Heavy metals in potable groundwater of mining-affected river catchments, northwestern Romania.
suspension. In this paper the model has been applied to a specific sedimentation tank design for the purpose of elucidating features of the model. From the limited number of simulations presented here it is evident that particle collision efficiencies, the particle size-density relationship, and the shape of the influent particle size distribution affect dramatically both the characteristics of the effluent size distribution and the overall tank performance. The collision efficiencies between particles and the particle size-density relationship were modeled, of necessity somewhat arbitrarily, since, to the knowledge of the authors, no related published results exist; both depend on the physical and biochemical nature of the flocs and will be unique for a particular suspension, so their determination requires experimental work. Scouring was modeled empirically, so conclusions cannot be drawn. Experimental and theoretical work on resuspension of cohesive sediments is in progress (6), and the results can be easily incorporated in the simulation. The simulations of tank operation under un-steady-state inflow conditions suggest that moderate variations in influent concentration and flow rate do not significantly affect the quality of the effluent. In summary, the model appears to give realistic simulations of the operation of a specific sedimentation tank. Clearly, further modifications, improvements, and trials will be necessary before it can be used with confidence in the design of new facilities. At this juncture, it appears that more experimental work on the nature of the particle size-density relationship, the resuspension of deposits, and the particle collision efficiencies is the crucial next step in improving the realism of the model.