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.
An alternative approach for combined water treatment as opposed to its CSO discharge into receiving water is its bypass to the inlet of secondary clarifiers (SC). To analyse the processes and to evaluate the performance of this approach, experiments and numerical modelling were carried out. In batch and pilot scale experiments major effects were identified and quantified. The Activated Sludge Model No. 3 (ASM3) was modified to simulate the batch and pilot scale experiments for implementation of the bypass-specific processes and thus to set up an overall balance of the relevant compounds. With some modifications of ASM3, good agreement of the modelling results with measurements of COD, nitrogen and phosphorus were achieved.
Neusiedlersee (in German) / Fertö tó (in Hungarian) is a shallow lake at the Austro-Hungarian border. In the late 1970s, the question arose what to do in order to protect the lake against eutrophication. A preliminary report established the need for point-source control as well as gave first estimates for non-point source inputs. The proposed point-source control was quickly implemented, non-point sources were - among other topics - studied in detail in the period 1982 - 1986. The preliminary work had shown, based on integrated sampling and data from literature, that the aeolic input outweighed the one via water erosion (work was for totP only). In contrast to this, the 1982 - 1986 study showed that (a) water erosion by far dominates over aeolic inputs and (b) the size of nonpoint-source inputs was assessed for the largest catchment area in pronounced detail, whereas additional estimates were undertaken for smaller additional catchment areas. The methods as well as the results are presented in the following. The paper concludes with some remarks on the present management practice of nonpoint-source inputs.
A process is introduced which utilizes secondary clarifiers for the treatment of combined sewage. Under storm water conditions, surplus sewage bypasses the aeration tanks after primary treatment and is directly introduced into the secondary clarifiers. The hydraulic capacity of existing activated sludge plants can be increased without additional tank volume. Particulate matter as well as dissolved compounds are removed to a high extent. Investigations on a full scale treatment plant (100,000 p.e.) show that the effluent quality is comparable with full biological treatment, even if the hydraulic loading is increased by 50%.
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