Vermi Composting

Introduction

This project set out to design and build a large-scale vermicomposting bin for use at the school, with the aim of providing a practical and sustainable solution to the food waste produced on campus every day. Vermicomposting is the process of using worms, typically red wigglers, to break down organic waste into a rich, nutrient-dense fertiliser known as vermicast or worm castings, along with a liquid byproduct called leachate that can be used as a liquid plant feed. Rather than sending food waste to a landfill, the bin converts it into something directly useful, closing the loop between waste and resource in a way that is visible and educational for students. The finished bin measures 2.4 metres in length, 1.2 metres in width, and 0.6 metres in height, giving it enough capacity to process a meaningful volume of food waste on a continuous basis. The project sits within the school's STEM programme and was designed, built, and documented by me, covering practical skills in fabrication, welding, and materials, as well as the biological and environmental principles behind composting. From the first ideas on paper through to the complications encountered during the build, this document tracks how the project evolved, the decisions that were made along the way, and what the finished system will mean for the school going forward.

Problem Solutions

Use

The vermicomposting bin will be a genuine asset to the school once it is up and running. The original concept had been to simply use a bathtub as the composting bin, but the limitations of that idea became obvious fairly quickly, a bathtub has no real capacity to handle the volume of food waste a school produces, and it offers no control over the process. This bin is built to a scale that can actually make a dent in the school's food waste output, turning it into usable fertiliser rather than sending it to landfill. It also integrates well into the school environment without being a burden to maintain. Even during school holidays, this won't be an issue, there are always staff and other people on campus, so the worms will continue to be looked after and the system kept running without relying on the academic calendar. It is a low-maintenance, long-term solution that serves both a practical environmental purpose and gives students a hands-on connection to sustainability.

Materials

The original plan was to take a pre-built frame we had found on campus and build upward from there, attaching walls to the existing structure to form the bin. It seemed like the most straightforward approach at the time: work with what was already there and save ourselves the effort of constructing something from scratch. As the project progressed, however, it became clear that this wasn't going to be practical. The pre-built frame turned out to be low-grade metal, and when we attempted to weld onto it, the heat was creating holes rather than solid joins, which made it unusable as a base. From there, we rethought the whole structure and decided it would actually be simpler and more reliable to build an inner frame ourselves. Metal rods were welded together to form a support structure sitting halfway up inside the bin, designed to hold the plastic sheets that would make up the walls. Angle line was then used as a sleeve or channel along the edges, gripping the sheets in place and keeping everything secure. The final material list came to eight plastic sheets, an angle line for the wall holders, and the welded metal rod inner frame.

Obstacles

The build came with its fair share of complications along the way. Materials took longer to arrive than expected, which pushed the timeline back and meant some decisions had to be made on the fly once things finally came in. The plastic sheets we had originally planned to use were far too thick; they would have required an excessive amount of plastic to work with, driven up costs significantly, and made the whole bin much heavier than it needed to be, so we moved to thinner sheets instead. That change also meant the larger angle line we had sourced for the original sheets was now too big, and we had to switch to a smaller size that suited the thinner material better. Even with the adjusted sheets, we found we didn't have quite enough to complete the walls and had to get additional plastic and melt it down to fill the gaps. Looking ahead, another challenge that still needs to be addressed is the mechanism for moving the finished compost through and out of the bin, a motor or auger system will need to be designed and built to do this properly, since the material won't move on its own at this scale.

Sketches

Idea

Putting a wood block was the first idea, we then switched to full plastic sheets and angle line

Measurements

Based on the pre built frame, these are lengths and widths needed

Dimentions

eight plastic sheets were needed to fill the spaces

Revised Plan

I have made significant progress on the construction of the vermicomposting bin since my last update. I have completed the bottom frame, which will support the waste and distribute the weight of the structure. During construction, I also revised my original design. Instead of using one large vat in which waste would move downwards and then be pushed along, I have decided to divide the bin into three separate compartments.

In the revised design, organic waste will initially be added to the first compartment, where the worms will feed on it and break it down. Once much of the material has been processed, the worms will be able to move through holes between the compartments towards the next supply of waste. This process will continue through all three compartments. The finished compost will then be removed through doors on the sides of the bin using a shovel.

This revised system should make the composting process easier to manage because each compartment can be used at a different stage of decomposition. It should also make harvesting the finished compost more practical, reduce the need to move large quantities of partially decomposed waste manually, and allow one compartment to be emptied or maintained without disturbing the entire bin. However, these benefits will depend on the placement of the connecting holes, the movement of the worms, and how effectively the compartments separate material at different stages of decomposition.

Floor & Load Distribution

One of the most important stages of construction was completing the bottom frame, which will support the waste and compost inside the bin. Because the structure is relatively large and will hold a considerable amount of material, I needed to ensure that the weight would be distributed evenly rather than concentrated on a few points. To achieve this, I constructed a supporting framework using squared tubing and angle line. I also created a mesh-like arrangement of metal supports and legs beneath the floor. This provides multiple points of support, helping distribute the load across the base and reducing the amount of weight that the pre-existing frame must carry. Welding this framework was challenging and time-consuming, particularly because the supports needed to be positioned and joined securely. However, this stage also gave me an opportunity to improve my welding technique. Some of my earlier welds needed to be revisited and strengthened, but as I continued working, my welds became more consistent. The structure can comfortably support my body weight during an informal test, which gave me an initial understanding of its strength. However, this is not a substitute for testing the frame under the actual load of wet organic waste and compost. My next priority is to ensure that the floor and supporting joints can withstand the intended load over time without bending or weakening.

Materials

The floor is being constructed using one-inch-thick plastic sheets, which are thicker than the sheets used for the walls and doors. This decision is intended to provide a stronger base because the floor will experience the greatest direct loading from the waste and compost. So far, I have used two plastic sheets for the floor. However, I saw that the dimensions and arrangement of the supporting framework made the original fitting method unsuitable. Consequently, I will need to cut new pieces and fit them more precisely to the frame. This has taught me that the dimensions of the metal framework and the plastic panels must be considered together. Even if the individual materials are suitable, the overall structure will not fit correctly unless their measurements and connection points are planned carefully. The main challenge now is ensuring that the floor fits securely against the supporting framework without leaving gaps through which waste or liquid could escape. I will need to measure the available spaces accurately, cut the plastic sheets to the correct dimensions, and secure them without creating weak points. I also need to consider drainage. Vermicomposting requires moisture, but excessive liquid can accumulate if the bin does not drain adequately. The floor will therefore need to retain the solid material while allowing any necessary drainage to be managed safely.

Almost finished first compartment

Hand cut angle line

Hinge

Inside compartment

reinforced with angle line

Challenges and Possible Solutions

Several challenges remain before the bin is ready for use.

Structural strength: The welds, supporting mesh and joints must withstand the weight of wet organic waste. I will inspect and reinforce weak connections and arrange controlled load testing before filling the bin.
Panel fitting: The floor panels do not fit the framework as initially planned. I will remeasure the structure and cut replacement pieces to fit accurately.
Door durability: The doors must remain aligned, secure and easy to operate. Reinforced hinges, bolts and handles should improve their reliability.
Containment and drainage: Gaps could allow waste or liquid to escape. I will inspect the joints, seal appropriate gaps and provide suitable drainage while retaining solid material.
Worm movement and conditions: The connecting holes must allow worms to move between compartments. I will monitor their movement alongside moisture, airflow and feeding conditions to determine whether the revised design works effectively.
Roof and weather protection: I still need to construct the roof and ensure that the bin is adequately protected while maintaining suitable ventilation for the worms.

Addressing these challenges systematically should help ensure that the finished bin is both structurally sound and practical to use.

Skills Developed & Reflection

This stage of the project has taught me that engineering involves more than following an initial plan. I have had to adapt my design to the limitations of the existing frame, correct mistakes and consider how each component affects the overall structure.

My welding skills have improved considerably. Although some of my first welds needed to be repaired, the process of identifying weaknesses and correcting them has made me more confident and consistent. I have also developed a better understanding of load distribution, reinforcement, material fitting and the importance of accurate measurements.

The change from one large vat to three compartments demonstrates how reflection can improve a design. Rather than continuing with the original plan, I reconsidered how the system would operate and how the finished compost would be harvested. The revised design should make maintenance and compost removal more manageable, although its effectiveness will depend on how well the worms move between compartments and how the waste decomposes.

My next steps are to finish fitting the floor, construct the remaining compartments, install the door hardware, add the roof and check the structure's integrity. Once it is complete, I will test the system with organic waste and worms, monitoring its stability, drainage, moisture and composting performance.

Overall, this project has strengthened my practical engineering skills and taught me the value of persistence and iterative design. My focus is now shifting from constructing the basic structure to ensuring that the completed vermicomposting system works efficiently, safely and reliably.

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