Handling of membrane concentrate from reclamation of water in polyester dyeing

This analysis presents the results of a study carried out on 6 alternative options for the disposal of membrane reject (concentrate) from a Danish polyester dyehouse. The options analysed comprise discharge to sewer (reference option and current practice), transport to biogas followed by sludge incineration, wet air oxidation, activated carbon, transport to hazardous waste treatment facility, and drying for zero-discharge. In most disposal scenarios considered it is advantageous to dewater the concentrate further from 2,5 %DS (dry solids) to 20 %DS in order to reduce its volume and thereby diminish the transport costs. Membrane filtration is a technology competitive to evaporation for dewatering at moderate DS contents that avoid the effects of fouling. The results obtained help concluding that discharge to sewer and biogas treatment are the less expensive options, as long as concentrate is free of pollutants that may disturb the treatment process or jeopardize further applications of the biodegraded residue. Total dewatering of the concentrate for zero liquid discharge is still the most expensive solution. The results obtained confirm that concentrate disposal is a major cost of industrial water recycling projects where the concentrate has low or no commercial value. In the scenarios analyzed, concentrate disposal costs represents between 10% and 70% of the total treatment costs per m3 of water recycled. It is therefore recommended to analyze in detail the available alternatives for concentrate disposal in order to identify these costs at an early stage of the projects.