ASSAYS FOR THE TERTIARY BIOLOGICAL TREATMENT OF WASTE-WATER USING AUTOTROPHIC BIOMASS

The conventional tertiary treatments for wastewater (chemical precipit ation, ion exchange, or membrane technology) are usually not carried o ut because of the high cost involved. When organic contamination occur s in rivers and streams, the polysaprobic zone generally presents a hi gh bacterial count as well as an absence of plankton and dissolved oxy gen, whereas the alpha-mesosaprobic zone and, to an even greater exten t, the beta-mesosaprobic zone, show a decline in the bacterial count a nd an increase in autotrophic organisms and dissolved oxygen at the ex pense 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 t he evolution of chlorophyll, nitrate, nitrite, ammonium, inorganic nit rogen, pH, conductivity, chemical oxygen demand (GOD, using the potass ium permanganate method), hardness, phosphate, chloride, and sulphate. The assays were done in both aerobiosis and anaerobiosis on a 9-day c ulture. Evolution was interpreted on the basis of the linear tendency and the mean values of the overall instantaneous specific rate (ISR) a nd that of the first three days of culture (ISR(3)). According to the linear tendency and ISR, the parameters of inorganic nitrogen, conduct ivity, hardness, and chloride evidence greater purification in the pro cess in aerobiosis, in which nitrogen fixation, when it occurs, does n ot take priority over the consumption of inorganic nitrogen, Purificat ion is clearly favored in conditions of anaerobiosis, however, for amm onium and phosphate. The results obtained demonstrate the viability of tertiary biologic sewage treatment using an autotrophic activated slu dge process. This type of treatment improves the quality of the efflue nt and increases yield, as the process is continuous and concurs with biomass recirculation. Although statistically significant differences were not established for aerobic/anaerobic conditions, a combination o f the two could increase effectiveness. (C) 1996 by John Wiley & Sons, Inc.