Bioremoval of toxic metals by the microbiome of biogas waste

Abstract

Microbial dissimilatory sulfate reduction is a promising methabolic pathway to solve the problem of polymetallic wastewater treatment. The process is based on the application of sulfates by microorganisms as the terminal electron acceptor. As a result, sulfates are reduced to sulfides, which precipitate a wide range of divalent cations in the form of insoluble metal sulfides. For this purpose, slightly soluble gypsum CaSO₄ were studied as electron acceptors. Gelatin was used as electron donors. As a result of the study, it was established that the process of sulfate reduction is quite active and contributes to the precipitation of metals. The use of gypsum prevents volley formation of sulfides, which ensures long-term and controllable process. It took 13 days for the complete precipitation of CrO₄^2- in the medium by the sulfide producing microbiome. Under conditions of addition of an active sulfate-reducing microbiome, the duration of metals precipitation was reduced to 11 days of cultivation. The precipitation efficiency in both variants was 100%. The efficiency of precipitation of Co²⁺ and Ni²⁺ under the conditions of using the active microbiome of sulfate reducers was 97.5% on the 16th day of cultivation. The efficiency of precipitation of Co²⁺ and Ni²⁺ under the conditions of using only the microbiome of biogas waste was slightly lower and amounted to 95.8%. Thus, the effectiveness of the process of using sulfate reduction with the use of sparingly soluble gypsum for the precipitation of such representative metals as Co²⁺, Ni²⁺ and CrO₄^2- has been experimentally confirmed. This approach can be used as a basis for the development of new biotechnologies for the treatment of polymetallic wastewater.