Characterization and performance of different types of hollow fibre membranes in a laboratory-scale MBR for the treatment of industrial wastewater

The use of a submerged membrane bioreactor for the treatment of industrial oil contaminated wastewater was investigated using microfiltration hollow fibre membranes. The membrane bioreactor worked with a hydrocarbon concentration ranging from 600 to 1500 mg/L in a sub-critical flux regime. The sludge concentration ranged from 14 g/L to 28 g/L. During the long-term bioreactor test, three further different membrane modules were tested in order to assess their critical flux in comparable conditions. The membranes investigated were different in materials, pore structure and size. The membranes with larger pore size showed a higher tendency to irreversible fouling. The MBR was able to treat wastewater with high removal efficiency (about 98%), low hydraulic retention time (about 10 h) and high biomass concentration.

A submerged membrane bioreactor for the treatment of industrial oil contaminated wastewater was studied. The MBR was able to treat oil contaminated wastewater with high removal efficiency (98%) in different operating conditions, low hydraulic retention times (around 10 h), high biomass concentration (from 14 to 27 g/L). The critical flux of three different types of membranes was assessed using the flux-step method proposed in literature. The PVDF membrane showed the lowest critical flux value (6 L m–2 h–1) which anyway was not very different from the value of the other two membranes (9 L m–2 h–1). It was found that i) the PP microfiltration membrane tested in the long-term experiment was fouled (although very slowly) also when permeating fluxes below the critical flux were used; ii) the microfiltration membranes were more sensitive to the irreversible fouling than the ultrafiltration membrane; iii) the membranes operating over their critical flux were irreversibly fouled and needed to be cleaned to recover their performance, iv) after the cleaning procedure water permeability could be not completely recovered, indicating that some material could be entrapped in the membrane struc- ture permanently. Although the PVDF membrane showed a lower value of critical flux it should be considered in a possible economic evaluation because of the lower fouling tendency.