Design For Accessibility: Getting it right from the start
Capstone Final.pptx
1. Engineering of Waste to Energy
Generation in the Last Frontier:
Bioenergy Production Utilizing
Wastewater in Remote Low-
Temperature Alaska
CASEY BALLARD, CARLY FITZ MORRIS, ALEXANDER KASKO, JOHN THOMAS LENCKE,
ANDREW LIN
CLEMSON UNIVERSITY, CLEMSON, SC
December 6, 2022
4. Background
● Alaskan temperatures lead to near
year-round permafrost
● Communities are extremely remote due
to Alaska’s size
● Modern plumbing appliances are
infeasible if not impossible
● Solution for human waste is a “honey
bucket” paired with intermittent lagoon
delivery
● Alaskans input their waste in a plastic
bag in the honey bucket, tie up the
waste, and discard in a lagoon
● Lagoons are sometimes far away and
travel is difficult due to dirt roads with
poor maintenance and harsh weather
conditions
Figure 1: Alaskan Mean Daily Temperatures
Figure 2: A Honey Bucket
5.
6. Figure 3: Extreme Climate Conditions Figure 4: Fairbanks, Alaska
Figure 5: Individual Transportation of Waste Figure 6: Accumulation of Waste in Lagoon Figure 7: Waste Disposal
7. Rationale
● Rural Alaskans living in freezing temperatures reaching -20°C during the
winter are without modern plumbing and waste disposal facilities
● By utilizing human waste through collection and anaerobic digestion, a
sustainable source of heat in the form of biogas will improve the health and
living conditions of many Alaskans
8. Goal
The goal of this project is to design a waste management system to produce
bioenergy for rural Alaskans by incorporating anaerobic digestion of human waste.
9. Objectives
The specific objectives of this project are:
1. To design a collective waste system
2. To design a bioreactor for waste digestion and biogas generation
3. To store, transport, and utilize methane in the form of biogas
10. Objective 1:
To Design a Collective Waste System
● TASK 1: To devise a structure that can store a community-wide amount of waste
for an extended period of time
● TASK 2: To design a system for easy-access waste entry to the digester
● TASK 3: To incorporate an effluent removal system for cleaning
11. Objective 2:
To Design a Bioreactor for Waste
Digestion and Biogas Generation
● TASK 1: To construct a psychrophilic batch reactor to produce methane from
community waste
● TASK 2: To evaluate the amount of insulation needed to keep the bioreactor
operating at 20°C
● TASK 3: To determine the microorganisms required to allow for anaerobic
digestion to occur
12. Objective 3:
To Store, Transport, and Utilize Methane in
the Form of Biogas
● TASK 1: To design a safe mechanism to collect methane gas to be used for
bioenergy production
● TASK 2: To determine a safe handling method to store methane
● TASK 3: To engineer a process for the methane collected to be used as heat by
the community
15. Literature Review
● Waste Collection and Storage
● Digester Operating Conditions
● On-Site Temperatures
16. Waste Collection and Storage
● 2,000 gallon tanks
○ Each tank can hold waste for an estimated 40 days for a population size of
100
○ Estimate each person produces 0.4 gallons of waste each day
○ 2,000 - 400 gallons (the amount of volume left at top of tank for gas) =
1,600 gallons
○ 1,600 / (0.4 *100) = 40 days
○ 40 days of digestion is also enough time for the reactions to take place and
methane to be produced
● Current AutoCAD drawing is based off of AutoCAD dimensions from Snyder
Industries Inc.
○ Chose this design based off of its ability for easy installation and meeting
all sizing and pricing criteria
17. Digester Operating Conditions
● Mixed Anaerobic Digester
○ Mixing method - Pumping settled substrate upward
● Flow Conditions
○ Intermittent inflow - Assumed due to practices of Alaskans
○ Fed Batch vs CSTR
● Operating Times
○ It is assumed that anaerobic conditions will soon occur in digester
○ Each digester will alternate being filled for 40 days
○ Once internal temperatures reach above the freezing point of water the
digesters are assumed to be operational
18. Operating Conditions of Influent
● Fecal Waste
○ Complex mix dependent upon diet
■ Carbohydrates, fats, proteins, and
fibers
○ Various methods of quantifying substrate
■ BOD, COD, VSS, TSS, ODM
■ Wet mass will be used
○ About 0.4 kg wet mass expected per
person per day
● Urine
○ High in nitrogen concentration
○ Accumulation of ammonia is an inhibitor
not modelled
○ Urine considered for volume addition to
digester
○ About 1 kg wet mass expected per person
per day
Figure 8: Distribution of
Components in Human Waste
19. Metabolism of
Substrate
● Hydrolysis is the rate limiting step
○ The remaining steps are
relatively spontaneous
● Environmental conditions for
remaining steps are outside the
scope of this project
○ pH, Salinity, product inhibition
Figure 9: The Flow of Anaerobic Digestion
20. Biogas Production
● Product formation as a
function of influent mass
○ Often considered as total
output for set input, not
kinetically
● Kinetic biogas production
○ Total methane production
as a function of hydrolysis
rate constant has been
used when hydrolysis is
rate limiting
Table 1: Ranges of Gas Components in Biogas
Table 2: Ranges of Biogas Generated from Animal Waste
21. On-Site Temperatures
● EPA shared temperature data collected from Fairbanks, Alaska
● Temperatures range from -26°C (-15°F) to 22°C (72°F)
● Temperatures will need to be accounted for in design
● Psychrophilic bacteria need to be kept between -10°C to 20°C, ideally around
20°C
● Digester heat generation is negligible, external sources of heat required
22. Materials and Methods
● Bioreactor Design
● Reactor Heating
● Methane Production
● Solar Power Generation
23. Bioreactor Design and Modeling
● The general design for the bioreactor consists
of two anaerobic digesters and a composting
tank. All of which is surrounded by a layer of
insulation
● Additionally, within the anaerobic digesters a
pump will continually mix the waste
● AutoCAD was chosen to model the design for a
couple of reasons
○ AutoCAD is a modelling software used to
create precise 2D and 3D drawings and
models.
○ AutoCAD is easy to use and has multiple
benefits including decreasing errors, better
quality, and creating an ease of
understanding.
Governing Equations
Volume = Retention Time * Input Rate
24. Heat Modeling Using COMSOL Multiphysics
● Sub-zero temperatures are very common in Alaska
● Heat modeling was done using COMSOL, used to
simulate multiple physics in a system
● Useful for changing variables to show a range of
scenarios
● A COMSOL model was used to simulate different
weather throughout the year and justify the use of
heaters to keep the reactor running at a psychrophilic
state
● COMSOL provided the ability to simulate the coldest
weather conditions in Alaska to show when the reactor
could stay above freezing temperatures and provide
operating months of the reactor
Heat Transfer Equations:
qo= h · (Text-T)
⍴Cpu ·⛛T+⛛· q = Q + Qted
25. Bioreactor Heating
● A cattle water heater was chosen to heat the
digesters
● Commonly used to heat large tanks of water
for cattle consumption during the winter
● Anaerobic digesters are comparable to cattle
water tanks due to their large water volumes
● Designed to heat the water automatically
when below a certain temperature, making
sure the reactor cannot freeze during
operation
● Will not melt the reactors because they are
designed for use in rubber, plastic, and steel
tanks
Figure 10 : Farm Innovators 1500W Tank Deicer
26. Bioreactor Insulation
● 6 inch insulation was chosen because of its
commercial availability
● A value of R19 means that every inch of
insulation thickness has an R-value of 3.2,
which matches the modeling values for the
insulation
Figure 11 : Owens Corning 6.25” Insulation
27. Methane Production Modeling Using
STELLA Architect
● STELLA was chosen for a couple of reasons
○ STELLA is a modelling software used for time
dependent processes.
○ STELLA is quickly adjustable for different
inputs(e.g. number of persons, waste
composition, temperatures)
● Modelling was focused mimicking results from prior
research performed with similar conditions.
Governing Equations
Hydrolysis Rate = kh*S
Biogas = (YP/S)*(1-EXP(-kh*t))*S
28. Determining the
Hydrolysis Constant
Governing Equation
● Chose oranges due do least change
with temperature and lack of high fiber
● Found
○ kh = EXP(-5430.1/T+16.598)
Figure 12: Hydrolysis Constant Related through Arrhenius Eq.
Figure 13: Arrhenius Equation of Orange Hydrolysis
29. Solar Power Generation Calculations
● Monthly Solar Energy Output Formula
● E = A ⨉ r ⨉ H ⨉ PR
○ E = Energy [kWh]
○ A = Area [m2]
○ r = Solar Yield [%]
○ H = Monthly Solar Radiation [kWh/m2/month]
○ PR = Performance Ratio
● Calculations based on Dr. Krause solar radiation values using ten 140 W
Output Solar Panel
30. Waste Intake
● A Liberty submersible grinder pump was chosen to
reduce particle size to a maximum diameter of 2 inches
● Generally used to shred large particles into small
fragments so the waste can be pumped into a sewage
system
○ Cloth towels, wipes, unwanted solids, and any other
personal hygiene products
● 3,450 RPM blade will shred plastic bags full of waste
Figure 14: Liberty Grinder Pump
31.
32. Reactor Mixing
● A Dayton centrifugal pump was chosen to
allow for mixing inside the anaerobic digester
● Generally used to pump diverse ranges of head
and capacity while outputting an adequate
flow rate
○ Water, organic matter, oils, and sewage
● Centrifugal pump will allow for any settled
solids to be mixed properly
Figure 15: Dayton Centrifugal Pump
33. Energy Generation
● On-site data collected by Dr. Krause shows
reliable solar radiation values in Fairbanks,
Alaska
● Solar panels were chosen as the main source
of energy for the system
● Common uses of solar panels include
electricity, heating and cooling, charging, and
many more applications
● Solar panels allow for an economically
sustainable energy source in remote areas
Figure 16: Solartech Power 140W Solar Panel
34. Energy Storage
● Sealed lead acid 12V DC batteries were chosen
as electrical storage energy devices
○ Common uses include providing emergency
bursts of power to startup applications
● Lead acid batteries chosen over gel batteries
because of functionality in colder climates
○ Glass mat allows battery acid to be
contained
○ Creates minimal resistance to allow higher
capacity and discharge rates
● Minimal operating temperature of -15°C
Figure 17: Grainger Sealed Lead Acid Battery
35. Energy Conversion
● Inverter chosen to convert DC power into AC
electricity to run applications
○ Common uses include backup power in off-
grid locations
○ Sine wave allows for operation of pumps and
heaters
● Includes overtemperature protection, surge
protection, and four outlets
● 5,000 W continuous output power with 10,000 W
peak output power
● Minimal operating temperature of -15°C
Figure 18: Aims Power Inverter
36. Gas Bags
● Biogas storage bag uses PVC as the main
material making it easy to transport simple
setup and anti-stretch
● It is suitable in both cold and hot areas,
ranging from -20℃ to -60℃
○ Has more than a 10 year lifespan
● It is resistant to acid, alkali corrosion and
good resistance to wear
Figure 19: Biogas Bag
42. Bioreactor Heating
● Monthly outdoor temperatures gave us the
baseline for determining the months of operation
for our reactor
● For the reactor to be at a minimum of 0°C, the
outside temperature must be around 10°C, which
starts during May and ends during November
● Temperatures above this ensure that the
digesters can operate at a minimum time of six
months
● During months of operation, the reactor can be
kept at an optimum temperature of 20°C
Figure 27: Temperature Ranges for Bacteria
43. Bioreactor Heating
● The reactor will take a long time to heat
to a sustainable operating temperature
● Waste can be added as soon as the
reactor is thawed, around mid-April
● The reactor will slowly warm up during
the spring with help from the heaters
while the air heats them up from the
outside, and they will be able to sustain
an internal temperature of 20°C from
June through October
● After October, the solar power will not
be able to sustain the heaters, and the
reactor will start to freeze as
temperatures drop
44. Determining the Data
for Temperature
● Internal reactor highs and
lows were plotted, providing
an equation for temperature
change throughout the
operating months
● Allows temperature to be
run as a variable with
respect to time in STELLA
Figure 28: Daily Reactor Internal Temperatures
53. Future Improvements
● Investigate bacteria to improve methane production
● Design better ways for bags from honey buckets to be disposed of
● Examine ways to lessen human interaction with unsanitary components of the
design
● Easier methods of methane collection and usage
54. Acknowledgements
We would like to acknowledge and thank Dr. Darnault, Dr. Krause,
Dr. Dodd, Dr. Drapcho, Jeannie Williamson, and the Biosystems
Engineering Department for their help in completing this project
for Senior Capstone Design.
