The non-Newtonian nature of sewage sludge means that its measured viscosity µs varies with shear rate due to the shear-dependent deformation of the flocculant solids (Yang et al, 2009). Viscosity affects the shear at the membrane interface, shear being a key parameter in promoting flux, and the dependency of apparent viscosity on temperature may then also be significant in determining flux.
Aquaculture is the fastest growing agriculture worldwide, supplying a substantial amount of seafood consumed today. The ‘recirculating aquaculture system’ (RAS) is an upcoming production system in intensive fish production, where over 90% of the water is recycled for production of live feed, larvae and fry and on-growing fish.
The Arenales del Sol WWTP in Spain combines biological treatment with nutrient removal with a submerged MBR system fitted with flat sheet (FS) ultrafiltration membranes, with an average treatment capacity of 10,000 m3/d (10 MLD). The plant provides high quality treatment to highly variable seasonal sewage inflow due to the nature of this popular coastal region.
About two years ago, we asked for the views of a range of MBR stakeholders regarding the perceived technical challenges facing MBRs: What is the main technical problem that prevents MBRs working as they should? We received 48 responses, mainly from practitioners working in the municipal sector. About a month ago, in our 2012 MBR survey, we asked the same question.
There is little doubt that, of the challenges faced in MBR operation, recovery of permeability is arguably the most critical. When the routine maintenance membrane clean fails to achieve the required recovery and more aggressive recovery cleans are also found wanting, then ex-situ cleaning becomes necessary. This invariably incurs extensive manual intervention, not always with guaranteed success.
The German river association Erftverband has been into MBRs for municipal wastewater treatment for more than a decade, installing the first such system in Germany and commissioning what was the largest membrane bioreactor in the world. The company’s experience in MBR operation provides a valuable insight into the technology.