Enhanced paper sludge dewatering and in-depth mechanism by oxalic acid/Fe2+/persulfate process

As a typical advanced oxidation process, Fe²⁺-persulfate (PDS) oxidation technology has been widely and efficiently reported for enhancing sludge dewaterability. However, higher dosage of Fe²⁺ must be added, which will restrain the oxidation efficiency of Fe²⁺-PDS process. In this work, the oxalic acid (OA)/Fe²⁺-PDS process was studied to improve paper sludge dewatering. With the OA dosage of 6 μmol (g total solid (TS))^-1, Fe²⁺ dosage of 0.3 mmol (g TS)^-1, and PDS dosage of 0.6 mmol (g TS)^-1, sludge dewaterability was improved more efficiently. The specific resistance to filtration and water content of sludge cake were decreased by 70.7% and 8.0%, respectively. In comparison with Fe²⁺-PDS process, the viscosities of sludge suspension and supernatant were further reduced by 3.73% and 51.77%, respectively, and the contents of extracellular polymeric substances fractions were increased. The improved sludge dewaterability in OA/Fe²⁺-PDS process was mainly contributed by the synergistic effect of oxidative disintegration by free radicals and flocs re-flocculation, the contributions of which were the orders: metal cations > sulfate radical > hydroxyl radical. OA enhanced the efficient disintegration of sludge flocs, released more bound water, generated more Fe³⁺-oxalate complexes, and finally increased the sludge particle size significantly, forming a larger aggregation and obvious cracks. Additionally, the stabilization of several heavy metals was improved due to the chelating capacity of OA. These works will provide a novel approach for sludge dewatering in the PDS oxidation process.

Advantages and Disadvantages of Bioplastics Production from Starch and Lignocellulosic Components

The accumulation of plastic wastes in different environments has become a topic of major concern over the past decades; therefore, technologies and strategies aimed at mitigating the environmental impacts of petroleum products have gained worldwide relevance. In this scenario, the production of bioplastics mainly from polysaccharides such as starch is a growing strategy and a field of intense research. The use of plasticizers, the preparation of blends, and the reinforcement of bioplastics with lignocellulosic components have shown promising and environmentally safe alternatives for overcoming the limitations of bioplastics, mainly due to the availability, biodegradability, and biocompatibility of such resources. This review addresses the production of bioplastics composed of polysaccharides from plant biomass and its advantages and disadvantages.

A one-step acidification strategy for sewage sludge dewatering with oxalic acid

Sewage sludge dewatering is an efficient approach to reduce the volume of sludge for the subsequent disposal. In this study, a novel one-step acidification sludge dewatering method was developed with using oxalic acid as a conditioner. In laboratory-scale experiments with the dosage of 200 mg/g dry solid (DS), the normalized capillary suction time and the specific resistance to filtration were respectively decreased by 78.7% and 60.0% after 30 min of oxalic acid conditioning, much more efficient than those conditioned with sulfuric acid and hydrochloric acid at the same pH value. This superior dewatering performance was attributed to two factors. One was that oxalic acid could more efficiently promote the hydrolysis of polysaccharide, especially pectins, to release bound water. The other was that OA could dissolve more Fe³⁺ and Al³⁺, as well as form precipitate with Ca²⁺ in sludge, which may act as flocculants or co-precipitator for the subsequent sludge particles coagulation. In pilot-scale experiments, the water content of oxalic acid conditioned sludge cake was reduced to 60% under the optimum conditions, while the reagent cost was as low as 110.0 USD/t DS. This work provides a cost-effective and easy-operated sewage sludge disposal technique, and also sheds light on the potential of oxalic acid in environmental waste treatment.

Maximization of monomeric C5 sugars from wheat bran by using mesoporous ordered silica catalysts

The hydrolysis process of a real fraction of arabinoxylans derived from wheat bran was studied. The influence of catalyst type and loading, reaction time and different metal cations were discussed in terms of the hydrolysis yield of arabinose and xylose oligomers as well as the formation of furfural as degradation product. A high yield of arabinoxylans into the corresponding monomeric sugars (96 and 94% from arabino- and xylo-oligosaccharides, respectively) was obtained at relatively high temperatures (180°C) and short reaction times (15min) with a catalyst loading of 4.8g of RuCl₃/Al-MCM-48 per g of initial carbon in hemicelluloses.

A Review of Water-Resistant Hemicellulose-Based Materials: Processing and Applications

Hemicelluloses, due to their hydrophilic nature, may tend to be overlooked as a component in water-resistant product applications. However, their domains of use can be greatly expanded by chemical derivatization. Research in which hydrophobic derivatives of hemicelluloses or combinations of hemicelluloses with hydrophobic materials are used with to prepare films and composites is considered herein. Isolation methods that have been used to separate hemicellulose from biomass are also reviewed. Finally, the most useful pathways to change the hydrophilic character of hemicelluloses to hydrophobic are reviewed. In this way, the water resistance can be increased and applications of targeted water-resistant hemicellulose developed. Several applications of these materials are discussed.

Hydrolysis of oligosaccharides over solid acid catalysts: a review

Mild fractionation/pretreatment processes are becoming the most preferred choices for biomass processing within the biorefinery framework. To further explore their advantages, new developments are needed, especially to increase the extent of the hydrolysis of poly- and oligosaccharides. A possible way forward is the use of solid acid catalysts that may overcome many current drawbacks of other common methods. In this Review, the advantages and limitations of the use of heterogeneous catalysis for the main groups of solid acid catalysts (zeolites, resins, carbon materials, clays, silicas, and other oxides) and their relation to the hydrolysis of model soluble disaccharides and soluble poly- and oligosaccharides are presented and discussed. Special attention is given to the hydrolysis of hemicelluloses and hemicellulose-derived saccharides into monosaccharides, the impact on process performance of potential catalyst poisons originating from biomass and biomass hydrolysates (e.g., proteins, mineral ions, etc.). The data clearly point out the need for studying hemicelluloses in natura rather than in model compound solutions that do not retain the relevant factors influencing process performance. Furthermore, the desirable traits that solid acid catalysts must possess for the efficient hemicellulose hydrolysis are also presented and discussed with regard to the design of new catalysts.