A comparative study of the characteristics and physical behaviour of different packing materials commonly used in biofiltration

In this study, the characteristics and physical behaviour of 8 different packing materials were compared. The materials were selected according to previous works in the field of biofiltration including organic and inorganic or synthetic materials. Results pre-selected those more acceptable support materials for the main function they have to perform in the biological system: high surface contact, rugosity to immobilize the biomass, low pressure drop, nutrients supply, water retentivity or a commitment among them. Otherwise, pressure drop have been described by means of the respective mathematic expressions in order to include phenomena in the classical biofiltration models.Peer ReviewedPostprint (author's final draft

Comparison of organic packing materials for toluene biofiltration

he paper focuses on the operation of a pilot plant with four biofilters operated in parallel for determining the suitability of coconut fiber, peat, compost from the digested sludge of a wastewater treatment plant and pine leaves as packing materials for biofiltration of toluene. Physical characteristics of packing materials such as specific surface area, density, pore size and elemental composition were determined for each packing material. Biological activity and packing capabilities related to toluene removal were determined during the startup and operation of the four biofilters under different conditions of nutrients, watering and inlet air relative humidity supply. Nutrient addition was key in improving removal efficiency (RE) and elimination capacity (EC) of biofilters. Feeding of medium with nutrients increased the RE and the EC by a factor of 2 to 4 than these found when supplying only tap water. Additionally, when extra nitrogen was supplied in the medium, RE and EC increased by a factor of 2. Nutrient addition also lead to a microbial population change from bacterial to fungal biofilters. It was denoted that watering control is necessary to improve fungal biofilters performance in terms of ensuring a proper washout of acidic by-products to avoid fungi inhibition and consequent lowered removal capacities.Peer ReviewedPostprint (published version

Influence of crude glycerol load and pH shocks on the granulation and microbial diversity of a sulfidogenic Upflow Anaerobic Sludge Blanket reactor

Bioscrubbers are an environmental-friendly alternative to valorize SO2 contained in flue gases to obtain elemental sulfur as final value-added product. The bottleneck of a SO2 bioscrubber relies on the heterotrophic reduction of the absorbed SO2 to obtain sulfide. In this study, the performance and stability of a sulfidogenic Upflow Anaerobic Sludge Blanket reactor (UASB) using crude glycerol was investigated during 6 months of operation under variable organic loading rates. The UASB presented a maximum elimination capacity and a sulfate removal efficiency of 110 mg S-SO42- L-1 h(-1) and 100%, respectively, when the chemical oxygen demand to sulfate ratio (COD/S-Sulfate) was 8.5 g O-2 g(-1) S-SO42-. The intermediate compounds identified from crude glycerol degradation were mainly propionic and acetic acid, which varied along the sludge bed together with the pH. Microbial diversity analyses of the sulfidogenic granular sludge showed that the most abundant sulfate reducing genera were Desulfovibrio spp. and Desulfobulbus spp. Methanosaeta and other fermentative/acidogenic microorganisms were also found in significant amounts. Particle size distribution analyses showed that biogas production allowed the granulation of the sulfidogenic sludge, which had an average particle size ranging from 729.3 mu m (lower part of the bed) to 391.7 mu m (upper part of the test). A short-term pH shock caused a detrimental effect over the system performance due to degranulation. Concomitantly, biogas production was interrupted and acetic acid was accumulated also causing a significant impact on microbial diversity. Unclassified Clostridiales, Desulfovibrio spp. and Desulfobulbus spp. showed a higher resistance to pH shocks

Performance characterization of a full-scale biofilter at an organic waste treatment plant

Data from the regular monitoring of a full-scale biofilter at a municipal solid waste treatment facility for the integral treatment of domestic residues was analyzed in order to assess potential operational problems and to evaluate reactor’s performance in terms of ammonia removal, the target odorous compound at the facility. Performance was assessed based on ammonia removal efficiency and elimination capacity. Average elimination capacities up to 1,6 g NH3 m-3 h-1 at average inlet loads of 2,1 g NH3 m-3 h-1 were found, which correspond to a low-loaded biofilter type. Year-round data collected and packing material analysis revealed a marked effect of water content in the packed bed of the biofilter which lead to reduced removal efficiencies.Peer ReviewedPostprint (published version

Dynamic modelling of ammonia biofiltration from waste gases

A dynamic model to describe ammonia removal in a gas-phase biofilter was developed. The math-ematical model is based on discretized mass balances and detailed nitrification kinetics that includeinhibitory effects caused by free ammonia (FA) and free nitrous acid (FNA). The model was able to pre-dict experimental results operation under different loading rates (from 3.2 to 13.2 g NH3h-1m-3). In par-ticular the model was capable of reproducing inhibition caused by high inlet ammonia concentrations. Alsoelimination capacity was accurately predicted. Experimental data was also used to optimize certain modelparameters such as the concentration of ammonia- and nitrite-oxidizing biomass.Peer ReviewedPostprint (published version

The role of water in the performance of biofilters: parameterization of pressure drop and sorption capacities for common packing materials

The presence of water in a biofilter is critical in keeping microorganisms active and abating pollutants. In addition, the amount of water retained in a biofilter may drastically affect the physical properties of packing materials and packed beds. In this study, the influence of water on the pressure drop and sorption capacities of 10 different packing materials were experimentally studied and compared. Pressure drop was characterized as a function of dynamic hold-up, porosity and gas flow rate. Experimental data were fitted to a mathematical expression based on a modified Ergun correlation. Sorption capacities for toluene were determined for both wet and dry materials to obtain information about the nature of interactions between the contaminant, the packing materials and the aqueous phase. The experimental sorption capacities of materials were fitted to different isotherm models for gas adsorption in porous materials. The corresponding confidence interval was determined by the Fisher information matrix. The results quantified the dynamic hold-up effect resulting from the significant increase in the pressure drop throughout the bed, i.e. the financial cost of driving air, and the negative effect of this air on the total amount of hydrophobic pollutant that can be adsorbed by the supports. Furthermore, the results provided equations for ascertaining water presence and sorption capacities that could be widely used in the mathematical modeling of biofilters.Peer ReviewedPostprint (author's final draft

Biomass accumulation in a biofilter treating toluene at high loads – Part 2: Model development, calibration and validation

In this work, a dynamic model describing volatile organic compounds abatement and the corresponding biomass accumulation is developed, calibrated and validated. The mathematical model is based on detailed mass balances which include the main processes involved in the system: advection, absorption, adsorption, diffusion, biodegradation and biomass growth. The model overcomes common assumptions considered in classical biofiltration models such as uniform, constant biomass distribution. The model was calibrated and validated using experimental data obtained from a biofilter packed with clay pellets during its operation from inoculation to clogging. The model was able to predict satisfactorily experimental data by calibrating only a minimum number of parameters such as the half-saturation constant for toluene and the volumetric maximum growth rate of microorganisms. Kinetic parameters were fitted by means of an optimization routine using toluene concentration profiles along the bed height of the biofilter. A confidence interval for each parameter was calculated based on the Fisher Information Matrix procedure. The model was satisfactorily validated during the operation of the biofilter under different process conditions. Biomass accumulation permitted to predict macroscopic, critical operating parameters such as the pressure drop through the bed. The model may help predicting energy consumption requirements as well as biomass clogging episodes due to excessive biomass growth.Peer ReviewedPostprint (author's final draft

Exploring the performance limits of a sulfidogenic UASB during the long-term use of crude glycerol as electron donor

SOx contained in flue gases and S-rich liquid effluents can be valorized to recover elemental sulfur in a two-stage bioscrubbing process. The reduction of sulfate to sulfide is the most crucial stage to be optimized. In this study, the long-term performance of an up-flow anaerobic sludge blanket (UASB) reactor using crude glycerol as electron donor was assessed. The UASB was operated for 400 days with different sulfate and organic loading rates (SLR and OLR, respectively) and a COD/S-SO42− ratio ranging from 3.8 g O2 g−1 S to 5.4 g O2 g−1 S. After inoculation with methanogenic, granular biomass, the competition between sulfate-reducing and methanogenic microorganisms determined to what extent dissolved sulfide and methane were produced. After the complete washout of methanogens, which was revealed by next-generation sequencing analysis, the highest S-EC was reached in the system. The highest average sulfate elimination capacity (S-EC = 4.3 kg S m−3d−1) was obtained at a COD/S-SO42− ratio of 5.4 g O2 g−1 S and an OLR of 24.4 kg O2 m−3d−1 with a sulfate removal efficiency of 94%. The conversion of influent COD to methane decreased from 12% to 2.5% as the SLR increased while a large fraction of acetate (35% of the initial COD) was accumulated. Our data indicate that crude glycerol can promote sulfidogenesis. However, the disappearance of methanogens in the long-term due to the out competition by sulfate reducing bacteria, lead to such large accumulation of acetate

Study of NH3 removal by gas-phase biofiltration: effects of shock loads and watering rate on biofilter performance

Ammonia biofiltration performance under shock loads episodes was studied in a reactor packed with coconut fiber as carrier material. Periodical gas and leachate samplings were analyzed and used to characterize the biofilter performance in terms of removal efficiency (RE) and elimination capacity (EC). Nitrogen fractions in the leachate were quantified to identify the experimental rates of nitritation and nitratation.. In a primary experiment a sudden increment of ammonia load was applied for 1 day by changing the ammonia inlet load from 5.2 to 29.1 g N.m-3.h-1. Even though stable operation was obtained (RE of 99.9%), a notable accumulation of nitrite was verified in the leachate. Experimental rates showed that nitritation increased at the same the same ratio that ammonia load was varied. However the nitratation seemed to be largely affected by high ammonia and nitrite concentration. In a subsequent experiment varying the inlet ammonia load, the system was rapidly recovered by increasing the watering rate. Since ammonia was partially removed by physicochemical process as observed in previous experiments, a final experimental was conducted to improve the nitritation capacity. The addition of inorganic carbon source demonstrated to enhance the capacity of the biofilter to degrade a higher amount of ammonia.Peer ReviewedPostprint (published version

Sulfidogènesi a partir de glicerol cru : el primer pas per a la producció de sofre biològic a partir d'efluents amb alta càrrega de sulfat

És d'interès estudiar els organismes sulfato-reductors en processos biotecnològics, en els quals aquests redueixen els sulfats i produeixen sulfur amb glicerol cru, per exemple. El camí, però, és complex per la toxicitat del sulfur resultant i per la competència amb organismes metanogènics que empren els derivats del glicerol per produir biogàs. La recerca present té, en última instància, la intenció de fabricar sofre elemental de manera eficient a partir d'aquest sulfur en una segona etapa de producció. Per fer-ho, és necessari avaluar la dinàmica del glicerol cru dins el reactor biològic, on es fabrica el sulfur, tenint en compte les condicions a les quals està sotmès.Es de interés estudiar los organismos sulfato-reductores en procesos biotecnológicos, en los que estos reducen los sulfatos y producen sulfuro utilizando glicerol crudo, por ejemplo. El camino, sin embargo, es complejo por la toxicidad del sulfuro resultante y por la competencia con organismos metanogénicos que emplean los derivados del glicerol para producir biogás. La investigación presente tiene, en última instancia, la intención de fabricar azufre elemental de manera eficiente a partir de este sulfuro en una segunda etapa de producción. Para ello, es necesario evaluar la dinámica del glicerol crudo dentro del reactor biológico, donde se fabrica el sulfuro, teniendo en cuenta las condiciones a las que está sometido.It is interesting to study sulfate-reducing organisms in biotechnological processes, in which these reduce sulfates and produce sulfides with crude glycerol, for example. However, is complex to get to this point, due to the toxicity of the resulting sulfide and the struggle with methanogenic organisms that use glycerol derivatives to produce biogas. The goal of the present research is to manufacture elemental sulfur efficiently with this sulfide in a second stage of production. To do so, it is necessary to evaluate the dynamics of crude glycerol inside the biological reactor, where sulfide is manufactured, taking into account the conditions to which it is subjected