Effects of Saccharomyces cerevisiae quorum sensing signal molecules on ethanol production in bioethanol fermentation process.

In this study, the concentrations of Saccharomyces cerevisiae quorum sensing signal molecules (QSMs) were determined, not to mention the exploration of the effects of exogenous S. cerevisiae QSMs on the sole fermentation of S. cerevisiae and co-fermentation of S. cerevisiae and Lactobacillus plantarum. The results showed that the concentrations of three signal molecules (2-phenylethanol (2-PE), tyrosol and tryptophan) produced by S. cerevisiae increased with a higher bacteria density, which tends to become stable up to 118.02, 32.05 and 1.93 mg/L respectively when cultivating for 144 h. Among the three signaling molecules, only 2-PE promoted the ethanol production capacity of S. cerevisiae. The ethanol concentration of the sole fermentation of S. cerevisiae loaded with 120 mg/L 2-PE reached 3.2 g/L in 9 h, which was 58.7% higher than that of the group without 2-PE addition. Moreover, 2-PE reduced the negative impact of L. plantarum on S. cerevisiae. Within 12 h of the co-fermentation of L. plantarum and S. cerevisiae, the ethanol concentration in the co-fermentation group loaded with 2-PE reached 5.6 g/L, similar to that in the group fermenting with sole S. cerevisiae, and the yeast budding rate was also restored to 28.51%. qRT-PCR results of S. cerevisiae which was in sole fermentation with 2-PE addition for 9 h showed that the relative expression levels of ethanol dehydrogenase gene ADH1 in S. cerevisiae decreased by 25% and the relative expression levels of MLS1, CIT2, IDH1,CIT1 decreased by 26%, 30%, 22%,18%, respectively, meant that the glyoxylic and tricarboxylic acid cycles were greatly inhibited, which promotes the accumulation of ethanol. The results of this study provide basic data for using QSMs more than antibiotics in the the prevention of contamination during the industrialized bioethanol production.

Dry anaerobic digestion of ammoniated straw: Performance and microbial characteristics.

This paper explores the influence of the mixing ratio of ammoniated straw to biogas residue on the stability and methane yield of dry anaerobic digestion and analyzes the structure of the microbial community with digestion time. Five reactors containing ammoniated straw and swine manure biogas residue at ratios of 5:1, 4:2, 3:3, 2:4 and 1:5 (total solids) were constructed, and neither total ammonia nitrogen nor free ammonia nitrogen was inhibited. Three reactors produced gas successfully. The reactor with a ratio of 3:3 (R3-3) yielded the best methane production, with a cumulative methane production of 115.13 mL/(g·VSadded). Analysis of the R3-3 microbial community showed that bacteria were dominant species. Archaea, mainly Methanosarcina, played an important role in anaerobic digestion and methane production. Methanobacterium, with high acid tolerance, was positively related to total volatile fatty acids (TVFA), playing a key role in preventing the acidification of the anaerobic digestion system.

Biochar derived from swine manure digestate and applied on the removals of heavy metals and antibiotics.

Swine manure digestate (SMD) is rich of functional groups. In this work, raw biochar (BC) was prepared from SMD by oxygen-limiting pyrolysis, and HCl-BC, NH3-BC and Mn-BC were obtained by modifying BC with HCl, NH3·H2O and KMnO4. The modified biochar was negatively charged and showed a larger specific surface area and total pore volume, and higher contents of Si-O-Si and O-H bonds and aromatic rings with CO bond. Among them, Mn-BC, was given a new Mn-O group. The adsorption capacities of biochar were determined using a model aqueous solution containing some metals and antibiotics. The adsorption experiment results showed that Mn-BC had a quite good capacity for Cu and Zn removal. And the removal efficiency of As (III), sulfadimidine and tylosin of 83.98%, 83.76%, and 77.34% respectively, was also observed by using Mn-BC. Mn-BC was considered to be a promising material for the adsorption of heavy metals and antibiotics.

Screening of a microbial consortium for selective degradation of lignin from tree trimmings.

To acquire microbial consortia with effectively precedent degradation of lignin, samples obtained from rotten trunks, rotten stumps and soil near it were screened and isolated after generations of subculture. The dynamic change illustrated that their community structures were affected by pH and tended to be stable after 6 days' cultivation. The desired one, named DM-1, was gained through successive cultivation for over 5 generations, whose high selectivity in lignin degradation was observed within 16 days' cultivation (SV = 2.78). Meanwhile, a remarkable reduction in the fiber crystallinity of tree trimmings (10.35%) resulted from the bio-degradation of DM-1, displayed a greater exposure of cellulose by selective removal of lignin. The diversity analysis of DM-1 was investigated by PCR amplification and 16S rDNA sequencing, indicated that mesorhizobium, cellulosimicrobium, pandoraea, achromobacter and stenotrophomones were the predominant genera. Furthermore, fungi (3 strains), bacteria (4 strains) and actinomycetes (5 strains) constituted 12 strains in total were gained by plate isolation from DM-1.

A new screened microbial consortium OEM2 for lignocellulosic biomass deconstruction and chlorophenols detoxification.

Recalcitrance limits biomass application in biorefinery. It is even more so when toxic chlorophenols are present. In this study, we screened a microbial consortium, OEM2, for lignocellulose deconstruction and chlorophenols detoxification through a short-term and efficient screening process. Microbial consortium OEM2 had a good buffer capability in the cultivation process and exhibited a high xylanase activity, with over 85% hemicellulose degradation within 12 days. Throughout the treatment process, 41.5% rice straw decomposition on day 12 and around 75% chlorophenols (MCP, 2,4-DCP, 2,4,6-TCP) removal on day 9, were recorded. Moreover, Fourier translation infrared spectroscopy (FTIR) analysis indicated that chemical bonds and groups (eg. hydrogen-bond, ß-1,4 glycosidic bond, lignin-carbohydrate cross-linking) in the rice straw were broken. Cuticle and silica layer destruction and subsequent exposed cellulose fibers were observed by scanning electron microscopy (SEM). Microbial consortium OEM2 diversity analysis by 16S rRNA gene sequencing indicated that Proteobacteria (41.3%) was the most abundant phylum and the genera Paenibacillus and Pseudomonas played an important role in the lignocellulose decomposition and chlorophenols detoxification. This study developed a faster and more efficient strategy to screen a specific microbial consortium. And the new microbial consortium, OEM2, makes lignocellulose more accessible and complex pollutants unproblematic in the further biorefinery process.

Screening of a microbial consortium for highly simultaneous degradation of lignocellulose and chlorophenols.

In this work, spent mushroom substrates were utilized for screening a microbial consortium with highly simultaneous degradation of lignocellulose and chlorophenols. The desired microbial consortium OEM1 was gained through successive cultivation for about 50 generations and its stability of composition was verified by denaturing gradient gel electrophoresis (DGGE) during screening process. It could degrade lignocellulose and chlorophenols at around 50% and 100%, respectively, within 7days. The diversity analysis and the growth characteristics of OEM1 during degradation process were investigated by PCR-DGGE combined with clone and sequence. The results indicated that OEM1 consisted of 31 strains. Proteobacteria and Bacteroidetes were the predominant bacterial groups. The dynamic change of OEM1 illustrated that consortium community structure was effected by pH and substrate alteration and tended to be stable after 6days' cultivation. Furthermore, bacteria (11 strains) and actinomycetes (2 strains) were obtained based on plate isolation and identified via 16S rDNA sequence.

Enhancing the quality of bio-oil and selectivity of phenols compounds from pyrolysis of anaerobic digested rice straw.

This study investigated the thermal decomposition characteristics and pyrolytic products of anaerobic digested rice straw (ADRS) by thermogravimetric (TG) and pyrolysis-gas chromatograph/mass spectrometry (Py-GC/MS) analysis. Compared with the raw rice straw (RS), the thermal decomposition temperature of ADRS was shifted to higher temperature zone and the second decomposition zone of cellulose (Toffset(c)-Tpeak) became narrower (14 °C less), which indicated that the composition of rice straw were changed significantly by the anaerobic digestion pretreatment. Py-GC/MS analysis showed that the quality of the bio-oil and the selectivity of pyrolytic products could be obviously improved by anaerobic digestion. The total yields of alcohols, acids, aldehydes, furans, anhydrosugars, and ketones pyrolysis substances decreased, while the yield of phenols increased. The yield of 4-Vinylphenol (4-VP) increased from 29.33%, 8.21% and 5.76% to 34.93%, 12.46% and 7.68% at 330, 450 and 650 °C, respectively, after anaerobic digestion.

Integration of Shiitake cultivation and solid-state anaerobic digestion for utilization of woody biomass.

Pretreatment technologies that can not only reduce the recalcitrance of woody biomass but also achieve a high benefit-cost ratio are desirable for bioenergy production from woody biomass. In this study, an integrated process was proposed and conducted by pretreating woodchips via Shiitake cultivation for improved methane yield during solid-state anaerobic digestion (SS-AD), and simultaneously producing mushrooms as a high-value co-product. Shiitake cultivation using woodchips as the main substrate ingredient obtained mushroom yields comparable to those using a commercial substrate. Enzymatic digestibility and cumulative methane yields (133-160 L kg(-1)VS during 62 days of SS-AD) of pretreated substrates (spent mushroom substrate) were at least 1.5 times as high as those of untreated woodchips. Compared to a sole SS-AD process, the integrated Shiitake cultivation/SS-AD process increased methane production and solid waste reduction per kilogram of woodchips by about 1.5 and 8 times, respectively.

Solid-state anaerobic co-digestion of spent mushroom substrate with yard trimmings and wheat straw for biogas production.

Spent mushroom substrate (SMS) is a biomass waste generated from mushroom production. About 5 kg of SMS is generated for every kg of mushroom produced. In this study, solid state anaerobic digestion (SS-AD) of SMS, wheat straw, yard trimmings, and their mixtures was investigated at different feedstock to effluent ratios. SMS was found to be highly degradable, which resulted in inhibition of SS-AD due to volatile fatty acid (VFA) accumulation and a decrease in pH. This issue was addressed by co-digestion of SMS with either yard trimmings or wheat straw. SS-AD of SMS/yard trimmings achieved a cumulative methane yield of 194 L/kg VS, which was 16 and 2 times higher than that from SMS and yard trimmings, respectively. SS-AD of SMS/wheat straw obtained a cumulative methane yield of 269 L/kg VS, which was 23 times as high as that from SMS and comparable to that from wheat straw.

Mesophilic anaerobic co-digestion of pulp and paper sludge and food waste for methane production in a fed-batch basis.

Co-digestion of pulp and paper sludge (PPS) and food waste (FW) in a batch-fed digestion system was conducted on a laboratory scale. Three reactors named A1, A2, and A3 were tested. PPS and FW mixed at different mass ratios of 1:3, 1:1, and 3:1, respectively, were loaded in the reactors. Bioconversion at high efficiency was obtained in the system. The accumulative methane yield of each reactor was 144mLg(-1)VSfed (A1), 256 mL g(-1) VSfed (A2), and 123 mL g(-1)VSfed (A3). The soluble chemical oxygen demand (COD) removal efficiencies reached 73.2% (Al), 93.9% (A2), and 79.6% (A3). A pH in the range 5.8-8.4 was obtained in the three reactors without adjustment due to the high buffer capacity of the mixing feedstock. No toxicity inhibitions of volatile fatty acids and NH3-N occurred in reactor A2. This study showed that it was good for co-digestion of PPS and FW in a mass ratio of 1:1 for methane production, which resulted in higher methane yield, a greater buffer capacity, a higher organics removal efficiency, and a more stable process.

Mesophilic batch anaerobic co-digestion of pulp and paper sludge and monosodium glutamate waste liquor for methane production in a bench-scale digester.

This paper presented results from anaerobic co-digestion of pulp and paper sludge (PPS) and monosodium glutamate waste liquor (MGWL). A bench-scale anaerobic digester, 10 L in volume was developed, to operate under mesophilic (37 ± 2°C) batch condition. Under versatile and reliable anaerobic conduct, high efficiency for bioconversion of PPS and MGWL were obtained in the system. The accumulative methane yield attained to 200 mL g(-1) VS(added) and the peak value of methane daily production was 0.5m(3)/(m(3)d). No inhibitions of volatile fatty acids (VFAs) and ammonia on anaerobic co-digestion were found. pH 6.0-8.0 and alkalinity 1000-4000 mg CaCO(3)/L were got without adjustment. This work showed that there was a good potential to the use of PPS and MGWL to anaerobic co-digestion for methane production.

Biological pretreatment enhances biogas production in the anaerobic digestion of pulp and paper sludge.

High efficient resource recovery from pulp and paper sludge (PPS) has been the focus of attention. The objective of this research was to develop a bio-pretreatment process prior to anaerobic digestion of PPS to improve the methane productivity. Active and inactive mushroom compost extracts (MCE) were used for pretreating PPS, followed by anaerobic digestion with monosodium glutamate waste liquor (MGWL). Laboratory-scale experiments were carried out in completely mixed bioreactors, 1-L capacity with 700 ml useful capacity. Optimal amount of active MCE for organics' solubilization in the step of pretreatment was 250 A.U./gVS( sludge). Under this condition, the PPS floc structure was well disrupted, resulting in void rate and fibre size diminishment after pretreatment. In addition, SCOD and VS removal were found to be 56% and 43.6%, respectively, after anaerobic digestion, being the peak value of VFA concentration determined as 1198 mg acetic acid L(-1). The anaerobic digestion efficiency of PPS with and without pretreatment was evaluated. The highest methane yield under optimal pretreatment conditions was 0.23 m(3) CH4/kgVS(add), being 134.2% of the control. The results indicated that MCE bio-pretreatment could be a cost-effective and environmentally sound method for producing methane from PPS.

Alkali pretreatment enhances biogas production in the anaerobic digestion of pulp and paper sludge.

The objective of this research was to develop an alkali pretreatment process prior to anaerobic digestion (AD) of pulp and paper sludge (PPS) to improve the methane productivity. Different concentrations of sodium hydroxide solution were used to pretreat PPS, and then followed by AD of PPS and monosodium glutamate waste liquor (MGWL). Laboratory-scale experiments were carried out in completely mixed bioreactors, 1L capacity with 700 mL worked. Optimal amount of sodium hydroxide for organics solubilization in the step of pretreatment was 8 g NaOH/100g TS(sludge). Under this condition, the PPS flocs structure was well disrupted resulting in the void rate and fiber size decreased after pretreatment, and SCOD increased up to 83% as well as the peak value of VFA concentration attained 1040 mg acetic acid/L during AD. The AD efficiency of PPS with and without pretreatment was evaluated. The highest methane yield under optimal pretreatment condition was 0.32 m(3) CH(4)/kg VS(removal), 183.5% of the control. The results indicated that alkali/NaOH pretreatment could be an effective method for improving methane yield with PPS.