Effect of the Aeration Strategy on NOB Suppression in Activated Sludge and Biofilm in a Hybrid Reactor with Nitrification/Denitrification

The purpose of the study was to analyse the impact of aeration strategies defined by the changes in the duration of aerated sub-phases, the ratio between non-aerated and aerated sub-phase times (R), and dissolved oxygen concentrations (DO) on the suppression of nitrite-oxidizing bacteria (NOB) in activated sludge and biofilm developing in a hybrid reactor with nitrification/denitrification. The primary factor causing NOB suppression both in biofilm and in activated sludge was an increase in the R-value (from 0 to 1/4 and from 1/4 to 1/3). After reducing the DO from 3 to 2 mg O2/L, there were no changes in the frequency of NOB occurrence, and no reduction in the nitrite oxidation rate was recorded. The abundance of Comammox bacteria was considerably affected by the change from continuous to intermittent aeration. Activated sludge showed a substantial increase in the quantity of clade A and B, whereas the quantity considerably decreased in biofilm.

Stability of Polymeric Membranes to UV Exposure before and after Coating with TiO2 Nanoparticles

The combination of photocatalysis and membrane filtration in a single reactor has been proposed, since the photocatalytic treatment may degrade the pollutants retained by the membrane and reduce fouling. However, polymeric membranes can be susceptible to degradation by UV radiation and free radicals. In the present study, five commercial polymeric membranes were exposed to ultraviolet (UV) radiation before and after applying a sol–gel coating with TiO2 nanoparticles. Membrane stability was characterized by changes in hydrophilicity as well as analysis of soluble substances and nanoparticles detached into the aqueous medium, and by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometry (EDS) for structural, morphological, and elemental distribution analysis, respectively. The TiO2 coating conferred photocatalytic properties to the membranes and protected them during 6 h of UV radiation exposures, reducing or eliminating chemical and morphological changes, and in some cases, improving their mechanical resistance. A selected commercial nanofiltration membrane was coated with TiO2 and used in a hybrid reactor with a low-pressure UV lamp, promoting photocatalysis coupled with cross-flow filtration in order to remove 17α-ethinylestradiol spiked into an aqueous matrix, achieving an efficiency close to 100% after 180 min of combined filtration and photocatalysis, and almost 80% after 90 min.

Impact of operational conditions on methane yield and microbial community composition during biological methanation in in situ and hybrid reactor systems

Background Biogas can be upgraded to methane biologically by adding H2 to biogas reactors. The process is called biological methanation (BM) and can be done in situ in a regular biogas reactor or the biogas can be transferred to a separate ex situ upgrading reactor. The hybrid BM concept, a combination of in situ and ex situ BM, has received little attention, and only a few studies have been reported. The hybrid BM has the advantage of resolving the issue of pH increment during in situ BM, while the size of the ex situ BM reactor could be reduced. Results In this study, the efficiency of in situ and hybrid biological methanation (BM) for upgrading raw biogas was investigated. The hybrid BM system achieved a CH4 yield of 257 mL gVS−1 when degrading a feedstock blend of manure and cheese waste. This represented an increase in methane yield of 76% when compared to the control reactor with no H2 addition. A 2:1 H2:CO2 ratio resulted in stable reactor performance, while a 4:1 ratio resulted in a high accumulation of volatile fatty acids. H2 consumption rate was improved when a low manure–cheese waste ratio (90%:10%) was applied. Furthermore, feeding less frequently (every 48 h) resulted in a higher CH4 production from CO2 and H2. Methanothermobacter was found to dominate the archaeal community in the in situ BM reactor, and its relative abundance increased over the experimental time. Methanosarcina abundance was negatively affected by H2 addition and was nearly non-existent at the end of the experiment. Conclusions Our results show that hybrid BM outperforms in situ BM in terms of total CH4 production and content of CH4 in the biogas. In comparison to in situ BM, the use of hybrid BM increased CH4 yield by up to 42%. Furthermore, addition of H2 at 2:1 H2:CO2 ratio in in situ BM resulted in stable reactor operation.

A Forward Feedback Control Scheme for a Solar Thermochemical Moving Bed Countercurrent Flow Reactor

Pelletized thermochemical energy storage media has the potential for long duration energy storage. The production of charged solid state energy storage media can be done within a cylindrical cavity chemical reactor that captures concentrated solar radiation from a solar field. Temperature stability of a solar reactor is directly influenced by the solar flux intercepted. This paper presents a low-order physical model to simulate the dynamic response of temperature inside a tubular plug-flow reactor prototype. Solid granular particles are fed to the tube from the top whereas a counter-current flowing gas enters the tube from the bottom. An in-house code was developed to model transient heat transfer of the tube wall, gas, and moving particles. The model was preliminarily validated with packed beds for different temperatures ranges and two gas flow rates. Dynamic response of the reactor temperature is simulated for different input power and gas/particle flow rates. The results show that the system response can be controlled efficiently by utilizing input power (solar flux) as a control parameter. A conventional PI controller is designed to control the temperature inside the reactor and to maintain it during the solar flux intermittency. Controller parameters are tuned using the Ziegler-Nichols method to ensure optimal system response. The results show that the feedback control model is successful in tracking different reference reactor temperatures within reasonable settling time of 30 minutes and eliminated overshoot. This study can be extended to include a hybrid reactor with a multi-input, multi-output variable system.

Impact of Operational Conditions on Methane Yield and Microbial Community Composition during Biological Methanation in a Hybrid Reactor System

Background: Biogas can be upgraded to methane biologically by adding hydrogen to biogas reactors. The process is called biological methanation (BM) and can be done in-situ in a regular biogas reactor or the biogas can be transferred to a separate ex-situ upgrading reactor. The hybrid BM concept, a combination of in-situ and ex-situ BM, has received little attention, and only a few studies have been reported. The hybrid BM has the advantage of resolving the issue of pH increment during in-situ BM, while the size of the ex-situ BM reactor could be reduced.Results: In this study, the efficiency of in-situ and hybrid biological methanation (BM) for upgrading raw biogas was investigated. The hybrid BM system achieved a CH4 yield of 257 mL gVS-1 when degrading a feedstock blend of manure and cheese waste. This represented an increase in methane yield of 76% when compared to the control reactor with no H2 addition. A 2:1 H2:CO2 ratio resulted in stable reactor performance, while a 4:1 ratio resulted in a high accumulation of volatile fatty acids. H2 consumption rate was improved when a low manure-cheese waste ratio (90%:10%) was applied. Furthermore, feeding less frequently (every 48 hours) resulted in a higher CH4 production from CO2 and H2. Methanothermobacter was found to dominate the archaeal community in the in-situ BM reactor, and its relative abundance increased over the experimental time. Methanosarcina abundance was negatively affected by H2 addition and was nearly non-existent at the end of the experiment. Conclusions: Our results show that hybrid BM outperforms in-situ BM in terms of total CH4 production and content of CH4 in the biogas. The application of hybrid BM increased CH4 yield up to 42%. Furthermore, addition of H2 at 2:1 H2:CO2 ratio in in-situ BM resulted in stable reactor operation.