Wenquan Ruan

Degradation of phenazone in aqueous solution with ozone: influencing factors and degradation pathways.

Oxidation kinetics and degradation pathways of phenazone (an analgesic and antipyretic drug) upon reaction with O3 were investigated. Kinetic studies on degradation of phenazone were carried out under different operating conditions such as temperature, pH, anions and H2O2 addition. Results showed that the degradation followed the pseudo-first-order kinetic model. The reaction rate constant (kobs) of phenazone reached the maximum at 20 °C (9.653×10(-3) s(-1)). The presence of NO3(-) could enhance the degradation rate, while the addition of HCO3(-), SO4(2)(-), Cl(-) and the rise of pH showed negative effects on the ozonation of phenazone. H2O2 addition increased the phenazone degradation efficiency by 45.9% with the optimal concentration of 0.135 mM. Reaction by-products were evaluated by UPLC-Q-TOF-MS, which allowed the identification of a total of 10 by-products. The transformation pathways of phenazone ozonation consisted mainly of electrophilic addition and substitution, pyrazole ring opening, hydroxylation, dephenylization and coupling. The toxicity of these intermediate products showed that they are expected not to be more toxic than phenazone, with the exception of P7 (aniline) and P10 (1,5-dimethyl-4-((1-methyl-2-phenylhydrazinyl)methoxy)-2-phenyl-1H-pyrazol-3(2H)-one).

Evaluation and characterization during the anaerobic digestion of high-strength kitchen waste slurry via a pilot-scale anaerobic membrane bioreactor

The anaerobic digestion of high-strength kitchen waste slurry via a pilot-scale anaerobic membrane bioreactor (AnMBR) was investigated at two different operational modes, including no sludge discharge and daily sludge discharge of 20 L. The AnMBR provided excellent and reliable permeate quality with high COD removal efficiencies over 99%. The obvious accumulations of long chain fatty acids (LCFAs) and Ca(2+) were found in the anaerobic digester by precipitation and agglomeration. Though the physicochemical process contributed to attenuating the free LCFAs toxicity on anaerobic digestion, the digestion efficiency was partly influenced for the low bioavailability of those precipitates. Moreover, higher organic loading rate (OLR) of 5.8 kg COD/(m(3) d) and digestion efficiency of 78% were achieved as the AnMBR was stably operated with sludge discharge, where the membrane fouling propensity was also alleviated, indicating the crucial significance of SRT control on the treatment of high-strength kitchen waste slurry via AnMBRs.

Insights into sludge granulation during anaerobic treatment of high-strength leachate via a full-scale IC reactor with external circulation system

In this study, a full-scale internal circulation (IC) reactor coupled with an external circulation system was developed to treat high-strength leachate from a municipal solid waste (MSW) incineration plant, in which anaerobic sludge granulation was intensively investigated. Results showed that the IC reactor achieved excellent treatment performance under high organic loading rates (OLR) of 21.06-25.16kg chemical oxygen demand (COD)/(m3∙day). The COD removal efficiency and biogas yield respectively reached 89.4%-93.4% and 0.42-0.50m3/kgCOD. The formation of extracellular polymeric substances (EPS) was closely associated with sludge granulation. Protein was the dominant component in sludge EPS, and its content was remarkably increased from 21.6 to 99.7mg/g Volatile Suspended Solid (VSS) during the reactor operation. The sludge Zeta potential and hydrophobicity positively correlated with the protein/polysaccharide ratio in EPS, and they were respectively increased from -26.2mV and 30.35% to -10.6mV and 78.67%, which was beneficial to microbial aggregation. Three-dimensional fluorescence spectroscopy (3D-EEM) and Fourier transform infrared spectroscopy (FT-IR) analysis further indicated the importance of protein-like EPS substances in the sludge granulation. Moreover, it was also found that the secondary structures of EPS proteins varied during the reactor operation.

A model based on feature objects aided strategy to evaluate the methane generation from food waste by anaerobic digestion

A model based on feature objects (FOs) aided strategy was used to evaluate the methane generation from food waste by anaerobic digestion. The kinetics of feature objects was tested by the modified Gompertz model and the first-order kinetic model, and the first-order kinetic hydrolysis constants were used to estimate the reaction rate of homemade and actual food waste. The results showed that the methane yields of four feature objects were significantly different. The anaerobic digestion of homemade food waste and actual food waste had various methane yields and kinetic constants due to the different contents of FOs in food waste. Combining the kinetic equations with the multiple linear regression equation could well express the methane yield of food waste, as the R2 of food waste was more than 0.9. The predictive methane yields of the two actual food waste were 528.22 mL g-1 TS and 545.29 mL g-1 TS with the model, while the experimental values were 527.47 mL g-1 TS and 522.1 mL g-1 TS, respectively. The relative error between the experimental cumulative methane yields and the predicted cumulative methane yields were both less than 5%.

Insights into influencing factor, degradation mechanism and potential toxicity involved in aqueous ozonation of oxcarbazepine (CHEM46939R1)

Oxcarbazepine (OXC), as a potent antiepileptic drug, is widely used in recent years, but its residue is potentially harmful to the environment. Although ozonation is a high-efficient technology for chemical oxidation during water treatment, it cannot completely mineralize organic matters, but partially transforms them into some unidentified by-products. In order to provide more insight into OXC ozonation process, the influencing factor, transformation mechanism and potential toxicity were comprehensively investigated in this study. The results showed that the optimal ozonation temperature was 20 °C with a pseudo-first-order reaction rate constant of 0.161 min-1. The increase of pH significantly enhanced OXC degradation, while the presence of bicarbonate caused a remarkable negative effect, manifesting that hydroxyl radical (OH) oxidation should play an important role in OXC ozonation. Moreover, transformation mechanism was further elucidated based on the identification of ten OXC-related by-products using UPLC-Q-TOF-MSn, which mainly consisted of electrophilic substitution, N-heterocyclic ring cleavage and re-arrangement, hydroxylation, carbonylation, demethoxylation and deamidation, etc. The toxicity evaluation, using US Environmental Protection Agency Toxicity Estimation Software Tool (US-EPA TEST), suggested that most identified by-products were probably more toxic than OXC itself. Besides, further experiments, by measuring inhibitory effect of ozonated mixture on Vibrio fischeri bioluminescence, demonstrated that by-products with higher toxicity tended to be accumulated under a short reaction time. Taken together, the present investigation provided valuable information for further understanding OXC ozonation process, and suggested that special attention should be paid to the control and elimination of toxic transformation by-products in future studies.

Evaluation of potassium as promoter on anaerobic digestion of saline organic wastewater

In this work, the effect of potassium on mesophilic anaerobic digestion (AD) of saline organic wastewater, which consisted of simulated effluents obtained from heparin sodium production, was studied. The results showed that the addition of potassium chloride (KCl) to saline organic wastewater enhanced the AD efficiency. The optimal dosage was found to be 0.174% when the salt (NaCl) content was 2.0%. Under this condition, the chemical oxygen demand (COD) removal efficiency, dehydrogenase activities, and the viability of microorganisms reached 62.7%, 55.7 TF μL-1, and 78.4%, respectively, which were 115.4%, 77.2%, and 20.3% higher than those without the addition of potassium chloride. The consumption of volatile fatty acids (VFAs) was enhanced during the AD process. Moreover, less humic-like and protein-like residues appeared in the wastewater after AD. Potassium could maintain the morphology of anaerobic microorganism under high salinity and showed a long-term effect.

Performance of enhanced biological phosphorus removal and population dynamics of phosphorus accumulating organisms in sludge-shifting sequencing batch reactors

The sludge-shifting sequencing batch reactor (SBR) is an enhanced biological phosphorus removal (EBPR) process for wastewater treatment. In this study, the enrichment of phosphorus accumulating organisms (PAOs) will be attempted by using different high concentration of substrates. In sludge-shifting SBR, activated sludge can be continuously shifted from the bottom of SBR to anaerobic zone/selector, which contains high concentration of substrates, through an orderly reflux between the paralleled SBRs. Denaturing gradient gel electrophoresis (DGGE) methods were used to monitor microbial diversity in sludge. Fluorescence in situ hybridization (FISH) was used to determine the microbial population profile and distribution map under different sludge shifting volumes. The synthesis of intracellular polymers in this process was also analyzed. Phosphorus removal efficiency as high as 96% ± 1.3% was achieved under a sludge shifting ratio of 30%. Synthetic efficiencies of polyhydroxybutyrate (PHB) by PAOs were improved at high sludge shifting ratios. FISH results demonstrated that the population of PAOs in the process increased under properly sludge shifting ratio and it significantly improved phosphorus removal efficiency. Sequencing results indicated that determined sequences (11 OTUs) belonged to Proteobacterium, Actinobacteria and Firmicutes, Pseudomonas kuykendallii, which played an important role in the process of P removal.

Performance and microbial community in a combined VF-HF system for the advanced treatment of secondary effluent

In this study, a laboratory-scale system combined a vertical flow constructed wetland (VF) with a horizontal flow constructed wetland (HF), which was used to treat the secondary effluent of a wastewater treatment plant. Removal efficiencies of 67.02%, 89.80%, 90.31% and 75.38% were achieved by the system for chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total nitrogen (TN) and total phosphorus (TP), respectively. The VF showed much higher average loading rates of COD, TP, NH4+-N and TN (7.96 g/m2/d, 0.076 g/m2/d, 0.31 g/m2/d and 0.99 g/m2/d) than in HF (0.65 g/m2/d, 0.016 g/m2/d, 0.25 g/m2/d and 0.50 g/m2/d), during the stable operation period. Biodegradation played a major role in pollutant removal, especially for COD and TN. The results of bacterial community analysis indicated that heterotrophic denitrifying bacteria (Hydrogenophaga and Flavobacterium) were the dominant contributors for nitrogen removal in the VF, while heterotrophic denitrifying bacteria (Rhodobacter, Flavobacterium and Dechloromonas) and the autotrophic denitrifying bacteria Sulfurimonas played the principal roles for nitrogen removal in the HF. Redundancy analyses showed that COD and NH4+-N were the important factors affecting the distribution of nitrogen removal bacteria in the VF, while pH, dissolved oxygen and oxidation-reduction potential were the key factors influencing the distribution of nitrogen removal bacteria in the HF.

High-solids fermentation of food wastes for biogas recovery by using horizontal anaerobic reactor

The biogas recovery from food wastes by anaerobic digestion was considered to be a feasible way for waste treatment. The system performance of high-solid anaerobic digestion of canteen food wastes by a horizontal reactor (8l) was investigated in this study. The TS of the reaction system was kept at 15%. The results indicated that biogas remained stable at about 650 ml/gTS when the volumetric loading rate (VLR) increased from 2 gTS/l.d to 8 gTS/l.d; however, it decreased at the VLR of 11 gTS/l.d. It suggested that VLR of 8 gTS/l.d was the optimal rate for this horizontal anaerobic reactor. After the adjustment of the running operation, the reactor remained stable with the accumulative biogas yield of 484 ml/gTS. The concentration of soluble chemical oxygen demand, ammonia nitrogen, volatile fatty acid, and alkalinity sharply increased to 41 024 mg/l, 2711 mg/l, 16 366 mg/l, and 14 250 mg/l at day 65 which reflected at the instable stage of the reactor, respectively. The maximum values of amylase and protease enzyme occurred at the initial stage of the reaction system with 1.42 U/ml (day 10) and 1.53 × 10−3 U/ml (day 17), respectively. After that, the two enzymes remained stable.The biogas recovery from food wastes by anaerobic digestion was considered to be a feasible way for waste treatment. The system performance of high-solid anaerobic digestion of canteen food wastes by a horizontal reactor (8l) was investigated in this study. The TS of the reaction system was kept at 15%. The results indicated that biogas remained stable at about 650 ml/gTS when the volumetric loading rate (VLR) increased from 2 gTS/l.d to 8 gTS/l.d; however, it decreased at the VLR of 11 gTS/l.d. It suggested that VLR of 8 gTS/l.d was the optimal rate for this horizontal anaerobic reactor. After the adjustment of the running operation, the reactor remained stable with the accumulative biogas yield of 484 ml/gTS. The concentration of soluble chemical oxygen demand, ammonia nitrogen, volatile fatty acid, and alkalinity sharply increased to 41 024 mg/l, 2711 mg/l, 16 366 mg/l, and 14 250 mg/l at day 65 which reflected at the instable stage of the reactor, respectively. The maximum values of amylase and protea...

Hydrogen consumption capacity assessment and its inhibition in the dry anaerobic digestion process from food waste

Hydrogen generation from food waste by dry anaerobic digestion was investigated, where different TS (total solid) contents (20%, 22%, 24%, 27%, and 30%) of the reaction system were compared, and the optimal TS was found to be 22%. The cumulative hydrogen yield began to decrease after 1.5 days, indicating a hydrogen consumption phenomenon in the reaction system. Such consumption can affect the hydrogen generation efficiency of the system. Therefore, to know the hydrogen consumption occurrence time and then take appropriate measures were important. The sludge from different reaction times of 2d, 4d, and 6d (G2, G4, and G6) was selected to evaluate the hydrogen consumption capacity. It was shown that the reaction system had a strong hydrogen consumption in all reaction bottles of G4, and the hydrogen consumption was the most intense when TS was 22%, which decreased from the peak value of 31.82 mmol/l to 29.47 mmol/L. Hydrogen production and consumption were not significant in G6; the only small change of hydrogen was observed (29.19–31.17 mmol/l). When TS was 22% and 30%, the quantity of homoacetogenic bacteria was the maximum of 3.08 × 109 copies/g and 2.39 × 109 copies/g on the 2nd day, respectively. As the most seriously hydrogen consumption group, G4 was chosen for the hydrogen consumption inhibition experiment by adding chloroform of 0.05%. It was indicated that the addition of chloroform could effectively suppress the hydrogen consumption when TS content of the reaction system was lower than 22%. This study can provide some useful information on the research of hydrogen consumption phenomenon and its inhibition.Hydrogen generation from food waste by dry anaerobic digestion was investigated, where different TS (total solid) contents (20%, 22%, 24%, 27%, and 30%) of the reaction system were compared, and the optimal TS was found to be 22%. The cumulative hydrogen yield began to decrease after 1.5 days, indicating a hydrogen consumption phenomenon in the reaction system. Such consumption can affect the hydrogen generation efficiency of the system. Therefore, to know the hydrogen consumption occurrence time and then take appropriate measures were important. The sludge from different reaction times of 2d, 4d, and 6d (G2, G4, and G6) was selected to evaluate the hydrogen consumption capacity. It was shown that the reaction system had a strong hydrogen consumption in all reaction bottles of G4, and the hydrogen consumption was the most intense when TS was 22%, which decreased from the peak value of 31.82 mmol/l to 29.47 mmol/L. Hydrogen production and consumption were not significant in G6; the only small change of hyd...