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Der Beitrag Biochar – a scalable solution in the fight against PFAS erschien zuerst auf PYREG GmbH.

Sources of PFAS contamination include paper mills, landfills, firefighting training facilities and fluorochemical plants. After decades of use, PFAS are ubiquitous in soils, groundwater and surface water. This puts pressure on wastewater treatment plants to adequately treat waste streams to prevent further spread of PFAS chemicals and increases pressure to remediate contaminated soils. This is where biochar comes into play.

Source: https://www.lemonde.fr/en/les-decodeurs/article/2023/02/23/forever-pollution-explore-the-map-of-europe-s-pfas-contamination_6016905_8.html

Scientific research has demonstrated that PFAS are eliminated by the process of pyrolysis. Kundu et al. (2021) found that > 90 % of PFOS and PFOA in sewage sludge were destroyed in a pyrolysis-combustion integrated process. Evidence from the US EPA Office of Research and Development (2021) carried out on the US-based company Bioforcetech’s commercially installed PYREG pyrolysis plant shows that pyrolysis at 600 °C for 10 minutes and combustion of pyrolysis gases at 850 °C eliminate PFAS from sewage sludge. Bioforcetech (2021) has reported 38 PFAS compounds that were all kept at or removed to below detection limit in the biochar in their pyrolysis and pyrolysis gas burning process. At the Fårevejle wastewater treatment plant in Denmark, sewage sludge pyrolysis at a temperature of 650 °C and a residence time of more than 3 minutes has showed to eliminate all 7 PFAS compounds previously detected in the feedstock.

In addition to PFAS destruction Biochar made from sludges, used as a sorbent, binds already existent contaminants due to his high surface and properties. What is a sorbent ? Previous studies have postulated that high surface area, porosity, and high carbon content are important for the sorption of organic pollutants (Ahmad et al., 2014, Cornelissen et al., 2005; Hale et al., 2016; Zimmerman et al., 2004 ). Nowadays, activated carbon (AC), generally from fossil coal sources such as anthracite, is the most commonly used sorbent for soil remediation due to its high porosity and high carbon content (Hagemann et al., 2018). Biochar is an alternative to activated carbon, which can be costly and chemical and energy intensive to produce (Ahmed et al., 2019). The main advantage of biochar over AC is its greater sustainability, as demonstrated by an endpoint life cycle analysis (Sparrevik et al., 2011) due to its potential for carbon sequestration (Smith, 2016) and reduced use of chemicals (Zheng et al., 2019). Biochar is often produced from wood-based sources (Hale et al., 2016). However, from a circular economy perspective, it is at least as attractive to use lightly contaminated waste such as sewage sludge as a substrate for the production of biochar sorbents. Pyrolysis of sewage sludge to biochar is the possibility of a more sustainable waste management alternative to landfill or incineration, as it would remove many of the contaminants present in the sludge, including much of the PFAS (Sajjadi et al., 2019), and produce a sorbent for PFAS.

Sewage sludge biochars as effective PFAS-sorbents

In May 2023, there was now a groundbreaking study showing that biochar from raw and digested sewage sludge can be used as an effective sorbent for PFAS in most environmental contexts, with similar or better efficiencies than AC. This study is performed with biochar produced at Lindum AS (Drammen, Norway) by slow pyrolysis at 700 °C and a residence time of 20 minutes for WCBC and SSBC2 and 40 minutes for SSBC1 using Biogreen technology. “High porosity in the right size range and carbon content were probably the main parameters responsible for the high sorption strength observed in the sludge-derived biochars, together with some possible influence of amine functional groups.” (Krahn, Cornelissen et al. 2023).

According to Prof. Cornelissen’s research team, further studies should examine a larger range of biochar samples prepared at different pyrolysis temperatures to identify the characteristics ideal for PFAS sorption, such as surface area, pore volume, carbon content and mineral content (mainly Ca and Fe). Finally, studying the effect of activation of sludge chars on sorption strength could be useful for further improving their sorption properties.

Der Beitrag Pyrolysis not only eliminates PFAS from sewage sludge, the biochar also absorbs PFAS in contaminated soils erschien zuerst auf PYREG GmbH.

Computer-controlled process

The core of the PYREG technology is the patented reactor in combination with the downstream FLOX combustion chamber (“FLOX” stands for flameless oxidation). In the reactor, the raw material is heated largely in the absence of air at high temperatures of around 500 to 700 °C for several minutes.  The computer-controlled process parameters – such as speed of conveyance of the feed material, temperature and air supply, is the key to recycling success. In the process, the phosphorus remains completely available for plants. And moreover: This treatment of sewage sludge offers great potential for the removal of many pollutants of high ecological and human health impact.

Carbonization destroys feedstock pathogens

Sewage sludge originates mainly from human excrements. Naturally, the sludge contains spores, pathogens, and pyrogens, which are of public health concern.[1] Standard hygienization of sewage sludge (e.g. heating of the sludge to 70 °C), does not eliminate all these contaminants.

The process conditions of pyrolysis (> 500 °C for more than three minutes) are much harsher even than approved sterilization conditions. Accordingly, pyrolysis eliminates all pathogens[2] and pyrogens contained in sewage sludge – including bacteria, fungi, vira, spores, parasites, antibiotic resistance genes etc. The final product, i.e. the biochar, is free of threats for public health.

Pyrolysis eliminates micropollutants from sewage sludge

Increasing concern is raised regarding the spreading of sewage sludge on farmland, due to the presence of micropollutants in sludges. Recent scientific research has demonstrated that pyrolysis will destroy or remove several types of micropollutants:

Organic pollutants (e.g. pharmaceuticals, hormone disrupting molecules):

Scientific evidence shows that at sufficiently high pyrolysis temperatures (> 500 °C) and long durations (> 3 min), all reference organic contaminants and micropollutants were completely or nearly completely degraded or driven off the solid material. A study published in 2019 by the German Ministry of Environment (Bundesumweltamt)[3] analyzed the residues of various pharmaceutical biosolids after pyrolytic treatment above 500 °C. After the process, all of the investigated pharmaceuticals were below the detection limit. The authors conclude: “With thermo-chemical treatments (i.e. pyrolysis) a complete destruction of the pharmaceutical residues is achieved. No further technical treatment measures are necessary.”

PFAS:

Per- and Polyfluoroalkyl Substances (PFAS) are eliminated by the process of pyrolysis. Kundu et al. (2021)[4] found that > 90 % of PFOS and PFOA in sewage sludge were destroyed in a pyrolysis-combustion integrated process. Evidence from the US EPA Office of Research and Development (2021)[5] carried out on the US-based company Bioforcetech’s commercially installed PYREG plant shows that pyrolysis at 600 °C for 10 minutes and combustion of pyrolysis gases at 850 °C eliminate PFAS from sewage sludge. Bioforcetech (2021)[6] has reported 38 PFAS compounds that were all kept at or removed to below detection limit in the biochar in their pyrolysis and pyrolysis gas burning process.

PAH:

Spreading sewage sludge on agricultural land is very common in Europe, although sludges potentially contain elevated levels of toxic polycyclic aromatic hydrocarbons (PAH). Properly designed pyrolysis processes can eliminate these chemical compounds, resulting in biochar with a PAH content below limit values or even detection limits: Moško et al. (2021)[7] demonstrated that slow pyrolysis at > 400 °C removes more than 99.8 % of the studied PCB, PAH, endocrine-disrupting chemicals, and hormonal compounds. The authors state: “High temperature (> 600 °C) slow pyrolysis can satisfactory remove organic pollutants from the resulting sludge-char, which could be safely applied as soil improver”.

Pyrolysis eliminates microplastic from sewage sludge

Research indicates that sewage sludge is a sink for microplastic. Thus, effective reduction of the plastic fragments is critical for potential dispersal.[8] Ni et al. (2020)[9] found that “Polyethylene and polypropylene, the two most abundant microplastics in sewage sludge, were entirely degraded when the pyrolysis temperature reached 450 °C.” Total concentrations of microplastic were reduced from 550.8 – 960.9 to 1.4 – 2.3 particles/g at pyrolysis temperatures of 500 °C. No microplastic with a particle size of 10-50 μm remained.

To illustrate the behavior of plastic during high temperature treatment (for example during pyrolysis), the thermal decomposition curves of PE and PP are shown in Figure 1. PE and PP thermal degradation shows a dramatic mass loss between 400 °C and 500 °C, while above 500 °C “the material degraded completely without leaving any noticeable residue.”[10] PET, a highly relevant plastic type regarding sewage sludge, starts to decompose at a temperature above 450 °C and transitions to the gas phase. PET decomposition is terminated in less than one minute (α = 1) at temperatures above 500 °C[11]. The cracked gases are of high calorific value and can be used for energy production. Thus, the pyrolysis of sewage sludge is a good method to drastically reduce microplastic in the environment.

 Figure 1: TG scans of PE and PP measured at a constant heating rate in two different test environments: inert atmosphere and in air.[12]

Sources:

[1]  Huygens, D., Garcia-Gutierrez, P., Orveillon, G., Schillaci, C., Delre, A., Orgiazzi, A., Wojda, P., Tonini, D., Egle, L., Jones, A., Pistocchi, A. and Lugato, E., Screening risk assessment of organic pollutants and environmental impacts from sewage sludge management, EUR 31238 EN, Publications Office of the European Union, Luxembourg, 2022, ISBN 978-92-76-57322-7 (online), doi:10.2760/541579 (online), JRC129690.

[2]  Paz-Ferreiro, Jorge, Aurora Nieto, Ana Méndez, Matthew Peter James Askeland, and Gabriel Gascó. 2018. “Biochar from Biosolids Pyrolysis: A Review” International Journal of Environmental Research and Public Health 15, no. 5: 956. https://doi.org/10.3390/ijerph15050956

[3]  Bundesumweltamt (2019) Arzneimittelrückstände in Rezyklaten der Phosphorrückgewinnung aus Klärschlämmen, Umweltforschungsplan des Bundesministeriums für Umwelt, Naturschutz und nukleare Sicherheit, Forschungskennzahl 3715 33 401 0, UBA-FB 002724 (https://www.umweltbundesamt.de/sites/default/files/medien/1410/publikationen/2019-03-29_texte_31-2019_arzneimittelrueckstaende-klaerschlamm_v2.pdf)

[4]  Kundu, S., Patel, S., Halder, P., Patel, T., Marybali, M. H., Pramanik, B. K., Praz-Ferreiro, J., Figueiredo, C. C., Bergmann, D., Surapaneni, A., Megharaj, M., Shah, K., Removal of PFASs from biosolids using a semi-pilot scale pyrolysis reactor and the application of biosolids derived biochar for the removal of PFASs from contaminated water, Environ. Sci.: Water Res. Technol., 2021, 7, 638–649

[5]  Gullet, B., EPA PFAS innovative treatment team (PITT) findings on PFAS destruction technologies, EPA Tools & Resources Webinar February 17, 2021

[6]  https://ccag.ca.gov/wp-content/uploads/2020/02/BFT_FEB_2020-1.pdf

[7]  Moško J, Pohořelý M, Cajthaml T, Jeremiáš M, Robles-Aguilar AA, Skoblia S, Beňo Z, Innemanová P, Linhartová L, Michalíková K, Meers E. Effect of pyrolysis temperature on removal of organic pollutants present in anaerobically stabilized sewage sludge. Chemosphere. 2021 Feb;265:129082. doi: 10.1016/j.chemosphere.2020.129082. Epub 2020 Nov 23. PMID: 33309446

[8]  Charles Rolsky, Varun Kelkar, Erin Driver, Rolf U. Halden, Municipal sewage sludge as a source of microplastics in the environment, Current Opinion in Environmental Science & Health, Volume 14, 2020, Pages 16-22, ISSN 2468-5844, https://doi.org/10.1016/j.coesh.2019.12.001.

[9]  Ni, B., Zhu, Z., Li, W., Yan, X., Wei, W., Xu, Q., Xia, Z., Dai, X., & Sun, J. (2020). Microplastics Mitigation in Sewage Sludge through Pyrolysis: The Role of Pyrolysis Temperature. Environmental Science and Technology Letters, 7, 961-967.

[10]  Sudip Ray, Ralph P. Cooney, chapter 9 – Thermal degradation of polymer and polymer composites, Myer Kutz, Handbook of environmental degradation of materials (third edition), william Andrew publishing, 2018, pp. 185-206, https://doi.org/10.1016/B978-0-323-52472-8.00009-5

[11]  Osman, A.I., Farrell, C., Al-Muhtaseb, A.H. et al. Pyrolysis kinetic modelling of abundant plastic waste (PET) and in-situ emission monitoring. Environ Sci Eur 32, 112 (2020). https://doi.org/10.1186/s12302-020-00390-x https://www.researchgate.net/figure/Reaction-progress-a-versus-the-temperature-for-the-PET-pyrolysis-where-the-coloured-and_fig1_343994995.

[12]  Sudip Ray, Ralph P. Cooney, chapter 9 – Thermal degradation of polymer and polymer composites, Myer Kutz, Handbook of environmental degradation of materials (third edition), william Andrew publishing, 2018, pp. 185-206, https://doi.org/10.1016/B978-0-323-52472-8.00009-5

Der Beitrag Carbonization of sewage sludge removes pollutants of high ecological and human health impact erschien zuerst auf PYREG GmbH.

Since 2015, PYREG has been installing its proven, sustainable and scalable biochar production plants at Waste Water Treatment Plants (WWTP) throughout Germany, Denmark, Czech Republic, Sweden, as well in the United States.  PYREG’s modular Systems have a small / compact footprint, which allows for integration with existing WWTP equipment such as sludge digesters, drying equipment, etc.

A significant revenue opportunity

Furthermore, the recovery of phosphorus in the wastewater treatment process ensures independence from costly mineral phosphorus imports that pollute the environment and the climate. Hence, what may seem like an additional financial burden for local authorities, is in reality, a significant revenue opportunity, as the carbonization recycling process not only produces P-fertilizer biochar, but also provides regenerative energy and enables valuable CO₂ removal certificates.  Hence, WWTPs can benefit from three revenue streams, whilst eliminating significant costs, such as sewage sludge transportation.

PYREG plants are now in operation at more than 50 locations around the world. And they also serve national environmental authorities, such as the US Environmental Protection Agency (EPA), as study and reference plants; an example is the PYREG plant operated at the Silicon Valley Clean Water (SVCW) WWTP, near San Francisco, California.

Biomass cycles

The heating of biomass in a low oxygen environment is called pyrolytic carbonization. In this process, organic carbon compounds are converted into a process gas and solid elemental carbon. While organic carbon compounds are degradable and natural decomposition releases greenhouse gases such as CO₂ or methane (CH₄) into the atmosphere, elemental carbon is stable for thousands of years. As long as this carbon is not burned, it does not react with any element and remains in its stable form as C. Thus, it can be considered a permanent carbon sink, when it is used as a soil amendment in arable farming.

The characteristics of the carbonization process

– A temperature and a process duration, high and long enough, respectively, to remove important impurities of the starting material such as viruses or micropollutants to “decompose” or “volatilize”
– The retention of important nutrients such as phosphorus in the solid phase.
– The ability to retain most of the carbon contained in the feedstock into stable carbon in the resulting biochar, thus providing a stable carbon sink. This process is referred Biochar Carbon Removal (BCR)

Autothermal carbonization

The PYREG process enables the conversion of organic residues to biochar with simultaneous recovery of thermal energy. The core of our technology is the PYREG reactor in combination with the downstream FLOX combustion chamber (“FLOX” stands for flameless oxidation). In the reactor, the raw material is heated largely in the absence of air at high temperatures of around 500 to 700 °C for several minutes.  The computer-controlled process parameters – such as speed of conveyance of the feed material, temperature and air supply, is the key to recycling success. The sewage sludge is almost completely pyrolytically carbonized in a controlled process. In the process, the phosphorus remains completely available for plants.

The volatile components are freed from entrained particles by hot gas filtration and burned flamelessly as hot process gas in the combustion chamber. The resulting combustion heat is partly used to heat the reactor, so that the process is thermally self-sufficient after the start-up phase.  Hence, PYREG Systems do not produce residues such as pyrolytic oil, which are costly and problematic to dispose of.

The FLOX combustion, with flue gas recirculation, in conjunction with hot gas filtration, allows very low flue gas emissions – especially low amounts of nitrogen oxides and dust – while simultaneously creating biochar and usable waste heat. Thus, PYREG Systems represent a NetZero technology, as they require significantly less energy to operate than the renewable energy they produce themselves.

Valuable output

The resulting excess heat is used for preparatory drying of the raw material or fed into heating networks. Alternatively, it can be used to generate electricity should that be a goal. The resulting biochar can be used as a high-quality fertilizer. This is possible because the carbonization process at more than 500 °C sanitizes and decontaminates the dried sludge. And: The phosphate recovery rate with this process is more than 98 %.

High fertilizing effect

The commitment to resource conservation requires us to recover phosphorus from sewage sludge to make it available to farmers. Of the methods for phosphorus recovery, carbonization at temperatures of 500 to 700 °C is among the most carbon efficient and results in a product that can used directly as a fertilizer for soil applications without further chemical extraction. In 2021, the Hessian State Laboratory (LHL) in Giessen, commissioned by the Hessian Ministry of the Environment conducted a trial to compare the plant availability of ten recycled phosphates with that of triple superphosphate (TSP) and with that of sewage sludge. The recyclates differed in terms of their production, composition and product form.
TSP is a calcium dihydrogen phosphate-containing fertilizer, which has a converted content of more than 46 diphosphorus pentoxide (P₂O₅). The phosphorus availability of the PYREG carbonate reached almost 90 % of the effect of the TSP (regrowth performance). This TSP fertilizer with 46% P₂O₅ costs currently between 700 and 800 €/t. Thus, municipalities will be able to generate revenues instead of incurring significant costs.

Climate protection benefits

Compared to conventional fertilizer, sewage sludge carbonates have a negative global warming potential. A study by the German Federal Environment Agency from 2019 comes to the conclusion that conventional fertilizer production in Germany emits about +1.2 kg CO₂-equivalents per kg of P₂O₅ [1]. Phosphate recovery processes such as precipitation in digested sludge or centrate or sewage sludge ash cause CO₂ emissions. Compared to the greenhouse gas potential of these processes PYREG carbonates from sewage sludge have a negative global warming potential of -4.01 kg CO₂ equivalents per kg P₂O₅. Consequently, the recovery of phosphate in the Pyreg process and the final application of the biochar contributes to the fight against global warming and to advance our goal of net zero.

In addition, the phosphate – recovery rate of the sewage sludge carbonates is more than 98%, which is within the range of other thermal treatments and is far better than that of precipitation processes with a recovery rate of less than 40 %.

No microplastics

Still the direct application of sewage sludge onto arable land is still a preferred method in some European countries. Researchers showed that sewage sludge contains significant amounts of microplastics. The elimination of microplastic contamination can only be achieved by high temperatures during treatment and a sufficiently long retention time. Ni et al. 2020 [2] stated that “polyethylene and polypropylene, the two most common microplastics in sewage sludge, are completely degraded at a carbonization temperature of 450 °C.”

No pathogens

Sewage sludge mainly consists of human excreta and naturally contains pathogens which by their very nature, are a significant risk to public health. The process conditions of pyreg carbonization of more than 500 °C for more than ten minutes are more extreme than those of the CDC (Centers for Disease Control and Prevention) of the U.S. Department of Health and Human Services.
According to the Steam Sterilization Disinfection and sterilization guidelines of the CDC, the minimum sterilization conditions are as follows 132 °C for four minutes or 250 °C to remove pathogens such as bacterial endotoxins under dry conditions (dry heat sterilization).

No contaminants

In a study published by the Federal Environmental Agency in 2019 pharmaceutical residues of various biosolids were analysed after pyrolytic treatments at over 500 °C[3]. After carbonization, all the parameters of the of the analysed pharmaceuticals were below the detection limit. The authors concluded that thermochemical treatments such as carbonization achieve complete destruction of the drug residues.

No PFASs

Another example: perfluorinated and polyfluorinated alkyl substances (PFAS) are very persistent, long-lived and accumulate in the environment and in our bodies. For this reason they are often referred to as “Forever Chemicals”. In this regard, a study by the US EPA from the year 2021 shows that the integrated carbonization and combustion process of the PYREG plant operated near San Francisco successfully eliminates PFASs [4].

Conclusion

The CO₂-emitting incineration of sewage sludge or the untreated application to soils  is no longer justifiable from the point of view of climate, environmental and health aspects. Instead, carbonization is a profitable process for recycling the valuable raw material(s) from sewage sludge and supplying it to agriculture as refined biochar.
For municipalities, this has several positive effects: they close material cycles, meet their decarbonization targets, generate significant amounts of renewable energy and create a high-quality, safe and environmentally friendly end product, which they can sell as an alternative to phosphorus fertilizer.

Sources:

1. Umweltbundesamt, „Ökobilanzieller Vergleich der P-Rückgewinnung aus dem Abwasserstrom mit der Düngemittelproduktion aus Rohphosphaten unter Einbeziehung von Umweltfolgeschäden und deren Vermeidung“, UBA Texte 13/2019, ISSN 1862–480
2. Ni et al., 2020, „Microplastics Mitigation in Sewage Sludge through Pyrolysis: The Role of Pyrolysis Temperature“, Environ. Sci. Technol. Lett. 2020, 7, 12, 961–967, https://doi.org/10.1021/acs.estlett.0c00740
3. Umweltbundesamt, „Arzneimittelrückstände in Rezyklaten der Phosphorrückgewinnung aus Klärschlämmen“, UBA Texte 31/2019
4. Environmental Protection Agency, „PFAS innovative treatment team (PITT) findings on PFAS destruction technologies“, February 17, 2021, https://www.epa.gov/chemical-research/pfas-innovative-treatment-team-pitt

Der Beitrag Waste-to-Value: From Sewage Sludge to Natural Fertilizer and Carbon Capture erschien zuerst auf PYREG GmbH.