3D Printed Feed Spacers for Wastewater Biological Treatment

Executive Summary (Abstract)

Across the globe fresh water scarcity is a huge issue. Reverse Osmosis and Nanofiltration systems are critical to the worlds clean water abundance, but there are a few problems within these systems. They face pressure drop, membrane damage, and biofouling which create a large loss of energy and increase in operational costs. Feed spacers are engineered and implemented into these systems to alleviate these challenges by providing the structural support to keep feed channel open and lessen bacteria build up. In this project 3D printed feed spacers for wastewater biological treatment will be created. The goal is to discover the ultimate 3D printed feed spacer that is more efficient than a regular spacer by experimenting with different geometries and materials. The use of Solid works and Fluent to design and test a prototype virtually will be key in the first steps of discovering a goal feed spacer. By 3D printing and testing the feed spacers with a membrane fouling simulator, data can be collected to guide and improve the next experiment and prototype design. The first element to be concerned with is the geometry followed by the material of the spacer. Studies have shown that alternating the strands in a feed spacer between thick and thin width can cause a lower pressure drop which is vital in lowering energy consumption. This also creates a fine-tuned flow pattern which reduces low flow patterns expecting to decrease biofouling. This geometry can be one of the first to explore along with trying out different filament shapes (square, circular, and triangle). After exploration and determination of an effective and efficient feed spacer geometry, the material can be explored. Various materials can be used to improve flow and reduce fouling, one example of this is an electroconductive polymer.

Broader Impact

Pressure driven membrane filtration systems can generate quality drinking water from a variation of impaired water sources such as brackish water. The need for clean, drinkable water is going to increase in years to come. This means there is going to be a large push for greater efficiency and cutting energy costs while boosting water output. The modification of feed spacers is going to make the process of reverse osmosis and nanofiltration more efficient and cost effective. Even if at a small scale at first these spacers will significantly help to produce more clean water. As of 2018 there are 844 million people across the world living without access to safe water (water.org). By placing these feed spacers in water systems, this number can drop in years to come by supply more efficient and cost-effective way.

Intellectual Merit

             The “3D printed feed spacers for wastewater biological treatment” that is designed for this project will ultimately be more efficient than a simple, ordinary feed spacer. The company Conwed has launched a project to innovate and research the next generation of feed spacers. Our group will learn from their already discovered information as well as other scientists and engineers work to master an even better prototype of a 3D printed feed spacer. This project will improve on problems which occur with regular feed spacers such as pressure drop, membrane damage, and biofouling. Many groups of people working on improving feed spacers seem to only focus on improving one aspect. By finding the best geometry combined with an ultimate material a feed spacer can be produced that stands out from the rest.

 

Table of Contents

Overview of Problem and Significance

Engineering Fundamentals of Problem

Deliverables

Tasks

Virtual

Hands on

Schedule

Background and Significance

Literature Review

Budget

Schedule with Work Breakdown Structure

References

 

Overview of Problem and Significance

 By the year 2020 approximately 30-40% of the world will be experiencing clean water scarcity. One method engineers can solve this problem is through the innovation of some of the most basic aspects of waste water treatment: feed spacers. The addition of a feed spacer is vital and has much room for improvement.  

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Engineering Fundamentals of Problem

The engineering problem dealt with here is the biofouling that occurs on the membranes in reverse osmosis and nanofiltration systems. Feed spacers are implemented and have an impact on the flow in the feed channel, but there is still an accumulation of bacteria on the membrane, or membrane fouling. This is a serious problem in the industry because it increases energy and costs. This project will engineer 3D printed feed spacers for waste water treatment that will utilize a new geometry and material to alleviate some of these problems to make the overall system use less energy. The goal is to make these 3D printed feed spacers more efficient than ordinary spacers.

Deliverables

Solid works design

Hydrodynamic Fluent model

3D printed feed spacer model

Results of fouling experiments

(This process is repeated for each spacer designed with a new geometry and/or material.)

Tasks

Virtual

Research previously implemented feed spacers and learn from their strong and week points

Create initial design in Solid Works

Test design hydrodynamics in Fluent displaying geometry influence

Hands on

Fabricate 3D print feed spacer model

Test model in fouling experiments

Repeat process with improvements for a new design and model

Schedule

Weeks 1-7: Design Phase

Weeks 8-14: First Prototype

Weeks 15-21: Verification, performance, and improvements

Weeks 22-28: Operational validation and conclusion

The RFP states that feeds spacers have a strong impact on reverse osmosis and nanofiltration membrane systems. A variety of bacteria species form biofilm and can be extremely challenging to remove. Permeation through the membrane was found to exacerbate the biofilm build up which decreases the permeate flux and increases power and cost consumption. Feed spacers in these membranes can give the structural support to allow the feed channel to stay open and also provide turbulent flow to mitigate solute concentration build-up at the membrane surface. In the end this 3D printed feed spacer can be compared to an ordinary one to show the improved efficiency.

Fresh water scarcity is a significant global problem and while the systems discussed above help to solve this problem, they face large quantities of energy loss cause from operational failures from biomass accumulation. Modifying feed spacers is going to help reduce the impact of biofouling on the performance of a membrane. Many aspects to improve spacers have been tried in the past such as covering the spacer in an antifouling coating, trying different thicknesses, different geometries, and a variety of materials. Utilizing the data from these past experiences will help to improve these spacers for more efficient waste water systems. Instead of lacking clean water and paying high costs for the production of clean water, the ultimate feed spacer can be discovered to implement into these systems and lessen these problems.

One study examined this issue of geometry with CFD modelling. They tested triangular, circular, and square filaments. The results are as follows. (Ahmad, Lau, & Abu Bakar, 2005)

In respects to pressure drop the triangular has the worst followed by the square then circular.

In respects to scouring which is dependent on local velocity magnitude, triangular had the best followed by square, then circular. Triangular was the best because the tip created the most drag.

In respects to turbulent intensity, triangular was the highest followed by square, then circular.

In respect to concentration factor reduction, triangular is the best followed by square, then circular.

At low Reynolds number it was recommended that triangular feed spacer geometry be used. The example given was at 200. There between circular and triangular feed spacers, the head loss is 0.0092 m greater in the triangular but there is a 6% improvement in concentration reduction

I cannot find more detailed data for the head loss at this time for a more thorough review.

Results of alternating between thick and thin strands.

shown to decrease pressure drop more than common spacer configurations in

The savings in energy consumption approximated from data is around 0.1 bar per RO element and approximately 5 percent reduction in specific energy consumption

The outcome from different coatings applied to the feed spacers and membranes at an attempt to improve efficiency.

Polydopamine coating on feed spacers and membranes and copper coatings on feed spacers did not have a great impact on pressure drop increase or biofilm accumulation

Polydopamine is a hydrophilic modification agent and was expected to repel bacteria

The copper coating was predicted to slow biological growth

A nanosilver deposition coating was applied to a commercial spacer

Efficient in obstructing biofouling in adjacent membranes

Displayed decrease in attachment of bacteria

(Koutsou, Yiantsios, & Karabelas, 2007) 

An important consideration is the presence of eddies that encourage scaling and fouling as fluid is trapped.

Transition to unsteady flow occurs at low Reynolds number flows at around 35-45.

It was found that with a few exceptions that when considering the ratio of distance between parallel filament to filament diameter one can obtain a lower pressure drop with higher ratio independent of the angle between filaments.

There a few geometries where increased shear stress does not lead to increased pressure drop

In analogous estimation, the cost of the project is estimated by comparing it with similar projects previously completed by Temple University. Since this project has not been conducted before, we can only make general estimations of the cost associated with it. It is safe to analogously estimate that this project will not exceed the $1000 budget allotted by Temple University.  This is primarily because the resources we will need to utilize are provided by the school.  For example, the 3D printer is free of charge for all Temple University students.  Furthermore, Temple has an educational license with the modeling software we will be using so that will be free as well.

Parametrically, we can estimate that we will spend $24.80 per kg of plastic used for the 3D printer.  We will likely have to explore other materials to be used in the 3D printer.  The price of the most commonly used materials ranges from $20-$50 per kg.  Since our model is on a small scale, it is unlikely that we will need for than 1 kg per material selected.  Purchasing the materials for the 3D printer will be the predominant cost of the project.

 One member of the group has solid pigmented ink and dye-based ink, both black, which may be appropriate for use.

A Three-Point Estimating consists of three main types of estimating techniques which follows as: Most Likely, Optimistic, and Pessimistic. Most likely is the most likely estimate of what the project will cost, optimistic is the best-case estimate, and pessimistic is the worst-case estimate. Our Most Likely, Optimistic and Pessimistic costs for the model(s) are follows as:

■ Most Likely: $800

■ Optimistic: $500

■ Pessimistic: $1,000

Phases: A) Planning, B) Design, C) Testing, D) Finalization

❖ A – Planning

➢ A1 – Initial geometry research

■ A1.1 – Research currently investigated geometries

 ➢ A2 – Determining materials to be used

■ A2.1 – Factors: Degradation in saltwater

■ A2.2 – Cost-Benefit Analysis of materials to be used

■ A2.3 – Artificial seawater. Available standards are ASTM D1141-98 or older ASTM D1141-52.

➢ A2 – Determine operating conditions

■ A2.1 – Input pressure, scale

➢ A3 – Solving any problems with selected geometries

 A3.1 – Hydrodynamic: Suboptimal turbulent flow

➢ A4 – Developing and interpreting costs associated with creating a model

❖ B – Design

➢ B1 – Initial spacer design on modeling software

➢ B2 – Investigate other design options and 3D print all options

➢ B3 – Hydrodynamic Fluent model displaying influence of feed spacer geometry

➢ B5 – Integrate chosen geometry/material with modeling software

❖ C -Testing

➢ C1 – Conduct tests on 3D printed models using fouling-simulator

■ C1.1 – Adjust parameters of design if results are unfavorable

➢ C2 – Conduct tests on final 3D printed feed spacer design

❖ D – Finalization

➢ D1 – Compile final results and design into comprehensive design document

➢ D2 – Ensure all project requirements are met

Ahmad, A., Lau, K., & Abu Bakar, M. (2005). Impact of different spacer filament geometries on concentration. Journal of Membrane Science, 138-152.

Araújo, P., Miller, D., Correia, P., van Loosdrecht, M., Kruith, J., Freeman, B., . . . Vrouwenvelder, J. (2012). Impact of feed spacer and membrane modification by hydrophilic, bactericidal and. Desalination, 1-10.

Koutsou, C., Yiantsios, S., & Karabelas, A. (2007). Direct numerical simulation of flow in spacer-filled channels: Effect of spacer geometrical characteristics. Journal of Membrane Science, 53-69.

Miller, D. J., Arau´jo, P. A., Correia, P. B., Ramsey, M. M., Kruithof, J. C., van Loosdrecht, M. C., . . . Vrouwenvelder, J. S. (2012). Short-term adhesion and long-term biofouling testing of polydopamine and poly(ethylene glycol) surface modifications of membranes and feed spacers for biofouling control. Water Research, 3737-3753.

Picioreanu, C., Vrouwenvelder, J., & van Loosdrecht, M. (2009). Three-dimensional modeling of biofouling and fluid dynamics in feed spacer channels of membrane devices. Journal of Membrane Science, 340-354.

Ronen, A., Lerman, S., Ramon, G. Z., & Dosoretz, C. G. (2015). Experimental characterization and numerical simulation of the anti-biofouling activity of nanosilver-modified feed spacers in membrane filtration. Journal of Membrane Science, 320-329.

Suwarno, S., Chen, X., Chong, T., Puspitasari, V., McDougald, D., Cohen, Y., . . . Fane, A. (2012). The impact of flux and spacers on biofilm development on reverse osmosis membranes. Journal of Membrane Science, 219-232.

Vrouwenvelder, J., von der Schulenburg, D., Kruithof, J., Johns, M., & van Loosdrecht, M. (2009). Biofouling of spiral-wound nanofiltration and reverse osmosis membranes: A feed spacer problem. Water Research, 583-594.

Yang, H.-L., Chun-Te, J., & Huang, C. (2009). Application of nanosilver surface modification to ROmembrane and spacer for mitigating biofouling in seawater desalination. Water Research, 3777-3786.