Material and microbial perspectives on understanding the role of biochar in mitigating ammonia inhibition during anaerobic digestion.

With the increasing adoption of carbon-based strategies to enhance methanogenic processes, there is a growing concern regarding the correlation between biochar properties and its stimulating effects on anaerobic digestion (AD) under ammonia inhibition. This study delves into the relevant characteristics and potential mechanisms of biochar in the context of AD system under ammonia inhibition. The introduction of optimized biochar, distinguished by rich CO bond, abundant defect density, and high electronic capacity, resulted in a significant reduction in the lag period of anaerobic digestion system under 5.0 g/L ammonia stress, approximately by around 63 % compared to the control one. Biochar helps regulate the community structure, promotes the accumulation of acetate-consuming bacteria, in the AD system under ammonia inhibition. More examinations show that biochar promotes direct interspecies electron transfer in AD system under ammonia inhibition, as evidenced by diminished levels of bound electroactive extracellular polymeric substances, increased abundance of electroactive bacteria, and notably, the up-regulation of direct interspecies electron transfer associated genes, including the conductive pili and Cytochrome C genes, as revealed by meta-transcriptomic analysis. Additionally, gene expression related to proteins associated with ammonium detoxification were found to be up-regulated in systems supplemented with biochar. These findings provide essential evidence and insights for the selection and potential engineering of effective biochar to enhance AD performance under ammonia inhibition.

Process and kinetics of azo dye decolourization in bioelectrochemical systems: effect of several key factors.

This study explored the influence of several key factors on the process and kinetics of azo dye decolourization in bioelectrochemical systems (BESs), including cathode potential, dissolved oxygen (DO) concentration of catholyte and biofilm formed on the cathode. The results show that azo dye methyl orange (MO) decolourization in the BES could be well described with the pseudo first-order kinetics. The MO decolourization efficiency increased from 0 to 94.90 ± 0.01% and correspondingly the reaction rate constant increased from 0 to 0.503 ± 0.001 h(-1) with the decrease in cathodic electrode potential from -0.2 to -0.8 V vs Ag/AgCl. On the contrary, DO concentration of the catholyte had a negative impact on MO decolourization in the BES. When DO concentration increased from zero to 5.80 mg L(-1), the MO decolourization efficiency decreased from 87.19 ± 4.73% to 27.77 ± 0.06% and correspondingly the reaction rate constant reduced from 0.207 ± 0.042 to 0.033 ± 0.007 h(-1). Additionally, the results suggest that the biofilm formed on the cathode could led to an adverse rather than a positive effect on azo dye decolourization in the BES in terms of efficiency and kinetics.

Enhancement of azo dye decolourization in a MFC-MEC coupled system.

Microbial fuel cells (MFCs) have shown the potential for azo dye decolourization. In this study, a MFC-MEC (microbial electrolysis cell) coupled system was established in order to enhance azo dye decolourization, and the influence of several key factors on reactor performance was evaluated. Moreover, a theoretical analysis was conducted to find the essential preconditions for successfully develop this MFC-MEC coupled system. The results indicate that the decolourization rate in the coupled system had a 36.52-75.28% improvement compared to the single MFC. Anodic acetate concentration of both the MFC and the MEC showed a positive effect on azo dye decolourization, while the cathodic pH of both MEC and MFC in the range of 7.0-10.3 had an insignificant impact on reactor performance in the coupled system. The theoretical analysis reveals that the MFC should have higher short-circuit electricity generation than the MEC before connecting together for a successful coupled system.

Hydrodynamics of an electrochemical membrane bioreactor.

An electrochemical membrane bioreactor (EMBR) has recently been developed for energy recovery and wastewater treatment. The hydrodynamics of the EMBR would significantly affect the mass transfers and reaction kinetics, exerting a pronounced effect on reactor performance. However, only scarce information is available to date. In this study, the hydrodynamic characteristics of the EMBR were investigated through various approaches. Tracer tests were adopted to generate residence time distribution curves at various hydraulic residence times, and three hydraulic models were developed to simulate the results of tracer studies. In addition, the detailed flow patterns of the EMBR were acquired from a computational fluid dynamics (CFD) simulation. Compared to the tank-in-series and axial dispersion ones, the Martin model could describe hydraulic performance of the EBMR better. CFD simulation results clearly indicated the existence of a preferential or circuitous flow in the EMBR. Moreover, the possible locations of dead zones in the EMBR were visualized through the CFD simulation. Based on these results, the relationship between the reactor performance and the hydrodynamics of EMBR was further elucidated relative to the current generation. The results of this study would benefit the design, operation and optimization of the EMBR for simultaneous energy recovery and wastewater treatment.

[Enhanced hydrolysis and acidification of waste activated sludge by alkyl polyglycosides].

The effects of biosurfactant alkyl polyglycosides (APG) on the hydrolysis and acidification of waste activited sludge including dosage of APG and hydrolysis time were investigated. It was found that APG reduced the tension of sludge hydrolysate, promoting sludge hydrolysis. The concentrations of SCOD, protein and soluble carbonhydrate reached the maximum within 12 h at the optimal dosage of 0.2 g x g(-1) TSS, rising from 4 280.2, 1 122.9 and 246.5 mg x L(-1) to 6481.1, 1 639.3 and 1205.8 mg x L(-1), respectively, and the short-chain fatty acids (SCFAs) concentration increased from 1309.9 mg x L(-1) to 2221.6 mg x L(-1) simultaneously, the percentage of individual SCFA changed as well, and the time required to reach the maximal SCFAs concentration will be prolonged with the increase of dosage. With increasing APG dosage, a-glucosidase relative enzyme activities increased from 1.5 to 2.5, while protease relative enzyme activity increased from 1.4 to 1.9 at low dosages and decreased to 1.5 at high dosages. Regardless of the biosurfactant APG, alpha-glucosidase and protease enzyme activities decreased along with the hydrolysis time. The pH showed a tendency of first decreasing and then increasing.