[Hongjie Water Service] Water Treatment Knowledge - Related Processes of Wastewater Treatment

Water treatment engineering mainly includes water supply treatment engineering and sewage treatment engineering.

Water treatment mainly refers to the process of clarifying, filtering, disinfecting, deodorizing, deodorizing, deodorizing, removing iron, softening, desalination, and desalination of raw water to remove various harmful impurities in the raw water, making it meet the water quality standards for people's daily life and production. Pure water preparation, seawater desalination, and drinking water preparation all belong to the scope of water treatment.

Wastewater treatment mainly refers to the purification of wastewater through physical, chemical, physicochemical, and biological processes, in order to meet the standards of discharge to a certain water body or reuse. Wastewater mainly includes domestic wastewater, production wastewater (including industrial wastewater), surface water, etc., with a wide range of categories. In daily life, people often mix concepts such as sewage, wastewater, and reclaimed water, which essentially belong to the concept of sewage. The sewage mentioned later is mainly industrial wastewater, so there may be situations of mixed use of wastewater and sewage.

Wastewater treatment is divided into primary treatment, secondary treatment, and tertiary treatment according to different levels of treatment.

Primary treatment: mainly removes suspended solid pollutants from wastewater, while most physical treatment methods can only meet the requirements of primary treatment. After primary treatment of sewage, BOD can generally be removed by about 30%, which does not meet the discharge standards. The first level processing belongs to the preprocessing of the second level processing.

Secondary treatment: mainly removes colloidal and dissolved organic pollutants (BOD, COD substances) from wastewater, with a removal rate of over 90%, making organic pollutants meet discharge standards, equivalent to the core process of water treatment.

Third level treatment: Further treatment of recalcitrant organic matter, nitrogen, phosphorus, and other soluble inorganic substances that can lead to eutrophication of water bodies. The main methods include biological denitrification and phosphorus removal, coagulation precipitation, sand filtration, activated carbon adsorption, ion exchange, and electroosmotic analysis.

Because the meaning of sewage is very broad, in real life, sewage treatment is often composed of multiple different types of sewage mixed together. Even for the same type of sewage, there are differences in process selection due to the high and low content of toxic and harmful substances in it. So in the process of sewage treatment, it is necessary to flexibly apply treatment processes and skillfully choose to merge or treat different types of sewage separately.

There are many methods for classifying sewage treatment processes, and we choose relatively common physical, chemical, and biological methods for classification. Choosing the corresponding process, combined with specific membrane treatment processes (such as electrodialysis, reverse osmosis, ultrafiltration, nanofiltration, microfiltration, etc.), can meet the majority of wastewater treatment process requirements.

Physical method: a physical or mechanical separation method. Common physical methods include precipitation, centrifugal separation, and flotation.

Chemical method: adding chemical substances to react with toxic and harmful substances in wastewater, achieving the purpose of digestion or separation. Common chemical methods include neutralization, oxidation, reduction, decomposition, coagulation, chemical precipitation, etc.

Physical chemistry method: Using the separation principles of physical chemistry to achieve the state separation of specific substances. Common physical and chemical methods include gas extraction, stripping, adsorption, extraction, ion exchange, electrolytic electrodialysis, reverse osmosis, etc.

Biological method: Utilizing the metabolism and degradation of microorganisms to transform organic matter into inorganic matter in wastewater. Common biological methods include aerobic, anaerobic, and enzymatic methods.

Several common process supplementary explanations:

Coagulation: The process of aggregating colloidal particles and small suspended solids in water through a certain method, such as adding chemical agents. Coagulation includes two processes: coagulation and flocculation. Coagulation mainly refers to the process of colloid destabilization and generation of small aggregates, while flocculation mainly refers to the process of destabilized colloid or small suspended particles coalescing into large flocculents. Agents that can play a corresponding role in coagulation and flocculation are collectively referred to as coagulants.

Common coagulants include polyaluminum chloride (PAC), ferrous sulfate, ferric chloride, polyacrylamide (PAM), etc.

The results of coagulation are influenced by various conditions such as the composition of sewage pollutants, pH, water temperature, and water flow. Different coagulants are selected according to different situations. When the pH value is generally alkaline or weakly alkaline, the coagulation and precipitation effect is better.

PH (acid-base) neutralization: also known as pH regulation, refers to the addition of a certain pH regulator to a wastewater solution in order to achieve the expected pH value. Common pH regulators include quicklime (calcium hydroxide), caustic soda (sodium hydroxide), various strong acids, and citric acid.

Oxidation-reduction method: The pollutants in wastewater are oxidized or reduced to transform into non-toxic and harmless new substances, achieving the purpose of treatment. Common redox methods include chemical oxidation, Fenton oxidation, wet oxidation, electrochemical method, photocatalytic oxidation, etc. The most commonly used oxidants include air (oxygen), ozone, chlorine gas, sodium hypochlorite, etc. The most common reducing agents include ferrous sulfate, iron filings, sodium bisulfite, sodium borohydride, etc.

1. Chemical oxidation method: A treatment technology that uses oxidants such as ozone, chlorine gas, potassium permanganate, chlorine dioxide, hydrogen peroxide, etc. to oxidize pollutants in wastewater into carbon dioxide and water.

Process characteristics: Simple process, fast reaction speed, and high cost of reagents. Chlorinated oxidants are mainly used for the treatment of wastewater containing phenols, cyanide, and sulfur.

Note: The ozone oxidation method also has the effect of sterilization, increasing the oxygen content in water, and reducing COD and BOD in wastewater.

2. Fenton oxidation method: A method of treating wastewater using Fenton reagents that combine ferrous ions with hydrogen peroxide. It is suitable for the treatment of organic wastewater such as ethers, nitrophenols, chlorophenols, aromatic amines, and polycyclic aromatic compounds that are difficult to degrade by biological and general chemical oxidation methods.

Process characteristics: The process is complex, efficient, low consumption, and has no secondary pollution.

Reaction mechanism: Under the catalysis of Fe2+, H2O2 produces active hydroxyl radicals · OH, which can decompose organic and reducing substances into inorganic substances such as CO2 and H2O.

There are two development trends in Fenton technology, one is photo Fenton technology that introduces ultraviolet light into the system, and the other is electro Fenton technology that combines Fenton reaction with electrolysis. The electric Fenton technology has advantages such as in-situ generation of H2O2 and Fe2+, increased mixing degree of sewage treatment through aeration, and assisted treatment of sewage through anodic oxidation and electro adsorption.

3. Wet oxidation method: It is a treatment process that uses oxygen or oxygen in the air to oxidize difficult to degrade organic matter in wastewater under high temperature and high pressure conditions, causing it to oxidize and decompose into easily biodegradable small molecule organic and inorganic substances.

Process characteristics: wide application range, high efficiency, speed, low pollution, and some substances can be recycled and reused. Widely used in the treatment of industrial wastewater such as cyanide containing wastewater, coal gasification wastewater, sulfur-containing wastewater, phenolic wastewater, and papermaking black liquor.

4. Electrochemical method: The process of using electrodes to generate strong oxidants, gases, or flocculants through electrochemical reactions in wastewater, in order to remove pollutants from the wastewater. According to the principle of action, it can be divided into electrolytic oxidation, electrical flotation, electrocoagulation, etc.

Electrolytic oxidation can be divided into direct electrolysis and indirect electrolysis. Direct electrolysis directly oxidizes or reduces pollutants on the electrode to remove them, while indirect electrolysis uses strong oxidants such as hydroxyl radicals and hypochlorite ions generated on the electrode surface under the action of an electric field to convert pollutants into easily degradable or harmless substances, purifying wastewater.

Electrical flotation is the use of gases generated during the electrolysis process, such as chloride ions in wastewater, which can cause chlorine gas to overflow, causing volatile impurities and light suspended solids in wastewater to float on the surface of the wastewater, thereby achieving the effect of wastewater purification.

Electroflocculation is the process of electrochemical treatment of wastewater that consumes iron or aluminum anodes to form iron or aluminum salt flocculants in the wastewater, removing colloids and suspended substances.

5. Photocatalytic oxidation method: Using N-type semiconductors such as TiO2 and ZnO as catalysts, combined with light to promote chemical reactions, organic pollutants in wastewater are oxidized and converted into non-toxic and harmless CO2 and H2O.

The mechanism is that under the irradiation of light, semiconductors cause water molecules to lose electrons, producing · OH with strong oxidizing ability, leading to the oxidation of various organic substances in wastewater. The effectiveness of photocatalytic treatment of wastewater is related to catalyst crystal structure, crystallinity, specific surface area, light intensity, pH, reactor, etc.

Aerobic method: A method of using aerobic microorganisms to degrade and metabolize wastewater under aerobic conditions. Common aerobic treatment methods include activated sludge method, biofilm method, biological contact oxidation, and biological fluidized bed method.

Anaerobic method: A method of treating wastewater through anaerobic microbial degradation and metabolism under anaerobic conditions. Common anaerobic treatment methods include anaerobic pond method, anaerobic filter bed method, anaerobic flow bed method, anaerobic expansion bed method, anaerobic rotating disc method, anaerobic tank method, upflow anaerobic sludge bed (UASB) method, etc.

The operating conditions of anaerobic method are more stringent than aerobic method, but the overall cost is lower. Usually, in order to achieve better treatment results, aerobic and anaerobic methods are combined.

Biological enzyme method: Organic matter forms free radicals through enzyme reactions, and then the free radicals undergo chemical polymerization reactions to form polymer compound precipitates.

More information can be found on the official website of Shenzhen Hongjie Water Technology Co., Ltd. www.execro.com. If you need it, you can call the company's hotline for free at 180 3800 0078, and we will be happy to serve you.