Influence of Forward Osmosis (FO) membrane properties on dewatering of molasses distillery wastewater

This work presents a comparison of three forward osmosis (FO) membranes viz. HTI-TFC, HTI-CTA, and aquaporin-TFC for water recovery from a high strength wastewater of sugarcane molasses distillery. Surface properties of the membranes were assessed using scanning electron microscopy (SEM), zeta potential measurement and attenuated total reflection infrared spectroscopy (ATR-IR).

A commercial magnesium chloride hexahydrate (MgCl2.6H2O) (1 M to 4 M) solution was used as the draw and a 3 M concentrationwas identified to be optimal in obtaining stable flux. During a 24 h FO operation, the average water flux and water recovery respectively were 2.8 L/m2h and 81% (HTI-TFC), 2.4 L/m2h and 71% (HTI-CTA) and 1.9 L/m2h and 66% (aquaporin-TFC).

FO operation over five 24 h cycles along with membrane physical cleaning after every cycle resulted in water recovery of 82-70% for HTI-TFC and HTI-CTA membranes and 65-52% for aquaporin-TFC membrane. The rejection of distillery wastewater components that contribute to the COD, melanoidins and antioxidants content was similar for all the three membranes.

Fouling due to deposits on the membrane surface occurred for all membranes but the ease of cleaning was better for HTI-TFC followed by HTI-CTA and aquaporin-TFC membranes. Periodic physical cleaning by water flushing was adequate to remove surface deposits. Overall, HTI-TFC membrane was most suited for concentrating distillery wastewater, but the effect of high reverse salt flux of this membrane needs to be further investigated.