International malt producer saves money with anaerobic digestion

In Australia, Muntons is best known for its range of home beer-making kits, made from UK malting barley to emulate classic beer styles from around the world.

However, the company is also a producer of a range of malt products for food manufacturers around the world. Muntons also believes in sustainable production. Since early 2016, the company has operated a novel closed-loop system, which turns some 80,000 tonnes of liquid malt waste into a high-quality biofertiliser at its production plant in Suffolk, England.

The basis of the system is a $9.4m, 499kW on-site anaerobic digestion (AD) plant that generates 25 per cent of the site’s electricity and turns 80,000 tonnes of liquid malt waste a year into quality organic digestate fertiliser, which is used by the company’s network of growers. In turn, they produce some of the 250,000 tons of barley needed to make 180,000 tonnes of Muntons’ malt each year. In the process, the company has saved more than 800 tonnes of CO2 emissions and saved more than $5.95m in electricity and waste disposal costs.

Muntons, which has sustainability at its core, first became interested in AD after analysis showed that 60 per cent of the carbon footprint of its supply chain came from the artificial fertiliser used by its barley growers. The company realised that if a proportion of the liquid waste it produces every year could be treated through AD, it could produce a high-quality, organic biofertiliser for its farmers to use instead therefore closing the loop between farm and fork and reducing its carbon footprint.

The new treatment removed the need for these journeys, and also captured nutrients such as phosphate, which were previously lost when treated effluent was discharged to the river. The digestate product is high in organic matter and acts as a soil conditioner and improver. It also has a longer period when it can be applied to the land than the liquid waste that was previously produced.

Ensuring digestate quality
Unlike conventional AD plants, Muntons’ plant uses a combination of both anaerobic and aerobic processes to treat its digestate, meaning that for technical reasons the resulting sludge cannot be certified as meeting the UK standards for compost and digestate. These standards, known as PAS110, provide a guarantee to users that the digestate product meets certain quality parameters and mean that it is exempt from further waste legislation, so that it can be applied to fields as a fertiliser. However, the process includes a pasteurisation step and the resulting material is treated in accordance with the requirements of the PAS110 standard for anaerobic digestate, based on conventional Hazard Analysis Critical Control Points (HACCP) principles. This helps to assure local farmers that the final biofertiliser contains no ergot or plant pathogens contaminants.

According to, Muntons’ site and waste water supervisor, Paul Mead, a pasteurisation system from HRS Heat Exchangers was a crucial part of the entire process.

“We want our biofertiliser to compete in the agricultural market with the likes of PAS110 digestate and other biosolids that have undergone pasteurisation. Even though we are considered low risk and all our feedstock is from traceable, food-grade grains, we felt that pasteurising our material is the best way to help us get End of Waste Certification. It also reassures local farmers that we will not contaminate their land with ergot or plant pathogens.”

Muntons commissioned a 3-Tank Batch Sludge Pasteuriser System with Energy Recovery from HRS Heat Exchangers to treat the anaerobic and aerobic wastes. Almost 200m3 (53,000 gallons) of high liquid waste, with a high chemical oxygen demand (COD), is treated each day and as well as the CO2 savings, the project has saved Muntons more than $5.95m in energy and disposal costs to date.

The digestate was blended with low COD effluent before being treated with Dissolved Air Flotation (DAF) in Muntons’ existing activated sludge plant. This stabilised the digestate and removed further COD, nitrates and phosphorus, prior to the effluent being discharged to local waterways in accordance with an Environment Agency permit. The remaining sludge was then pasteurised in the HRS 3 Tank unit and used as biofertiliser.

Although the material cannot be certified to PAS110, it has been granted End of Waste Certification by the UK Environment Agency, meaning that it can be used as a biofertiliser.

The benefits of pasteurisation
The HRS system works on a three tank principle; while one tank is being filled, the second tank holds the sludge at 70°C, at the same time as the third tank is being emptied (each process lasts one hour). Waste cooling water from the CHP engine is used to heat the sludge in corrugated tube-in-tube heat exchangers, which is more efficient than heating an entire tank of digestate.

HRS has also incorporated an energy recovery section into the process to make it more efficient – energy is transferred from the hotter (pasteurised) sludge to the colder (unpasteurised) sludge, reducing energy consumption by up to 70 per cent compared to conventional systems and using heat, which would otherwise be wasted. It also has the advantage of being able to run at a half flow rate, should the volume of digestate stock reduce, and the equipment’s monitoring features ensure that every batch of digestate can be traced back to the feedstock from which it was produced

Once pasteurised, the biofertiliser can be de-watered if required; it can be supplied for application either as a liquid for soil injection, or a solid for muck spreading. Analysis by Muntons has shown that their biofertiliser is higher in nitrogen, potash and sulphur than most other available biosolids, as well as being a good source of phosphate and magnesium.

The biofertiliser is used on local land from which the company sources its malting barley, but the company is also keen to stimulate the wider biofertiliser market. Muntons is also working with the University of Lincoln on a project to document the composition and effectiveness of the biofertiliser. This has initially demonstrated that lettuces grown with Muntons’ biofertiliser demonstrate quality and growth benefits over artificial fertilisers of similar nutrient concentration.

A further collaboration with University College London revealed that the digestate yields a type of bacteria that produces an antibiotic that kills multi-drug resistant E. coli bacteria.

“For Muntons this whole project has been about maximising efficiency. Although they have an abundance of heat, they still wanted to recapture what they could, and our heat exchangers provide 40 per cent heat regeneration,” said Matt Hale, international sales and marketing director at HRS. “Our system also allows the tanks to run at half flow rates if necessary, meaning they can still carry on pasteurising without having to wait to build up a stock of digestate. Working with a company like Muntons to deliver a truly revolutionary waste treatment plant shows exactly what is possible in terms of implementing the circular economy. The results that the biofertiliser is providing in trials and in the field show just what a valuable resource it is; this success could be repeated elsewhere around the world.”