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Wastewater treatment : biological and chemical processes
- Date_TXT
- New york : Springer , 1997
- Cote
- 628.162 HEN
- Auteur
- Mogens, Henze
- Type de document
- Livre
Description :
Wastewater flows are not steady or uniform, but vary from one hour to another, from day to day, from month to month and from year to year. When building a treatment plant, it is important to know the volumes of wastewater and their variations, now as well as in future. Based on the knowledge of the wastewater, the design of the treatment plant can be determined, taking into account the wastewater to be treated. In this connection measurements are useful; if such measurements do not exist, an estimate should be made. In respect of the volume of future wastewater, the development should of course be taken into account, i.e. a prognosis should be made.
Measurements of the volume of wastewater will be either in the form of curves or in the form of figures (metering). Fig 1.1 shows a diurnal variation for wastewater in the influent entering a treatment plant. The curve is the sum of domestic, industrial and public institution wastewater, infiltration and ex-filtration. There is no reason to consider the size of the individual contributions as the curve shows what reaches the treatment plant. In case of a projection of the volumes of wastewater and their variations, however, it is recommended to analyze the curve and the catchment area for the purpose of splitting up the sub-contributions as it will be easier to project these separately This is briefly dealt with in Sections 1.2 a By processing the data statistically a more detailed picture of wastewater variations is obtained. The different volumes of water (volume, maximum hour, maximum second, etc. over a 24-hour period) will often be normally distributed or log-normally distributed. Data sets for wastewater are never ideal as there will be irregularities which may, if they are too excessive, result in a special treatment of the data.
Fractile diagrams can be an important tool in the design of treatment plants. Fig 1.2 gives an example of such a diagram. The 60 per cent fractile is frequently used as an average load and a fractile of 85-90 per cent as a maximum load.