Sulfuric acid is the most used industrial chemical by amount and by number of applications. Its precursor sulfide is also present in the ore and reacts with oxygen to generate sulfate. Naturally, almost all these industrial applications generate sulfate-rich wastewater.
Such process water can, if released into an un-regulated, un-controlled environment, produce highly reactive, corrosive, and toxic hydrogen sulfide in anoxic zones and decisively contribute to the bad chemical status of river systems. In addition, there can be high concentrations of toxic heavy metals in such waters.
Indeed, 50 % of the rivers in Europe are considered as contaminated – so improvement of water quality is critical. Therefore, many industries and institutions are taking steps towards developing technologies to treat sulfate-rich wastewater capture sulfide and used in a variety of industrial applications. Through BIOMIMIC, we are developing technologies to treat sulfate-rich wastewater using a selected group of naturally occurring bacteria, known as sulfate reducing bacteria (SRB). To achieve the best possible performance of these processes the first step is to understand their mechanisms.
Sulfate reducing bacteria in different process waters
BIOMIMIC has performed experiments to study the sulfate reduction potential of SRB with two different process waters. BIOMIMIC has also performed small-scale tests wherein the effect of changes in the nature of the process water with respect to pH, salt content, sulfate and sulfide content on sulfate reduction efficiency were studied.
The results show that SRB enriched under different conditions respond differently to the process waters. Indeed, the response is clearly manifested through marked difference in sulfate reduction efficiency and rate. These differently enriched SRB cultures show different levels of tolerance towards challenging conditions of pH and salt concentration. Overall, this illustrates the robustness of the SRB consortia.
However, there is a consequence that the product of the process, namely dissolved H2S, should be removed from the process as effectively as possible. Furthermore, the results of the experiments were used to validate a mathematical model simulating the sensitivity of the SRB to the various conditions. Finally, the knowledge developed through the work detailed here will be useful when up-scaling the technology to the pilot-scale.
The process can be used to recover metals while simultaneously become a remediation solution. In Freiberg, the ore mine effluent water was treated by a process developed by GEOS (within BIOMIMIC), for a combined metal recovery and toxic contaminant removal such as Ni, As, Cd, Cu and Zn, which was very efficiently (90 % or more). In addition, RISE showed that in a designed mineral solution Zn could be recovered selectively as ZnS with a 99 % purity. This is a good start for future development at larger scale within the project. Validation experiments are planned during autumn and spring 2019–2020.