Effects of Feedstock Sources on Inoculant Acclimatization: Start-up Strategies and Reactor Performance

Correlations and impact of anaerobic digestion operating parameters on the start-up duration: Database construction for robust start-up guidelines

Anaerobic digestion (AD) has become a popular technique for organic waste management while offering economic and environmental advantages. As AD becomes increasingly prevalent worldwide, research efforts are primarily focused on optimizing its processes. During the operation of AD systems, the occurrence of unstable events is inevitable. So far, numerous conclusions have been drawn from full and lab-scale studies regarding the driving factors of start-up perturbations. However, the lack of standardized practices reported in start-up studies raises concerns about the comparability and reliability of obtained data. This study aims to develop a knowledge database and investigate the possibility of applying machine learning techniques on experimentation-extracted data to assist start-up planning and monitoring. Thus, a standardized database referencing 75 cases of start-up of one-stage wet continuously-stirred tank reactors (CSTR) processing agricultural, industrial, or municipal organic effluent in mono-digestion from 31 studies was constructed. 10 % of the total observations included in this database concern failed start-up experiments. Then, correlations between the parameters and their impacts on the start-up duration were studied using multivariate analysis and a model-based ranking methodology. Insights into trends of choices were highlighted through the correlation analysis of the database. As such, scenarios favoring short start-up duration were found to involve relatively low retention times (average initial and final hydraulic retention times, (HRTi) and (HRTf) of 26.25 and 20.6 days, respectively), high mean organic loading rates (average OLRmean of 5.24 g VS·d-1·L -1) and the processing of highly fermentable substrates (average feed volatile solids (VSfeed) of 81.35 g L-1). The model-based ranking of AD parameters demonstrated that the HRTf, the VSfeed, and the target temperature (Tf) have the strongest impact on the start-up duration, receiving the highest relative scores among the evaluated AD parameters. The database could serve as a reference for comparison purposes of future start-up studies allowing the identification of factors that should be closely controlled.

Organic matter removal performance, pathway and microbial community succession during the construction of high-ammonia anaerobic biosystems treating anaerobic digestate food waste effluent

This study aimed to establish anaerobic biosystems which could tolerate high ammonia, and investigate the microbial community structure in these reactors. High-ammonia anaerobic biosystems that could tolerate 3600 mg L^-1 total ammonia nitrogen (TAN) and 1000 mg L^-1 free ammonia nitrogen (FAN) were successfully established. The removal efficiencies of COD and total volatile fatty acids (TVFAs) in R1 with dewatered sludge as inoculum were 68.8% and 69.2%, respectively. The maximum methane production rate reached 71.7 ± 1.0 mL CH₄ L^-1 d^-1 at a TAN concentration of 3600 mg L^-1. The three-dimension excitation-emission matrix analysis indicated that both easily degradable organics and refractory organics were removed from ADFE in R1 and R2. Functional microorganisms which could bear high ammonia were gradually enriched as TAN stress was elevated. Lysinibacillus, Coprothermobacter and Sporosarcina dominated the final bacterial community. Archaeal community transformed to hydrogenotrophic methanogen. The synergy of Coprothermobacter and Methanothermobacter undertook the organic matter degradation, and was enhanced by increasing TAN stress. This study offers new insights into anaerobic bioremediation of ammonia-rich wastewater.

Improving anaerobic digestion of chicken manure under optimized biochar supplementation strategies

Anaerobic digestion of chicken manure was carried out in this study basing on central composite design to identify the most optimal strategy for biochar supplementation. Model of cumulative methane production (CMP) was established by using response surface methodology. The optimal conditions predicted accordingly, including manure loading of 51.8 g VS/L, biochar dosage of 3.3% VS_manure, and cellulose loading of 98.0 g VS/L, were expected to maximize CMP, i.e., 294 mL/g VS_manure. The results also demonstrated that biochar dosage and its interaction with manure loading were key factors with significant impact on CMP. Biochar dosage higher than 3.5% VS_manure was observed to weaken the transformation of organic substances to methane. Higher dosage of biochar could considerably reduce concentration of organic acids, total ammonia nitrogen, as well as soluble salts. Verification experiment supported validity of the optimal strategy and provided data for cost assessment, which showed positive cost balances from biochar supplementation.

Anaerobic Co-Digestion of Oil Sludge with Corn Stover for Efficient Biogas Production

The feasibility of anaerobic co-digestion for the utilization of oil sludge was verified using corn stover, to assess the influence of different raw material ratios and inoculum volumes on the properties of the generated gas. The anaerobic co-digestion method is a novel treatment technology, which may help to solve the problem of pollution by hazardous waste oil sand from the oil exploitation and smelting process. Results showed that single-oil sludge was not suitable for gas production as a digestive substrate due to the lack of organic materials and possible hazardous materials. With the increase in the quality of exogenous organic matter (corn stover), the cumulative gas production volume was proportional to the amount of corn stover material added. It was established that when the mass ratio of corn stover to oil sludge was 4:1, the gas production performance was optimal, with a cumulative gas yield of 1222.5 mL using an inoculum volume of 30 mL. The results of this study provide a fundamental parameter baseline for the treatment of oil sludge and the improvement of gas production efficiency.

Aerobic degradation of 2- and 3-fluoroaniline in mixed culture systems and microbial community analysis

Among three monofluoroanilines, 2-fluoroaniline (2-FA) and 3-fluoroaniline (3-FA) exhibit relatively poor biodegradability. This work examined their degradation characteristics in a mixed culture system and also analyzed the microorganism community. After acclimation for 58 d and 43 d, the high removal efficiency of 100% of 2-FA and 95.3% of 3-FA was obtained by adding 25 mg L^-1 of 2-FA or 3-FA to the two reactors, respectively. In addition, the high defluorination rates of 2-FA and 3-FA were observed to be 87.0% and 89.3%, respectively. The degradation kinetics showed that the maximum specific degradation rates of 2-FA and 3-FA were (21.23 ± 0.91) mg FA (g•VSS·h)^-1, and (11.75 ± 0.99) mg FA (g•VSS·h)^-1, respectively. PCR-DGGE analysis revealed that the unique bacteria degrading 2-FA were mainly composed of six genera (Novosphingobium, Bradyrhizobium, Aquaspirillum, Aminobacter, Ochrobactrum, and Labrys), and five genera that degraded 3-FA (Ochrobactrum, Aquaspirillum, Lachnobacterium, Bradyrhizobium, and Variovorax). Analysis of the key catabolic enzyme activities indicated that the simultaneous hydroxylation and dehalogenation were involved in monooxygenase elimination of 2-FA and conversion of 3-FA to 4-fluorocatechol by dioxygenase, indicating that enriched mixed cultures were effective to metabolize 2-FA or 3-FA by unconventional pathways to prevent the accumulation of toxic metabolites.