Engineering in Life Sciences

Anaerobic digestion (AD) for biogas production leads to several changes in the composition of the resulting digestates compared to the original feedstock (ammonia content, pH, carbon to nitrogen ratio, etc.), which are relevant for the plant availability of macro‐ and micronutrients after field application. Increased NH₄⁺‐N content in digested slurries compared to undigested slurries does not guarantee improved uptake efficiency of slurry nitrogen and increased savings in fertilizer nitrogen. AD of crop residues and cover crops leads to an increase in the total amounts of mobile organic manures within the farming system, resulting in a higher nitrogen use efficiency and an increased scope for target‐oriented nitrogen application in time and space, when needed by the crop, as an alternative to the site‐bound soil incorporation as green manures. AD of dairy manure appears to reduce the fraction of immediate plant available phosphorus and micronutrients. This does, however, not affect short‐term crop availability under field conditions. More studies are needed to improve current knowledge on sulfur losses during AD and fertilizer value of digestates.

The pollution of the environment with toxic metals is a result of many human activities, such as mining and metallurgy, and the effects of these metals on the ecosystems are of large economic and public‐healthsignificance. This paper presents the features and advantages of the unconventional removal method of heavy metals – biosorption – as a part of bioremediation. Bioremediation consists of a group of applications, which involvethe detoxification of hazardous substances instead of transferring them from one medium to another, by means of microbes and plants. This process is characterized as less disruptive and can be often carried out on site, eliminating the need to transport the toxic materials to treatment sites. The biosorption (sorption of metallic ions from solutions by live or dried biomass) offers an alternative to the remediation of industrial effluents as well as the recovery of metals contained in other media. Biosorbents are prepared from naturally abundant and/or waste biomass. Due to the high uptake capacity and very cost‐effective source of the raw material, biosorption is a progression towards a perspective method. The mechanism by which microorganisms take up metals is relatively unclear, but it has been demonstrated that both living and non‐living biomass may be utilized in biosorptive processes, as they often exhibit a marked tolerance towards metals and other adverse conditions. One of their major advantages is the treatment of large volumes of effluents with low concentrations of pollutants. Models developed were presented to determine both the number of adsorption sites required to bind each metal ion and the rate of adsorption, using a batch reactor mass balance and the Langmuir theory of adsorption to surfaces or continuous dynamic systems. Two main categories of bioreactors used in bioremediation – suspended growth and fixed film bioreactors – are discussed. Reactors with varying configurations to meet the different requirements for biosorption are analyzed considering two major groups of reactors – batch reactors and continuous reactors. Biosorption is treated as an emerging technology effective in removing even very low levels of heavy metal.

Biological sulfate reduction is increasingly replacing chemical unit processes in mining biotechnology. Sulfate reducing bacteria (SRB) can be used for treating ground‐ and surface waters contaminated with acid mine drainage (AMD), and for recovering metals from wastewater and process streams. Biologically produced H₂S precipitates metals as metal sulfides, while biogenic bicarbonate alkalinity neutralizes acidic waters. This paper reviews various passive and active SRB‐based alternatives as well as some process design aspects, such as reactor types, process configurations, and choices of substrates for sulfate reduction. The latest developments of using various low‐cost substrates together with new bioprocess designs are increasing the uses and applications of SRB‐based bioreactors in AMD control and selective metal recovery.

This article reviews the potential of anaerobic digestion (AD) for biogas production from livestock manure wastes and compares the operating and performance data for various anaerobic process configurations. It examines different kinds of manure waste treatment techniques and the influence of several parameters on biogas and methane yield. The comparison indicates that a variety of different operational conditions, various reactor configurations such as batch reactors, continuously stirred tank reactor (CSTR), plug flow reactor (PFR), up‐flow anaerobic sludge blanket (UASB), anaerobic sequencing batch reactor (ASBR), temperature phased anaerobic digestion (TPAD), and continuous one‐ and two‐stage systems, present a suitable technology for the AD of livestock manure waste. Main performance indicators are biogas and methane yield, degradation of volatile solids (VS), higher loading, and process stability with a short retention time.

Elicitation is a possible aid to overcome various difficulties associated with the large‐scale production of most commercially important bioactive secondary metabolites from wild and cultivated plants, undifferentiated or differentiated cultures. Secondary metabolite accumulation in vitro or their efflux in culture medium has been elicited in the undifferentiated or differentiated tissue cultures of several plant species by the application of a low concentration of biotic and abiotic elicitors in the last three decades. Hairy root cultures are preferred for the application of elicitation due to their genetic and biosynthetic stability, high growth rate in growth regulator‐free media, and production consistence in response to elicitor treatment. Elicitors act as signal, recognized by elicitor‐specific receptors on the plant cell membrane and stimulate defense responses during elicitation resulting in increased synthesis and accumulation of secondary metabolites. Optimization of various parameters, such as elicitor type, concentration, duration of exposure, and treatment schedule is essential for the effectiveness of the elicitation strategies. Combined application of different elicitors, integration of precursor feeding, or replenishment of medium or in situ product recovery from the roots/liquid medium with the elicitor treatment have showed improved accumulation of secondary metabolites due to their synergistic effect. This is a comprehensive review about the progress in the elicitation approach to hairy root cultures from 2010 to 2019 and the information provided is valuable and will be of interest for scientists working in this area of plant biotechnology.

This paper reviews the main microbial processes involved when toxic metals are removed from wastewater in constructed wetlands. Microbial activity is thought to play a key role in the detoxification of these metals. The paper concentrates on the microbial processes which affect the mobility, the toxicity and bioavailability of metals, namely biosorption, metal sulfide precipitation by sulfate reducers, redox transformations, and methylation, as well as microbe‐plant interactions. These reactions result in either the precipitation and accumulation of metals in wetland soils, or their volatilization and emission into the atmosphere. The possibilities of optimizing the microbially mediated reactions for the development of wetland technology are discussed as a long‐term metal retention strategy.

The electrospinning technology opens up enormous possibilities for the implementation of bio‐based materials and food hydrocolloids in numerous applications. In this context, chitosan is a sustainable, biocompatible, biodegradable, antimicrobial and non‐toxic polysaccharide of great relevance in many fields of application. Because of its abundance in nature and excellent biocompatibility, the cationic polysaccharide chitosan is a very promising polymer for producing functional nanofibers. Although the material has good physicochemical properties, the electrospinning of the polymer is far from easy. In the current study, the effect of an unprecedented number of parameters (including solvent nature, polymer origin, molecular weight and spinning conditions) on morphology is reported. The work also aims to ascertain the antimicrobial properties of the generated biofibers of chitosan and relate them to its chemical structure. Finally, a new route is provided to generate chitosan based nanoporous structures starting from blends of chitosan and polylactic acid.

The ability of bacterial strains to assimilate glycerol derived from biodiesel facilities to produce metabolic compounds of importance for the food, textile and chemical industry, such as 1,3‐propanediol (PD), 2,3‐butanediol (BD) and ethanol (EtOH), was assessed. The screening of 84 bacterial strains was performed using glycerol as carbon source. After initial trials, 12 strains were identified capable of consuming raw glycerol under anaerobic conditions, whereas 5 strains consumed glycerol under aerobiosis. A plethora of metabolic compounds was synthesized; in anaerobic batch‐bioreactor cultures PD in quantities up to 11.3 g/L was produced by Clostridium butyricum NRRL B‐23495, while the respective value was 10.1 g/L for a newly isolated Citrobacter freundii. Adaptation of Cl. butyricum at higher initial glycerol concentration resulted in a PD_max concentration of ∼32 g/L. BD was produced by a new Enterobacter aerogenes isolate in shake‐flask experiments, under fully aerobic conditions, with a maximum concentration of ∼22 g/L which was achieved at an initial glycerol quantity of 55 g/L. A new Klebsiella oxytoca isolate converted waste glycerol into mixtures of PD, BD and EtOH at various ratios. Finally, another new C. freundii isolate converted waste glycerol into EtOH in anaerobic batch‐bioreactor cultures with constant pH, achieving a final EtOH concentration of 14.5 g/L, a conversion yield of 0.45 g/g and a volumetric productivity of ∼0.7 g/L/h. As a conclusion, the current study confirmed the utilization of biodiesel‐derived raw glycerol as an appropriate substrate for the production of PD, BD and EtOH by several newly isolated bacterial strains under different experimental conditions.

Itaconic acid is a valuable platform compound for the production of bio‐based polymers, chemicals, and fuels. Ustilago maydis is a promising host for the production of itaconic acid from biomass‐derived substrates due to its unicellular growth pattern and its potential to utilize biomass‐derived sugar monomers and polymers. The potential of U. maydis for industrial itaconate production was assessed in pH‐controlled batch fermentations with varying medium compositions. Using 200 g/L glucose and 75 mM ammonium, 44.5 g/L of itaconate was produced at a maximum rate of 0.74 g L⁻¹ h⁻¹. By decreasing the substrate concentrations to 50 g/L glucose and 30 mM ammonium, a yield of 0.34 g/g (47 mol%) could be achieved. Itaconate production from xylose was also feasible. These results indicate that high itaconic acid titers can be achieved with U. maydis. However, further optimization of the biocatalyst itself through metabolic engineering is still needed in order to achieve an economically feasible process, which can be used to advance the development of a bio‐based economy.