|M.Sc Student||Shwartzman Zohar|
|Subject||Reliability Assessment of In-House Graywater Reuse|
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Eran Friedler|
|Professor Avi Ostfeld|
|Full Thesis text|
This study presents simulation model application for reliability analysis of MBR (Membrane Biological Reactor) based system for greywater treatment. The main objective was creating a treatment process simulation model for reliability analysis to assess the performance of the MBR treatment system under failures.
The IWA ASM1 served as the basis for the simulation, verified against experimental results from a pilot scale MBR greywater treatment plant.
Exploring system performance under failure scenarios was accomplished by propagation of failures through the system, while running the model in stochastic mode applying Monte-Carlo method.
The reliability analysis considered four types of failures: power, circulation pump, aeration system and damage to the membrane texture. The effect of cleaning agents and degree of service was also examined. The performance of the system was analyzed both under steady state and under stochastic influent quality.
The system is limited by three main hazards: Power failure, circulating pump failure and damage to the membrane texture. Membrane texture damage is considered the most risky, because effluent quality significantly deteriorates by mixed liquor that flows through the membrane surface. When there is a substantial damage to the membrane surface, the effluent BOD, COD, TKN, TSS concentrations reach extreme values of about 1,100 mg/l BOD, 6,400 mg/l COD, 500 mg/l TKN, 4,800 mg/l TSS. In addition, there is no reliable backup solution or maintenance which can ensure the health and safety of the users and the correct operation of the system, apart from monitoring the effluent.
The MBR system was found effective at stabilizing out considerable load variation. With the following influent concentration: TSS, 18-650 mg/l, COD, 50-950 mg/l, TKN, 3-30 mg/l, BOD, 70-600 mg/l the average effluent value was: TSS, 10.5 mg/l, COD, 15 mg/l, TKN, 2 mg/l, BOD, 2.5 mg/l. Nevertheless the system is more sensitive to changes in nitrogen components.
Within three operation alertness frames, only 1-6 hours alertness can guaranty reasonable effluents quality throughout the year.
The reliability analysis leads to the following recommendations:
a. Having redundancy to all sensitive electro-mechanical equipment.
b. Adding additional volume to the aeration basin, and to install an additional recirculation pump in order to limit biomass overflows form the reactor.
c. Adding regular maintenance procedures for the mechanical equipment.
d. Installing dissolved oxygen and water level controls.
e. Setting electronic warning for:
i. Electro mechanical failures
ii. Water level changes.
f. Monitoring the effluent quality.
g. Having maintenance alert of 1-6 hours