Bio-removal of heavy metals, using microbial biomass, increasingly attracting scientific attention due to their significant role in purification of different types of wastewaters making it reusable. Heavy metals were reported to have a significant hazardous effect on human health, and while the conventional methods of removal were found to be insufficient; microbial biosorption was found to be the most suitable alternative. In this work, an immobilized microbial consortium was generated using Statistical Design of Experiment (DOE) as a robust method to screen the efficiency of the microbial isolates in heavy metal removal process. This is the first report of applying Statistical DOE to screen the efficacy of microbial isolates to remove heavy metals instead of screening normal variables. A mixture of bacterial biomass and fungal spores was used both in batch and continuous modes to remove Chromium and Iron ions from industrial effluents. Bakery yeast was applied as a positive control, and all the obtained biosorbent isolates showed more significant efficiency in heavy metal removal. In batch mode, the immobilized biomass was enclosed in a hanged tea bag-like cellulose membrane to facilitate the separation of the biosorbent from the treated solutions, which is one of the main challenges in applying microbial biosorption at large scale. The continuous flow removal was performed using fixed bed mini-bioreactor, and the process was optimized in terms of pH (6) and flow rates (1 ml/min) using Response Surface Methodology. The most potential biosorbent microbes were identified and characterized. The generated microbial consortia and process succeeded in the total removal of Chromium ions and more than half of Iron ions both from standard solutions and industrial effluents. Keywords Waste water treatment Á Biosorption Á Microbial consortium Á Bioreactor Á Design of experiment Á Microbial immobilization Editorial responsibility: Xu Han.

Rhodotorula yeasts which are known as carotenogenic yeasts have a great industrial value due to their ability to produce carotenoids. In particular, the isolated yeast Rhodotorula sp. (strain ATL72) has been reported to be a promising producer of high concentrations of carotenoids. A combination of central composite design (CCD) and Plackett–Burman (PB) design was used to optimize carotenoids produced by this yeast. The optimum production of carotenoids was completed when the yeast was grown in a production medium composed of 3.7 g/L malt extract, 7.7 g/L fructose, 9 g/L urea, 35 g/L NaCl, and 1 g/L yeast extract at 27.5 °C, pH 6.7, and 180 rpm. Two batch runs in 1L and 7L bioreactors were conducted which increased the productivity of carotenoid concentration from 21.5 mg/L after 98h of incubation at the level of the shake flask to 229.9 mg/L after 47 h of incubation at the level of 7 L bioreactor. The carotenoid pigment was extracted in dimethylsulfoxide (DMSO), acetone, petroleum ether, and sodium chloride, and subsequently identified and characterized using the following: UV-visible scanning, thin layer chromatography, and gas chromatography/mass spectrometry.

Silver nanoparticles were successfully fabricated through a very simple, rapid, one-step photo-induced green approach.

Natural protection of the Bacillus thuringiensis-based biopesticides from inactivation by the UV component of the cosmic rays constitutes a big challenge to environmentalists, health concerned groups, and industry. Melanin pigment produced by a variety of microbes has the capabilities of protecting these types of biopesticides. A black melanin produced by a locally isolated strain of the yeast Hortaea werneckii EGYNDA08 possesses the qualities of a sun protectant agent. This UV bio-protectant increased the killing potency of a locally isolated B. thuringiensis subsp. aegypti (Bt-C18)-based biopesticide ninefold upon feeding the first instar larvae of the cotton leaf worm, Spodoptera littrolis. This black melanin was extracted, characterized, and exposed to different optimization process for the purpose of enhancing its productivity. The optimization process employed medium engineering techniques to generate a suitable cheap production medium not only at bench-scale level but also at the bioreactor level. These optimization techniques have led to increase the melanin produced by the local isolate of Hortaea werneckii EGYNDA08 up to 228 mg/l compared to 8 mg/l prior to optimization. This study concluded that black yeast melanin could be used at a wide range as a potential green alternative for the conventional chemically based sunscreens that currently used to protect biopesticides from inactivation by the cosmic rays.