An integrated approach for the phycoremediation of Pb(II) and the production of biofertilizer using nitrogen-fixing cyanobacteria

In recent years, growing attention has been directed toward the phycoremediation of heavy metals from bodies of water; however, many challenges remain. The nitrogen requirements for algal growth in nutrient-poor waters can lead to substantial costs. Moreover, proper management of the metal-loaded biomass is a concern. This study assessed the performance of two nitrogen-fixing cyanobacteria, Anabaena sp. and Nostoc muscorum, in treating Pb(II)-contaminated water without nitrogen under batch and fed-batch modes, as well as the subsequent utilization of the produced biomass as a biofertilizer. After 12 days of the batch mode with initial Pb(II) concentrations of 10, 20, 35, and 60 mg/L, Pb(II) removal efficiencies were 98.90%, 98.95%, 97.20%, and 84.98% by Anabaena sp. and 88.00%, 73.10%, 54.54%, and 26.83% by N. muscorum, respectively. Anabaena sp. sustained growth and Pb(II) removal under the fed-batch mode by adjusting hydraulic retention time based on the influent Pb(II) concentration. Decontamination of the metal-loaded Anabaena sp. biomass was performed and resulted in a Pb(II) desorption of 93%. The desorbed Anabaena sp. extract provided the nutrient requirements for Chlorella vulgaris. The proposed strategy provides simultaneous Pb(II) bioremediation and biofertilizer production in a system driven by light energy, atmospheric N₂, and CO₂.

Efficient high-solids enzymatic hydrolysis of corncobs by an acidic pretreatment and a fed-batch feeding mode

Corncob is an abundant and renewable resource that could be enzymatically hydrolyzed to fermentable sugar. A major impediment in corncob utilization is the low hydrolysis efficiency at high-solids content. This study attempted different pretreatment methods and fed-batch modes to achieve a 25% solids content hydrolysis with high yields. Natural corncobs were compared with acid-treated and acid-alkali-treated corncobs in terms of kinetics parameters, conversion rate and glucose titer. By feeding in batches, a "low amount and high frequency" mode (10%-3%-3%-3%-3%-3%, every 5 h) was confirmed to be optimal for a 25% high-solids hydrolysis system with a cellulase loading of 12 mg/g (7.3 FPU/g), resulted with an 84.4% glucose yield at 96 h. Our results demonstrated that combination of both optimized pretreatment method and fed-batch mode were a favored process model for high-solids hydrolysis of lignocellulose, boosting cellulose hydrolysis efficiency and sugar yields on an industrial scale.

Efficient biobutanol production by acetone-butanol-ethanol fermentation from spent coffee grounds with microwave assisted dilute sulfuric acid pretreatment

The integral valorization of potential sugars (cellulosic and hemicellulosic) from spent coffee grounds (SCG), a lignocellulosic residue, is proposed in this work. With this aim, the microwave assisted dilute sulfuric acid pretreatment has been optimized, leading to a hemicellulosic sugar recovery in the pretreatment liquid (HSR_L) and an enzymatic hydrolysis yield of 79 and 98%, respectively, at 160.47 °C and 1.5% H₂SO₄. Moreover, the complete digestibility of cellulose (enzymatic hydrolysis yield = 100%) was also discovered for non-pretreated SCG, which is very interesting. Secondly, the production of biobutanol, an advanced biofuel, is also proposed from pretreated SCG enzymatic hydrolysate and pretreatment liquid achieved under optimal conditions. These were fermented by Clostridium beijerinckii, yielding 95 kg butanol/t SCG (dry matter) and 151 kg acetone-butanol-ethanol/t SCG (dry matter).

Fed-batch like cultivation in a micro-bioreactor: screening conditions relevant for Escherichia coli based production processes

Objectives

Recombinant protein production processes in Escherichia coli are usually operated in fed-batch mode; therefore, the elaboration of a fed-batch cultivation protocol in microtiter plates that allows for screening under production like conditions is particularly appealing.

Results

A highly reproducible fed-batch like microtiter plate cultivation protocol for E. coli in a micro-bioreactor system with advanced online monitoring capabilities was developed. A synthetic enzymatic glucose release medium was employed to provide carbon limited growth conditions without external substrate feed and the required buffer capacity to keep the pH value within 7 ± 1. Accurate process design allowed for cultivation up to cell densities of 10 g biomass l⁻¹ without any limitations in oxygen supply [dissolved oxygen (DO) level above 30 %]. In the micro-bioreactor system (BioLector) online monitoring of cell growth, DO and pH was performed. Furthermore, the influence of the cultivation temperature, the applicability for different host strains as well as the transferability of results to lab-scale bioreactor cultivations was evaluated.

Conclusion

This robust microtiter plate cultivation protocol allows for screening of E. coli systems under conditions comparable to lab-scale bioreactor cultivations.