| As the available water resources for human have become limited, wastewater reuse are more and more popular. Metallurgy industry, a large water consumer, would save a lot of water if an advanced wastewater treatment is applied and then all reclaimed water could satisfy both high and low quality water requests separately. Nowadays combination of re-verse osmosis with other membrane processes is employed to desalt in many steel and iron corporations, which is called double-membrane procedure.However, oil is contained in wastewater discharged by metallurgy industries which would cause serious membrane pollution. In this context, optimizing parameters of the system and methods of removing oil were studied. (1) As oil was soluble in metallurgy wastewater,a micro-flocculation followed by sand filtration process was applied to de-crease the oil concentration of the water before going into the ultrafiltration unit. The pe-riod of the sand filtration and best combination of the running parameters were confirmed. (2) A serial of repeated single factor and orthogonal tests were designed to determine the concentration of the flocculant. Then some items from the effluent of each unit were in-vestigated respectively. (3) The degree of membrane pollution was judged with the exist-ing mathematic models according to the situation of this pilot-study system. (4) Mathe-matic models were built to study the economic cost of power consuming. The conclusions of the research are as followed:(1) Study on the parameters and the removal efficiency: Poly Alumina Chlorine (PAC) was chosen as the best effective flocculant and the concentration of 5mg/L was most ef-fective, since the comprehensive removing rates of COD, turbidity and oil was highest. The sand filter should be back washed for 10mins after 24hr-run. The turbidity volume was below 0.1NTU and the oil concentration was less than 0.5mg/L after the pretreatment. A combined cleaning model of gas scrub, flush with production of UF and mixed flush with gas and water for 60 seconds was thought to be effective after a filtration period of 40 minutes. The membrane flux was determined to be 50 L/m2.h.(2) Effects of the procedure: The average value of sludge deposit index (SDI) from the UF effluent was 1.51 far below 5 required before getting into RO unit. The turbidity of the RO effluent was nearly under the detection limitation, the oil concentration was below 0.1 mg/L and the conductivity was 13.2μs/cm which contributed an 98.5% of desalina-tion. (3) Study on the membrane pollution: micro-flocculation was found to be beneficial for oil removal by monitoring the items of the effluent from sand filter and UF. UF mem-brane was thought to be protected better according to the slower increasing of transfer membrane pressure (TMP) less than 1.5 MPa which is recommended by the membrane supplier. The UF pollution was more close to the pore compress model that showed no gel cake formed on the surface of UF membrane. Decrease in RO permeation was not ob-served , so RO membrane was not polluted seriously.(4) Research on modeling the cost of power consuming by RO filtration: operation pressure influenced the reclaim rate regularly. Several mathematic models were built ac-cording to the analysis on operating pressure. Which showed that the higher the tempera-ture of wastewater, the less it would cost. In contrast, the lower the recovery rate and con-ductivity required of the RO effluent, the less the energy was consumed.The trial has offered a promising technology for a followed demonstration wastewa-ter advanced treatment project of Wu Han, which has run more than 1 year with conti-nuous high removing efficient. Moreover, the RO permeation hasn't decreased and the RO membrane was not cleaned with chemicals. |
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