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The Improvement of the Sewage Treatment of the City of Winterthur and its Influence on the River Töss and its Underground Water Stream By HAKUMAT RAI Contents Acknowledgments 2 Research Problem 3 Research Program 4 Description of the River Töss Basin 4 Physiography 4 River Discharge 5 Catchment 7 Precipitation 7 Climatological Elements 8 Sources of Pollution 8 Material and Methods 11 Sampling Stations 12 Presentation of Data 15 A. Physical and Chemical Analyses 15 l. Temperature 15 2. pH-values 16 3. Carbonate and Total Hardness 18 4. Phosphate 22 5. Dissolved Oxygen (D.O.) 23 a) Saturation Deficit 26 b) Dissolved Oxygen Consumption Curves 28 6. Biochemical Oxygen Demand (B.O.D.) 30 7. KMnO4-Consumption 34 2 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 8. Nitrogenous Compounds (Inorganic) 38 a) Nitrate 38 b) Nitrite 38 c) Ammonia 40 9. Chloride 42 10. Detergents (Surfactants) 44 11. Suspended Matter 45 12. Total Volatile and Fixed Residue 46 13. Iron 49 B. Bacteriological Studies on the River Töss 49 1. Standard Plate Count (Total Count of Bacteria) 49 2. Coli and Coliform 52 C. Physico-Chemical and Bacteriological Characteristics of Sewage Treatment Plant Effluents and the Tributaries of the River Töss 55 1. Sewage Treatment Plants 55 2. Tributaries 59 D. Diurnal Varlation Studies in the River Töss 62 1. Diurnal Variation Studies at Winterthur Sewage Treatment Plant and River Töss 62 2. Diurnal Variation Studies at Rorbas Sewage Treatment Plant and River Töss . 69 E. Discussion 74 The Töss River Before and After the Construction of the Activated Sludge Unit at Winterthur Sewage Treatment Plant 74 Effect of Organic Matter 81 Influence of the River Töss on the Sanitary Condition of the River Rhein 82 Pollution Travel with Ground Water 84 Recommendations 91 Summary 92 Zusammenfassung 95 References 98 Acknowledgments This research project was sponsored in part by the Stiftung der Wirtschaft zur Förderung des Gewässerschutzes in der Schweiz and the Bauamt der Stadt WiHter- thur, and was coHducted at the Kantonales Laboratorium, Limnologische Abteilung, by the University of Zürich. My grateful thanks are due to Prof. Dr. E. A. THOMAS of the Department of Botany, University of Zürich, under whose guidance the present work was done. I am indebted to Dr. ERNST ROMANN, Director of the Kantonales Laboratorium for providing facilities, for his interest and encouragement. It is a pleasure to acknowl- edge the Amt für Gewässerschutz und Wasserbau des Kantons Zürich, Schweizerische Meteorologische ZeHtralaHstalt, Gas- und Wasserwerk der Stadt Winterthur and the authorities of the Eidgenössisches Amt für Wasserwirtschaft, Bern, for their assistaHce and information contributing to the research work of the survey. I am grateful to Prof. Dr. H. WANNER, Director of the Institut für AllgemeiHe Jahrgang 115 H. RAI. River Töss and its Underground Water Stream Botanik, University of Zürich, for critically goiHg through the manuscript and making valuable suggestions. And last but not least, my thaHks are due to Messrs. W. SCHNEEBELt, M. SPRING, P. LEUMANN and all personnel of the Laboratorium des Kantonschemikers for their valuable assistance during the survey. Research Problem Present publicity for water protection has made a large majority of the population aware of the necessity to protect the waters. Expansion iH number and variety of commercial production for urban, industrial and agricultural use has intensified the water quality control problem. Chemical industries, organic and inorganic, have expanded more rapidly than the population, their wastes frequeHtly beiHg unlike anythiHg found in nature. Past experience in coHventional waste treatment provides insufficient guidance for effective control of waste water from: textile, plastic, rubber, dye, detergeHt and maHy other petrochemical productions. The heavy use of synthetic organics for agricultural purposes is reflected in the appearance of such chemicals in streams receiviHg farmland drainage. CoHcentratioHs as low as one part iH a billion of some chemicals can cause such water damage as change in taste and odour, off-flavour in fish, toxicity to fish, ion-exchaHge damage, foamiHg, interference with oxygen transfer and interference with water-treatment processes. Toxicity to humans too is a conceivable effect of such pollutioH. IH this country a great number of waste-water treatment plants have come iHto operation. Although waters beloHg to the KantoHs, the scientific personnel in all the Kantons is understaffed and consequeHtly it is impossible to effect and maintain the necessary periodic coHtrol of the water and check the effectiveness of the purifica- tion systems. The most importaHt basic requirements for further establishmeHt of water protection in SwitzerlaHd are therefore missing. The Töss is a typical example of a river whose surface water sinks iHto the ground over loHg stretches, according to its ground water aHd surface water levels. At many places aloHg this river the underground water has to be utilized for drinking purposes. This river is heavily polluted downstream from the city of Winterthur to the point of its confluence with the River Rhein at Tössegg, siHce, as late as the Spring of 1966, there was only one mechaHical waste water treatment plant for the city of Winterthur. But duriHg the summer of 1966 an activated sludge treatment unit was added at Hard to the existiHg waste water treatment plant for the city of Winterthur. This raises the questions : a) in what way will this activated sludge process for waste water purification affect the saHitation of the River Töss; b) what other bigger or lesser sources of water contamiHatioH iH the catchment area of the river have to be eliminated until a satisfactory sanitation is reached; c) whether the endaHgered uHderground water stream of this river valley can, on the whole, be considered safe. 4 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 Research Program To answer these questions, the following studies were carried out: a) before starting operatioH of the activated sludge treatment plant at Winterthur, samples were collected from the Steigmühle (upper course) to its poiHt of con- fluence at Tössegg with the river Rhein; these were then thoroughly studied; b) over the same stretch of the river regular studies were carried out after starting the biological purificatioH operatioH at WiHterthur-Hard; c) diurnal variations of the quality and quantity of the sewage treatmeHt plaHt at differeHt stages of the treatment process were examined and the influence of the Winterthur sewage treatment plant effluent on the River Töss water was studied at different seasons and different water levels. Regular research on other sources of contamination was done, with special attention to the polluted tributaries and the effluent of the Rorbas sewage treatment plant, as these contaminants caH materially alter the normal state of the river. FiHally the River Rhein, above and below the confluence of the Töss, was also regularly stIdied to ascertain the influence of the polluted Töss on the less polluted Rhein. Description of the River Tss Basin Physiography The main physical features are indicated in Fig. 1. The river originates from two differeHt sources (Vordere and Hintere Töss), one west of the Welschenberg, at an altitude of 1240 m above sea level, and the other south of the SchiHdelberg, at an 500— 2.1Km 450 _z 0 400® F- r- 350— 5 K m. 300 18 21 212 I 25 126/2171 28/291 1 6 2 3 STATIONS Fig. 2. Profile of River Töss from Winterthur to Tössegg. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 5 altitude of 1120 In above sea level (Landeskarte der Schweiz, 1 : 25000, Blatt 1051, 1071 aHd 1072). These sources have very steep flows for 3 to 4 km, before their point of coHflueHce at Töss-Scheide, at an altitude of 794 m above sea level. From Töss- Scheide to Tössegg the poiHt of confluence with the River RheiH, the river is 54.2 kin loHg. It enters the state of Zürich at the south-easterH limits aHd runs diagonally towards the northern limits of the state, where it flows into the River Rhein. The river Töss is classified as a middle European pre-alpiHe river (FRÜH, 1930 and 1935). Throughout the year the river is fed almost entirely by raiH, aHd shows a quick increase in level in spring, during the thunderstorms and due to the melting of snow. It is characterized by its big differences between high and low levels. The low water levels occur iH late summer and from autumn through the winter, whereas the high water levels usually are due to summer rains. The differences between high and low water levels are even more effective due to the geological character of the catchment area, which is mainly very little permeable to water. The average fall of the river is 8.27%, but the fall is not eveHly distributed over the leHgth of the river. BetweeH Töss-Scheide and Steg there are rapids, and the average fall is between 11 aHd 19%, between Turbenthal and Sennhof it decreases to 7.6% and over the rest of the river it decreases to 4% (Fig. 2). River Discharge Flow data is tabulated in Table 1 aHd is illustrated iH Fig. 3. The mountain torrent character of the Töss is clearly demonstrated by the big variation in the water levels. Lowest flow measured was 0.8 m 3/sec. iH the lowest part of the river (Statistisches o o MONTHLY AVERAGES (1967-68) Fig. 3. Average Rate of Flow in the ® AVERAGE FLOW ON THE DAY OF SAMPLING. River Töss Gauged in the Neften- x--%MONTHLY AVERAGES (1921-67 ) bach. 1 1 I I I 1 I I 1 I 1 MAMJ JASON D J F 6 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 Table 1. Discharge in the River Töss (m 3/sec.) Gauged in the Töss at Neftenbach, 1967/68 Monthly Monthly Average Discharge on Average Maximum the Day of Sampling Date 1967 l.

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