Membrane filtration has gradually gained acceptance as the preferred pre-treatment for reverse osmosis (RO). In this paper, an integrated membrane bioreactor (MBR)/RO system for wastewater reuse treating real sewage water has been evaluated and the RO fouling has been characterised. The MBR achieved low values of organic matter, total nitrogen, PO(4)(3-), total organic carbon, turbidity and conductivity. Filtration with two different RO commercial membranes was performed after the MBR pre-treatment and the same average fouling rate (0.08 bar day(-1)) was noted. These results gained from the characterisation of the high quality MBR/RO permeate show its potential for water reuse. Inorganic precipitation appears to be the predominant form of fouling in the RO membranes. Calcium phosphate and alumino-silicates were identified by a scanning electron microscope combined with an energy dispersive X-ray and polysaccharides, amide and aliphatic structures were detected with attenuated total reflection infrared microspectroscopy.

The aim of the study is to evaluate the effectiveness of environmentally friendly antiscalant ADIC RO-18 AdicGreen in preventing the formation of scales in the reject, dispersing organic matter and inhibiting the colloidal fouling in the seawater reverse osmosis systems. The antiscalant developed is environmentally friendly because it is phosphorous and nitrogen free. Experimental tests were conducted in order to evaluate the ability of the antiscalant developed to disperse organic and colloidal matter. The results of filtration curves, operated under constant pressure (Modified Fouling Index), and the study using scanning electron microscopy with energy dispersive X-ray spectroscopy of the deposit adhered to filters, indicated that the antiscalant dosage retards filter fouling, and decreases the amount of clay retained on the filter, with respect to a filter without the presence of antiscalant. To evaluate the ability of this antiscalant developed to prevent scale formation in the reject of seawater reverse osmosis, a study in a RO pilot plant was carried out. The tests results demonstrated the antiscalant is effective in controlling inorganic scales and inhibiting the deposition of iron, aluminium, manganese and silica. A dosage of the antiscalant model and the scaling potential reduction for sparingly soluble species model were developed. The models calculate scaling potentials and recommend the minimum dosage of antiscalant to ensure the effective protection of the reverse osmosis membranes against scaling and fouling. Dosing the minimum effective antiscalant reduces operating costs for chemical treatment and minimizes treatment chemical discharge to the environment.

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