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Rethinking sludge to recover the rewards

01 July 2019

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Kevin Mooney, our Wastewater Sector Manager, spoke to WWT magazine back in May about the potential economic and environmental value of more efficient processing in sludge management. As we face an increasing population, and landfill burdens, there is a growing responsibility and global awareness to manage waste more carefully.

In case you missed it, you can read the article here:

 

Sludge management – a key driver

With an exploding population and urban development, the consequences of this expansion are many. This includes the heavy burden on our infrastructure, not just having to cope with load, but with potentially serious ancillary damage.

Grit attrition that occurs as sludge moves through pipes and systems is a key hazard. Blockages caused by material build up prove costly and result in significant repair downtime, as well as on-going renovation and replacement costs.

The onus is on the wastewater industry to improve the methodology and capacity for processing sludge and recover its useful elements for re-use.

We know that the characteristics of the sludge that the wastewater industry is responsible for is determined by a wide range of factors. These include regulatory or environmental aspects, regional industrial activity, and of course, population. The challenge of keeping up with all these demands means exercising greater responsibility and turning to technological innovation and creative methodologies.

Challenges, like increasing costs to transport sludge to suitable treatment or land use, or the possible emergence of expensive, private sludge management facilities, make the search for solutions more urgent.

A smarter process

As an industry, we must work tirelessly to develop and refine the equipment and methods to enable better waste resource management, including grit removal from sludge.

By using screening technology that can successfully remove both grit and rag from sewage sludges, sewage screenings and tank cleaning residues, segregated stockpiles of grit and rag can be created for reuse or low-cost disposal.Simple screening of the material without further treatment will not achieve adequate separation of materials to render it re-usable. The material must be put through a washing system which is specifically designed to separate the components on both size and density.

Downtime is money too, so technology that eliminates blockage caused by myriad materials that are pumped onto the screens, results in a reduction of downtime spent cleaning up the results of poor, or no screening. With high processing output rates, enabled by more efficiently screened sludge, flow is improved, causing less crippling damage.  Additional costs are therefore not incurred at this stage of processing, regardless of the treated sludge’s final destination.

Revenue potential

It goes without saying, wastewater services will be able to increase their handling capacity and improve the efficiency of their operations with the support of technology. Furthermore, along with less downtime, the weight of waste material is reduced. It produces a cost saving, which, in the light of increasingly stringent landfill laws and increasing gate fees, is more important than ever.

Under European Waste Code 19-12-09, any materials recovered that have undergone mechanical or biological treatment (MBT) can be used as feed stock for aggregate recycling. That means stones, grit and sand must be put through an MBT process designed to produce a product that is substantially free from organics and other contaminants.

Following separation, the material can then be further processed on site under a suitable quality protocol and sold as aggregate. The Waste & Resources Action Programme (WRAP) Protocol on the Recovery of Aggregates [1] from inert waste, allows any recovered material to achieve End of Waste status. Even though this process may incur some costs, it achieves a substantial saving by reducing landfill gate fees and tax. 

Energy potential

Not only does the extracted grit have revenue potential but the sludge without grit has significant energy potential also. With sludge trading opening up in 2020, sludge will no longer be seen as a waste, but rather, a commodity that can used in anaerobic digestion to produce energy. Sludge quality will be more important than ever before, and that this is another reason why rag and grit should be removed as efficiently as possible in the treatment process.

We are in an age where technology can really help to solve so many inefficiencies concerning use and waste of our resources. With our growing population, the waste water industry may not be able to control the amount of sewage it handles and the ensuing sludge. However, by being smarter about steps in the process chain, innovation is shining a light at the end of the tunnel when it comes to managing and repurposing it.

For more information on how we can help you with sludge management, get in touch or visit our solutions page

 

[1] https://www.mineralproducts.org/documents/aggregates_quality_protocol.pdf

 

 

Sludge screening Grit recovery Recycling wastewater Wastewater solutions