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It is imperative to search for appropriate processes to convert wastes into energy, chemicals, and materials to establish a circular bio-economy toward sustainable development. Concerning waste biomass valorization, hydrothermal carbonization (HTC) is a promising route given its advantages over other thermochemical processes. From that perspective, this article reviewed the HTC of potential biomass wastes, the characterization and environmental utilization of hydrochar, and the biorefinery potential of this process. Crop and forestry residues and sewage sludge are two categories of biomass wastes (lignocellulosic and non-lignocellulosic, respectively) readily available for HTC or even co-hydrothermal carbonization (Co-HTC). The temperature, reaction time, and solid-to-liquid ratio utilized in HTC/Co-HTC of those biomass wastes were reported to range from 140 to 370 °C, 0.05 to 48 h, and 1/47 to 1/1, respectively, providing hydrochar yields of up to 94 % according to the process conditions. Hydrochar characterization by different techniques to determine its physicochemical properties is crucial to defining the best applications for this material. In the environmental field, hydrochar might be suitable for removing pollutants from aqueous systems, ameliorating soils, adsorbing atmospheric pollutants, working as an energy carrier, and performing carbon sequestration. But this material could also be employed in other areas (e.g., catalysis). Regarding the effluent from HTC/Co-HTC, this byproduct has the potential for serving as feedstock in other processes, such as anaerobic digestion and microalgae cultivation. These opportunities have aroused the industry interest in HTC since 2010, and the number of industrial-scale HTC plants and patent document applications has increased. The hydrochar patents are concentrated in China (77.6 %), the United States (10.6 %), the Republic of Korea (3.5 %), and Germany (3.5 %). Therefore, considering the possibilities of converting their product (hydrochar) and byproduct (effluent) into energy, chemicals, and materials, HTC or Co-HTC could work as the first step of a biorefinery. And this approach would completely agree with circular bioeconomy principles.

Second-generation bioethanol production process was developed using pretreated empty fruit bunches (EFB). Consecutive acid/alkali EFB pretreatment was performed, first with HCl and then with NaOH with final washing steps for phenolic compounds elimination. Scanning electron microscopy images showed that EFB chemical treatments indeed attacked the cellulose fibers and removed the silica from surface pores. The optimization of enzymatic hydrolysis of EFB's cellulosic fraction was performed with 0.5%-4% v/v of Cellic® CTec2/Novozymes, different EFB concentrations (5%-15%, w/v), and hydrolysis time (6-72 H). Optimization essays were carried out in Erlenmeyer flasks and also in a 1 L stirred tank reactor. After enzymatic hydrolysis, a hydrolysate with 66 g/L of glucose was achieved with 2.2% (v/v) Cellic® CTec2, 15% (m/v) acid/alkaline pretreated EFB after 39 H of hydrolysis. A gain of 11.2% was then obtained in the 1 L stirred tank promoted by the agitation (72.2 g/L glucose). The hydrolysate was employed in bioethanol production by a new isolate Candida pelliculosa CCT 7734 in a separate hydrolysis and fermentation process reaching 16.6 and 23.0 g/L of bioethanol through batch and fed-batch operation, respectively. An integrated biorefinery process was developed for EFB processing chain.

The behavior of mixed samples (activated sludge and wastewater) was investigated after the addition of magnetite nanoparticles (NP-magnetite) in jar tests, with objective to increase the aggregation of sludge and improve its settleability, aiming for future application in granular sequencing batch reactors. The NP-magnetite was synthesized by the method of ion co-precipitation of Fe2+ and Fe3+ and characterized. The process of sludge sedimentation was evaluated for two different experimental strategies, with NP-magnetite concentrations between 25 and 150 mg L−1. The concentration of 75 mg L−1 was the most favorable to process, as evidenced by sludge volumetric index and density. The results presented indicate that the addition of nanoparticles has the potential to improve aerobic granular systems, increasing the settleability of seed sludge.

Biochar and hydrochar are carbonaceous materials with valuable applications. They can be synthesized from a wide range of organic wastes, including digestate. Digestate is the byproduct of anaerobic digestion (AD), which is performed for bioenergy (biogas) production from organic residues. Through a thermochemical process, such as pyrolysis, gasification, and hydrothermal carbonization - HTC, digestate can be converted into biochar or hydrochar. The addition of either biochar or hydrochar in AD has been reported to improve biochemical reactions and microbial growth, increasing the buffer capacity, and facilitating direct interspecies electrons transfer (DIET), resulting in higher methane (CH

Enzymes are proteins that have essential functions in all vital processes such as metabolism, gene expression, cell division, reactions of the immune system, and others. They play important roles in the biotechnology industry or medical diagnostics due to their very efficient way of catalyzing chemical reactions. The diversity of actions and applications of enzymes are due to different substrate and reaction specificities. Enzymes are actually classified into seven classes, namely oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, and translocases. The classification is related to the catalyzed reactions. This chapter presents the classification and nomenclature of these powerful biocatalyzers. Their data compilation, in textual and numeric forms, and three-dimensional macromolecular structural data, are very well organized in different available databases such as BRaunschweig ENzyme DAtabase, EXPLORE-ENZ, Carbohydrate-Active Enzymes, Protein Data Bank, and many others.

Dextran contamination is a serious problem of the sugar industry, which can be solved with the application of dextranases that may avoid significant product losses. However, the high costs of enzyme preparations make its use economically impracticable. Dextranase production from Penicillium aculeatum NRRL 2129 was carried out by solid-state fermentation (SSF) using brewer's spent grain (BSG) as an alternative substrate/support. Optimal conditions (dextran 15 g/L, ammonium sulfate 0.45 g/L, 70% initial humidity, pH 5 and 8 g of BSG) led to a maximum dextranase activity of 75.5 U/g dry matter. Kinetics parameters of produced dextranase were determined as Km 4.20 μM and Vmax 11.89 mol/min. The produced enzyme was efficiently applied on sugarcane juice, leading to a successful 72% decrease in dextran content after 10 min, showing a comparable performance with commercial dextranases, which brings promising perspectives for this process.

This work presented an integrated approach to recover nutrients and biomaterials from wastewater, resulting in a phosphorus-enriched biomaterial with the potential for additional applications. The present investigation explored phosphorus removal from liquid samples using ALE recovered from aerobic granular sludge. The pH of the phosphorus solution, dosage of ALE beads, temperature and initial phosphorous concentration were factors tested through a factorial experimental design, with the results compared with commercial seaweed alginate. The ALE recovery from discarded aerobic sludge granules was 21.29 ± 1.57%. ALE beads demonstrated the potential to remove phosphorus (49.54 ± 2.23%) from liquid samples better than commercial seaweed alginate (36.78 ± 2.10%). The results from the factorial experiment indicated pH and dosage of ALE beads as the main parameters for phosphorus removal. Regeneration of ALE beads and the phosphorus recovery experiments showed the potential of using this biomaterial as a biodegradable phosphorus slow-release source.

The aim of this study was to investigate the applicability of alginate-like extracellular polymers extracted from aerobic granular sludge, as a novel and innovative biosorbent for the removal of the dye methylene blue from aqueous solutions. The adsorption process using alginate-like exopolysaccharide (ALE) was investigated examining the influence of pH, adsorbent dosage, temperature and initial dye concentration. Moreover, kinetic models and isotherms were applied to describe the adsorption process. Maximum dye removals of 69% were achieved under the temperature of 35 °C, which was obtained with a contact time of 60 min. The optimum pH and biosorbent dosage were 8.0 and 117 g/L, respectively. The best-fitted model for ALE adsorption was the Langmuir model, while the pseudo-first-order model describes the kinetic behavior of the adsorption process best. ALE displayed a very similar adsorption behavior compared to alginate beads, indicating the potential of this new and sustainable biosorbent, which can be directly produced from wastewater.

The aim of this work was the use of Pleurotus ostreatus and Pleurotus sajor-caju for the previous lignocellulolytic decomposition of banana tree leaf straw and the further use of the degraded straw as substrate for the culture of Agaricus blazei. For optimising the production of A. blazei in terms of yield (Y%) and biological efficiency (BE%), adjustments to the composition of the substrate were evaluated in a 2(5) experimental design. The following components were tested in relation to % of substrate dry mass: urea (1 and 10%), rice bran (10 or 20%) or ammonium sulphate (0 or 10%), inoculum (10 or 20%) and the casing material (subsoil or burned rice husks). The best results (79.71 Y% and 6.73 BE%) were found when the substrate containing 10% of rice bran, without ammonium sulphate, inoculated with 20% and covered with subsoil was used.O cultivo de fungos comestíveis e medicinais utilizando resíduos da agroindústria vem se apresentando como uma alternativa econômica para o pequeno produtor rural, favorecendo a agricultura familiar do nordeste catarinense. Este trabalho avaliou o fungo Pleurotus para a decomposição lignocelulolítica de palha de folhas de bananeira e a utilização da palha residual como substrato para o cultivo de Agaricus blazei. Ajustes na composição do substrato residual de Pleurotus, tais como o tipo e a concentração da fonte de nitrogênio, a porcentagem de inóculo e a camada de cobertura, foram avaliadas. O substrato residual que mais favoreceu a produção de A. blazei em Eficiência Biológica (6,73%), Rendimento (79,71%) e menor tempo para emissão do primeiro primórdio (27 dias) foi o substrato residual de P. ostreatus inoculado com 20% de inóculo (ms), 10% de farelo de arroz (ms), sem sulfato de amônio e utilizando terra de subsolo como camada de cobertura.