Using oxidation-reduction potential as septicity control parameter during reclaimed wastewater transportation

During wastewater transportation, chemical and biological transformations m ay occur. Aerobic, anoxic, and anaerobic conditions exist depending on the presence or absence of dissolved oxygen and oxidized nitrogen compounds. Th e occurrence of anaerobic conditions has a negative effect on wastewater tr ansportation because of the usual subsequent sulfide generation process. In Tenerife, Spain, reclaimed wastewater used for agricultural purposes is tr ansported via a completely filled gravity pipe, 0.6 rn in diameter and 61 k m long. Because of the long residence time (approximately 30 to 40 hours), anaerobic conditions typically occur after 5 to 10 hours of flow. Field stu dies during transportation were conducted from November 1994 to July 1997. This paper describes a study of the evolution of septic conditions (aerobic , anoxic, and anaerobic) and the relationship between septicity and oxidati on-reduction potential (ORP), which can predict the occurrence of anaerobic conditions.