Technical Ande Conomic Performance Assessment Of A Ultrafiltration-reverse Osmosis Process For Wastewater Reclamation And Reuse

Wastewater reclamation and reuse is a viable and attractive approach to dealingwith the global water scarcity and becoming an emerging issue throughout the world.Ultrafiltration(UF)-reverse osmosis(RO) process have recently gained recognition asviable technologies for the wastewater reclamation due to their high removalefficiency of pollutants,stable water quality and easyoperation.However, membranefouling is still a major concern in the application of membrane technology as itdeteriorates the performance of membranes. The removal efficiency of pollutants ininfluent of the UF-RO process and the changes of membrane performance wereevaluated in this paper. Furthermore, the autopsy of a fouled RO membrane modulein the UF-RO process was made in the laboratory to figure out the main materialscausing RO membrane fouling.The turbidity of UF effluent was0.02-0.23NTU, while the value of siltingdensity index (SDI) was0.4-3.2. The turbidity and SDI of UF effluent could meet therequirement of feed water quality for RO system, which could protect RO from heavymembrane fouling to some extent. The removal of turbidity and chemical oxygendemand (COD) of UF system was94%and16%, respectively, while UF systemshowed no significant removal of ammonia nitrogen (NH3-N),total phosphorus (TP)and hardness. The water quality of RO permeate was DOC<1.00mg/L,NH3-N0.02-0.68mg/L, TP0.01-0.30mg/L, conductivity13-56us/cm, hardness3.99-34.80mg/L. In these two years, the water quality of RO permeate was well andstable, and could meet thewater quality requirement of the clients.The status of UF system was still well and the performance of UF membranechanged little after22months’ running compared to the original UF membrane. TheSDI value of UF effluent was kept under3.0and the transmembrane pressure (TMP)has increased a little. However, RO membrane was fouled a little and must be cleanedfrequently by chemicals. Standardized salt rejection didn’t change much, but thestandardized production capacity decreased and standardized membrane pressureincreased significantly. The autopsy of RO membrane showed that the percentage of organic pollutantand inorganic pollutant were79%and21%, respectively. The elements, Si, Ca, Al,Fe, Mn, Mg and so on were found on the RO membrane, while Si and Ca were themajor parts of inorganic pollutant.45%of the organic pollutant on the RO membranecan be dissolved by NaOH solution. The major organic pollutant on RO membranewas soluble microbial products (SMP) andhumic substances. Also, the majority oforganic pollutant was small molecular weight (<5kDa) organic pollutant.The average operating load rate in2012of UF-RO process was56%,which leadto a high total production cost5.36RMB/m3.If the operating load rate was100%, theproduction cost could decrease to3.66RMB/m3. Increasing the load rate of UF-ROprocess is the key to decrease the total production cost.