TRATAMENTO TERCIÁRIO DE EFLUENTE SECUNDÁRIO, USANDO A MICROALGA Chlorella sp. IMOBILIZADA EM MATRIZ DE ALGINATO DE CÁLCIO

Abstract

The contamination of water bodies by domestic and industrial wastewaters is one of the principle causes of environmental pollution causing eutrophication and a reduction in the sanitary quality of water resources. During various decades immobilized algae have been used in the treatment of wastewaters. The technology of immobilizing microalgae in beads of calcium alginate increases the photosynthetic longevity, viability, durability and cellular activity, This study investigated at laboratory scale, the potential of the microalgae Chlorella sp. in removing phosphorus and thermo-tolerant coliform bacteria from secondary effluents. The strains of Chlorella sp. species were isolated from a series of four shallow waste stabilization ponds 1m in width, 5m in length and 0.5m deep that were treating sanitary landfill leachate with high concentrations of ammonia. The experimental system comprised 10 bioreactors (with volumes from 0.1 to 1L), filled with beads of microalgae immobilized in calcium alginate at concentrations of 2%, 4% and 6%. The bioreactors were fed with effluent from a septic tank (TS) and from an intermittent sand filter (receiving the septic tank effluent). The bioreactors were operated in batch mode with contact times of 3 and 5h for phosphorus removal and 6h for thermo-tolerant coliform removal. The experiments were performed at 27 0 C and with illumination provided by 4 fluorescent tubes of 40 watts. The principal mechanisms involved in the treatment of the effluents were the photosynthetic activity of the microalgae and the biochemical reactions between the constituents of the immobilizing matrix and the effluent. Significant removals of total phosphorus (80%) occurred with 3h of contact in the bioreactors of volumes of 0.1 and 1.0L and mean reductions of 99,9999% for thermo-tolerant coliforms with contact times of 6h with the influent (mean concentration of 10 6 CFU/100ml) using bioreactors of a volume of 0.1L. In the bioreactors of 1L volume with microalgae immobilized in 4 and 6% alginate, the large volume of algal beads and the elevated concentrations of alginate limited light penetration and compromised effluent quality.