Disruption of granules by hydrodynamic force in internal circulation anaerobic reactor

Approaches in Design of Laboratory-Scale UASB Reactors

Up-flow Anaerobic Sludge Blanket (UASB) reactors are popular tools in wastewater treatment systems due to the ability to work with high feed rates and wastes with high concentration of organic contaminants. While full-scale industrial applications of UASB reactors are developed and described in the available literature, laboratory-scale designs utilized for treatability testing are not well described. The majority of published studies do not describe the laboratory UASB construction details or do use reactors that already had developed a trophic network in microbial consortia under laboratory environment and therefore are more stable. The absence of defined guidelines for geometry design, selection of materials, construction, operation rules, and, especially, the start-up conditions, significantly hamper researchers who desire to conduct treatability testing using UASB reactors in laboratory scale. In this article, we compiled and analyzed the information available in the refereed literature concerning UASB reactors used in laboratory environment, where information on geometry and/or operational conditions were provided in detail. We utilized the information available in the literature and the experience gained in our laboratory (Sustainable Waste to Bioproducts Engineering Center) to suggest a unified operation flowchart and for design, construction, operation, and monitoring for a laboratory-scale UASB reactors.

Multiscale hydrodynamic investigation to intensify the biogas production in upflow anaerobic reactors

Hydrodynamics plays a main role for the performance of an anaerobic reactor involving three phases: wastewater, sludge granules and biogas bubbles. The present work was focused on an original approach to investigate the hydrodynamics at different scales and then to intensify the performance of such complex reactors. The experiments were carried out respectively in a 3D reactor at macroscale, a 2D reactor at mesoscale and a 1D anaerobic reactor at microscale. A Particle Image Velocimetry (PIV), a micro-PIV and a high-speed camera were employed to quantify the liquid flow fields and the relative motion between sludge granules and bubbles. Shear rates exerted on sludge granules were quantified from liquid flow fields. The optimal biogas production is obtained at mean shear rate varying from 28 to 48s(-1), which is controlled by two antagonistic mechanisms. The multiscale approach demonstrates pertinent mechanisms proper to each scale and allows a better understanding of such reactors.

Identical full-scale biogas-lift reactors (Blrs) with anaerobic granular sludge and residual activated sludge for brewery wastewater treatment and kinetic modeling

Two identical full-scale biogas-lift reactors treating brewery wastewater were inoculated with different types of sludge to compare their operational conditions, sludge characteristics, and kinetic models at a mesophilic temperature. One reactor (R1) started up with anaerobic granular sludge in 12 weeks and obtained a continuously average organic loading rate (OLR) of 7.4 kg chemical oxygen demand (COD)/(m3 x day), COD removal efficiency of 80%, and effluent COD of 450 mg/L. The other reactor (R2) started up with residual activated sludge in 30 weeks and granulation accomplished when the reactor reached an average OLR of 8.3 kg COD/(m3 x day), COD removal efficiency of 90%, and effluent COD of 240 mg/L. Differences in sludge characteristics, biogas compositions, and biogas-lift processes may be accounted for the superior efficiency of the treatment performance of R2 over R1. Grau second-order and modified StoverKincannon models based on influent and effluent concentrations as well as hydraulic retention time were successfully used to develop kinetic parameters of the experimental data with high correlation coefficients (R2 > 0.95), which further showed that R2 had higher treatment performance than R1. These results demonstrated that residual activated sludge could be used effectively instead of anaerobic granular sludge despite the need for a longer time.

Performance and dynamic characteristics of microbial communities in an internal circulation reactor for treating brewery wastewater

A laboratory-scale internal circulation (IC) anaerobic reactor fed with brewery wastewater was operated at 35 degrees C + 1 degrees C. The influent was pumped into the bottom of the IC reactor by a pulse pump, whereas the effluent was drawn from the upper outlet and allowed to flow into the effluent tank. The biogas volume was recorded using a gas container connected to a biogas metre. The results indicated that the maximum organic loading rate (OLR) of the IC reactor was 19.5 kg chemical oxygen demand (COD)/m3/day; at which point, the dominant archaeal populations found in the sludge using the polymerase chain reaction with denaturing gradient gel electrophoresis were Methanosaeta species. The COD removal efficiencies of the reactor exceeded 85%, with a maximum specific methane production rate of 210 mL CH4/g volatile suspended solids (VSS)/day and a coenzyme F420 content of 0.16 micromol/g VSS, respectively. The main archaeal species in the sludge samples at different OLRs varied greatly, as compared with the organisms in the inoculated sludge. The dominant archaeal species in the treated sludge at low OLRs were Methanosarcina species, whereas those at high OLRs were Methanosaeta species.

Microscale investigation of anaerobic biogas production under various hydrodynamic conditions

This work presents an investigation at microscale of various mechanisms affecting anaerobic reactions within the microdevices. In particular, the effect of different hydrodynamic conditions associated with the granular particles' size and density on the biogas production was studied in order to intensify the performance of the anaerobic reactor. The image analysis techniques offer an opportunity to observe and quantify the nucleation and growth of biogas bubble at microscale on a single granule. In addition, the flow conditions were perfectly controlled in the microdevice, and the liquid flow fields were measured by a microparticle image velocimetry (micro-PIV) system. The effect of real hydrodynamic conditions exerted directly on granules onto the maximum biogas production rate was described for the first time. Finally, the role of hydrodynamic conditions on the biogas production at microscale is discussed through a straightforward relationship between the shear rates exerted on the granule and the optimal biogas production rate. The investigation reveals that big granules could have satisfactory biogas production ability under relatively weak hydrodynamic conditions. Thus they would be priority selection for industrial reactors.

Effects of increase modes of shear force on granule disruption in upflow anaerobic reactors

Sludge washout is listed among the top practical problems of the high rate upflow anaerobic reactors. This study investigated quantitatively two sludge washout processes operated under different hydrodynamic shear increase modes with the intervals of 1 and 10 days respectively. The results reveal that the sludge washout accompanying with large-scale granule disruption could lead to performance failure with heavy sludge loss ratio of about 46.1% at sludge loss rate about 0.35 gVSS L(-1) d(-1) during the process with shear increase interval of 1 day, while the highest sludge loss rate was only 0.12 gVSS L(-1) d(-1) during the process with 10-day interval. The intensified shear conditions could weaken the granules through inhibiting the extracellular polymers production and bioactivity. As consequences, an outbreak of large-scale granule disruption would raise and then significantly accelerate the sludge washout. Since long interval could provide the granules the opportunity to recover from these negative effects to some extent, the shear increase strategy of long interval over 10 days is favorably recommended to operate full-scale reactors during the start-up and shock load periods. The pioneer use of the micro particle image velocimetry in this study offers the possibility to discover the real hydrodynamic conditions around granules at microscale for the first time and reveals that the shear force exerts directly on the granular surface as a mechanical disruption force and big granules undergo high disruption force. The granule disruption is a result of the competition between the granule and the ambient hydrodynamic shear conditions rather than a process with shear force as a sole dominant factor. These could facilitate the understanding of the complicated interactions between the hydrodynamics and reactor performance and favor then a better control of the full-scale reactors.

Bubble formation dynamics in various flow-focusing microdevices

The aim of this study is to investigate three types of gas-liquid micromixer geometries, including a cross-shape and two converging shape channels for the bubble formation in different liquids. The bubble shape, size, and formation mechanism were investigated under various experimental conditions such as the flow rates of two phases, physical properties of the liquid, and mixer geometries. A micro particle image velocimetry technique and a high-speed camera were used to characterize and quantify gas-liquid flows. It was revealed that the bubble formation, in particular the bubble size, depends on the geometry of the mixing section between two phases. A correlation gathering numerous experimental data was elaborated for the estimation of the bubble size. The influence of different parameters such as the flow rate ratio between two phases, surface tension, and liquid viscosity is well taken into consideration on the basis of the understanding of the bubble formation mechanism at the microscale. This paper marks an original improvement in the domain where no flow field characterizations or correlations were established in flow-focusing devices.