1,3-Propanediol (PD) is a C3 diol with wide applications in biopolymers and personal care products. Microbial production of PD from crude glycerol (CG) has gained attention as a sustainable alternative to petrochemical routes, where yield and process cost are critical factors. In this study, the PD production potential of an adaptively evolved Levilactobacillus brevis PD20.100 was evaluated using fish protein hydrolysate (FPH), an industrial by-product of the fisheries sector, as a nitrogen source. Batch, fed-batch, and immobilized fermentation modes were investigated and compared with a conventional nutrient-rich modified MRS (mMRS) medium. Fermentation performance was assessed based on cell growth, substrate utilization, and formation of PD, lactic acid (LA), and acetic acid (AA). Batch fermentation with suspended cells in mMRS resulted in the highest PD titer of 39.75 g/L, while FPH-supported fermentation achieved a comparable PD concentration of 31.16 g/L. Although fed-batch and immobilized systems offered operational stability and reusability, they exhibited lower productivity. Overall, the results demonstrate that FPH can serve as a cost-effective and sustainable nitrogen source for microbial PD production, supporting the valorization of fish-processing by-products.

Wastes are unceasingly generated in the world, and most of them can be recycled, reused, or recovered to promote a circular economy. Among waste treatment approaches, the anaerobic digestion (AD) process has been considered as an ideal process due to its ecological benefits (reduction of unpleasant odor, pathogens accumulation, or greenhouse gas emission), social and economic advantages, and energy saving. In addition to biogas production, this process can be used to produce various bioproducts, such as biopolymers, bioplastics, biomass, biofertilizers, and biolipids. Interestingly, the AD process residue or digestate is a nutrient-rich by-product that can be used as a biofertilizer for agronomical purposes to balance N-P cycle in the soils. Despite of numerous benefits of AD, less than 1 % of waste is treated by this process. This process has the potential to be integrated with other waste treatment approaches to increase waste treatment efficiency. Therefore, it is essential to focus on each advantage and clarify ambiguity in order to satisfy more countries for employing AD for waste treatment. In this review, various benefits of AD are evaluated; and its potential impacts on particularly agriculture are examined in detail. Additionally, potential biomass and wastes that can be used for anaerobic digestion worldwide are deliberated. Besides, a critical perspective has been developed on the economic, environmental, and social evaluation of the benefits of AD and, as a final point, focused on an integrated circular cascading approach.

In this chapter, we discuss various bacterial derived secondary metabolites pigments which has antimicrobial properties. Though these metabolites were identified more than several decades ago, attention into their bioactivities has emerged in the last few decades. Their increasing acceptance is an outcome of their cost-effectiveness, biodegradability, noncarcinogenic property, and eco-friendly characteristics. This chapter has made an attempt to take an in-depth observation into the current bacterial derived pigments and their bioactivity against various microorganisms.