The conventional tertiary treatments for wastewater (chemical precipitation, ion exchange, or membrane technology) are usually not carried out because of the high cost involved.
When organic contamination occurs in rivers and streams, the polysaprobic zone generally presents a high bacterial count as well as an absence of plankton and dissolved oxygen, whereas the a-mesosaprobic zone and, to an even greater extent, the p-mesosaprobic zone, show a decline in the bacterial count and an increase in autotrophic organisms and dissolved oxygen at the expense of the inorganic nutrients.
This fact points to the possibility of developing a tertiary biologic treatment using algal biomass. With this reasoning, the experimental purification of a secondary effluent was carried out using multispecies microalgae cultures, and studying the evolution of chlorophyll, nitrate, nitrite, ammonium, inorganic nitrogen, pH, conductivity, chemical oxygen demand (COD, using the potassium permanganate method), hardness, phosphate, chloride, and sulphate. The assays were done in both aerobiosis and anaerobiosis on a 9-day culture. Evolution was interpreted on the basis of the linear tendency and the mean values of the overall instantaneous specific rate (ISR) and that of the first three days of culture (ISR,).
According to the linear tendency and ISR, the parameters of inorganic nitrogen, conductivity, hardness, and chloride evidence greater purification in the process in aerobiosis, in which nitrogen fixation, when it occurs, does not take priority over the consumption of inorganic nitrogen. Purification is clearly favored in conditions of anaerobiosis, however, for ammonium and phosphate.
The results obtained demonstrate the viability of tertiary biologic sewage treatment using an autotrophic activated sludge process. This type of treatment improves the quality of the effluent and increases yield, as the process is continuous and concurs with biomass recirculation. Although statistically significant differences were not established for aerobicianaerobic conditions, a combination of the two could increase effectiveness. 0 7996 by John Wiley & Sons, Inc.