Filtration
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Requirements
From an environmental safety perspective, the filters were one of the most important components. We required
filters which could completely prevent microbes from entering or leaving the system. This constraint requires
extremely reliable, and ultrapurifcation quality filters.
Design
After researching, we ultimately chose the SWT 0.1 Micron Absolute Rated Filter. Given the diameter of most
bacteria ranges from 0.2-2.0 micron, and the absolute 100% rating of the filter, the filter easily qualified.
Materials
The filter cartridges are composed of 100% polypropylene membranes which have a failure rating of 65 PSI.
Additionally, their lifetime are rated at 200 gallons, which equates to nearly 5 years of continuous operation
at 0.3 ml/min.
Assembly
The filters were housed in a polycarbonate framing with threading leading to an inlet and outlet stream.
Pumps
Requirements
Continuous monitoring requires a steady inflow of sample fluid to be supplied to the bioreactor. Given an
operational lifespan of at least 6 months using battery power supplemented with solar also required a low
power draw. Finally the flow rates required for a 100 ml continuous flow reactor are less than 1 ml/min.
Design
After researching low power draw pumps, we decided on the Bartels Mikrotechnik mp6 Micropump. The pump uses two
extremely small actuators which increase the flow of the fluid with a greater frequency supplied to the pump.
Since the flow rates are so small, the pressure head associated with the filters does not exceed the 600 mbar
maximum. A mp6-EVA electronic controller was also purchased from Bartels which allows external tuning of flow rate.
The original controller can only be supplied with at 2.5-5 V voltage source, so a step-down was necessary to be
compatible with the battery inside the device.
Material
Contamination and corrosion are always a concern in continuous operation. A benefit of the mp6 micropump is that
all surface in contact with the fluid is PPSU (polyphenylsulfone) , a heat and chemical resistant plastic.
Assembly
The micropumps were received in June to perform autoclaving testing on the parts. In October, after the remainder
of the device was assembled, the micro pumps were put online in the device and confirmed the ability to supply
continuous flow through the entire device including the two filters, mixer, reactor and piping.
Piping and Instrumentation
Requirements
To connect each component of the system including the filters, food tanks, sample ports, and
mixer requires a leak-proof, durable system. Additionally we required methods to calibrate the
flow rate of the fluids throughout the device, so pressure gauges and flow meters are necessary.
Design
After several drafts, our ultimate design was combination of 304/316 stainless steel piping, valves,
and adapters. FEP durable plastic tubing was used for connections between filters and ports which
require flexibility when servicing or reparing the device. A stainless steel in-line passive mixer was
included to avoid power drains from mechanical mixing. Two pressure gauges were included along the wetted
path to provide readings for calibration. Two 0.01-4 ml/min flow meters were added as well. The fluid can
be diverted from the calibration system using a 3-way diverter valves. Precision needle valves were included
after the feed out from both micropumps to control flow rate.
Materials
Both stainless-steel and fluorinated ethylene propylene plastics are sturdy and corrosion resistant. All fittings in the system were also 304/316 stainless steel. In summary,
these components allow an extremely tight-fitting system which should avoid leaks for extended operations
Food Tanks
Requirements:
Food storage vessels for long-term field deployment must be durable, corrosion resistant, and autoclavable to
prevent initial contamination. To avoid damage to electronic components necessitates a leak-proof design.
Design:
A battery of six one liter cylinders was chosen for its modularity and ease of fabrication.
Material Selection:
The choice of materials depended on the cost and durability of that material. Since we have
had prior experience with polycarbonate, we decided it would be best to continue to use
polycarbonate as the material for the containers. Polypropylene was used for the end caps
because it was chemically resistant and cheap.
Assembly:
The food tanks were all machined in-house at the Rhodes Hall Machine shop. The
polycarbonate clear tubing was glued together with the polypropylene via a super silicone
sealant adhesive to form a clean and strong seal.
Housing
Requirements:
The requirements that we found necessary for the chassis to operate were keeping it water-proof and impact resistant. Ultimate deployment would be in harsh environments and necessitates protective measures to prevent water supply from damaging electronic components
Design:
The design went through several iterations during the semester. After multiple home-design options, we concluded a Pelican heavy duty case would provide the support and safety we required. Not only was it sturdy and water-proof, but it was also large enough to be buoyant in water with up to 180 lbs of load.
Material Selection:
The polycarbonate material for the Pelican case was ideal in terms of stress and other parameters to handle the harsh wilderness.
Assembly:
Modifications to the Pelican case were performed to meet the of electrical components and supply of water samples to device. A 15 W solar panel was retrofitted to the lid of the case to provide replenish power supply. Inlet/outlet ports were drilled to allow piping system coming out of the top to serve as inlet and outlet ports for the water to enter and exit the device. A joint piece between the solar panel and power adapter was fabricated to serve as waterproofing connections from the Pelican case. Aluminium honey-comb plating was included and cut to size using water-jetting to act as both a housing for food tanks and batteries, and provide structural suppor.
Power
Requirements
To be deployable for the of target six months of operations requires an autonomous electrical source
in the wild without human repair or maintenance, recharge and store energy for extended periods of time.
A rugged device must also be able to survive bear attacks and tree falls, all while being environmentally
friendly and light enough to allow for floatation.
Design
After a series of designs, we chose a LPG Series gel electrolyte valve-regulated lead acid battery
(LPG12-100) from Leoch with a 15W mono-crystalline solar power panel from Instapark. While lead acid
batteries have the highest charge time and the lowest specific energy density, they are by far the
most reliable and durable batteries. Commonly used in boats and in conjunction with solar systems,
they are reliably sealed, well characterized, and easy to charge and operate with microcontrollers and
other complex circuitry. With a wide operating temperature, the model is also insensitive to occasional
deep discharge and has a high charge acceptance, key features for unpredictable solar recharge conditions
in the field. It is shock and vibration resistant and can be used in any orientation. Out of all the proposed
systems, this model also provided the best current output and voltage necessary to power the rest of our
mechanical and electrical parts. It also came cheap. The maximum current draw of the battery is 0.89A and
was shipped with a 12V charger controller, which prevents overcharging.
Materials
We were greatly concerned with the toxicity of some gel lead acid batteries, which is why our initial
prototype actually did not feature one. However, other less toxic battery systems are not as robust and
have a smaller operating temperature range, with some prone to short-circuiting. Valve-regulated and
tightly sealed, all components of the LPG12-100 are fully recycle and specially designed for outdoor usage.
The solar power panel has its mono-crystalline solar cells embedded in transparent vinyl acetate behind
tempered glass with heavy back sheet.
Assembly
We would like to give a special thanks to Professor Bruce Land, a Senior Lecturer in the Department of Electrical
and Computer Engineering at Cornell, for his advice and guidance. The battery was easily integrated into the
chassis of the device without alterations.
Software
Requirements
The method of data transfer had to be easily fixed, and supportive of some long distance information transfer.
The first criterion is due to the nature of the biosensor. Since the device would ideally be outside braving the
weathers for six months, we need it to be quickly replaced. Furthermore, the biosensor had to be able to transmit
data; it would be inconvenient if someone had to frequently go to the device to check the voltage readings.
Design
An Android phone was chosen as the best fit for the project as it satisfied both requirements. Notably, it achieved
the distance criterion well – as long as a cell tower was nearby, the information on the phone could be accessed from
anywhere with an internet connection. Furthermore, there existed a wide range of support for Android development that
did not exist for other platforms. These included tools such as the Apache API, a light weight server interface that
allowed the project to run more smoothly.
A server was also designed to partner with the Android device. The server was to use a MySQL table for data retrieval
and access - this allowed for easy testing and modularity.
Components
The choice of materials were generally the industry standard – we used the HTTP protocol to facilitate data transfer
and MySQL to store the data. For the phone, Samsung’s Galaxy Nexus was chosen mostly because of the third-party support
found for the phone concerning the Android to Arduino communication.
Assembly
The code for the Android device was written in Java using a Microbridge project as the method of communication between
the phone and Arduino. The basic Apache API was used to transfer data to a web server. For the server, the code was
written in PHP and tested with WAMPserver, a development tool that allowed local hosting of the MySQL tables.
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