Remediation of spent alkaline solutions in the production of cellulose fibers from Spanish broom by membrane operations

Spent alkaline solutions produced in the extraction cycle of cellulose fibers from Spanish broom (Spartiumjunceum L.) pose serious problems of environmental impact due to their high polluting load. A rational-ization of the whole extraction cycle could be obtained through the recycling, purification and reuse ofthe extracting solutions with significant reduction of the polluting load.In this work the use of ceramic microfiltration (MF) and ultrafiltration (UF) membranes in tubularconfiguration was investigated for the treatment of spent alkaline solutions coming from the extraction ofcellulose fibers in order to obtain a suitable solution reusable for new extraction cycles. For UF membraneswith molecular weight cut-off of 1 and 3 kDa, the effect of transmembrane pressure (TMP) and cross flowvelocity (CFV) on the permeate flux, total organic carbon (TOC) and lignin content was investigated.An integrated membrane process was proposed on the basis of experimental results. It includes apreliminary treatment of MF devoted to the removal of suspended solids from the spent solution, followedby a UF treatment of the microfiltered solution with 1 kDa tubular membranes. In optimized operatingconditions (TMP, 4.5 bar; CFV, 8.0 m/s; temperature, 25oC) the UF membrane showed a rejection towardTOC and lignin of 68.9% and 86.8%, respectively, and a steady-state permeate flux of about 12 kg/m2h.The integrated process permitted to reduce the initial TOC of the spent solution of 80%, producing a finalpermeate stream that can be reused for new extraction cycles.