• Energy Research

This study deals with formic acid removal in activated sludge processes, in particular in the processes carried out in sequencing batch reactors (SBRs). Formic acid removal has been investigated in a SBR fed with acetic and formic acids at equimolar concentrations. Biomass performance in the reactor has been investigated both by the analysis of the removal of the two substrates and by batch tests. Regarding SBR process, the obtained results show that a relevant difference occurred between formic and acetic acid profiles. Acetic acid was never found in the effluent and was always completely removed during the reaction phase. On the other hand, formic acid removal was determined by biomass acclimation, which is in turn determined by sludge age imposed to the system. Batch tests confirmed that formic acid removal occurs only if biomass is acclimated. It has been shown that the minimal sludge age to obtain complete formic acid removal is much higher than those predictable with the classical models of microbial growth in wastewater treatment processes. The advantages of SBRs over continuous-flow systems in the removal of formic acid have also been highlighted.

Biosorbing properties of sulphate reducing bacteria were tested to distinguish the amount of cadmium removed by bioprecipitation from that bound onto biomass surface (biosorption). Experimental results of cadmium abatement in batch growth tests (bioprecipitation tests) were then compared with metabolism-independent binding properties of SRB cell wall surface (biosorption tests performed with dead biomass). Experimental results showed that SRB inoculum removed 59 + or - 5% of sulphates in 21 days even in presence of cadmium (0-36 mmol L(-1)), while non-monotonous kinetic effects were observed for increasing Cd concentrations. Comparison between bioprecipitation and biosorption tests denoted a significant contribution of biosorption (77%) in total Cd removal (0.40 + or - 0.01 mmol g(-1)). Characterisation of bacterial acid-base surface properties by potentiometric titrations and mechanistic modelling denoted that carboxylic, phosphate and amino groups of cell wall are the main responsible of metal removal by biosorption mechanism.

AbstractBACKGROUND: In this study a comparison between two continuously operating fixed‐bed column systems was performed in order to select the best operating conditions in terms of organic sources for sulphate reducing bacteria (SRB). The first column system (solid substrate, SS) was filled with a solid reactive mixture containing the organic matter necessary for SRB growth, while the second one (liquid substrate, LS) was filled with inert material and continuously fed by ethanol.RESULTS: In the SS column 50 ± 10% sulphate abatement was reached at steady state, while metals were totally removed. Blank tests showed that biosorption was mainly responsible for both sulphate and metal removal. In the LS column, sulphate abatement was 70 ± 10% at steady state against 10 ± 5% of an identical column without inoculum (blank liquid substrate, BLS). Comparison with BLS showed that the main mechanism operating in this system was bioprecipitation. Estimated degradation rate constants for both SS and LS columns indicate similar performances (0.008 ± 0.001 and 0.0085 ± 0.0005 d−1 for SS and LS, respectively).CONCLUSIONS: LS column systems offer a valid alternative to conventional SS systems, avoiding the use of potentially harmful wastes as organic sources for SRB metabolism. Copyright © 2009 Society of Chemical Industry

A dynamic model was developed for representing the abatement of sulfates and metals in column reactors inoculated with sulfate reducing bacteria. The model framework includes both bioactive mechanisms (bioreduction of sulfates and bioprecipitation of metals) and passive abiotic mechanism (sorption onto the column filling). Sorption capacities of column filling material were determined by dedicated tests of sulfate and cadmium removal. These experimental data implemented in model framework denoted that before steady state sorption mechanism could predominate over bioactive mechanism. Sensitivity analysis confirmed that, varying sorption and bioreduction parameters in typical range of laboratory scale systems, sorption cannot be neglected before steady state. An operative equation was obtained by literature data and model simulations showing that in the majority of works reported in the literature the operational times used for column experiments are not sufficient to saturate column sorption capacity. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 70–80, 2014

Addressing the simultaneous removal of multiple coexisting groundwater contaminants poses a significant challenge, primarily because of their different physicochemical properties. Indeed, different chemical compounds may necessitate establishing distinct, and sometimes conflicting, (bio)degradation and/or removal pathways. In this work, we investigated the concomitant anaerobic treatment of toluene and copper in a single-chamber bioelectrochemical cell with a potential difference of 1 V applied between the anode and the cathode. As a result, the electric current generated by the bioelectrocatalytic oxidation of toluene at the anode caused the abiotic reduction and precipitation of copper at the cathode, until the complete removal of both contaminants was achieved. Open circuit potential (OCP) experiments confirmed that the removal of copper and toluene was primarily associated with polarization. Analogously, abiotic experiments, at an applied potential of 1 V, confirmed that neither toluene was oxidized nor copper was reduced in the absence of microbial activity. At the end of each experiment, both electrodes were characterized by means of a comprehensive suite of chemical and microbiological analyses, evidencing a highly selected microbial community competent in the biodegradation of toluene in the anodic biofilm, and a uniform electrodeposition of spherical Cu2O nanoparticles over the cathode surface.