NAMS 2002 Workshop - ICOM 2008

Drinking and Wastewater Applications V – 5
Friday July 18, 4:30 PM-5:00 PM, Maui
Importance of Membrane Reactor Design for Membrane Performance in
Biofilm-MBR
I. Ivanovic (Speaker), Norwegian University of Sci. and Tech., Trondheim, Norway -
torove.leiknes@ntnu.no
T. Leiknes, Norwegian University of Sci. and Tech., Trondheim, Norway
A Biofilm-MBR is an alternative concept to activated sludge - MBR where a
biofilm reactor is employed instead an activated sludge reactor, and where the
membrane reactor is designed only as an enhanced particle separation unit.
Possible advantages of this concept lie in the fact that biomass is attached to
suspended carriers and there is no need for sludge (i.e. biomass) recirculation in
the system. Additionally, only small amounts of biomass that become detached
from biofilm carriers need to be separated in membrane reactor. [1]. A lower
amount of suspended matter that needs to be separated gives less fouling
potential with regard to cake formation on the membrane surface. However,
submicron particles and colloidal organic matter remain significant foulants as
reported in previous studies [2][3][4]. For this study a small-scale pilot plant was
operated, consisting of moving-bed- biofilm reactor (working volume of 260 L),
coupled with a submerged membrane reactor (MR) with Zenon ZW10 hollow
fiber membrane modules (membrane area 0.93m 2 ). Municipal wastewater was
fed to the pilot plant and operated under low organic loading conditions, giving on
average >90 % ammonium removal. The biofilm reactor was operated with a 4
hour hydraulic retention time. Suspended solids (SS) in the effluent from the
biofilm reactor varied between 90 - 150 mg L -1 , while COD and FCOD were
between 120-242 and 25.9-43.1 mg O 2 L -1 respectively. The membrane reactor
was operated in a 5 minute cycle with production flux 35 LMH, backwash flux 42
LMH and recovery 96%. Continuous air scouring of the membrane was
employed for all tests with specific aeration demand (SADm) set on
approximately 1 Nm 3 airm -2 membrane areah -1 .
Three membrane reactor designs were compared: 1) a completely mixed reactor
(CM-MR), 2) membrane reactor with integrated sludge pocket (SP-MR) and 3) a
membrane reactor with a modified sludge pocket (MSP-MR). Volumes of the
membrane reactors were 9, 25 and 41 L respectively. Preliminary results
showing that design i.e. geometry of the membrane reactor play an important
role in membrane performance. Steady state concentrations of MLSS around the
membrane area were ~3900, ~1000, ~400 mg/L giving fouling rates within
production cycle of 20, 6, and 3×10 -5 bar sec -1 , respectively. Lower
concentrations of MLSS and COD around the membranes as a function of the
modified rector designs results in a better membrane performance. Reduction in