|M.Sc Student||Fabian Tal|
|Subject||Integration of a Submerged Aerated Fixed Biofilm Reactor|
with Advanced Oxidation Processes as a
Pretreatment for Membrane Separation
of Wastewater Effluents
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Carlos Dosoretz|
|Full Thesis text|
Advanced wastewater treatment using reverse osmosis (RO) membranes is considered nowadays the most generic technology for water reclamation and has been proven to reject most dissolved contaminants, including trace organics. Membranes biofouling and scaling which both lead to substantial chemical use and shorten membrane lifespan, are the main obstacles. In addition, the concentrated stream must be treated to remove contaminants before disposal.
The main hypothesis of this research is that lowering organic loading of secondary effluents by enhancing biodegradation of recalcitrant organics through partial oxidation in an integrated system will alleviate the propensity of biofouling on membranes and improve the efficiency of further brine treatment. Oxidation was targeted to activate the macro-fraction of dissolved organic carbon (DOC) of secondary effluents, soluble microbial products and natural organic matter through partial oxidation.
An experimental system consisting of a plug-flow-biofilm reactor filled with a porous support integrated with UV-H2O2 oxidation system on the recycle was operated continuously during 14 months. UV\H2O2 was chosen as the oxidation stage due to its simplicity, lab safety and the ability to split between photolysis and OH∙ oxidation. DOC removal in the integrated BIO-UV\H2O2 system achieved up to 50% DOC removal when the recirculation rate was 1:1 and up to 60% removal with recirculation rate of 3:1. 80% of total DOC removed was associated with biodegradation in the bioreactor and the remaining 20% was associated with mineralization in UV\H2O2 system. Reduction in absorbance at 254 nm and specific UV absorption (SUVA) before\after UV\H2O2 was consistent throughout the operation. Total nitrogen (TN) removal of 23% was consistently observed in the system while mass balance showed that 70% of TN was removed in the UV system and the rest was removed in the bioreactor. Hydrophobic interaction chromatography (HIC), Fourier Transform Infra-Red (FTIR) and Excitation/Emission Map Spectra (EMMS) analyses was applied on reactor effluents to identify the changes which occurred during this treatment. Both hydrophobic and hydrophilic fractions were effectively removed in the system. This was achieved from the combination of UV\H2O2 which transforms hydrophobic organic matter to hydrophilic and the biological process which preferably removes hydrophilic compounds. HIC analysis showed that hydrophobic acid was the most dominant fraction in reactor effluent which is also considered to be the most bio-recalcitrant fraction thus the remaining organics in reactor effluent were concluded to be non-biodegradable. FTIR analysis showed an increase in the 1050/1380 bands ratio after UV\H2O2 implying preferential degradation of proteins/aliphatic/ aromatic hydrocarbon (1380 cm-1 band) relatively to polysaccharides (1050 cm-1 band). Fluorescence regional integration of EMMS maps identified the removal of aromatic proteins, soluble microbial products and humic matter as the main fluorophores degraded. Biofouling potential of BIO-UV\H2O2 effluent was concluded to be negligible compared to the feed (untreated secondary effluent), as shown by biological oxygen consumption (Winkler).
Concluding, the novel integrated BIO-UV\H2O2 system proposed here successfully removed DOC components lowering membrane biofouling potential and potentially hindered quenching during brine treatment, thus increasing energy efficiency of brines treatment while improving micropollutants removal.