Tim Sullivan, technical director for H20K Water & Energy – an installer of plant equipment – stressed that digestate management was a big issue in the AD sector, especially for food feedstocks which can release high levels of nitrogen and ammonia.

He urged food producers to pre-treat their food waste streams where possible, and to avoid heavy logistics or handling methods such as using skips or forklifts.

“You need to deal with the feedstock as quick as possible – get it into a pumpable format as quick as you can by mashing it up with water,” he said.

Once pumped, the food should be stored in air tight vessels for odour control, he added. Also animal by-product regulations might require the need for pasteurisation processing equipment.

Sullivan emphasised the likelihood of downtime if the feedstock wasn’t prepared thoroughly enough.

“It’s important to keep the pipelines moving to prevent any clogs or blockages, so provide access or flushing to pipes,” he added.

These issues were echoed by Jamie Gascoigne, commissioning engineer at Marches Biogas, who advised that liquid feedstocks such as food waste would require different tank designs in the plant build compared to dry feedstocks such as poultry litter.

“Your feed system has to be reliable as it can be prone to failure – 90% of system failures that we encounter come from impurities or contaminants in the feedstock,” he said.

“If you understand your feedstock better, you will better understand what type of mixing system you need,” he added.

Both Gascoigne and Sullivan were speaking at the Anaerobic Digestion & Biogas Association annual exhibition in Birmingham last week.

Maxine Perella

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