Development Of Dynamic Numerical Models And Simulation For Typical Organic Pollutants In Songhua River

Surface waters, especially natural rivers always witness the rapid developmentand advancement of local industries and act as receiving waters for various kinds oforganic contaminants from municipal and industrial wastewaters, organic chemicalsin use, non-point source pollutions. Organic compounds with toxicity dischargedinto river probably bring negative impact on aquatic ecosystem by direct andindirect effects on organisms, and put human’s life to much inconvenience. It is,therefore, of significance for us to clearly understand the transport and fate oforganic pollutants in aquatic environment in order to implement effectively waterquality management and risk assessment.The demand for numerical models to simulate and predict the transport and fateof organic pollutants in the environment is a reflection of certain restrictions ofexperimental research, in some cases by time limitations, laborious fieldobservations, and undeveloped laboratory determination equipment. Numericalmodeling plays an important role in predicting the behavior of pollutants in theenvironment. For this, two kinds of models are developed in this paper.Dynamic multimedia model has been developed in this study that coupleshydrodynamics submodel and fugacity Ⅳ submodel, to simulate the long-termenvironmental fate of organic pollutants. In the first, the one-dimensional networkkinematic wave equation is used to calculate varying water flow, depth and velocity.In the second, Fugacity Ⅳ equations in which all parameters are shown inspatio-temporal variability are implemented to predict contaminant distributions inmultimedia environments.The dynamic multimedia model has been applied to simulate multimediaenvironmental fate of eight PAHs in the Songhua River in2007. Theil’s inequalitycoefficient test (TIC) is used to implement model validation for modeledconcentrations of eight PAHs in water compartment. From results, all TIC values areless than0.5, indicating simulated concentrations are in acceptable agreement withmonitoring data. Taking Nap as representative, calculation of mass balance of Naphas effectively demonstrates that the model program is running properly, of whichthe result shows total input and output mass fluxes in the whole environment systemare140.61×103Kg and40.26×103Kg respectively with the0.25%of relative error.From sensitivity analysis, contaminant concentration in water column is highly sensitive to emission intensity and riverine flow parameters whose sensitivitycoefficients are0.97and0.90, respectively.The resulting model is also applied to describe the multimedia environmentalbehavior of eight phenol compounds in the Songhua River in2007. Based on fieldobservations during different hydrological seasons of the year2007, the predictivepower of this model is evaluated by three different kinds of quantitative statisticalmethods, namely Nash-Sutcliffe efficiency (NSE), percent bias (PBIAS) and ratio ofthe root-mean-square to the standard deviation of measured data (RSR). Thegoodness-of-fit of model prediction for phenolic contaminants is, in general,agreeable. The conditions of NSR<0.5，RSR<=0.7and PBIAS∈[-70%，+70%] arefulfilled together for most of data points. The paired t-test result (P>0.05) indicatesthat there is no significant difference between simulated and observed data at thechosen significance level of0.05, although some outliers are present. For one focalcompound-2,4-DCP, the pathways and mass fluxes from the river system to thesurrounding environment are also evaluated. During simulation, mass flux ofriverine advection is the most remarkable and net output mass flux is around4500.1kg. Uncertainty analysis is performed by Monte Carlo stimulation to judgethe influence of variability of input parameters on modeled results. Modelsimulation indicates that phenolic pollution in the river during the low-flow periodof2012is remarkably reduced when compared to the same period of2007. Theresearch results indicate that this model can be applied in point-source pollutioncases in the river and has the ability to provide decision makers with valuablereference data for consideration of water pollution controls.For water pollution emergency, contaminant transport and fate model has beendeveloped in this study, which couples kinematic wave flow option withadvection-dispersion-reaction equation. The model includes kinetic processes suchas volatilization, photolysis and biodegradation, and diffusive mass exchangebetween water column and sediment layer as a function of particles settling andresuspension. It has been applied to simulate Nitrobenzene pollution emergency inthe Songhua River and concentration variances of Nitrobenzene in overlying watercolumn and underneath sediment bottom are obtained. For aqueous concentration,four kinds of quantitative statistical tests, namely NSE, PBIAS, RSR and TIC, areadopted to evaluate model performance. The results generally show that the modeledand detected concentrations exhibit good consistency. Flow velocity in the river ismost sensitive parameter to Nitrobenzene concentration in water column based onsensitivity analysis. It indicates flow velocity has important impact on bothdistribution and variance of contaminant concentration. The model performs satisfactory for prediction of organic pollutant fate in the river, with the ability tosupply necessary information for pollution event control and early warning, whichcould be applied to similar long natural rivers.We expect to establish numerical model to give a scientific guide for aquaticecosystem protection so that prevention, reduction and recovery of ecologicaldamage by water pollution can be realized with the aim of free-economic loss,maintenance of human health and ecosystem balance, harmony and sustainability ofpeople’s life and economic development.