Tratamento anaeróbio de drenagem de mina : estratégias de operação em batelada utilizando os subprodutos glicerol bruto e trub como fontes de carbono

Abstract

Mine drainage (MD) is an effluent rich in sulfate, metals, and metalloids that can compromise aquatic life in the receiving water bodies. Efforts have been made to make the biological treatment of MD more sustainable, using industrial by-products as a carbon source. This research used real DM in reactors in sequential batches with hydraulic detention time of 168 h and micro-aerobic atmosphere to evaluate the efficiency of the following electron donors: trub, brewery residue, and crude glycerol (GB), a by-product of biodiesel production. The evaluation was performed with ethanol and pure glycerol (PG) as positive electron donors parameters. In this step, an adaptation procedure was applied in which the inoculum was exposed to gradually higher concentrations of the substrate in each batch until reaching the COD/SO42- ratio of 3 at the end of 4 months. It was concluded that there was no difference in the efficiency in the removal of sulfate between the 4 types of substrates (89.1-92.3%), but there was acidification in the effluents of the treatment with PG, CG and trub (below 4.9) while with ethanol the effluent pH was 6. The biomass obtained at the end of this procedure with each substrate was compared by high-throughput sequencing with each other, with the sludge where only MD was added without adding a carbon source and also with the inoculum initial. The results showed that in the system where only MD was applied there was an increase in the relative abundance of sulfate-reducing bacteria (SRB) and Archaeas, while there was a decrease in the abundance of sulfur oxidizing bacteria (SOB). There was a decrease in the abundance of Archaeas with PG, CG, and mainly with trub. With these substrates, the SRB and SOB groups were also disadvantaged. With ethanol SRB were favored, but SOB and Archaeas were also favored. A second stage was developed using an inoculum which was stored with MD for 30 days. The fractional supply of carbon source (FSCS) was applied, where the amount of substrate referring to the COD/SO42- ratio of 3 was divided into equal portions added every 24 h. The GB was divided into 6 portions and the effluent obtained after 144 h of batching showed a neutral pH (6.83), reaching 94.15% of sulfate removal. The addition of trub in 6 portions was insufficient to avoid acidification of the system (effluent pH 4.26), interrupting the removal of sulfate in 39.65%. When the same amount of trub was applied in smaller portions over 7 days, a final effluent with a pH of 7.01 was obtained and the removal of sulfate was 88.49%. Two post-treatment options for the the destination of the residual COD in the effluent of the sulfidogenic phase were tested. The potential for methane generation was proven for the effluents from treatment with trub and CG, being greater for the former. The accumulation of added-value molecules was also investigated. The potential to produce mainly acetic, propionic, isobutyric, and butyric acids was confirmed in the trub system, and formic, acetic, propionic, and butyric acids in the CG system. Both evaluated by-products showed promise for a co-treatment with MD through the operational mode with FSCS proposed in this research, with the possibility of obtaining added value molecules produced by the anaerobic system of degradation of carbon sources.