Sistemas alagados construídos para tratamento de águas residuárias do processamento dos frutos do cafeeiro: eficiência e caracterização das comunidades microbianas / Constructed wetlands systems for wastewater treatment in the processing of coffee fruits: eficiency and characterization of microbial communities

Maike Rossmann

This study aimed to evaluate the influence of ryegrass cultivation (Lolium multiflorum Lam) and the artificial aeration of the affluent in the removal of organic matter, nutrients and phenolic compounds present in the ARC, as well as the diversity of microbial communities attached to the medium (gravel) and the rhizosphere of ryegrass, using T-RFLP multiplex analysis. For this, SACs of 0.6 m high x 0.5 m wide x 2.0 m long, filled with zero gravel to a height of 0.55 m were built in the area of Preprocessing and Storage of Agricultural Products of the Agricultural Engineering Department of UFV. The experiment was considering a Completely Randomized Design (CRD) with 20 replications, with two replicates per treatment and 10 assessments over time, and 4 SACs well characterized: (i) receptors modules of aerated affluent cultivated with ryegrass (aaSACc), (ii) receptors modules of aerated affluent non-cultivated, containing only the medium (gravel zero) (aaSAC), (iii) receptors modules of affluent non-aerated, cultivated with ryegrass (SACC) and (iv) receptors modules of affluent non-aerated, non-cultivated (SAC*). For oxygenation of the ARC, whose the planned treatment was application of aerated ARC, was established an aeration system in the storage and alimentation reservoir. The ARC was applied to an average flow of 0.020 m3 d-1, corresponding to a hydraulic retention time of approximately 12 days. The microbial diversity in the ARC applied in the system was determined in the rhizosphere of ryegrass and in the biofilm on the surface of the support media. Samples were collected at the end of the application of Hoagland solution, i.e., before application of ARC in the systems, and at the end of the experiment, approximately 120 days after the beginning of the ARC application. TRFLP multiplex was performed to compare simultaneously the genetic profile of the prokaryotes and fungi communities. The microbial community structure found in SACs was evaluated based on the indices of equitability of Shannon-Wiener J (J) and Shannon-Wiener diversity (H ). There were average removal efficiencies of 87, 84 and 73 % for COD, BOD and TSS, respectively, in the cultivated system receiver of nonaerated affluent (SACc). The highest average efficiencies in the removal of NT, PT, KT and FT were 69, 72, 30 and 72 %, respectively, in the cultivated system receiver of aerated affluent (aaSACc). The plant species cultivated and the aeration supplied to the ARC prior to their application in systems did not influence the overall average removal efficiencies of organic matter. However, the aeration provided showed a potential for improvement in the removal efficiency of compounds such as nitrogen, phosphorus and phenols, with the best results obtained by the combination the presence of vegetation in the SAC and artificial aeration of the affluent ARC. The presence of ryegrass in SACs also influenced the microbial community structure. Moreover, the system dynamics has changed its initial diversity, with indices ranging from the entry, bigger in cultivated SACs, and the output, higher in non-cultivated SACs. The aeration of the affluent did not influence the microbiota established in the system. Considering the lack of information available about the microbial communities that inhabit SACs, the approach based on T-RFLP multiplex was effective in obtaining new data about its structure and dynamics.

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