Wastewater treatment plants are designed to work effectively in a certain range of operating conditions, in relation to the values of flow rate, characteristics of the sewage, concentrations of constituents and load values. The standard design approach is based essentially on the assumption of steady conditions and the estimate of the wastewater conveyed to the plant in different scenarios (daily peak and night time minimum in dry weather conditions; total maximum flow rate during wet weather). The flow rates and pollutant load are however magnitudes that vary in time and space. The need therefore arises to modify the design procedures currently in use, abandoning the steady condition assumption and taking a dynamic approach. Knowledge of the variability of the quantitative and qualitative characteristics of civil wastewater are of decisive importance when locating and dimensioning the spillways and the pumping stations upstream of the treatment plants. The time diagram of the concentrations arriving at the treatment plant could also make it possible to opti-mise its management and obtain a better estimate of the equalization volumes. The article presents a model capable of characterising, in dry weather, the flow rate diagrams and pollutant loads in the sewer networks starting with the use of the main residential appliances (WC, washbasin, sink, shower, washing machine and dishwasher). Flow into the sewer is the result of an almost random use of domestic devices, each with its own character-istics and frequency of use connected to the particular time of day. These flows are intermittent and are characterised by a relatively short duration by which it is possible to interpret the habitual use of domestic devices in the residential units by the users (Butler et al 1995, 1996). For domestic devices the parameters average daily frequency of use, start time, average duration of use and volume discharged are estimated using a probabilistic process by estimating the standard deviation from the average value considering a normal distribution (Butler & Graham 1995). This assumption makes it possible to take account of the habits, lifestyles and different needs of the users which can induce consid-erable variability in the types and frequency of use. The same approach was used to characterise the inputs of pollutants arising from the use of residential devices. The COD (Chemical Oxygen Demand) was considered as a pollution parameter of the wastewaters, fixing an average daily input per capita of 120 gCOD/AE/d, for all the discharges. The per-centage values, on a daily average basis, of the individual devices were determined by referring to studies found in literature (Butler et al., 1995; Friedler and Butler, 1996; Almeida et al., 1999). The problems related to the lamination and equalisation of the hydraulic and pollutant loads due to the transfer of the wastewater into the sewer network were analysed. In the model used it was assumed that a generic sewer pipe behaves as if it were a continuous reactor with perfect mixing (CFSTR, Continuous-Flow Stirred-Tank Reactor), as developed also by Nielsen et al. (1992). In this first phase the model, applied to a single section of sewers with a limited number of users, seemed to represent a usable instrument at the design stage and in the management of an entire sewer net-work/treatment plant. The model proposed, applied previously for characterising the domestic water demand, was applied successfully for the first time for the distribution network of the municipality of Sparanise (Lombardi et al., 2018).

Silvagni, G., Volpi, F. (2019). Modeling of domestic wastewaters in sewer networks. In Giuseppe Frega & Francesco Macchione (a cura di), Technologies for integrated river basin management (pp. 557-569). Cosenza : EdiBios di Irene Olivieri.

Modeling of domestic wastewaters in sewer networks

Silvagni, G.;Volpi, F.
2019-06-19

Abstract

Wastewater treatment plants are designed to work effectively in a certain range of operating conditions, in relation to the values of flow rate, characteristics of the sewage, concentrations of constituents and load values. The standard design approach is based essentially on the assumption of steady conditions and the estimate of the wastewater conveyed to the plant in different scenarios (daily peak and night time minimum in dry weather conditions; total maximum flow rate during wet weather). The flow rates and pollutant load are however magnitudes that vary in time and space. The need therefore arises to modify the design procedures currently in use, abandoning the steady condition assumption and taking a dynamic approach. Knowledge of the variability of the quantitative and qualitative characteristics of civil wastewater are of decisive importance when locating and dimensioning the spillways and the pumping stations upstream of the treatment plants. The time diagram of the concentrations arriving at the treatment plant could also make it possible to opti-mise its management and obtain a better estimate of the equalization volumes. The article presents a model capable of characterising, in dry weather, the flow rate diagrams and pollutant loads in the sewer networks starting with the use of the main residential appliances (WC, washbasin, sink, shower, washing machine and dishwasher). Flow into the sewer is the result of an almost random use of domestic devices, each with its own character-istics and frequency of use connected to the particular time of day. These flows are intermittent and are characterised by a relatively short duration by which it is possible to interpret the habitual use of domestic devices in the residential units by the users (Butler et al 1995, 1996). For domestic devices the parameters average daily frequency of use, start time, average duration of use and volume discharged are estimated using a probabilistic process by estimating the standard deviation from the average value considering a normal distribution (Butler & Graham 1995). This assumption makes it possible to take account of the habits, lifestyles and different needs of the users which can induce consid-erable variability in the types and frequency of use. The same approach was used to characterise the inputs of pollutants arising from the use of residential devices. The COD (Chemical Oxygen Demand) was considered as a pollution parameter of the wastewaters, fixing an average daily input per capita of 120 gCOD/AE/d, for all the discharges. The per-centage values, on a daily average basis, of the individual devices were determined by referring to studies found in literature (Butler et al., 1995; Friedler and Butler, 1996; Almeida et al., 1999). The problems related to the lamination and equalisation of the hydraulic and pollutant loads due to the transfer of the wastewater into the sewer network were analysed. In the model used it was assumed that a generic sewer pipe behaves as if it were a continuous reactor with perfect mixing (CFSTR, Continuous-Flow Stirred-Tank Reactor), as developed also by Nielsen et al. (1992). In this first phase the model, applied to a single section of sewers with a limited number of users, seemed to represent a usable instrument at the design stage and in the management of an entire sewer net-work/treatment plant. The model proposed, applied previously for characterising the domestic water demand, was applied successfully for the first time for the distribution network of the municipality of Sparanise (Lombardi et al., 2018).
19-giu-2019
Settore ICAR/02 - COSTRUZIONI IDRAULICHE E MARITTIME E IDROLOGIA
Italian
Rilevanza internazionale
Capitolo o saggio
Wastewater treatment plants; sewer network; model
Silvagni, G., Volpi, F. (2019). Modeling of domestic wastewaters in sewer networks. In Giuseppe Frega & Francesco Macchione (a cura di), Technologies for integrated river basin management (pp. 557-569). Cosenza : EdiBios di Irene Olivieri.
Silvagni, G; Volpi, F
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/215127
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