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Municipal sewage

Municipal sewage refers to wastewater generated in cities, including wastewater discharged from households, factories, shops, and other places. These wastewaters usually contain various pollutants, such as organic matter, heavy metals, bacteria, etc.
Potential threat to the environment and human health.

Due to the imperfect sewage treatment technology and facilities in the early stages, domestic sewage, industrial sewage, and other sewage were directly discharged to surface water bodies after being treated by the municipal sewage treatment system and reaching standards in the sewage treatment plant.

With the continuous deepening of research on water treatment technology, as well as the development of environmental protection concepts and ecological construction, studies have found that after the effluent from sewage treatment plants is deeply treated, the water bodies that meet the water quality standards are then discharged into river waters or used in other fields, which can alleviate municipal problems—the impact of sewage on the local ecological environment. As time goes by, the quality of the ecological environment will be significantly improved.
 

What are the sources of municipal sewage ?

 
 
  • Domestic sewage: The sewage produced in domestic life, including sewage from kitchens and bathrooms, sewage from washing clothes, etc., all fall into the category of domestic sewage. This sewage enters the municipal sewage pipe network through sewers.
 
  • Industrial wastewater: Wastewater generated during the production process of various factories, enterprises, production bases, etc., including organic wastewater, chemical wastewater, grease wastewater, etc., will be discharged into the municipal sewage pipe network after treatment.
 
  • Medical wastewater: Wastewater generated by medical institutions such as hospitals and clinics contains various medical waste substances and needs to be discharged after strict treatment.
     
  • Commercial wastewater: The sewage produced by commercial places such as restaurants and shopping malls, including kitchen wastewater, clean water, etc., also needs to be discharged into the municipal sewage pipe network and treated.
 
  • Stormwater drainage: The stormwater drainage system is not connected to the municipal sewerage system, but under certain circumstances, such as pipe rupture and debris entering the stormwater pipe, rainwater may be mixed into the municipal sewerage network.
 
These are the main sources of municipal sewage. For different types of wastewater, local governments and environmental protection departments will take corresponding measures and technologies to purify and treat them to ensure that municipal sewage discharge meets ecological standards and protects the environment and public health.
 

What is the significance of municipal sewage treatment and reuse ?

 
First, municipal sewage treatment and reuse can help alleviate water shortage problems. In rapid social development, human society is facing a global water resources crisis. Currently, most countries and regions recognize the importance of sewage reuse for water resource security and have formulated a series of sewage treatment and treatment plans based on their development. Planning for reuse began to develop non-traditional water sources.

Investigations and studies have shown that if the sewage recycling rate reaches 20%, more than half of the city's water shortage will be solved. This shows the importance of municipal sewage treatment and reuse.

Secondly, the treatment and reuse of municipal sewage can maintain ecological balance. It can recycle useful substances in sewage, reduce sewage discharge, significantly avoid municipal sewage pollution of lakes and rivers, protect existing water resources from damage, and avoid eutrophication of water quality. The treated sewage can be used for agricultural irrigation, which has a certain degree of economic utility.

Finally, the treatment and reuse of municipal sewage is conducive to the sustainable development of cities and promotes the growth of towns in the direction of modernization and ecology. Through the top-level design of national government agencies and the entire process of its specific implementation in each town, society's understanding of municipal services can be enhanced. Understanding sewage can guide society in saving water and regulating its water use behavior, thus promoting the long-term and stable development of the city.
 

What are the methods for municipal sewage treatment?

According to different treatment principles, sewage treatment methods can be divided into physical treatment methods, chemical treatment methods and biological treatment methods:
 
  • Chemical treatment
    It uses chemical reactions to separate and recover pollutants in various forms in sewage, mainly including neutralization, coagulation, electrolysis, redox, air flotation, extraction, adsorption, ion exchange, and electrodialysis, etc.;
  • Biological treatment
    It uses the metabolism of microorganisms to convert dissolved and colloidal organic pollutants in sewage into stable and harmless substances. Biological treatment methods are divided into aerobic biological treatment and anaerobic biological treatment.
  • Physical treatment method
    It uses physical effects to separate pollutants in sewage, specifically including screening, sedimentation, flotation, filtration, and membrane methods;
 
Municipal sewage mainly comprises urban domestic and industrial wastewater that meets the "Water Quality Standard for Sewage Discharge into Urban Sewers." The composition and concentration of municipal sewage pollutants in different regions vary greatly, and combining the above methods is often required to remove different properties Of pollutants to meet reuse standard requirements.
According to the degree of treatment, sewage treatment methods can be divided into primary, secondary, and tertiary treatment:
 
  • Primary treatment
    It mainly removes floating and suspended solid pollutants in sewage, also known as pretreatment or secondary treatment;
  • Secondary processing
    It mainly removes organic pollutants in colloidal and dissolved states (i.e., BOD, COD substances) in sewage, usually using biological treatment;
  • Tertiary treatment
    It is used to remove refractory organic matter, nitrogen, and phosphorus further after primary and secondary treatment. The main methods include biological denitrification and phosphorus removal, coagulation precipitation, activated carbon adsorption, ion exchange, electrodialysis, and membrane Methods, etc., and tertiary treatment is often used as supplementary treatment after secondary treatment, such as for sewage recycling and reuse, also known as an advanced treatment.
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What are the main processes for municipal sewage treatment ?

 

The role of air flotation in municipal sewage treatment:

 
Solid-liquid separation: The air flotation method injects air bubbles into the water to cause the tiny particles suspended in the water to gather into more giant air bubbles and then float them up through buoyancy, thus achieving the separation of particulate matter and water. This helps remove suspended solids, solid particles, floating matter, etc., improving water quality.

Dissolved gas removal: During the rise of bubbles, many gases and tiny particles accumulate on the surface of the bubbles. It can also be used to remove dissolved gases, such as carbon dioxide, in water.

Removal of grease and suspended sediments: The air flotation method is very effective in removing grease, suspended sediments, and other impurities in municipal sewage. Through air flotation technology, these grease and particles can condense on the water surface to form scum, which facilitates subsequent treatment.

Pre-treatment: Air flotation is usually used as a pre-treatment link in the municipal sewage treatment process, which can effectively reduce the load of subsequent process units, protect membranes, biological filters, and other equipment, and improve treatment efficiency.

In general, as a mature water treatment technology, the role of air flotation in municipal sewage treatment is mainly reflected in solid-liquid separation, removal of suspended solids and grease, and removal of dissolved gases. It is essential for improving sewage treatment efficiency and water quality. It plays a vital role in promoting.
 
Application case(Preprocessing-physical method)
Qinhuangdao-Hongqisheng-Precision-Electronics-Organic-Wastewater-Project.jpg
Case Studies-Qinhuangdao Hongqisheng Precision Electronics Organic Wastewater Project

The organic wastewater generated during the preparation and treatment of PCB circuit boards contains a lot of nickel. The chemical precipitation method balances the water quality and quantity of the nickel-containing wastewater, then passes through a pH adjustment tank with a pH value of about 3~4. Fenton reagent is added to the oxidation tank to convert the hypophosphite in the nickel-containing wastewater into orthophosphate to complete the wastewater decomposition. The wastewater is then introduced into an alkalization tank, and an aqueous solution of calcium hydroxide is added to generate nickel hydroxide and calcium phosphate precipitates. A polymer flocculant is added, and precipitation is carried out using a high-efficiency inclined plate sedimentation tank.

READ MORE
Industrial-wastewater-Treatment.jpg
Case Studies-Dongtai Bizhiyuan Water Purification Industrial Wastewater

Yancheng Dongtai Bizhiyuan Water Purification Co., Ltd. Industrial Wastewater Treatment Plant. After being treated by flotation equipment, the effluent indicators meet the following requirements: SS≤ 10 mg/L, TP≤ 1.8 mg/L. The SS removal rate is ≥90%, and the TP removal rate is ≥70%.

READ MORE

Biofilter technology

 
Biofilter technology is a commonly used biological treatment process for wastewater treatment and water quality improvement. I use fixed or suspended biofilm to degrade and remove organic matter, ammonia, nitrogen, and other pollutants in wastewater.

This technology forms a biofilm by attaching microorganisms to the media filler. The biofilm provides many tiny voids and pores, allowing wastewater to pass smoothly and providing a rich biologically active area. At the same time, an aeration system is used to supply oxygen to aerobic microorganisms to meet their metabolic needs. Pollutants such as organic matter and ammonia nitrogen in the wastewater are degraded by microorganisms on the biofilm to complete water purification.

Because the biofilm provides a large attachment surface area and can accommodate many microorganisms, it has higher treatment efficiency. At the same time, the biological filter does not require additional chemicals, only appropriate aeration equipment is provided, and the operating cost is low. This technology is widely used in industrial wastewater treatment, urban sewage treatment, rural domestic sewage treatment, and other fields.
 
Have technical questions about your wastewater application ? 

UNITANK wastewater treatment process

 
The UNITANK sewage treatment process is developed under the continuous optimization of SBR sewage treatment technology. This process is also called the activated alternating sludge treatment process. The use of this process requires the support of a specific treatment tank. The shape of the sewage treatment tank is as follows: There need to be three rectangles in number, and they must be three different rectangles. The specific process for using them is as follows:

According to the situation of the sewage treatment tank, set up special oxygen supply facilities for it, and make holes in the wall or bottom channel to ensure that the three sewage treatment tanks can be connected; place the sewage treatment tank responsible for aeration in the middle, the remaining two are placed on both sides so that they can have the functions of sedimentation and aeration and unique sludge and water discharge outlets are designed on each sewage treatment;

During the municipal sewage treatment process, it is ensured that these three sewage treatment tanks can be interactively processed to balance and stabilize the drainage and water inflow conditions, thereby completing the entire process of the UNITANK sewage treatment process.

This process has significant advantages in municipal sewage treatment. It can effectively control the reaction time, degrade organic matter in sewage, and remove phosphorus and nitrogen well. At the same time, its alternating sewage treatment can be applied to the treatment of different wastewater to achieve Stable handling.

However, the system operation control management of this process is more complex and is more suitable for smaller-scale projects. It needs to be reasonably selected based on the characteristics of the project itself.
 

A2/O activated sludge technology

 
A2/O activated sludge technology is a commonly used biological treatment process for treating organic matter and ammonia nitrogen in wastewater. This technology combines anaerobic, anoxic, and aerobic links to convert sewage's organic matter and nitrogen compounds into harmless substances through microbial metabolism in sludge.

In the anaerobic stage, sewage undergoes fermentation by anaerobic microorganisms to decompose organic matter into small organic molecules that are efficiently utilized;

In the anoxic stage, anoxic microorganisms use the metabolites produced in the anaerobic stage as electron donors to decompose further and remove organic matter in the wastewater;

In the aerobic stage, in an aerobic environment, aerobic microorganisms use oxygen as an oxidant to convert organic matter and ammonia nitrogen in the water into carbon dioxide, water, and nitrates. This technology has the advantages of solid processing capacity and stable effluent quality. It is suitable for small and medium-sized urban sewage treatment plants, industrial wastewater treatment, rural sewage treatment, and other fields. Efficient and reliable wastewater treatment and resource recovery can be achieved through reasonable regulation and management. The process flow of A2/O activated sludge technology is shown in the figure.
 
A2 /O activated sludge technology process flow chart

Ultrafiltration sewage treatment process

 
The ultrafiltration sewage treatment process mainly uses the physical properties of impurities in sewage and the physical properties of the sewage itself to screen it to achieve liquid separation, which requires it to be under static pressure.

In the actual application process, technicians are required to formulate specific operation plans based on the sewage conditions, select ultrafiltration microporous membranes composed of molecular membranes and inorganic membranes, and apply pressure to the liquid in a targeted manner, allowing the ultrafiltration microporous membranes to It adsorbs polymer particles and colloids suspended in sewage to ensure that the surface of the ultrafiltration microporous membrane has screening properties and can intercept impurities in sewage as it passes through.

During the application process of the ultrafiltration sewage treatment process, attention should be paid to the treatment of the treatment environment, including working temperature, applied pressure, etc., to ensure that the work efficiency can meet the requirements of the ultrafiltration treatment process. Regarding specific environmental treatment, staff can select the optimal permeability amount based on relevant parameters such as operating pressure, operating cycle, and liquid flow rate, thereby improving its treatment effect on sewage.
 

AB sewage treatment process

 
The full name of the AB sewage treatment process is the adsorption biodegradation method. It is different from the traditional sewage treatment process. It does not have facilities such as a primary sedimentation tank and is a high-load treatment method.

Its application method divides the aeration tank into two high and low load stages AB, and sets up exclusive backflow systems and sludge sedimentation, respectively.

Section A is a high-load section. The average time for sewage in this stage is 30 minutes. During this 30-minute process, Section A can use the activated sludge's flocculation, sedimentation, and easy adsorption through the adsorption and degradation of activated sludge. Characteristics: it can quickly adsorb organic matter in municipal sewage, carry out corresponding degradation and differentiation work, and reduce the load of return effluent as much as possible. The selected adsorption organisms are generally community bacteria with a short mud age.

Section B is a low-load section, and its treatment method for municipal sewage is somewhat similar to conventional sludge treatment methods.

The main advantages of the AB sewage treatment process application are that it can treat sewage in two stages, has high decontamination efficiency, can ensure the stability and safety of the treatment system operation, and has good load and impact resistance.

In addition, the process has a shorter residence time and low consumption of power resources, which can reduce municipal sewage treatment costs to a certain extent. However, due to the high concentration of effluent water quality, this process can only be applied to projects with low effluent water quality requirements. Moreover, this process's denitrification and phosphorus removal effect is not ideal, so it is not widely used in actual projects.
AB method sewage treatment process composition diagram

Municipal wastewater reuse technology

Coagulation sedimentation advanced treatment technology

 
When conventional secondary treatment effluent contains suspended solids that are difficult to remove, advanced treatment technology for coagulation sedimentation can be considered.

This technology adds a coagulation tank after the secondary treatment of water. By adding chemicals to the sewage, the suspended matter in the water gathers into larger flocs under the action of flocculants. Then, it separates from the water body through sedimentation or air flotation, improving effluent water quality.

Coagulation and sedimentation technology includes three processes: mixing, coagulation, and flocculation. After the coagulation reaction is completed, the solid-liquid separation facility can effectively remove suspended solids with a particle size of 1 nm to 100 μm in the original secondary effluent. This technology is economical and mature, but the treatment effect is easily affected by changes in water quality, and its improvement in water quality is limited, and its application scope is limited.
 

Desalination wastewater reuse technology

 
The reuse direction of sewage needs to be consistent with the water quality after treatment. In the design of desalination sewage treatment, the chemical sludge separated from the sewage needs to be effectively treated.

For example, sludge containing rich chemical substances can be mixed and used in other industrial production fields to ensure that no secondary pollution is caused by sludge and to achieve high-efficiency and more environmentally friendly sewage reuse. In addition, during the treatment process, it is necessary to select appropriate technical means based on the use of recycled water.

Taking desalination sewage treatment technology as an example, desalted water is mostly used in industrial reuse technology. After the raw water is removed with lime and soda ash, the reused water is treated through a membrane device until it reaches the water standards of relevant industries.
 

Selective reuse technology mainly focuses on the method and direction of its reuse link. There are generally three methods:

  • Partition reuse method
    That is, specific municipal areas will be used as the basic units for sewage collection and reuse. Through reasonable planning by relevant departments, reuse pipes will be used as a way to reuse sewage to provide water resources for people's activities in the area. This technology is suitable for areas not far from sewage treatment plants.
  • Whole process reuse method
    That is, municipal sewage is collected and treated through the municipal drainage pipe network system and then reused through the pipe network.

    In selecting this municipal sewage reuse technology, it is necessary to realize that it has high-scale requirements for sewage treatment plants, and it needs to build a complete municipal sewage pipe network system to achieve it, which is suitable for new cities.
  • Selective reuse
    That is, they should selectively lay reuse pipelines, design the pipelines around large municipal buildings and residential areas, recycle the sewage generated, and establish small sewage treatment points at appropriate locations to treat small-scale sewage. The treated sewage will be used in municipal greening and other aspects to improve the utilization rate of water resources.

    Compared with the previous two technical methods, which are flexible, simple, and convenient, this technology can better adapt to the different sewage treatment needs of different regions, improve the consistency between demand and system supply, and ensure the health of the municipal government. develop.

Contact-limited recycling technology

 
At this stage, contact-limited reuse technology is a critical technical means for municipal sewage reuse. It is suitable for use when there are high requirements for recycled water.

Under normal circumstances, the qualification index of reused water is judged based on whether it can meet the water quality needs of the corresponding reuse point. In the actual treatment process, three-level treatment methods are often applied to control harmful substances in municipal sewage and ensure effectiveness. Its content in water can meet national control standards, so it can be put into the recycling process to realize the reuse of water resources.

At the same time, the three-level treatment method needs to be designed in strict accordance with relevant specifications for contact and restricted water reuse. At the same time, relevant units need to strengthen technical training and safety education for staff and their sewage treatment operations. Supervision is required to avoid losses caused by illegal operations, promote the safety and stability of municipal sewage reuse, and strengthen the balance between sewage discharge and reuse so that water resources can be effectively protected.
 

Membrane separation technology

 
Membrane separation technology is a method that uses unique membrane materials to treat wastewater and improve water quality.

It uses a semi-permeable membrane to separate suspended solids, dissolved organic matter, microorganisms, and ions in wastewater, thereby filtrating, concentrating, and removing specific wastewater components. Depending on the target pollutants, membrane materials can be divided into microporous membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes.

Microporous filtration membranes are usually used to remove particulate matter; ultrafiltration membranes can remove bacteria, colloids, and high molecular organic matter; nanofiltration membranes can remove dissolved organic matter and ions; reverse osmosis membranes can remove dissolved matter, ions, and microorganisms.

Membrane separation technology has the advantages of high treatment efficiency, stable water quality, a small footprint, and relatively simple operation and management. It is widely used in the standard improvement and transformation of sewage treatment plants.
 

Chlorination disinfection technology

 
Chlorination disinfection technology is a commonly used advanced treatment technology. It adds chlorine-containing chemicals such as chloride or hypochlorite to sewage to cause oxidation reactions with microorganisms in the wastewater, causing oxidation, dehydrogenation, chain scission, etc., function, thereby killing microorganisms.

The disinfection effect of this technology is affected by many factors, including chlorine concentration, contact time, water temperature, pH, and organic matter content in the sewage. Generally speaking, the higher the chlorine concentration and the longer the contact time, the better the disinfection effect.

However, chlorine disinfection is not sensitive to certain chlorine-resistant microorganisms or chemicals and can produce disinfection by-products. Therefore, when selecting a disinfection method, water quality characteristics, target disinfection effects, and environmental factors should be comprehensively considered and combined with other disinfection technologies for comprehensive treatment.
 
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