Anaerobic stabilization of waste activated sludge at different temperatures and solid retention times: Evaluation by sludge reduction, soluble chemical oxygen demand release and dehydration capability

Investigating functional mechanisms in the Co-biodegradation of lignite and guar gum under the influence of salinity

The biodegradation of guar gum by microorganisms sourced from coalbeds can result in low-temperature gel breaking, thereby reducing reservoir damage. However, limited attention has been given to the influence of salinity on the synergistic biodegradation of coal and guar gum. In this study, biodegradation experiments of guar gum and lignite were conducted under varying salinity conditions. The primary objective was to investigate the controlling effects and mechanisms of salinity on the synergistic biodegradation of lignite and guar gum. The findings revealed that salinity had an inhibitory effect on the biomethane production from the co-degradation of lignite and guar gum. The biomethane production declined with increasing salinity levels, decreasing from 120.9 mL to 47.3 mL. Even under 20 g/L salt stress conditions, bacteria in coalbeds could effectively break the gel and the viscosity decreased to levels below 5 mPa s. As salinity increased, the removal rate of soluble chemical oxygen demand (SCOD) decreased from 55.63% to 31.17%, and volatile fatty acids (VFAs) accumulated in the digestion system. High salt environment reduces the intensity of each fluorescence peak. Alterations in salinity led to changes in microbial community structure and diversity. Under salt stress, there was an increased relative abundance of Proteiniphilum and Methanobacterium, ensuring the continuity of anaerobic digestion. Hydrogentrophic methanogens exhibited higher salt tolerance compared to acetoclastic methanogens. These findings provide experimental evidence supporting the use of guar gum fracturing fluid in coalbeds with varying salinity levels.

A data-driven approach for revealing the linkages between differences in electrochemical properties of biochar during anaerobic digestion using automated machine learning

Biochar is commonly used to enhance the anaerobic digestion of organic waste solids and wastewater, due to its electrochemical properties, which intensify the electron transfer of microorganisms attached to its large surface area. However, it is difficult to create biochar with both high conductivity and high capacitance, which makes selecting the right biochar for engineering applications challenging. To address this issue, two Auto algorithms (TPOT and H2O) were applied to model the effects of different biochar properties on anaerobic digestion processes. The results showed that the gradient boosting machine had the highest predictive accuracy (R2 = 0.96). Feature importance analysis showed that feedstock concentration, digestion time, capacitance, and conductivity of biochar were the main factors affecting methane yield. According to the two-dimensional (2D) partial dependence plots, high-capacitance biochar (0.27-0.29 V·mA) is favorable for substrates with low-solid content (< 19.6 TS%), while the high-conductivity biochar (80.82-170.58 mS/cm) is suitable for high-solids substrates (> 20.1 TS%). The software, based on the optimal model, can be used to obtain the ideal range of biochar for AD trials, aiding researchers in practical applications prior to implementation.

Peroxydisulfate activation and versatility of defective Fe3O4@MOF-808 for enhanced carbon and phosphorus recovery from sludge anaerobic fermentation

Although being viewed as a promising technology for reclamation of carbon and phosphorus from excess sludge, anaerobic fermentation (AF) grapples with issues such as a low yield of volatile fatty acids (VFAs) and high phosphorus recovery costs. In this study, we synthesized Fe3O4@MOF-808 (FeM) with abundant defects and employed it to simultaneously enhance VFAs and phosphorus recovery during sludge anaerobic fermentation. Through pre-oxidization of sludge catalyzed by FeM-induced peroxydisulfate, the soluble organic matter increased by 2.54 times, thus providing ample substrate for VFAs production. Subsequent AF revealed a remarkable 732.73 % increase in VFAs and a 1592.95 % increase in phosphate. Factors contributing to the high VFAs yield include the non-biological catalysis of unsaturated Zr active sites in defective FeM, enhancing protein hydrolysis, and the inhibition of methanogenesis due to electron competition arising from the transformation between Fe(III) and Fe(II) under Zr influence. Remarkably, FeM exhibited an adsorption capacity of up to 92.64 % for dissolved phosphate through ligand exchange and electrostatic attractions. Furthermore, FeM demonstrated magnetic separation capability from the fermentation broth, coupled with excellent stability and reusability in both catalysis and adsorption processes.

Innovative cation exchange-driven carbon migration and recovery patterns in anaerobic fermentation of waste activated sludge

Despite numerous treatments have been developed to enhance anaerobic fermentation of waste activated sludge, the innovative cation exchange (CE) approach has been rarely reported, little attempt was conducted to revealcarbon source fate. The interphase carbon balance was illustrated to clarify endogenous carbon dissolution, biotransformation,and recovery patterns. By CE-mediated divalent cation removal, almost 34.72 % of particulate carbon sources were dissolved in 2-day treatment, corresponding to soluble carbon content of 1165.58 mg C/L. Most of the originally dissolved carbon sources (58.01-66.81 %) were bio-transformed to volatile fatty acids with high bioavailability, while the further transformation to biogas was inhibited, contributing to recoverable carbon source accumulation. Overall, 21.38 % of total solid carbon sources were recovered through 8-day fermentation, the carbon extraction was implemented by solid-liquid separation with carbon loss of 14.21-22.91 %, manifesting the valid carbon recovery of 85.05-87.96 mg C/g VSS. Such CE-driven carbon recovery provided negentropy benefits in sustainable cycle economy.

Sugarcane-bagasse-ash in enhanced mesophilic Co-digestion for biogas and nutrient recovery: A concept of developing rural circular bioeconomy

Conductive agro-industrial wastes as accelerants in the anaerobic digestion (AD) of organic waste is a good technique for developing a rural circular economy, such as producing bioenergy and biofertilizer. This study disclosed the a role of sugar cane bagasse ash (SCBA) in enhancing the bioenergy (biogas) yield and digestate fertility via anaerobic co-digestion (AcoD) of buffalo dung (BD) and vegetable residue (VR) under mesophilic conditions (37 ᴼC). Firstly, an optimal BD/VR ratio (1:3) was determined based on biogas yield by introducing five different BD/VR ratios (1:0, 3:1, 1:1, 1:3, and 0:1) into AcoD systems. Secondly, the biogas yield was increased further by adding SCBA at five different concentrations (0, 0.5, 1, 1.5, and 2 wt%). Experimental results disclosed that the 1.5 wt% of SCBA gave the highest cumulative biogas yield (153.67 mL/g VS), COD removal rate (31.18%), and fertility (5.08%). Moreover, a framework is suggested to understand the role of SCBA in the enhanced DIET mechanism. This work documents an environmentally friendly and economical technique for developing a rural circular bioeconomy via the AD of organic agro-waste.

Biogas energy generated from livestock manure in China: Current situation and future trends

This article investigates the current status of the livestock industry (cattle, pigs, sheep, and poultry) in China and assesses the potential for biogas production from anaerobically digested livestock manure. According to calculation results based on the latest data of livestock released by the National Bureau of Statistics of China in 2018, China produced 2 × 10¹² kg of manure pollution in 2017, with pig waste representing the largest single manure source. Biogas that can be converted from high organic containing manure is a kind of clean bioenergy with low carbon footprint. In 2017, the energy potential from manure-produced biogas was about 5.74 × 10¹²-6.73 × 10¹² MJ, which corresponds to 4-5% of China's total energy demand. Correlation analysis between biogas production and the livestock industry showed that crop production had significant effects on manure-generated biogas production. However, it is necessary to address the challenges when applying AD technology. Bioenergy potential from manure will be lost during material collection and transportation. Although large-scale livestock farming remains controversial, this type of farming can improve the energy recovery rate of livestock manure. How to gain benefits and maintain sustainable development is also a bottleneck for AD promotion. Reducing energy input in AD projects as well as enhancing the efficiency of methanogenesis of livestock manure are key factors for achieving a high net output of biogas projects. More inclusive strategies and a broader vision should be adopted to allow stakeholders to benefit from manure-generated biogas projects.

Static-magnetic-field coupled with fly-ash accelerant: A powerful strategy to significantly enhance the mesophilic anaerobic-co-digestion

The anaerobic-co-digestion (AcoD) of dairy-manure (DM) and aloe-peel-residue (ALR) waste is enhanced by combining static-magnetic-field (SMF) and fly-ash (FA). Varying SMF intensities (5-30 mT) were applied to the co-digestion digesters containing the optimum FA concentration (1.5 wt.%), which were selected from co-digestion systems with a varying FA (0-2 wt.%). All experimental groups exhibit the greater COD removal rates (51.56-64.19%) and cumulative biogas yields (604.14-671.64 mL/g VS) than reference group (37.77% and 433.19 mL/g VS). The digester with optimum FA concentration (1.5 wt.%) under 5 mT shows the highest biogas yield (671.64 mL/g VS), and exhibits superior digestate stability (45.4%) and fertility (7.01%) for fertilizer utilization. A powerful strategy for understanding the underlying mechanism of the SMF and FA accelerant in an enhanced AcoD system is proposed. This work documents an innovative technique for an enhanced AcoD system using the SMF coupled with FA accelerant.

Biogas production, waste stabilization efficiency, and hygienization potential of a mesophilic anaerobic plug flow reactor processing swine manure and corn stover

Swine manure and corn stover are abundant agricultural wastes which contribute to greenhouse gas (GHG) emissions, nutrient runoff leading to eutrophication, and a biosafety risk with respect to improper swine manure handling. Anaerobic co-digestion (AcoD) of swine manure and corn stover can mitigate these negative impacts while producing biogas as a renewable energy source. Semi-continuous mesophilic plug flow reactor (PFR operation) was studied during a step-wise increase in organic loading rate (OLR) over the range of 0.25-4.7 kg volatile solids added (VS) m^-3 d^-1, which corresponded to total solids content (TS) of 1.5-9.0%. Process stability was observed at all OLR, with the highest total biogas yield and methane content of 0.674 ± 0.06 m^-3 kg^-1 and 62%, respectively, at 0.25 kg m^-3 d^-1. As OLR and TS increased, VS reduction decreased and volatile fatty acids (VFA) increased due to shorter hydraulic retention times (HRT). Hygienization potential was assayed using fecal indicator bacteria (FIB), with some groups being reduced (E. coli, fecal coliforms) and others not (Clostridia spp., fecal enterococci). Lignocellulolytic enzyme activity trended upward as OLR was increased, highlighting changes in microbial activity in response to feeding rate.

Effects of digestion time in anaerobic digestion on subsequent digestate composting

Digestion time (DT) in anaerobic digestion (AD) on performance of subsequent digestate composting regarding compost maturity and greenhouse gas (GHG) emission was investigated. Digestates for composting were obtained after anaerobically digested mixture of dairy manure, corn stalks, and tomato residues (48:32:20, volatile solids based) with DT of 15, 30, and 45 days, respectively. Digestates were composted with corn stalks (85:15, wet weight based). Results showed approximately 30% and 70% of biochemical methane potential (342.0 L/kg VS_feedstock) were obtained when DT of 15 and 30 days. Digestate co-composting with cornstalks could be initiated effectively and reduced GHG emissions by 18.9-29.0% compared to compost with raw materials. DT of 30 and 45 days digestate composting cause benefit on germination index. DT of 45 days had the highest net power production in combine AD and composting system. DT of 30 days digestate composting was optimum choice for compost maturity and GHG emissions.

Use of solid residue from thermal power plant (fly ash) for enhancing sewage sludge anaerobic digestion: Influence of fly ash particle size

The influence of fly ash particle size on methane production and anaerobic biodegradability was evaluated. Assays with different fly ash particle sizes (0.8-2.36mm) at a concentration of 50mg/L were ran under mesophilic conditions. In anaerobic processes operating with fly ash, greater removal of both volatile total and suspended solids, chemical oxygen demand (total and soluble) was achieved, with an increase of methane production between 28% and 96% compared to the control reactors. The highest increase occurred at ash particles sizes of 1.0-1.4mm. The metal concentrations in the digestates obtained after anaerobic digestion of sewage sludge are far below those considered as limiting for the use of sludge in soils.