Recycling the Material from Dredging & Minimising Landfill : BLOG: Stop Dredging Being a Drudge - Recycle the 'Treasure'

Peter Hayes explains how the landfilling of problem materials from the dredging of waterways can be minimised and reuse and recycling maximised.

Whether for maintenance, flood prevention, in preparation for construction work, to improve the environment or simply to remove rubbish and waste from the water bed, dredging is an important part of waterways management. rather than being a problem, scraping the bottom can bring extra rewards.

Excavating sediment from the bed of a harbour, river, lake or other body of water is important, and brings many benefits – for example sediment in stream beds disrupts the natural food chain by destroying the habitat where the smallest stream organisms live and causing declines in fish populations. Dredging also helps from a logistical point of view, as it keeps waterways navigable.

Problem material

However, although dredging solves many problems, the substances collected pose a few of their own. Dredged material is often contaminated with heavy metals, oils and chemicals as a result of past actions, particularly shipbuilding, heavy industry and naval activities. Runoff from roads, railways and agricultural land also causes issues as it transfers a variety of materials and contaminants into the water.

Even if it is possible to find a landfill site that would accept dredgings, this material would be too prohibitively expensive to dispose of, due to its composition and weight. The toxins contained and nature of the material mean it can’t be used in other ways – such as repairing river banks, in flood defences or as fertiliser – so what should you do with it?

All is not lost

Solutions are now available which can process and treat contaminated dredging material, thus avoiding landfill costs and instead providing products, such as sand and stone, for reuse.

The first important step to process dredgings, which have the consistency of a solid/liquid sludge, is to dewater the material to make it easier to process.

The next stage in recycling and recovery is the processing of the dewatered material to recover sand, stone and organics. Rather than being treated as waste these can now be considered as independent revenue streams.

The remaining clay content contains the contaminants and needs to be further dewatered to ensure easy and cheap disposal. Although the aim is to send as little as possible to landfill, any material that can’t be diverted will need to be dewatered before it is accepted at any landfill site. Organics can go to landfill, or be sent on for further treatment.

The recovered excess water typically goes through a tertiary treatment process and can be returned to the original water channel.

The reusable materials produced from the process are of a high quality and there are options for many reuse markets. There are also opportunities to use this material for landscaping and bedding.

Further processing can remove heavy metal and hydrocarbon constituents from the waste water stream. This enables a wider range of more difficult, more lucrative waste streams to be processed.

Hidden treasures

Processing the dredged material rather than trying to dispose of it untreated can also unearth hidden treasures. So much human activity takes place in and around our waterways that it should come as no surprise that many items end up in sediment.

For instance, one operator found a variety of historic naval items when it undertook dredging work to clean up a harbour. It’s not just shopping trolleys that find their way into the water!

The pressure on our natural resources and landfill issues, including increasing costs and restrictions, mean that anything that can be extracted from waste and become a resource instead is to be especially valued.

This is a significant aspect of the ‘circular economy’ that needs to replace the linear model of resource consumption that follows a take-make-dispose pattern. It’s not just about saving the planet’s dwindling natural resources – as vital as that is – it’s also a business model that can improve profit levels.

Dredging is central to maintaining the circle of life in our waterways, by maximising the recovery and reuse of material, it can also play its part in the circular economy.

Peter Hayes is business development executive at waste management specialist CDEnviro

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