Is thermal drying part of our biosolids future?

Hydroflux can offer a range of biosolid processing solutions, from struvite harvesting, biogas recovery and drying.

As Australia builds a pathway for the sustainable management of biosolids, new technology is critical to developing a following among water utilities in Australia and New Zealand. What is that technology?

The consideration of technology, legislative change, public perception, circular economy thinking and emerging contaminants are part of a roadmap to managing biosolids.

However, many options exist for delivering such infrastructure within a large country like Australia. Biosolids management is a crucial topic worldwide, and the water industry can learn from what other countries are implementing.

Some countries have moved towards centralised digestion with hydrolysis pre-treatment to exploit higher gas yields and green energy. Others have mandated fertiliser recovery from sewage biosolids using thermal treatment. Regardless of which path is taken, exploiting the hidden energy potential of biosolids is common. A drying step is typically employed for advanced thermal processes and fertiliser recovery.

What is the drying step?

According to the United States Environmental Protection Agency (US EPA), heat drying (also known as thermal drying) is a technique where heat from direct or indirect dryers is used to evaporate water from wastewater solids.

It is one of several methods that can be used to reduce the volume and improve the quality of wastewater biosolids. However, an advantage of heat drying versus other biosolids improvement methods is that heat drying is ideal for producing Class A biosolids.

The US EPA says that Class A biosolids, as defined in 40 CFR Part 503, are biosolids that have met “the highest quality” pathogen reduction requirements confirmed by analytical testing and/or the use of a Process to Further Reduce Pathogens (PFRP) as defined in 40 CFR Part 257.

There are a few projects around Australia that involve thermal drying facilities. Significant opportunities exist for those wishing to turn their biosolids into a valuable resource.

Hydroflux and biosolids

Recently, Hydroflux was awarded the Thermal Dryer Package for the new Sludge Minimisation Facility of Wellington City in New Zealand. The McConnell Dowell-HEB Joint Venture was awarded a contract to construct the new facility, which will reduce sludge volumes by up to 80 per cent, reducing carbon emissions compared to the current disposal to landfills. It will also allow the sludge to be used sustainably, such as soil conditioner and fuel for industrial heat. The process will include advanced thermal hydrolysis, anaerobic digestion, dewatering and thermal drying.

Hydroflux Epco NZ was awarded the design and delivery of the thermal dryer, which will dry all the digested sludge post-dewatering. A HUBER BT12 Belt Dryer was selected for the process. This groundbreaking project will have environmental benefits like reduced waste and carbon emissions. The benefits include reduced biosolids disposal costs, greater reuse opportunities of the final dried product, exploitation of waste gas, and the associated sustainability outcomes.

The European experience

In Belgium, two new centralised biosolids management facilities under construction will provide pelletised sludge to industry as a fuel. Also, a feed source for mono-incineration will be used to produce green energy and phosphorous recovery – the West site will process 36,000 tonnes per annum, and the East Site will process up to 84,000 tonnes per annum. These centralised facilities will use HUBER BT Dryers and draw energy from waste heat from nearby wastewater treatment plants and industries.

The European experience has resulted in collaborations between industry and water utilities, aligned with circular economy thinking. HUBER is currently involved in several projects where a municipal biosolids drying facility is used as a power plant heat sink. The sustainability outcomes for both water utility and industry are significant.

Many global players from the industrial and manufacturing space have a common decarbonisation goal. For example, building material specialist Heidelberg Cement AG recently set itself targets for reducing carbon emissions. Partnering with HUBER, Heidelberg Cement has commissioned a BT Thermal Drying Facility that uses waste heat from their cement manufacturing process and biosolids from the local Water Authority.

The dried biosolid output of the waste heat-driven dryer is used as fuel in the cement manufacturing process and has a calorific value of approximately 10 megajoules per kilogram. The drying system will process 70,000 tonnes per annum of biosolids and provide about 194,000 gigajoules of energy per year, displacing more than 20,000 tonnes per annum of brown coal that was previously in use and avoiding 70,000 tonnes per annum of biosolids going to landfill.

Being a renewable energy source, using dried biosolids as a fuel is key to Heidelberg Cement’s path to becoming carbon neutral. Many power plants across Europe are implementing similar strategies.

What does this mean?

The above are just some examples of what is being done to unlock biosolids’ energy potential and harvest nutrients. Biosolid drying can benefit from reducing emissions, reducing transport costs, and exploiting waste gas streams. It also forms a crucial step in allowing future recovery of phosphorous and energy if an advanced thermal process were to be implemented in the long term.

Hydroflux is a driver of ANZ’s future resilience in biosolids handling and disposal, with exclusive access to some of Europe’s leading biosolids technology, case histories and knowledge.

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