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Sanctuary improved compost

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ENGR215 Project Page in Progress
This page is a project page in progress by students in Engr215. Please refrain from making edits unless you are a member of the project team, but feel free to make comments using the discussion tab. Check back for the finished version on 5/9/2016.

Fig 1: Three System Compost


The "Three Stage Rotating System" is the design that was chosen for the improved compost system at the sanctuary. Members of the Sanctuary want an improved compost system that will be more aesthetically pleasing, desirable, and easy to use. The project should also include improvements in rat-proofing and weather resistance. Additional requirements include low embedded energy of materials, preferably reused and re purposed materials.


Team Compost was created in the Fall of 2016 at the Humboldt State University's Engineering 215 class. Our client for the ENGR 215 class was The Sanctuary, a creative space for artists and people from the Humboldt community to use tools, take music classes, participate in community events, or teach a skill. A primary interest of the Sanctuary crew was sustainable living and design, so much of their yard was devoted to gardening, building, or composting. Because their old compost system was a do-it-yourself mash-up of an old metal pipe and some trash cans, the process was fairly inefficient and had the added problem of infestation by rats.

Problem statement and criteria

Team Compost's objective was to improve the Sanctuary's compost system by making the design inviting, accessible and rat-proof. The previous compost system was composed of two metal trash cans that were leaking and wet, and a finishing bin that was an old metal rusty container with a non functional lid. The project aimed to upgrade the Sanctuary's old system into a functional composter that is easy to use, easy to maintain, aesthetically pleasing and easily accessible, for a price not to exceed $400. The final design was dubbed the "Three Stage Rotating System."

Team Compost used a set of weighted criteria to best fit the design process to the Sanctuary's needs. The new compost system had to satisfy all criteria in order to last for multiple years. See below for a table that organizes the weighted criteria.

Criteria Importance Constraints
Ease of Use 7 The system's use is readily apparent and easily done by most people.
Durability 10 The improved compost system should last at least two years.
Ease of Maintenance 9 Requires little to no maintenance on the part of the owners.
Pest-Resistance 8 Must keep away pests and rats.
Cost 5 Cost must not exceed $400: $100 provided by the client and $75 per team member.
Aesthetics 4 The system must look inviting enough for people to want to interact with it.
Accessibility 6 Accessible for people of most heights, ages, and ability levels.

Description of final project

The final design met the criteria in a lasting, and effective way. Because the Sanctuary's old compost system was prone to rats, succumbing to the weather, and difficult to use, the new system had to be made of more durable materials while existing in a configuration that would repel invasion by pests. In response to these problems, the team formulated the "Three Stage Rotating System" design. The final configuration was comprised of a 55 gallon drum resting on rollers above a metal frame housing a secondary composting bin. A larger storage bin, made of wood palates, was located adjacent to the second stage. The rotating bin design solved two problems at once by elevating the freshest food-waste materials away from access by rats, and by allowing for easy turning and aeration of the compost. The rotating element was extremely important to the team and the client because stirring compost materials frequently can greatly aid in the efficiency of their break-down. Once material in the first stage was broken down enough it could easily be dumped directly into the second stage below, where it would finish decomposition before being transferred to the third stage storage bin.

Fig 2: Final Design for the Three System Compost

Photos and descriptions. Use gallery.


The table below lists materials used on the project and component costs.

Quantity Material Source Cost ($) Total ($)
1 Scrap metal street post(Telespar) Donated 0.00 0.00
1 55 Gallon Barrel Donated 0.00 0.00
4 Bicycle Forks The Bike library 10.00 40.00
4 Bicycle Hubs Donated 0.00 0.00
5 Road Signs Arcata Scrap 37.00 37.00
5 Wood Pallets Donated 0.00 0.00
84 Machine Screws Ace Hardware 00.30 25.20
60 Washers Ace Hardware 00.25 15.00
2 Hasp Ace Hardware 05.20 10.40
3 Hinge Ace Hardware 07.00 21.00
30 Nuts Ace Hardware 00.30 9.00
Total Cost $157.60

How to build

In order to build the compost system that was built for the Sanctuary, the steps are as follows.

How to build an improved compost system.
Caption Step 1 : Cut pieces of a recycled telespar street post into four equal pieces.
Caption Step 2 : Cut additional steel pipe or scrap into four pieces, two at 30 inches and two more at 19 inches.
Caption Step 3 : Use a grinder to grind the points that will be welded together. Weld into the shape of a table as a support for the rotating barrel. Weld two three foot, long, flat strips of metal on the bottom as support for the rotating barrel
Caption Step 4 : Weld the bicycle forks into the metal telespar posts. Place bicycle wheel hubs(rollers) on forks.
Caption Step 5 : Drill small holes in 55 Gallon barrel for aeration.
Caption Step 6 : Drill holes in side of drum, use plumber's tape or brackets to attach bamboo poles using machine screws, nuts and washers.
Caption Step 7 : Cut out door of desired dimensions in center of compost barrel, and re-attach in place using hinges.
Caption Step 8 : Attach two hasps to the front of the door and barrel to lock door shut when rotating.
Caption Step 9 : Drill holes through road signs and add three to the telespar support legs.
Caption Step 10: Add machine screws, nuts and washers to secure signs in place.
Caption Step 11: Weld metal hinges to the front of the two stage compost system on the left telespar post support leg. Drill holes and attach street sign to hinges.
Caption Step 12: Add handle and close door
Caption Step 13: Attach pin through hasps to ensure the security of the door
Caption Step 14: Lift system and place wire mesh beneath compost system. Place bricks and rocks on holes to secure mesh and keep rats out.


The ongoing cost of the system on the sanctuary is expected to be relatively low compared to the cost of implementation in hours and monetary cost. Most structural components are designed to minimize maintenance due to weather resistance. Parts that must be replaced due to weather corrosion are designed around materials that the sanctuary frequently acquires for free: bicycle wheel hubs used for rollers under the tumbler must be re-greased periodically, and wire mesh under the bins must be replaced every few years depending upon corrosion of wires. The hinge and hasp on the rotator door must be re-greased frequently, and in the event of rust must be replaced every 1-2 years to ensure structural strength. Tumbler support struts may need replacement as welded joints corrode.


The following guidelines should be followed to ensure proper functioning and longevity of the compost system.

  • Fill rotator barrel with material to be composted
  • Rotate compost at least three revolutions.
  • Remove the pin to release hasps, and empty contents into next bin.
  • Use tool to mix compost in second stage.
  • Grease bicycle hubs(rollers) and hinges and hasps to avoid corrosion.
  • Replace wire mesh underneath the rotating barrel and second stage.
  • Replace rollers
Every 3 years
  • Replace hinges.
  • The rotating support may need replacement if welded joints corrode.


This is only how to troubleshoot the compost system. For complex issues, the solution might just be fixing the tumbler.

Hinges or hasps are making it difficult to open Add grease to loosen hasps or hinges
Remove contents from Stage 1. Rotate door from Stage 1 face down, and remove lid from Stage 2. Open door and empty contents below.

Testing Results

Soon after completing work on the new system we transferred some of the Sanctuary's existing compost into the first stage tumbler. Initial load tests at 3/4 volume capacity were a resounding success. The door, the only sizeable weak point on the barrel, showed no signs of stress, and the roller supports turned smoothly and easily despite the significant weight in the tumbler. This page will be updated as the second and third stage are filled in the next few weeks.

Discussion and next steps


See Help:Footnotes for more.