Modeling and optimization of membrane lifetime in dead-end ultra filtration

In this paper, a membrane lifetime model is developed and experimentally validated. The lifetime model is based on the Weibull probability density function. The lifetime model can be used to determine an unambiguous characteristic membrane lifetime. Experimental results showed that membrane lifetime shortens if the average membrane fouling status increases. The lifetime modeling results are then used to determine the economic lifetime of membranes. Subsequently, the economic lifetime of a membrane is used to optimize membrane lifetime, i.e. minimizing the total costs. Based on the experimental results it can be concluded that the total costs are minimal if the average membrane fouling status is approximately 1.7× the membrane resistance.

Evaluation of different cleaning agents used for cleaning ultra filtration membranes fouled by surface water

This paper reviews the published literature on potential membrane fouling components, available cleaning agents and possible interactions between cleaning agents and fouling components. It also lists the cleaning models available in the literature, and evaluates the advantages and disadvantages of these models. Based on this outcome, a new cleaning model is proposed to capture cleaning dynamics for 10 different cleaning agents, varying from acidic, alkali and oxidizing to sequestering agents and detergents that were used to clean dead-end ultra filtration membranes fouled by surface water. The model is effectively fitted to the experimental data of the different cleanings. Two criteria are subsequently introduced to quantify the overall cleaning effect of a cleaning agent in terms of cleaning rate and cleaning effectiveness. For membranes fouled by surface water with high organic content it was found that caustic-and oxidizing cleaning agents give the best overall cleaning results.

Dynamic optimization of chemical cleaning in dead-end ultra filtration

In this paper a control strategy is formulated that minimizes the costs for a single chemical cleaning of a dead-end ultra filtration membrane. From the process model, the performance index and the constraints it can be derived that dynamic optimization will lead to a ‘maximum effort control problem’, in which the controls (cleaning flow and cleaning agent concentration) are either zero or maximum. The change from maximum to zero is called the switching point. This switching point depends on the overall cleaning time and the requested cleaning effectiveness. From the calculated optimal control strategy it follows that cleaning time can be significantly reduced, compared to conventional cleaning.

A structured modeling approach for dynamic hybrid fuzzy-first principles models

Hybrid fuzzy-first principles models can be attractive if a complete physical model is difficult to derive. These hybrid models consist of a framework of dynamic mass and energy balances, supplemented with fuzzy submodels describing additional equations, such as mass transformation and transfer rates. In this paper, a structured approach for designing this type of model is presented. The modeling problem is reduced to several simpler problems, which are solved independently: hybrid model structure and subprocess determination, subprocess behavior estimation, identification and integration of the submodels to form the hybrid model. The hybrid model is interpretable and transparent. The approach is illustrated using data from a (simulated) fed-batch bioreactor

Statistical analysis of data from accelerated ageing tests of PES UF membranes

In this research, membrane life-time was evaluated by means of accelerated ageing experiments. A pressure pulse unit was used to perform the ageing experiments in an accelerated way. An experimental design has been set up and four ageing factors were varied at two levels. The four ageing factors studied were: fouling status of the membrane, cleaning agent concentration, magnitude of the back pulse and number of applied back pulses. The integrity of the membrane modules was evaluated by means of permeability testing, pressure decay tests and bubble tests. Also tensile tests were performed to investigate the mechanical properties of the membrane modules. The collected data was used for an analysis of variance to determine which ageing factors and which combination of ageing factors influence membrane life time. The analysis showed that the fouling status in combination with the number of applied pressure pulses were significant ageing factors. Additional tensile tests confirmed these results.

Dynamic optimization of a dead-end filtration trajectory: blocking filtration laws

An operating model for dead-end membrane filtration is proposed based on the well-known blocking laws. The resulting model contains three parameters representing, the operating strategy, the fouling mechanism and the fouling potential of the feed. The optimal control strategy is determined by minimizing the energy consumption for a fixed final time and produced volume.\ud \ud It was found that constant power filtration leads to minimal energy consumption. Constant flux and constant pressure filtration have equal energy costs. However, compared to strategies with a non-decreasing pressure and non-increasing flux, the relative savings are small. Only if the fouling mechanism resembles standard blocking and the fouling resistance is large compared to the membrane resistance, it may be attractive to implement the optimal trajectory