by Laurenz Fischer, Switzerland, ELP 2014
Written on July 20, 2014.
During this year’s ELP we had a lecture about sustainable wastewater management by Slav Hermanowicz. He spoke about the development, and the state of the art technology in terms of wastewater treatment in developed countries. Slav Hermanowicz has conducted research and has taught at the University of California, Berkeley in the area of environmental engineering since 1983.
The first sewage water system was built to transport rainwater out of cities to protect them from floods. Soon after, people realized that these canals can also be used to transport excrement and other waste. The manual collection systems were soon replaced by sewage systems, which diverted the wastewater into nearby rivers. The release of more and more wastewater into water bodies leads to the enormous pollution of rivers and lakes. Due to the negative effect of polluted rivers on the health of humanity and nature, solutions had to be found to improve the water quality of water bodies around cities. Therefore, the first wastewater treatment plants were developed. Over many years, new wastewater treatment methods were investigated, which allowed eliminating pollutants more effectively. However, a lot of research is still done to optimize processes and efficiency.
Most city centers are dewatered in a mixed system, which means that there is only one sewer system that collects wastewater together with rainwater. In terms of wastewater treatment, separate sewer systems would be more efficient, due to a smaller drain and higher pollutant concentrations. Since the first sewer systems were originally built to transport rainwater, mixed-water systems are still widespread. The use of mixed-water systems thus has historical reasons.
To replace the mixed water systems with a separated system is, for a city like San Francisco, not economically feasible. For a separated system, almost every street would have to be broken up to replace the old channel with two new channels. The costs would be intolerable. And imagine the inevitable traffic chaos due to construction sites! For that reason most old cities continue operating a mixed-water system.
Although the consequences of inexistent wastewater treatment are known, there are still many cities in developing countries without sewer systems or without wastewater treatment plants. The buildup of sewage infrastructure is very expensive. Capital would be needed, which is not present. It would be ideal, if separated systems were already considered during the planning process of new systems. But, since financial resources for infrastructure are rare, it seems unrealistic to think about separated systems. The cities even lack the capital to build the cheaper mixed water systems, which would meet the fundamental requirements.
Although the problems the developed countries had and still have are known, it is almost impossible for developing countries to avoid making the same mistakes again. The technique to build efficient systems is available, but the financial resources to realize them aren’t.