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R-Urban London

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Field notes: The third ‘Build a Micro AD weekend’

The third ‘Build a Micro AD weekend’ (3rd & 4th October)
Last weekend we had another sunny couple of days working on the project. Our engineer, Guy, delivered the digester and prefeed tanks and the focus for the weekend was to finish the framework for the tanks, design the internal layout for all the systems that will be housed in the shipping container, and make up the anaerobic digester.

In the previous build weekend we had constructed two low-cost bunds; waterproof membranes in wooden frames that contain any spillage from the tanks. We’d also built the housing for the tanks. This weekend we had to finish these off, insulate them, and design in the access routes to feed, monitor and clean the system.
We worked in pairs or teams on a range of tasks, including:
• Salvaging timber (disassembling the temporary bridges used in the park during olympics )
• Insulating the digester and pre feed tank
• Modifying the digester tank
• Designing a stand for a manual macerating unit for the food waste
• Preparing the plumbing fittings for the prefeed tank

The Group:
We had a mixed group of about 15 volunteers coming from all over London and with different interests. Some people were just looking for a fun activity to get involved with on a sunny day, others were specifically interested in learning about using food waste to generate energy, with plans to build their own units in the future. Others wanted to share their skills from engineering, product design, hacking and architecture to help build this ground-up demonstration of a small-scale circular economy.

The aim is for these weekends to be about getting to know people, getting to know the process, but also find opportunities to develop the project.
We are looking for local E20 volunteers who would be interested in being part of the management team with us to help run our circular economy. We will need to start a food waste collection service and fertiliser distribution network. We have a number of local cafes and growing groups interested in providing waste, and in taking fertiliser.

We have space to open a micro café on site and are looking for people who would be keen to pilot it. The digester will generate gas for cooking on the site.

Upcoming tasks (next build weekend 17th & 18th October):
There are a number of separate closed systems to build for the unit which all have to be fitted in or on the shipping container. A key task for the coming weekend is to design the system layout and begin work on the connections which will allow the waste, water, gas, heat to flow between the different parts of the system:
a water system; water is needed to help the food waste circulate. Food waste is macerated before being fed into the pre-feed tank. This will be recirculated to help feed in fresh food waste and reduce water consumption but some water may still be needed to ensure it’s the right consistency to go through the pipework into the digester. We also need water to wash waste caddies and possibly to use in an onsite cafe. This means we need to have a rain harvesting and a clean/dirty water storage system.

A heating system; the microorganisms inside the digester need to be kept warm (approx. 36°C), to enable the food waste to break down and release the biogas.

A biogas system; the gas produced needs to be collected. It can be used in a boiler for the system’s own heating system, inside a polytunnel on site to extend the growing season, or in a gas burning for a mini kitchen / café.

An electricity system; we need electricity for the pumps, to monitor the system and for other uses on site. We’ll be using solar PV cells to generate electricity alongside a charge controller and batteries for storage. An inverter will be used to convert electricity from DC to AC where necessary however, we will try to keep as much of the digester and heating system running on DC as possible to avoid losses.

Next weekend (17th – 18th October)
This coming weekend we’ll be on site again and focusing on:
• Completing digester and pre-feed casing
• Installing water tanks (IBCs) and piping
• Wall layout for all control panels and biogas boiler
• Discussion on future management and the extended AD project
• Continuing to harvest timber
• Other tasks to be confirmed