Home > Carbon sink or swim: biochar win-win-win?

Carbon sink or swim: biochar win-win-win?

Project Number # 2073

Upcycling of biosolids into biochar as a win-win-win for environment, economy and community


Biosolids management is becoming an increased concern for the wastewater sector in recent times due to production of large volumes of biosolids, their higher processing/management costs, and the presence of emerging contaminants (Savan et al., 2020). 371,000 tonnes of dry biosolids is produced annually in Australia, out of which 67% ends up in agriculture use and 20% in land applications (ANZBP 2019). While biosolids can be a valuable resource due to the presence of organic carbon and nutrients; potential risks associated with heavy metals, pathogens and more importantly contaminants of emerging concern need to be appropriately managed. Owing to increased risk of land, air and water contamination by biosolids, effective management (or pre-treatment) of biosolids might be a pre-requisite in future before they are used for land application.  A contemporary approach of pre-treating biosolids to minimise risk of contaminants and recovering valuable resources (like biochar/ash and bioenergy) is thermo-chemical conversion. This involves biosolids being subject to controlled high temperature chemical processes either gasification (in presence of limited air supply) or pyrolysis (under inert oxygen free atmosphere).

Pyrolysis is carried out in oxygen free environment and the major products could be oil, syngas and biochar. Gasification is carried out under a partial oxygen environment (i.e. lower than stoichiometric requirement of combustion). Literature reports various applications of biochar/ash produced from pyrolysis and gasification.

The commercial applications and environmental, social and economic benefits of biosolids derived biochar/ash are not yet adequately identified, studied, and demonstrated in Australia and hence their potential remains unclear. Areas that require exploration include environmental and social risks and benefit analysis and identification of markets and potential price points of biosolids derived biochar/ash. Potential markets for biochar/ash could be agriculture as well as non-agriculture ranging from soil amendment, remediation, adsorbent, odour control, catalyst, energy storage. One example of potential environmental and social risks of using biosolids derived biochar/ash in agriculture sector as soil amendment is concentrated heavy metals in biochar/ash. It is important to consider, that not all biochar produced will be the same. Biochar produced from gasification and pyrolysis could be very different, with varying qualities. The reactor design and process conditions of these two processes, can have a direct impact on product stream composition and energy values. For example, if energy generation is intended purpose, the gasification process solid product stream will be ash, not biochar.

Even though detailed scientific and industrial studies focussed on these two technologies are available, there are no specific comprehensive studies or guidelines around biosolids pyrolysis or gasification, which can aid water industries in Australia to make informed decisions for technology selection. Therefore, it is essential that factsheets and frameworks are developed for assessing social, environmental and economic benefits of biosolids derived biochar/ash produced from pyrolysis and gasification. This will help wastewater utilities and the potential end-user of biochar/ash in making decision around the technology, biochar product quality and potential market application of the transformed products.

This project is part of our Whole Water Community of Interest


Identifying socio-economic-environmental benefits of biosolid derived biochar/ash

Biochar production from pyrolysis/gasification and its use as increasing soil carbon has been discussed as one of the most suitable low emissions technologies. The Australian Federal Government has identified increasing soil carbon as one of the major options to combat climate change. However, their socio-economic-environmental benefits are yet to be quantified in Australian as well as global context in order to realise potential of adopting biosolids to biochar route. Biochar for different applications will require different physcio-chemical properties such as functional groups, surface area, pH and cation exchange capacity. This project will develop factsheets around biosolids derived biochar for different applications (highlighting the requirement of specific physico-chemical properties) and develop an opinion based review article.

Understanding technological challenges

Biosolids can be converted to useful biochar, through the use of pyrolysis and gasification technologies. Both these processes are at different technology readiness levels (TRLs) and provide different product streams, with varying qualities, quality and energy compositions. Gasification is a 100 year old technology, and has different reactor configurations (fixed bed, fluidized bed, entrained flow, circulating dual fluid bed and plasma). All of these gasification systems have their own advantages and limitations. Advantages includes, good thermal efficiency, small pressure drop, feed stock flexibility, while drawback could include low syngas production, high tar formation and poor availability and long start up time of the engine. The selection of gasification technology should consider all these above-mentioned factors, along with feedstock quality, capacity and end use application. Pyrolysis is relatively younger than gasification. The benefit of pyrolysis over gasification is high quality biochar and higher carbon sequestration potential. The pyrolysis due to lower temperature operation is expected to have less metals and minerals into the gas phase and hence issues of slagging and fouling in the backend is expected to be less intensive compared to gasification. The gas yield and quality for pyrolysis will not be as good as gasification. The oil can be considered as a product but due to high nitrogen and oxygen content it requires further upgrade before any further use. Therefore, oil and gas vapours are generally recommended to be combusted and char is kept as a product by many technology providers.

Even though there is enough scientific evidence, that suggests biochar/ash produced from pyrolysis and gasification has potential to immobilise heavy metals or use as adsorbent or in construction, there are not many commercial operations in the world focusing on biosolids pyrolysis and gasification. In terms of the a regulatory framework, it is also unclear whether resultant biochar/ash from the process will be considered as a product or waste and how it will be treated across jurisdictions. The other main challenge with pyrolysis and gasification technologies is the secondary emissions of CO and other harmful contaminants such as SOx, NOx, NH3, SO2 HF, HCL, volatile organic compounds, dioxins, furans, heavy metals and particulate matters which will require extensive flue gas cleaning treatment. The pyrolysis and gasification processes will also produce wastewater containing mercury, PFASs, PAHs, PCBs, sulphates, chlorides and fluorides which requires further treatment or being sent back as an influent to the main wastewater treatment plant. For their acceptance as a trade wastewater, the guidelines of trade wastewater will need to be followed.

Even though, the potential benefits to gain from biochar production, significantly overweighs the limitations identified above, there is a lack of knowledge about gasification and pyrolysis technologies. Particularly in the Australian water sector where not much is understood about their ability to mange Australian biosolids. This limits their adoption at a commercial scale in Australia. Multiple factors need to be understood and considered according to the processing facilities requirement, while comparing and choosing the appropriate technology. This includes investigation of feedstock quality or any pre-treatment requirements, what is the sought out efficiency (Thermal/Electrical), pilot scale size (mass and energy flows), product quality, capital and operating costs, ease of operation (plant availability, maintenance pre-requisites), energy recovery feasibility (gas turbine /steam turbine integration), and contamination associated with the product streams.

Addressing environmental obligations

Biosolids are classified differently based on different State, Territory or National Guidelines. Environmental Protection Agencies (EPAs) are responsible for the development of guidelines for biosolids’ application (McLaughlin et al. 2007).  For example, in Victoria, waste is classified as industrial waste and priority waste. The waste treatment processing plant must classify, characterise, categorise the biochar product, in consistent with any designation issued by the EPA authority. The biochar and other effluents (fly ash, bottom ash, scrubber liquid) from the treatment facility must be categorized as hazardous and nonhazardous. Once categorised, the level of hazard needs to be determined, to enable further classification. Similarly, the flue gas emissions need to be defined or addressed according to guidelines provided in directive 2010/75/EU. Wastewater treatment industries, need to identify all product stream compositions and components, before conducting any trials, and also obtain necessary permits. However, there is no informative guideline that could help the treatment facility, to identify the environmental obligations and obtain necessary permits, before conducting any pilot trials. The project will study three different state EPA guidelines (NSW/ACT/VIC/Queensland) and identify commonalities or misalignment in them which will help brining regulators, water industry and technology providers on a same platform.

Overview of research program

The research program consists of 5 research projects as follows:

Project 1: Identifying opportunities for upcycling biosolids into biochar as a win-win for environment, economy and community.

Project 2: Identify common guidelines for categorising product stream in coordination with EPA officials.

Project 3: Develop standard operating and testing protocols, for different pyrolysis and gasification-based technologies.

Project 4: Shortlist Pyrolysis and Gasification technologies and evaluate them for participating industries biosolids samples.

Project description and Milestones

The project has been divided into 4 work packages (WPs). WPs descriptions are provided as below.

WP1: Establishing a missing link between technology, product and market for business case development for water sector

 Aims and Objectives

This project aims to develop factsheets around social, economic and environmental benefits of biosolids derived biochar/ash and identify risks, opportunities, markets and price points for various applications. Literature has reported several applications of biosolids derived biochar/ash, however their link to technology is missing. In this project an attempt will be made to establish links between technologies/processes, biosolids quality, socio-economic-environmental risks and benefits of biosolids to biochar route, biochar/ash properties and potential product markets.


Task 1: Understand different aspects of pyrolysis and gasification technologies and establish their link with biosolids and biosolids derived biochar

Detailed literature review will be conducted on potential applications of biosolids derived biochar/ash. As discussed earlier, different applications will require different feed stock properties. An attempt will be made to link different biochar/ash properties and their potential applications. Then technologies/processes will be reviewed as a next step to identify, which technology/process has the potential to produce certain type of biochar/ash. Biosolids type and potential variability in their quality will be reviewed thoroughly, with an aim to establish understanding, on how feedstock quality will affect technologies/processes, as well as resultant biochar/ash quality.

Task 2: Identify Opportunities and Gaps

Task 2 will mainly focus on identifying opportunities and gaps around applications of biosolids derived biochar/ash in agriculture and non-agriculture sectors  (i.e. construction material, building products, land scaping, catalyst, adsorbents). Major focus will be to perform environmental and social risks and benefit analysis with technologies and products and identification of markets and potential price points of biosolids derived biochar/ash. Task 2 will be performed using literature review, environmental risk assessment and customer or community focused surveys.

Task 3: Develop Factsheets

Information collected from tasks 1 and 2, will be utilised to develop informative factsheets for biosolids derived biochar/ash applications. The factsheets will provide glimpse of required feedstock quality, technology/process, operating conditions, and list of social, environmental, and economic factors for different applications. This will help water industry for developing a business case for biosolids conversion to biochar. The factsheets will be further converted into an assessment criteria for technology/process selection in project 3.

Task 4: Prepare Peer reviewed Opinion Article

Information derived from tasks 1, 2 and 3, will be used to develop an opinion article. The article will be return in the form of business case for Australian water industry for converting biosolids to biochar.

WP2: Develop guidelines for categorising product, waste and emission streams according to different state EPA definitions

Aims and Objectives

This project aims to develop guidelines for classifying various product, waste and emission streams produced from pyrolysis and gasification processes discussed in Project 1, in accordance with different state EPA requirements. As discussed earlier other than bioenergy, pyrolysis and gasification will produce flue gas and wastewater as potential emissions and waste streams respectively along with biochar, which may contain pollutants and contaminants. Different state EPAs will have different guidelines or codes to follow. The project will review 3-4 Australian state EPAs and develop flowcharts for the management and use of product, waste and emission streams. This will help Australian water industrial community, to pre-determine all regulatory requirements and obligations, before conducting any on site specific pilot-trials or integration activities.


Task 1: Identify different possible product, waste and emission stream components and compositions

Data from Project 1 will be used to identify different product streams for pyrolysis and gasification technologies. Literature data, process model and empirical correlations will be used to predict the compositions of each product stream, as a function of feed stock composition and technology utilised.

Task 2: Study different state EPA guidelines and identify opportunities and challenges for cross jurisdiction product acceptance

EPA guidelines from different state (VIC/NSW/ACT/Queensland) regulatory bodies will be studied and compared, to identify common classification and categorisation parameters. Comparison tables will be prepared to classify biochar and associated product streams, for cross jurisdiction application purposes, according to EPA guidelines across these states. EPA officials from different state-based regulators will be engaged to validate the developed comparison tables.

Task 3:  Develop Flowcharts, with list of required statutory approvals

Informative flowcharts will be developed for different technologies discussed in project 1. Product streams will be dissected based on guidelines discussed in project 2-task 2. A list of statutory pre-approvals, according to EPA requirements, that needs to be obtained prior to conducting any pilot scale trials, will be identified. EPA officials will be engaged, and the developed pre-approvals list will be vetted thoroughly. This list will be added as an appendix to the developed flow chart.

WP3: Develop selection criteria, testing protocol and standard trial framework for assessing different technologies

Aims and Objectives

There are more than 50 gasification and pyrolysis technology providers, globally. All these technologies differ from each other, on multiple factors, such as scalability, maturity, operation mode, feedstock variability, expected product type and quality, expected thermal/electrical efficiency, plant availability, and cost of installation and operation. Hence, it is vital to choose the right technology that fits the requirement of a particular wastewater treatment plant. Therefore, the aim of this project is to establish high level assessment criteria for the selection of technology and then develop appropriate testing protocol and standard trial framework for pilot-trialling of different technologies. The developed assessment criteria, testing protocols and trial framework will act as guidelines for the wastewater treatment plant, to choose and pilot-trial the most appropriate technology, suits their requirements.


Task 1: Development of high-level selection criteria

The factsheets developed in Project 1 will help establishing high level selection criteria for different technologies for different objectives and different type of biosolids. The selection criteria may include bioenergy production, energy neutrality, energy efficiency, high quality biochar production, carbon credits, contaminant destruction, environmental emissions reduction, meeting regulatory requirements, technology readiness level, commercial viability etc. This task will be performed using literature review and water industry partners and technology providers focused surveys.

Task 2: Development of testing protocols and standard trial framework

Once assessment criteria are established, then for each assessment criteria detailed testing protocols and standard trial framework will be developed. For example, to assess energy generation and neutrality, a detailed mass and energy balance related protocol will be developed, which will suggest measuring mass and energy data at various location of the plant. This will also help quantifying plant thermal/electrical efficiency. For assessing biochar quality, a series of analysis will be recommended. Examples may include pH, surface area, functional groups, cation exchange capacity, electrical conductivity, poly-cyclic aromatic hydrocarbons (PAHs), per- and ploy- fluoro alkyl substances (PFASs). For carbon credit estimation or forecasted carbon abetment, a measurement process and mass balance around carbon will be recommended. For environmental emissions, waste and emission streams characterisation and quantification protocols will also be developed.

WP4: Shortlisting of 3-5 technologies for conducting pilot-plant trials

Aims and Objectives

The objective is to identify, and shortlist technology providers for conducting pilot plant trials. The selection criteria, testing protocols and trial frameworks, developed in WP3, will be used in this process, to recommend an appropriate technology provider, who could deliver desired technical output (example: Product quality/Energy efficiency), under defined cost constraints, while addressing environmental obligations.


Task 1 – Seeking expression of interest (EOI) from technology providers via standard questioner prepared from the knowledge gained from WP1-3

Water industry partners will be involved in this process, to develop the questionnaire according to identified requirement or future pilot plant trial plans. Fact sheets developed in WP1- 3, will be used to finalise the standard questionnaires. This could be a targeted process, for example if requirement is for treating feedstock with high PFASs contamination, the questionnaire will be targeted towards technologies, which can destruct PFASs and produce high quality biochar. Similarly, if identified requirement is energy neutrality, the questionnaire will be targeted towards technologies, that could produce high quality syngas.

Task 2 – Assessment of submitted EOIs against key selection criteria developed in WP3

Selection criteria developed in WP3 -1, will be used to assess the EOIs. For example, if the EOIs were targeted towards energy production, criteria’s such as energy neutrality, energy efficiency, commercial viability, environmental emissions reduction, meeting regulatory requirements will be considered. In this process, Industrial partners will be continuously engaged in this process. The outcome of this collaborative exercise is expected to provide a list of top technology providers or processes, which are able to address the criteria’s discussed above.

Task 3 – Discussions with 3-5 shortlisted technology providers

In conjunction with collaborating industrial partner, shortlisted technology providers will be engaged. The shortlisted technology providers will be requested to provide business plan or cost estimates, against the testing protocols and trial framework developed in WP3-2.  Based, on the received data, a final technology provider, who could deliver both technical and environmental requirements, while addressing economic constraints, will be recommended.


ANZBP (2020) Australian Biosolids Statistics [Online]. Australian Water Association. https://www.biosolids.com.au/ guidelines/australian-biosolids-statistics/.

McLaughlin M, Warne MSJ, Stevens D, Whatmuff M, Heemsbergen D, Broos K, Barry G, Bell M, Nash D, Pritchard D (2007) Australia’s National Biosolid Research Program-how it came about, and what has it discovered? Water Practice Technol 2(4).

Savankumar Patel , Sazal Kundu , Pobitra Halder , Nimesha Ratnnayake, Mojtaba Hedayati Marzbali . Shefali Aktar,  Ekaterina Selezneva, Jorge Paz-Ferreiro , Aravind Surapaneni, C?´cero Ce´lio de Figueiredo ,Abhishek Sharma , Mallavarapu Megharaj , Kalpit Shah (2020). A critical literature review on biosolids to biochar: an alternative biosolids management option. Rev Environ Sci Biotechnol (2020) 19:807–841.

Waste disposal categories characteristics and thresholds, 1828.2, EPA Victoria,  https://www.epa.vic.gov.au/-/media/epa/files/publications/1828-2.pdf.

Waste classification assessment protocol, 1827.2, EPA Victoria,  https://www.epa.vic.gov.au/about-epa/publications/1827-2

DIRECTIVE 2010/75/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 24  November 2010 on industrial emissions. https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:334:0017:0119:en:PDF