Study On The Process Control And Membrane Fouling Cleaning Technology Of Flat Ceramic Membrane In Wanggao Wastewater Treatment Plant

This thesis focuses the research on a automatic control system for the flat ceramic membrane process in Wanggao wastewater treatment plant(WWTP),including the design,construction,operation and maintenance.PLC technology,SCADA system configuration and WinCC configuration software were used for the analyses and optimization of process auto-control and membrane fouling,its objectives are to construct an automatic control system suitable for the ceramic membrane process in Wanggao wastewater treatment plant,with optimized parameters and membrane cleaning methods.In the automatic control system,PLC is adopted as the core part of the whole control system,which is programmed to realize regular control functions and automatic running logic.With WinCC configuration software,process parameters and operating modes are coupled together to achieve better efficiency.The entire auto-control system is functionally divided into four layers,namely "operating layer","control layer","monitoring layer" and "network application layer." The operational layer includes the basic instrument and device components,which are the actual implementers of the control operation.The control layer as the core of the control system is operated by the configuration software.The monitoring layer and the network application layer provide the daily services in the wastewater plant,including data statistics,report printing and remote monitoring.Practical operation data of WWTP were used for the optimization of several important parameters from the aspects of water production efficiency,economic efficiency and membrane utilization efficiency.The results showed that larger water production period can be obtained,resulted in higher water production efficiency,better membrane utilization.On the other hand,however,larger membrane flux might speed up the consumption of membrane components,thus might shorten the lifetime of the ceramic membrane.Based on the operation data in Wanggao WWTP,during one cycle of production-backwashing of membrane treatment,the suitable water production time is 15 minutes,while backwashing time is 1.5 minutes,membrane flux is 40 LMH.The ceramic membrane fouling mechanism and potnetial cleaning methods were explored both in lab and in Wanggao site.It was found that the foulants on the ceramic membrane contained mixtures of inorganic scale and organic slime.Cleaning with either acid pickling or alkaline alone are not satisfactory,sequential cleaning with acid and base showed better performance.The optimized online cleaning method is as follows:washing with 0.6% hydrochloric acid first for 30 minutes,then with 0.6% NaOH and NaClO mixture for 30 minutes,finally with 0.6% hydrochloric acid for 30 minutes,the membrane flux recovered by 97% in lab test.The offline cleaning method is as follows:first soaking in 0.5% hydrochloric acid for 30 minutes,then soaking in 0.5% NaOH and NaClO mixture for 30 minutes,the membrane flux recovered more than 98% in lab test.The practical cleaning on site at Wanggao WWTP showed that the membrane flux recovered 70% 80% with the online cleaning scheme.This thesis privided a practical application case for the automatic control of flat-sheet ceramic membrane in wastewater treatment plant,it has substantial guiding significance in promoting application of ceramic membrane in wasteater treatment.