曝气塘可除去污水中大部分化学药物

2012 marked the 40th anniversary of the Clean Water Act, which established regulations for the discharge of pollutants to waterways and supported the building of sewage treatment plants. Despite these advances, sewage remains a major source of pharmaceuticals and personal care products (PPCPs) and naturally occurring hormones found in the environment. Many rural communities in the United States use aerated lagoon systems to treat their wastewater. The wastewater is pumped into at least one humanmade aerated lagoon（曝气塘）, in which oxygen-loving and anaerobic（厌氧的） microorganisms remove many of the contaminants. The water is then pumped into a series of other lagoons. Finally, the resulting water, known as the effluent, is discharged directly into a receiving stream.

The drugs, chemicals and hormone contaminants such as ibuprofen, caffeine and ethinyl estradiol from urban sewage treatment plants have been studied and monitored widely, but their occurrence in rural lagoon treatment systems is often overlooked.

In a new study led by Wei Zheng, a senior research scientist at the Illinois Sustainable Technology Center and an adjunct faculty member in the University of Illinois department of natural resources and environmental sciences, researchers determined the effectiveness of rural lagoon systems at removing these compounds from wastewater. The research was conducted jointly with the Illinois State Water Survey. The study appears in the journal Science of the Total Environment.

Scientists collected water samples in September and November from a rural wastewater treatment plant located in a small town in Illinois. The facility treats sewage wastewater in two aerated lagoons, using a sand tank for filtration. The effluent streams into a creek that flows into the Mackinaw River. The researchers collected samples from various steps during the treatment process for analysis.

The researchers then tested the samples for the presence of 21 commonly used PPCPs and hormones, including caffeine and ibuprofen.

The team found that the lagoon treatment system reduced concentrations of most of the tested compounds. The overall removal efficiency ranged from 88 to 100 percent in September, except for the compound carbamazepine, a drug used for the treatment of epilepsy and bipolar disorder that is notoriously difficult to remove from wastewater. There were no detectable steroid hormones in the aerated lagoons and effluent.

Interestingly, the samples collected in November contained higher concentrations of all detected PPCPs than the samples collected in September. According to Zheng, this is most likely because the microorganisms that break down the compounds work best in warm weather.

Although the efficiency of rural sewage treatment lagoons is relatively high, this study shows that there is a significant increase in the occurrence of PPCPs in surrounding watersheds with the effluent discharge, which could change the rural aquatic environment.