Fouling layer characterization and pore-blocking mechanisms in an UF membrane externally coupled to a UASB reactor

A pilot-scale UASB reactor coupled with an external ultrafiltration (UF) membrane was operated under three different hydraulic retention times (HRT: 4, 8 and 12 h) for municipal wastewater treatment in order to assess the composition and distribution of the fouling layer, as well as to identify the predominant fouling mechanisms. For that purpose, membrane autopsies were carried out based on fouling layer density determination, thermogravimetric, SEM and EDX analysis. Results showed a  variable density of the fouling layer (average values were 13.90 ± 0.22, 13.46 ± 1.15 and 12.78 ± 0.49 mg/cm2 for HRT of 4, 8 and 12 h, respectively), indicating that this parameter had an impact on the fouling density. Organic material was predominant in the fouling layer, being around 75% of its composition for the three HRT studied. Regarding pore-blocking mechanisms, standard blocking was the predominant mechanism at the beginning of filtration, coexisting at the end of it with cake filtration. In the first filtration cycle (1 h), after standard blocking,  intermediate and complete blocking developed simultaneously during a short period of time and, finally, cake filtration prevailed. However, in the last (19th) filtration cycle, standard blocking and cake filtration occurred  simultaneously from the  beginning, suggesting the existence of an irreversible fouling layer, in spite of  chemical cleaning.Keywords: fouling layer density, pore blocking mechanisms, irreversible foulin

Tratamiento Anaerobio de Aguas Residuales Municipales. Desarrollo de una Planta Paquete de Tratamiento de Aguas Residuales para casas Habitación

Se presentan elementos técnicos que sustentan la factibilidad de la opción de tratamiento anaerobio del programa de saneamiento del Valle de México

Model assessment on the non-isothermal methane biofiltration at ambient conditions

Direct anaerobic sewage treatment is increasingly adopted in several intertropical developing countries. The reduced carbon footprint of such facilities is based on its low electricity requirements and potential energy (biogas) recovery; however, if dissolved CH4 in the effluent is not controlled, this advantage will be drastically reduced. A suitable option to overcome this situation is to adopt CH4 desorption by an air stream, followed by bio-oxidation in compost biofilters. In such systems, the methanotrophic activity will increase the temperature in the biofilter to inhibiting values (above 40 °C), reducing the active volume of the compost media and its removal efficiency. This work addresses this process limitation, aiming to assess the temperature variations in the filter media and their effects on methane oxidation performance under different operating conditions. A comprehensive mathematical 2-D porous-medium based model was developed and then calibrated and validated with experimental data. The model considers heat, momentum, and mass balances under non-steady-state conditions, including heat exchange at the biofilter container wall influenced by daily ambient temperature fluctuations and solar radiation. Results obtained from 6 model simulations at different operating conditions show that temperatures above 40 °C are reached at the center-upper zones of the compost biofilter due to the heat transported from the methanotrophic active zones located at the bottom (inlet) and container wall. At midday (12 – 14 h), solar radiation on the wall contributes 14% of the total heat gained in a non-covered biofilter. The model highlights the importance of facilitating heat transport from the compost media to the surroundings; some practical recommendations are presented for that purpose

Upgrade of a petrochemical wastewater treatment plant by an upflow anaerobic pond

International audienceA petrochemical plant producing terephthalic acid faced a saturation of its wastewater treatment facilities due to an increase in production. In fact, the plant has been growing in recent years, and the effluents have been treated by reproducing the original activated sludge design. However, owing to lack of space, as well as energy consumption and sludge production reaching a certain level, the plant considered other options for coping with the new effluent flow and organic load. Based on the authors' previous experience with this wastewater, the consultant designed a process consisting of modifying an existing pond, in order to add an anaerobic step before the aerobic tanks already in operation. The anaerobic pond is a three-stage process, all included in the same adapted basin, with a distribution system in the bottom of each stage that creates an upflow pattern. Terephthalic acid wastewater is a mixture of several organic acids, with different anaerobic degradation kinetics, acetic and benzoic acids being more rapidly removed; the staged design takes this into account. The first two stages have a plastic floating cover (5,813 m 3 and 8,719 m 3 volume, respectively), while the third one is a conventional UASB type reactor (6,276 m 3 volume) with a gas-liquid-solid separation device on top. The design wastewater flow is 230 m 3 /h, with 10,300 mg/l COD, a pH of 4.5 and a temperature of 40 °C. There is an effluent recycling pump (510 m 3 /h) to control upflow velocities and eventual acidification problems in the first two stages. The reactor, seeded with anaerobically adapted waste sludge from the aerobic plant, is now under start up, with the expected performance

Characterization of the biofiltration of methane emissions from municipal anaerobic effluents

Atmospheric methane emissions from anaerobic effluents represent a source of greenhouse gases that can be mitigated by biofiltration. This study performs a comprehensive analysis on methane biofiltration using compost as packing to determine the limiting phenomena. A mathematical model calibrated by heterogeneous respirometry predicted the temperature effects (15–40 °C) on the kinetics of mass transport and biological reaction in a methanotrophic biofilm. It was validated through experimentation from steady state continuous runs (elimination capacities from 38 to 50 g m−3 h−1 with removal efficiencies of 62–80%). Results from model validation showed no significant differences (p-value ≥ 0.05) between the experimental methane elimination capacities and those predicted by the model at inlet 21 gCH4 m−3 (4% volume in air, at 20 °C and 0.78 atm). To assess the limiting phenomena, the global and biofilm effectiveness factors were evaluated. This analysis demonstrated a biofilm limitation, specifically due to methane diffusion within the biofilm at the conditions tested (19 min of empty bed residence time). Even if the optimal temperature for methane oxidation activity was between 25 and 30 °C, the lower reaction rates at other temperatures did not limit the methane biofiltration in the applied interval