Modeling the disintegration process in anaerobic digestion of tannery sludge and fleshing

"Mathematical modeling of anaerobic digestion (AD) is widely acknowledged as a powerful tool to v of the process and to support full-scale plant design, operation and optimization. In this work, a modified version of the IWA-ADM1 model is proposed to simulate the AD of tannery primary sludge (TPS) and fleshing, with special emphasis on the disintegration formulation. Multiple batch tests were performed at different inoculum/substrate VS-mass ratio, in order to evaluate the biodegradability of the two substrates and to provide experimental data for modeling purposes. Beside the necessary adjustments of substrates' COD fractionation, the structure modifications of the model focused on the disintegration and hydrolysis. The Contois Monod-based model was adopted to describe disintegration kinetics and the results were compared to the traditionally adopted first-order kinetic. The fate of particulate matter generated from biomass lysis was also questioned and a new model variable was introduced to account for cellular lysis products. Finally, a further modification differentiated substrate particulate matter into a readily and a slowly hydrolysable fraction. Batch tests confirmed that TPS and fleshing are suitable substrates for AD, exhibiting specific methane productions of: 0.26 ± 0.06 and 0.47 ± 0.05 Nm3 Kg−1VS, respectively. Modeling results showed that the proposed modifications were crucial for successful simulation of experimental data referring to fleshing, whereas did not have a significant effect on the results related to primary sludge degradation. This work is the first application of an IWA-ADM1-based model to AD of tannery waste.

Is "option B+" also being adopted in pregnant women in high-income countries? Temporal trends from a national study in Italy

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Towards an integrated removal of nitrogen and sulphur in biological treatments of tannery-like wastewaters

El present treball es centra en la integració de processos innovadors per a la remoció biològica de Nitrogen i Sofre. La desnitrificació parcial ha sorgit com a procés innovador per actuar en sinergia amb el anammox, com una alternativa a la nitritació parcial. En el cas de la desnitrificació impulsada per sulfurs, la desnitrificació autotròfica parcial (PAD) és una altra alternativa valuosa. La integració de la PAD amb el procés anammox (PAD/A) és d'especial interès per als tractaments d'aigües residuals riques en compostos de nitrogen i sofre, com les derivades de refineries de petroli, curtiembres i processament de peix. En el PAD/A, la desnitrificació autotròfica s'ha d'operar de manera que converteixi el nitrat a nitrit, per proporcionar el nitrit requerit pel anammox; la dessulfuració de l'biogàs podria aconseguir en la mateixa unitat, com a alternativa sostenible als tractaments fisicoquímics convencionals. En aquest marc, la present tesi va tenir com a objectiu aprofundir en l'aplicació de l'innovador procés PAD/A, en aigües residuals d'alta càrrega en nitrogno i sofre. El anammox i la PAD s'han estudiat en línies de treball paral·leles, abordant diferents qüestions relacionades amb els dos tractaments innovadors. Les aigües residuals de curtiembres es van seleccionar com a target per al PAD / A i es va estudiar la inhibició de la biomassa anammox. Es va aconseguir una ràpida posada en marxa d'un reactor gas-lift anammox amb càrregues volumètriques fins 0,48 gN-NO2-/l/d. Es va observar la precipitació mineral en els grànuls després de 130 dies d'operació. Es va realitzar un estudi extens per caracteritzar la composició de l'precipitat, així com el seu impacte en el rendiment de l'reactor, l'activitat de la biomassa i la població microbiana. Els resultats ofereixen coneixements útils per a l'estabilitat a llarg termini de sistemes granulars anammox. El possible efecte inhibidor dels compostos biorrefractarios i la salinitat de les aigües residuals de curtiembres es va avaluar mitjançant experiments en batch. Els resultats revelen que no es va poder atribuir una inhibició evident als compostos biorefractarios, mentre que es va observar una influència moderada deguda a el contingut de salinitat, que es pot abordar mitjançant una adequada aclimatació de la biomassa. Es conclou que no hi ha cap limitació tècnica per a l'aplicació de l'procés anammox en les aigües residuals de curtiembres. El PAD es va estudiar en un reactor CSTR, alimentat amb nitrat i sulfur. El treball va avaluar l'efecte de les ràtios S/N de l'influent i les condicions de SRT sobre el rendiment de l'acumulació de nitrits. Es va observar una acumulació reeixida de nitrit després d'una setmana de condició estable de limitació de S i es van assolir alts nivells de nitrit durant tot el treball experimental. En totes les fases experimentals es va observar una eficiència d'acumulació de nitrit de l'70-100%. Es va observar un clar canvi de població microbiana: el gènere Sulphurimonas va mostrar una abundància relativa de l'90% en l'inòcul i va ser superat gairebé del tot pel gènere Thiobacillus, després de 80 dies d'operació. S'especula que l'eficiència bioenergètica microbiana és una possible raó subjacent de l'canvi de població. Es va realitzar un estudi de termodinàmica per estudiar el canvi catabòlic observat. Els resultats indiquen que tot i que la desnitritación és una reacció molt favorable, la desnitratación podria ser una resposta energètica valuosa en cas de limitació de l'donador d'electrons. La estequiometria catabòlica de el procés es presenta de manera agregada com a eina de suport per al disseny i l'optimització de l'complex procés de desnitrificació autrotrófica, ja que ofereix totes les reaccions intermèdies i les possibles combinacions d'e-donador i e-acceptor.El presente trabajo se centra en la integración de procesos novedosos para la remoción biológica de Nitrógeno y Azufre, específicamente en el proceso de anammox y la desnitrificación autotrófica a base de sulfuros. La desnitrificación parcial ha surgido como proceso innovador para actuar en sinergia con el anammox, como una alternativa a la nitritación parcial. En el caso de la desnitrificación impulsada por sulfuros, la desnitrificación autotrófica parcial (PAD) es otra alternativa valiosa. La integración de la PAD con el proceso anammox (PAD/A) es de especial interés para los tratamientos de aguas residuales ricas en compuestos de nitrogeno y azufre, como las derivadas de refinerías de petróleo, curtiembres y procesamiento de pescado. En el proceso PAD/A, la desnitrificación autotrófica debe operarse de manera que convierta el nitrato en nitrito, para proporcionar el nitrito requerido por el anammox; la desulfuración del biogás podría lograrse en la misma unidad, como alternativa sostenible a los tratamientos físico-químicos convencionales. En este marco, la presente tesis tuvo como objetivo profundizar en la aplicación del novedoso proceso PAD/A, en aguas residuales de alta carga en nitrogno y azufre. El anammox y la PAD se han estudiado en líneas de trabajo paralelas, abordando diferentes cuestiones relacionadas con los dos tratamientos innovadores. Las aguas residuales de curtiembres se seleccionaron como target para el PAD/A y se estudió la inhibición de la biomasa anammox. Se logró una rápida puesta en marcha de un reactor gas-lift anammox con cargas volumétricas hasta 0,48 gN-NO2-/l/d. Se observó la precipitación mineral en los gránulos después de 130 días de operación. Se realizó un estudio extenso para caracterizar la composición del precipitado, así como su impacto en el rendimiento del reactor, la actividad de la biomasa y la población microbiana. Los resultados ofrecen conocimientos útiles para la estabilidad a largo plazo de sistemas granulares anammox. El posible efecto inhibidor de los compuestos biorrefractarios y la salinidad de las aguas residuales de curtiembres se evaluó mediante experimentos en batch. Los resultados revelaron que no se pudo atribuir una inhibición evidente a los compuestos biorefractarios, mientras que se observó una influencia moderada debida al contenido de salinidad, que se puede abordar mediante una adecuada aclimatación de la biomasa. Se concluye que no existe ninguna limitación técnica para la aplicación del proceso anammox en las aguas residuales de curtiembres. El PAD se estudió en un reactor CSTR, alimentado con nitrato y sulfuro. El trabajo evaluó el efecto de los ratios S/N del influente y las condiciones de SRT sobre el rendimiento de la acumulación de nitritos. Se observó una acumulación exitosa de nitrito después de una semana de condición estable de limitación de S y se alcanzaron altos niveles de nitrito durante todo el trabajo experimental. En todas las fases experimentales se observó una eficiencia de acumulación de nitrito del 70-100%. Se observó un claro cambio de población microbiana: el género Sulphurimonas mostró una abundancia relativa del 90% en el inóculo y fue superado casi por completo por el genero Thiobacillus, después de 80 días de operación. Se especula que la eficiencia bioenergética microbiana es una posible razón subyacente del cambio de población. Se realizó un estudio de termodinámica para estudiar el cambio catabólico observado. Los resultados indican que a pesar de que la desnitritación es una reacción muy favorable, la desnitratación podría ser una respuesta energética valiosa en caso de limitación del donador de electrones. La estequiometría catabólica del proceso se presenta de forma agregada como herramienta de apoyo para el diseño y la optimización del complejo proceso de desnitrificación autrotrófica, ya que ofrece todas las reacciones intermedias y las posibles combinaciones de e-donador y e-aceptor.The present work focuses on the integration of novel processes for the biological removal of Nitrogen (N) and Sulphur (S), specifically the anammox process and the sulphide-based autotrophic denitrification. In the recent years, partial denitrification (PD), i.e. the reduction of nitrate to the stage of nitrite typically over the oxidation of an organic electron donor, has emerged as a possible innovative process to act in synergy with anammox, as an alternative to partial nitritation whose long-term stability is reported to be critical in many applications. In case of sulphide-driven denitrification, partial autotrophic denitrification (PAD) is another valuable alternative. The novel integration of PAD with the anammox process (PAD/A) is of particular interest for the treatments of wastewaters highly rich in nitrogen and sulphur compounds, such as those derived from petroleum refineries, tanneries and fish processing. In the perspective of PAD/A implementation, S-driven denitrification should be operated in such a way to convert nitrate to nitrite only, in order to provide the nitrite supply required by the anammox biomass. Besides, biogas desulphurization could be accomplished in the same unit, as a sustainable alternative to the typically adopted chemical-physical treatments. Within this framework, the present thesis aimed at gaining insight on the application of the novel PAD/A process, in high-strength wastewaters. The anammox and the PAD process have been studied in parallel lines of work, addressing different issues related to the two innovative treatments. Industrial wastewater originated from vegetable tannery industry was selected as target stream for PAD/A implementation and the potential inhibitory drawbacks on the anammox granular biomass were studied. A fast start-up of an anammox gas-lift reactor was achieved with volumetric loads up to 0,48 gN-NO2-/l/d. Mineral precipitation on the granules' surface was observed after 130 days of operation. An extensive study was conducted in order to characterise precipitate composition as well as its impact on reactor performance, biomass activity and microbial population. The possible inhibitory effect of bio-refractory compounds and high salinity of vegetable tannery wastewater was assessed through batch test experiments. The outcomes revealed that no evident inhibition could be ascribed to the organic tannins-related fraction of the industrial matrix, whereas a moderate disturbance was observed for the salinity content, that can be addressed through proper biomass acclimation. Thereby, it is concluded that there is no technical limitation for the application of anammox process on vegetable tannery wastewaters. The PAD process was studied in a CSTR reactor fed by nitrate and sulphide. The work aimed at evaluating the effect of influent S/N ratios and SRT conditions on nitrite accumulation. Successful nitrite accumulation was observed after one week of stable and strict S-limiting condition and maintained throughout the experimental work. Nitrite accumulation efficiency of 70-100% and nitrite conversion efficiency of 70% were observed at all the experimental phases, calculated over the converted and influent nitrate, respectively. A clear microbial population shift was observed: Sulfurimonas showing 90% relative abundance in the seeding sludge was almost completely out-competed by Thiobacillus, after 80 days of operation. It is speculated that microbial bioenergetics is a possible underlying reason of the clear population shift. A thermodynamic-based study was conducted in order to study the catabolic change observed in the experimental work, i.e. from full denitrification to partial denitrification (denitratation). Results indicate that even though denitritation is a highly favourable reaction, the sole denitratation could be a valuable energetic response in case of electron donor limitation. Aggregated information on process catabolic stoichiometry are presented as support tool for process design and optimization of the complex S-based denitrification

The role of organic load and ammonia inhibition in anaerobic digestion of tannery fleshing

"In this study, batch tests on anaerobic digestion of tannery fleshing (skin-residue waste from hides’ tanning process), as sole substrate, have been performed with the purpose of assessing the effects of high substrate concentration and consequent ammonia inhibition on the process. Co-digestion with tannery primary sludge was also evaluated. According to the results, no inhibition occurred at initial organic load up to 5 gVS/l; an inhibited steady state was observed at 10 gVS/l, and system failure and instability was showed at the highest load of 20 gVS/l. Co-digestion with tannery primary sludge proved feasible, probably due to dilution effect. The observed ammonia and VFA accumulation over the experimental time-lapse is also discussed. Results are intended to increase knowledge on the technological application of anaerobic digestion of sole tannery fleshing, in the perspective of its application as on-site treatment solution for decentralised tanneries.

Integrating thermodynamics and mathematical modelling to investigate the stoichiometry and kinetics of sulphide oxidation-nitrate reduction with a special focus on partial autotrophic denitrification

In the present study, the stoichiometry of the Sulphur Oxidizing-Nitrate Reducing (SO-NR) process, with a focus on Partial Autotrophic Denitrification (PAD), has been evaluated through a thermodynamic-based study whereas a model-based approach has been adopted to assess process kinetics. Experimental data on process performance and biomass yields were available from a previous work achieving efficient PAD, where a biomass yield of 0.113 gVSS/gS was estimated. First, the free Gibbs energy dissipation method has been implemented, in order to provide a theoretical framework exploring the boundaries for sulphur oxidizing biomass yields. Second, a screening of available mathematical models describing SO-NR process was conducted and five published models were selected, in order to assess the most suitable model structure for describing the observed PAD kinetics. To the best of our knowledge, none of reported biomass yields are estimated in systems operating PAD as the main process and, analogously, none of the proposed models have been applied to case studies aiming at partial denitrification only. The work showed that the very low biomass yield of 0.117 ± 0.007 gVSS/gS, observed in a PAD system in our previous work, suggests that the conditions applied to achieve partial denitrification resulted in a high energy-dissipating metabolism compared to complete denitrification applications. Models' analysis revealed that nitrite accumulation can be described by a classical Monod kinetics if different μmax are adopted for each intermediate reaction, with Theil Inequality Coefficient values lower than 0.21 for both NO3− and NO2−. Nonetheless, adopting Haldane-type kinetics for nitrite uptake inferred higher identifiability to the model structure, resulting in confidence intervals below ±10% for all the parametric estimations. The thermodynamic and modelling outcomes support the experimental results obtained in the reference study and the critical comparison of model suitability to represent PAD process is believed pivotal to pave the way to its real-scale implementation

Evaluating the suitability of granular anammox biomass for nitrogen removal from vegetable tannery wastewater

In the present study, the potential inhibitory effect of biologically pre-treated vegetable tannery wastewater (TW) on anammox granular biomass was evaluated. Beside high organic and chemicals load, vegetable TW are characterised by high salinity and high tannins concentration, the latter belonging to a group of bio-refractory organic compounds, potentially inhibitory for several bacterial species. Recalcitrant tannin-related organic matters and salinity were selected as the two potential inhibitory factors and studied either for their separate and combined effect. Parallel batch tests were performed, with biomass acclimated and non-acclimated to salinity, testing three different conditions: non-saline control test with non-acclimated biomass (CT); saline control test with acclimated biomass (SCT); vegetable tannery wastewater test with acclimated biomass (TWT). Compared with non-saline CT, the specific anammox activity in tests SCT and TWT showed a reduction of 28 and 14%, respectively, suggesting that salinity, at conductivity values of 10 mS/cm (at 25 °C), was the main impacting parameter. As a general conclusion, the study reveals that there is no technical limitation for the application of the anammox process to vegetable TW, but preliminary biomass acclimation as well as regular biomass activity monitoring is recommended in case of long-term applications. To the best of our knowledge, this is the first work assessing the impact of vegetable TW on anammox biomass

A novel triphenylamine-based dye sensitizer supported on titania nanoparticles and the effect of titania fabrication on its optical properties

A new synthesised triphenylamine-based dye having a branched structure with one OH-ending branch able to interact with the surface hydroxyl moieties of mesoporous TiO2 is reported. Optical properties of the dye-titania hybrid material are presented and the higher efficiency of the dye on pure anatase TiO2 compared to the commercial Degussa P25, which contains a rutile phase component, is confirmed. The optical and chemical properties of the dye make it a promising candidate as a metal-free dye for DSSCs or as a host for a variety of transition or main group metal ions for different applications.A new synthesised triphenylamine-based dye having a branched structure with one OH-ending branch able to interact with the surface hydroxyl moieties of mesoporous TiO2 is reported. Optical properties of the dye-titania hybrid material are presented and the higher efficiency of the dye on pure anatase TiO2 compared to the commercial Degussa P25, which contains a rutile phase component, is confirmed. The optical and chemical properties of the dye make it a promising candidate as a metal-free dye for DSSCs or as a host for a variety of transition or main group metal ions for different applications