Seven Stages of Wastewater Treatment | PROBEST Water Quality Analyzers

Seven Stages, One Goal: Converting Wastewater into River-Dischargeable Effluent

A municipal wastewater treatment plant (WWTP) follows a well-engineered seven-stage treatment sequence. The single ultimate objective is to treat raw sewage and produce final effluent that meets regulatory standards and can be safely discharged back into rivers.

Throughout the whole process, two critical operational fundamentals govern all downstream units:

✅ Protect pumps from grit and debris

✅ Maintain stable, continuous oxygen supply for microorganisms in the biological treatment zone

1. Bar Screen

The bar screen is the first pretreatment unit. Mechanical rakes intercept plastics, textiles, rags and large solid debris before wastewater enters the pumping station.

Core function: Protect downstream pumps from clogging and mechanical damage.

2. Grit Removal Chamber

In the grit removal chamber, sand, gravel and heavy inorganic particles settle under gravity. This prevents grit from eroding pump impellers, pipe elbows and other downstream mechanical equipment.

3. Primary Clarifier

Primary clarification relies purely on gravity separation. Organic sludge settles to the bottom, while scum floats on the surface. This tank has no moving submerged components, making it a robust primary solid-liquid separation step.

4. Aeration Tank

Blowers deliver compressed air through fine-pore diffusers inside the aeration tank. Dissolved oxygen (DO) is the key requirement for aerobic microorganisms, which degrade organic pollutants in the wastewater.

 This is the heart of biological wastewater treatment.

5. Secondary Clarifier

The secondary clarifier settles the biological flocs produced in the aeration tank. Settled activated sludge is pumped back to the front end of the aeration tank, maintaining a continuous circulating microbial population for stable biological treatment.

6. UV Disinfection Channel

UV disinfection uses ultraviolet light instead of chemical disinfectants to inactivate pathogens. Disinfection performance follows the principle of UV intensity × contact time (UV dose). This is why the UV channel is designed long and shallow to guarantee sufficient contact time.

7. Discharge

After all treatment steps, the purified effluent is discharged back into the receiving river.

In essence, the entire WWTP operation answers two key questions:

Can we reliably convey raw wastewater?

Can we continuously supply enough oxygen (the “food” for microbes)?

About PROBEST — Professional Water Quality Analysis Instrument Manufacturer

PROBEST is a professional manufacturer specializing in water quality analysis and online monitoring instruments for wastewater treatment, environmental monitoring, industrial water and surface water applications.

PROBEST designs and manufactures a full range of online water quality sensors and analyzers, including dissolved oxygen (DO), pH, ORP, turbidity, suspended solids (MLSS), COD, ammonia nitrogen, total phosphorus, total nitrogen and UV-related monitoring parameters. These instruments are widely deployed in WWTP pretreatment, aeration tanks, secondary clarifiers, UV disinfection channels and final effluent discharge points.

✅ Core Advantages of PROBEST

1. Application-focused design: Instruments are purpose-built for harsh wastewater environments, resistant to fouling, corrosion and long-term continuous operation.

2. Stable real-time monitoring: Accurate DO, MLSS and pollutant parameter data support optimized blower control, activated sludge recycle and UV disinfection dosing adjustment, helping plants reduce energy consumption.

3. Complete product portfolio: From in-situ sensors to integrated online analyzers, covering the full 7-stage wastewater treatment process.

4. Reliable after-sales & technical support:

5. Global export capability: Suitable for overseas municipal and industrial wastewater projects, compatible with international PLC systems.

With precise water quality monitoring from PROBEST, wastewater treatment plants can better control every treatment stage, secure stable effluent quality and ensure compliant river discharge.

Contact PROBEST today for customized online water quality monitoring solutions for your wastewater treatment plant.