Frequently Asked Questions about Biological Wastewater Treatment Systems 1. What is a biological wastewater treatment system? A biological wastewater treatment system is a type of system that uses microorganisms to break down organic matter in wastewater

14 frequently asked questions about biological wastewater treatment systems

1. What are the sources of wastewater?

There are mainly two sources of wastewater: 1) domestic wastewater and 2) other wastewater sources. Domestic wastewater includes all wastewater from community residents, public toilets, hotels, golf courses, restaurants, schools, hospitals... Other wastewater is generated from sources such as industrial production, rainwater, surface runoff...

2. What are the typical components of wastewater?

The components of wastewater are diverse and depend on the discharge source. Domestic wastewater typically includes disease-causing microorganisms, biodegradable organic matter, nutrients (such as nitrogen and phosphorus), suspended solids, and may contain harmful compounds that can cause cancer.

On the other hand, industrial wastewater is more complex. They often have higher organic concentrations (e.g., BOD, COD, TOC,...), heavy metals, and suspended solids...

3. What benefits do wastewater treatment systems provide to humans?

Protect human health from pathogens and harmful chemicals.

Protect the environment by ensuring that parameters (BOD, COD, N, P, heavy metals, etc.) are within specified limits.

Help businesses comply with legal requirements throughout their operations.

4. What is biological wastewater treatment?

Biological wastewater treatment is one of the prominent methods for treating wastewater. The task of this system is to remove BOD (biochemical oxygen demand) and stabilize organic compounds in water.

By using various types of microorganisms, they have the ability to oxidize dissolved organic matter into mineral components of CO2 and H2O, while also adding biomass.

This method is often used to treat high-concentration organic matter such as domestic wastewater, restaurant wastewater, etc.

5. What are BOD and COD?

BOD: biochemical oxygen demand (BOD) - the amount of oxygen needed for aerobic microorganisms to decompose organic matter at a specific temperature over a period of time.

COD: chemical oxygen demand (COD) - the amount of oxygen needed to oxidize dissolved organic matter in water using a strong oxidizing agent.

6. Why is the COD value higher than the BOD value?

The COD value - chemical oxygen demand is the amount of oxygen consumed to oxidize organic pollutants into inorganic end products. This includes biodegradable and non-biodegradable components.

BOD is the oxygen needed for microorganisms to oxidize organic matter. Both are tests to measure the oxygen needed to oxidize organic matter in wastewater through a chemical oxidation process with a strong oxidizing agent like Potassium Dichromate. COD is closely related to BOD.

The difference here is that BOD is a test of the level of organic matter that can be biologically oxidized. While COD is a test of the amount of organic matter that can be chemically oxidized. In reality, more chemicals can be oxidized, so COD will be higher than BOD in wastewater.

7. What are nitrification and denitrification?

Nitrification: a biological process where ammonia (NH4+) is converted to nitrite (NO2-), and then to nitrate (NO3-).

Denitrification: a biological process where nitrate (NO3-) is converted to nitrogen gas (N2 and other gaseous products).

8. Where does wastewater go?

All wastewater is collected through the collection system. They are then transferred to treatment systems and discharged into the environment.

In some cases, if wastewater undergoes advanced treatment cycles, it can be reused for various purposes.

9. What is the difference between flocculent growth and biofilm growth?

During flocculent growth, microorganisms are maintained in a suspended state in the liquid. In contrast, biofilm growth - a biological film forms on adherent materials to assimilate and oxidize pollutants in wastewater.

10. What are the advantages of MBR over conventional activated sludge processes?

As a wastewater treatment technology, MBR is considered a superior technology compared to conventional activated sludge processes. In MBR, the membrane replaces the secondary clarifier to separate wastewater from activated sludge.

The main advantages of MBR technology are: 1) smaller aeration tank; 2) lower waste sludge production; and 3) better wastewater quality.

11. How to determine if the membrane is fouled?

The membrane performance is evaluated by monitoring the transmembrane pressure (TMP) drop and the recovery rate. High TMP values and low recovery rates indicate membrane fouling and the need for cleaning.

12. What is preliminary coarse screening?

Coarse screening is the process of removing wastewater components such as debris, soil, rocks, and grease that can cause maintenance issues in the treatment system and ancillary systems.

13. What is the purpose of aeration in MBR systems?

There are 2 main reasons for aeration:

• Provide dissolved oxygen (DO) to maintain a viable microbial population for biological treatment.
• To keep MLSS in a suspended state.

14. What is the anoxic process?

The process where nitrate (NO3-) is biologically converted to nitrogen gas in the absence of oxygen (denitrification).

Above are some questions and answers about biological wastewater treatment. Hopefully, the brief insights above will help you understand more about this solution and its effectiveness.

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