Study On The Optimization Design Of Ultrafiltration Water Treatment System

The shortage and pollution of water has become a serious worldwide problemwhich constrains the development of society, and it is an important method to solve itby various governance. The demand for high-quality water is increasing with thedevelopment of society. It has obvious advantages for ultrafiltration technology toreplace conventional pretreatment and thereby it has great application value in thefield of water treatment. However, at present the technical economical indices ofultrafiltration don’t reach the theoretical value and the design and operation ofultrafiltration technology are still need to be improved. With the continual emergenceof new technology, the new model should be put forward to describe the system. Theearlier studies didn’t consider the problem of membrane module cleaning andreplacement in all-around either. Based on the above, this paper analyses the processof ultrafiltration from the view of system engineering, taking the mathematicalprogramming as a tool, the author makes research on the optimization design ofultrafiltration water treatment system, and obtained the optimal results of the systemprocess. The main contents and results are as follows:1.The selection of membrane module in the process of ultrafiltration has beeninvestigated. Based on the principle of ultrafiltration and the property of ultrafiltrationsystem,the mathematical models of each unit are established according to microporetheory, and the relevant econmic models are given. Single-stage ultrafiltration systemprocess is considered. The membrane modules are divided into two types, high-fluxmembrane and low-flux membrane. The research problem can be expressed as anon-linear programming (NLP) with the minimum annual cost as target, whichincorporates thermodynamic and processing requirement constraints, and it can besolved by GAMS software. The results show that: the high-flux membrane should beselected for high feed concentration and low quality of production water, the low-fluxmembrane is chosen for low feed concentration and high quality of production water. 2.Regular cleaning is the key measure to prevent membrane fouling which willlead to the reduction of membrane performance. The problem of membrane modulescleaning for single-stage ultrafiltration water treatment system is investigated in thispaper. The membrane fouling model is modified and the criterion of cleaning is given.The chemical cleaning method of membrane modules can be expressed as amixed-integer non-linear programming (MINLP) problem with the minimum totaloperation cost as target during two years projection period while one month oneperiod, and the optimal cleaning time during the whole project period can be obtainedby solving it. The results of the example indicate that the chemical cleaning strategyand solving method proposed in this paper is effective for the membrane maintenance.3.Considering the replacement schedule of membrane modules, the further studyon the optimization design of ultrafiltration water treatment system is made. Thecleaning and replacement schedule of membrane modules during two years projectperiod can be taken into account simultaneously. The criterions of cleaning andreplacement are given. The optimization design of the system can be expressed as amixed-integer non-linear programming (MINLP) problem with the minimum totalannual cost as target during the whole project period. The steps for optimizationdesign are put forward as follows:①The mathematical model for ultrafiltration unit isgiven so as to simulate the ultrafiltration process;②Creating ultrafiltration systemmodel according to the above mathematical model;③Building up the membranefouling model and proposing the optimal cleaning and replacement strategy during thewhole project period according to the criterions of cleaning and replacement;④Therelevant economic model is established, which associates the system cost with designvariables;⑤Based on previous four steps, taking the mathematical programming as atool, the ultrafiltration water treatment system is designed. The results of twoexamples show that the cost is lower than that in practical application, whichillustrates that the optimization design method studied in this paper is feasible.