Radiotracer Applications in Wastewater Treatment Plants

Wastewater containing pollutants resulting from municipal and industrial activities are normally collected in wastewater treatment plants (WWTPs) for processing before discharge to the environment. The WWTPs are the last barrier against contamination of downstream surface waters such as rivers, lakes and sea. Treated wastewater is reused for irrigation, particularly in arid and semi-arid countries. Therefore, it is very important to maintain optimal operating conditions of WWTPs to eliminate or reduce environmental pollution. Wastewater treatment plants are complicated systems, where the processes of mixing, separation, aeration, biological and chemical reactions occur. A WWTP is basically a multiphase system, and the efficiency of an installation strongly depends on liquid, solid and gas phase flow structures and their residence time distributions (RTDs). However, the fluid dynamic properties of such systems are not yet completely understood, rendering difficult the theoretical prediction of important process parameters such as flow rates, phase distributions, mixing and sediment characteristics. Tracer techniques are very useful tools to investigate the efficiency of purification in WWTPs, aiding both their design and performance optimization. There are many kinds of tracers. Radioactive tracers are the most sensitive and are largely used for on-line diagnosis of various operations in WWTPs. The success of radiotracer applications rests upon their extremely high detection sensitivity, and the strong resistance against severe process conditions. During the last few decades, many radiotracer studies have been conducted worldwide for investigation of various installations for wastewater treatment, such as mixer, aeration tank, clarifiers, digester, filter, wetland and oxidation units. Various radiotracer methods and techniques have been developed by individual tracer groups. However, the information necessary for the preservation of knowledge and transfer of technology to developing countries has not yet been compiled. Standard procedures or guidelines for the tracer experiments, vital for the reliability of the experiments as well as for the acceptance of end users, have also not been established by international tracer community. The IAEA plays a major role in facilitating the transfer of radiotracer technology to developing Member States. The major radiotracer techniques have been implemented through IAEA technical cooperation projects. The sustainability of the technology and knowledge preservation calls for continuing human resource development and for establishing good practices. The education of specialists and continuous training of radiotracer practitioners is vital for the provision of quality services to environmental end users. This publication was prepared using the inputs from a meeting of experts held in June 2007 and lecture materials prepared for various IAEA regional training courses. It is intended to assist radiotracer groups in Member States to promote and apply radiotracer technology for better serving the environmental sector