The Microplastics Problem 

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Microplastics have invaded everyday life, causing problems for humans and animals. People can ingest microplastics in a number of ways, even by drinking single-use bottled water. 

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Studies have linked these microplastics to a number of human health problems, including increased risk of cancer and blood clots. 

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Microplastics also cause problems in the environment. In soil, microplastics can reduce crop productivity and fertility.  

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Because of issues like these, we need to remove microplastics from entering waterways through wastewater. 

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Researchers in Malaysia tested three different sewage treatment plants. They wanted to answer this question: How effective is a sewage treatment method in removing microplastics?  They found that the three methods removed most microplastics. 

The Basics and Sewage Treatment 

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Sludge is a solid byproduct of sewage treatment. 

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Influent means something that flows in. Here, influent refers to the raw sewage that goes into the sewage treatment plant. 

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Effluent refers to something that flows out. Here, effluent refers to the treated water coming out of the sewage treatment plant. 

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Sewage treatment plants aim to produce effluent safe to release into rivers, lakes, and other waterways. 

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The Types of Sewage Treatments of Microplastics Tested  

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Ishmail Sheriff, Nik Azimatolakma Awang, and Herni Binti Halim tested three different types of sewage treatment of microplastics. These three types were extended aeration, a sequencing batch reactor, and a mechanized oxidation ditch system. 

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Extended Aeration

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Firstly, extended aeration is a sewage treatment method that reduces the amount of sludge. Its four basic steps include screening, aeration, clarification, and sludge return.

• Screening: This process removes large solids.
• Aeration: Sewage mixes with microbes. The microbes eat waste. The microbes also eat each other, stopping them from over-multiplying.
• Clarification:  Microbes settle out from the now treated water.
• Sludge return: Most microbes are returned to the aeration tank.

Generally, this system reduces expenses in sludge removal but has a higher energy cost. 

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Sequencing Batch Reactor

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Next, a sequencing batch reactor is a treatment method that uses batches. It has five steps:

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• Fill: Sewage fills the tank. The dissolved oxygen must be at a certain level to prepare for the react step. 
• React: Microorganisms absorb waste in the sewage. This uses an aeration system. The microorganisms need enough dissolved oxygen.  
• Settle/Clarification: This step allows the solids to separate from the liquid. The sludge settles to the bottom of the tank. 
• Draw/Decant: The water is moved to the next treatment step. 
• Idle: The sludge is wasted.  

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This type of treatment can use one tank instead of three or four. 

Mechanized Oxidation Ditch System

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The third method the researchers tested was the mechanized oxidation ditch system. This system is “advanced aeration activated sludge,” capable of removing waste. 

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There can be a pre-treatment step to remove large solids. However, the mechanized oxidation ditch system can take sewage influent directly. 

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The system uses motors to move the sludge around and put oxygen in it. After treatment, the effluent is moved out. 

The Results of Studying Sewage Treatment of Microplastics  

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The researchers found that all three sewage treatments produced effluent uniformly low in microplastics. By contrast, the three sewage treatment plants took in influents with different microplastic concentrations. 

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The sequence batch system was the best in removal efficiency. The next most efficient method was extended aeration. 

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These findings are important, and will help us keep removing microplastics from sewage to enjoy safe water. 

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