Contaminação de estruvita precipitada a partir de efluente misto

Abstract

The production of struvite from different types of effluents from animal and anthropogenic origin has increasingly proven to be a good environmental choice, due to its potential to reduce the exploitation of natural phosphorus reserves, save energy in the production of nitrogen-based fertilizers and also avoid the disposal of these nutrients into water bodies, causing their degradation. The safety of applying this mineral in relation to the presence of microorganisms, originating from highly contaminated effluents used in its production, is still an issue that has been little explored. Within this context, this study aimed at elaborating a literature review on the topic, as well as verifying the microbial contamination of struvite precipitated from a mix of municipal wastewater + landfill leachate. The literature review demonstrated the potential adsorption of different groups of microorganisms to the struvite. Concentrations of 1,6 – 3,7 log10 cfu/g for bacteria e <0,8 log10 pfu/g for viruses have been reported. However, there are still several questions to be explored, as the mechanisms responsible for the presence of microorganisms near the crystals and treatment alternatives to reduce their concentrations in struvite prior to its use. In the experimental part of the study, the presence of microorganisms in struvite precipitated from the mixture of landfill leachate to municipal wastewater at different proportions (1%, 5% and 10%) was evaluated. The highest concentrations of microorganisms were found in the struvite obtained from the mix with 5% landfill leachate: 3.5 log10 pfu/g wet weight for somatic coliphages; 3.7 log10 pfu/g wet weight for F-specific coliphages; 5.8 log10 cfu/g wet weight for E. coli; 4,1 log10 cfu/g wet weight for aerobic endospores. The characterization of struvite obtained from the mix municipal wastewater + landfill leachate is believed to be unprecedented in the literature. Drying the precipitate at 40ºC until all moisture was removed demonstrated a significant reduction in microorganisms (up to 3.9 log10 for E. coli), but it was not enough to lead to a final concentration within the recommended range. As for the liquid matrix, there were significant reductions in the levels of microorganisms in some operational conditions. In addition, the remaining concentrations of nutrients, mainly nitrogen, allow the effluent to be subjected to further conventional biological treatment. Finaly, given the high levels of bacterial and viral indicators in the precipitate, the land application of struvite obtained from the mix of wastewater + landfill leachate may pose risks to human health. Therefore, the characterization of precipitate from wastewater + landfill leachate for pathogens (besides indicators) and the application of quantitative microbial risk assessment are recommended.