The Environment Agency is consulting on proposed changes to the standard rules set for biowaste treatment, including anaerobic digestion, composting and sewage sludge treatment.
The Agency is proposing to:
- withdraw some rules sets
- merge the existing small scale composting site to one rules set
- revise existing rules sets, including to reduce the number by transposing like for like activity
The EA set out a number of reasons why it needs to revise the biowaste rules, including the need to reduce incidents caused by the biowaste sector, including fires and odour nuisance, and to improve poor performance.
The Agency said that the cause of incidents and poor performance are mainly due to:
- inadequate design and poor construction standards
- lack of operational process control
- failure to have or follow an effective management system
- deficient maintenance systems
- inadequate pre-acceptance and acceptance checks, including unacceptable levels of feedstock contamination
Proposed amendments to the permitted activities table for AD to include:
- gas upgrading and injection to the grid
- digestate drying with abatement
- allowing pasteurised, separated digestate fibre to be composted in the open with abatement or under static aeration
- provision for safe storage of raw materials
- provision for safe storage of hazardous waste, such as spent engine oil and used carbon
Some of these provisions are not currently included in sewage sludge treatment permits.
The Agency has decided to consult on the proposed changes following the completion of audits of AD sites over a 3 year period and a review of data on AD and composting sites.
The EA said it had also had to respond to a significant number of incidents which have caused or had potential to cause pollution. It had also undertaken routine compliance visits that identified serious failures which posed a serious risk of pollution or harm to human health.
"Some challenging incidents" in the water sector despite its technical experience
Image: catastrophic failure of biogas holder at WwTW
Commenting on biogas generation in the water sector, the EA said the water industry has the longest historical experience in managing AD.
“However, these processes have also presented us with some challenging incidents despite the technical experience of the sector.”
As part of the consultation the Agency has published a paper setting out examples of incidents at a number of installations, Examples cited from the water sector at wastewater treatment works included:
1. A water company which was ordered to pay £93,980 after losing its appeal over a fine for noncompliance. Investigators had found that a unit to treat siloxanes – residues that build up in engines and reduce efficiency – had caught fire and exploded. Further investigations showed the company had no formal procedures for starting or shutting down the siloxane plant, emergencies or maintenance.
2. A water company which was fined £400,000 for polluting the air with potentially explosive biogas. An estimated 50,000M3 of biogas was lost to the atmosphere over 19 days as a result of the catastrophic failure (collapse) of the gas holder and the subsequent release of biogas via the pressure/vacuum release valves as a safety measure. The standby flare failed to operate and a temporary flare was not installed. The Fire Service had to be called because there was a risk of an explosion. The Environment Agency estimated that the global warming potential of the incident was equivalent to 456.6 tonnes of CO2.
3. A catastrophic foaming incident at a wastewater treatment works facility which resulted in a sewage sludge digester losing a significant proportion of its contents (ca 2,000m3) into the secondary digested sludge holding tank which over-topped – the tank was uncovered and the resultant spillage covered an area of ground around the tank. There was no secondary containment for the tank. There was a large increase in odour complaints caused by the high odour levels of the sludge/foam that was spilt.
Deadline to submit comments to the consultation is 28 February 2020 – click here to access the onsultation online.
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