AQUALUS

A semi-automatic research aid for collecting and filtering microplastics in estuaries and rivers.

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Abstract

Increasing levels of microplastic debris (<5 mm) have been detected across the world’s waterways, posing a serious threat to ecosystems. Microplastics are accumulating up the food chain, while breaking down along the way and releasing toxic chemicals. Active research is being conducted in this field; however, there is no standardized methodology for sampling microplastics, leaving researchers lacking the ability to efficiently and quantifiably measure the extent of this pollution.

Aqualus proposes a solution that delivers repeatable filtered samples of microplastics ranging 10-500 microns in size from volumes of water up to 500L at depths up to 15m. This is achieved by a boat mounted motor-released hose reel that lowers a pump to a specified depth determined by a depth sensor. The pumped water is dispensed into filtration chambers, collecting flow rates and sample volumes. Each chamber is composed of stacks of filters of decreasing fineness, collecting 5 ranges of microplastics from each depth, and discharging discarded water. 

Over the academic year, the team designed, built, and validated all components of this semi-autonomous system. Design and manufacturing choices were made to maximize the realization of key system characteristics and provide the greatest value to the researchers that will use this tool. Aqualus delivers filtered microplastic samples to researchers at higher volumes, deeper depths, and greater accuracies not achievable by any current sampling techniques. By achieving these goals Aqualus will provide data to help reduce plastic pollution and effect long-term policy change. 

Project Aqualus received the Judges’ Choice Award at the UPenn 2020 Mechanical Engineering and Applied Mechanics Senior Design Competition.

Overview

Course: Senior Design Capstone Project; Project Completed in a Team of 5

Focus: Storytelling; Research; Prototyping; Manufacturing; Testing

Timeline: August 2019-May 2020

Role: Mechanical Design and Manufacturing Lead; Digital and Graphic Design Lead

Need and Background

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It is estimated that around 8 million metric tons of plastic are introduced to the world's oceans each year. Plastics are as common on beaches as seagulls. However, what goes unnoticed are the microplastics, definitionally plastic particles smaller than 5 mm in size, that are washed on the beach, swirling in currents, suspended in water, and settled on the sea beds. Microplastics often result from larger plastics breaking down due to waves, wind abrasion, or ultraviolet radiation from sunlight. Additionally, a large amount of microplastics come directly from human waste, such as microbeads in personal care products, or plastic fibers from textiles. Microplastics have the potential to be extremely harmful to the environment due to their ability to break down and release toxins into waterways. They are also often digested by planktonic microorganisms, and are then able to make their way up the food chain—all the way to the fish that humans eat. The full effect of microplastics on ecosystems and human life is not known, but there are clear signs that they are damaging to natural life.

Researchers are realizing the possible long term effect microplastics can have on Earth, and they are working to understand and quantify microplastic contamination. However, researchers do not have standardized collection and analysis methods, making comparison between data extremely difficult. Due to these issues, it is hard for researchers to replicate the work of others, allowing for very little statistically significant data. In addition, most current sampling methods present their own problems, including inaccuracies and inabilities when sampling large amounts of data, collecting very small particles, and sampling at various locations. These issues surrounding microplastic collection make it extremely difficult to understand the extent of microplastic contamination in the world’s waterways, and halt the possibility of policy change or clean-up efforts to actually solve this problem. This exhibits a clear need for a better system to collect data surrounding microplastics.

System Constraints

The team interviewed more than 15 active researchers to determine the key quantitative system characteristics that an ideal solution should have. First, based on existing data of the concentration of microplastics in estuaries, a sample volume requirement of 500 liters is required to collect meaningful samples. The solution must sample at any depth up to 15 meters, the maximum depth of most rivers and estuaries in the Delaware River Watershed, and do this within an error of ±0.15 meters in order to acquire distinguishable data. To get usable data on concentration, a volume accuracy of ±2% of the total sample volume is also necessary. Thus, the system must be able to control the collection of water at a steady flow rate to gather repeatable samples. To provide a sufficient quantity of samples, researchers should be able to take at least 12 samples in their typical 6-hour sampling trip. We found that it is crucial to the researchers that microplastics are filtered from the water in the field, and plastics of up to at least 50 microns, with a reach goal of 10 microns, must be collected. Each sample must be collected in under 25 minutes due to the number of samples a researcher must collect in a trip. Finally, each sample collected must require no more than 2 minutes of hands-on attention to reduce the strain on the researcher.

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System Design

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Aqualus achieves all of these characteristics, providing a system with the necessary improvements to microplastic sample collection. Aqualus is composed of five main subsystems which are all housed on any standard research vessel: collection, depth control, fluid direction, filtering, and a user interface. The first subsystem, collection, includes a pump and flow rate sensor, in order to rapidly collect a large sample of water from a wide range of depths, and easily control and measure water flow. The depth control subsystem allows for Aqualus to sample at user specified depths between 0 and 15 meters with high depth accuracy, enabling researchers to collect distinguishable data on the profile of microplastics in the water column. The fluid direction system directs water into the filtration system, and off-board for cleaning. The filtration system consists of stacked mesh filters of decreasing pore size. This tiered system filters out larger particles so that finer meshes can be used to collect microplastics as small as 10 microns. The user interacts with the system through an Android app, where the researcher sets sample parameters and receives back real-time collected data. Because the system is attached to a boat, researchers can sample in specific sites of interest, like the mouth of a small stream or next to a runoff pipe. Aqualus is able to achieve these characteristics with less than two minutes of user interaction per sample, allowing users ample time to work on other parts of their research.

User Interaction

An important aspect of Aqualus is that it benefits the researcher (our prime stakeholder) and eases their collection process. Below is the detailed interaction process with descriptive images. 

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Prototyping and Testing

Aqualus was not completely finished due to the social distancing associated with Covid-19, but it stands in a near-completed form. The functionality of Aqualus was validated through a series of individual subsystem tests performed on multiple rounds of physical prototypes. These tests included ensuring Aqualus can actually collect accurate samples, resulting in a 98% capture of any microparticles put through the system. Additionally, all system characteristics were tested, ensuring Aqualus can reach depths, hold its position at those depths within ±0.15 meters, collect samples with flow rates as high as 20 L/min, and hold steady flow rates. All tests were successful, concluding Aqualus can achieve every one of the designed-for system characteristics.

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With Aqualus successfully meeting our system criteria defined by stakeholder needs, the team went back to the same researchers to discuss our solution. Stakeholders overwhelmingly approved the team’s design choices, and were extremely pleased with the work. Recommendations for future iterations of this design include sample storage, higher quality materials, greater levels of autonomy, better waterproofing, and the addition of more sensors and data collection abilities. We are also excited that our work will be continued by environmental science researchers at Penn!

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If you are interested in learning more, watch Team Aqualus present our final project here!

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