Cultivo de microalgas e redução de coliformes em efluente de tratamento anaeróbio
Marchello, Adriano Evandir
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Effluents from sewage treatment plants usually have high concentration of inorganic nutrients such as nitrogen (N) and phosphorus (P), which can be used for algal growth. Due to this possibility, the use of such wastewater can become a strategy for reducing the cost of microalgae production and/or reduction of costs in sewage treatment plants. This would result in the reduction of coliform bacteria and nutrients thereby improving the quality of effluent to be discharged. This research aimed to monitor the native community of microalgae and coliform bacteria from wastewater produced from anaerobic treatment of municipal sewage. Two bioassays were performed, an aerated and a non-aerated. Five liters samples of the wastewater were incubated in a greenhouse with semi-controlled environment using batch mode. The results showed no significant variation in pH for any of the bioassays. A reduction of 99.9% of colony forming units (CFU/mL) of both total coliforms and Escherichia coli was obtained after short period incubation. The concentrations of nutrients (N and P) decreased in the aerated bioassay, but not in the non aerated one. The growth curve of microalgae community presented an initial adjustment/adaptation phase only in the aerated bioassay, whereas in the nonaerated, microalgae growth was exponential since the beginning of incubation. The microalgae Chlorophyceae Chlorella vulgaris was dominant in the phytoplankton community in both bioassays coming to 99% of the total biomass. In the aerated bioassay, 12 taxa distributed into five classes were present (Chlorophyceae, Cyanophyceae, Chrysophyceae, Bacillariophyceae and Euglenophyceae), whereas in the non-aerated, only three classes were identified (Chlorophyceae, Cyanophyceae and Euglenophyceae), with 6 taxa. We conclude that the anaerobic sewage effluent supported algal growth, mainly the Chlorophyceae Chlorella vulgaris and improved the anaerobic sewage treatment wastewater quality, reducing their potential for eutrophication. We also conclude that effluent aeration is most useful when the objective is the production of microalgae and nutrients reduction.