FAQ: PYROCO Biosolids to Biochar Technology

December 2, 2022

Last month you attended webinar hosted by Iota ‘Insights From South East Water’s Journey with Next Generation Pyrolysis Technology’. Thank you again to all of our speakers. The large attendance and many interesting questions demonstrated strong interest in the topic. Due to time, we didn’t get to answer all questions. Please see below answers to the questions posed.


Expand on the use of torrefaction for reducing the mass of biosolids and other feedstocks at source location for ease of transport to centralised gasification/pyrolysis? The transport of feedstock to be pyrolysed is a key economic challenge with biochar.

Torrefaction is a good way to reduce the moisture content and increase solids content. It can certainly help in reducing transportation cost as well as help improving process efficiency. However, initial solids content, calorific value, and transportation parameters (cost, distance, emissions etc.) will need to be considered for cost-benefit analysis. Also, selection of efficient torrefaction technology is also crucial as it can have impact on product quality, process efficiency and overall cost.


“Is it the case that the heavy metals in the biochar is higher than previous land-drying products? Why is this so and what’s the impact on the environment, transport and land application uses?”

Heavy metals are effectively concentrated through the drying and pyrolysis process. Studies have shown that heavy metals are bound into the biochar structure and have limited leaching and significantly lower potential for availability into the environment. These are promising laboratory results that will hopefully be replicated in longer term field trials.


Given the low-medium temp, how is PFAS destroyed? Does it include capture of air emissions and destruction via a higher temperature process?

At the Demonstration Production Plant stage, we will be closely examining the potential for PFAS destruction in the PYROCO reactor.  Pilot-plant demonstrated very low (not detectable levels) of PFAS in biochar which demonstrates 100% removal. Pyrolysis temperature which is relatively low will only help getting PFAS into the gas phase. PFAS destruction will be assured in gas phase in combustor/thermal oxidiser at high temperatures using pyrolysis gas as the energy source.


What’s the PFAS and microplastic removal performance of PYROCO?

The pilot plant biochar analysis confirmed PFAS not present in biochar which is 100% removal in solids. No gas phase PFAS testing undertaken in PYROCO pilot plant but existing thermal oxidisers at gasification plants have confirmed PFAS destruction of >99%. PFAS destruction depends on temperature, time and turbulence. Likewise with microplastics. More a gas treatment issue than a PYROCO reactor issue.


Is there any chemical input to the process?

The gas phase scrubber will require chemicals as part of the scrubber process. This is required for all thermal process. The PYROCO plant based on oxygen free pyrolysis will produce less NOx and SOx compared to gasification which introduces limited oxygen to the scrubber for PYROCO will be smaller and use less chemicals. No other chemicals required.


Is there any wastewater stream from the process?

Scrubber water discharge will be directed to the treatment plant inlet works subject to testing.


Clarify the air emission process treatment of PYROCO compared to conventional gasification/combustion?

Similar process to gasification only smaller due to reduced gas volume, NOx and SOx related to the pyrolysis absence of oxygen and lower relative temperature. Cyclone separator, Thermal Oxidiser, NOx removal, Heat Recovery, Scrubber, PM10 removal, Activated Carbon Filter, Exhaust Stack


“Is the C in biochar more stable at lower temperatures? It was my understanding that higher H and O content of biochar resulted in C that was less stable. Low temp manure-type biochar’s tend to have a much lower soil residence time (i.e. 100 years of less) than higher temperature lignocellulosic materials (100+ years). But I agree, higher O content results in greater functionality/ exchange sites.”

Correct. We look at the H/C and O/C ratio. The lower the H/C and O/C ratio, higher is the carbon stability. When you pyrolyse biosolids, you mainly remove volatiles which includes C,H,O,N and S. This results into increase in a fixed carbon with lower H and O. Van Krevelen is generally used for stability comparison.


What are the waste streams from the process and how are these managed?

  1. Scrubber water which will be directed to the treatment plant inlet works subject to testing. Scrubber water analysis shows that they don’t have a very high levels of impurities and it can be managed as trade wastewater.
  2. Flue gas which after scrubbing (gas cleaning) is exhausted to environment.


What is the planned drying process for biosolids in the demonstration production plant? Is it energy neutral?

We will have biosolids from indoor solar drier sheds and outdoor stockpile areas well in excess of the 27% solids content for energy neutral process. The dryer will receive sufficient heat from the heat recovery process so no external heat source will be required.


If the business case is compelling, do you need ACCUs?

No ACCUs needed for the business case and in our business case assumptions we have assumed carbon credit income as zero. Personally over the 20 year life of the PYROCO plant I would expect biochar produced from biosolids will attract a carbon credit from both private and government schemes.


Who do you expect to be the end users for the biochar (and why these end users) and was there a sale price for biochar ($/t delivered) assumed in the business case? If so, what was the sale price?

End uses of biochar range from agriculture, landscaping, construction and roads just to name a few. An external report commissioned by South East Water has estimated that biochar prices could be $200-5000/t depending on the application. We have assumed a $200/t biochar sale price in the business case. A positive business case is achieved a much lower sale price but market assessment determined $200 as the lower end market price.


Expand upon the regular O&M maintenance issues?

Since PYROCO fluidised bed approach has no moving parts O&M cost risk is reduced. The front end feedstock preparation needs careful design to mitigate O&M cost risk.


Expand upon the upfront managing of quality feed (logistics)?

This is currently in design phase. The feedstock requires 0.3-2 mm particle size which will be achieved via milling and sieving. This is well understood industrial technology and will be robustly design to manage O&M cost risk.


When does PYROCO become viable to implement (based on PFAS limits, biosolids application costs ($$), net zero carbon target, NOx emissions reduction)?

The business case BAU cost for biosolids stockpile and land application was $204/t biosolids at 50% dry solids. Estimate equivalent cost for PYROCO biochar option is $140/t. This excludes a $ value for Scope 1 emissions.


What is the implementation cost of the PYROCO plant (M&E and its OPEX)?

Assumes 7% of capital cost for annual maintenance plus one full time FTE.


How will it expand beyond South East Water?

We will provide access to the technology through a sub-licence DB (Design Built) or DBO (Design, Bulit and Operate).


Explain the bio-availability of P in biochar?

Bio-availability of P in biochar will be low. Therefore, it becomes a slow phosphorous release fertiliser and avoids its leaching and runoff as well. Same happens for nitrogen.


What has been the community response to this thermal process and its application to biosolids?  What emissions is there from the process?

The pilot plant was located at the Greater Western Water’s Melton Treatment Plant and had a small footprint so minimal community impact. The demonstration operational plant to be located at a South East Water wastewater facility will also be relatively small footprint. We anticipate the removal of biosolids stockpiles with associated intermittent odours will have a positive community impact as will the 80% volume reduction in biochar with associated vehicle movements. We estimate the net emissions reduction to be 2,300 t/CO2e if South East Water convert all its annual biosolids (6000 t/yr) to biochar based on PYROCO technology.


What is the minimum dry solids concentration required for the process and what is the impact of high moisture content on the energy demand?

The business case and energy balance is being built on 27-50% solids biosolids.  Higher water content will reduce the thermal efficiency and may require supplementary energy input.  Higher solids content will be beneficial as it will provide higher calorific value in the feedstock.


Do you perceive a risk of new EPA regulation coming in that will make application of biochar/ biosolids not possible or non-viable in current applications?

It is becoming increasingly restrictive to distribute biosolids to land.  The contaminant (especially contaminants of emerging concern) reduction in converting it to biochar is likely to ensure that its use in agriculture will continue to be likely.


What is used to fluidise the bed if additional air is not used?

For fluidisation we are using gas from gas producer.


There are many organisations, in Australia who have already developed stable pyrolysis and gasification processors. Has the team reached out to these industry leaders?

Yes, we are in active discussion with a number of other facilities in Australia and even overseas. None of these facilities have been specifically designed to operate on biosolids. Also to-date we have found that the fluid-bed pyrolysis reactor technology is unique and beneficial versus other plants in terms of energy transfer and efficiency and in terms of product quality.


Have you completed any studies measuring the GHG emissions from the pyrolysis process and from the land application of the biochar produced (methane, nitrous oxide, CO2)?

The business case compared the GHG emission from BAU based on the NGERS methodology and the PYROCO technology with energy consumption and carbon sequestration biochar production based on first principles. Pyrolysis high quality biochar to targeted degraded land with slow release P and N. Also the stable C in biochar will facilitate soil health improvement and increased carbon sequestration. We have not considered this potential carbon sequestration in the receiving soil in our calculations.


At what rate do metals and sulphur compounds foul the heat exchanger?

The pyrolysis temperature is low and hence metals emissions are very minimal in the gas phase. Therefore, there are relatively less chances of fouling (via deposition of alkali/alkaline earth metal sulphates or chlorides) in the backend where temperature drops during heat recovery. Also, higher amount of alumino silicates present in biosolids restricts release of alkali and alkaline earth metals) by forming spinels of alkali/alkaline earth metal alumino silicates.


What temperature is used in PYROCO? Could you please explain how would PFAS be removed from biosolids if PYROCO is operated at low temperature?

PYROCO will be operated at 600-700 degree Celsius and adjacent thermal oxidiser will be operated at 900 degree Celsius. There is evidence that PFAS can be destructed at these conditions given enough time and flow.  Nevertheless, PFAS destruction will be assured in gas phase thermal oxidiser using pyrolysis gas as the energy source.


What hazardous areas implications are with pyrolysis compared with anaerobic digestion?

We completed a full HAZOP for the July 2021 Pilot Plant and will be undertaking one again for the Demonstration Production Plant. According to hazardous area classification (HAC), it falls under zone 2 and hence require proper hazard mitigation measures. This is very similar to any other thermal processes including coal-fired power plant and Anaerobic Digestor (AD) coupled with gas engine.


Was there a comparison of the percentage of emerging contaminants for influent waste, captured in separated solids to liquid waste to compare how much contaminants are removed?

To date an analyses are showing that (with the exception of heavy metals) all emerging contaminates are either removed or destroyed.


Will PYROCO biochar be able to generate ACCUs?



Would you say the pyrolysis of biosolids produces a more valuable product compared to gasification of biosolids? Is producing biochar or syngas a more valuable use of our biosolids?

A valuable product is just one desired outcome from pyrolysis (or gasification) of biosolids.  Contaminant destruction is also an important outcome.  Syngas production does not solve the contamination problem. Pyrolysis using the fluid bed technology in the absence of oxygen provides a higher carbon higher more consistently higher quality product compared to gasification.


“In the past sludge/biosolids in Victoria and Australia has been applied onto land. With the big drive to reach zero carbon emissions and the requirement for heat (energy) to achieve pyrolysis, why not utilize solar drying and then apply the dried sludge/biosolids at 80% dryness onto land?”

We are required to stockpile our biosolids for 1 to 3 years to ensure pathogen risk removed. We achieve 70% dry solids in our solar driers in summer at present and then stockpiled outdoors. Our biosolids therefore average 50-60% dry solids when being applied to land. The emissions associated with stockpiles and land application relate to Ammonia and NOx and to a much lesser extent transport. The production of biochar produces excess heat which will be used to dry feedstock to 80% dry solids so no external heat source required. We therefore benefit from carbon sequestration in the biochar and avoided emissions associated with stockpiling of biosolids and land application. The energy associated with the biochar plant operation and afterburners for exhaust gas management have been taken into account in the net emissions impact assessment. It is important to recognise the high emissions risk from biosolids stockpiles and land application associated with CH4 and NOx.

What has been the key to the partnership success with RMIT and what were the learnings?

The open and honest relationships have been key to building the relationship. Moving forward, applying more project management principles will be helpful. It would also have been valuable to run the pilot plant longer.


Is there more you can share about the high value carbon nano materials?

The value of the biochar can be further enhanced by exfoliating the high value carbon nano materials from the biochar surface to be sold in the market.


What are the advantages of PYROCO compared to PYREG?

PYROCO has higher heat and mass transfer coefficient given the fluidised bed and can achieve a uniform temperature for higher quality, is easier to scale up and offers overall higher process efficiencies.


Were the gas outputs analysed for pre cursor compounds?

Gas analysis was not completed as part of the pilot trial. Based on data from existing thermal plants, gas treatment requirements are well understood. Majority of the analysis suggested that PFAS, microplastics and other organic contaminants present in the biosolids were removed from the biochar.


How many hours of runtime has the plant experienced under demand load?

In July 2021 the pilot plant was run for a period of 30 days and approximately 120 total hours of pyrolysis mode.


Have you calculated a reduction in transports emissions?

There will be a volume reduction of up to approximately 80% depending on where biochar will be deployed.


What are the power requirements for the PYROCO solutions?

Six tonne per day pilot plant uses approximately 200-250 kilowatts axillary electricity requirement. The pilot plant will operate in a thermal energy neutral mode and will produce surplus waste heat.


Is there a minimum plant size for viability?

South East Water has considered the optimal plant size with respect to a modular solution, which was determined to be six tonne per day dewatered biosolids. Minimum viable size has not been assessed in detail but proposed current scale is deemed viable based on business case assessment.


Can you speak to the minimum solids content in relation to energy requirements?

If you have 25% biosolids and a minimum calorific value of 12 megajoules per Kg, the plant will generate sufficient thermal energy for drying.

How does biochar behave differently to biosolids in the soil?

Carbon in biochar is stable so no emissions once it is in the soil are very low, however, carbon emission will continue for biosolids in the soil. Biochar also has improved water retention and nutrients are slow release so very beneficial for degraded soils. Biochar can also benefit the soil structure and health hosting soil microorganisms.

Can you speak further to the destruction of PFAS?

To destroy PFAS, 2 seconds residence time above 900 degrees Celsius in a thermal oxidiser destroys PFAS. For the pilot plant, 0.6 seconds residence time resulted in the destruction of most of PFAS.


Which market will be targeted for biochar?

The intent will be to distribute biochar for broad acre application, which is a maturing market. An established market exists for road base and the compost industry initially. A potential market exists for activated carbon.


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