Hydrolysis of Chlorella by Cellulomonas sp. YJ5 Cellulases and Its Biofunctional Properties

Augmentation of Granular Anaerobic Sludge with Algalytic Bacteria Enhances Methane Production from Microalgal Biomass

The efficiency of anaerobic digestion relies upon activity of the inoculum converting organic substrate into biogas. Often, metabolic capacity of the inoculum needs to be augmented with new capabilities to accommodate changes in the substrate feed composition. However, bioaugmentation is not a widely used strategy possibly due to the lack of studies demonstrating successful applications. This study describes the bioaugmentation of granular anaerobic sludge digesting mixed algal biomass in batch-scale reactors. The addition of an algalytic bacterial mixture to the granular consortium increased methane yield by 11%. This study also investigated changes in the microbial 16SrRNA composition of the augmented and non-augmented granular inoculum, which demonstrates a significant change in the hydrolytic microbial community. Overall, the studies’ results aim to provide a feasible checklist to assess the success rates of bioaugmentation of anaerobic digestion applications.

Optimisation of the production of fermentable monosaccharides from algal biomass grown in photobioreactors treating wastewater

Biomass grown in wastewater treatment photobioreactors is a cheap raw material with high contents of carbohydrates, proteins and lipids. This work studies the production of fermentable monosaccharides from three biomasses grown in piggery wastewater (P), domestic wastewater (W) and synthetic medium (S) by applying chemical pretreatment and enzymatic hydrolysis, using a Taguchi design. ANOVA identified temperature, chemical reagent type and chemical reagent concentration as significant operational parameters. However, the biomass concentration, pretreatment time, enzyme dosage and enzymatic hydrolysis time had no remarkable effect. The bacterial content of the biomass had no relevant impact on carbohydrate and protein solubilisation but had a remarkable effect on the degradation of the released carbohydrates (57, 60 and 37% for P, W and S), while also affecting lipid solubilisation. Pretreatment with HCl 2 M at 120 °C resulted the optimal conditions, achieving a monosaccharide recovery of 53, 59 and 80% for P, W and S biomasses, respectively.

Fungal-assisted algal flocculation: application in wastewater treatment and biofuel production

BACKGROUND

The microalgal-based industries are facing a number of important challenges that in turn affect their economic viability. Arguably the most important of these are associated with the high costs of harvesting and dewatering of the microalgal cells, the costs and sustainability of nutrient supplies and costly methods for large scale oil extraction. Existing harvesting technologies, which can account for up to 50% of the total cost, are not economically feasible because of either requiring too much energy or the addition of chemicals. Fungal-assisted flocculation is currently receiving increased attention because of its high harvesting efficiency. Moreover, some of fungal and microalgal strains are well known for their ability to treat wastewater, generating biomass which represents a renewable and sustainable feedstock for bioenergy production.

RESULTS

We screened 33 fungal strains, isolated from compost, straws and soil for their lipid content and flocculation efficiencies against representatives of microalgae commercially used for biodiesel production, namely the heterotrophic freshwater microalgae Chlorella protothecoides and the marine microalgae Tetraselmis suecica. Lipid levels and composition were analyzed in fungal-algal pellets grown on media containing alternative carbon, nitrogen and phosphorus sources from wheat straw and swine wastewater, respectively. The biomass of fungal-algal pellets grown on swine wastewater was used as feedstock for the production of value-added chemicals, biogas, bio-solids and liquid petrochemicals through pyrolysis. Co-cultivation of microalgae and filamentous fungus increased total biomass production, lipid yield and wastewater bioremediation efficiency.

CONCLUSION

Fungal-assisted microalgal flocculation shows significant potential for solving the major challenges facing the commercialization of microalgal biotechnology, namely (i) the efficient and cost-effective harvesting of freshwater and seawater algal strains; (ii) enhancement of total oil production and optimization of its composition; (iii) nutrient supply through recovering of the primary nutrients, nitrogen and phosphates and microelements from wastewater. The biomass generated was thermochemically converted into biogas, bio-solids and a range of liquid petrochemicals including straight-chain C12 to C21 alkanes which can be directly used as a glycerine-free component of biodiesel. Pyrolysis represents an efficient alternative strategy for biofuel production from species with tough cell walls such as fungi and fungal-algal pellets.

Co-cultivation of fungal and microalgal cells as an efficient system for harvesting microalgal cells, lipid production and wastewater treatment

The challenges which the large scale microalgal industry is facing are associated with the high cost of key operations such as harvesting, nutrient supply and oil extraction. The high-energy input for harvesting makes current commercial microalgal biodiesel production economically unfeasible and can account for up to 50% of the total cost of biofuel production. Co-cultivation of fungal and microalgal cells is getting increasing attention because of high efficiency of bio-flocculation of microalgal cells with no requirement for added chemicals and low energy inputs. Moreover, some fungal and microalgal strains are well known for their exceptional ability to purify wastewater, generating biomass that represents a renewable and sustainable feedstock for biofuel production. We have screened the flocculation efficiency of the filamentous fungus A. fumigatus against 11 microalgae representing freshwater, marine, small (5 µm), large (over 300 µm), heterotrophic, photoautotrophic, motile and non-motile strains. Some of the strains are commercially used for biofuel production. Lipid production and composition were analysed in fungal-algal pellets grown on media containing alternative carbon, nitrogen and phosphorus sources contained in wheat straw and swine wastewater, respectively. Co-cultivation of algae and A. fumigatus cells showed additive and synergistic effects on biomass production, lipid yield and wastewater bioremediation efficiency. Analysis of fungal-algal pellet's fatty acids composition suggested that it can be tailored and optimised through co-cultivating different algae and fungi without the need for genetic modification.

Impacts of microalgae pre-treatments for improved anaerobic digestion: thermal treatment, thermal hydrolysis, ultrasound and enzymatic hydrolysis

Anaerobic digestion (AD) of microalgae is primarily inhibited by the chemical composition of their cell walls containing biopolymers able to resist bacterial degradation. Adoption of pre-treatments such as thermal, thermal hydrolysis, ultrasound and enzymatic hydrolysis have the potential to remove these inhibitory compounds and enhance biogas yields by degrading the cell wall, and releasing the intracellular algogenic organic matter (AOM). This work investigated the effect of four pre-treatments on three microalgae species, and their impact on the quantity of soluble biomass released in the media and thus on the digestion process yields. The analysis of the composition of the soluble COD released and of the TEM images of the cells showed two main degradation actions associated with the processes: (1) cell wall damage with the release of intracellular AOM (thermal, thermal hydrolysis and ultrasound) and (2) degradation of the cell wall constituents with the release of intracellular AOM and the solubilisation of the cell wall biopolymers (enzymatic hydrolysis). As a result of this, enzymatic hydrolysis showed the greatest biogas yield increments (>270%) followed by thermal hydrolysis (60-100%) and ultrasounds (30-60%).

A novel method to harvest microalgae via co-culture of filamentous fungi to form cell pellets

While current approaches have limitations for efficient and cost-effective microalgal biofuel production, new processes, which are financially economic, environmentally sustainable, and ecologically stable, are needed. Typically, microalgae cells are small and grow individually. Harvest of these cells is technically difficult and it contributes to 20-30% of the total cost of biomass production. A new process of pelletized cell cultivation is described in this study to co-culture a filamentous fungal species with microalgae so that microalgae cells can be co-pelletized into fungal pellets for easier harvest. This new process can be applied to microalgae cultures in both autotrophic and heterotrophic conditions to allow microalgae cells attach to each other. The cell pellets, due to their large size, can be harvested through sieve, much easier than individual cells. This method has the potential to significantly decrease the processing cost for generating microagal biofuel or other products.