Optimum operation conditions of direct capillary nanofiltration for wastewater treatment

Direct Capillary Nanofiltration (Direct CNF) is a new technique used for surface water and wastewater treatment in one step without pre-treatment. The CNF membrane module combines the favourable cleaning properties of capillary ultrafiltration membranes with the favourable separation properties of nanofiltration membranes in terms of removal of DOC, colour, bacteria, viruses and pesticides. Direct CNF was applied to Twente Canal surface water to produce high quality permeate in a single step. In this study, Direct CNF has been applied (for the first time) to wastewater treatment under continuous and stable process conditions. An important aspect was determination of the optimum operation conditions of the pilot plant. The optimum conditions for Direct CNF when applied to domestic wastewater are 15 minutes filtration time, 20 l/m2.h flux rate with undiluted domestic wastewater. The filtration can operate continuously under stable process conditions for approximately 8 hours. Subsequently the pilot plant must be chemically cleaned due to contamination of the membrane fibres. CNF shows high retention in removal of some parameters such as COD, BOD, iron, phosphate, total bacterial counts and lower retention for removal of Manganese while the removal of ammonia was very low.