BONANNI Pablo Sebastian
congresos y reuniones científicas
Growth of electro-active bacteria with biochar as chemical electron acceptor and electrode material
Institución organizadora:
Recently, electrically conductive materials were applied as filling material of treatment wetlands, giving rise to the new technology of Bioelectrochemical Wetlands or METland filters. Conductive materials enhance bacterial activity on the system boosting treatment efficiency. They allow the occurrence of a process known as direct interspecies electron transfer (DIET) in which electro-active microorganisms exchange electrons through the materials, without relying on chemical intermediates. Major drawbacks for the application of bioelectrochemical wetlands are the costand the availability of the conductive materials. Biochar is a conductive and biocompatible material obtained through the thermal decomposition (pyrolysis) of biomass residues and vegetable wastes and appears as a valid candidate for its use as filling material on bioelectrochemical wetlands. Its electrical conductivity, a parameter of major importance for the process of DIET, increases with pyrolysis temperature, but also does its cost. At low pyrolysis, temperature chemicals such as quinones, that are used as electron acceptors and electron donors for the growth of bacteria, areproduced and remain in the biochar. In this context, biochar obtained at low temperatures may also enhance bacterial activity. In this work, we show the results of our first experiments aimed at finding the pyrolysis conditions that result on an enhancement of wastewater treatment efficiency without compromising the cost. Biochar were obtained through pyrolysis of pruning residues at different temperatures ranging from 400 to 1200 ºC. The composition of the materials was analyzed through infrared spectroscopy (FT-IR) and Raman spectroscopy assays, to determine therelative amount of possible bacterial electron donors or acceptors. To analyze the growth of electro-active bacteria with biochar as chemical electron acceptor, G. sufurreducens was grown in batch with this material as the sole electron acceptor. Bacterial growth was followed by counting in a Neubauer chamber. The electrical conductivity of the materials was measured through 4-point probe electrodes. Biochar electrodes were used as growing substrate for G. sulfurreducens in electrochemical cells, to study the capacity of the bacteria to directly exchange electrons withthe material. Electrodes were polarized at 0.4 V vs SHE and the growth of the bacteria was followed by measuring the electric current through chronoamperometry. Materials obtained at lower temperatures, between 400 and 600ºC, that showed a higher proportion of quinones, allowed a higher growth of electro-active bacteria when used as chemical electron acceptors. Higher current densities were obtained when biochars obtained between 800 and 1000 ºC (that showed higher electrical conductivity) were used as electrodes. Current densities values were comparable to those obtained with graphite, the most common electrode material used for the growth of these bacteria. Besides, the scanning electronic microscopy images showed the development of a thick biofilms covering the surface of the electrodes, highlighting the compatibility of the material with electro-active bacteria. Ongoing assays, that include the scale up of the pyrolysis process, are aimed at determining which of these processes (growth as chemical electron acceptor or electron transfer through conductive material) is of greater importance for the performance of bioelectrochemical wetland