Bacillus thuringiensis Production Through Solid-State Fermentation Using Organic Fraction of Municipal Solid Waste (OFMSW) Enzymatic Hydrolysate

Abstract

This paper aims to explore an alternative pathway to valorize the organic fraction of municipal solid waste. It is based on the use of enzymatic hydrolysis to obtain a sugar-rich fraction with the potential for liquid fermentative processes and a partially hydrolyzed solid that is evaluated as a substrate for solid-state fermentation. Different strategies to modify the pH of the solid substrate to reach a neutral pH, suitable for the growth of biopesticide producer Bacillus thuringiensis, have been explored. The use of alkaline cosubstrates was evaluated on two different scales and temperature was assessed as a preliminary indicator of the scale-up viability of the process strategy. By ensuring a proper pH throughout the process, the growth and sporulation of Bacillus thuringiensis were achieved. The best cosubstrates and mixing ratios were 50% of digested sewage sludge and 25% of digested organic fraction of municipal solid waste, which led to a spore concentration of 1.1 × 109 spores g−1 of dry matter and 6.4 × 108 spores g−1 of dry matter, respectively. Overall, a reproducible and flexible solid-state fermentation process has been achieved for hydrolyzed organic municipal waste based on the use of alkaline urban wastes as cosubstrates. This valorization pathway fits with the concept of urban biorefineries. Graphical Abstract

Exploring biorefinery alternatives for biowaste valorization: a techno-economic assessment of enzymatic hydrolysis coupled with anaerobic digestion or solid-state fermentation for high-value bioproducts

“…In scenarios I and III, the solid digestate was used as a cosubstrate in the SSF process, contributing to the control of pH and maintaining its value close to the neutral range, adequate for Bacillus thuringiensis growth [ 17 , 32 ]. On the other hand, in scenarios II and IV, where no SSF for biopesticide production is performed, the produced digestate (25,551 t year −1 and 22,890 t year −1 , respectively) is directly sold as fertilizer, which is four times cheaper than the biopesticide ( Table 2 ).…”

“…The enzymatic hydrolysis to extract sugars from the OFMSW is performed in a closed tank at a 10% solid-to-liquid ratio (w/v), which is adjusted by adding distilled water and considering that the moisture content in the autoclaved OFMSW is 75% [ 31 , 32 ]. The commercial enzymatic cocktail selected is Viscozyme L® and it is dosed at 0.08 mL g −1 of dry OFMSW, as optimized in previous works [ 31 ].…”

Use of agro-industrial bio-waste for the growth and production of a previously isolated Bacillus thuringiensis strain

“…The alternative production of Bt could be enhanced by the use of agro-industrial residues as a nutrient source. These residues, which are rich in carbohydrates, amino acids and other organic compounds, can be used to promote bacterial growth and stimulate the expression of genes involved in toxin production [5,34]. The use of agro-industrial residues as substrates for microbial growth is a sustainable and cost-effective strategy to maximize biomass, spore and toxin production.…”

A Perspective of Solid-State Fermentation As Emergent Technology for Organic Waste Management in the Framework of Circular Bioeconomy

“…76 In this case, SSF can be also of help, as the solid fraction of the digestate can be used as substrate for the growth of strains that are able to produce biopesticides, biostimulants, and enzymes, among others. 16,56,77,78 Figure 6 shows how a slight modification of the sludge line of a typical wastewater treatment plant can convert the plant into a most profitable facility following the biorefinery principles.…”

“…This material is sometimes perceived as a problem because of their content in phytotoxic pollutants, , which hampers its typical application as soil organic amendment, where it presents great benefits . In this case, SSF can be also of help, as the solid fraction of the digestate can be used as substrate for the growth of strains that are able to produce biopesticides, biostimulants, and enzymes, among others. ,,, Figure shows how a slight modification of the sludge line of a typical wastewater treatment plant can convert the plant into a most profitable facility following the biorefinery principles.…”