On the specific character of wastewater system reliability indicators

Summary

Authors of technical literature related to various aspects of municipal wastewater disposal systems sometimes introduce notions and definitions that concede varying interpretations which is inaccurate, particularly when using mathematical tools. Therefore, the severity and definiteness of terminology under the circumstances are of special importance. The necessity, possibility and specific character of sewer reliability indicators are discussed. One of such indicators based on the hypothesis of the steady state of «failure-rehabilitation» processes is analyzed. The calculation of the introduced integrated municipal sewer reliability indicators essentially amounts to the estimation of the predictable volume of raw wastewater discharged from the system in some period because of the failure of some elements. One of the possible approaches to the solution of this problem in the context of the hypothesis of the steady origin of the sewer elements and facilities failure and rehabilitation flow is the method of segmentation and equivalenting. The ways of extending the suggested approach to an unsteady case when the failure flow rate shows seasonal periodicity or the network elements show tendency to «ageing» are designated.

Key words

sewerage network , reliability indicator , relative discharge volume , rate of failure , method of segmentation and equivalenting

Specificity and methodological features of evaluating the reliability of sewer networks in large cities

Summary

The paper draws attention to the structural differences of two equivalent subsystems of a single infrastructure of a water supply and wastewater disposal system in a large city: a water supply subsystem and a wastewater disposal subsystem. It is stated that by now there is no unified established concept regarding the quantitative measure of the reliability of the sewer network. Based on the results of a review of modern domestic scientific and technical literature, three approaches to evaluating the reliability of municipal wastewater disposal systems are singled out and critically analyzed. The capabilities determined by the accepted assumptions are identified, and the areas of practical use of each of them are specified.

Key words

reliability , sewerage network , state graph , method of segmentation and equivalenting , Kolmogorov equations , «destruction and replication» scheme

Sewer network reliability control

Summary

The fundamental possibility of the sewer network reliability control by developing (with subsequent implementation) mid- and long-term plans for its renovation according to the criterion of the minimum possible environmental risk is discussed. As a quantitative measure, an indicator of the operational reliability of the network is considered, i.e., the relative volume of wastewater not delivered to the treatment facilities because of the failures of the network structural elements. The assumptions and limitations of such control attributable to the specific features of the object, are discussed. An algorithm for developing a network renovation plan according to the environmental criterion is proposed using the method of object segmentation and equivalenting.

Key words

reliability , management , sewerage network , method of segmentation and equivalenting , environmental risk