Membrane bioreactors for sustainable water management
Introduction The Membrane Bioreactor (MBR) process (membrane activated sludge process) is an advanced wastewater treatment technology and constitutes a suspended growth activated sludge system, which instead of secondary clarifiers utilises low-pressure membranes for solid/liquid separation. As opposed to secondary clarification, the quality of solids separation is not dependent upon the mixed liquor suspended solids concentration, or the settling characteristic. Hence the fact that MBRs can operate with much higher mixed liquor suspended solid concentrations, which provides an intensified biological process. Accordingly, the two major benefits of the MBR process are substantially reduced land and space requirements, and the reclamation of water (permeate) of excellent quality, which is a valuable source for higher demand reuse applications.
Pre-Treatment of Municipal MBR Applications in Germany- Current Status and Treatment Efficiency
Since mid 1999 MBR technology is introduced into domestic wastewater treatment in Germany. First wwtps went in operation performing a conventional mechanical treatment (covering screens, grit chambers and grease traps) without any advanced mechanical pre-treatment stage. After a short operation period module-clogging and hence module sludging was observed. Thus, mechanical pre-treatment was upgraded introducing sieves, first of all to reduce hairs and fibrous substances. But today knowledge is relatively poor concerning effectiveness and treatment efficiency of the whole bunch of aggregates that had been brought to market and vary e.g. in gap size and gap geometry. This paper gives the basics of sieving, the current status of mechanical pre-treatment on German municipal MBR plants and exemplifies an investigation to determine treatment efficiency of two different sieve aggregates.
Production of xylanase by Aspergillus awamori on complex medium in stirred tank and airlift tower loop reactors
Abstract Aspergillus awamori was cultivated on complex medium containing wheat bran as sole carbon source in the precultures as well as in the main cultures in stirred tank and airlift tower loop reactors. The decomposition of the wheat bran particles by α -amylase and xylanase produced by the fungus was investigated by monitoring the enzyme activities, the CO 2 production rate, the concentrations of reducing sugars, glucose, xylose, phosphate and ammonium as well as by applying transmission electron microscopy. By applying synthetic medium in the preculture, the time lag was longer, the growth faster, the xylanase activity higher in the main culture, than by using wheat bran in the preculture. With increasing the stirrer speed the intimate contact between the pellets and the wheat bran was reduced, which caused a decrease of the growth and the xylanase production. By applying ground wheat bran, filamentous mycelium was formed, the growth and the substrate uptake rates increased, but the xylanase production decreased due to the less intimate contact between the fungus and the wheat bran. In the airlift tower loop reactor filamentous mycelium was formed due to the low specific power input. In spite of the high medium viscosity, high xylanase productivity was obtained. With ground wheat bran the particles were completely covered by filamentous mycelium, medium viscosity strongly increased and as consequence the growth and xylanase production decreased.