Process of rice straw degradation and dynamic trend of pH by the microbial community MC1

Bioaugmentation with methanogens cultured in a micro-aerobic microbial community for overloaded anaerobic digestion recovery

Anaerobic digestion (AD) is widely used for conversion of waste materials into biogas, but inhibition of methane production caused by overloading can be a major problem. The micro-aerobic microbial community MC1 was used to successfully culture methanogens, Methanosarcina acetivorans C2A and Methanosaeta thermophila NBRC 101360. The maximum 16S rRNA gene concentrations of Methanosarcina acetivorans C2A and Methanosaeta thermophila NBRC101360 were 1.06 × 10⁶ and 1.35 × 10³ copies/mL, respectively. The five key bacteria in MC1 were quantified to assess the effect of inoculation on the abundances of the bacteria in the mixed culture. The original MC1 total 16S rRNA gene concentration was 1.93 × 10⁸ copies/mL, and the total 16S rRNA gene concentration had increased to 4.79 × 10⁹ copies/mL on day 9 (p < 0.05). The proportions of the key strains in MC1+MST had changed by day 9. Cells were harvested and used to bioaugment and increase the pH values of the high- and medium-temperature anaerobic systems. After bioaugmentation, thermophilic AD recovered well. The cumulative amounts of gas produced were 44.78% and 28.28% higher in the MC1+MST and MC1 groups, respectively, than the sterilized control. The MC1+MST group gave better results than the chemical addition control group (CaCO₃). There was no clear effect of bioaugmentation in mesophilic AD. When compared with traditional pure culture of methanogens as inoculants, methanogen cultivation in MC1 was simple and there was no need to separate and purify the target strains. This simplified methanogenic bioaugmentation agent was useful to study the mechanism of bioaugmentation for the recovery from low pH inhibition, showing the potential for practical application.

Microbial Degradation of Zearalenone by a Novel Microbial Consortium, NZDC-6, and Its Application on Contaminated Corncob by Semisolid Fermentation

A novel microbial consortium (NZDC-6) was screened and characterized to detoxify the estrogenic mycotoxin zearalenone (ZEA), which commonly contaminates maize and is a major threat to food and health security. We found NZDC-6 to be thermophilic and highly effective, with a 90.3% ZEA degradation ratio at an optimum temperature of 60 °C. NZDC-6 was also effective at degrading the more estrogenic ZEA cognates, α-zearalenol (α-ZAL) and β-zearalenol (β-ZAL), with >90% degradation ratios. To evaluate a practical application, ZEA-contaminated corncobs were treated with NZDC-6 via semisolid fermentation. Measurements of physicochemical parameters and 16S microbial diversity and redundancy analysis (RDA) indicated that ZEA removal was most efficient at a low corncob solid content (< 5%), as a high solid content overwhelmed the microbial metabolic load, leading to increased dissolved oxygen and lowered pH. Our results demonstrate that the control of environmental variables is crucial for effective ZEA microbial removal in practical applications.

Pretreatment of non-sterile, rotted silage maize straw by the microbial community MC1 increases biogas production

Using microbial community MC1 to pretreat lignocellulosic materials increased the yield of biogas production, and the substrate did not need to be sterilized, lowering the cost. Rotted silage maize straw carries many microbes. To determine whether such contamination affects MC1, rotted silage maize straw was pretreated with MC1 prior to biogas production. The decreases in the weights of unsterilized and sterilized rotted silage maize straw were similar, as were their carboxymethyl cellulase activities. After 5d pretreatment, denaturing gradient gel electrophoresis and quantitative polymerase chain reaction results indicated that the proportions of five key strains in MC1 were the same in the unsterilized and sterilized groups; thus, MC1 was resistant to microbial contamination. However, its resistance to contamination decreased as the degradation time increased. Following pretreatment, volatile fatty acids, especially acetic acid, were detected, and MC1 enhanced biogas yields by 74.7% compared with the untreated group.

Enhancing anaerobic digestion of cotton stalk by pretreatment with a microbial consortium (MC1)

Microbial pretreatment is beneficial in some anaerobic digestion systems, but the consortia used to date have not been able to effectively increase methane production from cotton stalk. In this study, a thermophilic microbial consortium (MC1) was used for pretreatment in order to enhance biogas and methane production yields. The results indicated that the concentrations of soluble chemical oxygen demand and volatile organic products increased significantly in the early stages of pretreatment. Ethanol, acetic acid, propionic acid, and butyric acid were the predominant volatile organic products in the MC1 hydrolysate. Biogas and methane production yields from cotton stalk were significantly increased following MC1 pretreatment. In addition, the methane production rate from the treated cotton stalk was greater than that from the untreated sample.

Comparison and evaluation of concurrent saccharification and anaerobic digestion of Napier grass after pretreatment by three microbial consortia

Napier grass is potentially a viable feedstock for biofuel production. The present study investigated biological pretreatment of Napier grass by three microbial consortia followed by saccharification and anaerobic digestion. The pretreatment efficiencies of three microbial consortia were compared in terms of degradation ability, saccharide and biogas yield. The lignocellulose loss rates of Napier grass varied largely. The biomass pretreated by the consortium WSD-5 gave 43.4% and 66.2% total sugar yield under low and moderate loadings of commercial enzyme mixtures, while the highest yield was 83.2% pretreated by the consortium MC1 under a high enzyme loading. The maximum methane yield of pretreated samples by the consortia MC1, WSD-5 and XDC-2 were 259, 279, 247ml/g VS, respectively, which were 1.39, 1.49 and 1.32times greater than the values of the untreated controls. This study showed that pretreatments by MC1, WSD-5 and XDC-2 were capable of significantly enhancing both the saccharide and methane yields from Napier grass.

Promoting anaerobic biogasification of corn stover through biological pretreatment by liquid fraction of digestate (LFD)

A new biological pretreatment method by using liquid fraction of digestate (LFD) was advanced for promoting anaerobic biogasification efficiency of corn stover. 17.6% TS content and ambient temperature was appropriate for pretreatment. The results showed that C/N ratio decreased to about 30, while total lignin, cellulose, and hemicellulose (LCH) contents were reduced by 8.1-19.4% after pretreatment. 3-days pretreatment was considered to be optimal, resulting in 70.4% more biogas production, 66.3% more biomethane yield and 41.7% shorter technical digestion time compared with the untreated stover. The reductions on VS, cellulose, and hemicellulose were increased by 22.1-35.9%, 22.3-35.4%, and 19.8-27.2% for LFD-treated stovers. The promoted anaerobic biogasification efficiency was mainly attributed to the improved biodegradability due to the pre-decomposition role of the bacteria in LFD. The method proved to be an efficient and low cost approach for producing bioenergy from corn stover, meanwhile, reducing LFD discharge and minimizing its potential pollution.

Enhancing the anaerobic digestion of lignocellulose of municipal solid waste using a microbial pretreatment method

The use of biological pretreatment in anaerobic digestion systems has some potential; however, to date, these methods have not been able to effectively increase methane production of lignocellulose of municipal solid waste (LMSW). In this study a thermophilic microbial consortium (MC1) was used as a pretreatment method in order to enhance biogas and methane production yields. The results indicated that sCOD concentration increased significantly in the early stages of pretreatment. Ethanol, acetic acid, propionic acid, and butyric acid were the predominant volatile organic products in the MC1 hydrolysate. Biogas and methane production yields of LMSW significantly increased following MC1 pretreatment. In addition, the methane production rate of the treated LMSW was greater than that observed from the untreated sample.

Co-metabolic transformation of the neonicotinoid insecticide imidacloprid by the new soil isolate Pseudoxanthomonas indica CGMCC 6648

A new imidacloprid (IMI) degrading bacterium Z-9 (deposited number CGMCC 6648) was isolated and identified as Pseudoxanthomonas indica by 16S rRNA gene analysis. Two metabolites were identified as olefin and 5-hydroxy IMI by liquid chromatography-mass spectrometry and nuclear magnetic resonance analysis. P. indica CGMCC 6648 degraded 70.1% of IMI (1.22 mmol L(-1)) and formed 0.93 mmol L(-1) 5-hydroxy IMI and 0.05 mmol L(-1) olefin IMI in 6 days and in the presence of 100 mmol L(-1) glucose. The half-life of IMI degradation was 3.6 days. P. indica CGMCC 6648 transforms IMI via a co-metabolism mechanism and different carbohydrates have significant effects on 5-hydroxy IMI formation, whereas different organic acids have substantial effects on olefin IMI production. Lactose is the best co-substrate for IMI degradation and 5-hydroxy IMI formation with 0.77 mmol L(-1) degraded and 0.67 mmol L(-1) formed in 48 h, respectively. Pyruvate is the best co-substrate for olefin IMI formation with 0.17 mmol L(-1) produced in 96 h for all carbon sources tested. Pyruvate significantly stimulates the conversion of 5-hydroxy IMI to olefin IMI, whereas glucose slightly inhibits this reaction. P. indica CGMCC 6648 rapidly degrades IMI and forms olefin IMI, which may enhance its potential for biodegradation of IMI and increase its insecticidal activity, which can decrease the IMI dosage required.

Effect of pretreatment by a microbial consortium on methane production of waste paper and cardboard

A microbial consortium MC1 was used to pretreat filter paper, office paper, newspaper, and cardboard to enhance methane production. The results of pretreatment indicated that sCOD of hydrolysates of the four substrates increased significantly in the early stage, and peaked on day 7. During pretreatment, ethanol, acetic acid, propionic acid, butyric acid, and glycerol were the predominant volatile organic products in hydrolysates. MC1 had strong degradation ability on the four substrates, and the weight loss of filter paper, office paper, newspaper, and cardboard reached 78.3%, 80.5%, 39.7%, and 49.7%, respectively. The results of anaerobic digestion showed that methane production yields and rates of the four substrates significantly increased after pretreatment. This study is the first attempt to explore the microbial pretreatment method for anaerobic digestion of waste paper and cardboard. Microbial consortium pretreatment could be an effective method for enhancing methane production of waste paper and cardboard into bioenergy.

Effects of different pretreatment strategies on corn stalk acidogenic fermentation using a microbial consortium

The effects of sulfuric acid, acetic acid, aqueous ammonia, sodium hydroxide, and steam explosion pretreatments of corn stalk on organic acid production by a microbial consortium, MC1, were determined. Steam explosion resulted in a substrate that was most favorable for microbial growth and organic acid productions. The total amounts of organic acids produced by MC1 on steam exploded, sodium hydroxide, sulfuric acid, acetic acid, and aqueous ammonia pretreated corn stalk were 2.99, 2.74, 1.96, 1.45, and 2.21g/l, respectively after 3days of fermentation at 50°C. The most prominent organic products during fermentation of steam-exploded corn stalks were formic (0.86g/l), acetic (0.59g/l), propanoic (0.27g/l), butanoic (0.62g/l), and lactic acid (0.64g/l) after 3days of fermentation; ethanol (0.18g/l), ethanediol (0.68g/l), and glycerin (3.06g/l) were also produced. These compounds would be suitable substrates for conversion to methane by anaerobic digestion.

Degradation of corn stalk by the composite microbial system of MC1

The composite microbial system of MC1 was used to degrade corn stalk in order to determine properties of the degraded products as well as bacterial composition of MC1. Results indicated that the pH of the fermentation broth was typical of lignocellulose degradation by MC1, decreasing in the early phase and increasing in later stages of the degradation. The microbial biomass peaked on the day 3 after degradation. The MC1 efficiently degraded the corn stalk by nearly 70% during which its cellulose content decreased by 71.2%, hemicellulose by 76.5% and lignin by 24.6%. The content of water-soluble carbohydrates (WSC) in the fermentation broth increased progressively during the first three days, and decreased thereafter, suggesting an accumulation of WSC in the early phase of the degradation process. Total levels of various volatile products peaked in the third day after degradation, and 7 types of volatile products were detected in the fermentation broth. These were ethanol, acetic acid, 1,2-ethanediol, propanoic acid, butanoic acid, 3-methyl-butanoic acid and glycerine. Six major compounds were quantitatively analysed and the contents of each compound were ethanol (0.584 g/L), acetic acid (0.735 g/L), 1,2-ethanediol (0.772 g/L), propanoic acid (0.026 g/L), butanoic acid (0.018 g/L) and glycerine (4.203 g/L). Characterization of bacterial cells collected from the culture solution, based on 16S rDNA PCR-DGGE analysis of DNAs, showed that the composition of bacterial community in MC1 coincided basically with observations from previous studies. This indicated that the structure of MC1 is very stable during degradation of different lignocellulose materials.