The ability of selected cladoceran species to utilize domestic wastewaters in Mexico City.

The population growth patterns of four cladocerans, viz. Alona rectangula, Ceriodaphnia dubia, Moina macrocopa and Daphnia pulex on wastewaters from a treatment plant at Iztacalco, Mexico City were analyzed in this study. Crude wastewater (tank A) did not support A. rectangula and all animals in the replicates died after 5 days. A. rectangula with partially treated wastewater (tank B) showed growth curves similar to controls where algal density was 1 x 10(6) cells ml(-1). With wastewater from tank C (last stage before treatment with purifying agents such as chlorine), the populations maintained a low density (7 ind. ml(-1)). In wastewaters from tanks A and B, C. dubia showed no positive population growth, but in water from tank C, they maintained a low density (2 ind. ml(-1)). D. pulex showed no positive growth in all replicates involving wastewater. Only in controls (diet of algae Chlorella), the population density increased with time. M. macrocopa showed higher population growth in crude wastewaters than controls. Partially treated wastewater from tank B also resulted in a greater population growth than in the controls. However, when wastewater from the tank C was used, the population declined after day 12. Under comparable conditions, A. rectangula reached much higher peak abundances (55 ind. ml(-1)) than the rest of the cladoceran species. The rates of population growth (r) of the tested cladoceran species followed trends similar to the peak population densities. A. rectangula had the highest growth rates (0.25 per day) in controls and from the wastewater from tank B. The r-values were negative for A. rectangula and C. dubia in crude wastewater. For M. macrocopa the r-values were higher (0.19) in crude wastewater than in algae (0.15). However, r-values of M. macrocopa became negative when cultured in treated wastewater from tank C.