• Energy Research

The influence of ethanol on the degradation kinetics of linear alkyl benzene sulfonate (LAS) and organic matter was investigated using batch experiments with different initial LAS concentrations (8.3 mg L-1 to 66.9 mg L-1) and biomass immobilized on sand. Data were fitted with a substrate inhibition model. Concentrations of 2.4 mg LAS L-1 and 18.9 mg LAS L-1 (without and with ethanol) provided the maximum LAS utilization rate by the biomass (Sbm). For LAS degradation, ethanol addition favored a lower decrease in the specific substrate utilization rate (robs), even at the LAS concentration usually reported as inhibitory (> 14.4 mg L-1). For organic matter degradation, robs was higher with ethanol. Higher biomass differentiation was observed at higher LAS concentrations. With ethanol, microbial selection occurred at LAS concentrations near Sbm. At higher LAS concentrations, the dominance and diversity values did not change significantly with ethanol, whereas without ethanol, their behaviors were irregular.

Abstract Technical, economic and environmental aspects of implementing two-phase anaerobic digestion (AD), i.e., acidogenic + methanogenic systems, in sugarcane biorefineries for the treatment of vinasse were assessed based on different strategies to using the hydrogen-rich biogas (biogas-H2) generated via acidogenesis. Phase separation greatly enhanced the bioenergy recovered from vinasse AD compared with single-phase systems (methanogenic phase exclusively). The best results for generating electric energy were observed in combined cycle-based power plants that utilized biohythane (10.8 MW + 5.5 MW for the harvest and inter-harvest, respectively), which is the gaseous biofuel from blending biogas-H2 with the methane-rich stream from the methanogenic phase (biogas-CH4). Moreover, the results of this study indicated that scaling up two-phase AD systems is economically feasible for the treatment of sugarcane vinasse (net present value = USD 208.58–219.86 million) because a better or equivalent economic performance was attained compared with single-phase processes. Optimizing the alkalinization of methanogenic reactors strongly affected both the economic and environmental performance of the process, with better results observed with the use of low sodium hydroxide dosages (4 g NaOH kg−1COD). In summary, our results highlighted that two-phase biodigestion may enhance energy production from vinasse by 20–30% without impairing the profitability of the biorefinery and could lead to slight improvements in the environmental performance of the ethanol production chain via the use of an optimized alkalinization strategy.

This work focuses on the influence of the source of organic matter on the process of biomass adhesion on polyurethane foam matrices in fixed-bed anaerobic immobilized-sludge reactors. Five experiments were performed in differential 'gradientless' reactors fed with meat extract (protein), glucose, starch, lipids and complex substrate. The polyurethane foam colonization process was monitored temporally in each experiment to identify the amount of biomass buildup, extracellular polymer production and the morphological characteristics of the cells adhering to the support. Different immobilization patterns were observed for the different substrates used. The morphological variety was found to be dependent on the substrate constituents. Polymer excretion was apparently crucial in the colonization process of the polyurethane matrices and was likely related to cell fixation on the support. The production of extracellular polymeric substances speeded up the initial fixation of microorganisms on the polyurethane surface.

Hydrogen is a well-known clean energy carrier with a high energetic yield. Its versatility allows it to be produced in diverse ways, including biologically. Specifically, dark fermentation takes advantage of organic wastes, such as agro-industrial residues, to obtain hydrogen. One of these harmful wastes that is poorly discharged into streams is sugarcane bagasse pentose liquor (SBPL). The present study aimed to investigate hydrogen generation from SBPL fermentation in batch reactors by applying different food/microorganism (2–10 F/M) and carbon/nitrogen (10–200 C/N) ratios under mesophilic and thermophilic conditions. Biohydrogen was produced in all pentose liquor experiments along with other soluble microbial products (SMPs): volatile fatty acids (VFAs) (at least 1.38 g L−1 and 1.84 g L−1 by the average of C/N and F/M conditions, respectively) and alcohols (at least 0.67 g L−1 and 0.325 g L−1 by the average of C/N and F/M conditions, respectively). Thermophilic pentose liquor reactors (t-PLRs) showed the highest H2 production (H2 maximum: 1.9 ± 0.06 L in 100 C/N) and hydrogen yield (HY) (1.9 ± 0.54 moles of H2 moles of substrate−1 in 2 F/M) when compared to mesophilic ones (m-PLRs). The main VFA produced was acetate (>0.85 g L−1, considering the average of both nutritional conditions), especially through the butyrate pathway, which was the most common metabolic route of experimental essays. Considering the level of acid dilution used in the pretreatment of bagasse (H2SO4 (1%), 1.1 atm, 120 °C, 60 min), it is unlikely that toxic compounds such as furan derivatives, phenol-like substances (neither was measured), and acetate (<1.0 g L−1) hinder the H2 production in the pentose liquor reactors (PLRs). Sugarcane bagasse pentose liquor fermentation may become a suitable gateway to convert a highly polluting waste into a renewable feedstock through valuable hydrogen production.

The development of appropriate technologies for the treatment of formaldehyde discharged into the environment is important to minimize its impact. Aerobic systems have been employed, although alternative anaerobic treatments have also been widely studied, mainly due to their low energy consumption and sludge production. However, toxic substances can lead to disturbances in anaerobic reactors. Some research has already been developed on formaldehyde anaerobic biological treatment, but no consensus has yet been reached about its behavior nor has the most efficient system been identified. Aiming at finding supporting evidence for this issue, therefore, this study investigated the degradation and toxicity of formaldehyde in a Horizontal-Flow Anaerobic Immobilized Sludge Reactor. Formaldehyde concentrations of 26.2-1158.6 mg HCHO/L were applied in the reactor, resulting in formaldehyde and chemical oxygen demand removal efficiencies of 99.7% and 92%, respectively. Volatile fatty acids with up to five carbons, found during the degradation of formaldehyde, are believed to indicate that the degradation followed routes unlike those suggested in the literature, which reports the formation of intermediates such as methanol and formic acid. The Monod kinetic model adhered to the experimental data well, with apparent kinetic parameters estimated as r(app)max) = 2.79 x 10(-3) mg HCHO/mg SSVh and K (app)(s) = 242.8 mg HCHO/L.

Abstract Vinasse is a residue from bioethanol production that is produced in large quantities in Brazil and Europe and is applied to fields as a source of plant nutrients (fertirrigation). A side effect of this use is greenhouse gas (GHG) emissions during storage and transport in open channels to fields, and from fertirrigated soils. This study assessed GHG emissions in experiments simulating this vinasse management system, and the potential for reducing emissions of methane (CH4) and nitrous oxide (N2O) from vinasse via anaerobic digestion (AD) in biogas plants. During 21 days’ storage of untreated vinasse, 29% of dry matter (DM) and 40% of volatile solids (VS) were lost, which resulted in cumulative CH4 emissions of up to 43.8 kg CO2eq kg−1 C-vinasse. In contrast, there were no CH4 emissions from AD-treated vinasse (digestate) during storage. GHG emission was related to the biochemical characteristics of the untreated and digested vinasse. The accumulation of oxidised nitrogen (N) compounds was up to four-fold higher in soil amended with untreated vinasse than from digestate-amended soil. The N2O emissions from soil amended with untreated vinasse were also higher than from soil amended with digestate, ranging from 0.173 to 0.193 kg CO2eq m−2 in the former and from 0.045 to 0.100 kg CO2eq m−2 in the latter. Extrapolation of the results to a Brazilian case indicated that AD treatment prior to storage/transport and field application could reduce GHG emissions from the vinasse management chain by at least 48%, with further reductions from the use of biogas in power production.

Abstract The continuous search to combine clean energy supply with the efficient exploitation of bioenergy sources is one of the most recurring efforts to meet global energy demands on an environmentally friendly basis. Sugarcane biorefineries play a central role in this context by providing sugar, ethanol and bioelectricity. However, the high energy required in ethanol production limits resource recovery efficiency in conventional sugarcane processing, motivating the investigation of approaches that maximize energetic gains. This study proposes the application of anaerobic digestion (AD) as the core processing step in sugarcane biorefineries, providing performance data for the biomethanation of juice, molasses and vinasses from different sources, namely, first generation (1G; annexed and autonomous) and second generation (2G) ethanol production. A detailed scenarization-based assessment was also carried out, comparing the proposed AD-based schemes with conventional production chains. Relatively similar performances were obtained in the experimental step, irrespective of the compositional differences of the substrates. However, the energetic potential of juice- and molasses-based methane production was at least 2-fold higher than the ones of all types of vinasses (282.81–627.84 vs. 57.10–131.52 MJ TC−1). Scenario comparison indicated the production of biogas and sugar as the most efficient energetic exploitation (94.4%) of sugars from sugarcane. Finally, the energy returned on energy invested ratio estimated for biogas-derived electricity exceeded that of ethanol production by 400%. Thus, AD-based biorefineries have great potential to meet the energy efficiency criteria of sustainable development goals in the coming decades.

Abstract The application of thermophilic anaerobic digestion is a logical choice for the treatment of sugarcane vinasse (industrial wastewater from ethanol production) because this process enables the recovery of energy as hydrogen and methane without requiring energy for heat or interfering in its quality as a bio-fertilizer. Thus, this study evaluated the performance of thermophilic methanogenic up-flow sludge blanket reactors (UASB) operating continuously in single-stage (UASB I) and two-stage (UASB II) systems vinasse during the sugarcane harvesting season (180 days). The maximum methane yields were 250.9 NmL-CH4.g−1CODremoved and 316.0 NmL-CH4.g−1CODremoved for UASB I and II, respectively, corresponding to 71.7% and 90.3% of the maximum theoretical methane yield (350 NmL-CH4.g−1CODremoved). Furthermore, the energy production from the two-stage system was 25.7% higher than the single-stage system, indicating the need for an acidogenic phase to improve both the removal of organic matter and energy extraction from sugarcane vinasse.

The main objective of this work was to investigate the effect of volumetric loading rate (VLR), shock load, and alkalinity supplementation on the efficiency and stability of an Anaerobic Sequencing Batch Biofilm Reactor (AnSBBR) containing polyurethane foam cubes. Mixing in the reactor, which was kept at 30 +/- 1 degrees C, occurred by recirculating the liquid phase. The reactor treated 2.5 l cheese whey in 8-h cycles, at concentrations of 1, 2, and 4 g COD l-1, which corresponded to VLRs of 3, 6, and 12 g COD l-1 day-1, respectively. Application of single-cycle shock loads of 6, 12, and 24 g COD l-1 day-1 did not impair reactor performance. In addition, for VLRs of 3, 6, and 12 g COD l-1 day-1, alkalinity supplementation to the influent, at the end of each assay, could be reduced to 75, 50, and 50%, respectively, in relation to supplementation at the beginning of the assay. During reactor operation a viscous polymer-like material was formed between the polyurethane foam cubes, which increased at higher VLR. Finally, addition of salts to the influent improved reactor efficiency.