What are the Stages of Wastewater Treatment?

 Introduction

The wastewater generated from our industrial, domestic, and agricultural activities contains various pollutants. These include organic matter, nutrients such as nitrogen and phosphorus, pathogens, heavy metals, and chemicals. Once this wastewater is discharged into nature without treatment, it can seriously pollute water bodies, soil, and air, disrupting the ecological balance. We use various wastewater treatment equipment and processes to improve the quality of sewage. Among these processes is often divided into five levels. Today, let's discuss what these levels are and how they operate.

 

Primary Treatment

Primary treatment is the initial stage of wastewater treatment. Through physical methods such as screening and sedimentation, it can remove 60% of larger solids and suspended matter. At this stage, we set up a grille made of metal bars or meshes at the wastewater inlet to intercept large debris such as branches and plastic bottles. Then the wastewater enters the grit chamber. Through gravitational sedimentation, dense inorganic particles such as sand and stones in the wastewater will settle to the bottom of the chamber. Among them, horizontal flow, vertical flow, and aerated grit chambers are more common.

 

Secondary Treatment

Secondary treatment generally consists of an aeration tank and a final clarifier and aims to remove the remaining pollutants, especially organic matter. This treatment process revolves around aerobic treatment, anaerobic digestion, or a combination of both.

l Activated Sludge Process: This method involves introducing activated sludge rich in microorganisms into the aeration tank, and the microorganisms will consume the organic matter. Subsequently, the sludge containing microorganisms will settle in the clarifier, and part of the sludge will be returned to the aeration tank to continue the process.

l Trickling Filter: The wastewater trickles onto a bed of porous material (such as rock or plastic media), and microorganisms grow into a biofilm on the porous material. When the water flows through the biofilm, the microorganisms will consume the organic pollutants.

l Biofilm Process: In the aeration tank, we use components such as aeration diffusers and pumps to provide oxygen for the microorganisms. The microorganisms will grow on the surface of the rubber, EPDM membranes of the diffusers and consume the organic matter.

 

Tertiary Treatment

The wastewater after secondary treatment still contains suspended solids, nutrients such as nitrogen and phosphorus, and refractory organic matter. Tertiary treatment can reduce pollutants to extremely low levels. It intercepts suspended solids through a quartz sand filter bed. It also involves different membrane filtration technologies such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis to remove pollutants of different particle sizes. In addition, chemical precipitation is also used in this stage to remove nitrogen and phosphorus. Reagents such as lime, aluminum salts, and iron salts can react with phosphorus to form precipitates, and biological or chemical denitrification methods can reduce the nitrogen content in the wastewater.

 

Solid Treatment

The sludge generated in each link of wastewater treatment also contains organic matter, microorganisms, heavy metals, and other components. We will first concentrate it by gravity or mechanical means and then carry out stabilization treatment. Stabilization treatment includes:

l Anaerobic Digestion: Allowing microorganisms to decompose organic matter in an anaerobic environment, and the generated methane can be recycled.

l Aerobic Composting: Mix the sludge with conditioners. They will ferment under aerobic conditions and be made into compost for soil improvement.

 

Disinfection

Disinfection is the last step of wastewater treatment to kill pathogenic microorganisms. This includes the use of chlorine, sodium hypochlorite, chlorine dioxide, or ultraviolet disinfection. However, ultraviolet disinfection is a physical method and may not be suitable for wastewater with high turbidity.


 

Conclusion

Now we can summarize that the stages of wastewater treatment include primary, secondary, and tertiary treatment, as well as solid treatment and disinfection. In fact, these five periods are closely linked to improve the water quality and safety. If you are more interested in this or have any questions, please feel free to contact the expert team of AquaSust for consultation or leave a message in the comments.

 

 

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