Energetic utilization of corn stalk and elimination of methyl orange in ECMO-like integrated reactor: Co-occurrence of anaerobic digestion and aerobic treatment.

For the simultaneous energetic utilization of corn stalk and azo-dye contaminated wastewater, an ECMO-like integrated reactor was come up to achieve the biogas production and azo-dye degradation during anaerobic digestion (AD). Methyl orange (MO) was selected as the model compound for azo-dye. The ECMO-like reactor included AD main reactor with a spray device and solid-liquid separation components, integrated with an aeration reactor for biogas slurry. Methane yields of corn stalks (100.82 mL/g VS) were highest in the ECMO-like reactor, compared with reactors without aeration. As a stable metabolite, 4-aminobenzenesulfonic acid (4-ABA) was detected in AD, while it was assumed that the metabolites can be further transformed in the ECMO-like reactor (R3), due to the 4-ABA removal efficiency as 92.87 % after 35 days' digestion. Class Alphaproteobacteria and Clostridia were assumed as functional microbes responding to aeration. Overall, this ECMO-like integrated reactor provided a novel biotechnology strategy for agricultural and azo dye waste treatment.

Combined disposal of methyl orange and corn straw via stepwise adsorption-biomethanation-composting.

Agriculture wastes have been proved to be the potential adsorbents to remove azo dye from textile wastewater, but the post-treatment of azo dye loaded agriculture waste is generally ignored. A three-step strategy including sequential adsorption-biomethanation-composting was developed to realize the co-processing of azo dye and corn straw (CS). Results showed that CS represented a potential adsorbent to remove methyl orange (MO) from textile wastewater, with the maximum MO adsorption capacity of 10.00 ± 0.46 mg/g, deriving from the Langmuir model. During the biomethanation, CS could serve as electron donor for MO decolorization and substrate for biogas production simultaneously. Though the cumulative methane yield of CS loaded with MO was 11.7 ± 2.28% lower than that of blank CS, almost complete de-colorization of MO could be achieved within 72 h. Composting could achieve the further degradation of aromatic amines (intermediates during the degradation of MO) and decomposition of digestate. After 5 days' composting, 4-aminobenzenesulfonic acid (4-ABA) was not detectable. The germination index (GI) also indicated that the toxicity of aromatic amine was eliminated. The overall utilization strategy gives novel light on the management of agriculture waste and textile wastewater.

Micro-aeration: an attractive strategy to facilitate anaerobic digestion.

Micro-aeration can facilitate anaerobic digestion (AD) by regulating microbial communities and promoting the growth of facultative taxa, thereby increasing methane yield and stabilizing the AD process. Additionally, micro-aeration contributes to hydrogen sulfide stripping by oxidization to produce molecular sulfur or sulfuric acid. Although micro-aeration can positively affect AD, it must be strictly regulated to maintain an overall anaerobic environment that permits anaerobic microorganisms to thrive. Even so, obligate anaerobes, especially methanogens, could suffer from oxidative stress during micro-aeration. This review describes the applications of micro-aeration in AD and examines the cutting-edge advances in how methanogens survive under oxygen stress. Moreover, barriers and corresponding solutions are proposed to move micro-aeration technology closer to application at scale.

Synthesis of cellulose-based superabsorbent hydrogel with high salt tolerance for soil conditioning.

In this study, cellulose-based superabsorbent hydrogel was synthesized from sodium carboxymethyl cellulose (CMC-Na), acrylic acid (AA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) to enhance its water absorbency and salt tolerance for soil-conditioning applications in areas suffering from drought and soil salinization. Superabsorbent hydrogels (SHs) were prepared by CMC-Na and AMPS successfully, using chemical graft technology. Structure, morphology, thermal stability, and water absorbency of SHs were deduced. The cellulose-based hydrogel showed a high salt tolerance that the maximum water absorbency reached 604 and 119% in distilled water and saline water, respectively. The swelling behavior in aqueous solvents indicated that the water absorption of hydrogels was improved with the increasing ratio of CMC-Na. All SHs exhibited adsorption of nitrogen with the maximum adsorption of ammonia nitrogen 30 mg·g-1 and the presence of hydrogels could slow down the loss of nutrients in the soil. This study provided a feasible strategy that AMPS was substituted by CMC-Na to synthesize SHs with strong water absorbency and high salt tolerance which could be efficiently applied in agriculture as a soil conditioner.

Gases emission during the continuous thermophilic composting of dairy manure amended with activated oil shale semicoke.

NH3 and greenhouse gases emission are big problems during composting, which can cause great nitrogen nutrient loss and environmental pollution. This study investigated effects of the porous bulking agent of oil shale semicoke and its activated material on the gases emission during the continuous thermophilic composting. Results showed addition of semicoke could significantly reduce the NH3 emission by 74.65% due to its great adsorption capacity to NH4+-N and NH3, further the effect could be enhanced to 85.92% when utilizing the activated semicoke with larger pore volume and specific surface area. In addition, the CH4 emission in the semicoke and activated semicoke group was also greatly mitigated, with a reduction of 67.23% and 87.62% respectively, while the N2O emission was significantly increased by 93.14% and 100.82%. Quantification analysis of the functional genes found the abundance of mcrA was high at the massive CH4-producing stage and the archaeal amoA was dominant at the N2O-producing stage in all the composting groups. Correlation and redundancy analysis suggested there was a positive correlation between the CH4 emission and mcrA. Addition of semicoke especially activated semicoke could reduce the CH4 production by inhibiting the methanogens. For the NH3 and N2O, it was closely related with the nitrification process conducted by archaeal amoA. Addition of semicoke especially activated semicoke was beneficial for the growth of ammonia-oxidizing archaea, causing the less NH4+-N transformation to NH3 but more N2O emission.

Effects of humic acid modified oyster shell addition on lignocellulose degradation and nitrogen transformation during digestate composting.

The aim of this work was to investigate the performance of a novel humic acid modified oyster shell (MOS) bulking agent on the digestate composting. MOS was prepared by immobilizing humic acid onto oyster shell using solid phase grafting method, and then applied to the composting process. Results showed more obvious degradation of lignocellulose was observed in the MOS treatment, which was probably due to the high relative abundance of Actinobacteria. Moreover, the addition of MOS could significantly preserve NH4+ and reduce the NO3- generation with the decreasing abundance of ammonia-oxidizing bacteria and archaea. Besides, adding MOS reduced the N2O emission by 59.63% compared with the control. After composting, excitation-emission matrix fluorescence spectra demonstrated that the humification degree as well as compost maturity was enhanced with MOS added.

Addition of oyster shell to enhance organic matter degradation and nitrogen conservation during anaerobic digestate composting.

Anaerobic digested residue (DR) is the main by-product from biogas plants, and it is predominantly used as organic fertilizer after composting. To resolve the problems of long duration and nitrogen loss in conventional composting, bulking agents are always added during the composting process. In this study, oyster shell (OS) was used as a bulking agent for DR composting. Four treatments were conducted by mixing DR and OS at different concentrations (0%, 10%, 20% and 30%, based on wet weight) and then composting the mixtures for 40 days. The results showed that the organic matter (OM) degradation efficiency was enhanced by 5.62%, 12.15% and 16.98% with increasing amounts of OS addition. The increased content of microbial biomass carbon in the compost indicated a suitable living environment for aerobic microbes with added OS, which could explain the increased OM degradation efficiency. Compared with the control, the NH3 emissions in the treatments with 10%, 20% and 30% OS were decreased by 13.81%, 33.33% and 53.76%, respectively. The increase in total nitrogen content in the compost is probably due to the absorption of NH3 by OS. Results indicated that OS is a suitable bulking agent for DR composting and that the addition of 20-30% OS can significantly enhance composting performance.

Biotransformation of hexachlorocyclohexanes contaminated biomass for energetic utilization demonstrated in continuous anaerobic digestion system.

Lindane, the γ-hexachlorocyclohexane (HCH) isomer, was among the most used pesticides worldwide. Although it was banned in 2009, residues of Lindane and other HCH-isomers are still found with high concentrations in contaminated fields. For clean-up, phytoremediation combined with anaerobic digestion (AD) of contaminated biomass to produce biogas and fertilizer could be a promising strategy and was tested in two 15 L laboratory-scale continuous stirred tank reactors. During operation over one year by adding HCH isomers (γ, α and ß) consecutively, no negative influence on conventional reactor parameters was observed. The γ- and α-HCH isomers were transformed to chlorobenzene and benzene, and transformation became faster along with time, while ß-HCH was not removed. Genus Methanosaeta and order Clostridiales, showing significant enhancement on abundance with HCH addition, may be used as bioindicators for HCH dehalogenation in AD process. The potential for HCH degradation in AD system was restricted to axial Cl atoms of HCH and it showed slight enantioselective preference towards transformation of (+) α-HCH. Moreover, metabolite benzene was mineralized to CO2 and methane, deducing from tracer experiments with benzene-13C6. Overall, AD appears to be a feasible option for treatment of γ and α-HCHs contaminated biomass.

2H and 13C isotope fractionation analysis of organophosphorus compounds for characterizing transformation reactions in biogas slurry: Potential for anaerobic treatment of contaminated biomass.

The ability of anaerobic digestion (AD) to eliminate organophosphorus model compounds (OPs) with structural elements of phosphate, phosphorothioate and phosphorodithioate esters was studied. The enzymatic mechanism of the first irreversible degradation reaction was characterized using metabolite pattern and kinetic 2H/13C-isotope effect in original, cell-free and heat sterilized biogas slurry. The isotope fractionation study suggests different modes of degradation reactions. Representatives for phosphate ester, tris(2-chloroethyl) phosphate and tris(1,3-dichloro-2-propyl) phosphate, were hydrolyzed in biogas slurry without carbon or hydrogen isotope fractionation. Representatives for phosphorodithioate, Dimethoate and Malathion, were degraded in original slurry yielding carbon enrichment factor (εC) of -0.6 ±â€¯0.1‰ and -5.5 ±â€¯0.1‰ (-0.9 ±â€¯0.1‰ and -7.2 ±â€¯0.5‰ in cell-free slurry), without hydrogen isotope fractionation. Phosphorothioate degradation represented by Parathion and Parathion-methyl yielded surprisingly different εC (-0.7 ±â€¯0.2 and -3.6 ±â€¯0.4‰) and εH (-33 ±â€¯5 and -5 ±â€¯1‰) in original slurry compared to cell-free slurry (εC = -2.5 ±â€¯0.5 and -8.6 ±â€¯1.4‰; εH = -61 ±â€¯10 and -10 ±â€¯3‰) suggesting H-C bond cleavage. Degradation of Parathion and Parathion-methyl in sterilized slurry gave carbon but not hydrogen fractionation implying relative thermostable enzymatic activity with different mechanism. The correlation of 2H and 13C stable isotope fractionation of Parathion in biogas slurry showed distinct pattern (Λoriginal = 31 ±â€¯11, Λcell-free = 20 ±â€¯2), indicating different mechanism from chemical hydrolysis. Overall, AD can be a potential treatment for OPs contaminated biomass or contaminated organic waste material.

Characterizing chemical transformation of organophosphorus compounds by 13C and 2H stable isotope analysis.

Continuous and excessive use of organophosphorus compounds (OPs) has led to environmental contaminations which raise public concerns. This study investigates the isotope fractionation patterns of OPs in the aquatic environment dependence upon hydrolysis, photolysis and radical oxidation processes. The hydrolysis of parathion (EP) and methyl parathion (MP) resulted in significant carbon fractionation at lower pH (pH2-7, εC=-6.9~-6.0‰ for EP, -10.5~-9.9‰ for MP) but no detectable carbon fractionation at higher pH (pH12). Hydrogen fractionation was not observed during any of the hydrolysis experiments. These results indicate that compound specific isotope analysis (CSIA) allows distinction of two different pH-dependent pathways of hydrolysis. Carbon and hydrogen isotope fractionation were determined during UV/H2O2 photolysis of EP and tris(2-chloroethyl) phosphate (TCEP). The constant δ2H values determined during the OH radical reaction of EP suggested that the rate-limiting step proceeded through oxidative attack by OH radical on the PS bond. The significant H isotope enrichment suggested that OH radical oxidation of TCEP was caused by an H-abstraction during the UV/H2O2 processes (εH=-56±3‰). Fenton reaction was conducted to validate the H isotope enrichment of TCEP associated with radical oxidation, which yielded εH of -34±5‰. Transformation products of OPs during photodegradation were identified using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). This study highlights that the carbon and hydrogen fractionation patterns have the potential to elucidate the transformation of OPs in the environment.

Biotransformation and inhibition effects of hexachlorocyclohexanes during biogas production from contaminated biomass characterized by isotope fractionation concepts.

Hexachlorocyclohexane (HCH) production for pesticides was banned by Stockholm Convention (2009) due to its harmful and adverse effects on the environment. Despite this measure, many areas contaminated with former HCH production-waste products still require management. As a potential solution contributing to clean-up of these sites, anaerobic digestion (AD) of pesticide-contaminated biomass to produce biogas is a promising strategy. High pesticide concentrations, however, may inhibit biogas production. Therefore, laboratory-scale batch reactors were set up to investigate biogas reactor performance in presence of HCH. Inhibitory effects on biogas yield was observed with concentrations of HCH ≥ 150 mg/L. Carbon isotope composition of methane (δ13CCH4) showed significant fluctuation after an inhibition phase, indicating that HCH toxicity can affect the activity of acetoclastic methanogens. Furthermore, combined results of metabolites and carbon isotope fractionation factors (εc) demonstrated that α- and γ-HCH can be degraded to chlorobenzene and benzene via anaerobic reductive dechlorination.

Metabolomics reveals stage-specific metabolic pathways of microbial communities in two-stage anaerobic fermentation of corn-stalk.

Analysis of intracellular metabolites is essential to delineate metabolic pathways of microbial communities for evaluation and optimization of anaerobic fermentation processes. The metabolomics are reported for a microbial community during two stages of anaerobic fermentation of corn stalk in a biogas digester using GC­MS. Acetonitrile/methanol/water (2:2:1, by vol) was the best extraction solvent for microbial community analysis because it yielded the largest number of peaks (>200), the highest mean summed value of identified metabolites (23) and the best reproducibility with a coefficient of variation of 30 % among four different extraction methods. Inter-stage comparison of metabolite profiles showed increased levels of sugars and sugar alcohols during methanogenesis and fatty acids during acidogenesis. Identification of stage-specific metabolic pathways using metabolomics can therefore assist in monitoring and optimization of the microbial community for increased biogas production during anaerobic fermentation.