Abstract
A bacteriophage of Serratia marcescens was evaluated as a tracer in three appropriate aqueous environments and compared with an accepted tracer in two cases. The phage compared favourably with lithium chloride in demonstrating flow characteristics and retention times of various stages in the sewage treatment process. The phage exhibited virtually identical distribution in a marine harbour to spores of Bacillus subtilis var. niger (‘B. globigii’) 36–48 h after their addition to a sewage works' final effluent which entered an adjacent bay. Transit times of river water were accurately measured between two points under various flow conditions.