Preparation, characterization, adsorption kinetics and thermodynamics of novel magnetic chitosan enwrapping nanosized gamma-Fe2O3 and multi-walled carbon nanotubes with enhanced adsorption properties for methyl orange

A novel magnetic composite bioadsorbent composed of chitosan wrapping magnetic nanosized gamma-Fe(2)O(3) and multi-walled carbon nanotubes (m-CS/gamma-Fe(2)O(3)/MWCNTs) was prepared under relative mild conditions and was characterized. Adsorption of methyl orange (MO) onto m-CS/gamma-Fe(2)O(3)/MWCNTs was investigated with respect to pH, initial MO concentration, coexisting anions and temperature. Results of characterizations indicated that magnetic nanosized gamma-Fe(2)O(3) and MWCNTs have been wrapped by crosslinked chitosan. Introduction of MWCNTs could obviously increase the adsorption capacity (q(e)) of MO onto bioadsorbent by 2.2 times. Kinetics data and adsorption isotherm were better fitted by pseudo-second-order kinetic model and by Langmuir isotherm, respectively. Values of activation parameters such as free energy ( big up tri, openG degrees ), enthalpy ( big up tri, openH degrees ) and entropy (DeltaS degrees ) were determined as 3.15-3.78 kJ mol(-1), -9.94 kJ mol(-1) and -20.65 J mol(-1)k(-1), respectively, indicating that the adsorption was feasible, spontaneous and exothermic process in nature. After adsorption, m-CS/gamma-Fe(2)O(3)/MWCNTs could be effectively and fleetly separated by applying a magnetic field.

An inexact dynamic optimization model for municipal solid waste management in association with greenhouse gas emission control

Municipal solid waste (MSW) should be properly disposed in order to help protect environmental quality and human health, as well as to preserve natural resources. During MSW disposal processes, a large amount of greenhouse gas (GHG) is emitted, leading to a significant impact on climate change. In this study, an inexact dynamic optimization model (IDOM) is developed for MSW-management systems under uncertainty. It grounds upon conventional mixed-integer linear programming (MILP) approaches, and integrates GHG components into the modeling framework. Compared with the existing models, IDOM can not only deal with the complex tradeoff between system cost minimization and GHG-emission mitigation, but also provide optimal allocation strategies under various emission-control standards. A case study is then provided for demonstrating applicability of the developed model. The results indicate that desired waste-flow patterns with a minimized system cost and GHG-emission amount can be obtained. Of more importance, the IDOM solution is associated with over 5.5 million tonnes of TEC reduction, which is of significant economic implication for real implementations. Therefore, the proposed model could be regarded as a useful tool for realizing comprehensive MSW management with regard to mitigating climate-change impacts.

Simulation-based process optimization for surfactant-enhanced aquifer remediation at heterogeneous DNAPL-contaminated sites

Widespread use of dense non-aqueous phase liquids (DNAPLs) such as TCE and PCE has resulted in contamination of enormous valuable groundwater resources and become high-priority environmental problems. However, experiences from the past decades have demonstrated that DNAPL-contaminated sites were difficult to investigate and challenging to remediate. In this study, a simulation-based process optimization system was developed through integrating a multidimensional simulator, a multivariate statistical tool and an optimization model within a general framework for supporting decisions of surfactant-enhanced aquifer remediation (SEAR). A 3D multiphase and multi-component subsurface model was first provided to simulate SEAR process; dual-response surface models were then established to build a bridge between remediation actions and system performance; a nonlinear optimization model was then formulated for identifying optimal operating conditions for SEAR operations. The results in simulating a typical PCE spill event and the associated SEAR remediation operations in a heterogeneous subsurface indicated that SEAR would be capable of cleaning up the contaminated aquifer with improved efficiencies and cost-effectiveness compared with direct pump-and-treat actions. The regression-analysis results demonstrated that the proposed dual-response surface models were able to predict system responses under given operating conditions. The optimization results demonstrated that the developed simulation-optimization approach was effective in seeking cost-effective SEAR strategies for DNAPL-contaminated sites. With the developed method, optimum operation conditions under various environmental and economic considerations could be compiled into a database that would supports further studies of on-site process-control with injection and extraction rates being the main control variables.

Comparison of methods for total community DNA extraction and purification from compost

The differences on DNA yield and purity of three different DNA extraction protocols were compared with regard to the use for PCR and other molecular analyses. Total DNA was extracted from compost by the three protocols, and then was purified by spin-bind cartridges after being precipitated by PEG8000. The detection performed on a nucleic acid and protein analyzer showed that all three methods produced high DNA yields. The agarose gel electrophoresis showed that the fragments of crude and purified DNA had a length of about 23 kb. A eubacterial 16S rRNA gene-targeted primer pair was used for PCR amplification, and full length 16S rDNAs were amplified from all the purified DNA samples. After being digested by restriction endonucleases, the restriction map of amplified rDNA showed identical genetic diversity. The products of PCR using primer pair GC341F and 907R were also used for denaturing gradient gel electrophoresis analysis. The results indicated that high-quality DNA was extracted from compost by the three protocols, and each of the protocols is adapted to extract microbial genome DNA from compost expediently and cheaply.

Modeling biodegradation of toluene in rotating drum biofilter

Rotating drum biofilters (RDBs) are cost-effective for control of emissions of volatile organic compounds (VOCs) from waste gas streams. In this paper, a dynamic mathematical model is presented which simulates and predicts the variation in performance of a multi-layer RDB with time on the basis of the two-film theory. The model takes into account factors including biofilm growth and biomass loss, and a changing biofilm surface area and thickness assuming quasi-steady-state conditions in the two-phase system and uniform bacterial population. Toluene was assumed to be the only rate-limiting substrate. The model equations for the gas-phase mass balance and biofilm growth were solved using MATLAB based on the fourth-fifth-order Runge-Kutta technique, and the concentration profiles in the biofilms were obtained using the method of orthogonal collocation. Simulation results showed that the toluene removal efficiency decreased with increased toluene loading or increased duration of operation of the biofilter. Calculation results were compared to the experimental results, which demonstrated that the dynamic model provided a good simulation of the performance of the biofilter.

A two-dimensional water-quality model for a winding and topographically complicated river

In this paper, a two-dimensional numerical calculation algorithm for water-quality modeling is presented. The algorithm is designed specifically for river systems with complicated geometric conditions. When velocity field data of the river are not available, the numerical calculation algorithm for the water-quality modeling can be used to project river-water quality by using a topographic map of the river course and a finite element method. The calculation results of the water-quality model can show the concentration fields of various pollutants. The water-quality model was applied to a case-study in the Hengyang City section of Xiangjiang River in Hunan Province, China. The river under consideration is winding and has an isle between two branches. In 1995, Chinese government secured a World Bank loan to conduct a Waterways Project in the study region. It was expected that construction works in the river section might affect water quality. Given that the project would change the hydrological regime of the river system and discharges, and so would affect water quality, there would be a need for model results that would predict the water-quality impacts of the Waterways Project. In particular, the study intended to apply the model to identify changes in river-water quality associated with the construction of Dayuandu navigation key project. It is hoped that the numerical calculation algorithm for the water-quality modeling presented in this paper can also be applied to other shallow rivers with similar topographical conditions.

An integrated decision support system for the management of petroleum-contaminated sites

In this study, a decision-support system was developed for providing environmental managers with an integrated way for concisely analyzing and visualizing the subsurface contamination problem as well as a means for evaluating alternative remediation technologies. It integrated contaminant-transport modeling, risk assessment, and remediation-system design within a general framework. The developed system was applied to a site in western Canada that is contaminated by petroleum products. A three-dimensional multiphase multicomponent model was established, which provided a basis for further risk assessment. Several approaches based on different environmental guidelines were used to analyze risks due to the site contamination. The results suggested the urgency of taking remediation actions. Six remedial alternatives for cleaning up the site were recommended. Decisions could then be made based on a series of analyses and comparisons among the given alternatives.