilm will grow.

Advantages of the MBBR process over the activated sludge process

Activated sludge processes have the disadvantage that, by removing the excess sludge, a part of the microorganisms that are in suspension is also removed. Despite the return of the recirculation sludge from the decanter, the microorganisms reach a relatively young age.

In the MBBR process, the microorganisms immobilized on the supports have a substantially longer life. In this way, microorganisms are established in the biofilm that have specialized in difficultly degradable compounds and that have very long generation times. In general, the cleaning process is more stable than activated sludge processes and peak loads can be collected better.

DAS Environmental Expert GmbH uses a support material that has an extremely high specific surface area and thus makes MBBR bioreactors particularly compact. The shape of the filling materials further prevents the support material from blocking, thus achieving a high capacity for continuous space degradation.

Our MBBR plants can be designed as a compact plant or as modular bioreactors. Modular reactors require much less space than conventional activated sludge plants. No excavations or underground works are required. With the corresponding technical process design, our MBBR plant can be built and operated as a denitrification reactor.

Reduced amount of excess sludge in the biofilm process

As in any biological process to degrade organic carbon compounds, an excess of sludge is also generated in the MBBR. In the biofilm process, the quantity is biologically conditioned, but it is clearly lower than in an activated sludge process of equal capacity. However, the already clean wastewater must be separated from the generated sludge after treatment in the MBBR. This can be done for example by sedimentation in a settling tank. In the case of an indirect discharge in another treatment plant, it is possible to evaluate the elimination of a sludge separation, if the capacity and design of the treatment plant allow it and if it can be ruled out that there are unwanted sedimentation processes in the path of transport.

Biological wastewater treatment with the membrane bioreactor (MBR)

The membrane bioreactor (MBR) can also be used for the oxidation and nitrification of organic substances in wastewater. The degradation of toxic substances takes place in this case in a bioventilation tank with a high concentration of sludge.

The separation of the purified water and the activated sludge is carried out by ultrafiltration with the help of the membranes of this reactor. Such a membrane filter module can also be integrated submerged into existing biological treatment phases; however, a separate reactor can be more easily maintained.

The MBR process is ideal for the biological treatment of highly polluted industrial wastewater. In addition, it is often used also for the subsequent clarification of domestic and communal wastewater and for the treatment of gray, rain and surface water.

Due to the small size of the membrane pores, bacteria and viruses cannot pass the membrane filter, so it retains germs. The quality of the water in the purification process thus complies with the EU Bathing Water Directive. Thanks to their compact shape, MBR plants can be designed in a modular way as a container, thus constituting a completely mobile solution. This makes them particularly suitable for limited time use.

Biological cleaning of wastewater with the bacterial bed reactor

In wastewater treatment with a trickle flow reactor (TFR), wastewater is sprayed onto a fixed bed. This consists of a very light fine-grained support material, which after a few days (depending on the respective conditions) grows with a highly active mixed population.

The water flows continuously from top to bottom through the filling material; conversely, the ambient air is supplied to the plant by a fan. Since the load of the support material is not within a closed body of water, little pressure is needed for this. Thus, in the case of TFR technology, a sufficient oxygen supply for microorganisms can be obtained with very little effort. Fully automatic regeneration takes place at regular intervals through which the mixed microbial population is rejuvenated and excess biomass is washed out of the system without causing a loss in yield. Fine sludge can continue to be drained and, depending on site conditions, can be taken to composting or soil conditioning facilities.

Biological wastewater treatment with the SBR process

Sequential biological cleaning (Sequenced Batch Reactor – SBR) is an activated sludge technology for the treatment of wastewater in two separate parts of the plant. A primary settling is first used for the mechanical retention of coarse substances. This also serves as a collecting tank from which the contaminated wastewater is transported to an activation and settling tank called the SBR tank.

There, the incoming wastewater is cleaned in a cyclical process. For this, activated sludge is used, which contains a large number of microorganisms that eliminate organic substances from the wastewater. To ensure good mixing and oxygen supply, the waste water is stirred at regular intervals by supplying air.

This aeration phase is followed by a resting phase without aeration. In this, the activated sludge is deposited on the floor of the facility. On the contrary, in the upper part of the SBR tank a zone of purified water is formed. From this area, the treated wastewater is extracted and led to a drainage channel or an infiltration plant. The excess sludge is removed from the reactor floor by means of pumps. This is sent back to the primary settling. Then the cleaning process starts again.


Wastewater Treatment Procedure

Wastewater Treatment Procedures

There are multiple best available technologies (BAT) procedures for wastewater treatment. Our main competences are the detailed study and conceptual development of this procedure for wastewater treatment.

We works with a wide range of biological and physicochemical procedures for wastewater treatment. Our team develops individual wastewater treatment methods for you, meeting all your needs and requirements.


Biological wastewater treatment

Biological treatment systems aim to degrade organic substances contained in wastewater and reduce ammonium and nitrate loads. Our technology for the biological treatment of industrial and sanitary wastewater offers you the most complete and modern range of biological methods of wastewater treatment. These can be applied flexibly and efficiently in different sectors of industry.

With biological processes for the treatment of wastewater, we help you to comply with the legally prescribed discharge values, to save burdensome supplementary fees imposed on large polluters, to achieve a more respectful production of the environment and to design more efficient processes through the reuse of water.

In most cases, biological processes are also the best solution in the paper and pulp industry, in laundries and in the textile industry, in companies in the food industry and in agro-industry. Biological wastewater treatment facilities are used to degrade organic substances and ammonium and nitrate loads.

Physical-chemical wastewater treatment

Often, the physical-chemical treatment of wastewater consists of sub-steps, beginning with a separation of coarse and fine substances. Depending on the task to be performed, the wastewater can be further treated using a chemical process. By intelligently and efficiently applying the most convenient method, our experts design the solution that best suits your specific needs.

Screens and sieves remove harmful solid substances from the water. This mechanical process separates, for example, diapers, hair, wet wipes and sanitary napkins from the wastewater stream. Before cleaning industrial wastewater, the sieves also capture textile fibers, paper labels, plastic debris or production waste, such as potato peels or other peel debris.

Depending on the scope of application, fine or coarse screens are used. These clean the water by means of bars arranged in parallel. In contrast, sieves have screens, holes, and meshes. With various aperture sizes, from coarse sieves (> 20mm) to micro-sieves (<0.05mm), these separate from solid substances emerging from the coarse garbage resulting from our civilization, to sand and mud particles from the flow of water. sewage water.

Of vital importance is mechanical preliminary cleaning in the treatment of domestic wastewater. Especially the fibers, especially the extremely tear-resistant textile fibers of wet wipes and fleece or non-woven material, which contain the waters represent a challenge. These fibers tend to become entangled and can clog and cause extensive damage to pumps and agitators.


Effluent Analysis

Environmental study and analysis of wastewater for industrial and sanitary use

Projects therefore begin with the study and advice in your plant, in addition to taking samples and laboratory analysis. This process is completed with laboratory-scale testing procedures or the use of an on-site pilot plant.

Our portfolio of services for wastewater analysis

In order to plan new wastewater treatment plants or to improve the performance of existing plants and to optimize them, it is necessary first of all to carry out a comprehensive analysis of the wastewater in question. Basic data such as the volume of wastewater per day of production, the temperature of the wastewater and the available surface area are essential for the overall design of a plant.

In addition, in the laboratory our experts analyze the composition of the wastewater and the substances it contains. With the help of an individual checklist, we together with you draw up a comprehensive table of special parameters, such as:

Analysis of important parameters of wastewater:

  • Chemical and biological oxygen demand (COD; BOD)
  • Polycyclic aromatic hydrocarbons (HAP)
  • Aromatic hydrocarbons (benzene, toluene, ethylbenzene and xylene (BTEX))
  • Concentration of N in ammonium (NH4 ‑ N)
  • NItrogen Nitrate (NO3‑N)
  • Phosphate compounds (PO4 ‑ P)
  • Chloor
  • Heavy metals

Physico-chemical and microbiological laboratory tests of your wastewater

Study of wastewater

The study of wastewater constitutes the basis for the compilation of the basic parameters and the comprehensive development of a wastewater treatment concept. Our portfolio of services begins with the study of wastewater on site or in our laboratory. In addition, we carry out investigations in accordance with the regulatory framework for self-control of wastewater treatment plants, the evaluation of the results of the analyzes, the preparation of technical reports and water and wastewater balances. On this basis we identify the potentials for the optimization of the processes.

Its advantages:

  • Direct laboratory connection with planning and development engineers
  • Consolidated database for the elaboration of a specific procedure concept for the client
  • Recognition of the potential for optimization
  • Cost savings through process optimization
  • Commissioning, sampling and optimization – all from a single source

Study of wastewater in our laboratory

After taking samples on site, we carry out basic studies of the effluent samples in our laboratory to determine their chemical composition, which allows us to develop a laboratory-scale process.

We can perform the following testing procedures for you:

  • Activated carbon tests
  • Ion exchange test
  • Making breaking curves
  • Carrying out biodegradability tests
  • Physical-chemical precipitation and flocculation tests
  • Assays – PAO (advanced oxidation process)

Study of wastewater through pilot plants

On the basis of the preceding laboratory tests and the results of the tests carried out, the project design can begin. Alternatively, it is also possible to design a pilot plant on a semi-industrial scale to carry out tests on site. Our test facilities are completely prefabricated and this enables rapid analysis, even of difficult-to-treat wastewater.



Process optimization with effluent treatment systems

The increase in the volume of wastewater, the modification in the concentration of effluents, the change of the substances contained in the wastewater and / or the modifications of the permits on the use of water make it necessary, many times, to adapt or complement existing technology.

Our wastewater treatment laboratory helps you optimize existing wastewater treatment systems. In this sense, for us the concept of “green chemistry” comes first. That means for us, increasing energy efficiency, reducing environmental pollution, applying analytical methods to control environmental pollution and supporting safer processes.

We evaluate the effectiveness of existing wastewater treatment systems to ensure effective treatment of partial flows or full treatment of direct or indirect input. Our portfolio of services includes, among others:

Biological wastewater treatment:

  • Organic load degradation
  • Nitrification (oxidation of ammonia or ammonium ions to nitrate)
  • Denitrification (reduction of nitrate to basic nitrogen)

Physical-chemical treatment of wastewater:

  • Precipitation / flocculation
  • Separation of unwanted substances
  • Activated carbon processing
  • POA-Advanced oxidation process