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Recycling organic wastes into farmland faces a double challenge: increasing the carbon storage of soil while mitigating CO2 emission from soil. Predicting the stability of organic matter (OM) in wastes and treatment products can be helpful in dealing with this contradiction. This work proposed a modeling approach integrating an OM characterization protocol into partial least squares (PLS) regression. A total of 31 organic wastes, and their products issued from anaerobic digestion, composting, and digestion-composting treatment were characterized using sequential extraction and three-dimension (3D) fluorescence spectroscopy. The apportionment of carbon in different fractions and fluorescence spectra revealed that the OM became less accessible and biodegradable after treatments, especially the composting. This was proven by the decrease in CO2 emission from soil incubation. The PLS model successfully predicted the stability of solid digestate, compost, and compost of solid digestate in the soil by using only the characterized variables of non-treated wastes. The results suggested that it would be possible to predict the stability of OM from organic wastes after different treatment procedures. It is helpful to choose the most suitable and economic treatment procedure to stabilize labile organic carbon in wastes and hence minimize CO2 emission after the application of treatment products to the soil.

Hydrolysis is considered the limiting step during solid waste anaerobic digestion (including co-digestion of sludge and biosolids). Mechanisms of hydrolysis are mechanistically not well understood with detrimental impact on model predictive capability. The common approach to multiple substrates is to consider simultaneous degradation of the substrates. This may not have the capacity to separate the different kinetics. Sequential degradation of substrates is theoretically supported by microbial capacity and the composite nature of substrates (bioaccessibility concept). However, this has not been experimentally assessed. Sequential chemical fractionation has been successfully used to define inputs for an anaerobic digestion model. In this paper, sequential extractions of organic substrates were evaluated in order to compare both models. By removing each fraction (from the most accessible to the least accessible fraction) from three different substrates, anaerobic incubation tests showed that for physically structured substrates, such as activated sludge and wheat straw, sequential approach could better describe experimental results, while this was less important for homogeneous materials such as pulped fruit. Following this, anaerobic incubation tests were performed on five substrates. Cumulative methane production was modelled by the simultaneous and sequential approaches. Results showed that the sequential model could fit the experimental data for all the substrates whereas simultaneous model did not work for some substrates. © 2019

Anaerobic digestion is an increasingly widespread process for organic waste treatment and renewable energy production due to the methane content of the biogas. This biological process also produces a digestate (i.e., the remaining content of the waste after treatment) with a high fertilizing potential. The digestate composition is highly variable due to the various organic wastes used as feedstock, the different plant configurations, and the post-treatment processes used. In order to optimize digestate spreading on agricultural soils by optimizing the fertilizer dose and, thus, reducing environmental impacts associated to digestate application, the agronomic characterization of digestate is essential. This study investigates the use of near infrared spectroscopy for predicting the most important agronomic parameters from freeze-dried digestates. A data set of 193 digestates was created to calibrate partial least squares regression models predicting organic matter, total organic carbon, organic nitrogen, phosphorus, and potassium contents. The calibration range of the models were between 249.8 and 878.6 gOM.kgDM

International audience; Further characterization to properly assess the fate of organic matter quality during anaerobic digestion and organic carbon mineralization in soils is required. Organic matter quality based on its accessibility and complexity was employed to successfully classify 28 substrate/digestate pairs through principal components and hierarchical clustering analysis. The two first components explained 58.02% of the variability and four main groups were separated according to the feedstock type. A decrease in the accessibility (16–66%) and an increase in the complexity (34–98%) of the most accessible fractions was noticed. Besides, an increase of non-biodegradable compounds (17–66%) was globally observed after anaerobic digestion. The observed trends in the conversion of organic matter during anaerobic digestion have allowed to fill the gap in the modeling of the anaerobic digestion process chain. Indeed, partial least squares regressions have accurately predicted the organic matter quality of digestates from their inputs (R2 = 0.831, Q2 = 0.593) although the digester operational conditions (temperature and hydraulic retention time) were non-explicative enough. As a novel approach, the predicted digestate quality was used to feed a partial least squares regression model previously developed to predict organic carbon mineralization in soil. The combined models have predicted experimental organic carbon mineralization in soil (R2 = 0.697) with a model quality similar to the model for organic carbon mineralization in soil (R2 = 0.894). This is the first study that has successfully conceived an additional step in the prediction of organic matter fate from raw substrate before anaerobic digestion to soil carbon mineralization.

International audience; In recent years, anaerobic digestion (AD) of organic waste has raised as a winning strategy to produce energy and organic fertilizer. To optimize such a technology, mass balance is needed to model or simply monitor the process. This paper describes a theoretical framework allowing process indicators to be derived from estimates of organic waste elemental composition. Using a database of 128 typical feedstocks, semi-empirical equations are provided to estimate this elemental composition in case of a missing analysis. Then, a revised stoichiometric reaction of anaerobic digestion is proposed considering biomass yield and nitrogen. Biomass yield induces a more accurate estimation of the ammonia production and the volatile solids (VS) loss. The stoichiometric reaction allows the prediction of biogaz quality and mass loss and a correction factor for VS removal is proposed. The use of real case studies highlights the need to consider this correction (correction factor range: 1.01–1.2), especially for dry AD.

International audience; Defined as the residue from anaerobic digestion (AD), digestate refers to a set of materials with varied biochemical compositions. The objective of this study was to establish a digestate typology according to its fertilizing-value with data from literature and internal unpublished databases. To establish a relatively big database allowing the application of advanced statistics, usual fertilizing-value parameters were used: dry matter, volatile solids, C/N, C/Organic-N, total N (TN), total ammoniacal nitrogen (TAN), TAN/TN, total P and total K. Statistical analysis was performed on a dataset of 91 raw digestates, 34 solid fractions and 25 liquid fractions after separation. The resulting typology outlined that fertilizing-values are linked to AD feedstock and process. As case study regulations, no digestate (without any post-treatment) fulfilled French standards and the latest European Union regulation proposal on fertilizers. Options to reach regulations' product categories were discussed according to the typology. For the first time, a digestate typology was established based on fertilizing value, which can be a useful tool enhancing digestate management and policy making.

International audience; The simultaneous fate of organic matter and 4 endocrine disruptors (3 polycyclic aromatic hydrocarbons (PAHs) (fluoranthene, benzo(b)fluoranthene, and benzo(a)pyrene) and nonylphenols (NP)) was studied during the anaerobic digestion followed by composting of sludge at lab-scale. Sludge organic matter was characterized, thanks to chemical fractionation and 3D fluorescence deciphering its accessibility and biodegradability. Total chemical oxygen demand (COD) removal was 41% and 56% during anaerobic digestion and composting, respectively. 3D fluorescence highlighted the quality changes of organic matter. During continuous anaerobic digestion, organic micropollutants' removal was 22±14%, 6±5%, 18±9%, and 0% for fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, and nonylphenols, respectively. Discontinuous composting allowed to go further on the organic micropollutants' removal as 34±8%, 31±20%, 38±10%, and 52±6% of fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, and nonylphenols were dissipated, respectively. Moreover, the accessibility of PAH and NP expressed by their presence in the various sludge organic matter fractions and its evolution during both treatments was linked to both the quality evolution of the organic matter and the physicochemical properties of the PAH and NP; the presence in most accessible fractions explained the amount of PAH and NP dissipated.

International audience; This article aims at providing insight into the recirculation of (post-treated) solid digestate (SD) within digesters. Such a practice has been further identified as promising for anaerobically digesting recalcitrant feedstocks and for improving the energy efficiency of continuously stirred tank reactor (CSTR) agricultural biogas plants. Firstly, implementation strategies and the potential impact of SD direct recirculation on five CSTR biogas plants were investigated. According to the selected strategy, results indicated that plant methane production could rise by 0.6 to 6.3% or that a potential feedstock shortage of 64 to 1431 tons/year could be compensated. Secondly, the relevance of additional post-treatments for improving these initial results was evaluated. Thermo-chemical post treatments successfully increased SD biodegradability by 30 to 46% although their costs were not compensated by additional methane production. Short-term aerobic post-treatments failed in increasing SD biodegradability (up to 21% loss in biomethane potential). Hence, at full scale, a quick and direct recirculation of SD excluding any post-treatment appears to be the optimal condition to apply. Finally, conditions for the full-scale implementation of direct SD recirculation were theoretically studied. This practice has proved to increase the solid retention time by 11 to 38% and the plant total solid content by 6 to 20%. Thus, the critical point for its implementation should be the capacity of the plant mixing system to handle such an increase in solids. The relevance of SD recirculation needs to be determined on a case-by-case basis. Consequently, for the first time, this article provides a framework where the conditions can be identified for direct SD recirculation to be a relevant digestate management practice. Overall, this article demonstrates how direct SD recirculation can be a simple and low-cost mean for improving agricultural CSTR biogas plant efficiency. It also highlights the importance of achieving efficient digestate management in the biogas sector in order to reduce the costs of biogas production.

ispartof: FUEL vol:291 status: published

International audience; In recent years, anaerobic digestion of organic waste (OW) is rapidly appearing as a winning waste management strategy by producing energy and anaerobic digestates that can be used as fertilizers in agricultural soils. In this context, the management of the OW treatment process to maximize agro-system sustainability satisfying the crop nutrient demands represents the main goal. To investigate these traits, two protocols to assess the plant availability of digestate nitrogen (N) and phosphorus (P) were evaluated. With this aim, the N and P availability was determined on 8 digestates and 2 types of digestate-based compost from different OW via sequential chemical extractions (SCE). In addition, the digestates were tested in soil incubations and in plant pot tests with Italian ryegrass and compared with chemical fertilizer and a non-amended control soil. The N extracted from digestates via SCE was related to soil N mineralization and plant N recovery. The C: N ratio had negative impact on mineralized N and its recovery in shoots (ShootsN = −0.0085.(C/N)+0.172, r2 = 0.67), whereas water extractable mineral N was positevely related to the root N apparent recovery fraction (N-ARF) with (RootsN = 5E−5.Nsolublemin+0.0138, r2 = 0.53). The shoot P-ARF was positively correlated with the inorganic water extractable fraction of P (ShootsP =0.1153.H2O-Pi−0.2777.H2O-Po+0.0249, r2 = 0.71) whereas the root P-ARF was positively correlated with the less accessible fractions (RootsP = (b) 0.0955.NaHCO3-Po+0.0955.NaOH-Po-0.0584NaHCO3-Pi+0.0128, r2 = 0.8641). Feedstock digestate typology impacted the N and P recovery results leading to a better description of the typology properties and a first nutrients ARF prediction.

Agricultural biogas plants can suffer occasional feedstock shortages (poor harvest, storage …) and recirculation of solid digestate (SD) into digester has been identified as a simple way to offset methane production loss from these situations. Calculations show that recirculation of SD could offset for losses in plant methane production by up to 2.4%. In that context, two post-treatments were evaluated to enhance residual potential methane of agricultural SD. Effect of fungal solid state fermentation (SSF) of SD on subsequent methane production has never been explored before. It was hypothesized that: (i) ligninolytic fungi would be able to specifically use the complex fraction of SD for their growth and (ii) energy generation from the subsequent anaerobic digestion of the colonized SD will be enhanced. However, experiments showed that thermo-alkaline treatment of SD (used as alkalinization and sterilization process) and a high spawn level (20% w/w) were necessary to perform fungal SSF. Besides, the observed fungal activities on SD did not target specifically the most complex fractions. This led to uncontrolled organic matter losses and subsequent decreases of biodegradability and methane yield of SD (up to 50%). Therefore, fungal SSF of SD before its recirculation into biogas plants appeared not to be a viable option. Only thermo-alkaline treatment (CaO 2% w/w and 121 °C 30 min) enhanced methane yield of SD by 13% and decreased its complex fraction by 25%. Further studies on optimization of this post-treatment may enhance efficiency of SD recirculation strategy to offset plant methane production losses.

The aim of this chapter is to provide a description of the main methods used to assess biological transformation of biomass. It will address saccharification tests which account for the ability of biomass to release sugars during enzymatic hydrolysis. Biochemical methane potential (BMP) tests, which are widely used to assess anaerobic digestibility of biomass for the production of methane and BMP prediction by near infra-red spectroscopy will be presented. Biohydrogen potential (BHP), used to assess the ability to produce biohydrogen from biomass by dark fermentation will be described. Respirometry tests accounting for assessing aerobic degradability of biomass will be described. Incubation tests used to assess carbon and nitrogen degradation in soils will also be presented.

Direct landspreading of anaerobic digestates is the most common digestate management strategy. Nevertheless, digestate post-treatment can be unavoidable, especially for environmental services providers operating large-scale anaerobic digestion (AD) facilities. This review aims to assess the technical feasibility of achieving value-added products from digestates from urban and/or centralized AD plants (UC-AD). An exhaustive effort was dedicated to identifying and clarifying the available processing technologies and specific issues that can be related to UC-AD digestates. The valorization options were classified according to the final product destination. The result is a useful information source for assessing digestate valorization pathway given a local market and context. Agriculture was the first destination to be considered, as it allows a more direct closing of nutrient and carbon cycles. Several processes exist either for concentrating desirable characteristics of digestates, enhancing organic matter stability or producing pure and reformulated fertilizers. Thermal conversion processes are either under development or full-scale demonstration. They allow to valorize the solids through the production of biofuels and/or biochar and in the coming future, to start a whole biorefinery system. Similarly, biomass harvesting processes such as microalgae are under upscaling, enabling to valorize the nutrients of the digestate liquid phase while producing renewable biomass from sunlight. Several value-added products were already obtained in laboratory to pilot conditions from UC-AD digestates, for example, biopesticides, biosurfactants and composite materials. Adding to technical challenges, the quality variation of digestates, regulation barriers, public acceptance and the difficult access to new markets are among the main obstacles to UC-AD digestates valorization into value-added products.

The aim of this study was to investigate thermophilic (55 °C) aerobic digestion (TAD) as pre- and inter-stage treatment of sludge anaerobic digestion and to analyse the change in organic matter accessibility and complexity. Pre-treatment decreased methane yield (up to −70%), due to oxidation losses whereas inter-stage treatment slightly improved overall methane yield (+2.6%) and total COD removal (+5%) compared to control. Anaerobic degradability and COD removal in the second anaerobic stage significantly increased, by 13–40%. Organic matter fractionation showed that TAD led to an increase in sludge organic matter accessibility in all cases. Organic matter complexity, measured by fluorimetry, increased after TAD pre-treatment whereas it remained constant after inter-stage treatment. TAD was shown to be more efficient if applied to a more recalcitrant substrate and should thus be used as inter-stage treatment to avoid decreasing methane production.

The stability of digestate organic matter is a key parameter for its use in agriculture. Here, the organic matter stability was compared between 14 post-treated digestates and the relationship between organic matter complexity and biodegradability was highlighted. Respirometric activity and CH4 yields in batch tests showed a positive linear correlation between both types of biodegradability (R2=0.8). The accessibility and complexity of organic matter were assessed using chemical extractions combined with fluorescence spectroscopy, and biodegradability was mostly anti-correlated with complexity of organic matter. Post-treatments presented a significant effect on the biodegradability and complexity of organic matter. Biodegradability was low for composted digestates which comprised slowly accessible complex molecules. Inversely, solid fractions obtained after phase separation contained a substantial part of remaining biodegradable organic matter with a significant easily accessible fraction comprising simpler molecules. Understanding the effect of post-treatment on the biodegradability of digestates should help to optimize their valorization.

International audience; Digestate valorization is a key challenge for the feasibility of Anaerobic Digestion plants. In this study, humic-like substances (HLS) extracted from two digestates (sewage sludge and manure) were used for the biostimulation of hydroponic cultures of Lactuca sativa (lettuce) at different doses and compared to a commercial reference of leonardite HLS. Aerial biomass increase averages ranged from 7 to 30 %, but the results presented a high coefficient of variation (around 20 %). The commercial reference did not present statistically significant biomass yield improvement. The application of manure digestate extract at the higher fulvic-like acids dose (4.6 mg/L of dissolved organic carbon) presented the best and most significant results compared to the blank (Hoagland's solution only). However, this result cannot be strictly dissociated from the supplementary amounts of nutrients brought by the extracts. Additionally, all the products presented low heavy metal content compared to the recent EU regulation for biostimulants (2019/1009). This preliminary study confirmed the interest of extracting HLS from two digestates for application as biostimulants, shedding light on a new perspective for digestate valorization.

Séparation de phases et digestats : profils d’efficacité basés sur les intrants de digestion anaérobie et le choix du séparateur. Journées Recherche Innovation Biogaz Méthanisation - JRI 2018

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED [ADD1_IRSTEA]Valoriser les effluents et déchets organiques; International audience; Prediction of organic nitrogen mineralization into ammonium during anaerobic digestion is required for optimizing substitution of mineral fertilizer by digestates. The aim of this study was to understand organic nitrogen biodegradability and to investigate how it can be predicted from carbon biodegradability, and nitrogen bioaccessibility, respectively. Bioaccessibility was assessed using fractionation methods based on sequential extractions. Results showed that organic nitrogen was present in fractions whose bioaccessibility levels differed. Organic nitrogen and carbon biodegradability were also determined and compared. Results highlighted two groups of substrates: the first with an initial NH/TKN 30%, whose carbon and nitrogen biodegradability differ significantly. To enable prediction on all substrates, partial least square (PLS) regressions were carried out to link organic nitrogen bioaccessibility indicators to biodegradability. The models successfully predicted organic nitrogen biodegradability with a maximum prediction error of 10%.

International audience; In France, digestates from anaerobic digestion plants have to pass through homologation process or reach certain specific standards to be commercialized. In this study, valorisation processes regarding the production of added-value products from urban digestates are being explored. Humic Acids (HA) extracted from upcycled organic products such as composts have been demonstrated to improve soil fertility [1] and industrial applications have been proven more recently [2]. However, very few studies addressed HA-recovery from digestates [3]. Preliminary tests presented in this study were carried out in order to assess the feasibility of recovering HA from such urban digestates. The samples were a Food Waste/Cardboard digestate (FW/CB-D) from a pilot reactor and an Organic Fraction of Municipal Solid Waste digestate (OFMSW-D) from a full-scale plant. HA-extraction was tested on raw digestates and on its solid fractions after laboratory centrifugation. A practical approach for HA extraction was performed, adapted from [4]: NaOH 0.1 M was added until pH 12 was reached. The solution was stirred for 24h. After the alkaline extraction was performed, the digestate was centrifuged. The supernatant was filtered at 0.45 μm and acidified at different pH (1, 2, 3, 5 and 7). This solution was centrifuged to isolate the insoluble fraction containing HA. The recovered HA were redissolved for Fluorescence 3D analysis. Another acidification at pH 3 was performed where the precipitate was washed several times with distilled water and freeze-dried for Mid-Infrared analysis and calculation of recovering yields. Recovered HA were compared to HA isolated from a leonardite commercial solution and to references from the International Humic Substances Society (IHSS). Freeze-dried HA yields were low: from 3 to 4% (volatile solids:volatile solids) and 1 to 2%, for raw mass of FW/CB-D and OFMSW-D respectively. HA extracted from FW/CBD were observed to be similar to a river sediment reference from the International Humic Substances Society. The HA from OFMSW was closer to the HA isolated from the leonardite solution, but it presented more proteins in the 3D fluorescence spectra. When HAs were extracted from the solid fraction of digestates, HA extraction yields and spectra were almost unchanged. The pH for acidification played an important role in HA isolation. pH 1, 2 and 3 were observed to perform similarly (quality and quantity) but pH 5 and 7 resulted in less extraction of HA and poorer quality. Industrial feasibility of HA-like extraction from digestate would rely on extraction yields, product quality and residual matter management options. Experiments will be carried out in order to further evaluate the quality of the products regarding biodegradability and impact on root growth

International audience; Whether to enhance nutrients management for land spreading or as a previous-step for advanced treatments, digestate mechanical phase separation is present in many Anaerobic Digestion (AD) plants. A wide range of equipment is available including screw presses, centrifuges, belt presses and rotary drums. Up-to-date, few or maybe no study has critically regarded a database of digestate separation efficiency, mass balances and quality of outputs for different separators. To fill-up this gap, data from literature was gathered with an INRA’s database and operational data from SUEZ. From this database, two different analysis approaches were carried out. The first consisted to perform clustering analysis on complete fertilizing-value data of liquid fractions (LF, n = 38) and solid fractions (SF, n = 47) separately. The second approach consisted to calculate mass balances and separation efficiency indicators [1] when characterization of raw digestate and its associated LF and SF were available. The later consisted in digestate data from over 50 industrial scale digesters. The first approach resulted in a typology for LF (Figure 1A), and SF (Figure 2B). LF and SF were observed to be grouped according to AD feedstock (fibrous/non-fibrous) and separation equipment (low/high performance), with significant distinct fertilizing-values. The second analysis approach is still ongoing. Early results highlight the distinguishable performances of previously observed groups. A recurring lack of consistency on the mass balances of some elements such as nitrogen is observed and will be discussed.

Optimization of feeding strategy is an essential issue of anaerobic co-digestion that can be greatly assisted with simulation tools such as the Anaerobic Digestion Model 1. Using this model, a set of parameters, such as the biochemical composition of the waste to be digested, its methane production yield and kinetics, has to be defined for each new substrate. In the recent years, near infrared analyses have been reported as a fast and accurate solution for the estimation of methane production yield and biochemical composition. However, the estimation of methane production kinetics requires time-consuming analysis. Here, a partial least square regression model was developed for a fast and efficient estimation of methane production kinetics using near infrared spectroscopy on 275 bio-waste samples. The development of this characterization reduces the time of analysis from 30 days to a matter of minutes. Then, biochemical composition and methane production yield and kinetics predicted by near infrared spectroscopy were implemented in a modified Anaerobic Digestion Model n°1 in order to simulate the performance of anaerobic digestion processes. This approach was validated using different data sets and was demonstrated to provide a powerful predictive tool for advanced control of anaerobic digestion plants and feeding strategy optimization.

The recycling of biosolids and livestock manure in agriculture may lead to the introduction of antibiotic residues, i.e., parent molecule and transformation products, into amended soils. Their fate in soils can be approached through the assessment of their environmental availability. In this work, the environmental availability of sulfamethoxazole (SMX) and three transformation products (N4-acetyl-SMX, 3-amino-5-methylisoxazole, aniline) was assessed in soils amended with sludge compost or cow manure throughout a three-month incubation, using soft extractions with CaCl2, EDTA or cyclodextrin solutions. First, the freeze-storage of soil samples was shown to decrease the SMX extractability. The SMX extractability depended on the initial concentration, the amendment type and the extracting solution at day 0. From 1.9% up to 63% of the SMX total content was initially extractable. The lowest fractions were quantified in EDTA extracts in which the dissolved organic matter was the most complex and responsible for high matrix effects in mass spectrometry compared to CaCl2 extracts. The purification of cyclodextrin extracts highly reduced the matrix effects, but CaCl2 was considered as the most suitable extractant. SMX extractability strongly decreased after the first 8days of incubation to finally reach 0.4-0.8% after 84days, whatever the initial conditions. This high decrease could be related to humification observed through the increasing complexity of extracted dissolved organic matter. Very low levels of transformation products were quantified throughout the incubation period. The low environmental availability of SMX was mainly due to its sorption on soil organic matter and resulted in its low biotransformation in these amended soils.

Anaerobic digestion of organic residues can be used to produce both renewable energy (biogas) and organic fertilizer (digestate). The effect of posttreatments (liquid-solid separation followed or not by a composting step) and digestion process (wet or dry digestion) on physico-chemical and microbiological properties of 27 digestates originating from 19 French biogas plants was analysed. Results showed that post-treatments and digestion process had a significant effect on dry matter, organic matter and nutrients contents. Raw digestates from wet digestion and liquid fractions obtained after liquid-solid separation of digestates were similar to mineral fertilizers (dry matter content < 10%, nitrogen present mainly as ammonium form and potassium content of 57 g/kg of dry matter as mean value). Inversely, raw digestates from dry digestion and solid fractions of digestates were similar to organic fertilizers (dry matter content > 17% and nitrogen as organic form). Composting of solid fractions induced a decrease of the organic matter (40-52% of dry matter) and the total organic carbon contents (mean of 252 g/kg of dry matter) and an increase of dry matter content (> 40%). Statistical analyses lead to a classification of the digestates in three groups, based on their physico-chemical characteristics. A comparison with current French standards defining fertilizers for land application (NFU 44-051, NFU 44-095 and NFU 42-001) was also performed for each of the three groups of digestates. For composted solid fractions of digestate, values were in line with regulatory thresholds of NFU 44-051 and 44-095, whereas for the other digestates, dry matter content was too low and ammonium content too high. For NFU 42-001, dry matter, nitrogen and phosphorus contents were too low for most digestates. Furthermore, some digestates contained concentrations of Escherichia coli above regulatory limit concentrations of NFU 44-095 for land application. This study highlights the importance of physico-chemical and microbiological characterization of digestates to enrich current databases in order to improve the legislation for the use of digestates as organic fertilizer.; Dans un contexte de valorisation des digestats en tant que matière fertilisante pour un retour au sol, les caractéristiques physico-chimiques et microbiologiques de 27 digestats provenant de 19 sites français de méthanisation ont été mises en regard du posttraitement mis en oeuvre (séparation de phase avec ou sans compostage) et du type de procédé de méthanisation appliqué (en voie sèche ou liquide). Les résultats ont montré que les posttraitements et le type de digestion ont un effet significatif sur les taux de matière sèche, la matière organique et les éléments fertilisants. Ainsi, les digestats bruts de méthanisation en voie liquide et les fractions liquides possèdent des caractéristiques proches des engrais organiques (taux de matière sèche < 10%, azote majoritairement sous forme ammoniacale et concentration en potassium en moyenne de 57 g/kg de matière sèche), alors que les digestats bruts de méthanisation par voie sèche et les fractions solides présentent des caractéristiques proches des amendements organiques (taux de matière sèche > 17% et azote majoritairement sous forme organique). La stabilisation de la matière organique des fractions solides par compostage induit une diminution des taux de matière organique (40-52% de matière sèche) et des concentrations en carbone organique total (moyenne de 252 g/kg de matière sèche) et s’accompagne d’une augmentation du taux de matière sèche (> 40%). L’analyse statistique des données a permis de définir un classement des digestats en trois familles. Cette nouvelle typologie des digestats selon les posttraitements et le type de digestion pourrait être utile au choix de la filière de valorisation en qualifiant le caractère fertilisant ou amendant. Les valeurs obtenues pour chaque famille ont été comparées à celles exigées dans les normes relatives aux amendements organiques (NFU 44-051), composts de matières d’intérêt agronomique issues du traitement des eaux (NFU 44-095) ou engrais (NFU 42-001). Les fractions solides compostées sont généralement conformes aux critères d’évaluation des normes amendements et composts, alors que pour les autres digestats, le taux de matière sèche est trop bas et la concentration en ammonium trop élevée. Pour la norme engrais, les teneurs en matière sèche, en azote, voire phosphore, apparaissent insuffisantes pour la majorité des digestats étudiés. Par ailleurs, certains digestats présentent des concentrations élevées en Escherichia coli, ne respectant donc pas les seuils réglementaires de la NFU 44-095 pour pouvoir être utilisés en agriculture. Cette étude met en avant l’importance de la caractérisation physico-chimique et microbiologique des digestats en vue d’enrichir les bases de données pour faire évoluer la législation relative aux digestats de méthanisation.

Typologie des digestats de méthanisation à partir de paramètres usuels de valeur amendement/fertilisante. Journées Recherche et Industrie biogaz méthanisation - JRI 2017

International audience

Organic wastes are potential sources of both energy as well as crop production fertilizers. Correlations and models, involving organic matter characterization, have been previously described by several authors although there is still a lack in knowledge on the potential of simultaneous predictions of methane and organic fertilizer quality to optimize the wastes treatments. A methodology combining chemical accessibility and fluorescence spectroscopy was used to characterise 82 different organic wastes. Characterization data were compared with the biochemical methane potential (BMP), and with the biodegradable organic carbon obtained by soil incubation (C_bio). High correlations values were observed (R2 of 0.818 for BMP and 0.845 for C_bio). Model coefficients highlighted the differences and similarities between anaerobic and aerobic soil biodegradation, suggesting that anaerobic recalcitrant molecules could enhance soil fertility. This is a first step in the development of a tool for optimizing both types of valorisation according to agrosystem needs and constraints.

The development of anaerobic digestion involves both co-digestion of solid wastes and optimization of the feeding recipe. Within this context, substrate characterisation is an essential issue. Although it is widely used, the biochemical methane potential is not sufficient to optimize the operation of anaerobic digestion plants. Indeed the biochemical composition in carbohydrates, lipids, proteins and the chemical oxygen demand of the inputs are key parameters for the optimisation of process performances. Here we used near infrared spectroscopy as a robust and less-time consuming tool to predict the solid waste content in carbohydrates, lipids and nitrogen, and the chemical oxygen demand. We built a Partial Least Square regression model with 295 samples and validated it with an independent set of 46 samples across a wide range of solid wastes found in anaerobic digestion units. The standard errors of cross-validation were 90 mgO2⋅gTS−1 carbohydrates, 2.5 ∗ 10−2 g⋅gTS−1 lipids, 7.2 ∗ 10−3 g⋅gTS−1 nitrogen and 99 mgO2⋅gTS−1 chemical oxygen demand. The standard errors of prediction were 53 mgO2⋅gTS−1 carbohydrates, 3.2 ∗ 10−2 g⋅gTS−1 lipids, 8.6 ∗ 10−3 g⋅gTS−1 nitrogen and 83 mgO2⋅gTS−1 chemical oxygen demand. These results show that near infrared spectroscopy is a new fast and cost-efficient way to characterize solid wastes content and improve their anaerobic digestion monitoring.

International audience; The design and management of anaerobic digestion of sewage sludge (SS) require a relevant characterisation of the sludge organic matter (OM). Methods currently used are time-consuming and often insufficiently informative. A new method combining chemical sequential extractions (CSE) with 3D fluorescence spectroscopy was developed to provide a relevant SS characterisation to assess both OM bioaccessibility and complexity which govern SS biodegradability. CSE fractionates the sludge OM into 5 compartments of decreasing accessibility. First applied on three SS samples with different OM stability, fractionation profiles obtained were in accordance with the latter. 3D fluorescence spectroscopy revealed that the bioaccessible compartments were mainly constituted of simple and easily biodegradable OM while the unaccessible ones were largely made of complex and refractory OM. Then, primary, secondary and anaerobically digested sludge with different biodegradabilities were tested. Complexity revealed by 3D fluorescence spectroscopy was linked with biodegradability and chemical accessibility was correlated with sludge bioaccessibility.

The fate of organic matter during anaerobic digestion of sewage sludge was studied in batch systems thanks to a sequential chemical fractionation of the particulate phase coupled to fluorescence spectroscopy. Polycyclic Aromatic Hydrocarbons (PAHs) distribution within the organic pools was characterized from their analysis in the residual fraction after each extraction. Both methods were combined to understand the link between PAHs presence in organic pools and their spectral characterization after extraction. Two batch systems (sludge and inoculum mixture) were set up to study the impact of PAHs spiking on their fate and distribution. The sequential fractionation allowed us to extract and characterize about 50% of total Chemical Oxygen Demand. Moreover, fluorescence spectroscopy helped us to understand the organic pools evolution: the most easily extracted pools composed of protein-like molecules were highly degraded meaning that chemical accessibility mimics the bioaccessibility to degrading microorganisms. PAHs were present in all pools of organic matter but native PAHs were mainly present in low accessible (hardly extractable) fractions and during anaerobic digestion, they accumulated in the non-accessible (non extractable) fraction. Spiked PAHs were more dissipated during anaerobic digestion since spiking made them present in more accessible fractions. During the anaerobic digestion, contrary to native PAHs, spiked ones relocated toward less accessible organic fractions confirming the ageing phenomenon. PCA analysis showed that, in spiked mixture, PAHs presence in organic pools is linked to both PAHs physical–chemical properties and quality/quantity of the associated organic pools.

International audience; Within the AMEDEUS European project, a work package is dedicated to biological modelling of Membrane Bioreactors (MBR) processes as well as the impact of a pre-treatment by primary sedimentation on sludge production, sludge characteristics and permeate quality. The supposed interest of this pre-treatment is to decrease sludge production and to improve oxygen transfer by decreasing sludge concentration. Two MBR pilots were operated side by side under the same operating conditions, one fed by screened (1 mm screen) raw municipal wastewater and the other by primary settled raw municipal wastewater. This side by side operation allows a true comparison of the performances and model calibration. In average, screened water was observed to contain 30% more solids than settled water. In this study, the sludge age was fixed at 40 days and then modified to 15 days to calibrate the model on a broad range of operating conditions in order to validate and identify the biological activated sludge model (ASM) limits. With a sludge retention time (SRT) of 15 days, sludge production is less important in the pilot fed by settled water because of better bio-accessibility behaviour of settled water. In comparison with ASM1 default parameter values, calibrated parameters are quite different concerning nitrification and denitrification because of an improvement of oxygen transfer induced by lower floc size distribution (KOA=0.25–0.3g O2/m3, KOH=0.1g O2/m3). With a SRT of 40 days, model calibration is not validated and the pilot fed with screened water has a sludge production reduction that is less important than the one of the pilot fed by settled water where accumulation of inert organic matter is observed.

[EN] To enhance energy production from methane or resource recovery from digestate, anaerobic digestion processes require advanced instrumentation and control tools. Over the years, research on these topics has evolved and followed the main fields of application of anaerobic digestion processes: from municipal sewage sludge to liquid mainly industrial then municipal organic fraction of solid waste and agricultural residues. Time constants of the processes have also changed with respect to the treated waste from minutes or hours to weeks or months. Since fast closed loop control is needed for short time constant processes, human operator is now included in the loop when taking decisions to optimize anaerobic digestion plants dealing with complex solid waste over a long retention time. Control objectives have also moved from the regulation of key variables measured online to the prediction of overall process perfor- mance based on global off-line measurements to optimize the feeding of the processes. Additionally, the need for more accurate prediction of methane production and organic matter biodegradation has impacted the complexity of instrumentation and should include a more detailed characterization of the waste (e.g., biochemical fractions like proteins, lipids and carbohydrates)andtheirbioaccessibility andbiodegradability characteristics. However, even if in the literature several methodologies have been developed to determine biodegradability based on organic matter characterization, only a few papers deal with bioaccessibility assessment. In this review, we emphasize the high potential of some promising techniques, such as spectral analysis, and we discuss issues that could appear in the near future concerning control of AD processes., The authors acknowledge the financial support of INRA (the French National Institute for Agricultural Research), the French National Research Agency (ANR) for the "Phycover" project (project ANR-14-CE04-0011) and ADEME for Inter-laboratory assay financial support.

Organic matter characterization is the starting point to describe organic waste treatments mechanisms and to propose their modelling. Two relevant characterization methodologies were frequently used in the literature based on chemical extractions and fluorescence spectroscopy. However, they could not be generalised to all the type of wastes because of the different molecules targeted. Consequently, a new fractionation methodology was proposed to unify the characterization of a wide range of organic wastes. This new method was built by merging the two previously mentioned protocols to simulate bioaccessibility combined with 3D fluorescence spectroscopy to highlight the complexity of the extracted organic fractions. Sixty samples including representative samples used to validate the method were characterised according to their bioaccessibility and their complexity. Thanks to a principal component analysis, organic wastes were classified according to their nature, their complexity and accessibility. The applicability of this method in statistical or dynamic models is very promising.

International audience; Biochemical characterization of organic matter is becoming of key importance in wastewater treatment. The main objectives are to predict organic matter properties, such as granulation or flocculation, and hence treatment performance. Although standardized methods do exist for some organic molecules, such as volatile fatty acids or lipids, there are no standard methods to measure proteins and carbohydrates content, both biochemical families being the main components of sewage sludge. Consequently, the aim of the present work is to investigate the efficiency of several colorimetric methods to determine proteins and carbohydrates content as well as their compatibility with the sludge matrices. The different methods have been evaluated based on statistical criteria such as sensitivity, linearity, accuracy, rightness, and specificity using standard molecules such as Bovine Serum Albumin (BSA), glucose, cellulose and a certified reference product. The Lowry and the Dubois methods have been shown to be the best compromise for the considered criteria after having been tested on sewage sludge samples obtained from different locations in a wastewater treatment plant. In average, the measured volatile fatty acids, lipids, proteins and carbohydrates contents represented 80 +/- 7% (% volatile solids) of the organic matter. Proteins and carbohydrates represented in average 69 +/- 3%. This study underlined that the choice of a relevant methodology is of great importance for organic matter measurement. (C) 2012 Elsevier Ltd. All rights reserved.

International audience; A new model structure for the hydrolysis step is introduced in the IWA anaerobic digestion model no 1 (ADM1) in order to better represent the bioaccessibility of particulate organic matter. Two particulate organic matter fractions for waste activated sludge (WAS) samples were defined; a readily hydrolysable fraction (X-cr) and a slowly hydrolysable fraction (X-cs). These fractions were hydrolyzed according to a surface-limiting reaction. Batch anaerobic digestion test of untreated WAS was used to develop the model and calibrate the kinetic parameters and biomass concentrations. The validation was carried out with a similar substrate than the calibration but a thermal pretreatment was applied at two different conditions (110 degrees C and 220 degrees C). The behavior of thermophilic anaerobic digestion of WAS samples was effectively represented by the proposed model. No changes among kinetic parameter sets were done and the model is able to represent produced methane volume following the intrinsic changes of the WAS composition through the different thermal pretreatment conditions. Moreover, estimated parameters in 20 days of batch anaerobic digestion test were representative of continuous anaerobic digestion in a full-scale digester.

International audience; Membrane bioreactors (MBRs) have been increasingly employed for municipal and industrial wastewater treatment in the last decade. The efforts for modelling of such wastewater treatment systems have always targeted either the biological processes (treatment quality target) as well as the various aspects of engineering (cost effective design and operation). The development of Activated Sludge Models (ASM) was an important evolution in the modelling of Conventional Activated Sludge (CAS) processes and their use is now very well established. However, although they were initially developed to describe CAS processes, they have simply been transferred and applied to MBR processes. Recent studies on MBR biological processes have reported several crucial specificities: medium to very high sludge retention times, high mixed liquor concentration, accumulation of soluble microbial products (SMP) rejected by the membrane filtration step, and high aeration rates for scouring purposes. These aspects raise the question as to what extent the ASM framework is applicable to MBR processes. Several studies highlighting some of the aforementioned issues are scattered through the literature. Hence, through a concise and structured overview of the past developments and current state-of-the-art in biological modelling of MBR, this review explores ASM–based modelling applied to MBR processes. The work aims to synthesize previous studies and differentiates between unmodified and modified applications of ASM to MBR. Particular emphasis is placed on influent fractionation, biokinetics, and soluble microbial products (SMPs)/exo-polymeric substances (EPS) modelling, and suggestions are put forward as to good modelling practice with regard to MBR modelling both for end-users and academia. A last section highlights shortcomings and future needs for improved biological modelling of MBR processes.