Advances in the implementation of microbial biomass for the bioremediation of heavy metal-contaminated effluents

The biosorption and bioaccumulation of heavy metals contained in wastewater systems offer promising bioremediation opportunities for contaminated effluents. Therefore, our study aims to evaluate and optimize the bioremediation of a synthetic contaminated effluent with Cd(II) by the biomass of Rhizobium viscosum CECT 908, previously classified as Arthrobacter viscosus, both in batch and dynamic modes, under different experimental setups.

The results obtained with the inactive Rhizobium viscosum CECT 908 biomass as a biosorbent for Cd(II) showed that the maximum biosorption efficiency and uptake capacity was 93% and, respectively, 20.23 mgCd(II)/g biomass at pH 6. At higher pH values (e.g., pH 7), the biosorption yield and the uptake capacity decreased to 87% and, respectively, 14.73 mgCd(II)/g biomass. This may be due to the formation of soluble hydroxilated complexes of the metal ions and their competition with the biomass active sites. Results of this study demonstrated that, although both inactive and active Rhizobium viscosum CECT 908 cells have high sorption capacities for Cd(II) biosorption, the binding capacity of the inactive cells seems to be higher than that of active cells in optimized experimental conditions, being able to remove more than 89% of a 100 mg/L Cd(II) solution.

As a result, this process has the scalability to go from a laboratory scale to a full scale. In this context, we were able to assess the process environmental impacts through Life Cycle Assessment methodology, within the Sphera Product Sustainability Solutions Software. The most relevant impact categories considered were Climate change ecosystems (CCEs); Climate change human health (CCHh); Particulate matter formation (PMF); Acidification potential (AP); Global warming potential (GWP); Photochemical ozone formation (POF); Agricultural land occupation (ALO); Human toxicity (HTP); and Terrestrial ecotoxicity (TETP). The outputs generated from the process modelling in this software tool pointed towards detrimental environmental impacts resulting from energy consumption and reagent transport.