Waste and Biomass Valorization

Spent coffee grounds (SCGs) were utilized in the synthesis of a solid acid catalyst (SAC) through a carbonization–sulfonation process performed at low temperatures (350–500 °C for carbonization and 50–150 °C for sulfonation) and short processing times (1–10 h). The best SAC from the process was able to convert more than 90% of oleic acid to methyl oleate during esterification with methanol (10 mol OA/mol methanol, 80 °C, 7 h, 10%w/w catalyst loading). It was obtained by carbonizing SCG at 400 °C for 2 h and then sulfonating the biochar at 100 °C for 1 h. The reusability tests performed in 4 cycles at the same esterification conditions reveal loss of activity of about 70% of its original state, corresponding to a decrease in total acid and sulfonic acid densities from 4.22 and 3.36 mmol H+/g to 1.33 and 1.16 mmol H+/g, respectively. This process is a considerable improvement from that reported in previous works, having no activating agents in the carbonization process and with significantly shorter times for processing.

Separate collection of biowaste represents in Portugal only 2 % of total collected biowaste. Even though higher quality compost can be obtained through the separate collection of biowaste, this is generally regarded as more expensive and discarded as an option. In this work we assessed the viability of implementing the separate collection of biowaste targeting restaurants and canteens in city centers, using Aveiro as a case study. The current situation (no separate collection for biowaste) was compared with an alternative scenario in which biowaste was separately collected and valorized. The costs, constrains and the producers’ attitude towards such a collection scheme are presented and discussed. On average 0.46 kg of biowaste were produced per meal served. The acceptance of separate biowaste collection was high (67 %) among producers, and it could be increased further through informative campaigns and economic incentives such as pay-as-you-throw tariffs. Door-to-door collection of biowaste could reduce the cost per ton as much as 37 %, when compared to collection as unsorted waste. The major constrains for the implementation of separate collection of biowaste were the selection of alternative legal destinations to the MBT unit (which has the exclusivity to treat collected waste) and the lack of dedicated infrastructures at multimunicipal waste management facilities to handle separately collected biowaste.

The complexation behavior between 2-pyrone-4,6-dicarboxylic acid (PDC) and alkali metal ions was systematically estimated. The PDC complexes of alkali metal ions exhibit unique crystal structures due to the diverse coordination numbers of the metal ion. The crystal structure of the complex between PDC and cesium (Cs) ion suggests that the metal ion binary crosslinking and much coordination numbers of the Cs induce the preferential complex formation via sedimentation of the PDC–Cs complex. The minor electronegativity difference between the Cs and other alkali metals might be the determining factor in the structure of the complex the ion forms with PDC.

Poly-β-hydroxybutyrate (PHB) belonging to the polyhydroxyalkanoates family is a natural polyester used as a biodegradable plastic for various commercial applications. In this study, soil samples from the vegetable oil processing industry were used to screen for PHB-producing bacteria using Sudan black B staining. Among the isolated bacteria, PHB positive PSR-2 isolate was chosen as a potent PHB producer. The phylogenetic tree revealed that the PSR-2 isolate has a high 16S rRNA gene sequence similarity of 99.9% with Bacillus tequilensis. The PHB content of 2.8 ± 0.09 g/L was produced by PSR-2 isolate in 48 h in a nutrient broth medium containing 1% glucose compared to the PHB production of 1.6 ± 0.08% by the reference strain, Bacillus circulans. Taguchi method was used to optimize PHB production using the alkali-pretreated spent mushroom substrate of sugarcane bagasse (SMS-SB) as an additional carbon substrate along with other energy sources. The optimized factors in the contribution of PHB production from the highest- to the lowest-ranking are as follows: alkali-pretreated SMS-SB, glucose, glycerol, peptone, ammonium chloride, and potassium dihydrogen phosphate at 30 ºC, pH 7.0, which resulted in the production of 12.4 ± 0.95 g/L PHB was higher than the predicted value of 11.59 g/L. The synthesized PHB was characterized using Ultraviolet–visible spectrophotometry, Fourier transform infrared spectrometry, differential scanning calorimetry, thermogravimetric analysis, nuclear magnetic resonance spectroscopy, and gas chromatography-mass spectrometry. The results revealed the presence of hydroxyl (–OH), methyl (–CH3), methine (=CH–), methylene (–CH2–) and ester carbonyl (>C=O) groups, which confirmed the PHB structure. Thus, alkali-pretreated SMS-SB plays a significant role as an energy substrate for the production of PHB. This gives the knowledge to utilize cost-effective lignocellulosic agro-waste materials as a feedstock for the sustainable production of biodegradable PHB for many biomedical applications.

In order to conserve natural resources and prevent waste generation, effective utilization of industrial wastes and/or by-products for beneficial engineering applications becomes inevitable. In order to accomplish this, extensive research studies, exploring properties and new applications of waste materials in a sustainable and environmentally friendly manner, have been initiated worldwide. Red mud (RM, also known as bauxite residue) is one of the wastes generated by the aluminium industry and its disposal and utilization have been traditionally hindered due to the extreme alkalinity (pH about 10.5–13.5). To date, no comprehensive review on various properties of RM of different origin and associated challenges in using it as a beneficial engineering material has been performed. The objective of this study is first to critically appraise the current understanding of properties of RM through a comprehensive literature review and detailed laboratory investigations conducted on Indian RM by the authors, to assess and identify the potential engineering applications, and to finally discuss associated challenges in using it in practical applications. Physical, chemical, mineralogical and geotechnical properties of RMs of different origin and production processes are reviewed. Mechanisms behind the pozzolanic reaction of RM under different chemical and mineralogical compositional conditions are discussed. Environmental concerns associated with the use of RM are also raised. Studies relevant to leachability characteristics reveal that most of the measured chemical concentrations are within the permissible regulatory limits. Overall, the review shows that RM disposal and reuse is complicated by its extreme alkalinity, which is also noticed to be influencing multiple engineering properties. But with selected pH amendments, the treated RM is found to have significant potential to be used as an effective and sustainable geomaterial. The assessment is majorly based on the characteristics of Indian RMs; hence the adaptation of the findings to other RMs should be assessed on a case-by-case basis. Moreover, field studies demonstrating the performance of RM in various engineering applications are warranted.

Hiện nay, quá trình phân giải kỵ khí là công nghệ đã được chứng minh trong quản lý chất thải sinh học. Sự quan tâm nghiên cứu hiện tại được định hướng vào việc tối ưu hóa quy trình về năng suất biogas với sự chú ý đặc biệt đến các ứng dụng tiền xử lý cơ học nhằm thúc đẩy sự hòa tan của các hợp chất hữu cơ phức tạp trong chất thải sinh học. Một kỹ thuật tiền xử lý cơ học gần đây liên quan đến việc ép chất thải sinh học đã phân tách để tách biệt vật liệu thành các pha riêng biệt và dễ xử lý hơn, cụ thể là các phần chất thải sinh học bán lỏng và bán rắn. Mục tiêu của nghiên cứu hiện tại là xem xét các đặc điểm của phần bán lỏng và đánh giá quá trình phân giải kỵ khí dưới điều kiện môi trường mesophilic (37 °C) và thermophilic (55 °C) trong các reactor quy mô thí điểm CSTR. Phần bán lỏng thể hiện tiềm năng phân hủy sinh học cao với tỷ lệ chất bay hơi trên tổng chất rắn tăng (0.88) trong khi hàm lượng TS thấp (TS = 188 gTS/kg) thuận lợi cho các điều kiện vận hành của quy trình. Các quá trình phân giải kỵ khí mesophilic và thermophilic trong điều kiện ổn định cho thấy sức mạnh cao và tính kiên cường đối với các tham số quy trình như pH, độ kiềm, VFA, amoniac và mức độ amoni. Quá trình phân giải kỵ khí mesophilic và thermophilic đã cho năng suất biogas trung bình lần lượt là 0.79 và 0.90 m3biogas/kgTVS với 66.0 và 68.8 % hàm lượng metan.

One of the major by-products of the rice bran oil refining industry is rice bran gums (RBG). It is considered a waste product because it hardly fetches any revenue. However, the major component of RBG is phospholipids and the demand for phospholipids has seen steep rise, especially for its use in COVID-19 vaccines. Though soyabean and egg lecithin are the major sources of phospholipids, industries are striving for newer sources. RBG can be an alternative source. Presence of bran fines, darker colour, and relatively low quantity of phosphatidylcholine (PC) in crude RBG, are the major hindrances for its widespread applications. The primary question was whether the crude RBG can be valorized to be a source of phospholipids for use in food, cosmetics and pharmaceutical industries. Present work focuses on bleaching of crude RBG and preparation of powdered rice bran lecithin. Appreciable colour reduction was observed with sodium chlorite as bleaching agent. Furthermore, PC-enrichment of RBG was attempted for enhanced applicability in nutraceutical and pharmaceutical products. HPLC analysis showed PC enrichment of more than 50% under specific conditions of solvent used, solid-to-solvent ratio, time, and temperature. These observations are the first of its kind with regard to RBG.

The purpose of study was utilization of sugarcane bagasse, waste product of sugarcane industry, for production of xylooligosaccharides (XOS) and their evaluation of their prebiotic potential. The XOS production was carried out in two steps: alkaline extraction of xylan (5, 10 and 15%KOH and NaOH) followed by acid hydrolysis (0.25 and 0.50M H2SO4; 20, 40 and 60 min) of xylan, and quantified using high performance thin layer chromatography (HPTLC). The prebiotic potency of XOS was evaluated for probiotics viz. Lactobacillus brevis, Lactobacillus acidophilus and Lactobacillus viridescens in comparison to standard fructooligosaccharides (FOS). The chemical compositional analysis indicated that bagasse contain 28.42% hemicellulose out of which 21.46% was estimated to be xylan. Maximum yield of xylan (20.5%) was obtained with 15%NaOH treatment. The best treatments for xylan hydrolysis were found to be 0.25M H2SO4 for 20 and 40 min with concentrations of xylose, xylobiose and xylotriose to be 2.014, 2.106 and 1.228 mg ml− 1, respectively, in 20 min hydrolysis and 2.138, 1.502 and 0.824 mg ml− 1, respectively, in 40 min hydrolysis. XOS were found to be better prebiotics than standard FOS. Pure xylobiose was found to have highest positive effect on growth of all three bacteria tested indicating that effects of XOS were due to presence of xylobiose, xylotriose and XOS with higher degree of polymerization in xylan hydrolysates. Sugarcane bagasse xylan can be converted into XOS only by controlled acid hydrolysis leading to increased production of XOS which can be used as good prebiotics in drugs and food ingredients after their purification eliminating all the acidic and alkaline residues and also side products.

Floral waste has been considered one of the major concerns, even for those that may have industrial applications, such as dyes or perfumes. In the present study, the possibility of using Acacia dealbata flowers’ extracts and respective fractions as bioactive agents was explored in vitro systems. A. dealbata flowers were extracted with ethanol and the solid residue was further processed with (i) a sequence of organic solvents and (ii) a sequence of greener stages (aqueous, acid and microwave hydrogravity extraction). Total extraction yield and phenolic content were analysed. Ethanolic extracts presented more than 25% phenolic content. Their antiradical activity was evidenced by 85% of the ABTS radical scavenging potency of Trolox. For selected extracts different biological properties, including antibrowning, antilipogenic, anti-inflammatory and cytotoxicity against tumoral cells, were also evaluated. Different extracts were protective against neutrophils oxidative burst and moderately cytotoxic against colon carcinoma HCT-116 and lung adenocarcinoma A549 cells. A multistage extraction process with green solvents was suitable for the production of extracts and fractions from A. dealbata flowers with interesting biological properties. Extracts with higher activities were selected for further assessment as solvents in bioactive hydrogels, observing a positive correlation between gels softening and extracts bioactivity features.