Engineering 692, Montana de Luz, 2011: The Biodigester Team

Nathan Arroyo, Nicolas Campos, Melissa Lindsey, Sarah Watzman

I.Background

Montana de Luz, an orphanage in Honduras for children with HIV/AIDS, currently has a malfunctioning biodigester installed. A biodigester operates by digesting organic waste and turning it into methane gas, which can then be burned to use to power the orphanage’s appliances. The gases are formed from the breakdown of the organic waste (called influent) in the air-tight dome section of the biodigester. The output of the biodigester, called effluent, is nutrient-rich and extremely useful in farming or gardening.

More specifically, Montana de Luz has a fixed-dome biodigester. The influent is poured into a pipe, travelling into the ground to the main chamber. The top of the main chamber is at ground-level, and an air-tight door exists there to be used if looking inside the chamber becomes necessary. The gas pipe comes from the top of the dome as well, and it travels to the kitchen next to the chicken coop. The effluent comes out of the biodigester through a pipe above ground.

II.Participants

Nathan Arroyo is a fourth-year student in environmental engineering and has functioned as the team’s contact with Montana de Luz and Dr. Jay Martin. In-country, he updated the preliminary manuals created before departure and added necessary details to the manuals once back in the United States.

Nicolas Campos is a fifth-year student in mechanical engineering and has functioned as a translator from Spanish to English for the documentation provided before departure regarding Montana de Luz’s biodigester. He also was the main photographer for the project while in Honduras and translated manuals written by the team from English to Spanish.

Melissa Lindsey is a first-year pre-biomedical engineering student and has functioned as the team’s secretary. In country, her task was to keep detailed notes of progress made and data collected, and compiled these notes into the team’s final presentation.

Sarah Watzman is second-year mechanical engineering student and has compiled the information gathered by the team before, during, and after the trip into the final report. She served as the videographer while in Honduras.

III.Problem Definition

Montana de Luz currently has a fixed dome biodigester installed on its campus. Some documentation is available, but whether or not this documentation is for biodigesters in general or this specific one is unclear. Additionally, no documentation on how to properly operate or fix this biodigester exists.

Currently, the biodigester on site is not functioning properly. Originally, while discussing operations of biodigesters and potential problems causing them to malfunction, Dr. Martin suggested that the dome of Montana de Luz’s biodigester may be cracked. This would cause the gas produced through the anaerobic reactions in the chamber of the biodigester to leak out into the atmosphere instead of flowing into the gas pipe for use by the orphanage’s staff. Through email communication with the staff in Honduras, a crack in the dome was deduced as not the cause of malfunctioning since Saul was able to light a lamp powered by the gas pipe.

From pictures taken of the system last spring, the team has concluded that the influent is not acceptable for the biodigester to be operational – it appears to have too high of a ratio of solids to liquid. This has most likely caused the biodigester to be clogged in both the inflow and outflow pipes, stopping effluent from leaving the biodigester and inhibiting influent from entering it.

IV.Statement of Objectives

In general, the objective for this project is to get the biodigester at Montana de Luz into a functioning state. Mainly, this includes unclogging the inflow and outflow pipes. Once the pipes are cleaned, an inoculate (such manure) will be added to the main chamber to help restart the anaerobic digestion within the biodigester. Adding an inoculate will also help digest the already present materials within the main chamber in a more time-efficient manner.

Additionally, a secondary objective for this project is to define the operational parameters for the biodigester explicitly and in easy-to-use terms. This includes developing step-by-step instructions for diagnosing potential future problems for the biodigester and instructions for trouble-shooting these problems as well. These manuals will be written preliminarily before departure to Honduras and updated to coincide with observations made while at Montana de Luz. These manuals would serve to ensure that the staff at Montana de Luz knows how to properly operate the biodigester, and also make suggestions for fixing it in the future if it beings malfunctioning again. Along with these written manuals, pictorial posters will be made to hang in the administration office on site.

More specifically, under the scope of the manuals, a system for inputting the proper ratio of water to solid in the inflow tube will be developed. This will most likely consist of filling a bucket a certain number of times with water and mixing it with one bucketful of solid to be put in the biodigester as influent. In order to decrease the size of the solid pieces used as influent, a compost area near the biodigester will be developed, and suggestions for stirring it will be included in the manuals.

V.Detailed Plan of Action

  1. Evacuate gases from chamber
  2. Includes opening the gas pipe and cover to main chamber
  3. Clean debris from biodigester
  4. Includes cleaning the influent pipe, effluent pipe, and main chamber as well as the area surrounding the biodigester
  5. Would be best to move as much debris from the main chamber as possible
  6. Fill the biodigester with water
  7. Check and record chlorine levels of water before placing in biodigester
  8. Let water sit in biodigester until chlorine level is 1 part per million(ppm), 10 ppm at 3 days later then wait, 5 ppm at 2 days after that then wait, then below 5 ppm for a day
  9. Record amount of water poured into biodigester
  10. Leave chamber cover open
  11. Obtain initial charge of biomass
  12. Initial charge should be cow manure but chicken manure and otherbiomass will substitute fine
  13. Charge biodigester
  14. Test water again for chlorine levels
  15. If water is below 1ppm chlorine, charge biodigester with 8-10% of weightbiomass to water
  16. Stir contents of biodigester with a stick
  17. Create compost pit in a convenient location near biodigester
  18. Mark buckets for use
  19. Using geometric shape of bucket, devise system to input influent with a ratio of8-10% biomass from compost to water
  20. Average density of compost is 2000lbs/cm^3
  21. Post signs about usage
  22. Use appropriate materials to create signs
  23. Create sign for proper loading
  24. Create sign for no smoking or open flame near biodigester
  25. Create sign for feather test at gas outlet
  26. Conduct pH test on effluent
  27. pH is optimal between 7.0 and 8.5
  28. If pH is higher than 8.5, biodigester needs to be cleaned and restarted
  29. Let biodigester sit for 2 weeks to allow bacterial growth inside the chamber and to allow the compost pile to grow
  30. Train staff on usage through a training session including safety precautions
  31. Create manual for continued operation
  32. Includes operational and start-up procedures
  33. Includes safety procedures

VI.Implementation

  • Monday, March 21st, 2011
  • The biodigester had been cleaned previous to arrival. The inflow area was no longer clogged and liquid, instead of solid, was sitting in the outflow tube.
  • In order to get effluent from the biodigester to test the pH, water was added. After adding 2.5 buckets of water, effluent starting coming out of the outflow tube.
  • The effluent was tested with water test strips, and the pH was determined to be 8.5, which is too basic for a biodigester to run properly. A hose was put inside the inflow tube to run water into the biodigester to help neutralize the pH (ideal pH would be 7, and Montana de Luz’s water is cholorinated, making it slightly acidic). Since the orphanage lost electricity after lunch and water needed to be conserved, the hose was turned off mid-afternoon.
  • Since the compost pile sitting on the ground near the biodigester contained lots of trash, the pile was turned and moved towards the pig pens while the trash was removed.
  • The gases were evacuated from the gas lines by opening the valve connected to them for the stove next to the chicken coops. Using a lighter, no gas caught on fire so the pipes were concluded to be empty.
  • Brainstorming took place to get ideas for removing effluent from the biodigester. A bucket with a rope on it was the simplest idea, but Saul suggested creating a system for distributing the effluent to the garden, which included some sort of tank or crate with a valve on top of a wheelbarrow.
  • Brainstorming also took place to get ideas for composting. Alexandra suggesting using one of the pigpens since they are next to the biodigester and a contained area.
  • The pH was tested at the end of the day and was slightly lower than in the morning, at about 8.3.
  • A long metal rod was pushed down into the chamber of the biodigester through the outflow tube – the biodigester’s contents felt like wet sand.
  • Tuesday
  • With Saul’s help, a three-stage compost system was implemented in pigpen next to the fence by the biodigester.
  • Two walls were built out of cement blocks and mortar, with the back wall being offset from the front wall.
  • The first section closest to the door is for fresh waste to be put in the compost pile, the second section is for older compost not completely broken down, and the third section is for compost ready to use. The third section is over the drain in the back corner of the pigpen.
  • The finished compost will be used as influent (mixed with water) for the biodigester since it will be in small particles, not large chunks.
  • In the afternoon, the team began surveying for the map of Montana de Luz. See the addenda for details on this subproject.
  • Wednesday
  • The compost sitting in the open area near the biodigester was moved into its new home. The barrel of compost (which had been sitting for over a year) was turned over and moved into the new compost area as well.
  • The biodigester was determined to have already digested solid in it, meaning that it needed to be completely flushed and emptied.
  • Using the long metal rod, solids were found to be sitting about one meter down the inflow pipe.
  • Since the consistency of the material in the chamber was found to be slushy, the water which had been put into it had most likely just been flowing over the top, like water over wet sand.
  • In order to lower the pH to a usable level, the water would need to mix with the slush inside, which was not happening since only liquid was coming out as effluent.
  • Suggestions were made on how to empty the biodigester:
  • Saul said the cement cap could be removed and replaced after the solids were pulled out of the main chamber, but this would involve pulling the solids from the depths of the main chamber, which would be extremely difficult.
  • Renting a pump in Honduras would cost about 17,000 Lempira, or roughly $1,000, which was not within our budget.
  • The final decision was made to buy a septic pump in the United States and send it down to Montana de Luz with Ruth at the end of April, 2011. Saul could then use it to empty the biodigester as well as for the orphanage’s own septic tank.
  • The following details were found during research in the computer lab.
  • Compost needs to be turned about every 14 days to break up clumps and rotate the middle sections to the edges and vice versa.
  • Compost needs to be aerated and thus should sit in an open area, not closed in a barrel.
  • Compost needs to stay damp – not dripping with water but not dry either.
  • Different types of waste break down at different paces so food remains should be mixed with plant materials.
  • Bones and meat should not be composted.
  • When ready to use, compost should look like soil.
  • Outlines of the posters were made with Ruth’s help in translating. A poster was designed for each of the ideas below:
  • How much and how often to add water and organic materials to the biodigester
  • What to put in the biodigester and what not to put in it
  • How to turn the compost and how often, along with how much water to add
  • How to recognize when the compost is ready to be used as influent for the biodigester
  • A system for mixing the correct ratio of water to composted material was developed: Fill half of a bucket with compost and pour into the cemented inflow area. Then fill the inflow area with water until the line on the tube is covered. Mix the compost with the water then remove the tube to drain the mixture into the biodigester.
  • The door to the compost area was fixed to close completely since it did not previously. The drain in the ground for the final stage of the compost was covered with wire gauze since it was originally uncovered.
  • Thursday
  • In the morning, the compost in the new compost area was mixed, turned, and watered. The drier compost which had been sitting out in the open was put in the first section while the barrel of compost was put in the second section on Wednesday. These piles were mixed and watered so that they were damp, and then the compost was split between the two sections.
  • Since water had been flushed into the biodigester earlier in the week, effluent liquid was removed from the outflow area using buckets on a string. Effluent was removed until no liquid was above the opening of the outflow tube.
  • After lunch, Karin checked the Spanish translations of directions for the posters to be placed by the compost area and the biodigester. The posters were written/drawn and then covered in laminate sheets.
  • Friday
  • Friday morning consisted of working on the surveying project, details of which can be found in the addenda.
  • Friday afternoon consisted of presentations from the group to Alexandra, Karin, and Saul with Brad, stating what had been accomplished throughout the week, what needed to still be accomplished by Montana de Luz staff to maintain the project, and suggestions for the future.

VII.Results and Objectives Achieved

The compost system was successfully established inside the pigpen for three-stage composting. The orphanage can now place food waste (except meat and animal bones) in the first stage and once the process is finished, can use the compost as influent for the biodigester. Three posters were made and placed next to the compost area detailing what to put in the pile to compost, how to compost (including when to water and turn the piles), and how to know when the compost is finished.

Although the biodigester was not left in a working condition, prevalent information was obtained from the trip. The chamber of the biodigester was determined to contain already digested materials that were not flowing out of it due to a previous charge with too high of a ratio of solid to liquid. This conclusion was drawn from the pH of the effluent being too basic (around 8.5, suggesting that too much carbon from organic solids was inside the main chamber), the fact that mostly liquid was flowing out the outflow tube, the texture of the biomass inside the main chamber being slushy, and no gas coming out of the gas pipe in the kitchen during the flame test (indicating that the contents of the main chamber could not be further digested to produce more gases). To return the biodigester to a working condition, the team determined that sending a pump to Montana de Luz from the United States was the best decision, so that Saul could pump the solids out of the main chamber and begin the process with a clean slate.

Nevertheless, operational parameters were established and detailed in a poster hung next to the biodigester. Half a bucket of prepared compost is to be put into the concrete inflow area, then the area is to be filled with water to the line marked by the team on the pipe. This is to be mixed and then drained into the biodigester by removing the part of the pipe coming out of the concrete inflow area.

Also, an effluent transport system (ETS) was created to make distributing the effluent from the biodigester to the garden easier. A cooler was attached to the top of a wheelbarrow so that it could be easily moved from one location to another, and a small hose was attached to the drain valve of the cooler. When effluent liquid is placed inside the cooler and the valve is opened, the hose can be used to distribute the effluent to plants in the garden as fertilizer.