Study On Hollow Fiber Membrane And New Process Of Re-circulated Membrane Bioreactor

Membrane bioreactor is a new technology of wastewater treatment that has a lot of advantages compared with traditional process, e.g. small space, good quality of effluent, few excess sludge, stable running and so on. However, the flux of submerged membrane bioreactor (SMBR) is smaller and its membrane cost is more expensive. The cross-flow velocity of re-circulated membrane bioreactor (RMBR) is larger(3~ 5m/s) and its energy consumption is higher. These restricted the application of membrane bioreactors. In this paper, polypropylene hollow fiber membrane was characterized and used in a new process of RMBR.Firstly, crystal degree of polypropylene hollow fiber membrane was characterized by XRD and membrane surface was observed by SEM. Some other parameters of structure and performance, such as pore size, porosity and gas flux et al, were also detected.Secondly, RMBR was used to treat wastewater in a long continuously running period (lOOd). Since the 4th day, the water quality of effluent has been stable: CODcr<15mg/L, CODrem0vai>96.5%, turbidityO.17NTU and NH3-N<1.53mg/L while water quality of influent was as following: CODcr: 312~584mg/L, NHs-N: 16~40mg/L.At the same time, influence of adding powdered activated carbon (PAC) to membrane fouling was studied. If 0.5g (PAC)/L (mixed liquid) was added to bioreactor, CODcr of effluent was decreased to 4.22mg/L or less and CODremova! was increased to 98.9%~99.9%. Membrane fouling was retarded and RMBR could be run stably under a less cross-flow velocity because PAC acted as carrier of biomass and organic mass. It was found that critical membrane flux was increased with increasing cross-flow velocity between 0.9-1.9m/s. Under cross-flow velocity of 1.9m/s, critical membrane flux was enhanced from 72L/(m2.h) to 76 L/(m2.h) or 81 L/(m2.h) respectively when PAC or both PAC and alum(Al2(SO4)3 ?18 HjO) were added to the system. At the same time, critical re-circulation ratio was decrease about 10% and 20% respectively.-iii-Then, influence of temperature on membrane flux was also studied. Between 22~30癈, the flux was elevated 1.9% per 1癈 increased under the conditions of trans-membrane pressure (70kPa), cross-flow velocity (1.3m/s).Three methods were used to wash fouled membrane. Fouling materials were removed efficiently through cleaning physically or/and chemically and the flux was recovered with 47%~94%. It was also found that membrane flux was recovered with about 10% while inlet direction of membrane module was reversed.Finally, influence of trans-membrane pressure on membrane flux was studied: between 40~200KPa, the flux had an increasing trend lineally with increased pressure.If the new process is used, RMBR might be applied to wastewater treatment in a large scale because of lower energy consumption and higher membrane flux.