Preface

Wastewater treatment is a process used to convert wastewater into a treated effluent (outflowing of water to a receiving body of water) that can be returned to the water cycle with minimal impact on the environment or directly reused. Climate change, population growth, and water scarcity have contributed to a growing demand for sustainable management of water resources. With the application of nitrate-containing fertilizers, consumption of animal products, and industrial production activities, ever more ammonia and nitrate are being discharged into rivers and lakes, which may cause eutrophication and deterioration of aquatic environments.

Although there is no ammonia drinking water standard in the United States, the European community has established a maximum limit of approximately 0.5 mg/L and a guide level of 0.05 mg/L (EU Council, 1980). The maximum acceptable contamination level in drinking water is 10 mg/L nitrate nitrogen in the United States, Japan, and Korea, while the EU countries set the standard for nitrate nitrogen at 11.3 mg/L, and the World Health Organization recommends 11.3 mg/L nitrate nitrogen to protect against methemoglobinemia in bottle-fed infants. To protect aquatic ecological systems, a more stringent limit was imposed to point source dischargers into sensitive water bodies, such as Chesapeake Bay in the United States. Nitrification and denitrification are the fundamental processes in nitrogen removal in aquatic ecosystems. They play an essential role in both natural and engineered systems in terms of the nitrogen cycle.

This book reviews and updates the fundamental research and engineering experience on nitrification and denitrification. Although nitrification and denitrification are generally regarded as biological processes for the removal of ammonia, as well as nitrates and nitrites, this book covers a broad range of topics for ammonia and nitrate removal, including physical and chemical approaches.

While extensive research has been conducted on conventional wastewater treatment, this book is oriented to some interesting processes and selected applications such as photocatalytic reaction for nitrous oxide removal, autotrophic nitrogen oxidization, and the anaerobic ammonia oxidation process. Chapters in this book include:

Chapter 1: "Introductory Chapter: Ammonia Removal and Recovery"

Chapter 2: "Recent Progress and Current Status of Photocatalytic NO Removal"

Chapter 3: "Research on Partial Nitritation and Anaerobic Ammonium Oxidation Process"

Chapter 4: "The Contribution of Autotrophic Nitrogen Oxidizers to Global Nitrogen Conversion"

Chapter 5: "Removal of Nitrate and Nitrite by Donnan Dialysis: Optimization According to Doehlert Design"

This book opens possibilities for future research and innovation in the field.

Finally, during the course of editing and compiling this book, extensive support and guidance were received from Publishing Process Manager Ms Maja Bozicevic at IntechOpen The editor would like to express deep appreciation and gratefulness for her support.

> **Ivan Zhu** Evoqua Water Technologies, LLC, Pittsburgh, PA, USA

**Chapter 1**

*Ivan Zhu*

**1. Introduction**

**Figure 1.**

*Ammonium speciation in water at different pH [1].*

Introductory Chapter: Ammonia

With the application of nitrate-containing fertilizers, consumption of animal products, and industrial production activities, ever more ammonia and nitrate are being discharged into rivers and lakes, which may cause eutrophication and deterioration of aquatic environments. Traditionally, ammonia removal is achieved with biological processes such as nitrification, breakpoint chlorination, air stripping, reverse osmosis, zeolite adsorption, and so on. However, these processes either require high capital investment or are chemistry-intensive. Moreover, these processes focus on the removal instead of ammonia recovery. Ammonium nitrogen (N) is an important nutritional element in fertilizer besides phosphorus (P) and potassium (K). Recovering nutrients, instead of simply removing from wastewater, is drawing more attention to keep natural resources reliable and sustainable and minimize carbon footprint. Two processes focusing on nutrient removal and recovery have stood out in recent years and drawn attention from engineers, facility operators, and regulators.

In the application of a gas-permeable microporous membrane, the wastewater stream

is first adjusted to a pH value of at least 9.5 (**Figure 1**). And then, the stream passes through one side of the membrane and dissociates ammonium from water, and ammonia penetrates through the membrane; a dilute acid solution is circulated on the other side of the membrane, and sequesters ammonia to form ammonium sulfate (**Figure 2**).

Removal and Recovery

**2. Gas-permeable membrane for ammonia recovery**
