Multiple strategies for the development of multienzyme complex for one-pot reactions

Development of oriented multi-enzyme strengthens waste activated sludge disintegration and anaerobic digestion: Performance, components transformation and microbial communities

Low methane production and long retention time are the main dilemmas in current anaerobic digestion (AD) of waste activated sludge (WAS). This work used WAS as only substrate to prepare oriented multi-enzyme (ME) that directly used for WAS pretreatment. Under the optimal parameters, the highest activities of protease and amylase in ME could respectively reach 16.5 U/g and 580 U/g, and the corresponding methane production attained 197 mLCH4/g VS, which was increased by 70.4% compared to blank group. It was found that ME pretreatment could strengthen WAS disintegration and organic matters dissolution, lead to the soluble chemical oxygen demand (SCOD) was increased from the initial 486 mg/L to 2583 mg/L, and the corresponding volatile suspended solid (VSS) and extracellular polymeric substances (EPS) were reduced by 27% and 73.8%, respectively. The results of three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform infrared spectroscopy (FTIR) indicated that protein disintegration may be the critical step during the process of WAS hydrolysis with ME, of which the release of tyrosine-like proteins achieved the better biodegradability of WAS, while the results of X-ray photoelectron spectroscopy (XPS) showed that the formation of protein derivatives was the main harmful factor that could extend the lag phase of AD process. Microbial communities analysis further suggested that ME pretreatment facilitated the enrichment of acetogenic bacteria and acetotrophic methanogens, which caused the transition of the methanogenesis pathway from hydrogenotrophic to acetotrophic. This study is expected to furnish valuable insight for ME pretreatment on enhancing WAS disintegration and methane production.

Combustion properties and pollutant analysis of coal-blended bio-heavy oil fuel

Excessive carbon-dioxide emissions drive global climate change and environmental challenges. Integrating renewable biomass fuels with coal in power units is crucial for achieving low-carbon emission reductions. Coal blending with bio-heavy oil enhances the combustion calorific value of the fuel, improves combustion characteristics, and decreases pollutant emissions. This study found that bio-heavy oil with low sulfur (0.073%), low nitrogen (0.18%), low ash, and high oxygen (11.005%) content exhibits excellent fuel performance, which can be attributed to the abundant oxygen-containing functional groups (such as C[double bond, length as m-dash]O) in the alcohols, aldehydes, and ketones present in bio-heavy oil. Additionally, the residual moisture in coal-blended bio-heavy oil reduces the fuel's calorific value. The calorific value increases with a higher proportion of blended bio-heavy oil (28.1, 28.9, 32.1, 34.7, 40.6 MJ kg-1). Experiments on combustion flame shooting reveal that the combustion time of bio-heavy oils is significantly shorter than that of coal. As the proportion of blended bio-heavy oil increases, the flame height increases. Coal blending with bio-heavy oil involves three stages: water evaporation, volatile-matter decomposition, fixed-carbon combustion and mineral decomposition. This advances the combustion process and improves coal's ignition performance. Furthermore, the amount of gaseous pollutants (sulfur dioxide and nitrogen dioxide) in coal mixed with bio-heavy oil is relatively low, which is in alignment with the green environmental protection guidelines. The blending of coal with biomass fuel holds significant practical and strategic importance for developing high-efficiency, low-carbon, coal power units.