Investigation Of Anaerobic Digestion With Lanthanum-iron Oxide Under Carbamazepine Stress

Anaerobic digestion（AD）is a technique with large potential to recover methane（CH₄）from organic solid waste/wastewater,contributing to carbon neutrality in wastewater treatment plants,landfills,and industrial parks.The performance and operational stability of AD are influenced by a variety of factors,but the potential impact of pharmaceuticals and personal care products on AD is often overlooked.Carbamazepine,a typical antiepileptic drug,is frequently detected in sewage sludge and has been classified as an urban marker pollutant,its effects on AD have not been systematically explored.Although iron-based additives have been demonstrated to improve the stability and performance of AD,different types of iron-based materials have different modes of action on AD.Therefore,in this study,we systematically investigated the effects of carbamazepine on AD and prepared new iron-based materials,lanthanum-iron oxide nanoparticles（LaFeO₃ NPs）to enhance AD under carbamazepine stress.The specific researches are as follows:（1）Carbamazepine could seriously disturb AD performance,the CH₄ yield decreased from 275.12 to 182.04 m L/g lactic acid as the carbamazepine dosage rose from 0 to 0.14 m M.To better understand how the drug affected AD,model tests were conducted on four stages of hydrolysis,acidification,acetogenesis,and methanogenesis.The model tests indicated that such drug could promote the solubilization of inoculum,thereby releasing polysaccharides and proteins.However,the hydrolysis stage was highly restricted.Enhanced acidification and diminished acetogenesis and methanogenesis led to the accumulation of volatile fatty acids,which ultimately resulted in a significant decrease in CH₄ yield.The level of interference of carbamazepine on AD was concluded as follows:acetogenesis>methanogenesis>hydrolysis>acidification>solubilization.The high-throughput sequencing revealed the abundance of Chloroflexi increased from 21.5%to 26.7%as a main responsibility for the volatile acid accumulation.The acetoclastic methanogen Methanosaeta decreased from 59.86%to 44.78%,while the hydrogenotrophic methanogens Methanobacterium and Methanomassiliicoccus increased from 28%,0.5%to 37.9%and 4.1%,respectively.Although the recovery of CH₄ was limited for clean production,it was more recommendable to recover the volatile fatty acids from organic wastewater with carbamazepine.（2）LaFeO₃ NPs was prepared by a simple sol-gel method and its properties were characterized,while its effects on the acid-and methane-producing phases of two-phase AD were investigated.The CH₄ yield increased from 717.42 in the blank group to800.62 m L/g glucose with 25 mg/L LaFeO₃ NPs.The acid-producing phase was better promoted by LaFeO₃.The highest H₂ yield of 289.8 m L/g glucose was found at 100mg/L of LaFeO₃ NPs,being 47.6%higher than that from the control（196.3 m L/g glucose）.The relative abundance of Firmicutes increased from 54.2%to 67.5%.The large specific surface area of LaFeO₃ NPs provided sufficient sites for the colonization of Firmicutes and increased the bacterial access to nutrients.In addition,the La³⁺gradually released from LaFeO₃ NPs enhanced the transmembrane transport capacity of microbes,promoting glycolytic efficiency and Fe bioavailability,thereby raising hydrogenase content,elevating coenzyme F420 activity,and shifting the H₂ evolution to butyrate pathway for more H₂,volatile acids,and CH₄.（3）The adsorption removal of carbamazepine increased from 0 to 44.30%as the dose of LaFeO₃ NPs was increased from 0 to 200 mg/L,which provided the necessary prerequisites for bioaugmentation.Adsorption reduced the probability of direct contact between carbamazepine and anaerobes,partly alleviating the inhibition of carbamazepine on microbes.The highest CH₄ yield induced by LaFeO₃ NPs（25 mg/L）was 226.09 m L/g lactic acid,increasing by 30.06%compared to the control yield with a recovery to 89.09%of the normal methane yield.Despite the ability of LaFeO₃ NPs to restore normal AD performance,the biodegradation rate of carbamazepine remained below 10%due to its anti-biodegradability.Bioaugmentation was primarily reflected in the enhanced bioavailability of dissolved organic matter,while the intracellular LaFeO₃NPs increased coenzyme F420 activity by binding to humic substances.Under the mediation of LaFeO₃ NPs,a direct interspecies electron transfer system with Longilinea and Methanosaeta as functional bacteria was successfully constructed and the corresponding electron transfer rate was accelerated from 0.021 s^-1 to 0.033 s^-1.LaFeO₃NPs eventually recovered AD performance under carbamazepine stress in an adsorption and bioaugmentation manner.