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Abstract: With the aim of improving knowledge about the stability and reliability of anaerobic wastewater treatment systems, several researchers have studied the effects of operational or environmental variations on the performance of such reactors. In general, anaerobic reactors are affected by changes in external factors, but the severity of the effect is dependent upon the type, magnitude, duration and frequency of the imposed changes. The typical responses include a decrease in performance, accumulation of volatile fatty acids, drop in pH and alkalinity, change in biogas production and composition, and sludge washout. This review summarises the causes, types and effects of operational and environmental variation on anaerobic wastewater treatment systems. However, there still remain some unclear technical and scientific aspects that are necessary for the improvement of the stability and reliability of anaerobic processes. [Copyright &y& Elsevier]

The experimental central composite design 2 2 was applied to optimize the acetosolv process for lignin extraction from sugarcane bagasse, with an aim to replace the petroleum-derived phenols conventionally used for resin production. The highest acetosolv extraction yield (55% ± 4.5%) was achieved with an acetic acid concentration of 95% (w/w), containing 0.1% (v/v) HCl, at 187 °C for 40 min. Other optimal conditions for extraction, such as 187 °C, 15 min (OC 187;15 ) and 205 °C, 15 min (OC 205;15 ), were calculated from statistical models. The optimized acetosolv lignins were characterized by thermal analysis (TGA and DSC), size exclusion chromatography, and spectroscopic methods (FT-IR and HSQC-NMR). Compared to Kraft lignin, they exhibited higher thermal stability, low molar mass, p- hydroxyphenyl units as their major constituent, higher relative phenolic and total hydroxyl contents, and lower relative methoxyl group content. Accordingly, optimized acetosolv lignins seem to have structural features suitable for phenol-formaldehyde resin synthesis. [ABSTRACT FROM AUTHOR]

• Dairy wastewater (DW) is a potential substrate to produce carboxylic acids (CA). • Kinetic modeling is a useful tool to elucidate acidogenic fermentation kinetics. • High yield of CA (0.66 mgCA mgCOD A −1) was obtained from DW acidogenic fermentation. • Models that describe an exponential phase are suitable to simulate CA production. • Low concentrations of a medium-chain CA were achieved without e-donors addition. Carboxylic acids (CA) are high added-value compounds that can be produced via anaerobic fermentation by using agroindustrial residues as substrates. However, different compounds in wastewater impose uncontrolled metabolic pathways, in which the acidogenic fermentation kinetics need to be elucidated. This work aimed to assess the potential production of CA from dairy wastewater (DW) and to perform the kinetic modeling of the process. The experiments were conducted in quadruplicate batch reactors (250 mL of working volume) with inoculum from a brewery UASB at 0.61 ± 0.04 gCOD gVSS−1. To inhibit methanogenesis, 0.05 % (v/v) chloroform was added to the reactors. The tests showed that DW is a readily fermentable substrate to acidogenic microorganisms because it presents high rates of short-chain CA formation in the first two days of the experiment. The low concentrations of medium-chain CA found indicate that fats and proteins did not function as the main carbon source for DW fermentation. The yield obtained was 0.66 mgCA mgCOD A −1, which corresponds to 0.83 mgCOD CA mgCOD A −1. Kinetic modeling studies have shown that mathematical models that can describe an exponential phase, such as First-order and Fitzhugh models, are suitable for simulating the production of carboxylic acids. Finally, DW seems to be a promising substrate to be investigated in the carboxylic platform. [ABSTRACT FROM AUTHOR]

• Steam explosion enhances acetosolv for obtaining cellulosic pulp from oil palm fiber. • Steam explosion pretreatment enhances cellulosic pulp yield and quality. • Steam explosion at mild condition did not change lignin structure. The pretreatment of lignocellulosic material via steam explosion process can be used to decrease the energy and chemical consumption during pulping to obtain environmentally friendly building blocks and improve the quality of materials by reducing the hemicellulose content. The objective of this work was to optimize the extraction of building blocks (lignin and cellulose) from oil palm mesocarp fibers using steam explosion pretreatment, followed by acetosolv and bleaching. The experimental central composite design 22 was used to optimize the steam explosion procedure prior to the acetosolv and bleaching processes. Although steam explosion increased the cellulose pulp yield by 47 % compared to without pretreatment (25 % vs 17 %), at 210 °C for 3 min, these conditions were not favorable for lignin extraction, which decreased from 56 % without pretreatment to 46 %. Pretreated cellulosic pulp had a higher purity, thermal stability, and crystallinity. Lignin with or without pretreatment showed similar characteristics. Our findings demonstrate that steam explosion is an efficient pretreatment for improving the characteristics of cellulosic pulp without affecting the quality of lignin, highlighting the potential use of these building blocks in the production of cellulose nanoparticles such as crystals and fibrils, as well as in the substitution of non-renewable phenols in resins. [ABSTRACT FROM AUTHOR]