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Chapter 10

Introduction to Wastewater

Systems

According to the World Health Organization (WHO), 2.4 billion people lack access to
improved sanitation, which represents 42% of the world’s population. More than half of those
without improved sanitation—nearly 1.5 billion people—live in China and India. In sub-
Saharan Africa sanitation coverage is a mere 36%. Only 31% of the rural inhabitants in de-
veloping countries have access to improved sanitation, as opposed 73% of urban dwellers.
About 2 million people die every year due to diarrheal diseases; most of them are
children less than 5 years of age. The most affected are the populations in developing
countries who are living in extreme conditions of poverty, normally peri-urban dwellers
or rural inhabitants. Among the main problems responsible for this situation are (a) lack
of priority given to the sector, (b) lack of financial resources, (c) lack of sustainability of
water supply and sanitation services, (d) poor hygiene behaviors, and (e) inadequate
sanitation in public places including hospitals, health centers, and schools. Providing
access to sufficient quantities of safe water, providing facilities for the sanitary disposal
of excreta, and introducing sound hygiene behaviors are of capital importance to reduce
the burden of disease caused by these risk factors.
To meet the WHO Millennium Development Goals (MDGs) sanitation target, an addi-
tional 370,000 people per day between 2005 and 2015 should gain access to improved san-
itation. If this goal is met, the proportion of people without sustainable access to safe
drinking water and basic sanitation should be halved by 2015.
This chapter outlines the broad purpose and composition of wastewater systems. With
an understanding of the whys and wherefores of needed structures and operations as a
whole, we can proceed more fruitfully to a rigorous consideration of details. The practi-
tioner, too, does not move to detailed design until he has settled on a general plan.
Wastewater systems normally comprise (a) collection works, (b) treatment works, and
(c) disposal or reuse works. Together, their structures compose a sewerage or drainage sys-
tem. Although individual systems are in a sense unique, they do conform to one of the
types outlined in Fig. 10.1. As shown in the figure, wastewaters from households and in-
dustries are either collected along with stormwater runoff in the combined sewers of a
combined system of sewerage or are led away by themselves through separate sanitary
sewers, while stormwaters are emptied by themselves into the separate storm sewers of a
separate system of sewerage. The water-carried wastes from households are called domes-
tic wastewater; those from manufacturing establishments are referred to as industrial or
trade wastes; municipal wastewater includes both kinds. Combined sewerage systems are
common to the older cities of the world where they generally evolved from existing systems

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