Research On The Performance Enhancement Of Membrane Bioreactor For Treating Polluted Surface Water By Inoculating Exogenous Microorganism And Dosing Powder Activated Carbon

Source water deterioration risen from different kinds of pollution poses a significant challenge to conventional drinking water treatment process. A variety of novel techniques were investigated and applied to enhance or replace the conventional process for treating surface water polluted by organic matter and ammonia. It has been recognized that membrane bioreactor (MBR) which incorporates membrane filtration and biological treatment has a great advantage in removing organic matter and ammonia. Employing MBR process to treat polluted surface water has been widely studied, and a mass of conclusions have been drawn. However, there are a lot of factors that will influence the performance of MBR, and most of their effects are still remain ambiguous, leading to the necessity of further investigation. This dissertation mainly focuses on the countermeasures for solving the problems in MBR startup, removal of organic matter, and ammonia removal at low temperature, expecting to offer a valuable reference to real applications of MBR for treating polluted surface water.In order to address the problems of prolonged period and accumulation of nitrite during the startup of MBR, effects of inoculating exogenous microorganism on the performance of MBR during startup and steady operational periods were investigated. It was shown that inoculating with2g/L activated sludge enabled a quick startup and avoided the accumulation of nitrite; inoculating with2g/L sediment of river shortened the maturation period of nitrosobacteria and nitrobacterium. However, inoculating with exogenous microorganism hardly improved the removal of organic matter. In steady operational stage, MBR inoculated with exogenous microorganism and without performed very similarly. However, inoculating with exogenous microorganism at initial still improved the removal of biodegradable dissolved organic carbon (BDOC) to some extent.Aiming to the weakness of MBR in removing organic matter and in confronting the fluctuation of feed water, hybrid process of coagulation-sedimentation-MBR was built and effect of dosing point of powder activated carbon (PAC) on the performance of the process was investigated. It was shown that dosing PAC after sedimentation most effectively improved the organic matter removal. Accordingly, a pilot-scale MBR, into which PAC was directly dosed (named MBR(PAC)), was established to treat settled water (raw water from Dongjiang River). The pilot-scale MBR(PAC) effectively removed turbidity, organic matter, and ammonia in feed water. Another pilot-scale MBR(PAC) for treating settled water (raw water originated from Liuxi River) was established, and similar high organic matter removal as well as high ammonia removal were obtained. Operation parameters that can make the MBR(PAC) smoothly run for a long period was obtained.In order to tackle the problems in MBR under low temperature, including low activity of microorganism and high membrane fouling rate, effect of temperature on the performance of MBR for treating polluted surface water was investigated. Moreover, effect of high dosage of PAC on the performance of MBR under low temperature was also studied. It was shown that lower temperature led to lower removal efficiencies of ammonia, nitrite, and BDOC, but removals of CODMn, DOC, and UV254were barely impacted by low temperature. Additionally, low temperature increased membrane fouling rate. In comparison, with20g/L PAC dosed, the MBR exhibited much higher removal efficiencies of organic matter, BDOC, and ammonia than that in ordinary MBR; the cake layer resistance and the inner fouling of membrane were decreased; however, the high concentration ammonia in feed water could not be completely removed under2~3℃. Under4~5℃, removal efficiencies in MBR initially dosed by20g/L PAC (MBR(PAC-20)) and50g/L PAC (MBR(PAC-50)) remained similar for removing low concentration of ammonia; MBR(PAC-50) exhibited a superiority with high initial ammonia loading. When temperature decreased to2~3℃, high quality effluent (ρ(NH3-N)<0.5mg/L and ρ(NO2--N)<0.4mg/L) was still obtained from MBR(PAC-50).In order to deal with the seasonal change of temperature and quality of feed water, effect of enhancement techniques, i.e. dosing high concentration of PAC and inoculating exogenous biomass, on the performance of MBR for treating settled water (raw water from Songhua River) were investigated. It was shown that MBR without any enhancement exhibited low removals of organic matter and ammonia under low temperature, while dosing high concentration of PAC in MBR significantly improved the removal efficiencies of organic matter and BDOC, and membrane fouling was eliminated as well. But this enhancement could hardly increase the ammonia removal. Dosing exogenous microorganism that had adapted to low temperature could significantly improve ammonia removal in MBR, whiles this improvement worn off soon due to the accumulation of sludge floc into/onto membrane module. Dosing both exogenous acclimated microorganism and high concentration of PAC into MBR could allow the high ammonia removal originated from exogenous acclimated microorganism to remain more lasting. Temperature exerted a significant effect on the species and amount of ammonia oxidizing bacteria (AOB) in MBR. When water temperature was lower than2℃, the species and the amount of AOB in the MBR inoculated with exogenous acclimated microorganism were increased remarkably, which gave rise to the increasing ammonia removal.