Degradation Of Refractory Compounds Research Articles

Fe-loaded alginate hydrogel beads activating peroxymonosulfate for enhancing anaerobic fermentation of waste activated sludge: Performance and potential mechanism

The recovery of volatile fatty acids (VFAs) through anaerobic fermentation (AF) is usually restricted by the poor biodegradability of waste activated sludge (WAS). This study proposed a novel strategy, i.e. peroxymonosulfate (PMS) activated by Fe-loaded sodium alginate hydrogel beads (Fe-SA), to enhance AF performance. Experimental results demonstrated that the as-synthesized Fe-SA and PMS co-pretreatment synergistically enhanced WAS solubilization and VFAs production. The maximal VFAs yield of 2013 mg COD/L was achieved at the Fe-SA dosage of 4.0 mM/g TSS, which was 93.7% higher than that with sole PMS addition and 8.82 times higher than that of the control. Mechanistic studies elucidated that the generation of reactive radicals such as SO4•− and •OH from PMS was greatly induced by Fe-SA, which contributed to WAS disintegration and degradation of refractory compounds. Additionally, analysis of the key enzyme activities indicated that the Fe-SA could strengthen biological hydrolysis and acidogenesis of sludge during AF. Microbial analysis illustrated that Fe-SA evidently improved the abundances of fermentative microorganisms as well as functional gene expression via creating a favorable environment for microbial growth. This study demonstrated the applicable potential of Fe-SA hydrogel beads activating PMS for VFAs production and provides an important reference for developing advanced oxidation processes-based application in AF.

The presence of ferrihydrite enhances greenhouse gas-methane emission in the environment

Aquatic system is the major source of atmospheric methane. This study explored the influences of ferrihydrite, which is widely existed in natural aquatic system, on methane emission. Results showed that the presence of ferrihydrite led to 26.4% more methane emission. By tracking the transformation of organic compounds, it is revealed that the enhanced methane emission was attributed to greater hydrolysis and degradation of refractory compounds. More specifically, the remaining humic-like substances (HS) in ferrihydrite group (46.4 mg/L-C) were only half of that in control group (80.1 g/L-C) after 30-day incubation. The X-ray photoelectron spectroscopy spectrum confirmed the more active oxidation of organics occurred in ferrihydrite group. It was also found that ferrihydrite aided in sustaining microbial activity at stationary and starvation phases. Further study on microbial communities found that ferrihydrite promoted the enrichment of both functional and electroactive genera. This study provides insights into the greenhouse gas emission in natural environment.

Litter decomposition and the degradation of recalcitrant components in Pinus massoniana plantations with various canopy densities

To understand the decomposition characteristics of Pinus massoniana foliar litter and the degradation of its refractory compounds in plantations under five canopy densities, a litter bag experiment over a decomposition time of 392 days was carried out. The results show that canopy density significantly affected decomposition rates of litter and degradation rate of lignin and cellulose. Litter decomposition rates decreased significantly with decreasing canopy density. Both lignin and cellulose degradation rates were lower with canopy densities of 0.62 and 0.74 as compared with the three other densities. Lignin and cellulose losses were more rapid in the first 118 days. Soil fauna had significant impacts on litter decomposition and the degradation of refractory compounds. Canopy density had significant effects on factors such as soil properties and soil fauna community structure, which could be conducive to the decomposition of litter and the degradation of litter recalcitrant components. Canopy density between 0.6 and 0.7 might be a favorable management practice promoting litter decomposition and beneficial for the sustainable development of P. massoniana plantations.

Kinetic modeling and determination role of sono/photo nanocatalyst-generated radical species on degradation of hydroquinone in aqueous solution.

Experimental findings of sonophotocatalytic process were used in degradation of hydroquinone to assess kinetic modeling and determine the effect of various active radical species. First, the effects of three photocatalytic, sonocatalytic, and sonophotocatalytic processes were studied for hydroquinone removal to determine kinetic constants and calculate the activation energy of reactions, and then the selected process was evaluated to determine active radical species. The reactor was composed of two parts, one included ultrasonic probe (sonocatalytic part) with powers 22, 80, and 176W and the second part was the location of UV lamp (photocatalytic part) with tubular flow and power 15W. After three systems were examined and the efficient system was selected, the role of different active species such as hydroxyl radical (OH(·)), superoxide radical (O2 (·-)), hole (h(+)), electrons (e (-)), and single oxygen molecule ((1)O2) and contribution of each of them were determined in hydroquinone degradation. According to tests, the results of this study showed that sonophotocatalytic integrated method as selected system among three systems studied followed the first-order equation for hydroquinone degradation and active hydroxyl species with 45% and electron and hole with 15 and 10%, respectively, had the highest and lowest contributions to conversion of hydroquinone. The findings showed that dissolved oxygen increases the capability of active radical formation so that 28.2% of hydroquinone removal was increased under aeration compared to without aeration. Also, removal efficiency decreased 62% with N2 injection due to the withdrawal of oxygen from the sample. By adding 25Mm of sodium azide (NaN3) to stock solution, 46.5% reduction was developed because single oxygen ((1)O2) played the role of an active species. The advantages of integrated sonocatalytic and photocatalytic method are the generation of active radical species with more variety and ultimately the formation of higher amounts of powerful hydroxyl radical that increases degradation rates of refractory compounds and low-risk internal and final products. It has an appropriate performance in the degradation of refractory compounds by optimizing effective operational factors.

Oxygen availability and temperature as driving forces for decomposition of aquatic macrophytes

The decomposition of organic matter constitutes a fundamental ecosystem process where microorganisms, affected by temperature and oxygen availability, play a fundamental role. The decomposition rates interfere in the global carbon cycle and therefore, in the potential feedback to climate change. We addressed the individual and combined effects of water temperature (15, 20, 25 and 30°C) and oxygen availability (aerobic and anaerobic) on the decomposition of three aquatic macrophytes (Eichhornia azurea, Eleocharis sp. and Salvinia auriculata) in microcosms carried out for 120 days. A first-order kinetic model was adopted to describe the kinetics of the decomposition. The decomposition had a biphasic pattern of mass loss: labile/soluble fraction (≈15.4; 10.6 and 10.7% for E. azurea, Eleocharis sp. and S. auriculata, respectively) and refractory (≈84.2; 89.4 and 89.0% for E. azurea, Eleocharis sp. and S. auriculata, respectively). Based on the decomposition kinetics, the leaching process was faster than the degradation of refractory compounds. Comparing the effect of temperature and the availability of dissolved oxygen, the latter seems more relevant for the decomposition process of these plants. Oxygen availability accelerated the decomposition 1.25 times compared to anoxic conditions, while a temperature increase of 10°C accelerated it by 1.35 times. However, it is important to consider that these environmental variables act synergistically in the regulation of decomposition and therefore all of them influence the decomposition rates.

Removal of COD, phenols and ammonium from Lurgi coal gasification wastewater using A2O-MBR system

As a typical industrial wastewater, coal gasification wastewater has poor biodegradability and high toxicity. In this paper, a laboratory-scale anaerobic–anoxic–oxic membrane reactor (A2O-MBR) system was developed to investigate the treatment ability of coal gasification wastewater. The removal capacity of each pollutants used in this system were determined at different hydraulic residence times (HRT) and mixed liquor recycle ratios (R). The experimental results showed that this system could effectively deal with COD and phenol removal and remain in a stable level when the operational parameters altered, while the nitrification was sensitive to operational conditions. The best performance was obtained at HRT of 48h and R of 3. The maximum removal efficiencies of COD, NH4+-N and phenols were 97.4%, 92.8% and 99.7%, with final concentrations in the effluent of 71mg/L, 9.6mg/L and 3mg/L, respectively. Organics degradation and transformation were analyzed by GC/MS and it was found that anaerobic process played an important role in degradation of refractory compounds.