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The ability of the phenol-adapted Ralstonia eutropha to utilize formaldehyde (FD) as the sole source of carbon and energy was studied. Adaptation to FD was accomplished by substituting FD for glucose in a stepwise manner. The bacterium in the liquid test culture could tolerate concentrations of FD up to 900 mg L(-1). Degradation of FD was complete in 528 h at 30°C with shaking at 150 rpm (r = 1.67 mg L(-1) h(-1)), q = 0.035 g(FD) g(cell) (-1) h(-1). Substrate inhibition kinetics (Haldane and Luong equations) are used to describe the experimental data. At non-inhibitory concentrations of FD, the Monod equation was used. According to the Luong model, the values of the maximum specific growth rate (μ(max)), half-saturation coefficient (k(S)), the maximum allowable formaldehyde concentration (S(m)), and the shape factor (n) were 0.117 h(-1), 47.6 mg L(-1), 900 mg L(-1), and 2.2, respectively. The growth response of the test bacterium to consecutive FD feedings was examined, and the FD-adapted R. eutropha cells were able to degrade 1000 mg L(-1) FD in 150 h through 4 cycles of FD feeds. During FD degradation, formic acid metabolite was formed. Assimilation of FD, methanol, formic acid, and oxalate by the test bacterium was accompanied by the formation of a pink pigment. The carotenoid nature of the cellular pigment has been confirmed and the test bacterium appeared to be closely related to pink-pigmented facultative methylotrophs (PPFM). The extent of harm to soil exposed to biotreated wastewaters containing FD may be moderated due to the association between methylotrophic/oxalotrophic bacteria and plants.

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The potential of Ralstonia eutropha as a biocatalyst for desulfurization of dibenzothiophene (DBT) was studied in growing and resting cell conditions. The results of both conditions showed that sulfur was removed from DBT which accompanied by the formation of 2-hydroxybiphenyl (2-HBP). In growing cell experiments, glucose was used as an energy supplying substrate in initial concentrations of 55 mM (energy-limited) and 111 mM (energy-sufficient). The growing cell behaviors were quantitatively described using the logistic equation and maintenance concept. The results indicated that 2-HBP production was higher for the energy-sufficient cultures, while the values of the specific growth rate and the maintenance coefficient for these media were lower than those of the energy-limited cultures. Additionally, the kinetic studies showed that the half-saturation constant for the energy-limited cultures was 2 times higher than the energy-sufficient ones where the inhibition constant (0.08 mM) and the maximum specific DBT desulfurization rate (0.002 mmol g h) were almost constant. By defining desulfurizing capacity (D ) including both the biomass concentration and time to reach a particular percentage of DBT conversion, the best condition for desulfurizing cell was determined at 23% g L h which corresponded with the resting cells that were harvested at the mid-exponential growth phase.

Nowadays, large amount of municipal solid waste is because of electrical scraps (i.e. waste electrical and electronic equipment) that contain large quantities of electrical conductive metals like copper and gold. Recovery of these metals decreases the environmental effects of waste electrical and electronic equipment (also called E-waste) disposal, and as a result, the extracted metals can be used for future industrial purposes. Several studies reported in this review, demonstrated that the biohydrometallurgical processes were successful in efficient extraction of metals from electrical and electronic wastes. The main advantages of biohydrometallurgy are lower operation cost, less energy input, skilled labour, and also less environmental effect in comparison with pyro-metallurgical and hydrometallurgical processes. This study concentrated on fundamentals and technical aspects of biohydrometallurgy. Some points of drawbacks and research directions to develop the process in the future are highlighted in brief.

The clarification of carrot juice by cross‐flow microfiltration process was studied to determine the influence of different operating parameters such as transmembrane pressure (TMP) (1.5, 4.5 and 7.5 bar), cross‐flow velocity, which corresponds with Reynolds number, (300, 1,500 and 2,500) and feed temperature (20, 30 and 40C) on the flux and permeate properties. Results showed that the investigated parameters had a positive effect on the permeate flux. The TMP and temperature effects on the permeate flux was lower than the cross‐flow velocity effect. The permeate properties such as viscosity, density, pH and total soluble solid did not significantly change with variation in operating parameters, but permeate color and clarity was considerably affected at various treatment conditions. Eventually, the statistical analysis indicated that the interactional effect of cross‐flow velocity and TMP on the permeate flux was significant. PRACTICAL APPLICATIONS The polymeric membranes can be used in the microfiltration process for the clarification and stabilization of carrot juice. The membrane processes for clarification purposes represent a valid alternative to the use of traditional fining agents such as gelatin, bentonite and silica sol. It is because of environmental problems resulting from disposal of these fining agents as well as other difficulties that are confronted in separation processes. Clarified carrot juice coming from the microfiltration process can be commercialized or submitted to a concentration process in order to obtain a suitable product for the preparation of juices and beverages.