MODELING OF HEAVY METALS DISTRIBUTION IN THE THERMAIKOS GULF

MODELING OF HEAVY METALS DISTRIBUTION IN THE THERMAIKOS GULF H. Mpimpas, P. Anagnostopoulos and J. Ganoulis Department of Ciil Engineering Diision of Hydraulics and Enironmental Engineering Aristotle Uniersity of Thessalonii 54006 Thessalonii, Greece ABSTRACT To describe the distribution of heay metals lie cadmium, copper, lead and zinc in the Gulf of Thermaios located in Northern Greece, a two-dimensional finite element model is used for the numerical solution of the adection-diffusion equation. The model contains, except from the transport and diffusion of the heay metals, physical and chemical mechanisms, lie settling, resuspension and sorption. The elocity distribution in the Gulf for arious wind directions was deried from the numerical solution of a wind-induced circulation model, using the finite element technique. The concentration distributions of the heay metals in dissoled and particulate forms are presented in releant diagrams. ΠΡΟΣΟΜΟΙΩΣΗ ΤΗΣ ΚΑΤΑΝΟΜΗΣ ΒΑΡΕΩΝ ΜΕΤΑΛΛΩΝ ΣΤΟ ΘΕΡΜΑΪΚΟ ΚΟΛΠΟ H. Μπίμπας, Π. Αναγνωστόπουλος, Ι. Γκανούλης Τμήμα Πολιτικών Μηχανικών Τομέας Υδραυλικής και Τεχνικής Περιβάλλοντος Αριστοτέλειο Πανεπιστήμιο Θεσσαλονίκης 54006 Θεσσαλονίκη ΠΕΡΙΛΗΨΗ Για την περιγραφή της κατανομής βαρέων μετάλλων όπως το κάδμιο, ο χαλκός, ο μόλυβδος και ο ψευδάργυρος στον Θερμαϊκό Κόλπο που βρίσκεται στην Βόρεια Ελλάδα, εφαρμόζεται στην εργασία αυτή ένα αριθμητικό ομοίωμα πεπερασμένων στοιχείων που προσομοιώνει αριθμητικά την εξίσωση της μεταφοράς-διάχυσης. Το ομοίωμα περιγράφει, εκτός από την μεταφορά και διάχυση των βαρέων μετάλλων, φυσικούς και χημικούς μηχανισμούς, όπως η καθίζηση, η επαναιώρηση και η συσσωμάτωση. Η κατανομή των ταχυτήτων στον Κόλπο για διαφορετικούς ανέμους προέκυψε από την αριθμητική επίλυση ενός ομοιώματος ανεμογενούς κυκλοφορίας με τη χρήση της μεθόδου των πεπερασμένων στοιχείων. Η κατανομή της συγκέντρωσης των βαρέων μετάλλων σε διαλυμένη και σωματιδιακή μορφή παρουσιάζεται στα αντίστοιχα διαγράμματα. Proceedings of the International Conference "Protection and Restoration of the Enironment VI" Siathos, July 1-5, 00, Pages 319-36 Editors: A.G. Kungolos, A.B. Liaopoulos G.P. Korfiatis, A.D. Koutsospyros K.L. Κatsifarais, A.C. Demetracopoulos

30 Protection and restoration of the enironment VI 1. INTRODUCTION The Gulf of Thermaios, located in Northern Greece, is a semi-enclosed coastal area with seere pollution problems in the marine enironment. The city of Thessalonii, with about one million inhabitants and significant industrial actiity, is situated in the Northeast part of the Gulf. Among the arious pollutants discharging into the Gulf, heay metals contained in the industrial wastewater from industries in the surroundings are pollutants with special interest, because of their toxicity. To face this serious problem, it is necessary to now the concentration distribution of pollutants in the Gulf under different conditions. Numerical models constitute an efficient tool for the prediction of pollution for different scenarios. In the present study a water pollution model composed by the well-nown adection-diffusion equation is presented. The model accounts for four different pollutants, namely: cadmium, copper, lead and zinc. A finite element algorithm was used for the solution of the adection-diffusion equation with source terms for the four different pollutants. The model was applied for the study of pollution in the Thermaios Gulf, for water elocities obtained from a wind-induced circulation model.. THE MATHEMATICAL MODEL A mathematical water quality model is composed by a system of differential equations, which simulate the adection and diffusion of arious pollutants in a rier, a lae or sea. For the model presented herein the system of equations which describes the rate of change of the concentration of different heay metals under physical and chemical interactions, partitioned into dissoled and particulate form in the water (1) and in the sediments () can be expressed as [1]: c t c1 + U x c1 + V y c x c y Fp c h r c + h + ( F c F c ) 1 1 1 s 1 d d d1 1 = Dx + D y h ( F c F c ) c c c c c F c c c s p 1 r b d d1 1 + U + V = Dx + D y + + t x y x y h h h h d where: c 1 c is the concentration in water for the th pollutant (μg/l) is the concentration in sediments for the th pollutant (μg/g) U is the water elocity in the x direction (m/s); V is the water elocity in the y direction (m/s); D x is the diffusion-dispersion coefficient in the x direction (m/s ); D y is the diffusion-dispersion coefficient in the y direction (m/s ); is the settling elocity (m/s) s d is the sediment-water diffusion mass-transfer coefficient (m/s) r is the resuspension elocity (m/s) is the burial elocity (m/s) b F is the fraction of the total contaminant that is in particulate form p F d is the fraction of the total contaminant that is in dissoled form h is the water depth (m)

Physical and numerical modelling 31 The four (=4) heay metals used in the model are: cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). The alues of all coefficients [] used in the model are quoted in Table 1. TABLE 1. Values of the parameters used in the model Symbol Unit Value Symbol Unit Value D (m /s) 8 bpb 0.0000003 s Cd (m/s) 0.00003 bzn 0.000000 0.00005 F d1-0.8 Cd s Cu 0.00004 F d1-0.80 Cu s Pb 0.00006 F d1-0.85 Pb s Zn 0.0000006 F d1-0.86 Zn d Cd d Cu 0.0000005 F dcd - 0.00000 d Pb 0.0000004 F d Cu - 0.000003 0.0000007 F d - 0.000001 Pb d Zn 0.0000004 F d - 0.000004 Zn r Cd 0.0000001 F p - 0.18 Cd r Cu r Pb 0.0000003 F pcu - 0. r Zn 0.000000 F p Pb - 0.15 0.0000005 F p - 0.14 Zn b Cd b Cu 0.0000001 For the numerical solution of the adection-diffusion equation, the finite element technique was used. To oercome the problem of numerical diffusion arising from the adection term in the equations, the characteristic-galerin formulation was employed [3]. 3. APPLICATION IN THE GULF OF THERMAIKOS The main pollution sources which are inputted into the model, are located in the city of Thessalonii, in the outlets of the riers Dendropotamos, Galios, Axios, Aliamonas and Loudias, TABLE. Input pollutant loads in Thermaios Gulf Pollutant loads Pb (μg/l) Cd (μg/l) Cu (μg/l) Zn (μg/l) Thessalonii 100/100 10/10 30/30 150/100 Dendropotamos 40 10 60 Galios 50 10 60 Chalastra 0/0 / 5/5 40/40 Axios 40 10 60 Malgara 0 1 5 30 Loudias 0 1 10 40 Klidi 0 1 5 40 Aliamonas 40 10 60 which are discharging into the Gulf, and in the outlets of the drainage networs in Chalastra,

3 Protection and restoration of the enironment VI Malgara and Klidi, as shown in Figure 1. The alues of the input loads of the arious pollutants are gien in Table. THESSALONIKI R.DENDROPOTAMOS R.GALIKOS CHALASTRA1 CHALASTRA R.LOUDIAS MALGARA R.AXIOS KLIDI R.ALIAKMONAS Figure 1. The finite element mesh in the northern part of the Gulf, and the locations of pollution sources. 4. RESULTS The water elocity field was obtained by soling the depth-aeraged shallow-water equations in the domain of Thermaios Gulf using the finite element technique, for North and South wind directions of elocity 10 m/s [4]. The circulation in the upper part of the Gulf for North wind of elocity 10 m/s is displayed in Figure. For each wind direction the computational procedure was continued, until the distribution of pollutants in the Gulf was almost stabilized. From the four heay metals considered herein, the concentration of copper and lead in water is presented, and the concentration in sediments of copper and zinc. The concentration distribution of copper in the water for North wind is depicted in Figure 3, while that for lead is illustrated in Figure 4. The releant results for South wind are shown in Figures 5 and 6. The concentration of copper in the sediments for North wind is presented in Figure 7, while the concentration of zinc for South wind in Figure 8. From the study of the results we can obsere the influence of coastal circulation on the concentration distribution. The water elocities in the bay area at the upper part of the Gulf are ery small, thus diffusion is expected to be the dominant mechanism. In spite of that, differences for the same pollutant are obsered when a different wind direction is applied, with the South wind yielding heaier pollution in the bay. Thus, in spite of the small alues of water elocity, adection is important for the determination of pollution. From Figures 3 to 8 is eident that the concentration of heay metals is greater in the western part of the gulf where most of the pollution sources are located, and the pollution decreases significantly outside the bay. In addition, comparison of Figures 3 and 7 reeals, that the difference of concentration distribution of copper in water or sediments is ery small. The same result was found to be alid for the other pollutants as well.

Physical and numerical modelling 33 Figure. Circulation in the northern part of the Gulf, for North wind of elocity 10 m/s. Figure 3. Concentration distribution of copper in the water for North wind.

34 Protection and restoration of the enironment VI Figure 4. Concentration distribution of lead in the water for North wind. Figure 5. Concentration distribution of copper in the water for South wind.

Physical and numerical modelling 35 Figure 6. Concentration distribution of lead in the water for South wind. Figure 7. Concentration distribution of copper in the sediments for North wind.

36 Protection and restoration of the enironment VI 5. CONCLUSIONS Figure 8. Concentration distribution of zinc in the sediments for South wind. The concentration of four different heay metals in the Gulf of Thermaios was obtained by the use of a hydro-ecological model, based on the finite element technique. The model was applied for the prediction of the complicated behaiour and the interaction between the pollutants, for different climatic scenarios. The study of the results indicates the great influence of physico-chemical coefficients, input loads and climatic conditions on the distribution of heay metals in the Gulf. The predictions of the model are expected to compose a useful tool for the continuing efforts undertaen in recent years to reduce pollution in the Thermaios Gulf and especially in the area of the Bay of Thessalonii. REFERENCES 1. Shapra S.C. (1997) Surface water quality modeling, McGraw Hill.. Thomann R.V. and J. Mueller (1987) Principles of surface water quality modelling and control Harper Collins Publishers. 3. Mpimpas H. and P. Anagnostopoulos (001) An improed coastal circulation model based on the characteristic-galerin technique, Proc. of National Congress of Mechanics VI, Vol. 1, Aifantis, E.C. et al. editors, Thessalonii, Greece, July 001, pp. 39-44. 4. Anagnostopoulos P. and H. Mpimpas (1995) Finite element solution of wind-induced circulation and pollutant dispersion in the Thermaios Gulf, Proc. of Int. Conference on Computer Modeling of Seas and Coastal Regions II, Brebbia, C.A. et al. editors, Cancun, Mexico, September 1995, pp. 133-140.