Optimization of preparing a high yield and high cationic degree starch graft copolymer as environmentally friendly flocculant: Through response surface methodology

Preparation of cationic aggregates derived from sewage sludge for efficient capture of organic matter

Capturing the abundant organic matter residing in wastewater can not only reduce the emission of CO₂ from the source, but the enriched organics can also be used for anaerobic fermentation to generate and offset energy consumption in wastewater treatment processes. The key is to find or develop low-cost materials that can capture organic matter. Herein, sewage sludge-derived cationic aggregates (SBC-g-DMC) were successfully prepared via a hydrothermal carbonization process coupled with a graft copolymerization reaction for recovering organic matter from wastewater. Based upon preliminary screening of synthesized SBC-g-DMC aggregates regarding grafting rate, cationic degree, and flocculation performance, SBC-g-DMC_2.5 aggregate prepared with 60 mg of initiator, DMC-to-SBC mass ratio of 2.5:1, 70 °C, and 2 h of reaction time was selected for further characterization and evaluation. Results showed that SBC-g-DMC_2.5 aggregate has a positively-charged surface over a wide pH range of 3-11 and a hierarchical micro-/nano-structure, endowing it with an excellent organic matter capture efficiency (97.2% of pCOD, 68.8% of cCOD, and 71.2% of tCOD). Meanwhile, SBC-g-DMC_2.5 exhibits inappreciable trapping ability for the dissolved COD, NH₃-N, and PO₄^3-, guaranteeing the regular running of subsequent biological treatment units. Electronic neutralization, adsorption bridging, and sweep coagulation between cationic aggregates surface and organic matter were identified as the primary mechanisms for SBC-g-DMC_2.5 to capture organics. This development is expected to provide a theoretical reference for sewage sludge disposal, carbon reduction, and energy recovery during municipal wastewater treatment.

Novel approach on the synthesis of starch betainate by transesterification

Transesterification of starch with methyl betainate was studied for the first time, both in aprotic media and in solid state, and both under alkaline and acidic conditions. Betaine hydrochloride was first esterified in methanol, attaining a conversion of 86%. Starch was then converted into starch betainate in either N,N-dimethylformamide or dimethyl sulfoxide, and using sulfuric acid as catalyst or pre-activating the polymer in NaOH/ethanol. Furthermore, solid-state transesterification was carried out in a ball mill, for which sulfuric acid was replaced with the less corrosive sulfamic acid. Cationic starch esters were characterised by ¹H and ¹³C NMR spectroscopy, infrared spectroscopy, thermogravimetric analysis, viscometry, optical microscopy (in water) and scanning electron microscopy (dry). In solution, the process attained degrees of substitution up to 0.4. No by-products, dehydration, oxidation or colouring were detected, but starch underwent severe depolymerization in wet media. In solid state, whilst the resulting degree of substitution was lower, degradation was minimal. In any case, transesterification, with its variety of possibilities, yields cationic starches that offer a promising alternative to conventional ethers.

Chemical Modification of Cotton Fabrics by a Bifunctional Cationic Polymer for Salt-Free Reactive Dyeing

Cotton modification exhibited great potential in the fabric dyeing industry. A bifunctional cationic polymer with a moderate cationic degree and low molecular weight was achieved via free radical polymerization between dimethyl diallyl ammonium chloride and allyl glycidyl ether. Then, it was further utilized for the modification of cotton fabrics. The formation of the cationic polymer was identified using Fourier transform infrared and nuclear magnetic resonance spectroscopies. The structure and properties of both treated and untreated cotton were analyzed by X-ray photoelectron spectroscopy and scanning electron microscopy. The modified cotton fabrics could be salt-free dyed with reactive dyes at low temperatures. While obtaining satisfactory color fastness and leveling properties, the dyeability of the modified cotton was improved significantly compared with the conventional dyeing of native cotton. Besides, the prepared cationic polymer has good flocculating properties to avoid secondary pollution, suggesting high potential for achieving an economical and eco-friendly dyeing process.

Roles of functional microbial flocculant in dyeing wastewater treatment: Bridging and adsorption

Congo red (CR) is a typical and widely used azo dye in industries. It possesses the serious threat to ecosystem and public for its indiscriminate discharge. Microbial flocculant (MBF) with various functional groups is a potential flocculant applied in dyeing wastewater treatment, and it has the advantages of high treatment efficiency, biodegradability and non-toxicity. In this study, the functional groups, amino group, ammonium group and acyloxy group, were grafted onto MBF to further improve its thermal stability, solubility and performance. Grafting copolymerization occurred at the amino group of MBF was confirmed by XPS. Polyaluminum silicate (PSA) and self-prepared functional microbial flocculant, MBF-g-P(AM-DAC), played different roles in CR wastewater treatment. PSA contributed to charge neutralization, but its yielded flocs were small. On the contrary, MBF-g-P(AM-DAC) possessed weak charge neutralization but big flocs. Its settlement efficiency has significantly improved. The unsaturated active sites on MBF-g-P(AM-DAC) and its flocs contributed to the adsorption of CR in terms of high surface area and adsorption capacity of the flocs. Physical adsorption and chemical adsorption were both discovered in the treatment.

Optimization of biochar preparation from the stem of Eichhornia crassipes using response surface methodology on adsorption of Cd2

In this study, preparation of Eichhornia crassipes stem biochar (ECSBC) was optimized and applied for the removal of Cd²⁺ from aqueous solution. To obtain the best adsorption capacity of ECSBC, the response surface methodology (RSM) was used to optimize the preparation conditions of ECSBC (OECSBC). The interactions among heating time (X₁), heating temperature (X₂) and heating rate (X₃) were designed by Box-Behnken Design (BBD) experiments. The software gave seventeen runs experiment within the optimal conditions towards two response variables (removal rate and adsorption capacity for Cd²⁺). The results showed that the mathematical model could fit the experimental data very well and the significance of the influence factors followed the order as heating temperature (X₂) > heating rate (X₃) > heating time (X₁), and the influence of interaction term is: X₁ and X₂ (heating time and heating temperature) > X₂ and X₃ (heating temperature and heating rate) > X₁ and X₃ (heating time and heating rate). Based on the analysis of variance and the method of numerical expected function, the optimal conditions were heating time of 2.42 h, heating temperature of 393 °C, and heating rate of 15.56 °C/min. Under the optimum conditions, the predicted the maximum removal rate and adsorption capacity were 85.2724% and 21.168 mg/g, respectively, and the experimental value of removal rate and adsorption capacity for Cd²⁺ were 80.70% and 20.175 mg/g, respectively, the deviation from the predicted value were 5.36% and 4.69%. The results confirmed that the RSM can optimize the preparation conditions of ECSBC, and the adsorption capacity of OECSB was improved.

Novel approach for extraction of grape skin antioxidants by accelerated solvent extraction: Box-Behnken design optimization

Grape skin can be considered as an excellent and inexpensive source of polyphenol antioxidant compounds. A high-efficiency accelerated solvent extraction (ASE) method was developed for antioxidant polyphenols from grape skin. A three-factors three-level Box-Behnken design by response surface methodology was employed for optimization of extraction parameters in terms of total phenolic content, total anthocyanins content and antioxidant activity. The optimized condition was ethanol concentration of 48.80%, temperature of 50.79 °C and extraction time of 14.82 min. Under these conditions, the highest yields of polyphenol, the total phenolic content (15.24 mg GAE/g), total anthocyanins content (346.68 mg CGE/100 g) in grape skin, were obtained with significant antioxidant properties by DPPH, ABTS and FRAP assays. Moreover, the extracts from various grape skins by ASE, possessed ten main antioxidant polyphenols with the highest concentration of p-hydroxybenzoic acid and malvidin-3-O-glucoside. Compared with conventional solvent extraction, ASE extracted more amounts of polyphenols, exhibited more extraction level with shorter time and higher reproducibility.