This manual on Primary, Secondary and Tertiary Treatment sets out the general principles and practices which should be followed by those involved in the treatment of urban waste water. It provides criteria and procedures for the proper management, maintenance, supervision, operation and use of the processes and equipment required for the secondary treatment of wastewater. The Agency hopes that it will provide practical guidance to those involved in plant operation, use, management, maintenance and supervision. Where reference in the document is made to proprietary equipment, this is intended as indicating equipment type and is not to be interpreted as endorsing or excluding any particular manufacturer or system.