Levels of some toxic pollutants rise after treatment

Hepeng Jia/Tianjin, China

Many water treatment facilities in China are failing to remove toxic organic chemicals and levels of some chemicals are actually increasing during treatment, according to researchers from Nankai University, Tianjin. 

Sun Hongwen and her colleagues from Nankai’s College of Environmental Science and Engineering have spent several years monitoring levels of chemicals in water before and after treatment at sewage plants in northern China, including in the coastal city of Tianjin. Sun reported their results at the Chinese Chemical Society’s annual meeting in Tianjin in July.

One of the chemicals monitored by Sun’s team is nonylphenol, released during the breakdown of nonylphenol polyethoxylate detergents. Nonylphenol is an endocrine disrupter and, together with nonylphenol ethoxylates, is banned in the EU because of possible threats to human health.

Sun and her team found that the sewage treatment works only removed 60-70 per cent of nonylphenol polyethoxylate from water, while similar facilities in Europe and North America remove up to 90 per cent of the compound. To make matters worse, nonylphenol polyethoxylate degrades into smaller metabolites, such as nonylphenol, which could be 70 times more toxic than their precursors. ’These smaller molecules become more difficult to degrade, and they pose an increasing threat to the environment,’ warns Sun.

Activated sludge 

Sun’s team also discovered that sewage treatment increased levels of the industrial surfactants perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) - persistent organic pollutants (POPs) that may have metabolic, reproductive and neural toxicity. ’During the activated sludge process, which is efficient for conventional pollutants, some organic chemicals - such as nonylphenol, PFOS and PFOA - are not be degraded efficiently and their concentration may be elevated through the incomplete degradation of their precursors,’ says Sun ’Our sewage plants focus on processing conventional pollutants and monitoring things such as chemical oxygen demand, nitrates and phosphates. They don’t have the equipment to identify POPs, let alone process them,’ Sun told Chemistry World. 

Some European sewage plants also have the same problems with PFOS and PFOA, although levels of the pollutants are lower, says Sun. Last year, for example, Sun’s team identified the compounds in water leaving Swiss sewage treatment plants. ’A revolution in wastewater treatment technology is urgently needed,’ says Sun.

Zhang Pengyi, director of the Institute of Environmental Chemistry of Beijing-based Tsinghua University, thinks that Sun’s work offers valuable information on emerging polluting chemicals in the environment. ’But this should not indicate that sewage treatment plants are the source of the pollutants. PFOS and PFOA form through normal degradation processes of many chemicals in the common environment,’ he told Chemistry World.

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