Explicit temperature-based model for anaerobic digestion: application in domestic wastewater treatment in a UASB reactor

Influence of Digester Temperature on Methane Yield of Organic Fraction of Municipal Solid Waste (OFMSW)

This study evaluates the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) and digested sewage sludge (DSS) at lowered temperatures. AD batch tests for CH4 yield determination were carried out with DSS as inoculum between 23 and 40 °C. All results were related to organic dry matter and calculated for standard conditions (1013 hPa, 0 °C). The AD experiments at 40 °C and at 35 °C delivered specific CH4 yields of 325 ± 6 mL/g and 268 ± 27 mL/g for OFMSW alone. At lower temperatures, specific CH4 yields of 364 ± 25 mL/g (25 °C) and 172 ± 21 mL/g (23 °C) were reached. AD at 25 °C could be beneficial regarding energy input (heating costs) and energy output (CH4 yield). Plant operators could increase AD efficiencies by avoiding heating costs. The co-digestion of OFMSW together with DSS could lead to further synergies such as better exploitation of the energy potentials of DSS, but the digestate utilization could become problematic due to hygienic requirements. Efficiency potentials through lowered operating temperatures are limited. In further research, lowered process temperatures could be applied in the AD of energy crops due to large numbers of existing plants.

A Framework Based on Finite Element Method (FEM) for Modelling and Assessing the Affection of the Local Thermal Weather Factors on the Performance of Anaerobic Lagoons for the Natural Treatment of Swine Wastewater

Anaerobic lagoons are natural wastewater treatment systems suitable for swine farms in small communities due to its low operational and building costs, as well as for the environmental sustainability that these technologies enable. The local weather is one of the factors which greatly influences the efficiency of the organic matter degradation within anaerobic lagoons, since microbial growth is closely related to temperature. In this manuscript, we propose a mathematical model which involves the two-dimensional Stokes, advection–diffusion-reaction and heat transfer equations for an unstirred fluid flow. Furthermore, the Anaerobic Digestion Model No1 (ADM1), developed by the International Water Association (IWA), has been implemented in the model. The partial differential equations resulting from the model, which involve a large number of state variables that change according to the position and the time, are solved through the use of the Finite Element Method. The results of the simulations indicated that the methodology is capable of predicting reasonably well the steady-state of the concentrations for all processes that take place in the anaerobic digestion and for each one of the variables considered; cells, organic matter, nutrients, etc. In view of the results, it can be concluded that the model has significant potential for the design and the study of anaerobic cells’ behaviour within free flow systems.

Effects of Solids Retention Time on the Anaerobic Membrane Bioreactor with Yttria-Based Ceramic Membrane Treating Domestic Wastewater at Ambient Temperature

The effects of solid retention times (SRTs) (100 days, 50 days, 25 days) on the performance, microbial community, and membrane fouling of a lab-scale anaerobic yttria-based ceramic membrane bioreactor (AnCMBR) treating synthetic domestic wastewater at ambient temperature (31.2 ± 2.7 °C) were examined. The soluble chemical oxygen demand (SCOD) removal was higher (89.6%) at 25 days SRT compared with 50 days (39.61%) and 100 days (34.3%) SRT. At 100 days SRT, more Bacteroidetes, Firmicutes, and Proteobacteria were present in the microbial community. At 25 days SRT, more Chloroflexi, Synergistetes, and Pastescibacteria emerged, contributing to the stable performance. The SRT of 25 days has resulted in a more stable microbial community compared with 50 days and 100 days SRT. Both bacterial and archaeal community diversities were higher at 25 days SRT, and the specific production of soluble microbial by-products (SMPs) and extracellular polymeric substances (EPSs) were higher at 25 days SRT as well. Consequently, the membrane flux was lower at 25 days SRT with the increased particle size and the enhanced SMPs and EPSs production. Fourier transform infrared spectroscopy analysis (FTIR) and three-dimensional excitation and emission matrix (3D-EEM) analysis showed that protein and SMPs were the major membrane foulants at all SRT stages. In this study, SRT at 25 days was favorable for the stable operation of an AnCMBR treating domestic wastewater at ambient temperature.

Modelling of an anaerobic plug-flow reactor. Process analysis and evaluation approaches with non-ideal mixing considerations

This study shows the implementation of the Anaerobic Digestion Model (ADM1) in an anaerobic plug-flow reactor (PFR) with two approaches based on the use of consecutive continuous stirred tank reactors (CSTR) connected in serie for considering non-ideal mixing. The two-region (TR) model splits each CSTR into two regions, while the particulate retention (PR) model adds a retention parameter. The models were calibrated and validated based on experimental data from a bench-scale reactor treating cow manure. The PFR conventional model slightly outperformed the non-ideal mixing approaches. However, the PR model showed an increase in biomass retention time treating high solid content substrate. Biogas production was not sensitive to variations of the mixing parameters. The liquid fraction content was better represented by the PR model than the PFR and TR models. The study shows how reactor modelling is useful for monitoring and supervising biogas plants.

Evaluación inicial de parámetros de campo en un biodigestor anaeróbico para el tratamiento de aguas residuales

<p>El biodigestor anaerobio utilizado en este estudio, se diseñó para tratar agua residual doméstica en un sanitario de prueba, que se caracteriza por ser de: flujo continuo, baja carga orgánica y tener cuatro etapas de proceso. La importancia del prototipo estudiado radicó en las condiciones reales en que se probó. La primera etapa consistió en la selección del sitio, construcción del prototipo en ferrocemento con capacidad de 1m, impermeabilización y carga. En esta etapa se inoculó el reactor con materia orgánica procedente de las descargas del sanitario, durante el periodo de agosto a diciembre de 2011. La evaluación de este periodo consistió en la medición de parámetros de campo: pH, conductividad eléctrica, sólidos sedimentables, temperatura del influente y efluente del sistema que permitieron verificar el comportamiento del proceso del digestor durante la fase de arranque. Los resultados obtenidos para estas determinaciones a la entrada y salida del biodigestor respectivamente son los siguientes: pH (8.03; 8.43), conductividad eléctrica (1510.83 µS/cm; 1207.00 µS/cm), temperatura del proceso (19.2°C; 20.1°C), sólidos sedimentables (144.5mL/L; 0.02mL/L), oxígeno disuelto (4.5992 mg/L; 0.1924 mg/L) estos datos proporcionaron un punto de partida para el tratamiento de aguas residuales de tipo doméstica.</p>

Sequential UASB and dual media packed-bed reactors for domestic wastewater treatment - experiment and simulation

A wastewater treatment system composed of an upflow anaerobic sludge blanket (UASB) reactor followed by a packed-bed reactor (PBR) filled with Sorbulite(®) and Polonite(®) filter material was tested in a laboratory bench-scale experiment. The system was operated for 50 weeks and achieved very efficient total phosphorus (P) removal (99%), 7-day biochemical oxygen demand removal (99%) and pathogenic bacteria reduction (99%). However, total nitrogen was only moderately reduced in the system (40%). A model focusing on simulation of organic material, solids and size of granules was then implemented and validated for the UASB reactor. Good agreement between the simulated and measured results demonstrated the capacity of the model to predict the behaviour of solids and chemical oxygen demand, which is critical for successful P removal and recovery in the PBR.

Sewage treatment by an UAFB-EGSB biosystem with energy recovery and autotrophic nitrogen removal under different temperatures

A system combined an upflow anaerobic fixed bed (UAFB) and an expanded granular sludge bed (EGSB) was designed and verified as a success for treating real sewage with simultaneous energy recovery and autotrophic nitrogen removal. The impact of temperature (stepwise decreased from 30 °C to 20 °C and 10 °C) was a primary focus, aiming to reveal the response of the anaerobic digestion (AD) and anammox efficiency to the temperature variation. As the temperature decreases, the soluble chemical oxygen demand (sCOD) removal rate was 90.6%, 90.0% and 84.7%, respectively; total nitrogen (TN) removal was 69.4%, 48.8%, 38.4%, respectively; NH4(+)-N removal was 91.3%, 74.9%, 65.1%, respectively. Methanogenic activity of UAFB was significantly influenced by low temperatures, while the unavoidable growth of heterotrophic organisms in EGSB also contributed to the sCOD removal, even at 10 °C. Lower working temperature (10/20 °C) limited the growth and activity of ammonia-oxidizing bacteria (AOB) and anaerobic ammonia oxidation bacteria (AnAOB), but improved the nitrite-oxidizing bacteria (NOB) activity.

Modelling wastewater treatment in a submerged anaerobic membrane bioreactor

Mathematical modelling has been widely applied to membrane bioreactor (MBRs) processes. However, to date, very few studies have reported on the application of the anaerobic digestion model N.1 (ADM1) to anaerobic membrane processes. The aim of this study was to evaluate the applicability of the ADM1 to a submerged anaerobic MBR (SAMBR) treating simulated industrial wastewater composed of cheese whey and sucrose. This study demonstrated that the biological processes involved in SAMBRs can be modelled by using the ADM1. Moreover, the results showed that very few modifications of the parameters describing the ADM1 were required to reasonably fit the experimental data. In particular, adaptation to the specific conditions of the coefficients describing the wastewater characterisation and the reduction of the hydrolysis rate of particulate carbohydrate (khyd,ch) from 0.25 d(-1) (as suggested by the ADM1 for high-rate mesophilic reactors) to 0.13 d(-1) were required to fit the experimental data.

Treatment of domestic wastewater by an integrated anaerobic fluidized-bed membrane bioreactor under moderate to low temperature conditions

The performance of a novel integrated anaerobic fluidized-bed membrane bioreactor (IAFMBR) for treating practical domestic wastewater was investigated at a step dropped temperature from 35, 25, to 15°C. The COD removal was 74.0 ± 3.7%, 67.1 ± 2.9% and 51.1 ± 2.6% at 35, 25 and 15°C, respectively. The COD removal depended both on influent strength and operational temperature. The accumulation of VFAs (Volatile Fatty Acids) was affected by temperature, and acetic acid was the most sensitive one to the decrease of temperature. The methanogenic activity of the sludge decreased eventually and the methane yield was dropped from 0.17 ± 0.03, 0.15 ± 0.02 to 0.10 ± 0.01 L/Ld. And as compared with a mesophilic temperature, a low temperature can accelerate membrane biofouling. Proteins were the dominant matters causing membrane fouling at low temperature and membrane fouling can be mitigated by granular active carbon (GAC) through protein absorption.