Chemical Technology July 2015

Upgrading sewage plants using Endress+Hauser's technologies

How is all this regulated by law? Currently there are almost no limits set for the intrusion of trace elements. Legal limits are only defined for heavy metals and biocides. Many regulatory authorities in Europe have identified the problem. “In Switzerland, over 100 sewage treatment plants are to be refit- ted with an additional cleaning stage which will eliminate most micro pollutants,” says Stefan Vogel. After mechanical, biological, and chemical cleaning, this involves a fourth treatment in most cases. Concerns regarding trace elements have been raised at various conferences in South Africa. Currently no legislation has been imple- mented but various institutes are researching this important issue. What can be done to get rid of micro pollutants? The Swiss government-fundedwater research institute Eawag has looked into various large- scale technical methods, with two methods appearing to be the most suitable for use in communal sewage treatment plants: in ozoni- sation, the ozone blown into the water reacts with the trace elements and the cracked com- pounds are biologically degraded in a sand filter. In the treatment with powder-activated

Pesticides,drugsandcosmetics:moreandmoretrace elements contaminate our wastewater. Removing these micro pollutants requires new methods and Endress+Hauser has been part of this development right from the start. Ordinary sewage treatment plants remove solids mechanically with rakes and sedimen- tation tanks. Microorganisms in the biological treatment stage help to eliminate nitrogen charges. Most plants eliminate the remaining phosphate chemically by precipitation, with an increasing number of facilities also using biological methods at this stage. Micro pol- lutants are only partially retained. “These can be the active ingredients of drugs, biocides fromagricultural and construction chemicals, or ingredients of body care products and cleaning agents,” explains Stefan Vogel, Product Manager Water and Environmental at Endress+Hauser Switzerland. Some trace elements interfere in nature’s cycles in minute concentrations. Hormones and hormone-active substances, for example, compromise the growth and fertility of fish, crustaceans and amphibians; biocides im- pair the photosynthesis of algae and aquatic plants. Higher concentrations of micro pol- lutants are mainly found at places where sewage plants discharge into smaller rivers.

carbon, the molecules settle on the surface of the carbon and are incinerated together with the dried sewage sludge. Both the ozonisation and the powder-ac- tivated carbon treatment eliminate between 80 and 90 percent of the micro pollutants in wastewater, which means they are highly ef- fective. The installation of a powder-activated carbon treatment needs more space. Ozoni- sation is linked with higher energy needs, while powder-activated carbon requires material consumption. What’s the importance of measurement technology? Measurement technology is needed both for controlling ozonisation and for the treatment with powder-activated carbon. Beside flow, temperature and pressure sensors, liquid analysis is also used. The spectral absorption coefficient appears to be the most promising candidate as the key value; measuring the reduction/oxidation potential seems to be best suited to identify increased ozone For more information contact Hennie Pretorius on tel: +27 11 262 8000 or email info@za.endress.com z

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Chemical Technology • July 2015