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A Comprehensive Guide to Chemical Dosing Systems


Nowadays, chemical dosing is widely used in wastewater treatment solutions. Many wastewater treatment equipment manufacturers utilize this method/ principle to built high-performance and reliable wastewater treatment equipment. Here, this blog will provide a comprehensive guide to chemical dosing systems. And we hope this blog will help you better understand these systems and make better choices when necessary.

What Are Chemical Dosing Systems?

Chemical dosing is the transfer of chemicals to sewage, foul water or sludge-like fluids. It is often in preliminary wastewater treatment, as part of an anaerobic digestion process to extract energy from waste and clean industrial wastewater to be returned to natural waterways.

Chemical dosing systems are the facilities used to automatically inject reagents into a wastewater network to control septic tanks and odour emissions. The purpose of these systems is to control the level of the main odour source, H2S in the wastewater. A right system can bring an improvement of 95%. Because H2S is corrosive, chemical dosing can also prevent corrosion-related failures. In addition, Jinwantong systems ensure compliance with work health and safety (WHS) regulations.

Chemical dosing systems are commonly utilized in pump stations, sewer manholes, and rising mains. However, they can also be installed in any location where odour containment is necessary.

Chemical Dosing Systems

Types of Chemical Dosing Systems

According to the configurations they use, chemical dosing systems are commonly divided into three types: ferrous dosing systems, magnesium hydroxide dosing systems, and calcium nitrate dosing systems.

Ferrous Dosing System

Ferrous dosing is a kind of chemical dosing utilized to eliminate up to 95% of industrial odors. One of the main advantages of ferrous dosing is that it eliminates the cause of odors. By reducing the hydrogen sulfide gas content formed by chemical reactions in wastewater treatment, the ferrous dosing system can eliminate odors at the molecular level.

Due to a large amount of hydrogen sulfide gas produced, the smell of sewers is often a problem. The gas generation is caused by the decomposition of sulfates in the anaerobic reaction to form sulfides. Then, hydrogen is combined with these sulfides to generate hydrogen sulfide gas. In this case, chemical dosing systems can be the solution.

Ferrous dosing systems use ferric chloride or ferrous chloride as the dosing agent in wastewater. Biochemical reactions in wastewater produce sulfides. Unless other reactions are initiated, the sulfides will further react to form hydrogen sulfide gas, which generates the odor. Ferrous dosing causes the sulfide to combine with the dosing agent, which forms a precipitate in the waste stream. In this way, the formation of hydrogen sulfide is suppressed and the odour is reduced.

Ferrous dosing units can be introduced into sewer systems in a variety of ways, together with controllers custom-designed to match the specific application. The very best means of introducing ferrous dosing into sewage systems would be to dose into the rising main. In this case, the dose rate is readily controlled with the flow of the sewer.

The speed of chemical dosing in ferrous dosing systems can also be adjusted by two other ways. One is a direct connection between the pump control device and the sewer pump. The other is that an information transfer through the inline flow meter to the dosing controls. For pressure sewer systems, the latter is a good choice.

Magnesium Hydroxide Dosing System

Magnesium hydroxide dosing systems are specifically targeted at the production of hydrogen sulfide. This kind of chemical dosing systems consists of a storage container for chemical reagents (in this case, magnesium hydroxide), a syringe pump, and a control panel. Magnesium hydroxide dosing systems are usually located in sewer manholes, pumping stations or ascending mains. Sometimes they can even be injected directly into the sewer stream. The feed rate of chemical dosing depends on the flow of the wastewater stream.

SRBs that produce hydrogen sulfide thrive under specific biological conditions. In addition, the amount of hydrogen sulfide released from water depends on certain chemical conditions (for example, dissolved sulfide concentration, water temperature and pH, and turbulence of flow in sewers). This kind of chemical dosing systems work by changing these chemical conditions. At pH 7, roughly 50% of the dissolved sulfide can still exist as hydrogen sulfide. However, when the pH is increased to between 8 and 8.5, the concentrations will be fundamentally changed. When the pH value is lower than 6, the dissolved hydrogen sulfide and gaseous hydrogen sulfide will increase, but when the pH value is higher than 8, the sulfide will exist in the form of HS and remain in the chemical dosing solution, while the hydrogen sulfide gas will tend to zero. Therefore, controlling the pH value above 8 by adding magnesium hydroxide will reduce the presence of hydrogen sulfide and eliminate offensive odour. 

Another benefit of magnesium hydroxide is its effect on solids. The suspended solids are broken down and the heavy metals in the solution are removed. The sludge in the waste liquid treated with magnesium hydroxide can be directly processed to a landfill, thereby saving the cost of sludge treatment.

Calcium Nitrate Dosing System

Calcium nitrate is used in chemical dosing systems to reduce industrial odour to 90% by preventing wastewater from turning into septic tanks. One of the great advantages of calcium nitrate dosing systems is that they are harmless and biologically friendly, while still effectively controlling odour and corrosion.

Calcium nitrate dosing systems are commonly used in municipal wastewater and industrial water treatment facilities. All these dosing systems may be constructed within a shipping container, for easy transportation and short-term chemical dosing. Additionally, fenced compounds, metal enclosures or concrete cabin enclosures can be used to secure the chemical dosing systems.

In untreated wastewater, bacteria can cause chemical reactions that can produce active sulfides in solution. Hydrogen molecules combine with these sulfides to form a malodorous hydrogen sulfide gas. The nitrate in chemical dosing solutions provides an alternative source of oxygen that can disrupt the formation of hydrogen sulfide. Lower hydrogen sulfide concentrations mean less odour, less corrosion to assets and compliance with WHS regulations.

At Jinwantong, we are experts in chemical dosing and comprehensive odour control technology. We have over 13 years of experience. During this time, we have earned a reputation for innovative and reliable products. If you have any question about chemical dosing systems in wastewater treatment, you can contact us for professional answers.

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