Improving antibiotic removal and anaerobic digestion performance of discarded cefradine pellets through thermo-alkaline pretreatment.

Discarded cefradine pellets (DCP) as the hazardous wastes contain lots of bioavailable sucrose. Anaerobic digestion (AD) may be a promising technology for treating DCP, achieving dual goals of waste treatment and resource recovery. However, high concentration of cefradine will inhibit the AD process. This study applied thermo-alkaline pretreatment (TAP) to remove cefradine and improve the AD performance of DCP. Around 95% cefradine could be degraded to different intermediate degradation products (TPs) in TAP at optimal condition, and hydrolysis and hydrogenation were the main degradation pathways. Quantitative structure-activity relationship analysis indicated that the main TPs exhibited lower toxicity than cefradine, and DCP residues after TAP were almost not toxic to E. coli K12 and B. subtilis growth by antibacterial activity analysis. Therefore, TAP promoted the biomethane yield in AD of DCP residues (274.74 mL/g COD), which was 1.91 times that of control group. Besides, compared to control group, final cefradine concentrations in liquids and sludge were significantly decreased in AD system with TAP, lowering environmental risk and indicating stronger prospect for process application. Microbiological analysis revealed that acidogens (Macellibacteroides, Bacteroides), syntrophs (Syntrophobacter, Syntrophorhabdus), and acetoclastic Methanosaeta were enriched in AD system with TAP, which contributed to improving AD performance of DCP.

Enhancing anaerobic digestion performance of oxytetracycline-laden wastewater through micro-nano bubble ozonation pretreatment.

This study investigated the potential of micro-nano bubble (MNB) ozonation pretreatment to eliminate oxytetracycline (OTC) from wastewater and improve subsequent anaerobic digestion (AD) performance. The findings revealed that MNB ozonation achieved efficient OTC oxidation (>99 % in 60 min), and significantly enhanced methane production by 51 % compared to conventional ozonation (under 30 min of pretreatment). Additionally, MNB ozonation resulted in a decrease in the soluble chemical oxygen demand and reduced volatile fatty acid accumulation compared to conventional ozonation. Furthermore, the study sheds light on the profound impact of OTC and its oxidation by-products on the sludge microbiome. Exposure to OTC and its oxidation by-products resulted in alterations in extracellular polymeric substances composition and led to significant shifts in microbial community structure. This study highlights the promise of MNB ozonation as an effective approach for pharmaceutical pollutant removal and the optimization of AD performance in wastewater treatment, with implications for improved environmental sustainability.

Response of methanogenic system to long-term polycyclic aromatic hydrocarbon exposure: Adsorption and biodegradation, performance variation, and microbial function assessment.

Phenanthrene (PHE) as a typical polycyclic aromatic hydrocarbon (PAH) is prevalent and harmful to organisms in petroleum-polluted sites. The effects of PHE concentration levels on performance, microbial community and functions in methanogenic system were comprehensively investigated by an operation of UASB reactor (198 days) and a series of batch tests. The results found that PHE was prone to accumulate in reactor by sludge adsorption (Final concentration = 12.53 mg/g TS Sludge), which posed significant influences on methanogenic system. The removal of chemical oxygen demand (COD), NH4+-N and volatile fatty acids (VFAs) in reactor were reduced with PHE accumulation. Meanwhile, microbes with higher ATPase secrete more EPS activity to self-protect against PHE toxicity. Sequencing analysis showed that PHE interfered significantly diversity and structure of microbial community. For bacteria, PHE was toxic to Bacteroidetes and Latescibacteria, while syntrophs (f_Syntrophaceae, Syntrophorhabdus, etc.) involved in VFAs oxidation and aromatic organics degradation were tolerant of PHE stress. For archaea, acetoclastic methanogens (Methanosaeta) abundance was continuously diminished by 45.1% under long-term PHE exposure. Further functions analysis suggested that microbial community accelerated amino acid metabolism, energy metabolism and xenobiotics biodegradation & metabolism to satisfy physiological demanding under PHE stress. Combining batch tests of methanogenic metabolism proved that acetoclastic methanogenesis was negatively affected by PHE due to inhibition of functional enzymes (acetate kinase, phosphate acetyltransferase, etc.) expression. These findings may provide the basis for enhancing bioremediation of PAH pollution in anaerobic environment.

The dosage-effect of biochar on anaerobic digestion under the suppression of oily sludge: Performance variation, microbial community succession and potential detoxification mechanisms.

This study investigated the dosage-effect of biochar on the suppressed mesophilic digestion of oily sludge (OS) containing naphthalene (recalcitrant compound) and starch (easily bioavailable substrate). Methanogenesis was inhibited in control with OS, where biomethane yield (63.33 mL/gVS) was obviously lower than theoretical yield (260.55 mL/gVS). With adding optimal dose of biochar (0.60 g/gVS OS), the highest CH4 yield (138.41 mL/gVS) was 2.19 times of control. Meanwhile, the efficiencies of hydrolysis, acidogenesis and acetogenesis were significantly enhanced. However, excessive biochar (4.80 g/gVS OS) caused negative effects with methanogenic efficiency diminished by 32.5% and lag phase prolonged by 5.72 h. Dissolved organic matter (DOM) analysis showed that humic acid-like and fulvic acid-like components percentages of fluorescence regional integration were decreased because of the adsorption of biochar. In addition, biochar mediating interspecies electron transfer selectively enriched electroactive fermentation bacteria (Clostridium and Bacteroides) and acetoclastic Methanosaeta, which was responsible for promoting mesophilic digestion performance. The functional genes related to metabolism and environmental information processing were potentially activated by biochar. Above results indicate that moderate biochar application may mitigate the bio-toxicity suppression of OS, which help to provide a promising pathway for reinforcing oily wastes bio-treatment.

[Bmim]FeCl4 mediated inhibition and toxicity during anaerobic digestion: Dose-response kinetics, biochar-dependent detoxification and microbial resistance.

[Bmim]FeCl4, or 1­butyl­3-methylimidazolium tetrachloroferrate, is a typical ionic liquid (IL). Its recyclable, magnetic, multicomponent, and solvent-free nature makes it a particularly attractive ionic liquid for use in industrial processes. Despite its widespread use, the potential hazards that [Bmim]FeCl4 might pose to the environment, including productive microorganisms, have not been explored. In this study, the dose-response of [Bmim]FeCl4 in anaerobic digestion (AD) was investigated to assess the potential toxification and biochar-dependent detoxification in microbial communities, including enzymatic activity and molecule docking dynamics. Our results showed that methane production (31.52 mLmax/gVS) was sharply inhibited following [Bmim]FeCl4 treatment. Moreover, increasing the dosage of [Bmim]FeCl4 caused more dissolved organic matter (DOM) to be generated. Interestingly, 0.4 g/L of [Bmim]FeCl4 could stimulate the high activity of microbial hydrolase and ATPase. However, a higher concentration of 2.65 g/L prevented these enzymatic processes from continuing. At the cellular level, higher concentration of [Bmim]FeCl4 (>0.4 g/L) increased malondialdehyde (MDA) levels, leading to a higher cell lethal rate and weakening of the secondary structures of protein (especially, the amide I region). At the molecular level, the competitive H-bonding in the active sites caused low activity and consummated more energy. At the community level, structural equation modeling (SEM) revealed that [Bmim]FeCl4 and biochar were the main drivers for microbial community succession. For instance, high [Bmim]FeCl4 (8 g/L) benefited the growth of Clostridium sensu_stricto (from ≤1% to 27%). It is worth mentioning that biochar reversed the inhibition with high α-diversity, which caused a resurgence in the activity of previously inhibited ATPase and hydrolase. H2-trophic methanogens (Methanolinea and Methaofastidisoum) were sensitive to [Bmim]FeCl4 and decreased linearly while acetoclastic methanogens (Methanosaeta) were unchanged. These findings were consistent with the short-term activity tests and further verified by functional analysis.

Single and simultaneous effects of naphthalene and salinity on anaerobic digestion: Response surface methodology, microbial community analysis and potential functions prediction.

Polycyclic aromatic hydrocarbons (PAHs) are a persistent and prevalent class of pollutants in petroleum-contaminated saline environment, which pose potential harm to organisms. Researches on anaerobic biodegradation of PAHs are gradually emerging, but the response of anaerobic microorganisms to salinity changes and the co-effects of salinity and PAHs in anaerobic digestion (AD) system have seldom been reported. Thus, we investigated the variations of AD system performance and anaerobic microbial community caused by different concentrations of naphthalene (Nap) or/and NaCl based on Box-Behnken Design (0 mg/L ≤ Nap ≤150 mg/L, 0 g/L ≤ NaCl ≤25 g/L). The promoted efficiencies of acidogenesis and methanogenesis were found in presence of moderate NaCl or Nap, but high salinity (NaCl >4.4 g/L) weakened AD performance. Moreover, the high salinity (NaCl >4.4 g/L) and Nap resulted in reduced microbial Ca2+ Mg2+- ATPase activity, poor EPS secretion and the highest difference of the microbial operational taxonomic units (OTUs), and synergistically inhibited AD process. Microbiological analysis revealed that the relative abundance of Clostridium and acetoclastic Methanosaeta was increased by 2.01 times and 2.17 times in single Nap treated group compared to control. With the simultaneous addition of NaCl and Nap, Proteiniphilum and hydrogenotrophic methanogens (Methanobacterium, Methanofollis, and Methanolinea) occupied the major abundance. Potential functions prediction indicated that high salinity could disrupt the co-metabolism between carbohydrate metabolism and Nap degradation. This study provides basis for anaerobic bioremediation of PAHs-polluted saline environment.