Pollution Control and Resource Recovery

Sewage Sludge

Zhao Youcai, Zhen Guangyin

• Publisher: Butterworth-Heinemann
• Year: 2016
• Print ISBN: 9780128116395
• eBook ISBN: 9780128118542
• Topic: Technologie et ingénierie
• Subtopic: Gestion de l'environnement

Pollution Control and Resource Recovery: Sewage Sludge discusses several traditional and new environmentally friendly technologies for sewage sludge treatment and disposal. In addition, the book covers a range of new initiatives that are underway to promote and accelerate the development of related sciences and techniques. The book's authors builds a framework for developing various sustainable technologies for sewage sludge treatment and disposal, including advanced dewatering through chemical conditioning, solidification/stabilization, reuse for the development of construction and building materials, anaerobic bioenergy recovery, sanitary landfill, and odor control. - Explains environmentally friendly technologies for sewage sludge treatment and disposal, including advanced dewatering through chemical conditioning, solidification/stabilization, and anaerobic bioenergy recovery - Includes valuable guidelines for engineers to address sludge issues, such as sanitary landfill and odor control - Presents new developments and techniques that are on the horizon

Chapter One

Sewage Sludge Generation and Characteristics

Abstract

Sewage sludge, one of the main by-products from wastewater biological treatment process, is being continuously generated. It contains a myriad of toxic substances including pathogens such as viruses and worm eggs, heavy metals, and some organic contaminants, which create odors and hygiene concerns. Improper disposal and reuse of sewage sludge causes severe environmental impacts and health hazard to the public. The water industry is facing unprecedented economic and environmental constraints because of not only large amounts of sewage sludge produced but more stringent regulations. The processing of sewage sludge is one of the expensive items in a wastewater treatment plant, usually accounting for up to 50% of the total operating costs of the plant. Thus, the promotion of economically feasible treatment methods represents one of the most critical missions for environmental researchers. Nowadays, there have been several representative techniques for sewage sludge disposal applied in practice, for example, dewatering, composting, drying and incineration, anaerobic digestion, sanitary landfill, land application, and recycling as building materials. The technical feasibility of one method is dependent upon not only the degree of sludge stabilization, but also energetic and environmental benefits. In this chapter, sewage sludge production, special features of sewage sludge, and general processes of pollution control and resource recovery for sewage sludge are introduced; a deep comparison among dewatering, drying, incineration, composting, and sanitary landfill is made.

Keywords

Anaerobic digestion; Generation and characteristics; Incineration; Sanitary landfill; Sludge; Treatment of sludge

1.1. Sewage Sludge Production

In biological wastewater treatment process, the part of chemical oxygen demands (CODs) removed is converted into biosolids, which makes up sewage sludge. Sewage sludge usually represents 1–2% of the treated wastewater volume (Fig. 1.1). As per UN-Habitat's statistics, the existing wastewater treatment plants (WWTPs) in the United States, for instance, generate over 6.5 million tons of dry solids annually; it is estimated to be around 3.0 and 2.0 Mt per year produced in China and Japan, respectively (Fig. 1.2). The figures are naturally anticipated to increase in the near future when considering the growing applications of WWTPs in developing countries. The main disposal routes and rates are different in different countries, heavily depending upon the economic development level. As illustrated in Fig. 1.2, in developed countries such as the United States, the reuse and disposal rate reaches up to 94%, and it is roughly 97% in Japan, where more than half (52%) of sewage sludge is being recycled to produce building materials and 12% anaerobically digested for bioenergy recovery. Comparatively, the situation of sewage sludge use and disposal in developing countries is far beyond optimism. Note that for a sanitary landfill, the threshold of sludge water content is 60% from the view of safety regulations. The improper disposal not only causes the wasting of resources but also brings about a series of secondary disasters (e.g., landslide, environmental pollution, etc.). Sewage sludge management is highly complex and costly, representing a stern global challenge.

Figure 1.1 Sources and types of sewage sludge generated in wastewater treatment plants (WWTPs).

Figure 1.2 Estimated sewage sludge production as per the statistics of UN-Habitat and the situation of sewage sludge use and disposal. United States: From “US Wastewater Treatment Fact sheet” Pub. No. CSS04-14, 2015. China, Japan: Ministry of Land, Infrastructure, Transport and Tourism, Japan.

1.2. Special Features of Sewage Sludge

Sewage sludge floc is a multiphase medium and constitutes the vast majority of components including microbial aggregates, filamentous bacterial strains, organic and inorganic particles, extracellular polymeric substances (EPSs), and large amount of water. The composition of sewage sludge varies, depending upon the type and original components of the raw wastewater. EPSs, originating from the microbial activity (secretion and cell lysis) and/or from the wastewater itself, that is, from the adsorption of organic matter (e.g., cellulose, humic acids, etc.), are the major constituent of sludge organic fractions, mainly composed of proteins, polysaccharides, nucleic acids, humic substances, lipids, etc. (Fig. 1.3A). Depending on the spatial distribution within sludge floc matrixes, EPSs are usually divided into three categories: slime EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS). S-EPS are evenly distributed in the aqueous phase and LB-EPS extend from TB-EPS and are characterized by a highly porous and dispersible structure; comparatively, TB-EPS adhere to the surface of the bacterial cells inside the sludge flocs (Fig. 1.3B). The presence of these three-dimensional, gel-like, and negatively charged biopolymers governs the surface physicochemical properties of sludge matrixes. EPSs provide the protective shielding and prevent the cell rupture and lysis, thereby influencing sludge functional integrity, st...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• About the Authors
• Preface
• Summary
• Abbreviations
• Chapter One. Sewage Sludge Generation and Characteristics
• Chapter Two. Enhanced Sewage Sludge Dewaterability by Chemical Conditioning
• Chapter Three. Sewage Sludge Solidification/Stabilization and Drying/Incineration Process
• Chapter Four. Making of Sewage Sludge-Derived Controlled Low-Strength Materials (CLSMs)
• Chapter Five. Harvest of Bioenergy From Sewage Sludge by Anaerobic Digestion
• Chapter Six. Pollution Control and Recycling of Sludge in Sanitary Landfill
• References
• Index