The applicability of UV-absorption measurements at combined sewer overflows was investigated under different storm water conditions. Three specific rainfall events of different intensity, different duration and different intervals between the events were investigated. An individual evaluation of each single event resulted in an acceptable correlation between the UV absorption and the pollution measured as COD. A combined evaluation of the different events exhibited a very poor correlation which could not be used as pollution control parameter. Since the calibration procedure of the spectrometer used was not flexible enough to distinguish between different wastewater matrices from the different storm events the applicability of this type of spectrometer for the control of storm water overflows is questionable.
Two treatment plants - in the drainage area of Lake Neusiedl in Burgenland (Wulkatal, Eisbachtal)-with nitrification-denitrification and simultaneous precipitation of P were operated with an anoxic -anaerobic aeration tank to obtain biological P-removal. The results indicated that a complete denitrification is essential in the first tank to obtain release and biological uptake of phosphorus. Low loading in the Wulkatal-Plant resulted in incomplete denitrification and a biological P-removal of only 60 %. The dosage of a reduced amount of precipitant indicated a combined action of chemical and biological P-removal. In the Eisbachtal Treatment Plant with the same mode of operation - two aeration tanks of which the first was kept anoxic-anaerobic - a biological P-removal of more than 90 % was obtained under optimal process conditions. At low temperatures the removal efficiency was reduced. This could, however, be compensated by a reduced amount of precipitant. An average addition of about 1 g Fe/gP which is far below the theoretical amount for precipitation resulted in effluent concentrations below 1 mg P/1 over a period of two and half years.
At the high loaded Main Treatment Plant of Vienna (F/M ratio about 1 ky/kg.d) which has plug flow conditions in the aeration tanks and ferrous sulfate addition for the control of bulking, a significant biological P-removal has been observed. According to measurements at the 400.000 m3/d plant about 50 % of the P is removed by additional biological uptake.
The sewage-load variations in winter tourism areas are characterized by sudden increases--in the range of a factor two to three--within only a few days at the start and the end of the tourist season, especially at Christmas. The sudden load increases occur during periods of low wastewater temperatures, which is an additional demanding factor with respect to nitrogen removal. A full case study was carried out at WWTP Saalfelden, which is located near one of Austria's largest skiing resorts. The plant is designed for 80,000 PE and built according to the HYBRID-concept, which is a special two stage activated sludge process for extensive nutrient removal.
Upgrading of wastewater treatment plants under maximum use of existing structures is often an important requirement, but also useful due to a number of aspects. Because of a change in legal effluent requirements, a number of plants in Austria, typically aged 20+ years, were required to be extended. The two stage activated sludge HYBRID-process often provides an interesting design alternative for such plant upgrades, especially in case an anaerobic sludge treatment stage already exists. It provides high nutrient removal capacity at low area demand. The latter is especially important in cases where no or very limited extension area is available making it the key factor to preserve a site for future use. Based on two full stage case studies the adaptation of the plant layout, first operation results and a synthetic cost comparison to a conventional (single stage) plant extension are given.
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