1. Manual removal method: this is the most direct method, and duckweed can be fished out of the pool with a net bag or fishing net. But it needs more manpower and material resources, and its efficiency is low, so it is suitable for small-area waters.

2. Biological elimination method: Use some creatures that like to eat duckweed, such as grass carp, silver carp, carp, etc., to control duckweed reproduction. This method takes some time, but it is environmentally friendly and sustainable.

In order to fundamentally solve the problem of excessive duckweed, you may need to adjust some parameters in the sewage treatment process, such as:

1. Dissolved oxygen control: In some sewage treatment processes, such as denitrification deep bed filter, it is necessary to control the dissolved oxygen at a low level, such as below .5 mg/L. This may help to reduce the growth of duckweed.

2. control of influent ammonia nitrogen and total nitrogen: if the concentration of influent ammonia nitrogen and total nitrogen is too high, it may promote the growth of duckweed. According to your description, you may need to take measures to reduce the concentration of ammonia nitrogen and total nitrogen in the influent. This may include optimizing the sewage treatment process or installing pretreatment facilities at the water inlet.

3. Content of other substances in wastewater: Some substances may promote or inhibit the growth of duckweed. For example, if the wastewater contains more organic matter, it may promote the growth of duckweed; However, if the wastewater contains more heavy metal ions, it may inhibit the growth of duckweed.

The above information is for reference only, and it is recommended to consult professionals for specific treatment methods.