ABSTRACT
Landfill leachate is a complex wastewater which the composition and concentration of contaminants are influenced by the type of waste deposited and the age of landfill. In the last years, several processes or process combinations were developed and tested to reach requirements for the discharge of leachate. Among the new processes, membrane processes are considered as promising: reverse osmosis is one of the most widely used treatment in the Northwestern European countries and nanofiltration is gained in popularity during the last 5 years. Successful application of membrane technology for the treatment of landfill leachates, requires efficient control of membrane fouling. Two organic membranes of nanofiltration were used for pilot-scale testing. Leachates were subject to several pretreatments (pH modification, prefiltration and coagulation with FeCl3) to remove potential foulants including dissolved organic and inorganic substances, colloidal and suspended particles. These pretreatments do not enhance the performances (retention and permeation flux) of membranes because the pH range and the presence of Fe3+ ions contribute greatly to change the characteristics of organic matter and the surface charges of membranes. However, the results show that nanofiltration is sufficient to eliminate refractory COD, the permeates have a COD lower than the requirements for discharge.
Subject(s)
Filtration/methods , Waste Disposal, Fluid/methods , Water Purification/methods , Adsorption , Calcium/analysis , Calcium/chemistry , Chlorides , Coagulants/pharmacology , Colloids/chemistry , Environmental Monitoring/methods , Ferric Compounds/pharmacology , Flocculation , Hydrogen-Ion Concentration , Iron/analysis , Iron/chemistry , Membranes , Molecular Weight , Osmotic Pressure , Oxygen Consumption , Soil Pollutants/analysis , Surface Properties , Suspensions , Water Movements , Water Pollutants/analysisABSTRACT
The circulation of microorganisms in tangential flow filtration systems induces perturbations and then the damage of brittle cells. This work is focused on the shearing of two marine microalgae species (Skeletonema costatum and Haslea ostrearia), both largely cultivated in western France (Région des Pays de la Loire). We have studied the effects of the circulation of these cells in pumps and valves. For the pumps, it is shown that shear stress is due to the type of pump, but that mechanical shear can have different effects even if the pumps and the number or frequency of loops are the same. Hence other intrinsic parameters of the pump must be taken into account: rotating velocity (omega), capacity (Cyl = output flow/rotating velocity) or internal leakage (K = inner volume/capacity). In throttling valves, the aim is to correlate the effect of shear to a parameter related to the inner geometry of the valve and to operating conditions. An overall parameter is then evaluated: the pressure drop coefficient Kv which integrates both the type of valve (ball valve or globe valve type) and its opening degree. Kv is derived from the relationship DeltaH = Kvu2/2g. The modelling of the shear effects is now conceivable: basic descriptive data used so far (type of pump, geometry or opening degree of the valve, etc.) being completed and partially substituted by quantitative parameters (rotating velocity, capacity, or internal leakage for the pumps, Kv coefficient for the valves).