A composting bin made out of old used materials is presented in this project. The finished product has a capacity of approximately 2 cubic meters, divided in 2 compartments for allowing two separate batches of the compost to be made. A large volume allowed sufficient airflow and space which would speed up the composting process.

Compost is created from 2 components; organic "green" matter and organic "brown" matter. "Green" matter, such as food scraps and grass clippings is rich in nitrogen, while "brown" matter such as sticks and dead leaves are rich in carbon. Generally, compost is mixed in a 2:1 ratio, with 2 parts brown matter for 1 part green matter. The openness of the compost bin structure allows for easy access to turn the compost and add moisture, which will speed up the breakdown process.

The structure is made up of wood since it is a material that can handle the heat that is produced during the composting process. The usage of wood and garden fencing allows for the structure to be lightweight, which can allow for a greater ease of operation. The use of electric lighting wire as the joining element for the pieces of the bin is to allow for flexibility in the shape of the container, which is useful when the product inside is gradually shifting shape during decomposition. The Christmas lighting wires were chosen as the joining agents because as electric wires, they contain metal wiring inside them which will last much longer than the plastic coating of the electric wires and therefore increase the structural integrity and longevity of the bin. This allowed for good use of these lights which would have been trashed otherwise.

The logic behind the compartmentalized structure is so that the structure is modular; one can add or reduce the number of compartments with ease by simply replicating the necessary frames and joining them to the existing frame. Additionally, the entire structure can be easily dismantled, which allows for ease of access since compost requires to be turned over, with tools such as a pitchfork, to accelerate the decomposition process. Additionally, the use of garden fencing as the walls of the compost bin allows for proper aeration of the material inside. This, combined with adequate moisture, allows for the green and brown matter to turn into rich organic black compost (as seen in the picture on the left with green matter in the left compartment and black compost in the right compartment). Typically, the composting process takes 60 to 90 days, thereby making a two compartment bin a desirable option. As a result, four to six rounds of new compost can be created per year. To allow for the bin to be filled to maximum capacity, pizza boxes were used to line the back frame and stop grass clippings and dried leaves from falling out while filling. Eventually, the mass of the compost will settle and the volume will shrink dramatically as the matter decomposes (as seen in the picture on the right) and changes color, creating a denser pile of compost at the bottom of the bin.

Supplies

Old scrap wood (3x6.5 cm beams of varying lengths, and 3x3 cm beams of varying lengths)
Garden Fencing (approx. 6 square meters)
Christmas Lights wires (approx. 18 meters)
Drill Machine
Hammer
Metal (binding) wire salvaged from old construction
Nails & Screws (at least 6 cm long)
Old shoelaces for securing the front frame (with slip kno
Scissors
Wire cutters

Step 1: Model the Compost Bin

Using Fusion 360, model the desired pieces of wood and the materials that you will use to build the compost bin. Measure out the materials available and create a render of the bin.

Compost Bin - Final

Compost Bin - Final v2.f3z
Download View in 3D

Step 2: Build the Frames

Use the base pieces of wood and attach them to the vertical support pillars via screws and nails. Paint the base wood in order to increase its longevity and reduce its decomposition. Build all the frames separately at first.

Step 3: Attach the Gardening Fence

After the frames for the compost bin's walls are built, measure and cut out pieces of gardening fence to fit each of the respective frames. Use the Christmas lighting wires to tightly wrap around the frame and tie at frequent intervals along the length to secure the fence to the wooden frame.

Step 4: Join the Walls of the Bin

After the walls of the bin have been built, align them against each other and use old metal binding wire to tie and secure the frames to each other. For the divider frame, use a long nail along with the rope to properly secure the divider to the back frame.

Step 5: Settle Frame Into Ground

After the frame is built, dig a slight trench (1-2 inches deep) in the ground underneath the frame and place it in location. Fill the compartments of the semi-finished bin with the proper composition of green and brown matter, along with frequent water addition. This will get the composting process started.

Step 6: Attach the Front and Finish

Once the bin's compartments are filled, bring the front frame and place it in the front of the bin. Secure the front to the remaining frame by tying a slipknot for 2 strings and loop them around the outer edges of the front frame and mainframe. Ensure that the bin has maintained its structure after loading.