Anaerobic Digester Clean for a Major Pharmaceutical Manufacturer

Operations and Maintenance
Anaerobic digester with two engineering in front and wind turbine in background

Over time, solids build up in Anaerobic Digester tanks which reduce its effectiveness and the quantity of energy produced. To maximise performance and digester lifespan, routine cleaning and maintenance are essential.

In many cases, formal certification is required for insurance purposes.

We’ve recently carried out three Anaerobic Digester tank cleans and inspections for a major pharmaceutical manufacturer, on a site we have been maintaining and operating for nearly 20 years.

Due to the complexity of the work and the risks involved with highly explosive and toxic substances present, careful management and planning are essential to ensure safety and compliance with regulations and to retain biomass health for effective re-commissioning of the digester without incurring additional expense.

The AD Digestor cleaning and inspection process

The planning and preparation work for a digester clean project is a critical part of the process, to ensure the safest, least disruptive and most cost-effective approach. Process Safety must be incorporated through every stage of the project based on the site's unique characteristics.

On this large pharmaceutical manufacturing site, Alpheus's approach involved carrying out the three cleans and inspections in succession to allow the transfer of biomass between tanks, and for learnings to be carried through to subsequent cleans to maximise efficiency. This ensured no disruption to production and avoided temporary storage costs.

Each digester can house 660,000 gallons of liquid waste (3000m³), so this is no mean feat. The following process was carried out for each tank:

  1. Tank Empty
  2. Isolation of tank
  3. Pre-inspection Tank Purge (Nitrogen and Stormwater)
  4. Scaffolding for cleaning
  5. Tank Clean
  6. Tank Inspection (using drones instead of scaffolding)
  7. Remove scaffolding
  8. Post-inspection Tank Purge (Nitrogen and Stormwater)
  9. Transfer of Biomass from between tanks

With the last digester in the final commissioning stage, the project is on target to be completed on time and within budget with no disruption to production. 15-year inspection certificates have been issued for all three tanks ensuring optimal performance and that insurance requirements are met.

If not managed properly these projects can pose significant risks to safety and health, and costs can escalate if there are unplanned disruptions. Each Anaerobic Digestion (AD) plant is different, so it is important to factor in all variables to devise the safest and most effective approach. It is our approach to such projects that sets us apart, to give customers peace of mind from both a cost and safety perspective.

Scaffolding with empty anaerobic digester tank

Managing the process

Process safety

A comprehensive process safety approach from start to finish mitigates the risks associated with such a significant project, where the danger of explosion or escape of toxic substances is high. The most risky stages are the isolation and purging of the tank before the clean and preparing for re-commissioning. For each site, there are numerous factors to take into account to plan the best approach.

Our teams comprise highly trained process safety experts including experienced operators, engineers and process scientists who work closely with our clients to fully understand the site and challenges to plan and implement a compliant, safe and cost-effective solution.

Managing costs and minimising disruption

Engaging an expert in the management of such projects will not only protect your site, community and company reputation, it can help you mitigate disruption in production and protect your bottom line. For example, managing the biomass effectively during the process is essential to keep costs down and facilitate smooth recommissioning. This can be particularly challenging on smaller or more complex sites. A provider that is experienced in process safety and management will ensure you that this complex, but necessary job is as cost-effective and safe as possible.

For this project, we were able to plan to transfer and monitor biomass to ensure production could continue, and that biomass health was maintained, but on smaller sites with just one digester, an alternative solution would be required to facilitate the job.

How often should a digester tank be cleaned and inspected?

Digester tanks should be dewatered, cleaned out and inspected every 10 – 15 years to maintain effective operability.  Specific requirements vary depending on the size and type of the AD plant, as well as its location and the materials being processed.

What are the risks of delaying a digester inspection and clear-out?

Delaying an inspection and clear-out will lead to a severe build-up of solids which can cause several issues, some with serious consequences, including:

  • Reduced gas production and decreased biogas quality.
  • Increased Operating Costs.
  • Build-up of toxic substances that can inhibit microbial activity and pose health and safety risks when the digester is eventually opened for maintenance.
  • Structural Damage that could lead to leaks, spills, and costly repairs.
  • Odour Issues that may affect the local community and violate environmental regulations.
  • Regulatory Compliance Issues could result in fines, penalties, or shutdown of the facility.

Why choose Alpheus

We have over 30 years’ of experience in the operation and maintenance of water and wastewater treatment facilities and are part of one of the UK’s largest water companies, Anglian Water.  Between ourselves and our sister company CAW, we maintain and operate several AD plants across the UK and Ireland, with the F&B, Pharmaceutical and Municipal sectors.

Our approach to Process Safety and our scientific approach to continuous optimisation is what sets us apart. When it comes to the maintenance of AD plants and digester cleans, the requirements of every site are different so our expert team works closely with clients to understand their process and requirements to design and propose the most effective solution.

We’ve been operating and maintaining the wastewater treatment and AD plant for The Glenmorangie Company since 2020. Discover what Ed Thom, Distillery Manager, has to say about our approach and how it has helped them improve gas production on their plant by nearly 30% in our testimonial video.

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