Water Pollution Control

Suresh T. Nesaratnam

• Publisher: Wiley
• Year: 2014
• eBook ISBN: 9781118863800
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Umweltmanagement

Designed to accompany the new Open University course in Environmental Monitoring and Protection, this is one of four new titles which will equip the reader with the tools to undertake Environmental Impact Assessments (EIAs). Used in planning, decision-making and management, EIAs review both the theoretical principles and environmental considerations of engineering and environmental projects to help steer fundamental legislation in the right direction.

This book begins with a discussion of the basics of the hydrological cycle and a description of the natural aquatic environment including the normal composition of surface waters. Further chapters detail the sources of water pollution and the affects of water pollution including biological treatment of sewerage, sludge treatment and disposal, before addressing industrial wastewater treatment and water quality assessment.

Discover our e-book series on Environmental Monitoring and Protection, published in partnership with The Open University!
Find out more about the series editors, the titles in the series and their focus on water, noise, air and waste, and The Open University courses in Environmental Management.
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Section 1: Water basics

1.1 Introduction

We can all relate to water. We know we need it to survive – indeed, the early great civilisations of Egypt and Mesopotamia were centred on river valleys where there was a plentiful supply of fresh, clean water.

When we take water into our bodies, it is used in several ways. For example:

• for cooling – it helps keep our bodies at around 37 °C
• as a waste disposal medium
• as a conductor for nerve impulses
• as a component in the digestion of food
• as a solvent in which vital chemical reactions take place.

You can see from the above that even if you didn’t move an inch, your body would still need water to keep you alive.

Water is a fascinating subject, encompassing chemistry, biology and physics. Apart from keeping us alive, water is used extensively in industrial processes, for recreation and for transport. It is something we can’t do without.

The water we use for domestic purposes ought to be free from contaminants, yet water pollution is a major problem in many countries. According to the World Health Organization (WHO, 2002), about 1.7 million people die each year due to unsafe water, sanitation and hygiene. This text endeavours to outline the need for monitoring of the aquatic environment, leading to effective means of protection being put in place. It details various sources of water pollution, and describes the effects that different pollutants have on water. Sewage treatment is then considered in detail, and various treatment methods are presented; this is followed by sludge treatment and disposal. Next, the important subject of water quality testing is addressed, with details of the different tests. Industrial wastewater treatment is introduced, and the final section looks at river quality modelling.

The self-assessment questions (SAQs) located throughout the text will help you to review and remember what you have read.

1.2 The hydrological cycle

The hydrological cycle – the continuous cycling of water between land, open water surfaces and the sea, either directly or indirectly – is a complex process that has been known about for a long time (Figure 1). Probably the oldest reference to the hydrological cycle is found in the Chandogya, one of the principal Upanishads, which says ‘rivers … lead from sea to sea’. It reveals that as early as 1000 BCE, attempts were being made to interpret and explain recurrent phenomena on the basis of direct experience.

Figure 1 Early understanding of the water cycle?

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The identifiable mechanisms of the cycle are complicated not only by the characteristics of air–water–land interfaces across which the cycle operates, but also by climatic factors that vary in both time and space. The various operations and mechanisms within the cycle are illustrated in Figure 2.

Figure 2 The hydrological cycle (volumes are in Tm³ = 10¹² m³)

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1.3 The natural aquatic environment

Now that you have been introduced to the basic hydrological cycle, this subsection will consider the importance of water and how crucial dissolved oxygen is to aquatic life. The physical, chemical and biological characteristics of natural waters will then be explored. Importantly, how the parameters vary will be considered. Seasonal effects are important, as you might imagine.

1.3.1 Water, the medium of life

Water is an excellent solvent, so it is never pure – even in its ‘natural’ state, it contains a variety of soluble inorganic and organic compounds. Water can also carry large amounts of insoluble material in suspension. The amounts and types of impurities vary with location and time of year, and determine some of the characteristics of a particular watercourse.

One of the most important determining factors is the presence of organic material in solution or in suspension. Organic material can be used as food by the organisms living in natural water, provided the material is biodegradable. The basis of a trophic system in a river is the inorganic and organic materials it contains, their biodegradation by decomposer organisms, and the products of the photosynthetic activities of the primary producers (green plants and algae).

In water, as on land, the primary producers are eaten by herbivores (primary consumers) and these in turn are devoured by the secondary consumers (carnivores). The interdependence of these organisms gives a complex food web within which there are many food chains, the successive links in the chains being composed of different species in a predator–prey relationship. For a river, a typical food chain could be:

alga → protozoan → mayfly nymph → small fish (e.g. minnow) → large fish (e.g. pike)

Scavengers eat bottom debris, including dead organisms. Any uneaten dead organisms are broken down by decomposers (mostly bacteria and fungi), releasing nutrients that can be taken up by plants.

Through this cyclic movement of nutrients, the water environment achieves an ecological equilibrium. In theory, in any given stretch of water a balance occurs between the production of living material and the death and decomposition of organisms over a period of time. The river neither becomes choked with living organisms nor is devoid of them – although, depending on location and geological conditions, the numbers and varieties of organisms in the biota vary enormously. The maintenance of equilibrium is dependent on the complexity of biota and the interlinking of food chains and webs.

If the water contains low levels of plant nutrients then the conditions are said to be oligotrophic. This may occur when the physical and chemical characteristics of the land through which the water passes are such that nutrients are sparse or are not dissolved out of the soil and rocks.

The opposite condition, with high levels of nutrients in the water, is described as eutrophic; the gradual increase with time of plant nutrients in a body of water is called eutrophication.

Flowing and standing water

A typical river has several sources in high ground that are characterised by steep gradients, swift current velocities, and erosion of the surrounding rocks and soil. As the gradient lessens, the current velocity decreases and the river deepens and widens. The river then tends to deposit stones, gravel and sand. This variation in the flow downhill has a direct influence on the types of organisms and substratum to be found at different points along the river. The whole length of the river can be subdivided into different zones, each characterised by its own typical fauna and flora.

In contrast to rivers, standing bodies of deep water such as lakes and reservoirs may be affected by thermal stratification. Figure 3 illustrates this effect for a typical lake. In the summer, there is very little mixing between the cooler, denser water at the bottom of the lake (hypolimnion) and the warmer, less dense water at the lake surface (epilimnion). Thus, stream and river water running into the lake will tend to stay in the upper layer. This water carries nutrients, so organisms flourish in the epilimnion and there is a high rate of primary production. In the hypolimnion, the dead remains of primary production settle out, forming a layer of bottom sediment.

Figure 3 Thermal stratification of a lake

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The lack of mixing between the layers (stratification), together with the absence of light penetration to the bottom of the lake, determines the ecological characteristics of a deep lake or reservoir. In a deep lake, the absence of light prevents the ...

Table of contents

• Section 1: Water basics
• Section 2: Pollution of the aquatic environment
• Section 3: The effects of pollutants on the aquatic environment
• Section 4: Sewage treatment
• Section 5: Sludge treatment and disposal
• Section 6: Water quality tests
• Section 7: Industrial wastewater treatment
• Section 8: River quality modelling
• Glossary
• References
• Acknowledgements