Evaluation of MF and UF as pretreatments prior to RO applied to reclaim waste water for fresh water substituion in a paper mill: A practical experience

Abstract

A pilot plant study has been carried out to compare the effectiveness of different low pressure membrane systems (microfiltration and ultrafiltration) as pretreatments for a reverse osmosis system producing high quality reclaimed water from the effluent of a municipal wastewater treatment plant receiving a high percentage of industrial wastewater. The reclaimed water will be used to substitute fresh water in a paper mill. Although the implemented systems showed several problems derived from the unstable quality of the feed water, they were solid enough to keep a constant permeate quality; i.e. percentages of salt rejection above 99%, efficiencies in the removal of microorganisms to lower values than 1 CFU/100 mL, and final COD results below the detection limit (<5 mg L−1). In short, the quality of the produced reclaimed water was good enough to be used substituting fresh water in a paper mill. An enhanced monitoring of the quality of the water feeding the municipal wastewater treatment plant and an improved corresponding management of the treatments performed in there may be one of the keys to the success of this type of reclamation initiatives. Achieving constant disinfection, an appropriate design of the plants, and a good performance of cleaning operations were very important factors to be considered in order to fight against fouling. Temperature and the soaking time of chemical membrane cleanings were particularly well-optimized for the success of the treatment. Chloramines were compared to free chlorine as disinfection agent achieving satisfactory results.