Ciliated protozoa as indicators of a wastewater treatment system performance

In the food industry, where effluents contain very high concentrations of dissolved organic matter, in-situ treatment systems have been recommended. These systems require simple and inexpensive control parameters. According to the literature, to evaluate the system performance an inexpensive method is the microscopic observation of different protozoal species, combined with personal judgement of evaluators.

For a four-stage laboratory rotating biological reactor treating diluted corn-processing effluents, ciliated protozoa as indicator organisms of system performance were studied. Temperature, pH and dissolved oxygen were monitored. Dissolved organics, measured as chemical and biochemical oxygen demand (COD and BOD₅), gradually decreased along the reactor. Twelve protozoal species were identified. From them, 10 have been reported in the literature as commonly found inhabitants of aerobic municipal wastewater treatment plants. A correlation between six of the species with BOD₅ concentrations in the wastewaters along the reactor was found.