Performance and fouling mechanism of direct contact membrane distillation (DCMD) treating fermentation wastewater with high organic concentrations

In this study, direct contact membrane distillation (DCMD) was used for treating fermentation wastewater with high organic concentrations. DCMD performance characteristics including permeate flux, permeate water quality as well as membrane fouling were investigated systematically. Experimental results showed that, after 12 hr DCMD, the feed wastewater was concentrated by about a factor of 3.7 on a volumetric basis, with the permeate flux decreasing from the initial 8.7 L/m²/hr to the final 4.3 L/m²/hr due to membrane fouling; the protein concentration in the feed wastewater was increased by about 3.5 times and achieved a value of 6178 mg/L, which is suitable for reutilization. Although COD and TOC in permeate water increased continuously due to the transfer of volatile components from wastewater, organic rejection of over 95% was achieved in wastewater. GC–MS results suggested that the fermentation wastewater contained 128 kinds of organics, in which 14 organics dominated. After 12 hr DCMD, not only volatile organics including trimethyl pyrazine, 2-acetyl pyrrole, phenethyl alcohol and phenylacetic acid, but also non-volatile dibutyl phthalate was detected in permeate water due to membrane wetting. FT-IR and SEM–EDS results indicated that the deposits formed on the membrane inner surface mainly consisted of Ca, Mg, and amine, carboxylic acid and aromatic groups. The fouled membrane could be recovered, as most of the deposits could be removed using a HCl/NaOH chemical cleaning method.