Z O O F L A G E L L A T E S IN AN A N A E R O B I C W A S T E S T A B I L I Z A T I O N P O N D S Y S T E M IN M E X I C O F E R M [ N R I V E R A * , A L F O N S O L U G O , J E S O S P O N C E , F E R N A N D O L A R E S , and R I C A R D O O R T I Z Project of Conservation and Improvement of the Environment, Unit of Interdisciplinary Research of Health and Education Sciences (U.I.I.C.S.E.) E.N.E.P. IZTACALA, U.N.A.M., Los Reyes Iztacala, Estado de Mdxico, MEXICO (Received November 5, 1984; revised March 27, 1985) Abstract. A protozoological survey was performed on waste stabilization lagoons to isolate, identify, and determine the incidence of zooflagellates present in these waters. A correlation between the species foun and the physicochemical parameters determined was also done. Fifteen samplings were analyzed from Jun 1981 to April 1982. Free-living zooflagellates included: Bodo edax Klebs: Bodo caudatus Dujardin; Trepomonas agilis Dujardin; Pleuromonas jaculans Perty (all of them polisaprobic indicators); Bodo saltan Ehrenberg (a mesosaprobic indicator); and Bodomorpha minima Hollande. A human commensal specie Enteromonas hominis Da - Fonseca, was also isolated. The performance of the lagoons was predominant anaerobic.The temperature seemed to be the most influential factor on the incidence of the zooflagellates isolated, especially in winter time. 1. Introduction Stabilization ponds are excellent for wastewater biological treatment systems for removing or stabilizing organic matter. Especially in areas where there is enough la available, it is economical in construction as well as in maintenance and operat (Arceivala et al., 1970). Among the organisms that play an important role in this typ of wastewater treatment are bacteria, algae, fungi, rotifers and protozoa (Mara, Rivirre, 1979; Carranco et aL, 1984). Protozoa frequently found in stabilization ponds include some representative specimens of the zooflagellated group (H~_nel, 1979). role of protozoa in wastewater treatment systems is debated (Hand, 1979). Howeve since most of them are bacteriophagous (Grassr, 1952), it is supposed that they m act as bacterium -reducing organisms. Furthermore, bacteriophagous zooflagell together with other kinds of phagocytic protozoa, constitute links in the transf energy through the trophic levels of the food chain (Sleigh, 1979). Some zooflagella species may be also useful as indicators of different degrees of organic contaminati of water (Kolkwitz and Marsson, 1908; Slfidecek, 1961). There is also a pathogenic zooflagellate Giardia lamblia Stiles, the presence of which in the effluents of treatment systems may be hazardous to health. The pond system analyzed in this study is located close to a small village (Santo Tomfis Atzingo) of th state of Mexico at 19 ° 12'10" north latitude and 98°48'00" west longitude, at 24 above sea level. The prevailing climate of the area is temperate subhumid, with sum * Correspondence: Author for all corrspondence. Av. Universidad 220-4 Mrxico 03020 D.F. Mexico. Water, Air, and Soil Pollution 27 (1986) 199-214. © 1986 by D. Reidel Publishing Company.