Preferential association of PBDEs and PAHs with mineral particles vs. dissolved organic carbon: Implications for groundwater contamination at e-waste sites.

Polybrominated biphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) are commonly detected contaminants at e-waste recycling sites. Against the conventional wisdom that PBDEs and PAHs are highly immobile and persist primarily in shallow surface soils, increasing evidence shows that these compounds can leach into the groundwater. Herein, we compare the leachabilities of PBDEs vs. PAHs from contaminated soils collected at an e-waste recycling site in Tianjin, China. Considerable amounts of BDE-209 (0.3-2 ng/L) and phenanthrene (42-106 ng/L), the most abundant PBDE and PAH at the site, are detected in the effluents of columns packed with contaminated soils, with the specific concentrations varying with hydrodynamic and solution chemistry conditions. Interestingly, the leaching potential of BDE-209 appears to be closely related to the release of colloidal mineral particles, whereas the leachability of phenanthrene correlates well with the concentration of dissolved organic carbon in the effluent, but showing essentially no correlation with the concentration of mineral particles. The surprisingly different trends of the leachability observed between BDE-209 and phenanthrene is counterintuitive, as PBDEs and PAHs often co-exist at e-waste recycling sites (particularly at the sites wherein incineration is being practiced) and share many similarities in terms of physicochemical properties. One possible explanation is that due to its extremely low solubility, BDE-209 predominantly exists in free-phase (i.e., as solid (nano)particles), whereas the more soluble phenanthrene is mainly sorbed to soil organic matter. Findings in this study underscore the need to better understand the mobility of highly hydrophobic organic contaminants at contaminated sites for improved risk management.

Use of waste frying oil and coconut pulp for the production, isolation, and characterization of a new lipase from Moesziomyces aphidis.

Lipases comprise the third most commercialized group of enzymes worldwide and those of microbial origin are sought for their multiple advantages. Agro-industrial waste can be an alternative culture medium for producing lipases, reducing production costs and the improper disposal of waste frying oil (WFO). This study aimed to produce yeast lipases through submerged fermentation (SF) using domestic edible oil waste as inducer and alternative culture medium. The optimal culture conditions, most effective inducer, and purification method for a new lipase from Moesziomyces aphidis BRT57 were identified. Yeast was cultured in medium containing green coconut pulp and WFO waste for 72 h. The maximum production of lipases in SF occurred in a culture medium containing WFO and yeast extract at 48 and 72 h of incubation, with enzyme activities of 8.88 and 11.39 U mL-1, respectively. The lipase was isolated through ultrafiltration followed by size exclusion chromatography, achieving a 50.46 % recovery rate. To the best of our knowledge, this is the first study to report the production and purification of lipases from M. aphidis, demonstrating the value of frying oil as inducer and alternative medium for SF, contributing to the production of fatty acids for biodiesel from food waste.

Atlantic salmon (Salmo salar) waste as a unique source of biofunctional protein hydrolysates: Emerging productions, promising applications, and challenges mitigation.

The Atlantic salmon is an extremely popular fish for its nutritional value and unique taste among several fish species. Researchers are focusing on the utilization of Atlantic salmon waste for generating protein hydrolysates rich in peptides and amino acids and investigating their health benefits. Several technological approaches, including enzymatic, chemical, and the recently developed subcritical water hydrolysis, are currently used for the production of Atlantic salmon waste protein hydrolysates. Hydrolyzing various wastes, e.g., heads, bones, skin, viscera, and trimmings, possessing antioxidant, blood pressure regulatory, antidiabetic, and anti-inflammatory properties, resulting in applications in human foods and nutraceuticals, animal farming, pharmaceuticals, cell culture, and cosmetics industries. Furthermore, future applications, constraints several challenges associated with industrial hydrolysate production, including sensory, safety, and economic constraints, which could be overcome by suggested techno processing measures. Further studies are recommended for developing large-scale, commercially viable production methods, focusing on eradicating sensory constraints and facilitating large-scale application.

Impact of pre-exposure stress on the growth and viability of Lactobacillus acidophilus in regular, buriti pulp and orange byproduct fermented milk products.

The loss of probiotics viability in yogurts and fermented milk is a significant challenge in producing yogurt and fermented milk. Thus, pre-exposure of probiotics to stress conditions can be a viable alternative to increase the probiotic viability. Moreover, the use of fruit pulp and agro-industrial residues in these products has demonstrated promising results in promoting growth and improving the viability of probiotics. Thus, this study aimed to evaluate the effects of pre-exposure to acid, oxidative and osmotic stress on the growth and viability of Lactobacillus acidophilus in yogurts and naturally fermented milk containing buriti (Mauritia flexuosa Mart.) pulp or orange byproduct. L. acidophilus was individually pre-exposed to acid, oxidative, and osmotic stress and used in the production of yogurts and fermented milk to determine both the acidification profile and growth of the cultures. Furthermore, during cold storage, the post-acidification profiles and viability of microbial cultures added to the yogurts and fermented milk were monitored. Results showed that pre-exposure to stress conditions influenced the growth parameters as the growth rate (µ) and lag phase (λ) of L. acidophilus and the starter cultures of S. thermophilus and L. delbrueckii subsp. bulgaricus. Moreover, an increase in the viability of L. acidophilus - pre-exposed to acid stress - was observed on the 21st day of storage of natural yogurts containing orange byproduct compared with non-stressful conditions. This study reports new data on the growth of probiotic cultures pre-exposed to stress conditions in products added of pulps and agro-industrial residues, which have not yet been shown in the literature.

Bacillus subtilis fermented shrimp waste isolated peptide, PVQ9, and its antimicrobial mechanism on four Gram-positive foodborne bacteria.

Bacillus subtilis produces proteases that hydrolyze proteins to produce bioactive peptides. Given the mounting waste from processed shrimp, the antimicrobial potential of peptides isolated from B. subtilis fermented shrimp waste was explored. Among the five peptides screened using molecular docking prediction, PVQ9 (AVFPSIVGRPR) had strong antibacterial activity against four common foodborne Gram-positive bacteria, i.e., Staphylococcus aureus, Bacillus cereus, Mammaliicoccus sciuri, and Kurthia gibsonii. The minimum bactericidal concentrations (MBCs) were 62.5 µg/mL for S. aureus and B. cereus, and 31.3 µg/mL for both M. sciuri and K. gibsonii, with a time-kill of 3 h observed for all strains. Mechanistically, it was demonstrated that PVQ9 could destroy bacterial cell walls, change bacteria cell membrane permeability, bind to bacteria DNA, and cause cell apoptosis. Most importantly, peptide PVQ9 could inhibit the spoilage of bean curd or tofu contaminated with K. gibsonii. These findings suggest that PVQ9 could be a useful preservative in controlling foodborne pathogenic bacteria in soy products and other processed foods.

Soil colloids can significantly enhance spreading of polybromodiphenyl ethers in groundwater by serving as an effective carrier.

Polybromodiphenyl ethers (PBDEs), the widely used flame retardants, are common contaminants in surface soils at e-waste recycling sites. The association of PBDEs with soil colloids has been observed, indicating the potential risk to groundwater due to colloid-facilitated transport. However, the extent to which soil colloids may enhance the spreading of PBDEs in groundwater is largely unknown. Herein, we report the co-transport of decabromodiphenyl ester (BDE-209) and soil colloids in saturated porous media. The colloids released from a soil sample collected at an e-waste recycling site in Tianjin, China, contain high concentration of PBDEs, with BDE-209 being the most abundant conger (320 ± 30 mg/kg). The colloids exhibit relatively high mobility in saturated sand columns, under conditions commonly observed in groundwater environments. Notably, under all the tested conditions (i.e., varying flow velocity, pH, ionic species and ionic strength), the mass of eluted BDE-209 correlates linearly with that of eluted soil colloids, even though the mobility of the colloids varies markedly depending on the specific hydrodynamic and solution chemistry conditions involved. Additionally, the mass of BDE-209 retained in the columns also correlates strongly with the mass of retained colloids. Apparently, the PBDEs remain bound to soil colloids during transport in porous media. Findings in this study indicate that soil colloids may significantly promote the transport of PBDEs in groundwater by serving as an effective carrier. This might be the reason why the highly insoluble and adsorptive PBDEs are found in groundwater at some PBDE-contaminated sites.

Inhibition of jarosite heterogeneous crystallization on anglesite via in-situ formation of competitive substrate.

Heterogeneous crystallization is a common occurrence during the formation of solid wastes. It leads to the encapsulation of valuable/hazardous metals within the primary phase, presenting significant challenges for waste treatment and metal recovery. Herein, we proposed a novel method involving the in-situ formation of a competitive substrate during the precipitation of jarosite waste, which is an essential process for removing iron in zinc hydrometallurgy. We observed that the in-situ-formed competitive substrate effectively inhibits the heterogeneous crystallization of jarosite on the surface of anglesite, a lead-rich phase present in the jarosite waste. As a result, the iron content on the anglesite surface decreases from 34.8% to 1.65%. The competitive substrate was identified as schwertmannite, characterized by its loose structure and large surface area. Furthermore, we have elucidated a novel mechanism underlying this inhibition of heterogeneous crystallization, which involves the local supersaturation of jarosite caused by the release of ferric and sulfate ions from the competitive substrate. The local supersaturation promotes the preferential heterogeneous crystallization of jarosite on the competitive substrate. Interestingly, during the formation of jarosite, the competitive substrate gradually vanished through a dissolution-recrystallization process following the Ostwald rule, where a metastable phase slowly transitions to a stable phase. This effectively precluded the introduction of impurities and reduced waste volume. The goal of this study is to provide fresh insights into the mechanism of heterogeneous crystallization control, and to offer practical crystallization strategies conducive to metal separation and recovery from solid waste in industries.

Emerging deep eutectic solvents for food waste valorization to achieve sustainable development goals: Bioactive extractions and food applications.

Food waste, accounting for about one-third of the total global food resources wasted each year, is a substantial challenge to global sustainability, contributing to adverse environmental impacts. The utilization of food waste as a valuable source for bioactive extraction can be facilitated through the application of DES (Deep Eutectic Solvents). Acknowledging the significant need to tackle this issue, the United Nations integrated food waste management into its Sustainable Development Goals, hence, the present review explores the role of DES in bioactive compounds extraction from food waste. Various extraction processes using the DES system are thoroughly studied and the application of bioactive components as antioxidants, antimicrobials, flavourings, nutraceuticals, functional ingredients, additives, and preservatives is investigated. Most importantly, regulatory considerations and safety aspects of DES in food applications are discussed in-depth along with consumer perception and acceptance of DES in the food sector. The key hypothesis of the review is to evaluate emerging DES systems for their efficiency in bioactive extraction technologies and various food applications. Overall, this review provides a comprehensive understanding of utilizing DES for synthesizing valuable food waste-derived bioactive components, offering a sustainable approach to waste management and the development of high-value products.

The mechanisms of pH regulation on promoting volatile fatty acids production from kitchen waste.

The anaerobic acid production experiments were conducted with the pretreated kitchen waste under pH adjustment. The results showed that pH 8 was considered to be the most suitable condition for acid production, especially for the formation of acetic acid and propionic acid. The average value of total volatile fatty acid at pH 8 was 8814 mg COD/L, 1.5 times of that under blank condition. The average yield of acetic acid and propionic acid was 3302 mg COD/L and 2891 mg COD/L, respectively. The activities of key functional enzymes such as phosphotransacetylase, acetokinase, oxaloacetate transcarboxylase and succinyl-coA transferase were all enhanced. To further explore the regulatory mechanisms within the system, the distribution of microorganisms at different levels in the fermentation system was obtained by microbial sequencing, results indicating that the relative abundances of Clostridiales, Bacteroidales, Chloroflexi, Clostridium, Bacteroidetes and Propionibacteriales, which were great contributors for the hydrolysis and acidification, increased rapidly at pH 8 compared with the blank group. Besides, the proportion of genes encoding key enzymes was generally increased, which further verified the mechanism of hydrolytic acidification and acetic acid production of organic matter under pH regulation.

A simple and accurate method for the determination of Rh, Pd, and Pt in e-waste and spent automotive catalysts using HR-CS FAAS for assessing the value of secondary raw materials.

This work presents a simple and accurate method for the fast sequential determination of Rh, Pd, and Pt in spent automotive catalysts and e-wastes using high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS). Extensive research was carried out in model systems on the impact of potential interfering substances on analyte's signals measured in two types of flame (air-C2H2 and N2O-C2H2). Mutual analyte interactions were also taken into account. Different background corrections offered by the HR-CS AAS spectrometer were tested to obtain interference-free analyte signals and the best detectability. Using an air-C2H2 flame and 1 % La solution as a spectrochemical buffer provided good sensitivity and accurate determinations of Rh, Pd, and Pt using a simple calibration graph. Microwave-assisted leaching of PGE from waste samples with aqua regia at 240 °C for 60 min efficiently leached all target metals, which significantly simplified and shortened the sample preparation step. The detectability of the method (detection limit of 0.4, 0.6, and 5 mg kg-1 for Rh, Pd, and Pt, respectively) and precision (< 7 %) were satisfactory. The accuracy of the method was confirmed by analysis of certified reference materials (spent automotive catalyst (ERM-EB504), electronic scrap (BAM-M505a)), and calculated zeta score values. The recoveries for Rh, Pd, and Pt in ERM-EB504 were 93, 101, and 96 %, respectively, and for Pd in BAM-M505a, 97 %. The developed method can be used to assess the value of secondary raw materials, such as various types of spent catalysts and e-waste containing Rh, Pd, and Pt.

Achieving high-durability aqueous Zn-ion batteries enabled by reanimating inactive Zn on Zn anodes.

The heavy by-products generated on Zn anode surface decrease the active surface of Zn anodes and thus induce uneven Zn deposition, seriously reducing the service life of aqueous Zn-ion batteries (AZIBs). Herein, we propose an elimination strategy enabled by the coordination chemistry to dissolve the main by-products (Zn4SO4(OH)6·xH2O). Urea as a proof-of-concept has been applied as the reactivator in the electrolyte to catalytically produce highly active NH3 on the surface of the by-products. Then the NH3 can powerfully coordinate with the Zn2+ ion in the by-products to form the soluble complex [Zn(NH3)4]2+. Consequently, the proposed electrolyte can not only lead to the timely decomposition of the by-products to prevent the Zn anode from inactivation during cycling, but also repair the waste Zn anodes for reutilization. The action mechanism has been systematically demonstrated via theoretical simulation and experimental study. As a result, the high durability with ultrahigh cumulative capacity of 10,600 mAh cm-2 for the Zn||Zn symmetric cell has been achieved at 40 mA cm-2. Particularly, the dead Zn||Zn symmetric cells and Zn||LiFePO4 full cells have been successfully reactivated. This study lights a new route to extend the cell lifespan and reuse waste Zn-ion batteries.

A review on digital transformation in healthcare waste management: Applications, research trends and implications.

At present, both emerging and developed economies have faced the challenge of higher healthcare waste generation. Developed countries are using these technologies to manage healthcare waste and cope with the challenge. Emerging economies are still struggling to understand and implement digital technologies in healthcare waste management, posing a danger to partners handling toxic and hazardous waste. The proper handling of healthcare waste is essential for social and environmental sustainability. Digital technologies that drive digital transformation in the healthcare sector impact the traditional way of managing healthcare waste. Digital technologies include artificial intelligence, blockchain, the Internet of Things, sensors, data analytics and radio frequency identification. These technologies can potentially address vehicle route planning and scheduling problems, resource optimisation, real-time tracking and the visibility of healthcare waste management. Apart from economic and environmental concerns, the operational workforce also takes care of societal well-being and implements waste management strategies and policies. Past research has focused on integrating blockchain technology to enhance traceability and transparency in waste collection and disposal activities. However, the application and impact of these technologies for managing different operations of healthcare management with sustainability is a gap bridged by the present study. This study adopts a systematic literature review to identify research trends, applications and implications of digital transformation. It proposes a digital technology-driven framework for healthcare waste management for further research.

Blending phosphogypsum to mitigate radionuclide leaching for sustainable road base applications.

Production of phosphoric acid generates a calcium sulfate byproduct known as phosphogypsum (PG). PG is not considered a suitable standalone road base material because of concerns such as strength and presence of radionuclides. This paper investigates the latter, specifically the influence of blending PG with common alkaline road base aggregates - limerock (LR) and recycled concrete aggregate (RCA) - on radionuclide leaching. Radionuclide leaching from several PG sources was assessed for gross alpha, gross beta, uranium, and combined radium (226 + 228). Solution pH affected Ra226 mobility, with minimum concentrations exhibited at a pH in the range of 6 to 8. Mobile Ra226 concentrations in RCA blends decreased compared to original PG; Ra226 mobility initially increased at low LR replacements but decreased with increasing mass of LR (50 %-75 %). The data suggest an additional mechanism beyond pH alone impacted Ra226 mobility from the blends, possibly the binding or substitution of radium by elevated concentrations of Ba, Sr, or Ca. Blending with RCA resulted in radionuclide concentrations below respective drinking water thresholds, mitigating leaching concern from PG-RCA road base blends. PG-LR blends can meet regulatory limits when incorporating appropriate PG sources, providing an avenue for PG-amended road base materials. The blending approach reduced Ra226 mobility from PG-amended base, accommodating more PG use, serving as an alternative scenario to end-of-life stacking.

Synergistic effect of rhamnolipid and Bacillus mucilaginosus on detoxification and activation of municipal solid waste incineration fly ash.

In recent years, the substantial increase in municipal solid waste incineration fly ash (MSWIFA) production has made its treatment a critical issue. However, the high toxicity of MSWIFA makes its utilization still in the exploratory stage. In this study, the heavy metal leaching rate, particle size distribution and activity index of MSWIFA were tested to investigate the detoxification and activation effects of Bacillus mucilaginosus on MSWIFA by introducing rhamnolipid. The results show that the microbial treatment can greatly increase the leaching rate of heavy metals in MSWIFA and its 28-day and 90-day activity indexes, especially by the synergistic treatment. For the Bacillus mucilaginosus and rhamnolipid treated MSWIFA (BR-MSWIFA), the maximum leaching rates follow the order from high to low of 85.57% Cr, 78% Cu, 76.38% Zn, 62.78% Pb and 37.65% Mn, while having a low mass loss of less than 5%, which is important for its reuse. Moreover, compared with the untreated MSWIFA (U-MSWIFA), the average particle sizes of Bacillus mucilaginosus treated MSWIFA (B-MSWIFA) and BR-MSWIFA decrease from 8.39 µm to 7.80 µm and 4.31 µm, and the 28-day activity indexes increase from 80.19% to 101.59% and 110.61%. The effect mechanism is that rhamnolipid not only can promote the growth, reproduction, and metabolic acid production of Bacillus mucilaginosus, but also disperse the extracellular polymeric substance (EPS) and MSWIFA particles, thus increase their contact area and the bioleaching. This study provided a theoretical foundation for the harmless treatment and resource utilization of solid wastes containing heavy metals.

Advancements in microbial-mediated radioactive waste bioremediation: A review.

The global production of radioactive wastes is expected to increase in the coming years as more countries have resorted to adopting nuclear power to decrease their reliance on fossil-fuel-generated energy. Discoveries of remediation methods that can remove radionuclides from radioactive wastes, including those discharged to the environment, are therefore vital to reduce risks-upon-exposure radionuclides posed to humans and wildlife. Among various remediation approaches available, microbe-mediated radionuclide remediation have limited reviews regarding their advances. This review provides an overview of the sources and existing classification of radioactive wastes, followed by a brief introduction to existing radionuclide remediation (physical, chemical, and electrochemical) approaches. Microbe-mediated radionuclide remediation (bacterial, myco-, and phycoremediation) is then extensively discussed. Bacterial remediation involves biological processes like bioreduction, biosorption, and bioprecipitation. Bioreduction involves the reduction of water-soluble, mobile radionuclides to water-insoluble, immobile lower oxidation states by ferric iron-reducing, sulfate-reducing, and certain extremophilic bacteria, and in situ remediation has become possible by adding electron donors to contaminated waters to enrich indigenous iron- and sulfate-reducing bacteria populations. In biosorption, radionuclides are associated with functional groups on the microbial cell surface, followed by getting reduced to immobilized forms or precipitated intracellularly or extracellularly. Myco- and phycoremediation often involve processes like biosorption and bioaccumulation, where the former is influenced by pH and cell concentration. A Strengths, Weaknesses, Opportunities, and Threats (SWOT) analysis on microbial remediation is also performed. It is suggested that two research directions: genetic engineering of radiation-resistant microorganisms and co-application of microbe-mediated remediation with other remediation methods could potentially result in the discovery of in situ or ex situ microbe-involving radioactive waste remediation applications with high practicability. Finally, a comparison between the strengths and weaknesses of each approach is provided.

The potential role of iron-carbon micro-electrolysis materials in curtailing lag-phase stimulates kitchen waste anaerobic digestion at different solid contents: Performance, synergistic effect and microbial response.

High-solid anaerobic digestion (HSAD) of kitchen waste was generally faced to the common problems such as systemic acidification, prolonged lag-phase time and low methane production. Iron-carbon micro-electrolysis (ICME) materials exhibited advantages that porous structure, large specific surface area and excellent conductivity. It was beneficial for organic compounds to hydrolysis. Moreover, ICME materials could establish direct interspecies electron transfer (DIET) pathway between bacteria and methanogens. ICME materials were commonly used to enhance the AD of wastewater, but they were rarely applied to HSAD of kitchen waste. In this study, ICME materials were utilized to enhance HSAD of kitchen waste at different solid content conditions. The results showed that the highest cumulative biogas yield (705.23 mL/g VS) was obtained in the experimental group (TS = 10%), which was 94.15% higher than that of the control group. At the same time, the addiction of ICME could shorten lag-phase time. Electrochemical characteristics and XPS analysis showed that ICME materials promoted the release of Fe2+ in the AD system and acceleration of direct interspecies electron transfer between microorganisms. Microbial community analysis showed that ICME materials enriched electroactive bacteria (Proteiniphilum), Methanosarcina, Methanobrevibacter and Methanofollis. Functional gene prediction revealed that ICME materials increased the relative abundance of carbohydrate transport and metabolism and coenzyme transport and metabolism. It provided a potential measure to treat kitchen waste.

Mitigating greenhouse gas emission and enhancing fermentation by phosphorus slag addition during sewage sludge composting.

During the composting of sewage sludge (SS), a quantity of greenhouse gases has been produced. This study aimed to clarify the microbial mechanisms associated with the addition of industrial solid waste phosphorus slag (PS) to SS composting, specifically focusing on its impact on greenhouse gas emissions and the humification. The findings indicated that the introduction of PS increased the temperature and extended the high-temperature phase. Moreover, the incorporation of 10% and 15% PS resulted in a decrease of N2O emissions by 68.9% and 88.6%, respectively. Microbial diversity analysis indicated that PS improved waste porosity, ensuring the aerobic habitat. Therefore, the environmental factors of the system were altered, leading to the enrichment of various functional bacterial species, such as Firmicutes and Chloroflexi, and a reduction of pathogenic bacterium Dokdonella. Consequently, incorporating PS into SS composting represents an effective waste treatment strategy, exhibiting economic feasibility and promising application potential.

Exploring compost production potential and its economic benefits and greenhouse gas mitigation in Addis Ababa, Ethiopia.

The increasing amount of municipal organic waste (MOW) and human excreta (HE) has led to socio-economic and environmental challenges in the cities of developing countries. This study estimated MOW and HE, compost production potential from MOW and HE, and compost application potential for urban agriculture fertilization, economic benefits, soil carbon sequestration, and greenhouse gas (GHG) mitigation in Addis Ababa, Ethiopia, for the period 2025-2050. MOW was forecasted using the Holt-Winters forecasting model. HE was estimated using the daily average rate of HE generation. The compost production potential was estimated using the forecasted MOW and HE. Compost fertilization was determined by considering compost nitrogen (N), phosphorus (P), and potassium (K) and the fertilizer requirements of cereals and vegetables. The economic benefits of compost were determined by considering the price of compost-equivalent urea, NPS, and potassium chloride fertilizers. The mitigation of GHG emissions from compost application was estimated using the IPCC Tier 1 method. The forecasted quantities of MOW, HE, and compost for 2050 are 301, 462, and 343 Gg, respectively. The compost could supply 5 Gg of N and 2.2 Gg of P in 2050, sufficient to fertilize 14,129 ha of vegetable fields. The economic benefits of using compost as a substitute for synthetic fertilizers could reach 10 million USD in 2050. Compost production and application could offset the total GHG emissions of Addis Ababa by 13.1 % (10,241Gg CO2-eq year-1) in 2050. The application of compost generated from MOW and HE in Addis Ababa can substitute synthetic fertilizers, provide economic benefits, and mitigate GHG emissions.

Value-added utilization technologies for seaweed processing waste in a circular economy: Developing a sustainable modern seaweed industry.

The global seaweed industry annually consumes approximately 600,000 tons of dried algal biomass to produce algal hydrocolloids, yet only 15-30% of this biomass is utilized, with the remaining 70-85% discarded or released as scum or wastewater during the hydrocolloid extraction process. This residual biomass is often treated as waste and not considered for further commercial use, which contradicts the principles of sustainable development. In reality, the residual algal biomass could be employed to extract additional biochemical components, such as pigments, proteins, and cellulose, and these ingredients have important application prospects in the food sector. According to the biorefinery concept, recycling various products alongside the principal product enhances overall biomass utilization. Transitioning from traditional single-product processes to multi-product biorefineries, however, raises operating costs, presenting a significant challenge. Alternatively, developing value-added utilization technologies that target seaweed waste without altering existing processes is gaining traction among industry practitioners. Current advancements include methods such as separation and extraction of residual biomass, anaerobic digestion, thermochemical conversion, enzymatic treatment, functionalized modification of algal scum, and efficient utilization through metabolic engineering. These technologies hold promise for converting seaweed waste into alternative proteins, dietary supplements, and bioplastics for food packaging. Combining multiple technologies may offer the most effective strategy for future seaweed waste treatment. Nonetheless, most research on value-added waste utilization remains at the laboratory scale, necessitating further investigation at pilot and commercial scales.

Effect of metakaolin and lime addition on geopolymerization of construction and demolition waste.

Construction and demolition waste generates the largest amount of waste by volume, which threatens sustainable development and adversely affects the environment. These wastes contain a significant amount of aluminosilicates that have the potential to be used as building materials for value-added applications applicable to alternative construction materials. This study aims to synthesize geopolymers from brick powder using metakaolin/lime as additives and compare their physico-mechanical properties. The compressive strengths of the geopolymer products GP-1, GP-2, and GP-3 developed at 28 days from brick powder and metakaolin/lime with the activator solution were found to be 8.35, 21.30, and 25.0 MPa respectively, 2.55 and 2.99 times higher when metakaolin and lime were added. FTIR spectra and SEM-EDX micrographs of the reaction products showed structural changes and formation of aluminosilicate hydrate and calcium silicate hydrate gel with Al2O3/Na2O ratios of 0.75, 1.67, and 1.98 respectively. The reaction products containing SiO2/(SiO2 + Al2O3 + Fe2O3) ratios of 0.70 and 0.76 were found to be desirable. The geopolymer product GP-3 was found to have a higher bulk density and mechanical strength than those of GP-1 and GP-2. These products are found to be very hard, with potential applications in construction industries to conserve the environment.