August 11, 2013
I’m on the plane flying home from Accra as I type this final blog entry. I’ve concluded my summer work with Waste Enterprisers but I don’t think Waste Enterprisers has finished it’s work with me.
John and Troy working on the insulation experiment.
In the last few weeks we devised and executed the insolation experiments, which were run very similarly to the Activity Factor Experiment, but now without the covering. We immediately saw interesting results. Obviously, finally allowing the sun to shine on the sludge makes a huge difference on the evaporative rates. The real challenge was to quantify and understand that difference to the point where we can predict the how much, how fast, and how expensive. It is a large task that included heavy experimentation, literature review, and mathematical modeling to reach our best idea of how to predict this complicated process.
I was assigned a task to create a yearly evaporation and cost model. I made a Matlab function to take in matrices of climate data, 10 hours a day for 365 days that uses the evaporation model to determine how much water will evaporate each hour, recalculate how dry the sludge is and then compute the next hour’s evaporation based on the new sludge’s Activity Factor (the coefficients of which were determined by our research earlier in the summer). The function then computes the daily and yearly evaporations and costs ($/tonne). It is very useful for determining how climate conditions affect drying on different time scales. It can also be used to see the effects of the height to length ratio of the drying greenhouse. Likewise, it will also be used to automatically set the optimum operating conditions for hourly weather conditions (i.e. fan speed, wind inlet, etc.).
John and Troy with their colleagues.
In my time in Accra I have learned a lot of things that I know will be assets to my future as an engineer. One thing comes from the lead process engineer who emphasized that the success or failure of a team depends on how much they like each other. The friendship among team members for me allowed me to begin producing useful work from the very beginning of my time at Waste Enterprisers to the very end. I learned that for everyone to work well, the members of the team need to value each other’s work and opinions so that each can be motivated and productive. Rather than just feeling like you’re doing contracted work for an organization, you feel you are part of the organization, which is much more efficient and rewarding. I also learned that setting long-term and short-term measurable goals is very important. If you don’t measure you’re progress you often end up achieving far less than your potential. I’m very grateful for the opportunity provided to me by Cal Energy Corps and Waste Enterprisers.
July 10, 2013
All the reconstituted sludge and the results in ziploc bags for oven analysis.
Work continues to go swimmingly in Accra. I have been spending a considerable amount of my time analyzing the psychometric data from Mombassa in order to determine what the best and worst days for sludge drying will look like in Kenya. I have been using MATLAB to sort the data, which I imported from NASA’s Atmospheric Science Data Center as cell arrays. Then, determining that the best days for sludge drying would have the greatest driving force for evaporation, I calculated each day’s driving force and then sorted the days by that criteria and looked for trends in the key parameters: relative humidity, temperature, and insolation. With this information, we have a good approximation of our potential production during different times of the year. Also, we can now consider the worst case conditions to determine if active drying will be needed to supplement the passive solar drying in order to meet contract agreements with buyers.
Prepping for the oven evaporation analysis.
This past week we finished the first phase of our Activity Factor Experiment with results that make good physical sense and are in line with the literature. We ran three experiments for each of seven wetnesses of sludge (25-80% T.S.). The qualitative results were as expected: the wetter the sludge the more water evaporated from it. We designed these experiments with an opaque covering so that insolation would not be a factor, which was necessary because it could vary from day to day depending on the weather, and would not be factored into our calculations at this stage. Now, to confirm our findings in spite of solar insolation differences we devised another experiment using the same set up but running all seven samples at once. In the previous experiments we saw that drying rates are linear, so we need only take before and after measurements rather than measuring every minute for an hour. Because we can now process seven times as much sludge on our experiments we have to reconstitute much more. So I bought bigger buckets and then spent over an hour just reconstituting dried sludge. Starting with three kilograms of 90% TS sludge, I added water to get the desired wetness. This will make running lots of experiments with equal starting points much easier in the upcoming week.
I also ran a ‘Value of Moving Air’ Experiment, which is a cost-benefit experiment to determine whether or not forced convection is cost-effective for sludge drying. This is an all-day experiment run for around 6 hours. The next day, the before/after samples are taken to an old laboratory that belonged to a now-abandoned wastewater treatment plant. After paying a service fee, we are allowed to use their ovens – this is after fixing them and calibrating them and buying metal sample trays for them, since we’re actually the only ones who use this lab – to evaporate the leftover water, so we can determine the initial and final %TS of the samples for before and after. The difference indicates how effective forced vs. natural convection is. This evaporation rate ratio is then compared to the cost ratio. Because many (especially lab) materials are not available, we have to make do with what we can get. For example, the team simply bought thin metal and had it cut into squares for sample trays. A week ago, I went to get the edges cut and sides bent up to prevent the sludge samples from falling off of the trays and botching the oven evaporation analysis.
John and his team missing one of their colleagues.
This kind of research and development for a business is very practical and well-communicated throughout the Waste Enterprisers organization, with information, summaries, and reports quickly shared with all. The team works very well together, sharing tasks and helping one another, as well as asking for critiques to proposed experimental designs and derived conclusions from their results. We constantly question each other’s assumptions to make sure we are heading in the right direction. The organization has opened my eyes to the possibilities for my future as an engineer outside of continued education or working for a big company, an option that I had been interested in since a child, but had fallen by the wayside in the midst of my studies: entrepreneurship, specifically social enterprise.
June 24, 2013
The Amenesi Falls that John cycled to.
I think this Saturday’s mountain biking adventure parallels how the research here has been going. It was my first time mountain biking. I chose a 43 km journey in the very hot sun to a waterfall I had never heard of before. I fell three times. I got blisters on my hands and scrapes along my arms and legs. I still can’t sit right, but when we finally got to our destination it was all worth it. Throughout the trek, there were long stretches of dirt road surrounded by dense, green forests or pineapple, corn, and cassava farms on either side that eventually ran through little villages where children yelled “Obruni” or those that really wanted to show off their English, “Obruni, how are you? I’m fine.” I liked to think they were cheering me on, but they were mostly just excited to see obrunis (white person in Twi). As the guy who rented us the bikes warned, the trip would be a test of endurance and require some previous biking experience, so has been my research here in Ghana so far. And now there are only good memories of Saturday’s trip and the difficulties are only something to laugh about with those that you went through it with.
John preparing the fecal sludge for the tests they are running.
In the past few weeks we completed construction of the table for determining the activity factor and began running the experiments for a spectrum of wet sludges (from 25-80% total solids). Recording and analyzing results as we went along we also made several adjustments. Initially we used a 13x13cm tray for holding the sludge, but after an hour we only got 5-6g drop in mass (due to evaporation of water) so we decided to make a tray shallower and with a larger surface area, 28.5×28.5cm. Along with many more adjustments, we also had to accommodate the fan so that it would give a strong and steady air flow across the tray. We then achieved over 20g of evaporated water in an hour for the wetter samples. What’s really essential to having success here is being able to put up with a lot of “fresh-type” products breaking without getting too frustrated and giving up. There’s usually a way to fix the power strips, generators, scales, and even tape measures that “spoil.” We can usually only perform three one hour experiments despite being at the site for around 5-6 hours each day. I can count the days where nothing went wrong on one finger. A co-worker has taught me the value of just taking things apart and putting them back together, or when all else fails “just oil it and hit it against something hard.” So now, essentially all our power strips have been opened and had their circuit breaker bypassed and reassembled.
After all these experiments we go back to our computers and start working on the spreadsheets that Troy Hodges, my CEC buddy, primarily created to input all our data and automatically calculate all the psychrometric properties and eventually the output of the activity factor with the measured change in mass. Amazingly, even our very first tests gave us results in the range we were expecting. After repeating the experiment for 40% and 50% TS we got the same result for each one. This was one of those moments where you see a few kids cheering you on. After that, we got some more varied data at the very wet and very dry end, but are narrowing down these errors by refining our testing techniques. Just today we were able to get the best readings yet by restricting the air flow into the chamber with a plastic bag surrounding the fan. Following the example of our co-workers who have been here longer, I am amazed at how the simplest pieces of trash (another man’s treasure) can solve some seriously vexing problems.
John fixing an electrical fan while on the job.
Along with the hands-on work of constructing, reconstituting, and experimenting, we do a lot of thinking. It doesn’t sound that hard, but can be the most difficult part of the work. We are trying to remember every part of our education and general observations of our physical world to hypothesize what will in the end be the best solution for optimized solar drying. We work with a consultant out of Colorado who researches the psychrometric data for the area of a proposed full-scale plant. With him we are able to predict possible scenarios using ballpark figures to decide which solar drying techniques (or combination of techniques) are feasible while considering best-case and worst-case scenarios, as well as the driving capital and operating costs for a site that would be built to last 30 years (CBE 140 with Prof. Reimer provided a great introduction into economic analysis of engineering design). According to our conversations we design and execute new experiments, which are delegated to certain team members. One important one that I will mention is ‘The Value of Moving Air’ Experiment, which aims to tell us conclusively, how much value there is to moving air across the sludge for increased drying rate compared to its operating cost. With this information, we will get one step closer to designing our full-scale process. It’s great to be exposed to process as well as economic analysis to have our questions and opinions considered and valued as we all work together to move forward toward something that we would all love to see accomplished.
After many scrapes, bruises, and falls, some big and some small, we’ve seen some little waterfalls and intermittent villages, but we continue to press forward, “having a perfect brightness of hope,” seeking after the real waterfall that was the reason we all started this journey.
June 9, 2013
John working at Waste Enterprisers in Accra, Ghana.
Waste Enterprisers (WE) is a startup sanitation and renewable energy company based out of Accra, Ghana. The company started under founder and CEO Ashley Murray, who received her doctorate degree from UC Berkeley. She envisioned a way to deal with the sanitation problem in developing countries where the local governments cannot or will not pay tens of millions of dollars to companies to dispose of the waste, so really the job does not get done. In Accra, over 100 trucks dump human waste directly into the ocean every day. That is the current solution. So, the company decided that it would have to treat waste as a resource, or input, rather than a wasteful byproduct that had to be discarded. Fast forward two years and WE has shown that it can successfully process human waste into a high-energy fuel (about 18 MJ/kg). Successful burning trials in industrial burners have confirmed its usefulness.
Now the company must make this product profitable. The company believes private profit can be a powerful incentive for social change. In order to expand this program to a full-scale plant it must be proven economically viable to attract investors. Since, the process has been proven feasible, it’s really a question of optimizing all the parts. The fecal sludge comes in very wet and, in essence, it must be dried before it can be burned. There are several options for drying the sludge that can be used in series. There is passive gravitational dewatering through screens, active dewatering through mechanical presses, passive drying through solar drying, and active dewatering through thermal heating, which requires electric energy as an input. In order to be profitable the passive solar drying method really needs to be studied more. It could be done by open air drying, greenhouse drying, thin channel drying combined with forced convection, or a cabinet dryer which utilizes the stack effect to induce air flow. We will investigate which of these options is best-suited to maximize throughput of waste as well as maximizing the drying (or water evaporating) and the cost-effectiveness of each.
Along with optimization of the solar drying process, we are trying to complete and validate a theoretical model for evaporation of water that’s based on a model used for recreational pools. It takes into account wind speeds, temperature, and relative humidity, as well as an “activity factor” that is a coefficient that can change according to movement in the water, whether it be splashing or otherwise. We intend to complete this model by building an apparatus to simulate the model and run it at different wetnesses (that’s what we call percent total solids, or %TS). We expect the activity coefficient to vary with wetness because of cracking that occurs in the sludge which will affect the surface area exposed to the air. I get to use a lot of what I learned last semester in my Chemical Engineering classes. Thermo (CBE 141) was essential to understanding the psychrometrics data we must analyze to know how to optimize the evaporation in different cities. Transport Processes (CBE 150A) is essential for understanding and validating the theoretical model as well as designing a solar dryer that takes advantage of forced and natural convection.
The work in Ghana is very challenging and satisfying. Part of the company’s goals are to stimulate local economies by using exclusively the local supply chain for parts. We have gone to the timber market as well as other nearby markets to buy wood, sheet metal, nuts, bolts, screws, brackets, wheels, fans, and capacitors. Although, Ghana is an English-speaking country, most people are more comfortable tribal languages such as Twi and Ga, and many things have different names here (i.e. ‘butterfly nut’ is used instead of ‘wing nut’). It is very fun getting to know how things work here such as all the sourcing, engineering, planning, and building that go into executing a great idea. I am able to work independently and make my own decisions about what is the best way to achieve the ‘deliverables’ I commit to each week for the team. I am learning much more than I expected and am grateful for this chance to learn about engineering, teamwork, entrepreneurship, and foreign business practices.