Anaerobic Biological Systems Research Articles

The important role of high sludge concentration in anaerobic biological systems with low COD/SO42- sulfate-containing wastewater predicted by machine learning: Insights from microbial community and metabolic pathways

In anaerobic biological systems, sulfate reduction efficiency is influenced by multiple factors synergistically, particularly under low chemical oxygen demand-to-sulfate ratio (COD/SO42-) conditions. Enhancing sulfate reduction efficiency under low COD/SO42- conditions is challenging due to the deficiency of electron donors. In this study, two anaerobic systems were operated with a gradual decrease in COD/SO42-. The primary objective was to investigate the correlations among various influential factors, the efficacy of sulfate reduction, and the progression of microbial communities. The results showed that even with a decrease in COD/SO42- to 0.1, the sulfate reduction efficiency could reach 70% under high sludge concentration. Machine learning predictions identified sludge concentration as the most influential factor under low COD/SO42- conditions. The functional gene analysis confirmed that the sulfate reduction under high sludge concentration was primarily governed by the dissimilatory pathway and exhibited minimal reliance on COD/SO42-. These findings provide theoretical support and a novel approach for the anaerobic biological treatment of sulfate-containing wastewater under low COD/SO42- conditions.

Prediction of artificial neural network for sulfate removal from wastewater and application analysis of key factors in anaerobic biological system

Prediction and application of the SO42- removal performance of an anaerobic biological system was conducted through the integration of artificial neural networks (ANNs). The present investigation involved the utilization of Radial Basis Function Neural Networks (RBFNN) and Multilayer Perceptron Neural Networks (MLPNN) for more rigorous prediction of SO42- removal rates. The findings of the study demonstrated that reducing the chemical oxygen demand (COD) to sulfate ratio (COD/SO42-) led to a consequent decline in the removal of SO42-. In the context of predicting SO42- reduction under conditions characterized by low COD/SO42-, MLPNN exhibited superior suitability when compared to RBFNN. The sulfate removal process was primarily influenced by various operation parameters, with the COD/SO42- being particularly influential. The proposed sensitive MLPNN model contributed to the prediction of effluent quality and potential real-time adjustments of wastewater treatment operations. The predictive evaluation of effective sulfate (SO42-) removal from sulfate-rich wastewater under various operation parameters is a significant point of guideline.

Assessing the effect of green tuff as a novel natural inorganic carrier on methane-producing activity of an anaerobic sludge microbiome

The upflow anaerobic sludge blanket (UASB) process is an anaerobic biological system that is widely used for the treatment of a variety of wastewater owing to its benefits such as low energy requirements and energy recovery as methane gas; however, unstable reactor performance is often observed. To solve this problem, several inert inorganic carriers and polymer materials have been studied for stabilization of the sludge microbial community and promotion of methane production. In this study, we demonstrate the effects of green tuff (GT) as a novel natural inorganic carrier on methane-producing activity (MPA) in combination with syntroph/methanogen-utilizable substrates and on the microbial community assembly of methanogenic batch cultures fed with granular sludge collected from UASB reactors treating milk- (MMW) or soy sauce- (SSW) manufacturing wastewater. The MPAs of MMW cultures with GT were 4.56- (propionate), 2.01- (n-butyrate), 1.37- (n-valerate), and 1.22- (benzoate) fold higher than those without GT. Likewise, SSW cultures with GT showed 1.34- (acetate) and 1.42- (propionate) fold higher MPA than those without GT. These results indicate that GT has potential to enhance MPAs during methanogenic degradation of these substrates. According to 16S rRNA transcripts-based community profiling, populations of syntrophic bacteria (Syntrophobacter and Smithella) and hydrogenotrophic methanogens (Methanobacterium and Methanolinea) in the cultures with GT were higher than in those without GT. Therefore, GT can be a potential solution for the activation of syntrophic partnerships and improvement/stabilization of reactor performance.

Immobilized redox mediators on modified biochar and their role on azo dye biotransformation in anaerobic biological systems: Mechanisms, biodegradation pathway and theoretical calculation

In this study, a novel solid-phase redox mediator (RM) was manufactured via immobilizing anthraquinone-2-sulfonate (AQS) onto modified biochar (BC). The RM was used to enhance the anaerobic granular sludge (AGS) driven anaerobic biodegradation of azo dyes. Prepared at the optimal pyrolysis temperature of 550 ℃, the AQS modified BC550 exhibits a higher adsorption capacity of about 12.81% toward AQS compared to that of commercial granular activated carbon (GAC). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses showed that BC550-AQS contained more redox moieties (quinone and C = O) than GAC-AQS, indicating that the BC550 is suitable as a carrier of immobilized AQS. During the 36-h reaction, incubation of BC550-AQS as the solid-phase RM obviously enhanced the capacity of AGS (BC550-AQS + AGS), evidenced by the maximum percentage of Reactive Red 2 (RR2) decolorization (92.27%), which increased up by 80.55% and 14.48% compared to the controls (BC550-AQS, 17.95%) and (GAC-AQS + AGS, 78.61%). Besides, BC550-AQS exhibits good reusability and a higher RR2 decolorization rate (per AQS dosage) over 15 consecutive cycles. The mechanism of biodegradation pathway of RR2 initiated by BC550-AQS was studied using liquid chromatography-mass spectrometry and chemical computation. Density-functional theory calculations successfully predict that the RR2 biodegradation pathway mainly includes azo bond cleavage and electron attraction with a stronger electron affinity. This work not only proposes a deep insight into the biodegradation pathway of RR2 by employing BC550-AQS in an anaerobic biological system but also develops effective solid-phase RMs for efficient removal of contaminants from wastewaters by biological treatment.

Characterization of hydrogen production and microbial community shifts in microbial electrolysis cells with L-cysteine

L-cysteine is used to improve efficiency in anaerobic biological systems as an oxygen scavenger, electron shuttle and substrate source. The performance of MEC by addition of L-cysteine was investigated during start-up and operation phases, respectively. Results showed that the maximum current density of 6.36 ± 0.14 A/m2, hydrogen yield of 1.08 ± 0.05 m3/m3 and energy efficiency of 130% were achieved with L-cysteine adding during operation phase. By contrast, the addition of L-cysteine during the start-up phase reduced the energy efficiency by more than 30%. The microbial community analysis revealed that a higher microbial community richness and diversity were achieved, the enrichment of Sulfuricurvum, Sulfurospirillum, Desulfovibrio and other electroactive microorganisms indicated their relative abundance could be regulated by L-cysteine during start-up phase when L-cysteine was added. This study provided an alternative method to enhanced hydrogen production and a better understanding of the mechanism of L-cysteine action in MEC performance.

Effects of electron donor on biological nitrogen removal efficiency and microbial community distribution of anaerobic biological system

Effects of electron donor on biological nitrogen removal efficiency and microbial community distribution of anaerobic biological system

Membrane Bioreactors for Anaerobic Treatment of Wastewaters

Anaerobic biological treatment systems can offer a number of advantages over their aerobic counterparts. The operational costs associated with anaerobic systems are typically lower than with aerobic systems, and anaerobic systems also generate less waste sludge. In addition, the energy associated with the biogas produced during anaerobic biological treatment can potentially be recovered. However, to date, the use of conventional anaerobic biological systems for the treatment of dilute wastewaters has been relatively limited. The present study was designed to address this current knowledge gap. The specific objectives of the present study were (1) to assess and compare the treatment performance of external and a submerged membrane AnMBRs operated at different OLRs when treating a low strength municipal wastewater at a relatively low temperature, (2) to assess and compare the membrane filtration characteristics of mixed liquors generated in external and submerged membrane AnMBRs, (3) to assess and compare the membrane filtration characteristics of a mixed liquor in AnMBRs when filtering through inorganic and organic membranes, and (4) to assess and compare the membrane filtration characteristics of the mixed liquors generated in AnMBRs to the mixed liquor generated in an aerobic MBR operated with the same influent wastewater. This title belongs to WERF Research Report Series ISBN: 9781843397601 (Print) ISBN: 9781780403946 (eBook)

Economic importance and application options of some industrial sludge conditioned by different treatment methods

Industrial sludge was obtained from four industries: aluminium extrusion, brewery, pharmaceutical and textile processing factory and treated by aerobic, anaerobic, physicochemical, combined aerobic/physicochemical and combined anaerobic/physicochemical methods. The results showed that the final destination of the sludge would determine the type and degree of treatment required for the sludge. Physicochemical method generally increases the quantity of sludge solids, thus making the sludge suitable for land reclamation; also, the firmer and denser floc characteristics of the physicochemicallly treated sludge makes the methods a better alternative if conditioned sludge are to be used to reinforce cement for brick making. Biological treatment methods (aerobic and anaerobic) can be used to reduce the quantity of sludge before disposal. Solids destruction is closely related to biogas production. If using sludge as a source of fuel is the focus, the anaerobic biological system may be the best option. Aerobic biological method and the combined aerobic/physicochemical methods are good options for ammonia reduction. Anaerobic biological method is best for improving the nitrogen content and hence the protein content of sludge so as to use the waste sludge as feeds for poultry birds and livestock. Economic values, application and disposal options of the various sludge are discussed.

Reporter proteins for in vivo fluorescence without oxygen

Fluorescent reporter proteins such as green fluorescent protein are valuable noninvasive molecular tools for in vivo real-time imaging of living specimens. However, their use is generally restricted to aerobic systems, as the formation of their chromophores strictly requires oxygen. Starting with blue-light photoreceptors from Bacillus subtilis and Pseudomonas putida that contain light-oxygen-voltage-sensing domains, we engineered flavin mononucleotide-based fluorescent proteins that can be used as fluorescent reporters in both aerobic and anaerobic biological systems.

Novel biological removal of hazardous chemicals at trace levels

Of recent concern is the removal of toxic compounds in wastewaters, soils, and groundwater to concentrations in the low microgram per litre level or less. Threshold limits to bioremediation exist and must be considered in biological treatment schemes to achieve such limits. These limits may be related to reaction kinetics or thermodynamics. Techniques for removing compounds below threshold levels exist that rely on appropriate approaches such as plug flow treatment. Novel biological methods exist for removal of refractory contaminants to low levels. Examples are provided for removal of trace levels of chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE), that employ dehalorespiration under anaerobic conditions or cometabolism under aerobic conditions. These approaches are currently being used in engineered systems or through natural attenuation for remediation of soils and groundwater. Successful results offer insights for similar removals of trace chemicals in both aerobic and anaerobic biological systems for treatment of wastewaters and sanitary landfills.

Volatile fatty acids as indicators of process imbalance in anaerobic digestors

In continuously stirred tank reactor experiments, with manure as substrate at thermophilic temperatures, the use of volatile fatty acids (VFA) as process indicators was investigated. Changes in VFA level were shown to be a good parameter for indicating process instability. The VFA were evaluated according to their relative changes caused by changes in hydraulic loading, organic loading or temperature. Butyrate and isobutyrate together were found to be particularly good indicators. Butyrate and isobutyrate concentrations increased significantly 1 or 2 days after the imposed perturbation, which makes these acids suitable for process monitoring and important for process control of the anaerobic biological system. In addition it was shown in a batch experiment that VFA at concentrations up to 50 mM did not reduce the overall methane production rate. This showed that VFA accumulation in anaerobic reactors was the result of process imbalance, not the cause of inhibition, thus justifying the use of VFA as process indicators.

Innovative Biological Systems for Anaerobic Treatment of Grain and Food Processing Wastewaters

AbstractThe application of two innovative fixed film and suspended growth anaerobic biological systems to the treatment of grain and food processing wastewaters is discussed. A fluidized bed fixed film system and a suspended growth membrane system are described. The technical and economic factors dictating which system is selected for treatment of a specific industrial wastewater are discussed. Case history results from successful operation of full‐scale, demonstration, and pilot‐scale systems treating respectively, soy whey, cheese whey, and wheat flour processing wastewaters are presented.