5 Dissolved Air Flotation (DAF) for Wastewater Treatment

• Identify the source and general types of wastewater odors. • List three potential impacts of odors. • List three factors affecting the existence of odors. • Name a commonly used method to reduce odors from wastewater. • Describe three methods for solving odor problems in air.

Introduction Every year in South Africa an estimated R500m is spent on chemicals used in the treatment of drinking and waste water. Most of this money is allocated on the basis of tenders issued and contracts awarded. The evaluation of tenders is generally undertaken by a team of people from various disciplines within the awarding organization and the decisions they make can have a significant effect on the quality of water or waste that is produced and also on the finances of the organization for which they work. It is obvious therefore that these decisions – which chemicals to use, how much to use, how much should be paid, who is the most professional supplier – are important ones and ones that should be taken whilst in possession of the most factual and impartial information. This guide aims to provide those decision-makers, and other users of water treatment chemicals, with specific and useful information about water treatment chemicals. It is a chemistry text book aimed specifically at those people who have to make informed decisions but who have not had a formal education in chemistry or whose chemistry education has not been specific in detail relevant to water treatment chemicals. It does not, however, aim to be a comprehensive chemistry textbook and chemicals not used in water treatment are not discussed; nor are properties that are irrelevant to the water treatment application of the chemical. The guide is designed to serve as a reference book with each chapter being self contained and specific. It will be easily understood by those readers that do not have a formal chemistry education and hopefully will provide some useful additional insight and information to those that The guide is divided into ten chapters and includes an appendix at the end that contains various useful equations. The contents of each chapter are listed below.

The Swedish Environmental Protection Agency (EPA) has determined a need to introduce advanced treatment for pharmaceutical residues in wastewater. An additional benefit of such a treatment is that it would also include the treatment of other hazardous substances.The extent to which pharmaceutical residues risk becoming a problem depends on local conditions such as the sensitivity of the receiving waters. While this is an important variable to consider, the Swedish EPA believes that the sensitivity of the receiving waters should not be the only consideration when setting requirements for treatment. The amount of released pharmaceutical residues and long-term effects should also be considered in decision making and justification. The investment and operational costs of introducing advanced treatment depend in part on the size and current capacity of treatment facilities, which is why size limitations can be an additional consideration when setting requirements.

The content of this technical sheet on “aerated ponds” is based primarily on the following publications: “Aerated Pond”, compiled by Eawag (Swiss Federal Institute of Aquatic Science and Technology), Dorothee Spuhler (international Gmbh) published on SSWM (http://www.sswm.info) (2015). “Aerated, partial mix lagoons”, Technology Fact Sheet 832-F-02-008, published by U.S. EPA (2002). “Principles of design and operations of wastewater treatment pond systems for plant operators, engineers, and managers”, EPA/600/R-11/088, published by U.S. EPA (August 2011).