Diego Sales Márquez

Comparison studies of feedwater pre-treatment in a reverse osmosis pilot plant

In this paper, results and associated costs in wastewater reclamation studies carried out in an advanced experimental plant for wastewater reuse in Chiclana de la Frontera, (Cadiz, South of Spain) are showed. The plant has the most advanced technology for wastewater reclamation including a reverse osmosis (RO) unit. For these experiments cellulose acetate membranes have been selected due to its lower tendency to fouling. The secondary effluent (from an activated sludge unit) was pre-treated, prior to RO to avoid membrane fouling, with three extension levels: intense (coagulation-flocculation with ferric chloride and polyelectrolite, and high pH sedimentation), moderate (coagulation-flocculation with ferric chloride and polyelectrolite and sedimentation) and minimum (only sedimentation). In overall experiments different reagent concentrations were tested. The optimum for membrane protection, in terms of calcium, conductivity and bicarbonates reduction resulted to be the intense treatment using pH = 10.5, ferric chloride: 25 mg/L, and anionic polyelectrolite: 0.5 mg/L). Membrane performance varied with pre-treatment extension but not reclaimed water quality. The resulting permeate quality was high rendering any type of reuse application possible. Associated experimental costs together with the experimental results obtained indicate that intense pre-treatment is recommended in order to membrane protection and to guarantee the safety of wastewater reclamation process.