Performance evaluation of micro-aerobic hydrolysis of mixed sludge: Optimum aeration and effect on its biochemical methane potential

31 Páginas; 8 Figuras; 3 TablasThis study evaluated the performance of a micro-aerobic hydrolysis of mixed sludge and its influence as a pretreatment of this waste for its subsequent anaerobic digestion. Three experimental series were carried out to evaluate the optimum micro-aeration levels in the range from 0.1 to 0.5 air volume/min.reactor volume (vvm) and operation times within the range of 24–60 h. The maximum methane yield [35 mL CH4/g volatile suspended solids (VSS) added] was obtained for an aeration level of 0.35 vvm. This methane yield value increased 114% with respect to that obtained with the non-aerated sludge. In the micro-aeration process carried out at an aeration level of 0.35 vvm, increases in soluble proteins and total sugars concentrations of 185% and 192% with respect to their initial values were found, respectively, after 48 h of aeration. At the above micro-aerobic conditions, soluble chemical oxygen demand (CODS) augmented 150%, whereas VSS content decreased until 40% of their initial respective values. Higher COD increases and VSS decreases were found at 60 h of micro-aeration, but the above parameters did not vary significantly with respect to the values found at 48 h.The authors acknowledge gratefully the financial support of FONDECYT through Project 1030315 (Chile).Peer reviewe

Advances in the biological removal of sulphides from aqueous phase in anaerobic processes: A review

64 Páginas; 6 Tablas; 5 FigurasIn this paper, we review the latest developments in biological methods used in the removal of hydrogen sulphide, present in the liquid phase in anaerobic reactors. The toxicity of H2S to methane-forming microorganisms and the problems caused by the presence of this compound in the biogas generated during this process, as well as the main causes of hydrogen sulphide generation in anaerobic processes of wastes are also reviewed. We especially discuss the fundamentals in applying micro-aerobic conditions to remove dissolved hydrogen sulphide from the aqueous phase of an anaerobic reactor. The alternative technology of simultaneous removal of sulphide, nitrate, and organic matter is under recent investigation. Therefore, this review paper includes a study and analysis of the microbiological basis of this technology, the physical and chemical factors that influence the process and the potential application of this technology on different types of wastewaters and situations. Also considered are the fundamentals of both biofilm reactors and microbial fuel cells desulphurization. Because relatively few studies on modeling desulphurisation processes are available, we discuss the advances made in that area.The authors would like to acknowledge the financial support provided by Fondecyt projects: 1130108, 1150285 and 1130315.Peer reviewe

Autotrophic and heterotrophic denitrification for simultaneous removal of nitrogen, sulfur and organic matter

24 Páginas; 5 Tablas; 5 FigurasThe aim of this investigation was to assess the startup and operation of a laboratory-scale hybrid UASB-Anaerobic Filter Reactor (UASFB) of 1 L volume, kept at 30°C, in order to carry out a simultaneous autotrophic and heterotrophic denitrification process. First, the heterotrophic and autotrophic populations were separately enriched, with specific cultures and subsequently the UASFB was inoculated with 2 g L−1 of volatile suspended solids (VSS), with a ratio of 1.5:1 (autotrophs: heterotrophs). The influent or synthetic wastewater used was composed of: Na2S2O3·5H2O, CH3COOK, NaNO3, NaHCO3, K2HPO4, NH4Cl and saline solution. The concentrations varied depending on the organic loading rate (OLR), nitrogen loading rate (NLR) and sulfur loading rate (SLR) applied. In the UASFB reactor, two experimental conditions were tested and assessed: (i) COD/N ratio of 3.6 and SLR of 0.75 kg S m−3 d−1; and (ii) COD/N ratio of 5.8 and SLR of 0.25 kg S m−3 d−1. The results obtained demonstrated that an inoculum coming from an anaerobic reactor was able to carry out the process, obtaining a maximum nitrate removal of 85.3% in the first stage of operation and 99.5% in the second stage. The recovery of sulfur in form of sulfate in the effluent did not present a tendency to stabilize during the measured time, with a maximum thiosulfate removal of 32.5%, when the SLR was lowered to 0.25 kg S m−3 d−1. The maximum organic matter elimination, measured as COD, was 75.8%, which indicates the relatively good performance and behavior of the heterotrophic microorganisms.The authors wish to express their gratitude to FONDECYT, Project No. 1130108 (Chile), for its financial support.Peer reviewe

A new and simple kinetic model for assessing the dynamic behavior and simulating the biochemical methane potential (BMP) of sewage sludge in the presence of fly ash

BACKGROUND: The modeling of anaerobic digestion of sewage sludge including the effect of fly ash has been studied only scarcely and has focused mainly on the accumulated methane (CH). The present work was aimed at assessing the complete dynamic behavior of the biochemical methane potential (BMP) of sewage sludge in the presence of fly ash, including both the liquid and gas phases. The model was calibrated and validated for BMPs using eight fly ash concentrations (10, 40, 25, 50 150, 250, 350 and 500 mg L). RESULTS: The calibration showed that the model fits well with the experimental data, with the values of the parameters falling in the range reported in the literature. The calibrated model was able to describe properly the behavior of soluble chemical oxygen demand (COD) and volatile solids in the liquid phase, with normalized root mean square error (NRMSE) and correlation coefficients (CC) ranging from 0.4052 to 0.2729 and 0.6246 to 0.8172, respectively. For the gas phase, the model was able to represent accurately the daily CH production and accumulated CH, with NRMSE and CC ranging from 0.8915 to 0.07194 and 0.5051 to 0.9736, respectively. CONCLUSIONS: The proposed model is robust and valid for all the tested conditions. © 2018 Society of Chemical Industry.The authors would like to acknowledge the financial support provided by FONDECYT (Chile) under project 1170103, and the grant ‘Becas Iberoamerica. Jóvenes Profesores e Investigadores, Santander Universidades Convocatoria 2017’ received by César Huiliñir Curío.Peer Reviewe

A new model of batch biodrying of sewage sludge, Part 2: Model calibration and validation

<p>The calibration and validation of a new model of batch biodrying of sewage sludge are presented. The calibration was performed with experimental data from the literature, while the validation was performed with new experimental data. The model was successfully calibrated with experimental data, with the values of parameters falling in the range of values reported. The new model also represented the behavior of the experimental data for all the variables measured, showing that it is robust and valid for the simulated conditions. Simulations showed that continuous high aeration increased the efficiency of the process.</p

Assessment of a UASB reactor with high ammonia concentrations: Effect of zeolite addition on process performance

© 2014 Elsevier Ltd. The UASB process for wastewater treatment has been extensively studied, but the use of zeolite to improve UASB reactor performance has rarely been explored. In this study, a UASB reactor modified with natural zeolite operating at high nitrogen concentrations (0.5, 0.7 and 1 g/L) was evaluated. Two laboratory bioreactors, one with zeolite and one without, were operated at ambient temperatures ranging between 18 °C and 21 °C. The experimental phase had a start-up period of 21 days. In the reactor with zeolite, the pH was found to be between 7.9 and 9.1, with a COD removal efficiency of about 60% after 80 days of operation at ammonia concentrations of between 0.229 and 0.429 g/L in the effluent. In the reactor without zeolite, the pH was between 8.3 and 9.3, and the COD removal efficiency was about 40% at ammonia concentrations between 0.244 and 0.535 g/L in the effluent. The addition of zeolite also decreased the volatile suspended solids (VSS) concentration in the effluent, generating a biomass with larger granules and higher settling rates as compared to a UASB reactor without zeolite. Taking the lower ammonia concentration, the higher COD removal and the improved granulation into account, it can be concluded that natural zeolite positively influenced the behavior and performance of the UASB reactor operating with high nitrogen concentrations.Peer Reviewe

A new and simple kinetic model for assessing the dynamic behavior and simulating the biochemical methane potential (BMP) of sewage sludge in the presence of fly ash

BACKGROUND: The modeling of anaerobic digestion of sewage sludge including the effect of fly ash has been studied only scarcely and has focused mainly on the accumulated methane (CH). The present work was aimed at assessing the complete dynamic behavior of the biochemical methane potential (BMP) of sewage sludge in the presence of fly ash, including both the liquid and gas phases. The model was calibrated and validated for BMPs using eight fly ash concentrations (10, 40, 25, 50 150, 250, 350 and 500 mg L). RESULTS: The calibration showed that the model fits well with the experimental data, with the values of the parameters falling in the range reported in the literature. The calibrated model was able to describe properly the behavior of soluble chemical oxygen demand (COD) and volatile solids in the liquid phase, with normalized root mean square error (NRMSE) and correlation coefficients (CC) ranging from 0.4052 to 0.2729 and 0.6246 to 0.8172, respectively. For the gas phase, the model was able to represent accurately the daily CH production and accumulated CH, with NRMSE and CC ranging from 0.8915 to 0.07194 and 0.5051 to 0.9736, respectively. CONCLUSIONS: The proposed model is robust and valid for all the tested conditions. © 2018 Society of Chemical Industry.The authors would like to acknowledge the financial support provided by FONDECYT (Chile) under project 1170103, and the grant ‘Becas Iberoamerica. Jóvenes Profesores e Investigadores, Santander Universidades Convocatoria 2017’ received by César Huiliñir Curío.Peer Reviewe

Simultaneous nitrification–denitrification of wastewater: effect of zeolite as a support in sequential batch reactor with step-feed strategy

35 Páginas; 3 Tablas; 11 FigurasOne of the technologies used for wastewater nitrogen removal consists in simultaneous nitrification–denitrification. The low microbial growth rate and the low availability of organic material for the denitrification stage make it necessary to study new operational conditions and the use of microbial supports. The aim of this study was to evaluate the operational behavior of a simultaneous nitrification–denitrification process in a sequential batch reactor utilizing zeolite as a biomass support and step-feed strategy. Two reactors of 2 L were used, one with zeolite and another without zeolite, both operated at constant temperature (31 °C), varying nitrogen loading rate (NLR) from 0.041 to 0.113 kg total Kjeldahl nitrogen (TKN/m3/day). After 209 days, removals higher than 86 and 96 % in nitrogen compounds and organic matter were obtained, respectively. There was not accumulation of nitrate and nitrite in any case; this means that there was a simultaneous nitrification–denitrification in the reactors. The incorporation of zeolite in the system held higher concentration of biomass in the reactor; this led to reduce start-up to 21 days and to improve 11.31 % removal kinetic. The use of a step-feed strategy prevents events of inhibition by substrate, even duplicating tolerance to higher NLR for the same operation time.The present study thanks the Conicyt-Fondecyt for the financial support given to the following projects: Nos. 1090414/2009 and 1130108/2013.Peer reviewe

Start-up and performance of UASB reactors using zeolite for improvement of nitrate removal process

A first study on the use of Chilean natural zeolite of different particle sizes (0.5, 1 and 2mm in diameter) in laboratory-scale batch denitrificant reactors was carried out with the aim of assessing the microbial communities adhered to this material. Molecular techniques such as fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE) fingerprints revealed a high microbial diversity with a strong presence of Gammaproteobacteria (70% of the total microorganisms) in reactors with zeolite 0.5mm in diameter. Archaea were only detected in the reactors with zeolite 1mm in diameter. In addition, the acclimatization and start-up of two UASB reactors (one without zeolite and the other with added zeolite 1mm in diameter) were conducted following three consecutive and progressive stages using upward velocities from 0.10 to 0.44m/h in order to establish an experimental protocol suitable for the start-up of this type of reactors. Total (100%) nitrate reduction was achieved in the UASB reactors with and without zeolite on the 7th and 11th days, respectively, of the second stage of the start-up period, showing the suitability of the use of this material in this type of reactors. Finally, a third study carried out with both UASB reactors operating in continuous mode at a high organic loading rate (44kgCOD/m3d) and a very low HRT (2.5h) revealed that the reactor with zeolite achieved a nitrate removal efficiency of 92.4% at a nitrogen load of 6.42kgNO3 -/(m3d). This last study also demonstrated the robustness of the UASB reactor with zeolite under nitrate load variations. © 2014 Elsevier B.V.The authors wish to express their gratitude to Fondecyt Project No.1090414 (Chile) for its financial supportPeer Reviewe

Sulfur-based mixotrophic denitrification with the stoichiometric S0/N ratio and methanol supplementation: effect of the C/N ratio on the process

3 Figuras.-- 2 TablasThe impact of the organic carbon to nitrate ratio (C/N ratio) on mixotrophic denitrification rate has been scarcely studied. Thus, this work aims to investigate the effect of the C/N ratio on the mixotrophic denitrification when methanol is used as a source of organic matter and elemental sulfur as an electron donor for autotrophic denitrification. For this, two initial concentrations of NO3--N (50 and 25 mg/L) at a stoichiometric ratio of S0/N, and four initial C/N ratios (0, 0.6, 1.2, and 1.9 mg CH3OH/mg NO3- -N) were used at 25 (±2) °C. The results showed that when using a C/N ratio of 0.6, the highest total nitrogen removal was obtained and the accumulation of nitrites was reduced, compared to an autotrophic system. The most significant contribution to nitrate consumption was through autotrophic denitrification (AuDeN) for a C/N ratio of 0.6 and 1.2, while for C/N = 1.9 the most significant contribution of nitrate consumption was through heterotrophic denitrification (HD). Finally, organic supplementation (methanol) served to increase the specific nitrate removal rate at high and low initial concentrations of substrate. Therefore, the best C/N ratio was 0.6 since it allowed for increasing the removal efficiency and the denitrification rate.Authors would like to acknowledge the financial support provides by FONDECYT (Chile) under Project 1170103 and a PhD fellowship 21200655 awarded to D. Yanez-Sevilla.Peer reviewe