Guangxu Yan

Sensitivity and uncertainty analysis for Abreu & Johnson numerical vapor intrusion model.

This study conducted one-at-a-time (OAT) sensitivity and uncertainty analysis for a numerical vapor intrusion model for nine input parameters, including soil porosity, soil moisture, soil air permeability, aerobic biodegradation rate, building depressurization, crack width, floor thickness, building volume, and indoor air exchange rate. Simulations were performed for three soil types (clay, silt, and sand), two source depths (3 and 8m), and two source concentrations (1 and 400 g/m(3)). Model sensitivity and uncertainty for shallow and high-concentration vapor sources (3m and 400 g/m(3)) are much smaller than for deep and low-concentration sources (8m and 1g/m(3)). For high-concentration sources, soil air permeability, indoor air exchange rate, and building depressurization (for high permeable soil like sand) are key contributors to model output uncertainty. For low-concentration sources, soil porosity, soil moisture, aerobic biodegradation rate and soil gas permeability are key contributors to model output uncertainty. Another important finding is that impacts of aerobic biodegradation on vapor intrusion potential of petroleum hydrocarbons are negligible when vapor source concentration is high, because of insufficient oxygen supply that limits aerobic biodegradation activities.

A comprehensive evaluation of re-circulated bio-filter as a pretreatment process for petroleum refinery wastewater

Conventional biological treatment process is not very efficient for the treatment of petroleum refinery wastewater (PRW) that contains high-concentration of organic contaminants. Prior to biological treatment, an additional pretreatment process for PRW is required for the effluent to meet the discharge standards. While re-circulated bio-filter (RBF) has been applied as a pretreatment process in several PRW treatment plants, its effects have not been comprehensively evaluated. In this study, the parameters of operation, the changes in pollution indexes and contaminant composition in an engineered RBF have been investigated. We found that mainly highly active de-carbonization bacteria were present in the RBF, while no nitrification bacteria were found in the RBF. This indicated the absence of nitrification in this process. The biodegradable organic contaminants were susceptible to degradation by RBF, which decreased the Biological Oxygen Demand (BOD5) by 83.64% and the Chemical Oxygen Demand (CODCr) by 54.63%. Consequently, the alkalinity and pH value of RBF effluent significantly increased, which was unfavorable for the control of operating parameters in subsequent biological treatment. Along with the decrease of CODCr, the RBF effluent exhibited a reduction in biodegradability. 834 kinds of recalcitrant polar organic contaminants remained in the effluent; most of the contaminant molecules having complex structures of aromatic, polycyclic and heterocyclic rings. The results of this study showed that RBF could efficiently treat PRW for biodegradable organic contaminants removal; however, it is difficult to treat bio-refractory organic contaminants, which was unfavorable for the subsequent biological treatment process operation. An improved process might provide overall guarantees for the PRW treatment.

Refining wastewater treatment using EGSB-BAF system

AbstractThe performance of an expanded granular sludge bed (EGSB) in combination with a biological aerated filter (BAF) system for petroleum refining wastewater treatment was investigated. The system was monitored for two months at a hydraulic retention time of 17.5 h and a digestion temperature of 34 ± 1°C. The results showed that the total chemical oxygen demand (CODCr) and oil removal efficiencies were up to 90 and 87%, respectively, with the average CODCr and oil concentrations of 85 and 11 mg/L in the system effluent. Moreover, almost 97% of suspended solids (SS) were removed by the system and the effluent SS concentration was only 15 mg/L. The sludge yield coefficient of 0.0036 mg/mgCODCr showed a low excessive sludge production for the EGSB reactor. The excellent treatment performance indicated that this EGSB-BAF system could be appropriate for refining wastewater treatment. Besides, methane yield was only about 0.21 mLCH4/mgCODCr in the EGSB reactor, lower than the theoretical yields. The poor met...

Biodegradability evaluation of pollutants in acrylonitrile wastewaters based on particle size distribution

AbstractAcrylonitrile wastewaters (ANWs) treatment is a big trouble for chemical fiber industry in China, and there was not yet an effective biological treatment technology for ANWs due to the lack of detailed analysis on the biodegradability of pollutants. In this work, two typical point-source ANWs, acrylonitrile synthesis wastewater (ANSW), and acrylonitrile polymerization wastewater (ANPW) were fractionated by gradient membrane separation method based on the pollutants particle size distribution (PSD). Moreover, biochemical oxygen demand/chemical oxygen demand (COD) ratios, oxygen uptake respirometric tests, dehydrogenase activity tests, and simulated aeration tests were integrated to evaluate the biodegradability of PSD-based pollutants in ANWs. The results showed that most COD were from dissolved fractions in both of ANSW and ANPW. For ANSW, the soluble fractions had greater biodegradation potential than particulate and colloidal fractions. Colloidal fractions are easier to be biodegraded than parti...

Anaerobic Biochemical Treatment of Wastewater Containing Highly Concentrated Organic Cyanogen

Abstract The first and second stage of chilled wastewater in acrylic fibersitrile process and wastewater in acrylic fibers process are biodegraded under anaerobic conditions. Toxicity of acrylonitrile, acetonitrile, polymers, and cyanide in the wastewaters to the production of methane has been studied. Results suggest that the first and second stage chilled wastewaters from acrylonitrile process and wastewater from acrylic fibers process cannot be biodegraded well. CODBD of the first and second stage chilled wastewaters from acrylonitrile process is 36.3 and 45.8. CODBD of the wastewater from acrylic fibers process is 53.0. Acetonitrile, acrylonitrile, polymers, and cyanide are toxic to anaerobic bacteria in the highly concentrated organic cyanogens containing wastewater, inhibiting the methane-producing activity. Half inhibition concentration (50% IC) to anaerobic methane-producing activity is 1,300, 320, 85, and 50 mg/L for polymers, acetonitrile, acrylonitrile, and cyanide, respectively. Acrylonitrile is a metabolizing and physiological toxin, acetonitrile and polymers a metabolizing toxin, and cyanide a physiological and sterilizing toxin.

Characterization of Dietzia cercidiphylli C-1 isolated from extra-heavy oil contaminated soil

Bioremediation of extra-heavy oil contaminated soil has become a hot research field. It is difficult for extra-heavy oil to be degraded by bacteria. In this study, strain C-1 was isolated from Venezuelan extra-heavy oil-contaminated soil. Morphological, physiological and phylogenetic analysis identified strain C-1 as Dietzia cercidiphylli. The strain could degrade 25.58 ± 0.48% of extra-heavy oil at an initial concentration of 100 mg L−1 in 14 days with the degradation rate constant of 0.021 per day. GC-MS analysis demonstrated that the strain could effectively degrade medium (C13–C17) and longer (C44) length chain n-alkanes. This is the first report that the Dietzia strain can degrade extra-heavy oil, especially C44 n-alkanes. Dietzia cercidiphylli C-1 could be applied in extra-heavy oil contaminated soil bioremediation in the future.

Screening and identification of aerobic denitrifiers

With the standards of the effluent quality more stringent, it becomes a quite serious problem for municipalities and industries to remove nitrogen from wastewater. Bioremediation is a potential method for the removal of nitrogen and other pollutants because of its high efficiency and low cost. Seven predominant aerobic denitrifiers were screened and characterized from the activated sludge in the CAST unit. Some of these strains removed 87% nitrate nitrogen at least. Based on their phenotypic and phylogenetic characteristics, the isolates were identified as the genera of Ralstonia, Achromobacter, Aeromonas and Enterobacter.