Principles, Equipment Selection, Process Design, and Typical Cases of Chemical Wastewater Treatment

As industrial production scales continue to expand, suspended solids, colloids, organics, heavy metals, ammonia nitrogen, sulfides, chromaticity, and other refractory pollutants in industrial wastewater are becoming increasingly complex. A single treatment method is often difficult to simultaneously meet discharge, reuse, and environmental management requirements. Therefore, chemical wastewater treatment is widely applied in industrial wastewater pretreatment, advanced treatment, and comprehensive wastewater treatment systems.

Chemical treatment methods mainly utilize chemical reactions, substance transformation, and mass transfer processes to cause pollutants in wastewater to undergo neutralization, oxidation-reduction, coagulation, precipitation, adsorption, or phase transfer. Subsequently, unit operations such as precipitation, filtration, and flotation are used to achieve the separation of pollutants from the water body.

For actual projects, selecting wastewater treatment equipment is not simply choosing a single piece of equipment. Instead, it requires establishing a complete process route by combining factors such as influent water quality, wastewater volume, pollutant types, treatment targets, discharge requirements, operating costs, and subsequent sludge disposal.

ECOLINK TECHNOLOGY focuses on product matching, technical support, and one-stop services for water treatment chemicals and equipment. We assist customers in analyzing chemical treatment processes, reagent configurations, and equipment combination schemes according to the characteristics of different industrial wastewaters.

I. What is Chemical Wastewater Treatment?

Chemical wastewater treatment is a category of treatment technologies that utilizes chemical reactions and mass transfer actions to separate, remove, or transform pollutants in wastewater.

Compared with methods that rely solely on physical separation, chemical treatment can target partial dissolved pollutants, colloidal pollutants, and pollutants with specific chemical properties. For example:

Acidic or alkaline pollutants can be adjusted through neutralization reactions;

Colloids and fine suspended solids can form larger flocs through coagulation;

Part of the dissolved metal ions can be converted into insoluble substances through chemical precipitation;

Certain organics or inorganics can be transformed through oxidation-reduction reactions;

Residual organics, chromaticity, and other pollutants can be further removed using adsorption materials such as activated carbon.

Therefore, chemical treatment units in industrial wastewater treatment typically do not exist in isolation, but are combined with processes such as adjustment, sedimentation, filtration, air flotation, biochemical, or membrane treatment.

II. What are the Common Chemical Treatment Processes?

According to different pollutant properties and treatment targets, chemical treatment processes can be classified into multiple types.

1. Neutralization Method

The neutralization method mainly adjusts the pH value of wastewater to bring it to neutral or close to a suitable treatment range.

In industrial wastewater, excessively high or low acidity and alkalinity may not only affect subsequent treatment units, but also cause equipment corrosion and abnormal subsequent chemical reactions. Therefore, pH adjustment is often an important frontline step in wastewater treatment processes.

In actual engineering, the neutralization process needs to consider:

Influent pH changes;

Acid and alkali concentrations;

Water volume fluctuations;

Reagent dosing methods;

Agitation intensity;

Reaction time;

pH requirements of subsequent treatment processes.

Common equipment includes regulation tanks, online pH monitoring systems, dosing systems, and agitation reaction equipment.

2. Coagulation Method

Coagulation is a very common chemical treatment method in industrial wastewater treatment.

Colloidal particles in wastewater usually have good stability and are difficult to settle rapidly relying solely on gravity. By dosing coagulants, colloidal stability can be reduced, causing fine particles to aggregate.

On this basis, water treatment chemicals such as polyaluminum chloride (PAC) and polyacrylamide (PAM) can also be used to further promote floc formation.

The typical process can be represented as: Wastewater - Coagulant Dosing- Rapid Mixing -Flocculation Reaction - Floc Formation - Sedimentation/Flotation Separation

Among them, the coagulant is responsible for destroying colloidal stability, while the flocculant helps form more distinct and easily separable flocs.

Under different water quality conditions, reagent types, dosing amounts, reaction times, and agitation conditions all need to be determined through beaker tests or field trials.

III. How Does Chemical Precipitation Remove Dissolved Pollutants?

Although coagulation and chemical precipitation are frequently combined for use, their action mechanisms are not completely identical.

The chemical precipitation method mainly uses the addition of precipitants to cause chemical reactions with dissolved pollutants in wastewater, forming precipitates that are insoluble in water.

For example, in some industrial wastewaters, heavy metal ions can be converted into insoluble compounds through appropriate precipitation reactions, and then achieved through sedimentation or filtration for solid-liquid separation.

The typical flow is: Pollutant Analysis - Reagent Selection-Chemical Reaction -Precipitation Generation - Solid-Liquid Separation - Subsequent Treatment

For heavy metal wastewater, reagents cannot be determined simply based on pollutant names; metal types, concentrations, pH, complexation states, and final discharge requirements must also be considered.

Therefore, the design of chemical wastewater treatment schemes should take actual water quality testing and experimental results as an important basis.

IV. Oxidation-Reduction Method: An Important Means to Treat Refractory Pollutants

The oxidation-reduction method uses oxidants or reductants to change the chemical properties of pollutants, degrading or transforming them into substances with lower toxicity or easier treatment.

Depending on pollutant properties, different oxidation-reduction systems can be adopted.

In the attached case, the wastewater of a certain chemical plant contains a large amount of ammonia nitrogen, sulfides, and organics, and is treated using a combined process of regulation, oxidation, coagulation, flotation, filtration, and disinfection.

Among them, wastewater first enters the regulation tank to adjust water volume, water quality, and pH value, then enters the oxidation reactor where chlorine gas and oxygen are added for oxidation-reduction reactions, converting ammonia nitrogen and sulfides into harmless nitrogen gas and sulfates.

Such processes illustrate that in actual industrial wastewater treatment equipment systems, chemical reaction units typically need to operate synergistically with subsequent solid-liquid separation and filtration equipment.

V. Adsorption Method Suitable for Advanced Treatment

The adsorption method mainly utilizes the large specific surface area and surface activity of adsorbents to adsorb part of the organic or inorganic substances in wastewater onto the surface or interior of the material.

Common adsorption materials include:

Activated carbon;

Resins;

Zeolites;

Other materials with specific adsorption properties.

Adsorption is usually suitable as a pretreatment, advanced treatment, or targeted treatment for specific pollutants.

For example, high chromaticity, turbidity, and organic matter may exist in papermaking wastewater. After completing coagulation and flotation, activated carbon can be further utilized for adsorption treatment to improve effluent water quality.

Therefore, when designing wastewater treatment equipment and processes, whether to adopt an adsorption unit requires a comprehensive judgment combining target pollutants, effluent requirements, and adsorbent regeneration or replacement costs.

VI. Extraction Method Applicable to Phase Transfer of Specific Pollutants

The extraction method uses organic solvents or other liquids to transfer target pollutants from the wastewater phase to another phase, thereby achieving separation.

This method is not applicable to all industrial wastewaters, but needs to be selected according to the chemical properties and phase equilibrium characteristics of the pollutants.

In practical engineering, key considerations include:

Whether target pollutants have properties suitable for extraction;

Whether the selection of the extractant is reasonable;

Whether extraction efficiency is stable;

Extractant loss issues;

Subsequent extraction phase treatment methods;

System safety and environmental protection requirements.

Therefore, the extraction process is more suitable for targeted treatment in specific industries and specific pollutants.

VII. What Are the Advantages of Chemical Wastewater Treatment?

A reasonably designed chemical treatment system features strong pollutant targeting and process flexibility.

1. Broad Pollutant Removal Range

Chemical treatment can adopt corresponding treatment methods for different pollution factors such as organics, inorganics, heavy metals, microorganisms, chromaticity, turbidity, and odor.

For complex industrial wastewater, different chemical treatment units can be combined so that different pollutants can be controlled separately at different stages.

2. Broad Industry Application Range

Chemical treatment can be used for industrial wastewater, domestic sewage, and partial agricultural wastewater, and can also serve as pretreatment or post-treatment for other treatment processes.

For example: Chemical Treatment -Biochemical Treatment

Or: Biochemical Treatment- Chemical Coagulation-Filtration/Adsorption

Different combination methods should be determined based on water quality and treatment targets.

3. Relatively Flexible Process Adjustments

By adjusting reagent types, dosing amounts, reaction conditions, and reaction times, the treatment system can be adjusted in response to water quality changes.

However, "simple operation" does not mean process control can be neglected. During actual operation, reagent dosing, pH, ORP, reaction time, and solid-liquid separation effects all need continuous monitoring.

VIII. What Needs Attention in Chemical Treatment Process Design?

1. Reagent Selection Cannot Take a "One-Size-Fits-All" Approach

The selection of chemical reagents should combine:

Pollutant types;

Pollutant concentrations;

Raw water pH;

Water temperature;

Water volume;

Treatment target;

Subsequent treatment processes;

Sludge properties;

Final discharge or reuse requirements.

For example, in coagulation treatment, the same coagulant is not necessarily applicable to all industrial wastewaters.

The combination of polyaluminum chloride and polyacrylamide also requires determining optimal dosing conditions through experiments.

Therefore, wastewater treatment reagents and equipment need to be considered synchronously rather than purchasing equipment separately before deciding on reagents.

2. Control Dosing Amount, Dosing Sequence, and Reaction Time

Chemical treatment effectiveness depends not only on the reagent itself, but is also closely related to the dosing method.

Key controls are needed for: Dosing Concentration - Dosing Amount -Dosing Location- Dosing Sequence- Mixing Intensity - Reaction Time - Solid-Liquid Separation

If reagent dosing is insufficient, it may lead to a decrease in pollutant removal rates; if dosed excessively, it may increase operating costs and generate more chemical sludge.

For polymer flocculants such as polyacrylamide, considerations must also be given to dissolution, aging, shearing, and dosing methods.

IX. What Byproducts Does Chemical Treatment Generate?

Although chemical treatment can remove pollutants, it may simultaneously generate byproducts such as sediment, filter cake, scum, waste liquid, and even exhaust gas.

For example, after chemical precipitation removes heavy metals, metal-containing precipitates are generated; coagulation treatment forms chemical sludge; air flotation systems may produce water-containing scum.

These byproducts cannot be simply regarded as ordinary waste, but require subsequent treatment or disposal according to their composition and hazardous characteristics.

Therefore, a complete industrial wastewater treatment system must focus not only on the final effluent, but also on: Pollutant Fate + Sludge Generation Amount + Sludge Moisture Content + Sludge Disposal Cost

This is also an important link easily overlooked in actual engineering design.

X. How to Choose Appropriate Wastewater Treatment Equipment?

When selecting wastewater treatment equipment, one should not look solely at equipment prices or appearance, but should make a comprehensive judgment based on process applicability, operational stability, and life-cycle cost.

The attachment proposes three important principles: economy, feasibility, and reliability.

1. Economy

Comprehensive considerations require:

Initial equipment investment;

Installation costs;

Reagent costs;

Electricity consumption;

Labor costs;

Maintenance costs;

Sludge treatment costs;

Equipment service life.

A low purchase price does not necessarily mean a low total cost.

For example, if certain equipment has a lower initial investment but higher energy consumption and frequent consumable replacements, its long-term operating expenses might conversely be higher.

2. Feasibility

The process scheme needs to consider equipment supply, materials, personnel, maintenance capabilities at the project location, and compatibility with other treatment units.

For overseas projects, additional considerations include:

Local electrical standards;

Power supply conditions;

Installation conditions;

Operator proficiency levels;

Spare parts supply;

Chemical supply;

Marine shipping and on-site installation conditions.

Therefore, when industrial wastewater treatment equipment manufacturers provide schemes, they need to understand not only the equipment itself, but also fully comprehend project site conditions.

3. Reliability

Reliability mainly involves stability during long-term system operation.

Attention must be paid to:

Automatic control systems;

Online pH monitoring;

Dosing systems;

Agitation systems;

Pumps and valves;

Solid-liquid separation equipment;

Sludge discharge systems;

Safety protection;

Emergency bypass.

For continuously running industrial projects, equipment stability is often more important than short-term treatment efficiency.

XI. Common Chemical Reactors and Their Applicable Scenarios

Stirred Reactor

Stirred reactors promote full contact between wastewater and chemical reagents through mechanical agitation, and can be used in processes such as neutralization, coagulation, and chemical precipitation.

Its characteristics include:

Relatively simple structure;

Flexible operation;

Faster mixing speed;

Strong adaptability.

It should be noted that excessively high agitation intensity may destroy already formed flocs; therefore, coagulation reactions usually need to distinguish between rapid mixing and slow flocculation stages.

Spray Reactor

Spray reactors increase gas-liquid or liquid-liquid contact area through spraying methods, and can be used for partial oxidation-reduction and adsorption-related processes.

Its characteristics are a relatively compact structure and strong mass transfer, but it may suffer from issues such as high water consumption, uneven spraying, and nozzle clogging.

Fluidized Bed Reactor

Fluidized beds use gas or liquid to put solid particles into a fluidized state, thereby enhancing mass transfer and heat transfer.

Its characteristics are:

Higher mass transfer efficiency;

More uniform reaction;

Relatively stable temperature.

However, structural and control requirements are higher, so engineering design must be combined with specific projects.

XII. What Are the Common Solid-Liquid Separation Equipment?

1. Sedimentation Tank

Sedimentation tanks use gravity to achieve solid-liquid separation, removing suspended solids, colloids, and chemical precipitates.

Advantages include simple structure, stable operation, and relatively low operating costs.

Disadvantages are a larger footprint and the generation of sludge.

Therefore, in projects with limited land resources, the comprehensive applicability of sedimentation tanks versus equipment like air flotation and filtration needs to be compared.

2. Filter

Filters retain suspended solids, colloids, and residual precipitates through filter media.

The attachment points out that filters feature high treatment efficiency, a smaller footprint, and good effluent quality, but filter media are easily clogged, requiring cleaning or replacement, and operating costs are also relatively high.

Common filter media include quartz sand and activated carbon.

3. Flotation Unit

Flotation units bring suspended solids, colloids, oils, and some organic matter to the water surface via micro-bubbles, and then achieve solid-liquid separation by scraping scum.

For oily wastewater, light flocs, and some suspended solids that are difficult to settle, air flotation processes may be more suitable than pure sedimentation.

In actual wastewater treatment system design, sedimentation and flotation do not have an absolute superiority or inferiority; choices should be made based on floc density, pollutant properties, land footprint conditions, and treatment targets.

XIII. Three Typical Chemical Wastewater Treatment Cases

Case 1: Chemical Plant Comprehensive Wastewater

Wastewater from a chemical plant contains large amounts of ammonia nitrogen, sulfides, and organics.

Its treatment flow is: Regulation Tank-Oxidation Reactor - Coagulation Reactor - Flotation Unit-Filter- Disinfection Tank

First, water volume, quality, and pH are adjusted via the regulation tank; subsequently, it enters the oxidation reactor, where chlorine gas and oxygen are added for oxidation-reduction reactions, converting ammonia nitrogen and sulfides into harmless nitrogen gas and sulfates.

Polyaluminum chloride and polyacrylamide are then added for coagulation, making organics and suspended solids form flocs, which are then separated through solid-liquid separation via flotation.

Finally, it passes through quartz sand and activated carbon filtration, undergoes disinfection by sodium hypochlorite, and is then discharged or reused.

This case reflects the combination relationship among chemical wastewater treatment equipment: different devices respectively undertake oxidation, coagulation, separation, filtration, and disinfection tasks.

XIV. Why Does Electroplating Wastewater Require Combined Chemical Treatment?

Wastewater from an electroplating plant contains large amounts of heavy metals, cyanides, and organics.

Its treatment route is: Regulation Tank-Oxidation Reactor-Chemical Precipitation Reactor -Sedimentation Tank- Filter- Disinfection Tank

Water volume, quality, and pH are first controlled through the regulation tank.

Hydrogen peroxide and ozone are subsequently added to treat cyanides and organics via oxidation-reduction reactions.

The oxidized wastewater enters the chemical precipitation reactor, where precipitants such as sodium hydroxide, ferric sulfate, and aluminum sulfate are added to make heavy metals and other dissolved substances form water-insoluble precipitates.

Solid-liquid separation is then carried out through a sedimentation tank, followed by filtration using quartz sand and activated carbon, and final discharge or reuse after sodium hypochlorite disinfection.

This case illustrates that for electroplating wastewater with complex compositions, a single treatment unit is often difficult to cover all pollutants, requiring multi-stage treatment according to pollutant characteristics.

XV. Coagulation, Air Flotation, and Adsorption in Papermaking Wastewater

Wastewater from a papermaking mill contains large amounts of chromaticity, turbidity, and organics.

Its process flow is: Regulation Tank - Coagulation Reactor - Flotation Unit - Adsorption Reactor-Disinfection Tank

First, the regulation tank is utilized to stabilize water volume, quality, and pH; then polyaluminum chloride and polyacrylamide are added for coagulation to form flocs of organics and suspended solids.

An air flotation unit is subsequently utilized for solid-liquid separation, followed by activated carbon adsorption to further reduce chromaticity, turbidity, and organics.

Sodium hypochlorite is finally adopted for disinfection.

This flow has certain reference value for understanding papermaking wastewater treatment processes, and also illustrates that chemical treatment can adopt multiple technology combinations according to different pollutants.

XVI. How to Determine a Wastewater Treatment Process Suitable for a Project?

In actual projects, it is not recommended to directly select schemes based on "commonly used equipment in a certain industry."

A more reasonable engineering process typically includes the following steps:

Step 1: Collect Raw Water Data

At least the following must be understood:

Wastewater source;

Daily treatment capacity;

Peak flow rate;

pH;

COD;

BOD;

SS;

Ammonia nitrogen;

Total nitrogen;

Total phosphorus;

Chromaticity;

Heavy metals;

Salinity or TDS;

Temperature;

Special pollutants.

Step 2: Clarify Treatment Targets

It is necessary to clarify whether the final target is: Standard discharge, reuse, or entry into subsequent membrane treatment systems? Different targets correspond to different treatment depths.

If it finally enters an RO system, the front end must focus on controlling suspended solids, colloids, organics, and other factors that may cause membrane fouling.

Step 3: Conduct Experimental Verification

For processes such as coagulation, precipitation, oxidation, and adsorption, laboratory beaker tests or bench-scale tests are recommended.

Experimental highlights can include:

Optimal reagent type;

Optimal dosing amount;

Optimal pH;

Floc size;

Settlement velocity;

Effluent turbidity;

Sludge generation amount.

Through experimental data, operational risks after engineering scale-up can be reduced.

Step 4: Determine Equipment Combination

Select according to experimental results: Regulation Equipment + Dosing System + Reaction Equipment + Solid-Liquid Separation Equipment + Filtration Equipment + Advanced Treatment Equipment

Instead of determining equipment first and then working backward to find water quality suitable for the equipment.

XVII. How ECOLINK TECHNOLOGY Helps Customers Match Schemes

For overseas industrial wastewater projects, equipment procurement is often not just purchasing a machine, but involves multiple links such as chemical reagents, equipment, process coordination, documentation files, and on-site operation.

The service focus of ECOLINK TECHNOLOGY is centered on matching water treatment chemicals and water treatment equipment around actual customer needs.

We can assist customers in analyzing according to project conditions:

Wastewater type;

Treatment capacity;

Pollutant characteristics;

Chemical reagent requirements;

Coagulation and flocculation schemes;

Solid-liquid separation methods;

Filtration requirements;

Subsequent treatment requirements like RO/UF/EDI;

Equipment configuration;

Technical data;

Sample testing;

Product stability;

Batch quality control.

For chemical products, PAC, PAM, and other water treatment agents can be matched according to actual projects; for equipment projects, process combinations can be integrated based on customer water volume, quality, and final effluent requirements.

This "product + technical support + equipment matching" model can help customers reduce communication costs of searching for chemical suppliers and equipment suppliers separately.

XVIII. Why Not Compare Only Wastewater Treatment Equipment Prices?

In international procurement, equipment quotes are usually only part of the project cost.

Customers also need to consider: Equipment Investment + Chemical Reagents + Electricity + Labor + Maintenance + Spare Parts + Sludge Disposal + Equipment Lifespan

For example, while certain equipment has a lower purchase price, if long-term operation requires frequent filter material replacements or consumes large amounts of electrical energy, its actual life-cycle cost may not be low.

Therefore, when comparing wastewater treatment equipment manufacturers and schemes, it is recommended to comprehensively compare from the following aspects:

Whether the process matches;

Whether equipment treatment capacity meets requirements;

Whether materials are suitable for wastewater properties;

Whether the degree of automation conforms to site personnel conditions;

Whether the reagent system is reasonable;

Whether subsequent maintenance is convenient;

Whether spare parts are easy to obtain;

How sludge and byproducts are treated;

Whether the effluent meets final requirements;

Whether the total life-cycle cost is reasonable.

XIX. Future Development Directions of Chemical Treatment Methods

As industrial wastewater becomes increasingly complex, traditional single chemical treatment processes are developing toward the direction of "multi-technology synergy."

Future industrial wastewater treatment projects may pay more attention to:

Combination of Chemical Treatment and Membrane Technology

Reducing membrane fouling risks through pretreatments such as coagulation, precipitation, and filtration, combined with membrane technologies such as UF and RO to achieve advanced treatment and water reuse.

Precision Reagent Dosing

Utilizing online pH, turbidity, flow, and other water quality monitoring data to achieve more precise dosing control and reduce overdosing.

Automated Operation

Improving system operating stability and reducing manual operation errors through PLCs, online instruments, and automatic dosing systems.

Sludge Reduction and Resource Utilization

Reducing chemical sludge generation amounts while ensuring pollutant removal effects, and further exploring ways of sludge dewatering and resource utilization.

Therefore, future chemical treatment wastewater treatment pays attention not only to "whether it can be treated," but also to "how to operate stably, economically, and long-term."

XX. Conclusion: Choosing the Right Process is More Important Than Choosing a Single Equipment

Chemical treatment methods are one of the important technologies in the industrial wastewater treatment system, capable of treating multiple pollutants through different mechanisms such as neutralization, coagulation, chemical precipitation, oxidation-reduction, adsorption, and extraction.

However, no fixed process is applicable to all wastewaters.

A truly reasonable scheme should be judged through this complete chain: Water Volume -Water Quality - Pollutants - Treatment Target - Experimental Testing - Reagent Selection - Process Combination - Equipment Configuration -Operating Cost - Sludge Disposal

For customers needing to purchase wastewater treatment equipment, water treatment chemicals, or complete industrial wastewater treatment schemes, it is recommended to provide as complete water quality and operating data as possible in the early project stages. Through preliminary technical analysis and experimental verification, chemical reagents, reaction conditions, solid-liquid separation methods, and final equipment configurations can be determined more accurately.

ECOLINK TECHNOLOGY focuses on water treatment chemicals and equipment, providing water treatment solutions that better suit actual project demands for customers across different countries and industries through product matching, technical support, sample testing, and one-stop services.

If you are looking for treatment schemes suitable for industrial wastewater, chemical wastewater, electroplating wastewater, papermaking wastewater, or other complex wastewaters, targeted analysis can be carried out based on actual water volume, water quality, and target effluent requirements.