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We report the relationship between enrichment of adapted populations and enhancement of community functional resilience in methanogenic bioreactors. Although previous studies have shown the positive effects of acclimation, this work directly investigated the relationships between microbiome dynamics and performance of anaerobic co-digesting reactors in response to different levels of an environmental perturbation (loading of grease interceptor waste [GIW]). Using the methanogenic microbiome from a full-scale digester, we developed eight sets of microbial communities in triplicate using different feed sources. These substrate-specific microbiomes were then exposed to three independent disturbance events of low-, mid- and high-GIW loading rates. This approach allowed us to directly attribute differences in community responses to differences in community composition. Despite identical inocula, environment (digester operation, substrate loading rate, and feeding patterns) and general whole-community function (methane production and effluent quality) during the cultivation period, different substrates led to different microbial community assemblies. Lipid pre-acclimation led to enrichment of a pool of specialized populations, along with thriving of sub-dominant communities. The enrichment of these populations improved functional resilience and process performance when exposed to a low level of lipid-rich perturbation compared with less-acclimated communities. At higher levels of perturbation, the communities were not able to recover methanogenesis, indicating a loading limit to the resilience response. This study extends our current understanding of environmental perturbations, feed-specific adaptation, and functional resilience in methanogenic bioreactors.IMPORTANCEThis study demonstrates, for the first time for GIW co-digestion, how applying similar perturbations to different microbial communities was used to directly identify the causal relationships between microbial community, function, and environment in triplicate anaerobic microbiomes. We evaluated the impact of feed-specific adaptation on methanogenic microbiomes and demonstrated how microbiomes can be influenced to improve their functional (methanogenic) resilience to GIW inhibition. These findings demonstrate how an ecological framework can help improve a biological engineering application, and more specifically, increase the potential of anaerobic co-digestion for converting wastes to energy., Competing Interests: The authors declare no conflict of interest.

Biological floc size is an important reactor microenvironment parameter that is often not experimentally controlled due to a lack of suitable methods. Here, we introduce the Couette-Taylor bioreactor (CTB) as an improved tool for controlling biological floc size, specifically as compared with bubble-column sequencing batch reactors (SBRs). A CTB consists of two concentric walls, either of which may be rotated to induce fluid motion. The induced flow produces hydrodynamic shear which is more uniform than that produced through aeration in SBRs. Because hydrodynamic shear is a major parameter controlling floc size, we hypothesized the ability to better control shear rates within a CTB would enable better-controlled floc sizes. To test this hypothesis, we measured the particle size distributions of activated sludge flocs from CTBs with either inner (iCTB) or outer (oCTB) rotating walls as well as SBRs with varying height to diameter ratios (0.5, 1.1, and 9.4). The rotation speed of the CTBs and aeration rate of the SBRs were varied to produce predicted mean shear rates from 25 to 250 s -1 . Further, the shear rate distributions for each experiment were estimated using computational fluid dynamics (CFD). In all SBR experiments, the floc distributions did not significantly vary with shear rate or geometry, likely because shear rates (estimated by CFD) differed much less than originally predicted by theory. In the CTB experiments, the mean particle size decreased proportionally with increased hydrodynamic shear, and iCTBs produced particle size distributions with smaller coefficients of variation than oCTBs (0.3 vs. 0.5-0.7, respectively)., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The optimal design and operation of photosynthetic bioreactors (PBRs) for microalgal cultivation is essential for improving the environmental and economic performance of microalgae-based biofuel production. Models that estimate microalgal growth under different conditions can help to optimize PBR design and operation. To be effective, the growth parameters used in these models must be accurately determined. Algal growth experiments are often constrained by the dynamic nature of the culture environment, and control systems are needed to accurately determine the kinetic parameters. The first step in setting up a controlled batch experiment is live data acquisition and monitoring. This protocol outlines a process for the assembly and operation of a bench-scale photosynthetic bioreactor that can be used to conduct microalgal growth experiments. This protocol describes how to size and assemble a flat-plate, bench-scale PBR from acrylic. It also details how to configure a PBR with continuous pH, light, and temperature monitoring using a data acquisition and control unit, analog sensors, and open-source data acquisition software.

Microbial community assembly (MCA) processes that shape microbial communities in environments are being used to analyze engineered bioreactors such as activated sludge systems and anaerobic digesters. The goal of studying MCA is to be able to understand and predict the effect of design and operation procedures on bioreactor microbial composition and function. Ultimately, this can lead to bioreactors that are more efficient, resilient, or resistant to perturbations. This review summarizes the ecological theories underpinning MCA, evaluates MCA analysis methods, analyzes how these MCA-based methods are applied to engineered bioreactors, and extracts lessons from case studies. Furthermore, we suggest future directions in MCA research in engineered bioreactor systems. The review aims to provide insights and guidance to the growing number of environmental engineers who wish to design and understand bioreactors through the lens of MCA. [Display omitted] [ABSTRACT FROM AUTHOR]

Effective and low-cost dynamic membrane bioreactors (DMBR) can be a strong option for wastewater treatment in developing countries. The goal of this study was to investigate the effect of rice husk addition on the DMBR's nitrogen removal performance. Tests were performed at both lab-scale and pilot-scale facilities. Results showed that rice husk served as a suitable biofilm carrier as well as an effective denitrification carbon source. In lab-scale experiments, the removal efficiency of rice husk amended DMBR for chemical oxygen demand (COD), , and total nitrogen (TN) was 96.7, 96.3, and 80.4%, respectively. Results from the pilot-scale DMBR system showed that removal efficiency for COD and was 90.3 and 95.2%, respectively, whereas TN removal was comparatively lower (50.5%). Fluorescence in situ hybridization (FISH) analysis showed that the bacterial population was higher in the rice husk added DMBR than the controlled DMBR, and ammonia-oxidizing bacteria were the main components of total heterotrophic bacteria. Overall, the rice husk dosing has improved the simultaneous nitrification-denitrification (SND) rate by 9.7% in DMBR and can be an economical and effective carbon source for the total nitrogen removal process. [ABSTRACT FROM AUTHOR]

The cake layers play a key role in the rejection of particles in dynamic membrane bioreactors and produces most of the resistance. This research aims to directly observe and measure the transient structure of the cake layers at different times and depths. The results showed the membrane flux remained relatively stable for the first 30 h, but decreased from 110 L/m 2 h to 88 L/m 2 h in the next 20 h. The membrane resistance was highly correlated with the cake layer thickness. The porosity and average pore diameter obtained from the scanning electron microcopy (SEM) pictures displayed no temporal variations, as only the new generated surface of the cake layer can be observed by SEM. However, the specific pore volume and surface area based on the Brunauer–Emmett–Teller (BET) nitrogen adsorption results displayed an initial decline, from 0.30 cc/g to 0.22 cc/g, due to the disappearance of the small diameter pores (1–10 nm) with time. The large diameter pores (30–250 nm) accounted for the majority of the cumulative pore volumes in all samples, as well as in the top layer, middle layer, and bottom layer. The specific pore volume and specific surface area exhibited a decline from the top layer to bottom layer, from 0.38 cc/g to 0.21 cc/g, due to the blockage of large diameter pores. In addition, BET nitrogen adsorption data provided comprehensive structural characteristics of the cake layers. [ABSTRACT FROM AUTHOR]