Biochars from solid digestates as sorbing materials for metal(loid)s removal from water

Jätevesilietteen (SSD) ja kiinteän jätteen lietteen orgaaninen osuuden (OFMSWD) katsotaan tällä hetkellä olevan vaihtoehtoisia raaka-aineita biocharin tuotantoon käsittelyn jälkeisen korkean jäljelle jääneen kiinteän orgaanisen jätteen määränsä ansiosta. Kiinteän lietteen pyrolyysi tunnetaan vaihtoehtoisena menetelmänä, jolla edistetään orgaanisten jätteiden kierrätystä ja tuotetaan lisäarvoa tuottavia biotuotteita (esim. biochar). Yleisesti biochar on paljon alhaisempi sorptiokapasiteetti metalloid teihin verrattuna aktiivihiiliin. Siksi kemiallisen käsittelyn katsotaan olevan vaihtoehto biocharin pinnan ominaisuuksien parantamiseen ja täten paremman metall(oid)ien sorptiokyvyn indusointiin biocharin pinnalla. Tässä työssä, SSD ja OFMSWD pohjaiset biochar it käsiteltiin 2 M KOH:lla tai 10% H2O2:lla jonka jälkeen ne eräpestiin tai eräpestiin ja kolonnipestiin ultrapuhtaalla vedell'. Fysikokemialliset ominaisuudet mukaanlukien isoelektrisen pisteen pH:n (pHPZC), Brunauer-Emmet-Tellerin pinta-alan (SBET) ja kationinvaihtokapasiteetin (CEC) määriteltiin kaikille biochareille, tavoitteena liittää niiden paremmat pintaominaisuudet metall(oid)ien lisääntyneeseen sorptiokykyyn. Kaikkia biochareja käytettiin sen jälkeen kemiallisen käsittelyn ja biochar pesun vaikutuksen tutkimiseen Pb(II):n, Cd(II):n ja As(III, V):n sorptiokäyttäytymiseen eräsoprptiokinetiikan ja isotermian avulla. Lisäksi, As redox-tila jakauma (As(III) ja As(V)) As(III):n sorption aikana biochar pintaan ja neste yhdisteeseen määriteltiin käyttämällä kiinteä-nesteuuttoa ja sen jälkeistä nesteen kromatograafista analyysia. Tulokset osoittivat pHPZC:n, SBET:n ja CEC:n lisääntymisen biocharin kemiallisen käsittelyn jälkeen Pb(II):n, Cd(II):n ja As(V):n tehostetun sorptiokyvyn mukaisesti. Esimerkiksi maksimaalinen sorptiokapasiteetti (Qm) kasvoi 1,6 umol g⁻1:stä (As(V)) ja 15,4 umol g⁻1:stä (Cd(II)) raakaa SSD-biocharista arvoon 8,1 umol g⁻1 (As( V)) ja 306,1 μmol g⁻1 (Cd(II)) H2O2:n ja KOH-käsittelyn jälkeen (alussa pH 5,0). Samoin Pb(II):n Qm:ää lisättiin 31,4 μmol g⁻1:stä (raakaa SSD-biocharia) 121,9 μmol g⁻1:een H2O2-modifioidulla SSD-biocharilla. Pb(II):n sorptiokapasiteettia ei kuitenkaan määritetty KOH-käsittelyn jälkeen, koska Langmuir-isotermimallia ei saatu sopimaan kokeellisiin tuloksiin. Tämä osoittaa, että KOH-modifioidun SSD-biocharin riittämätön pesu voi haitata Pb(II)-sorptiota, joka johtuu liuenneista orgaanisista yhdisteistä, jotka voivat olla vuorovaikutuksessa Pb2+:n kanssa ja siten muodostaa Pb-ligandikomplekseja liuoksessa. Lisäksi As redox -jakauma osoitti suurta hapetusta (70%) As(III):sta As(V):hen KOH-modifioidussa SSD-biocharissa eräpesulla, kun taas As(III) hapetettiin osittain (7%) KOH-modifioitu SSD-biochar, jossa on erä- ja myöhemmät kolonnipestiin. Tämä korostaa pesumenettelyn tärkeää merkitystä metall(oid)in sorptiolle, erityisesti Pb(II):lle ja As(V):lle. As-uutto ja sen jälkeinen nestekromatografinen analyysi suoritettiin onnistuneesti As(III):n hapettumisen kvantitatiivisen palautumisen ja säilyttämisen saavuttamiseksi askorbiinihapon avulla. Sorptiokinetiikan aikana As(III) voi olla stabiili tai osittain hapettunut biochar käsittelystä riippuen. Lisäksi biochar materiaali indusoi voimakkaan As(III):n hapettumisen ja vähäisemmän hapettumisen liuenneiden yhdisteiden vapautumisella biocharista. Yhteenvetona voidaan todeta, että liete biocharit, joilla on kemiallinen käsittely ja oikeanlainen biochar pesumenettely, voidaan käyttää onnistuneesti sorbentteina Pb(II), Cd(II) ja As(III, V) sorptiokyvyn parantamiseksi. Lisäksi As redox-jakauma biocharilla ja nestemäisissä liuoksissa sorption aikana voidaan saavuttaa As-uutolla ja kromatografisella analyysillä, mikä antaa paremman käsityksen As(III):n ja As(V):n välisestä transformaatiosta biochar-neste-sorptiossa systeemissä.Sewage sludge digestate (SSD) and the organic fraction of municipal solid waste digestate (OFMSWD) are currently considered as alternative feedstocks for biochar production due to the high amount of the organic solid waste remaining at the end of the treatment. The pyrolysis of solid digestate is known as an alternative to promote the recycling of organic wastes and generate added-value bio-products (e.g. biochar). Generally, the digestate biochar has a much lower sorption capacity for metal(loid)s compared to activated carbons. Therefore, chemical treatment is considered as a potential option to improve the biochar surface properties and thus inducing a better sorption ability for metal(loid)s on the biochar surface. In this present work, the SSD and OFMSWD derived biochars were treated with 2 M KOH or 10% H2O2 followed by batch washing or batch and subsequent column washings with ultrapure water. The physicochemical properties including the pH of point of zero charge (pHPZC), the Brunauer-Emmett-Teller surface area (SBET) and cation exchange capacity (CEC) were determined for all the biochars in order to link their improved surface properties to the enhanced sorption ability for metal(loid)s. All the biochars were then used to study the influence of chemical treatment and biochar washing procedure on the sorption behavior of Pb(II), Cd(II) and As(III, V) through the batch sorption kinetics and isotherms. Moreover, the As redox state distribution (i.e. As(III) and As(V)) during the As(III) sorption onto the biochar surface and in liquid solution was determined by using solid-liquid extraction followed by liquid chromatographic analysis. Results showed increases of the pHPZC, SBET and CEC after chemical treatment of the biochar, in accordance with the enhanced sorption ability for Pb(II), Cd(II) and As(V). For instance, the maximum sorption capacity (Qm) was increased from 1.6 μmol g−1 (As(V)) and 15.4 μmol g−1 (Cd(II)) on the raw SSD biochar to 8.1 μmol g−1 (As(V)) and 306.1 μmol g−1 (Cd(II)) after the H2O2 and KOH treatment, respectively (at initial pH 5.0). Similarly, the Qm of Pb(II) was also increased from 31.4 μmol g⁻1 (raw SSD biochar) to 121.9 μmol g⁻1 on the H2O2 modified SSD biochar. However, the sorption capacity for Pb(II) was not determined after KOH treatment due to the failing of the Langmuir isotherm model to fit the experimental data. This indicates that insufficient washing of the KOH-modified SSD biochar can hinder the Pb(II) sorption due to the release dissolved organic compounds from this biochar that may interact with Pb2+ and thereby forming Pb-ligand complexes in the solution. In addition, the As redox distribution showed a large oxidation (70%) of As(III) to As(V) in KOH-modified SSD biochar with batch washing, while As(III) was partially oxidized (7%) in the KOH-modified SSD biochar with batch and subsequent column washings. This highlights an important role of washing procedure for sorption of metal(loid)s, particularly for Pb(II) and As(V). The As extraction followed by liquid chromatographic analysis was successfully established to quantitatively recover and preserve As(III) oxidation with the use of ascorbic acid. During the sorption kinetics, As(III) may be stable or partially oxidized depending on the biochar treatment. In addition, the oxidation of As(III) was strongly induced by the biochar material and to a lesser extent by the release of dissolved compounds from the biochar. In summary, digestate biochars with the chemical treatment followed by a proper biochar washing procedure can be successfully used as potential sorbents to enhance the Pb(II), Cd(II) and As(III, V) sorption capacity. Moreover, the determination of As redox distribution on the biochars and in liquid phase during the sorption process can be achieved through the As extraction and chromatographic analysis, providing a better understanding of the transformation between As(III) and As(V) in the biochar-liquid sorption system

Review of biochar role as additive in anaerobic digestion processes

because of the urgent need to provide renewable energy sources and efficiently manage the continuously growing amount of organic waste. Biochar (BC) is an extremely versatile material, which could be produced by carbonization of organic materials, including biomass and wastes, consistently with Circular Economy principles, and “tailor-made” for specific applications. The potential BC role as additive in the control of the many wellknown critical issues of AD processes has been increasingly explored over the past few years. However, a clear and comprehensive understanding of the connections between BC and AD is still missing. This review paper analyses and discusses significant references (review articles, research papers and international databases and reports), mostly published in the last 10 years. This review is aimed at addressing three key issues related to the better understanding of the BC role in AD processes: 1. Investigation of the influence of BC properties on AD performances and of their ability to counteract its main challenges; 2. Assessment of the optimal BC production chain (i.e. feedstock-pyrolysis-activation) to achieve the desired features; 3. Evaluation of the economic and environmental advantages connected to BC use in AD processes, compared to conventional solutions applied to address AD challenges

Biochars de digestats comme sorbants pour le traitement des eaux contaminées par des métal(loïde)s

Sewage sludge digestate (SSD) and the organic fraction of municipal solid waste digestate (OFMSWD) are currently considered as alternative feedstocks for biochar production due to the high amount of the organic solid waste remaining at the end of the treatment. The pyrolysis of solid digestate is known as an alternative to promote the recycling of organic wastes and generate added-value bio-products (e.g. biochar). Generally, the digestate biochar has a much lower sorption capacity for metal(loid)s compared to activated carbons. Therefore, chemical treatment is considered as a potential option to improve the biochar surface properties and thus inducing a better sorption ability for metal(loid)s on the biochar surface. The biochars were treated with 2 M KOH or 10% H2O2 followed by batch washing or batch and subsequent column washings with ultrapure water. The physicochemical properties including the pH of point of zero charge, the surface area and cation exchange capacity were determined for all the biochars in order to link their improved surface properties to the enhanced sorption ability for metal(loid)s. All the biochars were then used to study the influence of chemical treatment and biochar washing procedure on the sorption behavior of Pb(II), Cd(II) and As(III, V) through the batch sorption kinetics and isotherms. Moreover, the As redox state distribution (i.e. As(III, V)) during the As(III) sorption onto the biochar surface and in liquid solution was determined by using solid-liquid extraction followed by liquid chromatographic analysis. Results showed increases of the sorption ability for Pb(II), Cd(II) and As(V) after chemical treatment. For instance, the maximum sorption capacity (Qm) of Cd(II) was increased from 15.4 µmol g−1 on the raw SSD biochar to 306.1 µmol g−1 after the KOH treatment (at initial pH 5.0). Similarly, the Qm of Pb(II) was also increased from 6.5 mg g⁻1 (raw SSD biochar) to 25 mg g⁻1 on the H2O2 modified SSD biochar. However, the sorption capacity for Pb(II) was not determined after KOH treatment due to the failing of the Langmuir isotherm model to fit the experimental data. This indicates that insufficient washing of the KOH-modified SSD biochar can hinder the Pb(II) sorption due to the release dissolved organic compounds from this biochar that may interact with Pb2+ and thereby forming Pb-ligand complexes in the solution. This highlights an important role of washing procedure for Pb(II) sorption by the biochar. The As redox distribution showed a large oxidation (70%) of As(III) to As(V) in KOH-modified SSD biochar with batch washing, while As(III) was partially oxidized (7%) in the KOH-modified SSD biochar with batch and subsequent column washings. The As extraction followed by liquid chromatographic analysis was successfully established to quantitatively recover arsenic (i.e. As(III, V)). The oxidation of As(III) was strongly induced by the biochar and to a lesser extent by the release of dissolved compounds from the biochar. In summary, digestate biochars with the chemical treatment followed by a proper biochar washing procedure can be successfully used as potential sorbents to enhance the Pb(II), Cd(II) and As(III, V) sorption capacity. Moreover, the determination of As redox distribution on the biochars and in liquid phase during the sorption process can be achieved through the As extraction and chromatographic analysis, providing a better understanding of the transformation between As(III) and As(V) in the biochar-liquid sorption systemLes digestats des boues d'épuration (SSD) et les digestats de la fraction organique des déchets ménagers (OFMSWD) ont été récemment considérés comme des sources potentielles pour la production de biochars en raison des quantités grandissantes de digestats solides restant à la fin de la digestion anaérobie. La pyrolyse des digestats solides est connue comme une technique pour promouvoir le recyclage des déchets organiques et générer des bio-produits à valeur ajoutée (i.e. biochar). En outre, en raison d'une capacité de sorption des métal(loïde)s des biochars moins bonnes par rapport aux charbon actifs traditionnels, la modification chimique des biochars bruts est considérée comme une alternative pour améliorer les propriétés de surface des biochars et induire ainsi une meilleure capacité de sorption des métal(loïde)s. Les biochars ont été traités avec 2 M de KOH ou 10% de H2O2, suivis d'un lavage en batch seul ou batch combiné avec un lavage en colonne à l’aide d'eau ultrapure. Les analyses des propriétés de biochar, le pH du point de charge nulle, la surface spécifique et la capacité d'échange cationique ont été effectuées sur les biochars bruts et modifiés afin de relier leurs propriétés de surface au comportement de sorption vis-à-vis des métal(loïde)s. Tous les biochars ont ensuite été utilisés pour étudier l'influence du traitement chimique et de la procédure de lavage des biochars sur le comportement de sorption du Pb(II), Cd(II) et As(III, V) à travers l’étude de la cinétique et des isothermes de sorption. De plus, l’évolution de l'état redox As (i.e. As(III, V)) pendant la sorption de l'As(III) sur la surface du biochar et en solution liquide a été déterminée par extraction solide-liquide suivie d'une analyse en chromatographie liquide.Les résultats ont montré des augmentations de la capacité de sorption pour le Pb(II), le Cd(II) et l’As(V) après traitement chimique du biochar. Par exemple, la capacité de sorption maximale (Qm) (Cd(II)) a été augmentée de 15,4 µmol g−1 sur le biochar de SSD brut à 306,1 µmol g−1 après le traitement au KOH (au pH initial de 5,0). De même, la valeur de Qm du Pb(II) a augmenté de 6,5 mg g−1 (biochar de SSD) à 25 mg g−1 sur le biochar modifié par H2O2. Néanmoins, la capacité de sorption du biochar SSD modifié par KOH n'a pas été déterminée en raison de l’impossibilité de modéliser les données expérimentales avec le modèle de l’isotherme de Langmuir. Cela indique qu'un lavage insuffisant du biochar SSD modifié par KOH peut inhiber la sorption de Pb(II) en raison de la libération de composés organiques dissous de ce biochar pouvant interagir avec Pb2+ et ainsi former des complexes Pb-ligand dans la solution. Ceci met en évidence le rôle important de la procédure de lavage sur l’efficacité de la sorption du Pb(II) sur le biochar. L’étude de la distribution de l’état redox de l'arsenic a montré une oxydation importante (70%) de As (III) en As (V) dans le biochar SSD traité au KOH avec lavage par batch, tandis que l'As(III) a été partiellement oxydé (7%) dans le biochar SSD traité au KOH avec un lavage en colonne. L'extraction de l’arsenic fixé par les biochars suivie d'une analyse par chromatographie en phase liquide a été établie avec succès pour récupérer quantitativement de l'As(III, V) Il a été montré que l'oxydation de As(III) était fortement induite par le biochar et, dans une moindre mesure, par des composés dissous libérés par les biochars.En résumé, les biochars de digestat modifiés par traitement chimique suivi d'une procédure de lavage appropriée du biochar peuvent être utilisés avec succès comme sorbants de Pb(II), Cd(II) et As(III, V). En outre, l'évolution de la distribution redox de l’arsenic dans les biochars et les solutions liquides à l'aide de l'extraction de liquide solide et de l'analyse chromatographique a été déterminée. Cela permet de mieux comprendre la transformation entre As(III) et As(V) lors la sorption de l’arsenic sur les biochar

Biochars from solid digestates as sorbing materials for metal(loid)s removal from water

Jätevesilietteen (SSD) ja kiinteän jätteen lietteen orgaaninen osuuden (OFMSWD) katsotaan tällä hetkellä olevan vaihtoehtoisia raaka-aineita biocharin tuotantoon käsittelyn jälkeisen korkean jäljelle jääneen kiinteän orgaanisen jätteen määränsä ansiosta. Kiinteän lietteen pyrolyysi tunnetaan vaihtoehtoisena menetelmänä, jolla edistetään orgaanisten jätteiden kierrätystä ja tuotetaan lisäarvoa tuottavia biotuotteita (esim. biochar). Yleisesti biochar on paljon alhaisempi sorptiokapasiteetti metalloid teihin verrattuna aktiivihiiliin. Siksi kemiallisen käsittelyn katsotaan olevan vaihtoehto biocharin pinnan ominaisuuksien parantamiseen ja täten paremman metall(oid)ien sorptiokyvyn indusointiin biocharin pinnalla. Tässä työssä, SSD ja OFMSWD pohjaiset biochar it käsiteltiin 2 M KOH:lla tai 10% H2O2:lla jonka jälkeen ne eräpestiin tai eräpestiin ja kolonnipestiin ultrapuhtaalla vedell'. Fysikokemialliset ominaisuudet mukaanlukien isoelektrisen pisteen pH:n (pHPZC), Brunauer-Emmet-Tellerin pinta-alan (SBET) ja kationinvaihtokapasiteetin (CEC) määriteltiin kaikille biochareille, tavoitteena liittää niiden paremmat pintaominaisuudet metall(oid)ien lisääntyneeseen sorptiokykyyn. Kaikkia biochareja käytettiin sen jälkeen kemiallisen käsittelyn ja biochar pesun vaikutuksen tutkimiseen Pb(II):n, Cd(II):n ja As(III, V):n sorptiokäyttäytymiseen eräsoprptiokinetiikan ja isotermian avulla. Lisäksi, As redox-tila jakauma (As(III) ja As(V)) As(III):n sorption aikana biochar pintaan ja neste yhdisteeseen määriteltiin käyttämällä kiinteä-nesteuuttoa ja sen jälkeistä nesteen kromatograafista analyysia. Tulokset osoittivat pHPZC:n, SBET:n ja CEC:n lisääntymisen biocharin kemiallisen käsittelyn jälkeen Pb(II):n, Cd(II):n ja As(V):n tehostetun sorptiokyvyn mukaisesti. Esimerkiksi maksimaalinen sorptiokapasiteetti (Qm) kasvoi 1,6 umol g⁻1:stä (As(V)) ja 15,4 umol g⁻1:stä (Cd(II)) raakaa SSD-biocharista arvoon 8,1 umol g⁻1 (As( V)) ja 306,1 μmol g⁻1 (Cd(II)) H2O2:n ja KOH-käsittelyn jälkeen (alussa pH 5,0). Samoin Pb(II):n Qm:ää lisättiin 31,4 μmol g⁻1:stä (raakaa SSD-biocharia) 121,9 μmol g⁻1:een H2O2-modifioidulla SSD-biocharilla. Pb(II):n sorptiokapasiteettia ei kuitenkaan määritetty KOH-käsittelyn jälkeen, koska Langmuir-isotermimallia ei saatu sopimaan kokeellisiin tuloksiin. Tämä osoittaa, että KOH-modifioidun SSD-biocharin riittämätön pesu voi haitata Pb(II)-sorptiota, joka johtuu liuenneista orgaanisista yhdisteistä, jotka voivat olla vuorovaikutuksessa Pb2+:n kanssa ja siten muodostaa Pb-ligandikomplekseja liuoksessa. Lisäksi As redox -jakauma osoitti suurta hapetusta (70%) As(III):sta As(V):hen KOH-modifioidussa SSD-biocharissa eräpesulla, kun taas As(III) hapetettiin osittain (7%) KOH-modifioitu SSD-biochar, jossa on erä- ja myöhemmät kolonnipestiin. Tämä korostaa pesumenettelyn tärkeää merkitystä metall(oid)in sorptiolle, erityisesti Pb(II):lle ja As(V):lle. As-uutto ja sen jälkeinen nestekromatografinen analyysi suoritettiin onnistuneesti As(III):n hapettumisen kvantitatiivisen palautumisen ja säilyttämisen saavuttamiseksi askorbiinihapon avulla. Sorptiokinetiikan aikana As(III) voi olla stabiili tai osittain hapettunut biochar käsittelystä riippuen. Lisäksi biochar materiaali indusoi voimakkaan As(III):n hapettumisen ja vähäisemmän hapettumisen liuenneiden yhdisteiden vapautumisella biocharista. Yhteenvetona voidaan todeta, että liete biocharit, joilla on kemiallinen käsittely ja oikeanlainen biochar pesumenettely, voidaan käyttää onnistuneesti sorbentteina Pb(II), Cd(II) ja As(III, V) sorptiokyvyn parantamiseksi. Lisäksi As redox-jakauma biocharilla ja nestemäisissä liuoksissa sorption aikana voidaan saavuttaa As-uutolla ja kromatografisella analyysillä, mikä antaa paremman käsityksen As(III):n ja As(V):n välisestä transformaatiosta biochar-neste-sorptiossa systeemissä.Sewage sludge digestate (SSD) and the organic fraction of municipal solid waste digestate (OFMSWD) are currently considered as alternative feedstocks for biochar production due to the high amount of the organic solid waste remaining at the end of the treatment. The pyrolysis of solid digestate is known as an alternative to promote the recycling of organic wastes and generate added-value bio-products (e.g. biochar). Generally, the digestate biochar has a much lower sorption capacity for metal(loid)s compared to activated carbons. Therefore, chemical treatment is considered as a potential option to improve the biochar surface properties and thus inducing a better sorption ability for metal(loid)s on the biochar surface. In this present work, the SSD and OFMSWD derived biochars were treated with 2 M KOH or 10% H2O2 followed by batch washing or batch and subsequent column washings with ultrapure water. The physicochemical properties including the pH of point of zero charge (pHPZC), the Brunauer-Emmett-Teller surface area (SBET) and cation exchange capacity (CEC) were determined for all the biochars in order to link their improved surface properties to the enhanced sorption ability for metal(loid)s. All the biochars were then used to study the influence of chemical treatment and biochar washing procedure on the sorption behavior of Pb(II), Cd(II) and As(III, V) through the batch sorption kinetics and isotherms. Moreover, the As redox state distribution (i.e. As(III) and As(V)) during the As(III) sorption onto the biochar surface and in liquid solution was determined by using solid-liquid extraction followed by liquid chromatographic analysis. Results showed increases of the pHPZC, SBET and CEC after chemical treatment of the biochar, in accordance with the enhanced sorption ability for Pb(II), Cd(II) and As(V). For instance, the maximum sorption capacity (Qm) was increased from 1.6 μmol g−1 (As(V)) and 15.4 μmol g−1 (Cd(II)) on the raw SSD biochar to 8.1 μmol g−1 (As(V)) and 306.1 μmol g−1 (Cd(II)) after the H2O2 and KOH treatment, respectively (at initial pH 5.0). Similarly, the Qm of Pb(II) was also increased from 31.4 μmol g⁻1 (raw SSD biochar) to 121.9 μmol g⁻1 on the H2O2 modified SSD biochar. However, the sorption capacity for Pb(II) was not determined after KOH treatment due to the failing of the Langmuir isotherm model to fit the experimental data. This indicates that insufficient washing of the KOH-modified SSD biochar can hinder the Pb(II) sorption due to the release dissolved organic compounds from this biochar that may interact with Pb2+ and thereby forming Pb-ligand complexes in the solution. In addition, the As redox distribution showed a large oxidation (70%) of As(III) to As(V) in KOH-modified SSD biochar with batch washing, while As(III) was partially oxidized (7%) in the KOH-modified SSD biochar with batch and subsequent column washings. This highlights an important role of washing procedure for sorption of metal(loid)s, particularly for Pb(II) and As(V). The As extraction followed by liquid chromatographic analysis was successfully established to quantitatively recover and preserve As(III) oxidation with the use of ascorbic acid. During the sorption kinetics, As(III) may be stable or partially oxidized depending on the biochar treatment. In addition, the oxidation of As(III) was strongly induced by the biochar material and to a lesser extent by the release of dissolved compounds from the biochar. In summary, digestate biochars with the chemical treatment followed by a proper biochar washing procedure can be successfully used as potential sorbents to enhance the Pb(II), Cd(II) and As(III, V) sorption capacity. Moreover, the determination of As redox distribution on the biochars and in liquid phase during the sorption process can be achieved through the As extraction and chromatographic analysis, providing a better understanding of the transformation between As(III) and As(V) in the biochar-liquid sorption system

Biochars de digestats comme sorbants pour le traitement des eaux contaminées par des métal(loïde)s

Sewage sludge digestate (SSD) and the organic fraction of municipal solid waste digestate (OFMSWD) are currently considered as alternative feedstocks for biochar production due to the high amount of the organic solid waste remaining at the end of the treatment. The pyrolysis of solid digestate is known as an alternative to promote the recycling of organic wastes and generate added-value bio-products (e.g. biochar). Generally, the digestate biochar has a much lower sorption capacity for metal(loid)s compared to activated carbons. Therefore, chemical treatment is considered as a potential option to improve the biochar surface properties and thus inducing a better sorption ability for metal(loid)s on the biochar surface. The biochars were treated with 2 M KOH or 10% H2O2 followed by batch washing or batch and subsequent column washings with ultrapure water. The physicochemical properties including the pH of point of zero charge, the surface area and cation exchange capacity were determined for all the biochars in order to link their improved surface properties to the enhanced sorption ability for metal(loid)s. All the biochars were then used to study the influence of chemical treatment and biochar washing procedure on the sorption behavior of Pb(II), Cd(II) and As(III, V) through the batch sorption kinetics and isotherms. Moreover, the As redox state distribution (i.e. As(III, V)) during the As(III) sorption onto the biochar surface and in liquid solution was determined by using solid-liquid extraction followed by liquid chromatographic analysis. Results showed increases of the sorption ability for Pb(II), Cd(II) and As(V) after chemical treatment. For instance, the maximum sorption capacity (Qm) of Cd(II) was increased from 15.4 µmol g−1 on the raw SSD biochar to 306.1 µmol g−1 after the KOH treatment (at initial pH 5.0). Similarly, the Qm of Pb(II) was also increased from 6.5 mg g⁻1 (raw SSD biochar) to 25 mg g⁻1 on the H2O2 modified SSD biochar. However, the sorption capacity for Pb(II) was not determined after KOH treatment due to the failing of the Langmuir isotherm model to fit the experimental data. This indicates that insufficient washing of the KOH-modified SSD biochar can hinder the Pb(II) sorption due to the release dissolved organic compounds from this biochar that may interact with Pb2+ and thereby forming Pb-ligand complexes in the solution. This highlights an important role of washing procedure for Pb(II) sorption by the biochar. The As redox distribution showed a large oxidation (70%) of As(III) to As(V) in KOH-modified SSD biochar with batch washing, while As(III) was partially oxidized (7%) in the KOH-modified SSD biochar with batch and subsequent column washings. The As extraction followed by liquid chromatographic analysis was successfully established to quantitatively recover arsenic (i.e. As(III, V)). The oxidation of As(III) was strongly induced by the biochar and to a lesser extent by the release of dissolved compounds from the biochar. In summary, digestate biochars with the chemical treatment followed by a proper biochar washing procedure can be successfully used as potential sorbents to enhance the Pb(II), Cd(II) and As(III, V) sorption capacity. Moreover, the determination of As redox distribution on the biochars and in liquid phase during the sorption process can be achieved through the As extraction and chromatographic analysis, providing a better understanding of the transformation between As(III) and As(V) in the biochar-liquid sorption systemLes digestats des boues d'épuration (SSD) et les digestats de la fraction organique des déchets ménagers (OFMSWD) ont été récemment considérés comme des sources potentielles pour la production de biochars en raison des quantités grandissantes de digestats solides restant à la fin de la digestion anaérobie. La pyrolyse des digestats solides est connue comme une technique pour promouvoir le recyclage des déchets organiques et générer des bio-produits à valeur ajoutée (i.e. biochar). En outre, en raison d'une capacité de sorption des métal(loïde)s des biochars moins bonnes par rapport aux charbon actifs traditionnels, la modification chimique des biochars bruts est considérée comme une alternative pour améliorer les propriétés de surface des biochars et induire ainsi une meilleure capacité de sorption des métal(loïde)s. Les biochars ont été traités avec 2 M de KOH ou 10% de H2O2, suivis d'un lavage en batch seul ou batch combiné avec un lavage en colonne à l’aide d'eau ultrapure. Les analyses des propriétés de biochar, le pH du point de charge nulle, la surface spécifique et la capacité d'échange cationique ont été effectuées sur les biochars bruts et modifiés afin de relier leurs propriétés de surface au comportement de sorption vis-à-vis des métal(loïde)s. Tous les biochars ont ensuite été utilisés pour étudier l'influence du traitement chimique et de la procédure de lavage des biochars sur le comportement de sorption du Pb(II), Cd(II) et As(III, V) à travers l’étude de la cinétique et des isothermes de sorption. De plus, l’évolution de l'état redox As (i.e. As(III, V)) pendant la sorption de l'As(III) sur la surface du biochar et en solution liquide a été déterminée par extraction solide-liquide suivie d'une analyse en chromatographie liquide.Les résultats ont montré des augmentations de la capacité de sorption pour le Pb(II), le Cd(II) et l’As(V) après traitement chimique du biochar. Par exemple, la capacité de sorption maximale (Qm) (Cd(II)) a été augmentée de 15,4 µmol g−1 sur le biochar de SSD brut à 306,1 µmol g−1 après le traitement au KOH (au pH initial de 5,0). De même, la valeur de Qm du Pb(II) a augmenté de 6,5 mg g−1 (biochar de SSD) à 25 mg g−1 sur le biochar modifié par H2O2. Néanmoins, la capacité de sorption du biochar SSD modifié par KOH n'a pas été déterminée en raison de l’impossibilité de modéliser les données expérimentales avec le modèle de l’isotherme de Langmuir. Cela indique qu'un lavage insuffisant du biochar SSD modifié par KOH peut inhiber la sorption de Pb(II) en raison de la libération de composés organiques dissous de ce biochar pouvant interagir avec Pb2+ et ainsi former des complexes Pb-ligand dans la solution. Ceci met en évidence le rôle important de la procédure de lavage sur l’efficacité de la sorption du Pb(II) sur le biochar. L’étude de la distribution de l’état redox de l'arsenic a montré une oxydation importante (70%) de As (III) en As (V) dans le biochar SSD traité au KOH avec lavage par batch, tandis que l'As(III) a été partiellement oxydé (7%) dans le biochar SSD traité au KOH avec un lavage en colonne. L'extraction de l’arsenic fixé par les biochars suivie d'une analyse par chromatographie en phase liquide a été établie avec succès pour récupérer quantitativement de l'As(III, V) Il a été montré que l'oxydation de As(III) était fortement induite par le biochar et, dans une moindre mesure, par des composés dissous libérés par les biochars.En résumé, les biochars de digestat modifiés par traitement chimique suivi d'une procédure de lavage appropriée du biochar peuvent être utilisés avec succès comme sorbants de Pb(II), Cd(II) et As(III, V). En outre, l'évolution de la distribution redox de l’arsenic dans les biochars et les solutions liquides à l'aide de l'extraction de liquide solide et de l'analyse chromatographique a été déterminée. Cela permet de mieux comprendre la transformation entre As(III) et As(V) lors la sorption de l’arsenic sur les biochar

Assessing arsenic redox state evolution in solution and solid phase during As(III) sorption onto chemically-treated sewage sludge digestate biochars

International audienceThis work aimed to determine arsenic redox state distribution during As(III) sorption onto 14 chemically-modified biochars. A solid-liquid extraction protocol using phosphoric (0.3 M) and ascorbic (0.5 M) acids at 80 °C for 20 min was established to ensure a quantitative recovery and stability of As(III) during the extraction. During sorption experiments, the redox conversions of As occurred and As(III) was either stable or partially oxidized in solution. The As distribution strongly varies depending on the biochar chemical treatment performed as well as the selected washing procedures (batch versus column washings). As(III) oxidation was favored with the KOH-modified biochar washed in batch mode. This oxidation was mostly induced by the biochar solid compounds rather than by soluble compounds released in solution. The As redox state distribution of As sorbed onto the biochars was successfully assessed using the extraction procedure. Arsenic was predominantly sorbed as As(III) (76-92%) onto the biochars

Anaerobic Digestion of Fruit Waste Mixed With Sewage Sludge Digestate Biochar: Influence on Biomethane Production

International audienceThe main aim of this study was to evaluate the biomethane potential (BMP) of fruit waste by incorporating additives such as sewage sludge biochar at different inoculum-to-substrate ratios (ISRs) of 2, 1.5, and 1 (wt./wt.). The results showed an improvement in the maximum methane production by 13, 20, and 27% upon the addition of sewage sludge biochar produced at 350 • C for ISR of 2, 1.5, and 1 (wt./wt.), respectively, and an increase 12, 18, and 22% for the added biochar produced at 550 • C for ISR of 2, 1.5, and 1 (wt./wt.), respectively, compared to the BMP tests performed without the addition of biochar (i.e., the control). Biochar addition reduced volatile fatty acid (VFA) formation during the digestion of fruit waste as compared to the control reactor, which is a strong indication that the metabolic process of the system was streamlined to methanogenesis. The maximum methane yield for the tested fruit substrates was 285.7 mL CH4/g in the presence of biochar prepared at a low temperature (350 • C). This value is higher than one obtained with same amount of biochar prepared at a higher temperature (550 • C). The results from this study showed that the effectiveness of the anaerobic digestion process depends on the ISR, biochar dose, and the pyrolysis temperature used for the production of the sewage sludge digestate biochar

Changes of sewage sludge digestate-derived biochar properties after chemical treatments and influence on As(III and V) and Cd(II) sorption

International audienceThis work seeks to extend the knowledge on the effect of chemical treatment of sewage sludge digestate (SSD)-derived biochar for the As(III and V) and Cd(II) sorption ability using potassium hydroxide (KOH) or hydrogen peroxide (H2O2). Results showed the increases of the pH of point of zero charge, the Brunauer-Emmett-Teller (BET) surface area and cation exchange capacity (CEC) after chemical treatment of biochar. The sorption ability was enhanced from 1.6 μmol g−1 (As(V)) and 16.1 μmol g−1 (Cd(II)) on raw biochar to 8.5 μmol g−1 (As(V)) and 318.5 μmol g−1 (Cd(II)) on KOH-modified biochar. Furthermore, arsenic redox distribution showed a large oxidation (70%) of As(III) to As(V) in KOH-biochar with batch washing, while a partial oxidation (7%) was observed in KOH-biochar with batch and subsequent column washing. The washing procedures after KOH treatment play an important role on arsenic sorption, due to the release of phosphate (PO43−) as well as organic matter from the biochar that may subsequently lead to the oxidation of As(III) to As(V). Our findings highlight the potential influence of biochar on the redox transformation of As(III) to As(V) and therefore requires a careful assessment while investigating the fate of As in aquatic environments

Anaerobic digestion of fruit waste mixed with sewage sludge digestate biochar: Influence on biomethane production

The main aim of this study was to evaluate the biomethane potential (BMP) of fruit waste by incorporating additives such as sewage sludge biochar at different inoculum-to-substrate ratios (ISRs) of 2, 1.5, and 1 (wt./wt.). The results showed an improvement in the maximum methane production by 13, 20, and 27% upon the addition of sewage sludge biochar produced at 350°C for ISR of 2, 1.5, and 1 (wt./wt.), respectively, and an increase 12, 18, and 22% for the added biochar produced at 550°C for ISR of 2, 1.5, and 1 (wt./wt.), respectively, compared to the BMP tests performed without the addition of biochar (i.e., the control). Biochar addition reduced volatile fatty acid (VFA) formation during the digestion of fruit waste as compared to the control reactor, which is a strong indication that the metabolic process of the system was streamlined to methanogenesis. The maximum methane yield for the tested fruit substrates was 285.7 mL CH4/g in the presence of biochar prepared at a low temperature (350°C). This value is higher than one obtained with same amount of biochar prepared at a higher temperature (550°C). The results from this study showed that the effectiveness of the anaerobic digestion process depends on the ISR, biochar dose, and the pyrolysis temperature used for the production of the sewage sludge digestate biochar