Abstract
Six artificial wetlands, sized for the daily wastewater of 5 to 100 persons, were examined for two years monthly in each case directly and seasonally in particular as well as additionally by means of a new inspection-piece technology. The prepurifying was done either by multi-chamber-putrid-pits or rotting filters, the main cleaning was done by subsurface flow wetlands either with underground or superficial filling. The results were compared with those of rotting filter models under standardized conditions and with those of sewage treatment plants. With all examined water purification systems, carry along of epidemic exciters by means of dead and living vectors was a weak point. In contrast to a constant amount of germs in the inlet water of sewage treatment plants with a number of E. coli and faecal streptococci of on the average between log 5 and log 4 KBE/ml, a strongly varying amount of germs between log 1 and log 5 KBE/ml were found in the inlet water of decentralized artificial wetlands. The median of the number of germs in to most screened wetland "Nord-1" was for faecal streptococci in the inlet about 2,3 x log 3 CFU/ml, after the rotting filter about 9,3 x log 3 CFU/ml, after the reed patch about 9,3 x log 1 CFU/ml and after the pond about 1,8 x log-1 CFU/ml. The number of germs in the brook was not measurably changed by the wetlands outlet. By means of a new inspection-piece-technology, which prevented the washing out from germs, it could be proven that Salmonella Typhimurium survived up to 14 months in artificial wetlands as well as in rotting filters. By contaminating the wetlands with Salmonella Typhimurium a case of epidemic was simulated. In each attempt the germs passed the plants and could be isolated in the discharge at the latest after 14 days. Expectations, that the material resulting in the rotting filter would be hygienically harmless according to the defaults of the KrW/AbfG valid since 1998, was not fulfilled. In a hygienic-comparative evaluation between rotting filters and multi-chamber-putrid-pits first fared more badly. First of all because the material resulting there was too little, too firmly and too damp than that a rotting could take place so that it needed a storage time from up to 12 months to get an acceptable germ reduction. And secondly existed during this time a permanent reservoir of pathogens, which can be a special endangerment because of short infection ways in the rural area. The hygienically most justifiable way of the utili-zation of rotting filter contents was the sterilizing with at least 60 kg/m3 quicklime followed by digging up into a field. The multi-chamber-putrid-pit against it was practical to handle, operates nearly maintenance free, was operating stably, it took place a sufficient holding back of solids and the content could be delivered to a conventional sewage treatment plant. It had a minimum health risk due to the closed way of building. The only disadvantage was their small capacity for maximally two households. A sufficiently dimensioned wetland (> 2 m2/EGW), which was horizontal subsurface flowed and fed underground, was suitable to reduce hygienically relevant micro organisms sufficiently in the summer and in the winter. All other artificial wetlands reached a stable and clear cleaning achievement only by an added pond. |
