Comparative effects of ferric hydroxide and (semi) conductive iron oxides on the anaerobic digestion of oxytetracycline-contaminated dairy manure.

Additives, such as iron oxides, have been used in anaerobic digestion (AD) to promote direct interspecies electron transfer and to boost methane yield. However, the function of additives in the AD of antibiotic-contaminated organic wastes remained unclear. In this study, the effects of ferric hydroxide and (semi) conductive iron oxides, namely hematite and magnetite, on the AD of oxytetracycline (OTC)-contaminated dairy manure were investigated. Each iron oxide was assigned to a set of experiment where 0.25 g/L of OTC was added to 1 L batch digesters, while the concentration of iron oxide was varied from 0.08 to 0.34 g/L. Generally, magnetite was the most effective iron oxide to enhance methane yield in OTC-free dairy manure followed by ferric hydroxide and hematite. However, when the manure was contaminated with OTC, higher methane yield was observed in ferric hydroxide followed by hematite, while the lowest was with magnetite. In all digesters, the highest methane yield was observed with ferric hydroxide at 0.08 g/L, which was 1.43-fold of that with OTC and without iron oxides. The kinetic studies of methane yield demonstrated that the addition of iron oxides in the AD of OTC-contaminated dairy manure did not shorten the lag phase period despite the increase of methane yield. Thus, the increase of methane yield with ferric hydroxide was attributed to the possible formation of Fe-OTC complex, which attenuated the inhibition of OTC. A strategy to recover OTC residue in the AD was proposed using magnetite, a ferromagnetic particle, and high gradient magnetic separator.

Impacts of iron oxide and titanium dioxide nanoparticles on biogas production: Hydrogen sulfide mitigation, process stability, and prospective challenges.

Anaerobic digestion for biogas production is one of the most used technology for bioenergy. However, the adoption of nanoparticles still needs further studies. Therefore, this study was designed to examine the effect of metal oxide nanoparticles (MONPs) at four different concentrations in two different combinations, 20 (R1) and 100 (R2) mg/L for Fe2O3, 100 (R3) and 500 (R4) mg/L for TiO2, and a mixture of Fe2O3 and TiO2 at rates of 20, 500 (R5) and 100, and 500 (R6), on hydrogen sulfide (H2S) mitigation, biogas, and methane (CH4) yield during the anaerobic digestion of cattle manure (CM) using an anaerobic batch system. The results showed that H2S production was 2.13, 2.38, 2.37, 2.51, 2.64, and 2.17 times lower than that of the control (R0), respectively, when the CM was treated by the aforementioned MONPs. Additionally, biogas and CH4 production were 1.09 and 1.105, 1.15 and 1.191, 1.07 and 1.097, 1.17 and 1.213, 1.10 and 1.133, and 1.13 and 1.15 times higher than those of R0 when R1, R2, R3, R4, R5, and R6 were supplemented with MONPs, respectively. The highest specific production of biogas and CH4 was 336.25 and 192.31 mL/gVS, respectively, which was achieved by R4 supplemented with 500 mg/L TiO2 NPs, while the corresponding values in the case of R0 were 286.38 and 158.55 mL/gVS.

Valorizing waste iron powder in biogas production: Hydrogen sulfide control and process performances.

Biogas is composed of different gases including hydrogen sulfide (H2S), which is a hazardous gas that damages pipes and generators in anaerobic digestion system. The objective of this study was to control H2S by waste iron powder produced by laser cutting machine in a steel and iron industry. Waste iron powder was mixed with dairy manure at a concentration between 2.0 and 20.0 g/L in batch experiments, while the concentration was varied between 1.0 and 4.0 g/L in bench experiment. In batch experiment, a reduction of up to 93% of H2S was observed at waste iron powder of 2.0 g/L (T1), while the reduction was of more than 99% at waste iron powder beyond 8.0 g/L (T4 âˆ¼ T6). The total sulfide concentration (ST) increased together with waste iron powder concentration and was fitted with a quadratic equation with a maximum ST of 208.0 mg/L at waste iron powder of 20.2 g/L. Waste iron powder did not have significant effect on methane yield in batch and bench experiments. However, hydrolysis rate constant was increased by almost 100%, while the lag-phase period was reduced to half in test digesters compared to that in control digester. In bench experiment, H2S concentration was reduced by 89% at 2.0 g/L, while 50% at 1.0 g/L. Therefore, waste iron powder was effectively removed H2S and did not affect negatively anaerobic digestion process.

High-solids anaerobic mono-digestion of riverbank grass under thermophilic conditions.

The purpose of this study was to investigate the potential of high-solids anaerobic mono-digestion of riverbank grass under thermophilic conditions, focusing on the effects of the strength and the amount of inoculum. Ensiled grass was inoculated with three different inocula; inoculum from liquid anaerobic digester (LI), inoculum from dry anaerobic digester (DI), and mixture of LI and DI (MI), at feedstock-to-inoculum ratio (FIR) of 1, 2 and 4. The ensiling process of riverbank grass reduced moisture content (p>0.05), while the hemicellulose content was significantly increased from 30.88% to 35.15% (p<0.05), on dry matter basis. The highest methane production was at an FIR of 2 with MI (167L/kg VSadded), which was significantly higher (p<0.05) than with DI, but not significant compared to LI (p>0.05). At an FIR of 4, digesters inoculated with LI and DI failed to produce methane, whereas 135LCH4/kg VSadded was obtained with MI. The kinetic studies showed that at an FIR of 1 with LI and MI, the inoculum had less of effects on the hydrolysis rate constant (0.269day-1 and 0.245day-1) and methane production (135 versus 149L/kg VSadded); rather, it affected the lag phase. In a thermophilic HS-AD of riverbank grass, the mixture of inoculum with low and high total solids content (TS) helps increase the TS of inoculum and digestion process. An FIR of 2 was deducted to be the limit for a better startup time and higher volumetric productivity of methane.

Effects of handling parameters on hydrogen sulfide emission from stored dairy manure.

Hydrogen sulfide (H2S) emission from liquid manure in the process preceding field application is an important issue in fertigation systems. Given that H2S poses a significant health risk, it is important to determine the effects of different handling parameters on H2S emissions to prevent health risks to farmers. In this study, the effects of total solids (TS; 3, 5, 7, 9, and 11%) and mixing speed (100, 200, 300, and 400 rpm), duration (5, 15, 30, and 60 min), and frequency (one, two, three, and four times a day) on H2S emissions from two different dairy manures were investigated. The results indicate that the quantity of sulfur-containing substrate intake determines the potential of dairy manure to emit H2S because manure from cows fed with concentrate-based feed generates higher amounts of H2S than manure from cows fed with forage-based feed. The H2S concentration increased with TS concentration and reached a maximum of 1133 ppm at a TS of 9%; thereafter, it decreased with further increases in TS concentration. H2S emission increased with mixing speed with a peak concentration of 3996 ppm at 400 rpm. A similar trend was observed for mixing duration. However, there were no significant differences between the amounts H2S emitted at different frequencies of mixing (P > 0.05). The results indicate that mixing speed, duration, and TS are the major determinants of the quantity of H2S emitted from dairy manure. Therefore, to prevent health risks associated with H2S emission from dairy manure, it is recommended that the mixing speed and duration should be kept as low as possible, while a TS concentration of above 9% should be applied during the fertigation of dairy manure.

Anaerobic co-digestion of dairy manure and Japanese knotweed (Fallopia japonica) under thermophilic condition: Optimal ratio for biochemical methane production.

Anaerobic co-digestion of animal manure and lignocellulosic biomass is a potent approach for sustainable biomethane production. Co-digestion of dairy manure (DM) and Japanese knotweed (JK), which was collected from a riverbank, was investigated at five different DM-to-JK mixing ratios (100:0, 90:10, 80:20, 60:40, and 0:100; wet weight basis) under thermophilic condition. The results showed that the methane yields obtain from the co-digestion of DM and JK were much higher than that obtained from JK alone (104 ml/gVS), which indicates the synergistic effect and the benefits of co-digesting JK with DM. The highest methane yield (232 ml/gVS) was obtained from the DM-to-JK ratio of 90:10, which was 14.9% and 123.1% higher than that from DM and JK alone, respectively. It also showed the highest synergistic effect (61 ml/gVS). However, further increase in JK ratios led to the decrease in methane yield and synergistic effect. Therefore, applying the co-digestion of DM and JK at a ratio of 90:10 is recommended for biomethane production.

Kinetic study of oxytetracycline and chlortetracycline inhibition in the anaerobic digestion of dairy manure.

This study was aimed to investigate the mechanisms of oxytetracycline (OTC) and chlortetracycline (CTC) inhibition in anaerobic digestion (AD) using four kinetic models. The results showed that the inhibition rate of OTC was faster than CTC at OTC and CTC between 0.04 and 1.28 g/L. Hydrolysis rate constant was linearly and positively correlated with OTC and increased from 0.172 to 0.193 d-1, 0.164 to 0.179 d-1 and 0.251 to 0.285 d-1 using first-order kinetic, Fitzhugh and Cone models, respectively, while the maximum specific methane production rate was linearly and negatively correlated with CTC and decreased from 0.028 to 0.016 L/gVS. Cone model was found to give the most satisfactory fitting results followed in descending order by first-order kinetic, Fitzhugh and modified Gompertz models. The kinetic modeling of methane yield helped explain the mechanism of OTC and CTC inhibition in the AD process and provided essential information for further process improvement.

Effect of solid-liquid separation on anaerobic digestion of dairy manure in semi-continuous stirred tank reactors: Process performance and digestate characteristics.

The objective of this study was to investigate the effect of solid-liquid separation on anaerobic digestion of dairy manure in semi-continuous stirred tank reactors. Reactors fed with liquid fraction of dairy manure (screened liquid manure) were kept in water baths at mesophilic (Run 1) and thermophilic (Run 3) temperatures, respectively, while reactors fed with water diluted manure and kept at mesophilic (Run 2) and thermophilic (Run 4) temperatures as control reactors. The performances of reactors were compared in terms of biogas and methane production, and digestate characteristics. The methane yields obtained from screened manure were higher than those from diluted manure at both mesophilic and thermophilic temperatures, while the highest methane yield was 185 L/kg VSadded under thermophilic temperature. Solid-liquid separation also had improved the effect on digestate fertilizer characteristics. Among four digestates from reactors, the highest contents of nutrients, N (4.12 g/kg) and P (2.36 g/kg) were found in Run 3, while the highest content of K (3.42 g/kg) was found in Run 1. These results showed the benefits of solid-liquid separation of dairy manure on process performance and digestate characteristics.

Prospects for biogas production and H2S control from the anaerobic digestion of cattle manure: The influence of microscale waste iron powder and iron oxide nanoparticles.

Improving the quality and quantity of biogas usually requires pre-treatment to maximize methane yields and/or post-treatment to remove H2S, which involves considerable energy consumption and higher costs. Therefore, this study proposes a cost-effective method for the enhanced anaerobic digestion (AD) of dairy manure (DM) without pre/post-treatment by directly adding waste iron powder (WIP) and iron oxide nanoparticles (INPs) to batch digesters. The results showed that the addition of iron in the form of microscale WIP (generated from the laser cutting of iron and steel) at concentrations of 100 mg/L, 500 mg/L, and 1000 mg/L improved methane yields by 36.99%, 39.36%, and 56.89%, respectively. In comparison, the equivalent dosages of INPs improved yields by 19.74%, 18.14%, and 21.11%, respectively. Additionally, the highest WIP dose (1000 mg/L) achieved the maximum improvement in the rate of hydrolysis (k), which was 1.25 times higher than in control reactions, and a maximum biomethane production rate (Rmax) of 0.045 L/gVS/d according to kinetic analysis models (i.e., first-order and the Gompertz kinetic models). The rate of H2S production was also significantly reduced (by 45.20%, 58.16%, and 77.24%) using the three WIP concentrations in comparison with INPs (which achieved reductions of 33.59%, 46.30%, and 53.52%, respectively). Therefore, the direct mixing of WIP with cattle manure is proposed as a practical and economical means of addressing complex and high-cost pre- and post-treatments that are otherwise required in the digestion process.

Potential of anaerobic digestate of dairy manure in suppressing soil-borne plant disease.

Frequent use of pesticides to control soil-borne plant disease leads to environmental pollution and the development of pesticide resistance in phytopathogens. Soil amendment is considered to have the potential of suppressing plant disease because of its biological properties. However, information on anaerobic digestate is limited. In this study, potential of antagonistic activities of anaerobic digestate against phytopathogens were investigated by detecting the amounts of antagonistic bacteria (Bacillus and Pseudomonas) in anaerobic digestates of dairy manure. The results showed that anaerobic digestion increased the total amounts of Bacillus and Pseudomonas in digestate. Bacillus suppressed growth of phytopathogens, while Pseudomonas did not show any antagonistic activities. These results indicated that Bacillus was an effective antagonistic bacterium in digestate against phytopathogens. Furthermore, two selected isolates, B11 (Bacillus subtilis) and B59 (Bacillus licheniformis), were applied in field experiments and showed significant reduction in percent infection of potato late blight (Phytophthora infestans). These results demonstrate the benefits of digestate in suppressing soil-borne plant diseases caused by antagonistic bacteria.