Scenarios (a)–(c) are created to study the effect of the chemical surface charge of carbon electrodes on capacitive deionization using symmetric carbon electrode pairs.
Horizontal rotating reactors offer many advantages for enzymatic hydrolysis of viscous biomass slurries; however, they do not provide homogenous mixtures since motion is only in the angular direction. Multi-directional mixing is important for dispersing enzymes and carrying products away from reaction sites. The objective here was to experimentally quantify mixing times and axial dispersion coefficients in a horizontal rotating bioreactor. Mixing times were of the same order as reaction times, indicating that enzymatic hydrolysis could be as much controlled by diffusion and mixing effects as by the complex reaction mechanism. The dispersion coefficient for the highest solids slurry was 20× less than the lowest solids slurry, which is indicative of the difference in free water and the magnitude change of viscosity with relatively small addition of solids. The slow mixing times and low dispersion may be an acceptable tradeoff with significantly lower power requirements compared to a conventional vertical reactor.
In two-stage anaerobic expanded granular sludge bed (EGSB) reactors, up to one-third of the chemical oxygen demand (COD) content is naturally preacidified in a first stage preacidification (PA) tank and then fed to a second stage digester for conversion to methane. Hydrogen, an intermediate product of the first stage, could be theoretically captured escaping from the PA tank and sent to the digester to biologically convert the carbon dioxide to methane for biogas enhancement. Pilot-scale tests were conducted to assess the impact of introducing hydrogen gas on biogas quality enhancement and substrate removal efficiency in an EGSB digester fed with distillery wastewater at mesophilic temperature (35°C). The amount of hydrogen introduced, 0.15 or 0.30 L/ (L biogas $day), was less than what could be theoretically captured escaping from the PA tank. Biogas quality was enhanced by *10% to 20% and the energy yield increased by *33-42% depending on the hydrogen injection rate. COD removal efficiency remained constant at about *98% with and without hydrogen. The Monod model maximum substrate removal rate constant slightly increased, while the half-saturation coefficient slightly decreased with the added hydrogen, both indicating that hydrogen injection did not negatively affect substrate removal efficiency or biomass culture stability.
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