Natural and anthropogenic sources of metals in the ecosystem are perpetually increasing; consequently, heavy metal (HM) accumulation has become a major environmental concern. Human exposure to HMs has increased dramatically due to the industrial activities of the 20th century. Mercury, arsenic lead, chrome, and cadmium have been the most prevalent HMs that have caused human toxicity. Poisonings can be acute or chronic following exposure via water, air, or food. The bioaccumulation of these HMs results in a variety of toxic effects on various tissues and organs. Comparing the mechanisms of action reveals that these metals induce toxicity via similar pathways, including the production of reactive oxygen species, the inactivation of enzymes, and oxidative stress. The conventional techniques employed for the elimination of HMs are deemed inadequate when the HM concentration is less than 100 mg/L. In addition, these methods exhibit certain limitations, including the production of secondary pollutants, a high demand for energy and chemicals, and reduced cost-effectiveness. As a result, the employment of microbial bioremediation for the purpose of HM detoxification has emerged as a viable solution, given that microorganisms, including fungi and bacteria, exhibit superior biosorption and bio-accumulation capabilities. This review deals with HM uptake and toxicity mechanisms associated with HMs, and will increase our knowledge on their toxic effects on the body organs, leading to better management of metal poisoning. This review aims to enhance comprehension and offer sources for the judicious selection of microbial remediation technology for the detoxification of HMs. Microbial-based solutions that are sustainable could potentially offer crucial and cost-effective methods for reducing the toxicity of HMs.

The aim of this study was to determine the optimal conditions for dark fermentation using agro-industrial liquid wastewaters mixed with sweet sorghum stalks (i.e., 55% sorghum, 40% cheese whey, and 5% liquid cow manure). Batch experiments were performed to investigate the effect of controlled pH (5.0, 5.5, 6.0, 6.5) on the production of bio-hydrogen and volatile fatty acids. According to the obtained results, the maximum hydrogen yield of 0.52 mol H₂/mol eq. glucose was measured at pH 5.5 accompanied by the highest volatile fatty acids production, whereas similar hydrogen productivity was also observed at pH 6.0 and 6.5. The use of heat-treated anaerobic sludge as inoculum had a positive impact on bio-hydrogen production, exhibiting an increased yield of 1.09 mol H₂/mol eq. glucose. On the other hand, the pretreated (ensiled) sorghum, instead of a fresh one, led to a lower hydrogen production, while the organic load decrease did not affect the process performance. In all experiments, the main fermentation end-products were volatile fatty acids (i.e., acetic, propionic, butyric), ethanol and lactic acid.

The need for alternative energy sources is constantly growing worldwide, while the focus has shifted to the valorization of biomass. The aim of the present study was to determine the optimal pH and hydraulic retention time (HRT) values for treating a mixture of sorghum biomass solution with liquid cow manure (in a ratio 95:5 v/v) through anaerobic digestion, in a two-stage system. Batch tests were initially carried out for the investigation of the pH effect on bio-hydrogen and volatile fatty acids (VFA) production. The highest hydrogen yield of 0.92 mol H₂/mol carbohydrates_consumed was obtained at pH 5.0, whereas the maximum degradation of carbohydrates and VFA productivity was observed at pH 6.0. Further investigation of the effect of HRT on hydrogen and methane production was carried out. The maximum yield of 1.68 mol H₂/mol carbohydrates_consumed was observed at an HRT of 5 d, with H₂ productivity of 0.13 L/L_R·d. On the other hand, the highest CH₄ production rate of 0.44 L/L_R·d was achieved at an HRT of 25 d, with a methane yield of 295.3 mL/g VS_added, whereas at a reduced HRT of 20 d the process exhibited inhibition and/or overload, as indicated by an accumulation of VFAs and decline in CH₄ productivity.