Emptying & washdown of 30,000m² storage tank for Anaerobic Digestion Plant.

In September 2024, Mayglothling Waste successfully completed the emptying and washdown of an anaerobic digestion (AD) plant at a farm in Herefordshire. Over the course of eight days, the team, led by a site foreman, carried out the work to a high standard while strictly adhering to all health and safety protocols. The plant owner, Mr Edward Morris, was highly impressed with the professionalism and efficiency of the service provided.

‘…a company capable of handling a job of this scale professionally is rare’

This was the first time the tank had been emptied and Mr Morris sought a reliable contractor to complete the task efficiently. After some research, Mayglothling was selected due to their strong local reputation and Technical Sales Head, Donovan’s prior experience with AD plants.

Digestate management was key to the success of the operation through use of storage facilities on site and transportation to neighbouring grass fields. The cleaning works were tied to coincide with the availability of arable and grass land so flexibility and timing with the farm’s needs were key. The thorough tank wash-down by Mayglothling removed all grit, solids and waste water.

Overview of the AD Plant.

The AD plant in question was an 0.5-megawatt site, responsible for processing 35 tonnes of feedstock daily, consisting of:

The plant features a 30,000m² storage tank with a semi-flow plug digester, made up of an inner and outer ring. The plant has been designed for efficiency, including a sloping inner floor and pits in the outer ring to help capture grit and speed up emptying. The heat generated from the digestion process is repurposed to warm chicken sheds, enhancing overall operational sustainability.

Reasons for the Works:
In line with EA regulations, the tank needed inspecting. The works carried out by Mayglothling removed accumulated sludge and grit, preventing future blockages and ensuring efficient biogas production. Regular cleaning minimizes wear on mixers, pumps, and pipes, prolonging equipment lifespan. It also helps control harmful gas build-up, preventing pressure imbalances caused by excessive solids. Compliance with these legal and operational standards promotes a safer working environment for plant personnel while extending the plant’s lifespan by identifying and addressing cracks, corrosion, and structural wear before they lead to failures.

Challenges & Solutions of AD Plants.

Grit and Stone Traps:
Upon emptying, only 4-5 inches of grit were found in the tank, highlighting the effectiveness of well-managed input materials. However, the traps showed signs of buildup caused by silage pit surface material entering the system. To mitigate this, the farm plans to resurface the silage pits with tarmac, reducing grit entry and minimizing future accumulation.

Feedstock Adjustments:
The plant previously utilized rye as a feedstock; however, its use was discontinued due to its aggressive impact on fliptips. Similarly, the farm is currently evaluating the continued use of sugar beet, as its high liquid content can lead to potential imbalances in the digestion process and storage challenges for the resulting fertiliser.

Infrastructure Alterations:
It was noted that flanged pipework would have been preferable to direct cuts for maintenance access during the emptying. Greater on-site water flow would have also been beneficial for the wash-down process.Execution & Outcomes The 8-day job was carried out professionally and efficiently by Mayglothling. The team, led by a competent site foreman, worked in an organized manner, ensuring timely completion of the tank cleaning and maintenance minimal operational disruption and full compliance with health and safety

Regulations. Health and safety concerns were thoroughly addressed with use of gas alarms and breathing apparatus, employment of CXCS specialists to oversee compliance and strict adherence to PPE requirements.

Client Satisfaction & Feedback

Would you recommend Mayglothling?
“Certainly, yes. Finding a company capable of handling a job of this scale professionally is rare. I prefer to stay local, as those are the people you trust.” “The strong personal relationship with Donovan was excellent. His availability via mobile was particularly valuable and added a key level of trust. It took a lot of weight off my shoulders” – Edward Morris (Plant Owner).

Summary from Technical Services Manager at Mayglothling:
“After receiving a phone call from Ed Morris reference an AD tank clean, I took a visit to site to discuss emptying. Whilst on site, the tank had been lowered of liquid and the manway doors were open which allowed me to take a look at the amount of grit that was left within the tank. After discussing the job, a time scale of 12 days was decided before the inspection of the tank was due. I decided the best option would be to use both of our high-volume jet vacs and a 5-team confined space crew, with a site supervisor.We commenced with emptying the tank and tipping into the silage pit ready for land spreading. I made sure to visit the site frequently and kept in touch with Ed to monitor how things were progressing. The job was successfully completed within the 12-day window for the inspection to take place and Ed and myself were pleased with the outcome.” – Donavan Tompkins (Technical Services Manager).

Final Status
The tank is now fully operational, with efforts focused on restoring it to full heat capacity.