Hazardous Waste Management, Volume II

Characterization and Treatment Processes

Sukalyan Sengupta

• Publisher: Momentum Press
• Year: 2018
• Print ISBN: 9781945612909
• eBook ISBN: 9781945612916
• Topic: Technology & Engineering
• Subtopic: Ecology
• Index: Technology & Engineering

This second volume focuses on treatment technologies that are commonly applied at hazardous waste sites and site characterization.

Environmental engineers are responsible for cradle-to-grave handling and management of a hazardous waste. To fulfil this responsibility, a practicing engineer needs to apply their knowledge of federal, state, and local regulations; environmental audits; toxicology; site characterization; and treatment processes to transform the hazardous waste site to a condition where it cannot cause adverse effect to human health and the environment.

Volume I of this series covered the regulatory landscape, basic environmental chemistry principles, fate and transport of contaminants, toxicology, and risk assessment. This second volume focuses on treatment technologies that are commonly applied at hazardous waste sites and site characterization. It covers physicochemical processes (air stripping, adsorption, ion exchange, and reverse osmosis), incineration, stabilization and solidification, biological treatment, and land disposal. Numerous solved examples provide a step-by-step approach to apply these technologies in real-life situations. The two volumes combined present a clear roadmap to the reader to integrate these topics in practice.

CHAPTER 1

PHYSICOCHEMICAL TREATMENT PROCESSES

Hazardous waste sites may be contaminated with various toxic compounds, and therefore to remove these hazardous compounds, environmental engineers need to develop an arsenal of technologies and the maturity to adopt the most appropriate technology/technologies for a particular scenario. These technologies may be broadly classified as physical–chemical (also known as physicochemical), thermal, stabilization, and encapsulation of the waste (so the toxic components cannot migrate out of it), biological, and land disposal. This chapter discusses four common physicochemical technologies that are widely employed in hazardous waste decontamination.

1.1 AIR STRIPPING

Air stripping is a physicochemical process used to remove volatile compounds from a liquid phase (water) to a gas phase (air) by promoting vigorous contact between the two phases. It is routinely used to treat groundwater contaminated with volatile organic compounds (VOCs) at low concentrations.

The most common method of contacting air with contaminated water is in a stripping tower, as shown in Figure 1.1. The tower is filled with a high surface-area-to-volume-ratio packing material and air flows in opposite direction to that of water, known as countercurrent flow. Mass exchange takes place between the aqueous and the vapor phase, and the air stream that leaves the tower at the top carries the contaminant with it, typically at a much lower concentration that meets air quality standards. The treated groundwater can then be discharged to a surface water-receiving body or pumped to effect groundwater recharge. If the concentration of the volatile organic contaminant is too high in the influent, its resulting concentration in the exhaust may be too high for air quality standards, and thus the off-gases may need to be treated.

Figure 1.1. Sketch of an air-stripping tower (packing material image courtesy: www.ceramic-honeycombs.com/plastic/Plastic_Tripack_Tower_Packing.htm)

The design of an air stripper entails expedited mass transfer of the volatile compound from the aqueous phase to the gas phase. The “Two-film” theory (Whitman 1923) (a full discussion of this topic is outside the purview of this book) states that the mass transfer of the volatile compound between water and gas is limited by diffusion through thin films at the water–gas interface. A mass balance for an air stripper is discussed in the next section.

1.1.1 MASS BALANCE FOR AIR STRIPPER

where

(set by environment regulations)

z = height above bottom of air stripper [L...

Table of contents

• Cover
• Title Page
• Copyright Page
• Contents
• Acknowledgments
• Chapter 1 Physicochemical Treatment Processes
• Chapter 2 Incineration
• Chapter 3 Stabilization and Solidification
• Chapter 4 Biological Treatment
• Chapter 5 Land Disposal
• Chapter 6 Site Characterization
• About the Author
• Index