An integrated nanofiltration + evaporation solution for high strength rubber wastewater treatment, water reuse and zero liquid discharge

Treatment of wastewater from the demoulding process in rubber part manufacturing, where polymeric demoulding agents are used, has been a challenge to the industry due to its high strength (COD>10,000 mg/L) and low biodegradability of the main organic content in the wastewater. Currently, a thermal process, typically boilers followed by evaporators, is commonly employed to treat the wastewater at rubber factories. Besides frequent boiler maintenance due to severe fouling caused by the wastewater, high energy costs are nearly prohibitive. At Cikautxo, a rubber part manufacturer located in the Basque Country in Spain, the energy bill is currently approximately €4.2/m3 treated wastewater. PROMETHEUS is a research project funded by the European Commission under the 7th Framework Programme with an aim to develop an integrated solution for treatment of rubber wastewater. Following an initial bench-scale membrane screening a pilot study was carried out at Cikautxo in the first half of 2012 to test the proposed solution. Nanofiltration with a NF270 membrane was tested and reject water from NF270 was collected and then fed to a full size compression-driven evaporator for further volume reduction. Without any pre-treatment, the nanofiltration process was able to be maintained at a permeate flux of 11 liter/m₂/h for over 30 hours in-between flux recovery cleanings. A higher treating capacity for the evaporator was observed for treating the NF reject in comparison with the boiler blowdown, due to lower salt concentrations in the NF reject. The NF+evaporator solution can reduce the energy costs by 55% (down to €1.9/m3 treated wastewater).