Worming way to unclogging waste wetlands
Print Edition
EARTHWORMS are helping to reduce clogging in artificial wetlands used to treat sewage in rural areas surrounding Shanghai.
Artificial wetlands are a low cost and technologically simple way to treat sewage. However, poor design and management can lead to clogging which results in pollution.
Research by the Shanghai Academy of Environmental Sciences, showed that a particular species of earthworm — Eisenia foetida — can effectively reduce clogging matter and dredge the wetlands.
Artificial wetlands are rich in water plants such as canna and calamus, which absorb the chemical contents of nitrogen and phosphorus.
Their roots also help purify other substances.
“In winter, dead plants which are not removed can effect the wetlands’ functioning, while an excess amount of sewage can lead to clogging,” said an engineer at the academy’s water environment research center.
“The wetlands then become ‘sticky,’ and the ponding of sewage causes insect and pollution problems.”
A report by United States Environmental Protection Agency showed that about half of artificial wetlands face clogging problems after five years of use.
The problem can be solved by changing the soil under-layer, but that is costly.
According to the academy’s research, about 10 percent of the clog matter is protein and polysaccharides.
Despite this low percentage, they are the main cause of clogging.
“And they happen to be the favorite food of Eisenia foetida,” said the engineer.
“Our test results showed that the metabolism and uptake by Eisenia foetida could effectively reduce the clog matter content at a higher average removal rate than micro organisms alone. Their movements also help dredge the wetlands.”
A test was held by the academy at a 100-square-meter wetland in Fengxian District where 1.5 kilograms of the worms were used.
They absorbed about 0.18-0.25 grams of clog matter.
After three weeks, the porosity rate of the wetlands’ under-layer had been increased by 3 percentage points.
Due to the habits of earthworms, the solution only suits wetlands in rural areas, not urban.
The application of earthworms has already fixed clogging in projects in Qingpu and Chongming districts.
In 2016, more than 200,000 tons of domestic sewage was produced in Shanghai’s rural areas per day.
A certain amount of the sewage was discharged directly into rivers due to a lack of sewage treatment.
By the end of last year, sewage treatment facilities, including those using wetlands, covered 56 percent of rural area households. By the end of 2020, the figure should rise to 75 percent.
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