Sustainable bio-hydrothermal sequencing treatment for asbestos-cement wastes

Our plain-English summary of Sustainable bio-hydrothermal sequencing treatment for asbestos-cement wastes, by D. Spasiano, V. Luongo, M. Race, et al (Journal of Hazardous Materials, 2019).

The study

• Authors: D. Spasiano, V. Luongo, M. Race, A. Petrella, S. Fiore, C. Apollonio, F. Pirozzi, U. Fratino, A.F. Piccinni
• Journal: Journal of Hazardous Materials
• Published: 2019;364:256-263
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In this paper, the treatment of asbestos-cement waste (ACW) has been attempted by a dark fermentation (DF) pre-treatment followed by hydrothermal and anaerobic digestion (AD) treatments. During DF, glucose, employed as a biodegradable substrate, was mainly converted to H2-rich biogas and organic acids (OAs). The latter caused the dissolution of the cement matrix and the partial structural collapse of chrysotile (white asbestos). To complete the chrysotile degradation, hydrothermal treatment of the DF effluents was performed under varying operating conditions (temperature, acid type, and load). After the addition of 5.0 g/L sulfuric acid, a temperature decrease, from 80 °C to 40 °C, slowed down the treatment. Similarly, at 100 °C, a decrease of sulfuric, lactic or malic acid load from 5.0 g/L to 1.0 g/L slowed down the process, regardless of acid type. The acid type did not affect the hydrothermal treatment but influenced the AD of the hydrothermal effluents. Indeed, when malic acid was used, the AD of the hydrothermally treated effluents resulted in the highest production of methane. At the end of the AD treatment, some magnesium ions derived from ACW dissolution participated in the crystallization of struvite, an ecofriendly phosphorous-based fertilizer.

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In plain English

This laboratory study tested a three-step treatment on asbestos-cement waste (Eternit slate) containing chrysotile. First, sludge microbes fermented glucose with the waste, producing hydrogen and organic acids. These acids dissolved the cement but only 48% of the chrysotile's magnesium, so the chrysotile was only partly broken down. Second, the mixture was heated with sulfuric, lactic or malic acid. With 5 g/L sulfuric acid, the chrysotile's magnesium layers fully dissolved within 8 hours at 80 °C and 100 °C, but took 24 hours at 40 °C. At 100 °C, acid type made no statistically significant difference, and 1.0 g/L of acid did not complete dissolution. Third, 30-day digestion of bottles holding 9 mL of liquid treated with 5 g/L acid plus 91 mL of sludge yielded 312 mL of methane with malic, 301 mL with lactic and 269 mL with sulfuric acid. The final sludge contained struvite, a fertilizer mineral. The authors concluded the fibres were destroyed within 8 hours at 80 °C and 100 °C, adding that choosing the best acid and dose needs a cost analysis from at least pilot-scale experiments.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment on a treatment process for asbestos-cement waste (dark fermentation, then hydrothermal treatment, then anaerobic digestion); no people were studied
• Who was studied: An asbestos-cement waste sample from an Eternit slate containing chrysotile fibres, treated at 5 g/L. Sludge from a dairy-farm anaerobic digestion plant in Capaccio (Salerno, Italy) supplied the microbes
• Exposure: Chrysotile in asbestos-cement waste, treated by glucose dark fermentation and then by heating at 40 to 100 °C with sulfuric, lactic or malic acid at 0 to 5.0 g/L
• Main results:
  • During dark fermentation, the dissolved magnesium equalled only 48% of the total magnesium in the chrysotile, meaning the chrysotile was only partly dissolved
  • Average hydrogen production during dark fermentation was 246 mmol at 63 h and 489 mmol at the end of the process (133 h)
  • With 5 g/L sulfuric acid, the brucite-like sheets of chrysotile fully dissolved after 8 h at 80 °C and 100 °C, but only after 24 h at 40 °C
  • At 100 °C and the same acid load, acid type (sulfuric, lactic, malic) made no statistically significant difference to dissolution
  • More than 90% magnesium removal from chrysotile was reached after 4 h, 8 h and 12 h with acid at 5 g/L, 2.5 g/L and 1.25 g/L respectively. At 1.0 g/L, dissolution was not complete with any of the three acids
  • The digestion tests used effluents from treatment at 100 °C with 5 g/L acid. Each test mixed 9 mL of effluent with 91 mL of digester sludge and was kept at 38 °C for 30 days. Methane production was 312 mL with malic acid, 301 mL with lactic acid and 269 mL with sulfuric acid
  • X-ray analysis of the final digestion solids found struvite, with hydroxylapatite to a lesser extent, among other minerals
• The authors' conclusion: The authors concluded that complete destruction of the asbestos fibres was achieved within 8 h at 80 °C and 100 °C, and that lower temperatures needed longer treatment. They also concluded that proper management of the digestion sludge may lead to phosphorus-based fertilizers
• Limitations the authors state:
  • The authors stated that only a cost analysis based on at least pilot-scale experiments can identify the best acid type and load
  • The authors stated that producing fertilizer from the sludge is a hypothesis not yet tested

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Chrysotile.

Related studies

• Dark fermentation process as pretreatment for a sustainable denaturation of asbestos containing wastes — D. Spasiano (2018)
• Change of carcinogenic chrysotile fibers in the asbestos cement (eternit) to harmless waste by artificial carbonatization: petrological and technological results — M. Radvanec, L. Tuček, et al. (2013)
• Thermochemical destruction of asbestos-containing roofing slate and the feasibility of using recycled waste sulfuric acid — S.N. Nam, S. Jeong, et al. (2014)
• Neutralization of cement-asbestos waste by melting in an arc-resistance furnace — J. Witek, R. Kusiorowski (2017)
• Classification and management of asbestos-containing waste: European legislation and the Italian experience — F. Paglietti, S. Malinconico, et al. (2016)
• Crystal chemistry of the high temperature product of transformation of cement-asbestos — A. Viani, A.F. Gualtieri, et al. (2013)

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