Effects of propionic acid concentration on anaerobic digestion of pig manure

Effect of Pretreatment by Freeze Vacuum Drying on Solid-State Anaerobic Digestion of Corn Straw

As a common agricultural waste, corn straw (CS) has a refractory structure, which is not conducive to anaerobic digestion (AD). Appropriate pretreatment is crucial for addressing this problem. Thus, freeze vacuum drying (FVD) was proposed. In this study, fresh CS (F-CS) pretreated (5 h, −40 °C) by FVD and naturally dried CS (D-CS) were compared. Differences in substrate surface structure and nutrient composition were first investigated. Results show that a loose and porous structure, crystallinity, and broken chemical bonds, as well as higher proportions of VS, C, N, cellulose, hemicellulose, and crude proteins in F-CS show a potential for methane production. Besides, process performance and stability were also examined in both high (4, VS basis) and low (1, VS basis) S/I ratio AD. A higher degradation ratio of hemicellulose as well as richer dissolved microbial metabolites, coenzymes, tyrosine-like proteins, and hydrolysis rate of particulate organic matter in the F-CS system enhanced the efficiency of methane conversion. The cumulative methane yield increased from 169.66 (D-CS) to 209.97 (F-CS) mL/gVS in the high S/I ratio system (p = 0.02 < 0.05), and 156.97 to 171.89 mL/gVS in the low S/I ratio system. Additionally, 16S-rRNA-gene-based analysis was performed. Interestingly, the coordination of key bacteria (Clostridium_sensu_stricto_1, Bacillus, Terrisporobacter. Clostridium_sensu_stricto_7, Thermoclostrium, UCG-012, and HN-HF0106) was more active. Poorer Methanosarcina and Methanomassiliicoccus as well as richer Methanobrevibacter and Methanoculleus stimulated the co-relationship of key archaea with diverse methanogenesis pathways. This study aims to verify the positive effect of FVD pretreatment on AD of CS, so as to provide a reference for applications in waste management.

Bio-hydrogen and methane production from two-phase anaerobic digestion of food waste under the scheme of acidogenic off-gas reuse

Anaerobic hydrolysis of food wastes sourced from bakery (T1), Chinese restaurant (T2), western-style restaurant (T3), and wet market (T4) were performed in leach bed reactors under the scheme of acidogenic off-gas reuse in methanogenic reactor. Results showed that food waste in T3 achieved the highest hydrogen production of 61.0 L/kg·VS_added. Highest activity of hydrogenase in both leachate and digestate samples confirmed the superior performance of H₂ production in T3. Mixed acid fermentation with domination of acetate and butyrate was observed in all four treatments, whereas variations in quantification and speciation of the acidogenic products were closely related to the composition of substrates. High volatile solids (VS) removal (76.7%) was observed in T3 while VS reduction rates of the other treatments ranged from 37 to 55%. High COD production of 0.65 gCOD /g·VS_added together with the reuse of elevated acidogenic off-gas ensured the highest specific CH₄ production of 0.42 L/g·VS_added in T3.

Fermentation of wet-exploded corn stover for the production of volatile fatty acids

Volatile fatty acids (VFA) have been used as platform molecules for production of biofuels and bioproducts. In the current study, we examine the VFA production from wet-exploded corn stover through anaerobic fermentation using rumen bacteria. The total VFA yield (acetic acid equivalents) was found to increase from 22.8g/L at 2.5% total solids (TS) to 40.8g/L at 5% TS. It was found that the acetic acid concentration increased from 10g/L to 22g/L at 2.5% and 5% TS, respectively. An increased propionic acid production was seen between day 10 and 20 at 5% TS. Valeric acid (4g/L) was produced at 5% TS and not at 2.5% TS. Composition analysis showed that 50% of the carbohydrates were converted to VFA at 5% TS and 33% at 2.5% TS. Our results show that rumen fermentation of lignocellulosic biomass after wet explosion can produce high concentrations of VFA without addition of external enzymes of importance for the process economics of lignocellulosic biorefineries.

The effect of feeding high fat diet to beef cattle on manure composition and gaseous emission from a feedlot pen surface

BACKGROUND

Dietary manipulation is a common practice to mitigate gaseous emission from livestock production facilities, and the variation of fat level in the diet has shown great influence on ruminal volatile fatty acids (VFA) and enteric methane generation. The changes in dietary fat levels influence rumen chemistry that could modify manure nutrient composition along with odor and gaseous emissions from manure management facilities.

METHODS

A field experiment was carried out on beef cattle feedlots to investigate the effect of four levels of dietary fat concentrations (3 to 5.5 %) on the manure composition and gaseous emissions (methane-CH4, nitrous oxide-N2O, carbon dioxide-CO2 and hydrogen sulfide-H2S) from the feedlot pen surface. The experiment was carried out over a 5-month period from June to October during North Dakota's summer-fall climatic condition. Air and manure sampling was conducted five times at a 20-30 day intervals.

RESULTS

Overall, this research indicated that fat levels in diet have no or little effect on the nutrient composition of manure and gaseous emission from the pens with cattle fed with different diet. Though significant variation of gaseous emission and manure composition were observed between different sampling periods, no effect of high fat diet was observed on manure composition and gaseous emission.

CONCLUSIONS

It can be concluded that addition of fat to animal diet may not have any impact on gaseous emission and manure compositions.

Multi-phased anaerobic baffled reactor treating food waste

This study was conducted to identify the performance of a multi-phased anaerobic baffled reactor (MP-ABR) with food waste (FW) as the substrate for biogas production and thereby to promote an efficient energy recovery and treatment method for the wastes with high organic solid content through phase separation. A four-chambered ABR was operated at an HRT of 30 days with an OLR of 0.5-1.0 g-VS/Ld for a period of 175 days at 35 ± 1°C. Consistent overall removal efficiencies of 85.3% (CODt), 94.5% (CODs), 89.6% (VFA) and 86.4% (VS) were observed throughout the experiment displaying a great potential to treat FW. Biogas generated was 215.57 mL/g-VS removed d. Phase separation was observed and supported by the COD and VFA trends, and an efficient recovery of bioenergy from FW was achieved.

Effect of Volatile Fatty Acid Concentration on Anaerobic Degradation Rate from Field Anaerobic Digestion Facilities Treating Food Waste Leachate in South Korea

The purpose of this study was to investigate the effect of volatile fatty acid concentration on anaerobic degradation rate of food waste leachate in the anaerobic digestion facilities. The anaerobic digestion facilities treating food waste leachate (FWL), codigestion with food leachate and animal manure (A-MIX), and codigestion with food waste leachate and sewage sludge (S-MIX) were selected for this study. In accordance with the regulation under Wastes Control Act in South Korea, the guideline of volatile solid removal rate for anaerobic digestion facility is set as 65% for anaerobic degradation efficiency. Highest volatile solids removal rates were achieved from FWL (63.5%) than A-MIX (56.4%) and S-MIX (41.2%). Four out of eight FWLs met the guidelines. The concentration of volatile fatty acids, therefore, was analyzed to determine the relationship with volatile solid removal rate. The results showed that, in order to meet the Korean guideline of 65% volatile solid removal rate, volatile fatty acid concentrations should remain below 4,000 mg/L on the field anaerobic digestion facilities treating FWL. Volatile fatty acid concentrations should be used along with others as an operational parameter to control and manage the anaerobic digestion process.

Modeling the pH effect on sulfidogenesis in anaerobic sewer biofilm

Wastewater pH affects the transfer of H2S from liquid to gas and hence impacts on the extent of odour and corrosion. Sewage pH may change significantly in sewer networks due to, for example, the fermentation of organic compounds, particularly when the hydraulic retention time is long, the discharge of trade wastes that are organic-rich or with extreme pH, and the intentional addition of alkali to raise the sewage pH. Such a variation of pH is expected to affect sulfate reduction by sewer biofilms. In this work, experimental studies were carried out to reveal the detailed effects of pH on sulfidogenesis by anaerobic sewer biofilms developed in a laboratory sewer reactor fed with real sewage, and the potential causes for the inhibitory effects observed under both high and low pH conditions. The data clearly showed that the sewer biofilm had the highest sulfate reduction rate at around neutral pH (6.5-7.5), and the activity decreased when pH was higher or lower. The data also suggested that the inhibiting effect at a higher pH is likely due to the inhibitory effects of free ammonia, while at a lower pH it is more likely due to the pH itself. An inhibition model formulated based on the above hypotheses was able to adequately describe the measured sulfide production rates under different pH levels and different free ammonia concentrations, as well as data previously reported in literature. The calibrated model was used to simulate sulfide production in a sewer network receiving alkali dosage. The model adequately predicted sulfide production in the network, which could not be achieved with a model not considering the pH effect.

Anaerobic digestion of glycerol and co-digestion of glycerol and pig manure

The potential of glycerol obtained from transesterification of waste cooking oil as a main carbon source for biogas production was investigated. The glycerol was highly contaminated with oils and fats and was pretreated with sulfuric acid. Using a carbon source of glucose as a control, we compared biogas production from the acid-treated glycerol in a synthetic medium and the acid-treated glycerol mixed with pig manure. The anaerobic digestion of acid-treated glycerol with supplement in a synthetic medium was found to be satisfactory at organic loading rates (OLR) between 1.3, 1.6 and 2.6 g chemical oxygen demand (COD) L(-1) d(-1). The maximum methane yield of 0.32 L at Standard temperature and pressure (STP) g(-1) COD removal was achieved at an OLR of 1.6 g COD L(-1) d(-1) and the methane content was 54% on an average. At a higher organic loading rate of 5.4 g COD L(-1) d(-1), the propionic acid to acetic acid ratio was higher than the critical threshold limit for metabolic imbalance. Anaerobic digestion of acid-treated glycerol with pig manure was also investigated at the COD ratio of 80:20 (glycerol:pig manure). The anaerobic digestion of acid-treated glycerol with pig manure was found to be satisfactory at organic loading rates between 1.3, 1.7, 2.9 and 5.0 g COD L(-1) d(-1) in terms of COD reduction (>80%) and methane content of (62% on an average). However, the biogas production rate was found to significantly decrease at the highest load. The maximum methane yield of 0.24 L STP g(-1) COD removal was achieved at an OLR of 1.3 g COD L(-1) d(-1).

Influence of substrate concentration and moisture content on the specific methanogenic activity of dry mesophilic municipal solid waste digestate spiked with propionate

The objective of this study was to evaluate the influence of substrate concentration and moisture content on the specific methanogenic activity (SMA) of a fresh dry mesophilic digestate from a municipal solid waste digester plant. For this purpose, SMA tests were performed under mesophilic conditions into glass bottles of 500 mL volume used as batch reactors, during a period of 20-25 days. Propionate was used as substrate at concentrations ranging from 1 to 10 gCOD/kg. Four moisture contents were studied: 65%, 75%, 80% and 82%. Experimental results showed that propionate concentration and moisture content strongly influenced the SMA. The highest SMA was observed at a substrate concentration of 10 gCOD/kg (11.3 mgCOD gVS(-1) d(-1) for the second dose of propionate) and at a moisture content of 82% (7.8 mgCOD gVS(-1) d(-1) for the second dose of propionate, at a concentration of 5 gCOD/kg). SMA was found to decrease linearly when decreasing the moisture content.

Pilot-scale anaerobic digestion of screenings from wastewater treatment plants

The anaerobic digestion of screenings from a municipal wastewater treatment plant was studied in a 90 L pilot-scale digester operated at 35 degrees C under semi-continuous conditions. In the first 4 weeks, a dry solids residence time of 28 days was applied, but the installation of inhibitory conditions was observed. Feeding was therefore suspended for 4 weeks to allow the digester to recover from inhibition, and then progressively increased up to a constant load of 6 kg of raw waste per week, corresponding to an average residence time of about 35 days of dry solids. At this stage, biogas production stabilized between 513 and 618 Nl/kg VS(added) per week, with methane contents around 61% v/v. The results of this work thereby supported the feasibility of (co-)digestion as a potential alternative treatment of screenings from municipal wastewater treatment plants.

Anaerobic digestion of municipal solid waste as a treatment prior to landfill

Anaerobic digestion of organic fraction of municipal solid waste was conducted in pilot-scale reactor based on high-solid combined anaerobic digestion process. This study was performed in two runs. In Run 1 and Run 2, pre-stage flushing and micro-aeration were conducted to determine their effect in terms of enhancing hydrolysis and acidification in ambient condition. In Run 2, after pre-stage, the methane phase (methanogenesis) was started-up after pH adjustment and inoculum addition in mesophilic condition. Acidified leachate produced in pre-stage was used for percolation during active methane phase. At the end of methane phase, air flushing was conducted before unloading the digesters. Hydrolysis and acidification yield of 140 g C/kg TS and 180 g VFA/kg TS were achieved, respectively in pre-stage. Micro-aeration exhibited an equivocal result in terms of enhancing hydrolysis/acidification; however it showed a positive effect in methane phase performance and this needed further investigation. Leachate percolation during methane phase showed an enhanced methanization when compared to the reactors without leachate percolation. After 60 days, 260 l CH(4)/kg VS was obtained. Based on the waste methane potential, 75% biogas conversion and 61% VS degradation were achieved.