Maximum Cumulative Methane Production Research Articles

Impact of roxithromycin on waste activated sludge anaerobic digestion: Methane production, carbon transformation and antibiotic resistance genes

The macrolide antibiotic roxithromycin is widely detected in varying aquatic environments, especially in the wastewater systems, as an emerging contaminant and leads to significant impacts on the microorganisms involved. In this study, the impact of a shock load of roxithromycin on waste activated sludge (WAS) anaerobic digestion was comprehensively investigated. The biochemical methane potential tests showed that the methane production from WAS anaerobic digestion was significantly inhibited by roxithromycin. With the dosage of roxithromycin increasing from 0 to 1000 μg/L, the maximum cumulative methane production decreased from 163.5 ± 2.6 mL/g VS to 150.9 ± 4.5 mL/g VS. In particular, roxithromycin inhibited the acidogenesis and methanogenesis in WAS anaerobic digestion, leading to the decreased methane production. The methanogenic archaea in the studied system mainly belonged to the genera of Methanoseata, Candidatus Methanofastidiosum and Methanolinea and their relative abundances also decreased with roxithromycin addition. The analysis of antibiotic resistance genes (ARGs) in the digested sludge indicated that the abundances of most ARGs detected in this study were increased with roxithromycin exposure, suggesting the potential of growing antibiotic resistance, which was probably caused by enhancing the effect of esterases, methylases and phosphorylases. This work reveals how roxithromycin affects the WAS anaerobic digestion and the change of ARGs in the anaerobic digestion with roxithromycin exposure, and provides useful information for practical operation.

Effect of different co-treatments of waste activated sludge on biogas production and shaping microbial community in subsequent anaerobic digestion

Different pretreatment approaches enhance hydrolysis and biogas production of waste activated sludge (WAS). However, the best WAS pretreatment method may vary for different purposes. The aim of this study was to compare different combined treatments using potassium ferrate, alkali, and ultrasonication treatment in terms of hydrolysis, biogas production, and microbial community structure during subsequent anaerobic digestion. The soluble chemical oxygen demand (SCOD) increased sharply during sludge pretreatment. Co-treatment with potassium ferrate and ultrasonication (PF + ULT) provided the highest concentration of SCOD (10,206 mg/L) and volatile fatty acids (VFAs) (9160 mg/L). Maximum cumulative methane production, 752.6 mL during 21 days of subsequent anaerobic digestion, was achieved for alkali and ultrasonication (ALK + ULT) co-treated sludge, a 39.3% improvement compared with raw sludge. Our results indicate that PF + ULT and ALK + ULT co-treatments are suitable for methanogenesis in subsequent anaerobic digestion. Co-treatment typically improves biogas production and sludge hydrolysis relative to a single pretreatment. Illumina sequencing of 16S rRNA genes showed that sludge subjected to ALK pretreatment and ALK + ULT co-treatment contained the same predominant populations, and the community structure of PF was similar to PF + ULT. Principal coordinate analysis (PCoA) based on weighted UniFrac distance indicated differences in the microbial communities of the pretreated and raw sludges. The predominant archaeal populations were Methanomassiliicoccus and Methanobacterium in the ALK + ULT and ALK pretreated sludges, and the majority were Methanomassiliicoccus (76.82%) in PF + ULT co-treated sludge, indicating that different pretreatment methods could substantially shape archaeal communities of pretreated sludge. These results reveal that sludge pretreatment not only impacts sludge hydrolysis and biogas production, but also significantly influences the microbial community in subsequent anaerobic digestion.

Mesophilic Anaerobic Co-digestion of Olive-Mill Waste With Cattle Manure: Effects of Mixture Ratio

The co-digestion of agri-food by-products and livestock manure is a feasible alternative for waste management and the recovery of biogas provides an option to generate renewable energy. A series of batch experiments were carried out in order to investigate the mesophilic anaerobic co-digestion of two-phase olive-mill waste (2POMW) and cattle manure (CM) in different mixtures (2POMW:CM = 50:50; 60:40; 75:25; 85:15). In addition, the biodegradability of the co-substrates was studied in order to analyze the performance of the co-digestion process. The results obtained in this study indicate that 2POMW has a low biodegradability since a high soluble organic matter concentration and a low accumulated methane production were obtained at the end of the corresponding biodegradability test. However, CM is more easily biodegradable in mesophilic anaerobic conditions. The co-digestion of both wastes produced an enhancement of the hydrolytic-acidogenic phase, increasing the organic matter potentially bioavailable as volatile fatty acids (VFAs) and the biogas productivity, as a consequence of the subsequent degradation of VFAs by methanogens. However, an accumulation of VFA, principally propionic acid, was observed in the reactors with higher proportions of 2POMW. The volatile solids (VS) removal increased with the 2POMW percentage of the mixture up to 75% fresh weight. The increase of 2POMW above 75% led to a decrease in total VS removal. Moreover, a decrease in methane production was observed for the 85:15 mixture, as a consequence of the high concentration of propionic acid, which is a known inhibitor of methanogenesis. The maximum cumulative methane production and methane yield were achieved in the 75:25 mixture with values of 18.70 L and 112.40 LCH4/kgVSadded, respectively. Compared with 2POMW, the co-digestion produced an increase of 264-319% in the volume of accumulated methane (L), 293-351% in the methane yield (LCH4/kgVSadded) and 312-342% based on the VS consumed (LCH4/kgVSremoved). These results suggest that the mixture of these agro-industrial by-products could be effective to enhance biogas production and organic matter removal from 2POMW.

Feasibility of dry anaerobic digestion of beer lees for methane production and biochar enhanced performance at mesophilic and thermophilic temperature

This study investigated the feasibility of dry anaerobic digestion using beer lees as substrate and the effect of cow manure-derived biochar addition on dry anaerobic digestion performance at mesophilic and thermophilic temperature, respectively. With TS content of 25%, maximum cumulative methane production and yield were achieved to be 5230 ± 91 mL d−1 and 220.1 ± 7.7 mL g−1 VS at mesophilic condition and 7386 ± 134 mL d−1 and 310.4 ± 9.2 mL g−1 VS at thermophilic condition in the control cultures. The biochar addition has a positive effect in improving dry anaerobic digestion performance. The maximum cumulative methane production and yield in the cultures with 10 g L−1 biochar were substantially improved by 82.9% and 82.6% at mesophilic condition and 47.2% and 46.8% at mesophilic condition when compared to the control.

Effect of COD/SO42- Ratio on Anaerobic Digestion of Penicillin Bacterial Residues

In order to assess the sulfate-induced inhibition of anaerobic digestion of antibiotic manufacturing bio-waste. The effect of COD/SO42- ratio on biogas production potential and substrate utilization characteristics during the acidogenic phase of anaerobic digestion of penicillin bacterial residues were investigated through batch experiments. The results obtained indicated that biogas production was gradually enhanced after 10 days of anaerobic digestion. However, the maximum cumulative methane production probably exceeded about 208 mL·g-1(on TS basis) since COD/SO42-≥3. Because adaptive acclimation, more than 71% COD removal, which may have been converted to methane, was achieved. Consequently, at COD/SO42-≤1.5, methane production was suppressed by 49% and 100% when the organics and SO42- removal rates were less than 17% and 5%, respectively. This indicated that methanogens and sulfate-reducing bacteria were inhibited at high sulfate loading rates. In addition, the COD balance analysis revealed that less than 9.1% of the COD was converted to methane. However, 5.0%-9.0% of the COD was used for sulfate reduction. This means that methanogens are more susceptible than sulfate-reducing bacteria to sulfide-induced inhibition. The S balance showed that the reduced sulfate was mainly present as sulfide in the digester. A small fraction of it was present as hydrogen sulfide in the biogas. The analysis of substrate utilization characteristics during the acidogenic phase revealed that methanation of soluble protein was initiated after methanation of soluble carbohydrate.

Simultaneous ammonia stripping and anaerobic digestion for efficient thermophilic conversion of dairy manure at high solids concentration

A major challenge to take high rate advantage of thermophilic anaerobic digestion (AD) is overcoming ammonia inhibition without adding any significant cost to the process. A concept of thermophilic AD with simultaneous ammonia stripping was tested for treating dairy manure at high total solids concentration (TS%) as an attempt to address this challenge. The results showed that ammonia inhibition occurred at 1.8–2.4 g/L total ammonia nitrogen (TAN) concentration which corresponded to 10% TS as a threshold concentration. Thermophilic AD of dairy manure efficiency at the threshold TS% was significantly improved by simultaneously stripping ammonia with the optimum stripping rate of 1 L min−1. The required time for reaching stable state was 4 days shorter than control, and the highest methane content (56.5–75.5%) was obtained. The ammonia stripping strategy maintained TAN level below the inhibition limit of 1.5 g/L throughout AD process. The maximum cumulative methane production of 192.3 L/kg-volatile solids (VS) was obtained, which was 2.3-fold the control. Therefore, simultaneous ammonia stripping overcame the ammonia inhibition on thermophilic AD of dairy manure at the threshold TS%. The proposed concept simplified the system by combining ammonia stripping and thermophilic AD within the same digester.

Effect of Methanogenesis of Residue from Thermal Pre-treatment Sludge by Anaerobic Fermentative Hydrogen Production

The municipal sludge of Wastewater treatment plants generate a mass of municipal sludge is becoming an extremely environment issue. Effective utilization of the sludge to generate benefits concern many scholars. This research worked systematically to study the condition of gas production of sludge by thermal pre-treatment and compared a large differance among the maximum cumulative methane production in the sludge of high temperature thermal treatment. The inoculum via 75°C thermal pretreatment for 10min mixed sludge substrates by different temperature pre-treatment for 30min. The optimum methane production was obtained from 160°C, and the 120°C was worse in the methane produciton. The max accumulated hydrogen and methane production were 3.57mL and 235.97mL respectively of 160°C; the max accumulated methane production was 193.24mL of 120°C. Compared the metabolic process of anaerobic fermentation of methane, the degradation of organic matter in the sludge substrate by 160°C for heat treatment was better than that of 120°C.

Methane production from wheat straw with anaerobic sludge by heme supplementation

Wheat straw particles were directly used as substrate for batch anaerobic digestion with anaerobic sludge under 35°C to evaluate the effects of adding heme on methane production. When 1mg/l heme was added to the fermentation process with no agitated speed, a maximum cumulative methane production of 12227.8ml was obtained with cumulative methane yield of wheat straw was 257.4ml/g-TS (total solid), which was increased by 20.6% compared with 213.5ml/g-TS of no heme was added in the reactor. Meanwhile, oxido-reduction potential (ORP) level was decreased, the activity of coenzyme F420 was significantly improved and NADH/NAD+ ratio were the highest than other experimental groups. These results suggest that heme-supplemented anaerobic sludge with no agitated speed may be providing a more reductive environment, which is a cost-effective method of anaerobic digestion from biomass waste to produce methane with less energy consuming.

Experimental studies and mathematical modeling of an up-flow biofilm reactor treating mustard oil rich wastewater

Bioremediation of lipid-rich model wastewater was investigated in a packed bed biofilm reactor (anaerobic filter). A detailed study was conducted about the influence of fatty acid concentration on biomethanation of the high-fat liquid effluent of edible oil refineries. The biochemical methane potential (BMP) of the liquid waste was reported and maximum cumulative methane production at the exit of the reactor is estimated to be 785 ml CH 4 (STP)/(g VSS added). The effects of hydraulic retention time (HRT), organic loading rate (OLR) and bed porosity on the cold gas efficiency or energy efficiency of the bioconversion process were also investigated. Results revealed that the maximum cold gas efficiency of the process is 42% when the total organic load is 2.1 g COD/l at HRT of 3.33 days. Classical substrate uninhibited Monod model is used to generate the differential system equations which can predict the reactor behavior satisfactorily.

The use of a specific function to estimate maximum methane production in a batch‐fed anaerobic reactor

AbstractA readily biodegradable substrate was used to assess the value of using a mathematical function of y = ymaxexpm/x as a simplified method of determining the maximum methane production (Gmax) in a batch anaerobic reactor. Experimental results to test the method used three different initial substrate loadings in pre‐acclimatised completely mixed anaerobic reactors. Gas production was found to follow a typical trend that has previously been described by first order reaction kinetics; for the purpose of fitting the linearisation, it requires a value for maximum cumulative methane production. Use of the modified specific function to yield the equation G = Gmaxexpm/t showed that the experimental gas production curve could be estimated with a high degree of similarity. This was confirmed by a statistical analysis using the method of residuals which gave a correlation coefficient (R2) greater than 0.97 between experimental and estimated values. Using a graphical linearisation of the specific function produced a simplified method of predicting Gmax. The value obtained was then used in a first order kinetic model to derive the specific coefficient rate (Ko), which was in agreement with other methods used for its determination. Copyright © 2004 Society of Chemical Industry