A shift from anaerobic digestion to dark fermentation in glycol ethylene fermentation

Metagenomic analysis of ethylene glycol contamination in anaerobic digestion

Anaerobic digestion is an established method for the biological conversion of waste feedstocks to biogas and biomethane. While anaerobic digestion is an excellent waste management technique, it can be susceptible to toxins and pollutants from contaminated feedstocks, which may have a detrimental impact on a digester's efficiency and productivity. Ethylene glycol (EG) is readily used in the heat-transfer loops of anaerobic digestion facilities to maintain reactor temperature. Failure of the structural integrity of these heat transfer loops can cause EG to leak into the digester, potentially causing a decrease in the resultant gas yields. Batch fermentations were incubated with 0, 10, 100 and 500 ppm (parts per million) of EG, and analysis showed that the EG was completely metabolised by the digester microbiome. The concentrations of EG tested showed significant increases in gas yields, however there were no significant changes to the digester microbiome.

Life cycle energy consumption, environmental impact, and costing assessment of coal to ethylene glycol processes via dimethyl oxalate and formaldehyde

The popularization of conventional dimethyl oxalate to ethylene glycol (DMOtEG) has kept ongoing in the past decade in China. Recently, a northern China factory in construction attracts attention using alternative formaldehyde to ethylene glycol (FtEG) route. Thus, a question arises about the individual comparative advantages of these two processes. So, this paper conducts a systematic modeling analysis of DMOtEG and FtEG, and the life cycle assessment is performed by SimaPro v9 to compare their impact. The results indicate the inferiority of life cycle energy consumption and life cycle cost of FtEG to those of DMOtEG due to the high energy consumption and pollutant emissions. Moreover, most impact categories of FtEG are worse than the DMOtEG as global warming, and photochemical oxidant formation potential. Despite this, FtEG still wins for better potentials in ozone formation, fine particulate matter formation, and terrestrial acidification because of less nitride emissions. In addition, the decrease in energy consumption and external cost will significantly decrease the life cycle cost under controllable catalyst costs of FtEG. These results describe the impact categories of DMOtEG and FtEG and provide a basis to help decision-makers develop coal to ethylene glycol processes.

Plastic and Waste Tire Pyrolysis Focused on Hydrogen Production—A Review

In this review, we compare hydrogen production from waste by pyrolysis and bioprocesses. In contrast, the pyrolysis feed was limited to plastic and tire waste unlikely to be utilized by biological decomposition methods. Recent risks of pyrolysis, such as pollutant emissions during the heat decomposition of polymers, and high energy demands were described and compared to thresholds of bioprocesses such as dark fermentation. Many pyrolysis reactors have been adapted for plastic pyrolysis after successful investigation experiences involving waste tires. Pyrolysis can transform these wastes into other petroleum products for reuse or for energy carriers, such as hydrogen. Plastic and tire pyrolysis is part of an alternative synthesis method for smart polymers, including semi-conductive polymers. Pyrolysis is less expensive than gasification and requires a lower energy demand, with lower emissions of hazardous pollutants. Short-time utilization of these wastes, without the emission of metals into the environment, can be solved using pyrolysis. Plastic wastes after pyrolysis produce up to 20 times more hydrogen than dark fermentation from 1 kg of waste. The research summarizes recent achievements in plastic and tire waste pyrolysis development.

Microbial Biogas Production from Pork Gelatine

This research describes the results of the anaerobic digestion of gelatine as a potential hydrogen source with heat-shocked inoculum. The concentrations of applied gelatine were of VSS (volatile suspended solids) ranging from 10 g VSS/L to 30 g VSS/L. The initial process pH was 5.5, and, depending on the concentration, reached pH values from 7.5 to 7.8 after 55 days. Although the inoculum was heat-shocked in 30 g VSS/L of collagen, the process that occurred was hydrogenotrophic anaerobic digestion. In gelatine concentrations below 30 g VSS/L, hydrogen production was dominant only during the first 5 days of the experiments. Then, there was a change from dark fermentation to hydrogenotrophic methane production. The optimal hydrogen and methane yields resulted from the concentrations of 10 g VSS/L (7.65 mL ± 0.01 mL H2/g VSS and 3.49 ± 0.01 L CH4/g VSS). Additionally, 10 g VSS/L had the lowest accumulated emission of hydrogen sulphide (10.3 ± 0.01 mL of H2S), while 30 g VSS/L (0.440 ± 0.01mL H2S/g VSS) produced the lowest yield. After a lag time, the hydrogen production and hydrogen sulphide grew with a specific ratio, depending on the concentration. The hydrogen sulphide emission and sulphur added analysis proved that hydrogen sulphide originating from biogas created by bacteria remains longer than that from a substrate.

Modelling of dark fermentation of glucose and sour cabbage

In the article, modified Anaerobic Digestion Models 1 (ADM-1) was tested for modelling dark fermentation for hydrogen production. The model refitting was done with the Euler method. The new model was based on sets of differential equations. The model was checked for hydrogen production from sour cabbage in batch and semi-batch in 5 g VSS (volatile solid suspension)/L and at the semi-batch process from glucose at 5 and 10 g VSS/L. Added parameters determined the conversion of a substrate, hydrogen production, and stress parameters. In the case of a semi-batch process, for one month, cumulative hydrogen production from sour cabbage of 5 g VSS/L was 0.9 L of cumulative hydrogen volume and from glucose 5 g VSS/L (in case of feeding 2 g VSS/L every two days) 2.5 L of cumulative hydrogen volume. At the bacterial population level, hydrogen production was a continuous process at an adequate range of population size and environmental parameters.