Advances in process design, techno-economic assessment and environmental aspects for hydrothermal pretreatment in the fractionation of biomass under biorefinery concept.

The development and sustainability of second-generation biorefineries are essential for the production of high added value compounds and biofuels and their application at the industrial level. Pretreatment is one of the most critical stages in biomass processing. In this specific case, hydrothermal pretreatments (liquid hot water [LHW] and steam explosion [SE]) are considered the most promising process for the fractionation, hydrolysis and structural modifications of biomass. This review focuses on architecture of the plant cell wall and composition, fundamentals of hydrothermal pretreatment, process design integration, the techno-economic parameters of the solubilization of lignocellulosic biomass (LCB) focused on the operational costs for large-scale process implementation and the global manufacturing cost. In addition, profitability indicators are evaluated between the value-added products generated during hydrothermal pretreatment, advocating a biorefinery implementation in a circular economy framework. In addition, this review includes an analysis of environmental aspects of sustainability involved in hydrothermal pretreatments.

Evaluation of sweet potato for fuel bioethanol production: hydrolysis and fermentation.

The enzymatic starch hydrolysis and bioethanol production from a variety of sweet potato developed for bioenergy purposes (K 9807.1) on the basis of its high starch yields, was studied. Drying at 55°C and 95°C of sweet potato neither affected the sugar content nor the starch enzymatic hydrolysis efficiency. Simultaneous saccharification and ethanol fermentations for dry matter ratio of sweet potato to water from 1:8 to 1:2 (w/v) were studied. Fresh sweet potato and dried at 55°C (flour) were assayed. At ratios of 1:8, similar results for fresh sweet potato and flour in terms of ethanol concentration (38-45 g/L), fermentation time (16 h) and sugar conversion (~ 100%) were found. At higher dry matter content, faster full conversion were observed using flour. A higher ratio than that for fresh sweet potato (1:2.2) did not improve the final ethanol concentration (100 g/L) and yields. High ethanol yields were found for VHG (very high gravity) conditions. The sweet potato used is an attractive raw matter for fuel ethanol, since up to 4800 L ethanol per hectare can be obtained.

Energy consumption evaluation of fuel bioethanol production from sweet potato.

The energy consumption for different operative conditions and configurations of the bioethanol production industrial process from an experimental variety of sweet potato (Ipomea batatas) K 9807.1 was evaluated. A process simulation model was developed using SuperPro Designer® software. The model was based on experimental data gathered from our laboratory experiments and technology and equipment suppliers. The effects of the dry matter ratio of sweet potato to water, the fermentation efficiency, and sweet potato sugar content, on the energy consumption (steam and electricity) were respectively evaluated. All factors were significant. The best ratio of dry matter to total water to work with fresh sweet potato was 0.2 kg dry sweet potato/kg water, as for greater ratios was not found a significant reduction in energy consumption. Also, the drying of the sweet potato previous its processing was studied. It presented an energy consumption greater than the energetic content of the bioethanol produced.

Isolation and selection of native microorganisms for the aerobic treatment of simulated dairy wastewaters.

Milk fat/protein degrading microorganisms were isolated from different locations of a dairy wastewater treatment system with the goal of developing an inoculum for bioaugmentation strategies. Eight isolates, identified by 16S rRNA gene sequence analysis as belonging to the genera Bacillus, Pseudomonas, and Acinetobacter, were tested for their ability to remove COD and protein from a milk-based medium (3000 mg/L COD) and compared to a commercial bioaugmentation inoculum. The Acinetobacter isolate exhibited a pellet-type growth in liquid culture, a property that could potentially aid in the separation of microbes and liquid phase following treatment. Based on the individual degradation capacity and growth behavior of the isolates, three microorganisms were further selected and tested together. This consortium exhibited a COD removal similar to the commercial inoculum (57% and 63%, respectively), but higher protein (consortium: 93%; commercial inoculum: 54%), and fat removals (consortium: 75%; commercial inoculum: 38%).

Performance of a commercial inoculum for the aerobic biodegradation of a high fat content dairy wastewater.

The effectiveness of a commercial inoculum for degrading a dairy wastewater with high fat content was evaluated, and compared with an activated sludge inoculum from a dairy wastewater treatment pond. Both inocula reached similar chemical oxygen demand removal in batch experiments. The population dynamics was also studied by determining heterotrophic counts. Predominant microorganisms were differentiated by colony morphology and genomic fingerprinting (BOX-PCR) analysis. The higher population diversity and the wider range of CO2 production rate observed in batch reactors inoculated with activated-sludge, indicated that microorganisms from this inoculum were well adapted and may have had synergic activity for the degradation of the dairy effluent. When the bioreactor was operated with the commercial inoculum in continuous mode, according to its microbial growth kinetics, other microorganisms became predominant. These results showed that inoculated microorganisms did not persist in the open system and periodic addition of microorganisms may be needed to achieve a high performance treatment.

Kinetic properties of a commercial and a native inoculum for aerobic milk fat degradation.

The aerobic fat biodegradation potential and growth characteristics of a commercial and a native inoculum (activated sludge from a dairy wastewater treatment pond), were evaluated. Batch tests were conducted with a medium based on butter oil, as the sole source of carbon, and mineral salts. Residual fat, biomass and CO(2) production were measured. Overall fat removal values were above 78% for both inocula. The growth kinetics of the commercial and native inocula followed Haldane and Monod models respectively. Both inocula showed a similar behaviour when butter oil concentration was under 360 mg/l; at higher values, the difference between the growth rates increased as a consequence of the inhibition exhibited by the commercial inoculum. The selection of an inoculum for bioaugmentation of bioreactors in the wastewater treatment requires a comprehensive knowledge of their degradation ability and tolerance to fluctuating compounds and of the operational conditions that will be utilized.