Integrated two-phase acidogenic-methanogenic treatment of municipal sludge with thermal hydrolysis

The purpose of this research was to investigate the impact of two process configurations integrating two-phase anaerobic digestion (AD) of municipal sludge with thermal hydrolysis (TH). The TH was positioned either before or after the acidogenic fermentation phase. The fermentation process was carried out under the semi-continuous flow regime with a retention time of three days. The TH was done at a temperature of 170 °C and for 30 min. Among all the tested scenarios, the TH of sludge followed by the acidogenic fermentation resulted in the highest COD solubilization ratio (39.5%) and volatile fatty acids production (6,420 ± 400 mg/L), which was 630% and 500% more than that of the raw sludge, respectively. The sequential TH/fermentation process achieved 40% higher ultimate methane yield (240 mL/g COD) than the non-pretreated (raw) sludge. Positioning TH after the fermentation process reduced the ultimate methane yield to 231 240 mL/g COD, although it was still 32% higher than that of the raw sludge. The analysis of methane production rate and biodegradation kinetics data suggested the formation of refractory intermediates during the thermal process of sludge, which reduced the overall performance rate during the first week of the AD process. It was also revealed that acidogenic fermentation of thermally-processed sludge could diminish the adverse effect of the recalcitrant compounds formed during the thermal hydrolysis on the subsequent AD process.

A comprehensive dataset on anaerobic digestion of cattle manure, source separated organics, and municipal sludge using different inoculum sources

The dataset reported in this article provides quantitative data on anaerobic digestion of cattle manure, source separated organics (SSO), primary sludge (PS), and thickened waste activated sludge (TWAS) using different inoculum sources. The discussion and interpretation of the data are provided in another publication entitled “Comparison of liquid and dewatered digestate as inoculum for anaerobic digestion of organic solid wastes” [1]. The data presented in this article include 1) the gas chromatography (GC) procedure of determining the biogas composition, 2) the procedure of converting the daily biogas/methane production data from the experimental condition (mesophilic temperature of 38 °C and room pressure) to the standard temperature (0 °C) and pressure (1 atm) condition, 3) the specific methanogenic activity data, and 4) the methane daily production rate data, and 5) the organics biodegradation kinetic rates.

Comparison of liquid and dewatered digestate as inoculum for anaerobic digestion of organic solid wastes

In this study, the application of liquid and dewatered digestate was compared for the inoculation of the anaerobic digestion (AD) process. In addition to the specific methanogenic activity and biohydrogen potential tests, biochemical methane potential assay was also conducted using four different types of municipal and industrial waste streams (primary sludge, thickened waste activated sludge, source separated organics, and cattle manure). The specific methanogenic activity of the digestate cake (5.0 ± 0.5 mL-CH₄/g-VSS.d) was higher than that of the liquid digestate (3.4 ± 0.2 mL-CH₄/g-VSS.d) for the food to microorganism ratio of 0.5. The BMP results also revealed that regardless of the type of the substrate used, the application of the digestate cake as inoculum achieved statistically significantly higher methane production rate compared to the utilization of liquid digestate, most likely due to the lower concentration of dissolved contents (i.e., ammonia, soluble organic matter, heavy metals, etc.) in the diluted digestate cake. Despite the increased process rate, no statistically significant effect of the type of the inoculum was observed on the ultimate methane yield. The biohydrogen potential test revealed the similar performance of the digestate- and digestate cake-inoculated digesters in terms of biohydrogen and volatile fatty acids production. The findings of this study suggest that the digestate cake can be used as an effective alternative to the liquid digestate for the inoculation of full-scale anaerobic digesters, reducing the transportation volume by up to 90%.

Enzymatic pretreatment of lignocellulosic biomass for enhanced biomethane production-A review

The rapid depletion of natural resources and the environmental concerns associated with the use of fossil fuels as the main source of global energy is leading to an increased interest in alternative and renewable energy sources. Particular interest has been given to the lignocellulosic biomass as the most abundant source of organic matter with a potential of being utilized for energy recovery. Different approaches have been applied to convert the lignocellulosic biomass to energy products including anaerobic digestion (AD), fermentation, combustion, pyrolysis, and gasification. The AD process has been proven as an effective technology for converting organic material into energy in the form of methane-rich biogas. However, the complex structure of the lignocellulosic biomass comprised of cellulose, hemicelluloses, and lignin hinders the ability of microorganisms in an AD process to degrade and convert these compounds to biogas. Therefore, a pretreatment step is essential to improve the degradability of the lignocellulosic biomass to achieve higher biogas rate and yield. A system that uses pretreatment and AD is known as advanced AD. Several pretreatment methods have been studied over the past few years including physical, thermal, chemical and biological pretreatment. This paper reviews the enzymatic pretreatment as one of the biological pretreatment methods which has received less attention in the literature than the other pretreatment methods. This paper includes a review of lignocellulosic biomass composition, AD process, challenges in degrading lignocellulosic materials, the current status of research to improve the biogas rate and yield from the AD of lignocellulosic biomass via enzymatic pretreatment, and the future trend in research for the reduction of enzymatic pretreatment cost.