Easy-dose digester additive delivers 400% ROI for Essex AD plant

A one-a-day easy-dose digester additive from FM BioEnergy has boosted gas output at BioWatt’s Katharos Organic AD plant, delivering a 400% return on investment.

The 1MW facility in Thaxted, Essex, initially took part in a nine-week trial of FM BioEnergy’s new BC.MICROcon5 digester supplement, which contains the exact daily dose of five key trace elements in a safe-to-handle, digestible tab that requires no mixing, measuring or pouring. After seeing an instant rise in methane levels and finding the product safer and easier to use than traditional additives, BioWatt have placed an order for a year’s supply of the supplement, not only for their Katharos site but also for two other plants that they operate.

“BC.MICROcon5 has proved its worth in terms of boosting our biogas output. It’s simple and safe to use and is popular with staff on site – it really is a game changer.”

Alex Monks, Chief Operating Officer, BioWatt.

Reaching operational tipping point

When BioWatt took over the operation of Katharos Organic AD plant in 2017, the maize-fed facility was running at an average of 25% of its operational capacity. Following improvements by the BioWatt team, performance reached 60% output. However, this became the tipping point – when the feeding rate was increased, the biology would become unstable causing both output and CH₄ content to suddenly drop. FM BioEnergy were already acting as biological consultants for another of BioWatt’s sites, so Alex Monks enquired to see if the team could help at Katharos, too.

FM BioEnergy’s General Manager, Tim Elsome, soon discovered the issues were due to a micronutrient/trace element deficiency: “The biological environment was not ideal – FOS/TAC levels were elevated at 0.88 and the pH was low at 7.2. Results from our lab revealed this was due to a severe deficiency in five of the most critical trace elements needed to maintain a healthy digester biology.”

5-in-1 easy dose supplement

Tim explained that FM BioEnergy’s brand-new digester additive product – BC.MICROcon5 – contains the exact daily dose for a 1MW plant of these same five essential trace elements: nickel, selenium, cobalt, tungsten and molybdenum. It was developed by FM BioEnergy’s German product partner Schaumann BioEnergy in response to customer demand for an additive that is safe to handle and easy to dose. Alex agreed to take part in a nine-week trial of the product to see if it could help the Katharos plant overcome its biological inhibition and reach operational target.

The first stage was a correctional or ‘impulse’ dose, which involved feeding 45 days’ worth of BC.MICROcon5 into the digester within just 30 minutes over three feed batches.

“Almost overnight, we could see that we were producing more gas,” says Alex. “Not only that but the gas contained higher levels of methane – our CH₄ readings were already up by 3%.”

Safe to handle

The second stage of the trial – the maintenance phase – then began, which saw operators feed one tab of the product into the 1MW digester each day, for a period of nine weeks.

“Much like a dishwasher tablet, the handy-sized tabs are individually wrapped and coated with a water-soluble film, meaning they are safe to handle,” outlines Tim. “Just like taking a daily multivitamin to keep your body healthy, all site staff need to do is feed one tablet into the digester each day to keep the biology stable. The dosage is based on a typical 1MW plant, but it’s easy to flex up or down – for a 500kW facility just add one tab every two days, and so on.”

After using the product for just a few days, Alex reported that the tabs were much easier and safer to use compared to traditional liquid or bagged powder digester additives. Feeding was remarkably simple, too: “We just dropped one tab into the feed hopper each day – job done! Plus, it took up hardly any storage space on site.”

Increased methane levels

At the end of the nine week trial, the FM BioEnergy team analysed the results and were delighted with what they found. “When compared to the starting data, the Katharos plant saw an increase of 3.05m³ of methane (CH₄) and 12.2 kWh^e per tonne of feedstock,” reveals Tim. “In financial terms, this translates into an incredible 400% return on their investment over the course of the trial.”

For Alex, this represents a new era in biological management for BioWatt. “Combined, the improvements in biogas output plus the ease of use mean that BC.MICROcon5 has more than proved its worth. It’s safer, cleaner, easier, more accurate, saves us space on site and has quickly become part of our daily digester care regime. We’ve already purchased 12 months’ supply for the Katharos site and have recently placed further orders for two more of our plants.”