Anaerobic digestion of spectinomycin mycelial residues pretreated by thermal hydrolysis: removal of spectinomycin and enhancement of biogas production

Quantitation of antibiotics in fresh fermentation medium by hydrophilic interaction chromatography mass spectrometry

This study presents the development of a sophisticated liquid chromatography-mass spectrometry approach leveraging hydrophilic interaction chromatography (HILIC) for the quantification of kanamycin and spectinomycin in fermentation media. The method was validated per International Council for Harmonisation guidelines, demonstrating robust linearity, precision, and accuracy. To mitigate pronounced matrix effects common to complex fermentation matrices, sample preparation was thoroughly optimized with solid-phase extraction employing MCX sorbent, thereby enhancing recovery rates and minimizing analytical interference. The validated protocol demonstrated high correlation coefficients (R > 0.998), underscoring its robustness and reliability for the accurate quantification of antibiotics in challenging bioprocess environments, providing a valuable analytical tool for bioreactor system monitoring.

Volatile fatty acids recovery and antibiotic degradation from erythromycin fermentation residues by combined thermal pretreatment and anaerobic fermentation: Insights into microbial communities and metabolic pathways

High resistance of erythromycin has been the key factor restricting the disposal of erythromycin fermentation residues (EFR). Considering the high sensitivity of erythromycin to acidic conditions, anaerobic fermentation may be a good approach for EFR treatment, through which pH decreases along with the volatile fatty acids (VFA) accumulation. This study firstly explored the EFR treatment by combined thermal pretreatment and anaerobic fermentation. Results showed that thermal pretreatment and anaerobic fermentation exhibited a synergistic effect on erythromycin removal. Erythromycin concentration decreased to 20.0 mg/L with the maximum removal rate of 60.0%, which was 140% and 71.4% higher than erythromycin removal by sole thermal pretreatment and anaerobic fermentation. Thermal pretreatment induced the increased VFA production by 22.3% with the highest VFA concentration of 5325.4 mg/L. Microbial analysis shows that thermal pretreatment stimulated erythromycin degradation and VFA production by increasing the microbial diversity and enriching the functional enzymes involved in acetate-producing pathways.

Understanding the mechanism of enhanced anaerobic biodegradation of biodegradable plastics after alkaline pretreatment

Biodegradable plastics (BPs) tend to replace conventional plastics, which increases the amount of BP waste entering the environment. The anaerobic environment exists extensively in nature, and anaerobic digestion has become a widely used technique for organic waste treatment. Many kinds of BPs have low biodegradability (B_D) and biodegradation rates under anaerobic condition due to the limitation of hydrolysis, so they still have harmful environmental consequences in anaerobic environment. There is an urgent need to find an intervention method to improve the biodegradation of BPs. Therefore, this study aimed to investigate the effectiveness of alkaline pretreatment in accelerating the thermophilic anaerobic degradation of ten widely used BPs, such as poly (lactic acid) (PLA), poly (butylene adipate-co-terephthalate) (PBAT), thermoplastic starch (TPS), poly (butylene succinate-co-butylene adipate) (PBSA), cellulose diacetate (CDA), etc. The results showed that NaOH pretreatment significantly improved the solubility of PBSA, PLA, poly (propylene carbonate) (PPC), and TPS. Except for PBAT, pretreatment with an appropriate NaOH concentration could improve the B_D and degradation rate. The pretreatment also reduced the lag phase in the anaerobic degradation of BPs such as PLA, PPC, and TPS. Specifically, for CDA and PBSA, the B_D increased from 4.6 % and 30.5 % to 85.2 % and 88.7 %, with increments of 1752.2 % and 190.8 %, respectively. Microbial analysis indicated that NaOH pretreatment promoted the dissolution and hydrolysis of PBSA and PLA and the deacetylation of CDA, which contributed to rapid and complete degradation. This work not only provides a promising method for improving the degradation of BP waste but also lays the foundation for its large-scale application and safe disposal.

Base-catalyzed hydrolysis of spectinomycin in aqueous solutions: Kinetics and mechanisms

Hydrolysis plays an imperative role in the abiotic transformation process of antibiotics in aqueous solutions. However, little information is available on the hydrolysis process of spectinomycin (an aminocyclitol antibiotic). This study systematically investigated the spectinomycin hydrolysis kinetics and mechanisms under different pH via experiments and density functional theory (DFT) computation. Hydrolysis was first conducted in a pure water system under pH of 4.0-9.0 and temperature of 25 °C, 50 °C and 70 °C, respectively. Results showed that hydrolysis was highly dependent on pH and temperature. When pH > 6.0, spectinomycin hydrolysis was accelerated by the catalysis of OH^-. Meanwhile, the hydrolysis rate increased with the elevation of temperature. Then, for the reference of the practical environment, the general base-catalyzed hydrolysis and mechanisms were studied under environmental pH 6.0-8.0 and 25 °C. DFT calculation demonstrated that base-catalyzed hydrolysis of spectinomycin could be more thermodynamically and kinetically favorable based on the lower Gibbs free energies of reaction and Gibbs free energies of activation. Further, instead of specific base catalysis (OH^-), the general base catalysis (e.g., phosphate buffer) was also found to promote hydrolysis efficiency. The antibacterial activity and ecotoxicities of the hydrolysis product were analyzed to be lower than the precursor, thereby decreasing the environmental impact of spectinomycin.

Enhanced medium-chain fatty acids production from Cephalosporin C antibiotic fermentation residues by ionizing radiation pretreatment

Antibiotic fermentation residues (AFRs) have been classified as hazardous waste in China. Anaerobic fermentation may be a good approach for AFRs treatment, through which value-added chemicals could be obtained simultaneously. This study firstly explored medium-chain fatty acids (MCFAs) production from AFRs through two-stage anaerobic fermentation, and gamma radiation was adopted for AFRs pretreatment. The results showed that both antibiotics removal and MCFAs production from AFRs were significantly promoted by gamma radiation pretreatment. No residual Cephalosporin C (CEP-C) was detected in gamma radiation treated groups after fermentation. Highest MCFAs concentration of 90.55 mmol C/L was obtained in 50 kGy treated group, which was 2.22 times of the control group. Genera that were positively correlated with MCFAs production were enriched in gamma radiation treated groups, like genus Paraclostridium, Terrisporobacter, Caproiciproducens and Sporanaerobacter, while genera that were negatively correlated with MCFAs production were diminished during the chain elongation process, like genus Bacteroides and NK4A214_group. Enzymes analysis suggested that the promoted MCFAs production was induced by the enrichment of functional enzymes involved in Acetyl-CoA formation and RBO pathway. This work suggested that gamma radiation pretreatment and two-stage anaerobic fermentation could achieve the dual benefits of AFRs treatment and value-added chemicals recovery.

Preparation of phosphoric acid modified antibiotic mycelial residues biochar: Loading of nano zero-valent iron and promotion on biogas production

Antibiotic mycelial residues (AMRs), as recyclable hazardous waste, can realize efficient utilization by reasonable treatment. To solve the problems of undeveloped pore structure and low specific surface area existed in AMR biochar, this study first modified biochar by phosphoric acid (H₃PO₄) to prepare PBC (H₃PO₄-modified biochar). Then, PBC was used as carrier to load nano zero-valent iron (nZVI) for preparation of nZVI/PBC. Finally, the biochar materials were used to promote anaerobic digestion (AD) of corn straw. The results showed that H₃PO₄-modification can effectively improve the specific surface area, pore structure, and electron donating capacity of AMRs biochar. The using of PBC as carrier to load nZVI attenuated the agglomeration of nZVI particles. Both PBC and nZVI/PBC improved the AD process, with biogas yield enhanced by 29.63% and 29.26%, respectively. The nZVI/PBC exhibited higher ability in maintaining the stability of AD system and promotion of fiber degradation than PBC.

Feasibility of Coupling Anaerobic Digestion and Hydrothermal Carbonization: Analyzing Thermal Demand

Anaerobic digestion is a biological process with wide application for the treatment of high organic-containing streams. The production of biogas and the lack of oxygen requirements are the main energetic advantages of this process. However, the digested stream may not readily find a final disposal outlet under certain circumstances. The present manuscript analyzed the feasibility of valorizing digestate by the hydrothermal carbonization (HTC) process. A hypothetical plant treating cattle manure and cheese whey as co-substrate (25% v/w, wet weight) was studied. The global performance was evaluated using available data reported in the literature. The best configuration was digestion as a first stage with the subsequent treatment of digestate in an HTC unit. The treatment of manure as sole substrate reported a value of 752 m3/d of biogas which could be increased to 1076 m3/d (43% increase) when coupling an HTC unit for digestate post-treatment and the introduction of the co-substrate. However, the high energy demand of the combined configurations indicated, as the best alternative, the valorization of just a fraction (15%) of digestate to provide the benefits of enhancing biogas production. This configuration presented a much better energy performance than the thermal hydrolysis pre-treatment of manure. The increase in biogas production does not compensate for the high energy demand of the pre-treatment unit. However, several technical factors still need further research to make this alternative a reality, as it is the handling and pumping of high solid slurries that significantly affects the energy demand of the thermal treatment units and the possible toxicity of hydrochar when used in a biological process.

Thermal treatment's enhancement on high solid anaerobic digestion: effects of temperature and reaction time

The methane production rate of high solid anaerobic digestion (HSAD) was poor although it was a promising technology with the advantages of small reactor, low energy consumption, and less digestate. In our research before, thermal treatment was proved to enhance HSAD's methane production rate via both batch experiments and continuous experiments of swine manure. However, the effect or investigation of thermal treatment's temperature-time combinations was not yet reported. In this study, swine manure was firstly thermally treated in 500-mL glass bottles with 400-mL work volume at 45-65 °C for 1-4 days. HSAD experiment of 10% solid content was then set up. The VS ratio of substrate to inoculum was 1:1. Thermal treatment at 45 °C (3 days), 55 °C (1 day), and 65 °C (3 days) could obtain the highest methane production rate, which was around 40% higher. Kinetics analysis suggested that the degradation of swine manure was quite different at different temperatures. Furthermore, energy assessment indicated that "thermal treatment + HSAD" had significant advantages in improving HSAD economic feasibility, because the improved methane production rate could compensate for the extra energy utilized for thermal treatment. Heat treatment at 45 °C (4 days) was preferred when the heating equipment was limited. Heat treatment at 55 °C (1 day) was preferred when the floor space and reactor volume were restricted. Heat treatment at 65°C (3 days) was preferred when the requirement of the digestate's sanitary condition is strict.