Aplicação de Bacillus cereus e Enterococcus faecalis, isolados de bacalhau seco salgado (Gadus sp), no tratamento de resíduos sólidos agroindustriais salinos por compostagem controlada

Abstract

The activity of the agroindustries has caused impacts to the environment, among them the contamination of soil, groundwater and surface, atmosphere. In the food industry, salt is used in several stages of food processing, and is also considered the most consumed ingredient by humans. In the marine fishing industry salt is present since the discharge of material and the effluent generated when treated gives rise to so-called salty fish effluent seasoning, this waste released to the environment without treatment causes serious environmental problems such as the inhibition of the microbiota natural environment affecting the biogeochemical cycle. One of the tools for the treatment of this saline residue is the composting process, which can be applied in the treatment of various agroindustrial solid wastes. One issue to be discussed is the presence of salt in this residue. The osmotic pressure causes the inhibition of the growth (activity) of the natural microbiota and can lead to death by extravasation of the cellular content. To solve these problems, the addition of halophilic and / or halotolerant strains would be an alternative for the composting of this saline residue. Therefore, one of the objectives of this work was to isolate and identify, by PCR, halophilic bacteria from a salt food matrix such as salted dry cod. The results showed that the Bacillus cereus, Enterococcus faecalis and Lactobacillus spp strains were the most promising when submitted to bacterial multiplication in broth supplemented with 7.5% NaCl. Another objective of this work was to evaluate the microcompaction of the sludge mixture of saline fish, rice husk and sawdust with the addition of B. cereus, E. faecalis and their consortium in the days of the composting process. The results demonstrated efficacy in the reduction of the electrical conductivity in the period studied by the strains used in the treatments. The pH, even though it showed a drop during composting, remained above 6, a standard established by the Brazilian legislation for the commercialization of the compost. During the whole composting period, the nitrogen content remained low, due to the use of halotolenating bacteria, although they are used as probiotics, causing denitrification, thus raising the percentage of nitrogen during the experiment. In relation to carbon the percentage of carbon had an insignificant drop during the process, the percentage of carbon found during the experiment is answered by the high microbial activity obtained in carbon percentages below 45% at the end of the 26 days of incubation. The humidity for the treatments with addition of probiotics were within the standard stipulated by MAPA, between 40 and 60%, contrary to the treatments without the inocula that presented values above. And mineral matter presented higher values at the end of composting due to microbial action and reduction of organic matter and mineral formation. The saline fish sludge from the effluent treatment station obtained better results with addition of inoculum, as addition of another residue rich in nitrogen, modification of volume / volume and structuring material, and greater time of composting. Despite these observations, the results presented were within the brazilian legislation.