21 Common Sewage Pollutants: Sources, Treatment Methods and Engineering Control Guide

Sewage contains a wide variety of pollutants. Heavy metals, oxygen-consuming organic matter, nitrogen and phosphorus nutrients, and toxic inorganic substances directly affect the stability of treatment processes and discharge compliance. The 21 common sewage pollutants have wide sources, and treatment requires a combination of biochemical, chemical precipitation, and advanced oxidation methods. pH value, as the core control parameter, directly determines biological activity, precipitation efficiency, and equipment corrosion resistance. NiuBoL NBL-PHG-206 industrial online pH sensor adopts the glass electrode method, patented long-life reference system, and RS-485 Modbus RTU protocol, providing reliable sewage pH online monitoring solutions for system integrators, IoT solution providers, project contractors, and engineering companies. This article systematically sorts out the sources, treatment methods, and pH control points of 21 pollutants to help engineering teams optimize wastewater treatment processes and achieve precise process control and compliant discharge.

Engineering Significance of Online Monitoring of Sewage Pollutants

In the mixed treatment of industrial wastewater and domestic sewage, pollutant concentrations fluctuate greatly and the composition is complex. Traditional laboratory analysis cannot meet real-time control requirements. The online monitoring system supports PLC, DCS, or SCADA integration through continuous collection of key parameters to achieve over-limit early warning and linkage regulation. As a basic indicator, pH value directly affects COD removal rate, ammonia nitrogen nitrification and denitrification efficiency, and heavy metal precipitation rate. It is the core control point of wastewater treatment plants.

NiuBoL NBL-PHG-206 is suitable for wastewater monitoring in high-pollution industries such as chemical, printing and dyeing, electroplating, and pharmaceutical. The IP68 protection rating adapts to corrosive environments. The dual high-impedance differential amplifier has strong anti-interference ability, with a response time T90 < 30s. Combined with Pt1000 automatic temperature compensation, it ensures data accuracy. In engineering practice, the sensor can be linked with COD, ammonia nitrogen, and total phosphorus online instruments to form multi-parameter monitoring nodes, significantly reducing manual inspection costs and improving system stability.

Sources, Impacts and Treatment Methods of 21 Common Sewage Pollutants

The following systematically sorts out 21 typical pollutants by category, focusing on sources, environmental impacts, mainstream treatment processes, and the role of pH control to provide references for engineering selection.

1. Oxygen-Consuming Organic Matter (Easily Biodegradable)

Sources: Domestic sewage, food processing, papermaking, petrochemical, chemical fiber, pharmaceutical, and printing and dyeing wastewater.

Impact: Microbial decomposition consumes dissolved oxygen, leading to black and odorous water bodies. When BOD5 > 10 mg/L, dissolved oxygen approaches zero.

Treatment Methods: Push-flow activated sludge method, SBR/CASS process, biofilm method, or MBR membrane bioreactor.

pH Control: Optimal pH 6.5–8.5. Too acidic or too alkaline inhibits microbial activity. NiuBoL sensors monitor inlet and outlet pH in real time to ensure efficient operation of biochemical tanks.

2. Refractory Biodegradable Organic Matter

Sources: Organic chlorides, organophosphorus pesticides, organic heavy metal compounds, and aromatic long-chain compounds, mainly from pesticide, plastic, and chemical wastewater.

Impact: Conventional activated sludge is difficult to degrade, leading to persistent COD exceedance.

Treatment Methods: Special microbial cultivation, anaerobic pretreatment to improve biodegradability followed by secondary biochemical treatment, or advanced oxidation.

pH Control: Anaerobic section pH 6.5–7.5. Oxidation process requires precise control to optimize free radical generation.

3. Organic Nitrogen and Ammonia Nitrogen

Sources: Organic nitrogen such as protein and urea comes from leather and meat processing; ammonia nitrogen comes from steel, oil refining, fertilizer, and deamination reactions in fresh wastewater.

Impact: Leads to eutrophication of water bodies. Ammonia nitrogen toxicity inhibits fish respiration.

Treatment Methods: Biological nitrification-denitrification, stripping, air stripping, ion exchange.

pH Control: Optimal pH for nitrification is 7.5–8.5, and for denitrification 6.5–7.5. NiuBoL pH meters are used for precise regulation in nitrification tanks.

4. Phosphorus and Organic Phosphorus

Sources: Phosphorus-containing detergents, domestic waste, and industrial wastewater (hypophosphite, organic phosphorus).

Impact: Causes eutrophication of water bodies and algal blooms.

Treatment Methods: Biological methods (AO, A2O, oxidation ditch) + chemical phosphorus removal (PAC, PFS). High-concentration organic phosphorus requires advanced oxidation pretreatment.

pH Control: Optimal pH for chemical phosphorus removal is 8–10. Biological phosphorus removal requires a stable neutral environment.

5. Acid and Alkali Wastewater

Sources: Chemical, chemical fiber, acid production, electroplating, metal processing (inorganic acid/organic acid) and papermaking, printing and dyeing, leather (alkali).

Impact: Corrodes pipelines and equipment, destroys ecological balance.

Treatment Methods: Neutralization treatment (for low concentration) or recycling (for high concentration).

pH Control: Core indicator. Discharge standard is 6–9. NiuBoL sensors provide real-time feedback on neutralization dosing.

6. Oil Pollutants

Sources: Petroleum, textile, metal processing, food processing, and domestic sewage.

Impact: Forms oil film that blocks oxygen exchange.

Treatment Methods: Oil separator, air flotation, coarse granulation coalescence. Different devices are selected according to the form (free, emulsified, dissolved).

pH Control: Emulsified oil demulsification pH 4–6 or 8–10 to optimize coagulation effect.

7. Pathogenic Microorganisms

Sources: Hospital, slaughter, leather, and biological product wastewater.

Impact: Spreads diseases.

Treatment Methods: Chlorine, chlorine dioxide, ozone, ultraviolet disinfection, and ultrafiltration if necessary.

pH Control: Disinfection efficiency is affected by pH. Optimal pH for residual chlorine disinfection is 6.5–7.5.

8. Nitrate and Nitrite

Sources: Fertilizer, steel, gunpowder, meat processing, and by-products of aerobic biological treatment.

Impact: Nitrite is carcinogenic. Children drinking high-nitrate water are prone to poisoning.

Treatment Methods: Biological denitrification, electrodialysis, reverse osmosis, ion exchange.

pH Control: Optimal pH for denitrification is 7–8.

9. Fluoride

Sources: Fluorine-containing products, coke, electronics, electroplating, glass, and pesticide production.

Impact: Causes skeletal fluorosis and other health hazards.

Treatment Methods: Precipitation (lime, alum) + adsorption.

pH Control: Optimal pH for precipitation is 8–9.

10. Sulfide

Sources: Oil refining, printing and dyeing, leather, and anaerobic reduction of sulfate wastewater.

Impact: Odor, corrosion, and toxicity.

Treatment Methods: Flocculation precipitation or stripping to convert to H₂S.

pH Control: Stripping requires alkaline environment.

11. Cyanide

Sources: Electroplating, mining, coking, plastic, and dye industries.

Impact: Highly toxic.

Treatment Methods: Chlorine oxidation, ozone oxidation, electrolytic oxidation.

pH Control: Oxidation efficiency is high under alkaline conditions.

12. Phenol

Sources: Oil refining, chemical, coking, and papermaking industries.

Impact: Toxicity and carcinogenicity.

Treatment Methods: Extraction, activated carbon adsorption, biological method, chemical oxidation.

pH Control: Optimal pH for biodegradation is 7–8.

13–21. Heavy Metals and Organic Toxins (Silver, Nickel, Lead, Chromium, Mercury, Organic Chlorine, Benzo[a]pyrene, Cadmium, Arsenic)

Sources: Electroplating, metallurgy, battery, pesticide, and plastic industries.

Impact: Bioaccumulation, carcinogenicity, and teratogenicity.

Treatment Methods: Chemical precipitation (hydroxide/sulfide), ion exchange, adsorption, electrolytic recovery.

pH Control: Key parameter. For example, after Cr(VI) reduction, trivalent chromium precipitation pH 8–10. Optimal pH for hydroxide precipitation of Cd, Pb, Ni, Hg, etc. is 8.5–11. Arsenic co-precipitation pH 6–8. NiuBoL sensors monitor sedimentation tank pH in real time to ensure removal rate compliance.

Application of NiuBoL NBL-PHG-206 Online pH Sensor in Sewage Monitoring

NBL-PHG-206 is suitable for monitoring inlet/outlet water, equalization tanks, biochemical tanks, and sedimentation tanks in sewage plants. The patented reference solution slowly seeps out (lasting more than 20 months), adapting to highly polluted environments. The 3/4 NPT interface supports submersible or pipeline installation. The Modbus RTU protocol facilitates integration with multi-parameter systems. In engineering projects, it can be linked with flow meters and COD/ammonia nitrogen instruments to achieve pH-dosing closed-loop control, reducing chemical consumption and ensuring compliant discharge.

Product Selection Guide and Integration Precautions

Selection focus: Range 0～14.00, accuracy ±0.1 pH, operating temperature 0～50℃, pressure resistance ≤0.2 MPa. For highly corrosive wastewater, prioritize patented electrodes. During integration, RS-485 bus uses single-end grounding. Power supply 12～24V DC, low power consumption 0.2W@12V is suitable for distributed nodes. Clean the sensor and perform two-point calibration before installation. Regular maintenance ensures stable response.

NBL-PHG-206 Online pH Sensor Technical Parameters

Sensor Maintenance and Care

Before measurement, clean with distilled water and blot dry. When not in use, insert into 3mol/L KCl protective solution. Regularly check wiring terminals and wipe with anhydrous alcohol. Clean glass membrane deposits with dilute hydrochloric acid. Calibrate after maintenance. Replace promptly if response is abnormal.

FAQ

Q1: What is the impact of sewage pH on heavy metal precipitation?

A: Most heavy metals (such as lead, cadmium, nickel, chromium) have optimal pH 8–10 for hydroxide precipitation. NiuBoL sensors can adjust alkali dosing in real time to ensure stable removal rate.

Q2: How is pH controlled in the ammonia nitrogen nitrification process?

A: Nitrifying bacteria have optimal pH 7.5–8.5. Activity drops significantly below 6.5. Sensors link with alkali dosing systems to maintain stability.

Q3: Why is online pH monitoring required for acid-alkali wastewater neutralization?

A: Real-time feedback on dosing amount avoids excess or insufficiency, ensuring effluent pH 6–9 and reducing chemical consumption.

Q4: Is NBL-PHG-206 suitable for highly polluted industrial wastewater?

A: The patented reference system has long life. IP68 protection adapts to corrosive environments. It is widely used in electroplating, chemical, and printing and dyeing wastewater monitoring.

Q5: How does Modbus RTU integrate with wastewater treatment PLC?

A: Standard protocol directly maps registers and supports multi-point networking without additional conversion modules.

Q6: What are the pH requirements for demulsification of oil pollutants?

A: Emulsified oil demulsification is usually controlled at pH 4–6 or 8–10. Sensors ensure optimal coagulation effect.

Q7: How to determine whether the sensor needs to be replaced?

A: When response time in buffer solution exceeds 1 minute or calibration deviation exceeds indicators, replacement is recommended.

Q8: What information needs to be provided for project selection?

A: Wastewater composition, temperature and pressure, installation method, communication requirements, and integration platform to facilitate matching the optimal configuration.

Summary

Treatment of 21 common sewage pollutants relies on precise process control, and pH value is the core parameter running through the entire biochemical, precipitation, and neutralization processes. NiuBoL NBL-PHG-206 online pH sensor provides reliable monitoring means for wastewater treatment projects with its high stability and easy integration characteristics. Standardized selection, installation, and maintenance can significantly improve treatment efficiency, reduce operating costs, and ensure compliant discharge. System integrators and engineering companies can rely on this solution to build intelligent wastewater treatment systems. For technical parameter confirmation, prototype testing, or customized integration solutions, please contact the NiuBoL professional team to jointly promote efficient project implementation.

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