Dr David Tompkins, Head of Knowledge Exchange & Innovation at Aqua Enviro. Aqua Enviro is the UK consultancy within SUEZ Water Technologies & Solutions.

Biosolids (or treated sewage sludges) typically have two markets – land application and incineration.  Application to land, in compliance with the regulatory and good practice requirements, is still considered the best practicable environmental option in most cases.  Alongside Spain and France, the UK recycles the majority of biosolids to these markets, with an emphasis on agricultural land.

However, this approach is not universal, and other nations have taken different approaches.  Biosolids are largely incinerated in the Netherlands, due to absence of suitable landbank – the high density of livestock businesses meaning that there is insufficient available land there to accept nutrients from other sources.  In Germany we have seen a move to incineration of sludges from larger works – driven by concerns around the quality of biosolids and their suitability for land application.  Alongside this, Germany has recognised the need to keep phosphorus within the active economy, and this resource must be recovered from incinerator ashes in most cases.  Biosolids from smaller works can continue to be applied to land.

Within this context, the PR19 process is gaining momentum – and Ofwat are pressing ahead with their development of a ‘bioresources’ market, bioresources being a catch-all that covers both treated and un-treated sewage sludges.  What might a direction of travel look like?  

On the one hand we have witnessed the roll-out of the Biosolids Assurance Scheme – a welcome development that adds transparency and consistency to biosolids’ management, particularly when applied to agricultural land. 

On the other hand, we have also seen a huge increase in public awareness of the issue of plastics in the water / aquatic environment.  When might this awareness extend to encompass plastics in the soil / terrestrial environment?  What could be the impact on current biosolids’ recycling routes if this was to happen?  Could the industry become the victim of ministerial whim, as soil-based markets are prohibited as a quick fix to the unquantified ‘problem’ of plastics in sludges?  Will we see a diversion of biosolids to commercial energy-from-waste facilities?

Whilst there are no simple answers to these questions, we can be confident that haulage of bioresources represents the most significant single cost in sludge management for most UK water & sewerage companies.  Strategic planning for cross-boundary trading, treatment and end markets should become an increasingly common feature of the UK market – with a renewed focus on thickening and (particularly) de-watering technologies that can cost-effectively reduce haulage costs.