Fouling resistant compact hollow-fiber module with spacer for submerged membrane bioreactor treating high strength industrial wastewater

Long-term investigations carried out in a submerged membrane fungi reactor treating textile wastewater revealed the excellent fouling prevention capacity of spacer-filled hollow-fiber modules. The type and arrangement of the spacers governed the overall rigidity of the modules and played the critical role in avoidance of sludge intrusion and retrieval of the original state (cleaning). A hybrid module (fiber packing density = 61.5%, surface area = 1.07 m2) obtained by winding a rigid spacer (thickness = 1 mm, opening = 7 mm × 7 mm) on the surface of a module originally containing a flexible thin spacer (opening = 1 mm × 1 mm) exhibited the optimum rigidity so as to minimize intrusion of sludge while simultaneously allowing washout of the small amount of sludge trapped within it. Periodic in situ chemical backwashing with a small dose (500 mg Cl L−1, 100 mL m−2, twice/week) and intermittent surface-cleaning with a specially designed aeration device (aeration intensity = 1 L min−1, duration = 1 min per 30 min) enabled stable operation for a prolonged period under the selected average flux (1.27 × 10−7 m3 m−2 s−1) and mixed liquor suspended solids (MLSS) concentrations (up to 25 g L−1). Under the similar conditions, four-fold reduction in total consumptions of both chemical and air was possible when the developed module was placed within a coarse-pore (50–200 μm) pre-filtration cage. A reactor-design with a settling zone and a feeding mode comprising split of the influent through the settling zone and from the top may be utilized to maintain an optimum MLSS concentration in direct contact with the membrane, thereby further improving the ease of fouling mitigation.