Post commissioning of the UK's largest Dry Anaerobic Digestion Plant at a large operational waste management facility, an increase in ammonia levels substantial in surface water was evidenced. These levels were substantially above the permitted discharge limits for the facility, resulting in the client being required to treat surface water as leachate until the cause was established and a remedy implemented. As substantial increase in facility operating costs was incurred.

FRS instructed OIS to investigate the cause of the increase in ammonia levels. OIS carried out the investigation and reported back that cross contamination was occurring.

Findings:

• A number of septic tanks
• The AD leachate and percolate tanks leaked, are below ground and in direct contact with the AD plant's surface water drainage systems
• Ammonia levels in the AD Bio filter effluents were greater than 8000mg/l
• The AD Bio filter recirculation tank is installed blow ground, was leaking and was in direct contact with the AD plant's surface water drainage, discharging Bio filter recirculation water into the surface water drainage with ammonia greater than 8000mg/l
• The existing reedbed was not performing adequately and was not capable of meeting the PPC permit obligations

OIS submitted the findings to FRS. FRS, then instructed OIS to submit proposals to remedy the issues found. These included the following:

Following instruction from the Council to develop the sites, Exemptions from the requirement ot apply for Waste Management Licences were registered with SEPA. Site preparation involved:

• An aeration system be constructed to treat the site's surface water
• That a new treatment system would provide for treatment of contaminated run off from the compost slab
• That a new treatment system would provide for the treatment of surface water from the AD plant, (previously the AD surface water had an independent SuD's approved system
• That the discharge parameters of the surface water should be increased to reflect the risk to receiving waters
• That the surface water management plan be revised to reflect these changes and the actual activities on the site that are being performed
• That the PPC Permit be revised and a variation submitted to correct these activities and include the surface water treatment.

SEPA approved these proposals, FRS then instructed OIS to design CQA the works which were completed accordingly. The CQA verification report and revised surface water management plan, which also includes the revised discharge parameters were issued to SEPA and approved.