Valorization of crude glycerol and eggshell biowaste as media components for hydrogen production: A scale-up study using co-culture system

Strategies to enhance production of metabolites in microbial co-culture systems

Increasing evidence shows that microbial synthesis plays an important role in producing high value-added products. However, microbial monoculture generally hampers metabolites production and limits scalability due to the increased metabolic burden on the host strain. In contrast, co-culture is a more flexible approach to improve the environmental adaptability and reduce the overall metabolic burden. The well-defined co-culturing microbial consortia can tap their metabolic potential to obtain yet-to-be discovered and pre-existing metabolites. This review focuses on the use of a co-culture strategy and its underlying mechanisms to enhance the production of products. Notably, the significance of comprehending the microbial interactions, diverse communication modes, genetic information, and modular co-culture involved in co-culture systems were highlighted. Furthermore, it addresses the current challenges and outlines potential future directions for microbial co-culture. This review provides better understanding the diversity and complexity of the interesting interaction and communication to advance the development of co-culture techniques.

Eggshells & Eggshell Membranes- A Sustainable Resource for energy storage and energy conversion applications: A critical review

As the world strives to achieve a sustainable future, the exploration of alternative and renewable raw materials for energy storage and energy conversion has gained significant attention. A growing trend on "Waste to Energy" approach has attained prominence. Accordingly, chicken eggshells, a residual from poultry industry, have emerged as a promising candidate due to their abundant availability, low cost, and unique physical and chemical properties. This review article presents an overview of recent advancements in utilizing eggshell waste for energy storage and energy conversion applications. It discusses the transformation of eggshells usage into functional materials, along with their performance in various energy-related applications. The potential of eggshell-based materials in improving energy efficiency and reducing environmental impact is highlighted, providing insights into the future prospects of this sustainable resource.

Pilot-scale production and in-situ application of petroleum-degrading enzyme cocktail from Alcanivorax borkumensis

Petroleum degrading enzymes can be used as an alternative way to improve petroleum bioremediation approaches. Alcanivorax borkumensis is an alkane-degrading bacteria that can produce petroleum degrading enzymes such as alkane hydroxylase and lipase. In this study, pilot-scale Alcanivorax borkumensis fermentation was developed for producing large volumes of petroleum degrading enzymes cocktail (∼900 L). Different process conditions, such as inoculum age 72 h and size 4% v/v, temperature 30 ± 1 °C, agitation speed at 150 rpm and, fermentation period 3 days were determined as the optimum for producing alkane hydroxylase and lipase activity. The oxygen transfer capacity was studied for obtaining better bacterial growth and higher enzyme activities in bioreactor process optimization as well as scale-up. Results showed that the maximum values of oxygen mass transfer coefficient (k_La), oxygen uptake rate (OUR), oxygen transfer rate (OTR), alkane hydroxylase, lipase, and cell count were 196.95 h^-1, 0.92 mmol O₂/L/h, 1.8 mmol O₂/L/h, 222.49 U/mL, 325 U/mL, and 8.6 × 10¹⁰ CFU/mL, respectively. Compared with the bench-scale bioreactors, the 150 L fermenter showed a better oxygen transfer rate which affected the cell growth that doubled the number and enzymes production that increased. Then, the enzyme cocktail was used for a field test in a diesel source zone using a 5-spot well pattern. The results showed a significant reduction in concentrations of C10 - C50 (from 36% to > 99%) after one injection of enzyme cocktail, mainly for the contaminated soils located in the saturated zone of the unconfined aquifer. This study confirmed the scaling-up ofalkane-degrading enzyme production to an industrial-scale and its application for effective bioremediation of petroleum contaminated sites.

Immobilization of nitrifying bacteria on composite based on polymers and eggshells for nitrate production

Nitrification is a key step in biological nitrogen transformation which depends on the performance of specialized microorganisms. Generally, nitrifying bacteria present a low growth rate and performance which can be improved when immobilized as a biofilm. The development of new materials suitable for the immobilization of nitrifying microorganisms is very important in nitrification and wastewater treatment. In this study, the effect of eggshell powder on biofilm formation by Nitrosomonas europaea an ammonium-oxidizing bacteria and Nitrobacter vulgaris a nitrite-oxidizing bacteria, on new polymeric supports were analyzed. Polylactic acid, polyvinyl chloride and polystyrene were tested to produce polymer-eggshells powder composites and used as biofilm supports for nitrifying bacteria. The support material was characterized to identify the most suitable polymer-eggshells powder combination for the cell adhesion and biofilm formation. The nitrification results showed a highest nitrate production of 42 mg NO₃^--N/L with polylactic acid-eggshell composite, with the best surface properties for cellular adhesion. Finally, scanning electron microscopy micrographs confirmed the best biofilm formed on polylactic acid-eggshell.

Advances and Applications of Clostridium Co-culture Systems in Biotechnology

Clostridium spp. are important microorganisms that can degrade complex biomasses such as lignocellulose, which is a widespread and renewable natural resource. Co-culturing Clostridium spp. and other microorganisms is considered to be a promising strategy for utilizing renewable feed stocks and has been widely used in biotechnology to produce bio-fuels and bio-solvents. In this review, we summarize recent progress on the Clostridium co-culture system, including system unique advantages, composition, products, and interaction mechanisms. In addition, biochemical regulation and genetic modifications used to improve the Clostridium co-culture system are also summarized. Finally, future prospects for Clostridium co-culture systems are discussed in light of recent progress, challenges, and trends.

Yeast-driven whey biorefining to produce value-added aroma, flavor, and antioxidant compounds: technologies, challenges, and alternatives

Whey is a liquid residue generated during the production of cheese and yogurt. It has a pH between 3.9 and 5.6, and a high chemical oxygen demand (COD), from 60 to 80 g/L. Whey contains lactose, proteins, and minerals. Globally, approximately 50% of the whey generated is untreated and is released directly into the environment, which represents an environmental risk. To overcome whey management problems, conventional thermo-physical valorization treatments have been explored, which are complex, costly and energy-intensive. As an alternative, whey fermentation processes employing bacteria, fungi and yeast are economical and promising methods. Among them, yeast fermentation creates value-added products such as antimicrobials, biofuels, aromas, flavors, and antioxidants with no need for previous conditioning of the whey, such as hydrolysis of the lactose, prior to whey biorefining. The biorefining concept applied to whey is discussed using chemical and biological transformation pathways, showing their pluses and minuses, such as technical drawbacks. The main challenges and solutions for the production of fusel alcohols, specifically for 2-phenylethanol, are also discussed in this review.

A review on recent trends in reactor systems and azeotrope separation strategies for catalytic conversion of biodiesel-derived glycerol

The increasing demand for biodiesel (BD) as a renewable and sustainable energy source has impelled the generation of abundant and low-cost byproduct glycerol, which accounts for 10 wt% of total BD production and requires urgent utilization. The transesterification reaction, which utilizes glycerol and dimethyl carbonate (DMC) to synthesize valuable glycerol carbonate (GC) is an established reaction pathway to valorize oversupplied glycerol. Commercialization of inexpensive GC is constrained by the nature, stability, and basicity of applied catalyst, reaction conditions, types of the reactor system and separation methods of reaction products. This study presents a review and diversity of recent reports on reactor systems and DMC-methanol azeotrope separation strategies explored in GC synthesis from biodiesel-derived glycerol. Also, recent trends on heterogeneous catalysts, their performance, and the effects of reaction conditions were presented. Conducted studies revealed that the choice for reactor systems is constrained by factors such as energy consumption and operational safety and a significant mild reaction conditions could be realized using a microwave reactor. Furthermore, the reactive-extractive distillation and pervaporation processes showed high energy-efficiency and appreciable separation of DMC-methanol azeotrope. Thus, the development of stable catalyst and process intensification to fabricate an integrated reactor-separation system with high energy efficiency are fundamental and must be explored. This study portrays the recent research effort made in this direction and the limitations that require urgent attention.

State of the art and challenges of biohydrogen from microalgae

Biohydrogen from microalgae has attracted extensive attention owing to its promising features of abundance, renewable and self sustainability. Unlike other well-established biofuels like biodiesel and bioethanol, biohydrogen from microalgae is still in the preliminary stage of development. Criticisms in microalgal biohydrogen centered on its practicality and sustainability. Various laboratory- and pilot-scale microalgal systems have been developed, and some research initiatives have exhibited potential for commercial application. This work provides a review of the state of the art of biohydrogen from microalgae. Discussions include metabolic pathways of light-driven transformation and dark fermentation, reactor schemes and system designs encompassing reactor configurations and light manipulation. Challenges, knowledge gaps and the future directions in metabolic limitations, economic and energy assessments, and molecular engineering are also delineated. Current scientific and engineering challenges of microalgal biohydrogen need to be addressed for technology leapfrog or breakthrough.

Valorization of egg shell as a detoxifying and buffering agent for efficient polymalic acid production by Aureobasidium pullulans NRRL Y-2311-1 from barley straw hydrolysate

Stepwise formulation of a versatile and cost-effective medium based on barley straw hydrolysate and egg shell for efficient polymalic acid production by A. pullulans NRRL Y-2311-1 was carried out for the first time. The strain did not grow and produce polymalic acid when dilute acid pretreated barley straw hydrolysate (total fermentable sugars: 94.60 g/L; furfural: 1.01 g/L; hydroxymethylfurfural: 0.55 g/L; acetic acid: 5.06 g/L) was directly used in medium formulation without detoxification (e.g. charcoal pretreatment). When CaCO₃ in the medium formulation was substituted with egg shell powder, efficient production of polymalic acid was achieved without a detoxification step. Utilization of 40 g/L of egg shell powder led to 43.54 g polymalic acid production per L with the productivity of 0.30 g/L/h and yield of 0.48 g/g. The bioprocess strategy used in this study can also be utilized for mass production of several other industrially important microbial organic acids and biomaterials.

Seed Pretreatment for Increased Hydrogen Production Using Mixed-Culture Systems with Advantages over Pure-Culture Systems

Hydrogen is an important source of energy and is considered as the future energy carrier post-petroleum era. Nowadays hydrogen production through various methods is being explored and developed to minimize the production costs. Biological hydrogen production has remained an attractive option, highly economical despite low yields. The mixed-culture systems use undefined microbial consortia unlike pure-cultures that use defined microbial species for hydrogen production. This review summarizes mixed-culture system pretreatments such as heat, chemical (acid, alkali), microwave, ultrasound, aeration, and electric current, amongst others, and their combinations to improve the hydrogen yields. The literature representation of pretreatments in mixed-culture systems is as follows: 45–50% heat-treatment, 15–20% chemical, 5–10% microwave, 10–15% combined and 10–15% other treatment. In comparison to pure-culture mixed-culture offers several advantages, such as technical feasibility, minimum inoculum steps, minimum media supplements, ease of operation, and the fact it works on a wide spectrum of low-cost easily available organic wastes for valorization in hydrogen production. In comparison to pure-culture, mixed-culture can eliminate media sterilization (4 h), incubation step (18–36 h), media supplements cost ($4–6 for bioconversion of 1 kg crude glycerol (CG)) and around 10–15 Millijoule (MJ) of energy can be decreased for the single run.

Bioprocessing of Biodiesel Industry Effluent by Immobilized Bacteria to Produce Value-Added Products

Biodiesel industrial effluent rich in crude glycerol (CG) was processed to produce value-added product. Under continuous culture system, Bacillus amyloliquefaciens strain CD16 immobilized within its biofilm, produced 3.2 L H₂/day/L feed, over a period of 60 days at a hydraulic retention time of 2 days. The effective H₂ yield by B. amyloliquefaciens strain CD16 was 165 L/L CG. This H₂ yield was 1.18-fold higher than that observed with non-biofilm forming Bacillus thuringiensis strain EGU45. Bioprocessing of the effluent released after this stage, by recycling it up to 25% did not have any adverse effect on H₂ production by strain EGU45; however, a 25% reduction in yield was recorded with strain CD16. Biofilm forming H₂ producers thus proved effective as self-immobilizing system leading to enhanced process efficiency.