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Feature: Going underground

In the next few weeks, contracts are expected to be signed for the UK debut of a pioneering underground waste collection system that can also build recycling into the operation from the outset. If it proves successful here, it could see a marked reduction in the bulky collection banks that are such a feature of today’s built environment. It would also cut down on the number of vehicles needed for emptying and collecting recyclable material.

The Envac system, developed by Swedish company Envac Centralsug, is a fully enclosed vacuum system. It has several collection points, linked together by piping that transports the waste to a central collection station. Waste deposited at one of the inlets is stored temporarily in a chute on top of a discharge valve. The inlets empty automatically at regular intervals through a control system that switches on fans to create a vacuum in the network of pipes. An air inlet valve opens to allow transport air to enter the system.

Gravity causes the refuse to fall into the horizontal network of pipes and it is sucked away to the collection station. It then falls into a compactor.

The manufacturer says the system can easily separate waste for recycling. Extra inlets are added for each category of refuse, and the control system directs a diverter valve to convey each category of sorted waste into the correct container.

In theory, it is seamless and cuts out several stages of the conventional collection system for recyclables. However, the degree to which recyclable waste is separated at source has room for further refinement.

Company spokesman Jonas Tørnblom told MRW: “Generally, there is an outlet for organic waste that can be composted, another to handle plastics, paper and cardboard and a third for waste that cannot be recycled. The system generally does not take glass because it can be abrasive.”

As a rule, recyclable material would need to be sorted at a recycling plant but, says Tørnblom, “we could extend the degree of separation by adding extra inlets to the system”.

Envac is cautious about giving details of the UK project, but it is “confident” that contracts will be signed on time. If all goes well, the system will start with three waste streams, each transported individually.

All Envac systems now in operation have recycling built-in. Barcelona has eight in operation while Stockholm and Copenhagen are committed users. Two years ago, Almere was the first city in the Netherlands to install a wide-ranging collection system linking all waste disposal from housing, offices, shops and restaurants to the underground network. Now even the city’s litter bins have been connected.

For the past few years, the UK has been quietly looking into the feasibility of introducing underground waste collection with recycling potential. A team from the Welsh School of Architecture at Cardiff University examined the pneumatic system installed in the historic city of Leon, in the north west of Spain and with a population of 150,000. The project attracted EU funding of 5.2 million (£3.6m).

Although the team picked out such disadvantages as high investment costs and the inconvenience to residents and businesses when the system was being built, it liked the selective waste collection at source and the fact that the system was cheaper to operate than traditional municipal waste collection.

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