Fed-batch anaerobic digestion of raw and pretreated hazelnut skin over long-term operation

Fed-batch treatment attenuates diffusional limitation while preparing high solid microfibrillated cellulose from Gelidium amansii

This study investigates the effects of fed-batch treatment on the fibrillation degree and properties of Gelidium amansii-derived microfibrillated cellulose (MFC). Fed-batch milling was conducted with the initial solid loading of 1 % w/v followed by three stages of feeding to obtain a final solid concentration of 5 % w/v. This process provides a high-solid MFC of around 10 %, while batch milling only provides the maximum solid loading of 4 %. It also reduces approximately 83 % power consumption of batch milling at the same solid loading (4 %). The obtained MFC 5 % has lower fibrils length (14.9 µm) and width (16.46 nm), but higher consistency index (>250 Pa.s) than MFC 1 % (22 µm, 21 nm, 5.88 Pa.s). The crystallinity and maximum decomposition temperatures of both MFCs are comparable, varying at 49-53 % and 318 °C-320 °C. In summary, fed-batch treatment is promising for the techno-economic development of MFC production by lowering energy and maintaining product quality.

Improved methane production from ultrasonically-pretreated secondary sedimentation tank sludge and new model proposal: Time series (ARIMA)

Secondary sedimentation tank sludge (SSTS) is a severe type of waste that needs to be treated to prevent human health risks. Anaerobic digestion (AD) alone can be ineffective for treating SSTS due to low substrate biodegradability. This study proposes the use of ultrasonic pretreatment (UP) on SSTS for 0 - 60 min. UP effect on SSTS was analyzed through the actual specific energy input, nominal energy input, and soluble chemical oxygen demand. The highest cumulative methane yield (CMY) of 241.56 mL/g VS obtained during the AD of the pretreated substrate (i.e., 30 min) was 58.4% higher than that of untreated SSTS. The resulting CMY curves were subsequently simulated via the modified Logistic and Gompertz, Artificial Neural Network, Auto-Regressive Integrated Moving-Average (ARIMA) models. As a novel proposal for predicting CMYs, the ARIMA model is recommended due to its simplicity and better performance than sigmoidal models (R2 = 0.9975 - 0.9988).

Phenanthrene removal from a spent sediment washing solution in a continuous-flow stirred-tank reactor

The issue of polycyclic aromatic hydrocarbons (PAHs) is widespread in marine sediments involving ecological systems and human health. Sediment washing (SW) has proven to be the most effective remediation approach for sediments polluted by PAHs, such as phenanthrene (PHE). However, SW still raises waste handling concerns due to a considerable amount of effluents generated downstream. In this context, the biological treatment of a PHE- and ethanol-containing spent SW solution can represent a highly efficient and environmentally-friendly strategy, but its knowledge is still scarce in scientific literature and no studies have so far been conducted in continuous mode. Therefore, a synthetic PHE-polluted SW solution was biologically treated in a 1 L aerated continuous-flow stirred-tank reactor for 129 days by evaluating the effect of different pH values, aeration flowrates and hydraulic retention times as operating parameters over five successive phases. A PHE removal efficiency of up to 75-94% was achieved by an acclimated PHE-degrading consortium mainly composed of Proteobacteria, Bacteroidota and Firmicutes phyla through biodegradation following the adsorption mechanism. PHE biodegradation, mainly occurring via the benzoate route due to the presence of PAH-related-degrading functional genes and a phthalate accumulation up to 46 mg/L, was also accompanied by a reduction of dissolved organic carbon and ammonia nitrogen above 99% in the treated SW solution.

Microbial protein production from sulfide-rich biogas through an enrichment of methane- and sulfur-oxidizing bacteria

This study evaluated the possibility of combining methane oxidizing bacteria (MOB) with sulfur oxidizing bacteria (SOB) to enable the utilization of sulfide-rich biogas for microbial protein production. For this purpose, a MOB-SOB mixed-culture enriched by feeding both methane and sulfide was benchmarked against an enrichment of solely MOB. Different CH₄:O₂ ratios, starting pH values, sulfide levels and nitrogen sources were tested and evaluated for the two enrichments. The MOB-SOB culture gave promising results in terms of both biomass yield (up to 0.07±0.01 g VSS/g CH₄-COD) and protein content (up to 73±5% of VSS) at 1500 ppm of equivalent H₂S. The latter enrichment was able to grow also under acidic pH (5.8-7.0), but as inhibited outside the optimal CH₄:O₂ ratio of 2:3. The obtained results show the capability of MOB-SOB mixed-cultures to directly upcycle sulfide-rich biogas into microbial protein potentially suited for feed, food or biobased product applications.

Organosolv pretreatment for biorefineries: Current status, perspectives, and challenges

Biorefineries integrate processes for the sustainable conversion of biomass into chemicals, materials, and bioenergy so that resources are optimized and effluents are minimized. Despite the vast potential of lignocellulosic biorefineries, their success depends heavily on effective, economically viable, and sustainable biomass fractionation. Although efficient, organosolv pretreatment still faces challenges that must be overcome for its widespread utilization, mainly related to solvent type and recycling, robustness regarding biomass type and integration of hemicellulose recovery and use. This review shows the recent advances and state-of-the-art of organosolv pretreatment, discussing the advances, such as the use of biobased solvents, whilst also shedding light on the perspectives of using the streams - cellulose, hemicellulose, and lignin - to produce biofuels and products of high added value. In addition, it presents an overview of the existing industrial implementations of organosolv processes and, lastly, shows the main scientific and industrial challenges and opportunities for this process.

Use of N-Methylmorpholine N-oxide (NMMO) pretreatment to enhance the bioconversion of lignocellulosic residues to methane

Lignocellulosic residues (LRs) are one of the most abundant wastes produced worldwide. Nevertheless, unlocking the full energy potential from LRs for biofuel production is limited by their complex structure. This study investigated the effect of N-methylmorpholine N-oxide (NMMO) pretreatment on almond shell (AS), spent coffee grounds (SCG), and hazelnut skin (HS) to improve their bioconversion to methane. The pretreatment was performed using a 73% NMMO solution heated at 120 °C for 1, 3, and 5 h. The baseline methane productions achieved from raw AS, SCG, and HS were 54.7 (± 5.3), 337.4 (± 16.5), and 265.4 (± 10.4) mL CH4/g VS, respectively. The NMMO pretreatment enhanced the methane potential of AS up to 58%, although no changes in chemical composition and external surface were observed after pretreatment. Opposite to this, pretreated SCG showed increased porosity (up to 63%) and a higher sugar percentage (up to 27%) after pretreatment despite failing to increase methane production. All pretreatment conditions were effective on HS, achieving the highest methane production of 400.4 (± 9.5) mL CH4/g VS after 5 h pretreatment. The enhanced methane production was due to the increased sugar percentage (up to 112%), lignin removal (up to 29%), and loss of inhibitory compounds during the pretreatment. An energy assessment revealed that the NMMO pretreatment is an attractive technology to be implemented on an industrial scale for energy recovery from HS residues.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13399-022-03173-x.

Ultrasounds application for nut and coffee wastes valorisation via biomolecules solubilisation and methane production

Lignocellulosic materials (LMs) are abundant feedstocks with excellent potential for biofuels and biocommodities production. In particular, nut and coffee wastes are rich in biomolecules, e.g. sugars and polyphenols, the valorisation of which still has to be fully disclosed. This study investigated the effectiveness of ultrasounds coupled with hydrothermal (i.e. ambient temperature vs 80 °C) and methanol (MeOH)-based pretreatments for polyphenols and sugar solubilisation from hazelnut skin (HS), almond shell (AS), and spent coffee grounds (SCG). The liquid fraction obtained from the pretreated HS was the most promising in terms of biomolecules solubilisation. The highest polyphenols, i.e. 123.9 (±2.3) mg/g TS, and sugar, i.e. 146.0 (±3.4) mg/g TS, solubilisation was obtained using the MeOH-based medium. However, the MeOH-based media were not suitable for direct anaerobic digestion (AD) due to the MeOH inhibition during AD. The water-based liquors obtained from pretreated AS and SCG exhibited a higher methane potential, i.e. 434.2 (±25.1) and 685.5 (±39.5) mL CH₄/g glucose_in, respectively, than the HS liquors despite having a lower sugar concentration. The solid residues recovered after ultrasounds pretreatment were used as substrates for AD as well. Regardless the pretreatment condition, the methane potential of the ultrasounds pretreated HS, AS, and SCG was not improved, achieving maximally 255.4 (±7.4), 42.8 (±3.3), and 366.2 (±4.2) mL CH₄/g VS, respectively. Hence, the solid and liquid fractions obtained from HS, AS, and SCG showed great potential either as substrates for AD or, in perspective, for biomolecules recovery in a biorefinery context.