Improvement in nitrification through the use of natural zeolite: Influence of the biomass concentration and inoculum source

A batch nitrification process was studied using synthetic wastewater as substrate and Chilean natural zeolite as biomass carrier at ambient temperatures (20 °C). Three groups of experiments were carried out: a first experimental set (I) with and without added zeolite using initial biomass concentrations of 1,000 and 2,000 mg VSS/L; a second set of experiments (II) with added zeolite and at the same initial biomass concentrations. In these two experimental sets, biomass from an activated sludge process located in an urban wastewater treatment plant at La Farfana, Santiago de Chile, was used as inoculum (1). Finally, a third set of experiments (III) was carried out with zeolite at an initial biomass concentration of 1,000 mg VSS/L using an inoculum derived from an activated sludge process treating wastewater from a paper mill (inoculum 2). Nitrifying biomass concentration values in the range of 13,000-18,800 mg VSS/L were achieved when initial biomass concentrations varied between 1,000 and 2,000 mg VSS/L. Inoculum (1) generated higher biomass concentrations than inoculum (2). Ammonium N removals higher than 70 % were obtained in experimental sets II and III when zeolite was used. For both initial biomass concentrations tested, an exponential biomass growth was observed up to the second day of operation, and a slight decrease was evident afterwards, achieving stationary values after 10-12 days of operation. The third experimental set (III) revealed that the highest N consumption took place between days 11 and 16 of digestion. © 2013 Islamic Azad University (IAU).The authors wish to express their gratitude to FONDECYT project no. 1090414 (Chile) and to the University of Santiago de Chile (Chile) for providing financial support.Peer Reviewe

Kinetic study of the methanogenic step of a two-stage anaerobic digestion process treating olive mill solid residue

5 páginas, 4 figuras, 1 tabla.A kinetic study of the methanogenic step of a two-stage anaerobic digestion process treating two-phase olive oil mill solid residue (OMSR) was conducted at mesophilic temperature (35 °C). The anaerobic digestion of OMSR was carried out in two different steps. After a hydrolytic–acidogenic stage, working at an organic loading rate (OLR) of 12.9 g COD L−1 day−1 (COD: chemical oxygen demand), the effluents or acidified OMSR obtained were employed for feeding a second or methanogenic step. For the methanogenic step, OLRs of between 0.8 and 22.0 g COD L−1 day−1 were studied (corresponding to hydraulic retention times (HRTs) of between 142.9 and 4.6 days). The substrate treated in the second phase (acidified OMSR) had a high total concentration in volatile fatty acids (14.5 g CH3COOH L−1) and a high percentage of acetic acid as the main methane precursor (57.5% of the total concentration). As a consequence of the first step a high stability in the methanogenic stage was achieved. A total chemical oxygen demand balance was developed over the methanogenic step. For this model two considerations were taken in account: (1) volumetric flow constant during the experiments (the volume of effluent that was taken from the methanogenic reactor every day was equal to the volume of acidified OMSR fed). (2) Constant concentration of methanogenic microorganisms during the experiments (the slow growing rate of the methanogenic microorganisms makes it possible for the concentration of microorganisms over the process to remain constant). The cellular maintenance coefficient (m) and methane yield coefficient (YG/S) were found to be 0.016 g COD removed g−1 VSS day−1 and 0.261 L CH4 g−1 COD removed, respectively.The authors wish to express their gratitude to the Spanish “Ministerio de Educacion y Ciencia” (Project REN 2001-0472/TECNO) and the FECYT for providing financial support.Peer reviewe

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

Estudio cinético del proceso de biometanización de las aguas de condensación del proceso de concentración térmica del alpechín

A kinetic study of biomethanation has been carried out by using condensed water from the thermal concentration process of olive mill wastewater, which contained an organic load (6 g/l COD) that prevented it from reusing or spillage.
 Two fluidized-bed bioreactors were used, one of them containing suspend biomass for reference, and the other with biomass supported on Sepiolite for the immobilization of microorganisms effecting anaerobic digestion.
 The Chen-Hashimoto model of methane production has been applied, obtaining the values of the kinetic parameters μ<sub>max</sub> and K for each case studied.
 The results showed an increase in the kinetic constants for the reactor with Sepiolite in relation to the one used as reference, and the value for K kinetic constant was duplicated.<br><br>Se ha efectuado un estudio cinético del proceso de biometanización de las aguas de condensación procedentes del proceso de concentración térmica del alpechín, cuya carga orgánica (6,0 g/l de DQO) impide su posible vertido o reutilización. Para ello, se utilizan dos reactores de lecho fluidizado, uno con biomasa suspendida (testigo) y otro con biomasa soportada sobre Sepiolita para inmovilización de las bacterias responsables del proceso.
 Se aplica el modelo de Chen-Hashimoto de producción de metano obteniéndose los valores de los parámetros cinéticos μ<sub>max</sub> y K casos estudiados.
 Se obtiene un aumento de las constantes cinéticas en el reactor que contiene Sepiolita respecto al testigo, llegando a duplicarse el valor de la constante K en el reactor con biomasa soportada

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

Estudio cinético comparativo del proceso de digestión anaerobia del alpechín en los intervalos mesofílico y termofílico de temperatura

A kinetic study of anaerobic digestion of olive mill wastewater in the mesophilic (from 30ºC to 40°C) and thermophilic (from 50ºC to 60ºC) ranges of temperature has been carried out. Two reactors containing suspended biomass were used.
 The Chen-Hashimoto substrate utilization kinetic model has been applied, obtaining the values of the maximum specific growth rate of microorganisms, μ<sub>max</sub>,. and the kinetic constant, K, for each case studied.
 The obtained results showed an increase of 55% and 34% for μ<sub>max</sub> and K, respectively, of the thermophilic anaerobic digestion process in relation to the mesophilic process.
 The substrate utilization maximum rate value was reached for the hydraulic retention times of 7,7 and 11,6 days, for the thermophilic and mesophilic processes, respectively.<br><br>Se ha efectuado un estudio cinético del proceso de digestión anaerobia del alpechín en los intervalos mesofílico (de 30ºC a 40ºC) y termofílico (de 50ºC a 60°C) de temperatura, utilizando dos reactores de lecho fluidizado con biomasa suspendida.
 Se aplica el modelo de utilización de sustrato propuesto por Chen- Hashimoto, obteniéndose los valores de la velocidad máxima de crecimiento específico de microorganismos, μ<sub>max</sub>, y de la constante cinética del proceso, K, para cada uno de los casos estudiados.
 Se obtiene un aumento de los parámetros cinéticos μ<sub>max</sub>. y K, del 55% y 34% respectivamente, en el proceso de digestión anaerobia termofílico respecto al mesofílico.
 El valor máximo en la velocidad volumétrica de utilización de sustrato se alcanza para un tiempo de retención hidráulico de 7,7 y 11,6 días en los procesos termofílico y mesofílico, respectivamente

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

Depuración aerobia de las aguas de condensación del proceso de concentración térmica del alpechín

A study of aerobic treatment in batch regime of condensed water from thermal concentration process of olive mill wastewater was carried out. An 80% of wastewater organic substances was removal after the third day of fermentation. The substrate removal rate follows a zero-order kinetic for high concentrations, and a first-order kinetic for low organic matter concentration, during the last days of fermentation. The kinetic parameters (qmax and Ks) were obtain by Michaelis- Menten model.Se ha efectuado un estudio del proceso de depuración aerobia, en régimen discontinuo, de los condensados resultantes del proceso de concentración térmica del alpechín. Se comprueba que el 80% de la materia orgánica presente en este agua se elimina a partir del tercer día de fermentación. La velocidad de eliminación de sustrato sigue una cinética de orden cero para altas concentraciones del mismo y una cinética de primer orden para bajas concentraciones de materia orgánica, es decir, durante los últimos días de fermentación. Se aplica el modelo de Michaelis-Menten de eliminación de sustrato para la obtención de los parámetros cinéticos qmax y Ks que rigen este proceso

Screening of biomethane production potential from dominant microalgae

The use of microalgae for biomethane production has been considerably increasing during the recent years. In this study, four dominant species belonging to the genera Scenedesmus, Chlorella, Dunaliella and Nostoc were selected. The influence of different genera with several morphological, structural and physicochemical characteristics on methane production was assessed in biochemical methane potential (BMP) tests. The ultimate methane yield values were 332 ± 24, 211 ± 2, 63 ± 17 and 28 ± 10 mL CH/g VS for Scenedesmus obliquus, Chlorella sorokiniana, Dunaliella salina and Nostoc sp., respectively. The highest methane production was achieved by microalga species that had no complex cell wall or wall basically composed by proteins and simple sugars such as in S. obliquus, whereas lower methane yields were found for D. salina and Nostoc sp., due to the salinity effects and cell wall composition in terms of complex polysaccharide and glycolipid layers, respectively. Kinetic constant values obtained in the BMP tests ranged between 1.00 ± 0.08 and 0.097 ± 0.005 days for D. salina and S. obliquus, respectively.The authors express their gratitude to Marie Curie's International Research Staff Exchange Scheme (PIRSES-GA-2011-295165) and Junta de Andalucía government (RNM-1970) for providing financial support.Peer Reviewe

Harmonization of VFAs measurement by GC: something more than R2 to evaluate the calibration function

Anaerobic digestion is sensitive to many environmental factors requiring a robust control of this process. One of the analytical measurements considered as key parameter is the volatile fatty acids (VFAs) content. Total amount of volatile acids (TVFA) to control the relative changes over time has been suggested as a useful tool. However, TVFA does not provide sufficient information to reveal the overall reactor performance, and individual components have been considered of particular interest. Although some attempts have been described as on-line measurements for individual VFAs, normally they are determined by off-line chromatographic techniques (GC and HPLC). A previous interlaboratory study showed the lack of harmonization in the analytical methodologies dealing to individual VFAs, and giving an overall analytical performance rather poor. One of the reasons to justify these results was the inappropriate calibration procedures. It is widely used to check the linearity of the calibration curves based on the correlation and determination coefficients. However, these statistical parameters are erroneously interpreted. The objective of this interlaboratory study was to achieve the harmonization of results. By this way, the use of internal standard methodology (ISTD) should be useful to obtain accurate calibration functions. In addition, five different statistical parameters such as lack of fit test, residual standard deviation, relative standard deviation of the slope, relative standard deviation of the sensitivity and relative error were proposed to evaluate the linearity of calibration curves. Of these, lack of fit was unable to detect appropriately the linearity mainly due to its sensitivity to the precision of analytical results. The rest of statistical parameters reported could be considered as starting point for comparative purposes, being useful as acceptance criteria. The principal advantage of the GC/ISTD analytical methodology was the normalization of the slopes obtained by the participating laboratories, being very helpful to the harmonization of results.Peer Reviewe