The Industrial Emissions Directive (IED) takes an integrated approach to controlling pollution to air, water and land, and sets challenging industry standards for the most polluting industries, aiming to prevent and reduce harmful industrial emissions, while promoting the use of techniques that reduce pollutant emissions and are energy and resource efficient.

Although the requirements of the IED were transposed into the Environmental Permitting Regulations (EPR) in 2013, between 2014 and 2019 the UK water industry operated in a holding position, as originally the Environment Agency (EA) deemed that sewage sludge anaerobic digestion facilities were covered by the Urban Wastewater Treatment Directive. However, in 2019, the EA revoked this exclusion and informed the Water and Sewerage Companies (WaSCs) that they needed to comply with the requirements of the IED.

These requirements are cascaded through the EPR and require facilities to use Best Available Techniques (BAT), with the facilities’ Environmental Permit (EP) including bespoke Improvement Conditions (IC) for IED compliance. In addition to this, any permitted facility should employ a series of appropriate measures, which are the standards relating to the storage, treatment, and transfer of waste, including, amongst others, process efficiency and emissions control.
Although site specific, for AD facilities, the ICs typically include the requirement to demonstrate the stability of the treated digestate, the provision of an anaerobic digester cover plan and a digestate store enclosure plan. The EP may set out emission value limits (EVL) for any channelled emissions from covered tanks, including EVLs not for methane, but for hydrogen chloride and total volatile organic compounds (TVOC) including methane, and the limit values are low, especially the requirement for 20 mg/m3 for TVOCs. 

BAT aren’t just a concept, they are defined in a reference document for waste treatment. Regarding emissions, a critical component of BAT is BAT14, which deals with preventing, or reducing diffuse emissions to air, and includes requirements for minimising the number of potential diffuse emission sources, and to contain, collect and treat diffuse emissions. However, the requirement for covering all post-digestion storage tanks is potentially in conflict with both BAT14d (which acknowledges that the use of enclosed equipment may be restricted by safety considerations such as the risk of explosion), and the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR), which although requires the avoidance and minimisation of releases, it requires the prevention of the formation of an explosive atmosphere.

The occurrence of explosive atmospheres presents challenges with environmental regulations. Although IED promotes the reduction in pollutant emissions, it does not consider safety. Safety has to take precedence when engineering any solutions that are achieving marginal environmental gains in mitigating process emissions. BAT does acknowledge the risk of explosion, but it disregards energy and resource efficiency. Achieving an ELV of 20 mg/m3 for TVOCs using BAT, may force the widespread application of regenerative thermal oxidation, where, nonsensically, the carbon footprint of the abatement technology is likely to be higher than an untreated emission. 

An expert panel will discuss the challenges and unintended consequences of implementing the IED at AD facilities, including the requirement to cover all sludge tanks, the containment of diffuse emissions, and the requirement to abate all channelled emissions. 

Time allowing, discussions may extend to alternative appropriate BAT techniques, residual biogas, dissolved methane, ammonia, and odour nuisance. Secondary containment will have to wait for a separate session.