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JUNCAO, as energy grass, was used in mesophilic anaerobic digestion (MAD) to produce methane, which has a huge market potential in biomass energy. This study was conducted to evaluate the characteristics of MAD of Arundo donax cv. Lvzhou No.1 (Lvzhou No.1) and Pennisetum giganteum z.x.lin (P. giganteum) (the growth cycle of 5 months), and explore the relationship between microbial community structure and its function during MAD process. The results showed that cumulative biogas production and cumulative methane content Lvzhou No. 1 (370.37 mL/g VS and 280.08 mL/g VS) with richer nutrition were higher than those of P. giganteum (313.04 mL/g VS and 233.78 mL/g VS) within 30 days of MAD. And the maximum methane concentration could increase to 78% and 75%, respectively. The volatile fatty acid (VFA) of Lvzhou No. 1 and P. giganteums showed a trend of increasing at first then decreasing, and reached the production peak on the first day (1372.40 mg/L) and second day (1061.18 mg/L), respectively. Hemicellulose of both was preferentially degraded with the highest degradation rate (48.27~77.45%). At last, the microbial community analysis suggested that the dominant bacteria in the MAD system at the phylum level belonged to Firmicutes, Bacteroidetes, and Euryarchaeota. Among them, unidentified_Clostridiales and Ruminofilibacter exhibited dominance in the production of acidic substances in this system, and methanogenic function was mainly associated with Methanosaeta. In conclusion, this study would provide new evidence for MAD of JUNCAO as new energy resources, which would pave the way for large-scale MAD of energy plants in the future. [ABSTRACT FROM AUTHOR]

Disposal of food waste is generally carried out by incineration, composting, or digestion. Anaerobic digestion of food waste is one of the alternatives for the disposal of food waste. The objective of this work was to investigate the effects of mixing speed and agitator type on biogas production from food waste in pilot plant digesters. Biogas production from food waste was carried out at mixing speeds 20, 5 rpm, and intermittent mixing conditions with turbine and propeller agitators. The highest biogas production obtained with intermittent mixing was 125 L and 123 L from turbine and propeller agitator respectively which is 30% higher than biogas obtained in the stratified digester. Lowest biogas production was obtained at a speed of 20 rpm. Kinetic study of anaerobic digestion was carried out by modified Gompertz model which fits well for experimental data with the coefficient of determination (R2) 0.99. Turbine agitator showed the best results with the highest biogas production rate of 9.2 L/day in a minimum hydraulic retention time (HRT) of 17 days. A significant reduction in HRT of 26% was achieved with intermittent mixing of turbine agitator as compared to the stratified digester. The results showed a 99% reduction in COD and a 97% reduction in BOD of effluent from digester with intermittent mixing facility as compared with inlet substrate values. [ABSTRACT FROM AUTHOR]

The anaerobic digestion performance correlates with the functional microbial community. Mesophilic and thermophilic digestions of vegetable waste were conducted, and dynamics of the microbial community were investigated. The mesophilic and thermophilic collapsed stages occurred at organic loading rates of 1.5 and 2.0 g VS/(L d) due to the accumulation of volatile fatty acids with final concentrations of 2276 and 6476 mg/L, respectively. A high concentration of volatile fatty acids caused the severe inhibition of methanogens, which finally led to the imbalance between acetogenesis and methanogenesis. The mesophilic digestion exhibited a higher microbial diversity and richness than the thermophilic digestion. Syntrophic acetate-oxidizing coupled with hydrogenotrophic methanogenesis was the dominant pathway in the thermophilic stable system, and acetoclastic methanogenesis in the mesophilic stable system. The dominant acidogens, syntrophus, and methanogens were unclassified_f__Anaerolineaceae (8.68%), Candidatus_Cloacamonas (19.70%), Methanosaeta (6.10%), and Methanosarcina (4.08%) in the mesophilic stable stage, and Anaerobaculum (12.59%), Syntrophaceticus (4.84%), Methanosarcina (30.58%), and Methanothermobacter (3.17%) in thermophilic stable stage. Spirochaetae and Thermotogae phyla were the characteristic microorganisms in the mesophilic and thermophilic collapsed stages, respectively. These findings provided valuable information for the deep understanding of the difference of the microbial community and methane-producing mechanism between mesophilic and thermophilic digestion of vegetable waste. [ABSTRACT FROM AUTHOR]

This research study evaluates various pre-treatments to improve sewage sludge solubilization prior to treatment by mesophilic anaerobic digestion. Microwave, thermal, and sonication pre-treatments were compared as these pre-treatments are the most commonly used for this purpose. The solubilization of sewage sludge was evaluated through the variation in soluble total organic carbon (sTOC, mg/L) and soluble total nitrogen (sTN, mg/L). Thermal and microwave pre-treatments increased sTOC/VS by 19.2% and 83.4% (VS, total volatile solids), respectively, after applying lower specific energy through (20 kJ/g TS, approximately) (TS, total solids) unlike the sonication pre-treatment, which required 136 kJ/g TS. Although sTN content did not increase significantly with the pre-treatments with respect to sTOC, both showed proportional trends. Sonication pre-treatments allowed the highest increase in volatile fatty acids (VFA) with respect to the raw sewage sludge (15% ∆VFA/sTOC). Methane production with and without pre-treatment was also evaluated. Methane production increased by 95% after applying sonication pre-treatment compared to the methane production of raw sewage sludge. Thermal and microwave pre-treatments entailed lower improvements (29% and 20%, respectively). Economically, thermal pre-treatments were the most viable alternative at real scale. [ABSTRACT FROM AUTHOR]

Polyacrylamide (PAM) is generally employed in wastewater treatment processes such as sludge dewatering and therefore exists in the sludge. Furthermore, it degrades slowly and can deteriorate methane yield during anaerobic digestion (AD). The impact or fate of PAM in AD under thermophilic conditions is still unclear. This study mainly focuses on PAM degradation and enhanced methane production from PAM-added sludge during 15 days of thermophilic (55°C) AD compared to mesophilic (35°C) AD. Sludge and PAM dose from 10 to 50 g/kg TSS were used. The results showed that PAM degraded by 76% to 78% with acrylamide (AM) content of 0.2 to 3.3 mg/L in thermophilic AD. However, it degraded only 27% to 30% with AM content of 0.5 to 7.2 mg/L in mesophilic AD. The methane yield was almost 230 to 238.4 mL g VSS on the 8th day in thermophilic AD but was 115.2 to 128.6 mL/g VSS in mesophilic AD. Mechanism investigation revealed that thermophilic AD with continuous stirring not only enhanced PAM degradation but also boosted the organics release from the sludge with added PAM and gave higher methane yield than mesophilic AD. [ABSTRACT FROM AUTHOR]

Biological treatments, such as activated sludge process, are common methods to treat municipal and industrial wastewaters. However, they produce huge amounts of waste activated sludge (WAS). The excess sludge treatment and disposal are a challenge for wastewater treatment plants due to economic, environmental, and regulatory factors. In this study, photo-Fenton pretreatment (oxidation using hydrogen peroxide and iron catalyst aided with UV light) was optimized using response surface methodology (RSM) and central composite design (CCD) to determine the effects of three operating parameters (HO dosage, HO/Fe molar ratio, and irradiation time) on disintegration and dewaterability of WAS. MLVSS removal, capillary suction time (CST) reduction, sCOD, and EPS were obtained as 70%, 25%, 12,000 mg/L, and 500 mg/L, respectively, at the optimal conditions, i.e., 725 g HO/kg TS, HO/Fe molar ratio 80, and irradiation time 40 min. Two batch-fed completely mixed mesophilic anaerobic digesters were then operated at 15-day solid retention time (SRT) and 37 ± 0.5 °C to compare the digestibility of untreated and photo-Fenton pretreated sludge in terms of volatile solids (VS) reduction, COD removal, and biogas production at steady-state operations. Photo-Fenton pretreatment followed by anaerobic digestion of WAS was very effective and yielded 75.7% total VS reduction, 81.5% COD removal, and 0.29-0.31 m/kg VS·d biogas production rate, compared to 40.7% total VS solid reduction, 54.7% COD removal, and 0.12-0.17 m/kg VS·d biogas production rate for control. Thus, photo-Fenton can be a useful pretreatment step in sludge management. [ABSTRACT FROM AUTHOR]

As antibiotic resistance continues to spread globally, there is growing interest in the potential to limit the spread of antibiotic resistance genes (ARGs) from wastewater sources. In particular, operational conditions during sludge digestion may serve to discourage selection of resistant bacteria, reduce horizontal transfer of ARGs, and aid in hydrolysis of DNA. This study applied metagenomic analysis to examine the removal efficiency of ARGs through thermophilic and mesophilic anaerobic digestion using bench-scale reactors. Although the relative abundance of various ARGs shifted from influent to effluent sludge, there was no measureable change in the abundance of total ARGs or their diversity in either the thermophilic or mesophilic treatment. Among the 35 major ARG subtypes detected in feed sludge, substantial reductions (removal efficiency >90 %) of 8 and 13 ARGs were achieved by thermophilic and mesophilic digestion, respectively. However, resistance genes of aadA, macB, and sul1 were enriched during the thermophilic anaerobic digestion, while resistance genes of erythromycin esterase type I, sul1, and tetM were enriched during the mesophilic anaerobic digestion. Efflux pump remained to be the major antibiotic resistance mechanism in sludge samples, but the portion of ARGs encoding resistance via target modification increased in the anaerobically digested sludge relative to the feed. Metagenomic analysis provided insight into the potential for anaerobic digestion to mitigate a broad array of ARGs. [ABSTRACT FROM AUTHOR]

The removal of four pharmaceutically active compounds, i.e., anti-inflammatory painkiller diclofenac (DCF), lipid-regulating agent clofibric acid (CFA), epilepsy drugs carbamazepine (CBM), and broad-spectrum anti-bacterial agent triclosan (TCS), present in sewage sludge was investigated using anaerobic digestion processes in the mesophilic and thermophilic modes. Sludge retention times (SRTs) were set at 10, 15, and 20 days, respectively, for the mesophilic mode and 7, 15, and 20 days, respectively, for the thermophilic mode. The effective isolation and purification pre-treatment to extract the target compounds from the sewage sludge samples were firstly established, followed by gas chromatography-mass spectrometer analysis to identify and quantify them. The removal efficiencies of the target compounds could be raised to a certain extent with the increase on SRTs, especially under the mesophilic condition. The removal of CFA and TCS under thermophilic condition hardly varied when the SRTs were above 15 days. All the compounds could be partly removed from the sewage sludge under the two temperature conditions, particularly TCS that was reduced by about 74 %. Besides, CFA, firstly reported in this study, could be reduced by maximal 65 %. On the whole, the thermophilic mode was more conducive to the removal of CBM and TCS, but did not have a noticeable effect on the removal of CFA. Furthermore, DCF could be better removed in the mesophilic mode. In addition, NH-N accumulation in this measured range might positively affect the removal of the selected compounds, particularly in the mesophilic mode. [ABSTRACT FROM AUTHOR]