Relating Methanogen Community Structure and Function in Anaerobic Digesters

A deeper understanding of how microbial community structure relates to process function would help improve anaerobic digester design. This dissertation describes both qualitative and quantitative relationships between anaerobic digester function and microbial community structure. Community structure was characterized using banding pattern intensities from denaturing gradient gel electrophoresis (DGGE) for the mcrA gene of methanogenic Archaea. The first project compared a single-stage continuously mixed stirred tank reactor (CSTR) and staging with an acidogenic CSTR followed by a methanogenic CSTR. After seeding with the same biomass, these unique process configurations exhibited different function and qualitatively different methanogen communities. Compared to a single-stage CSTR, staging increased the maximum rate of methane production by 41, 26, and 57% with propionate, acetate, and hydrogen, respectively. Additionally, the staged digester produced 10% more methane and achieved 10% greater volatile solids (VS) destruction. The second project also provided a qualitative relationship: methanogen community structure impacted digester function upon bioaugmentation. Specific methanogenic activity (SMA) with propionate statistically increased (up to 57%) in six of nine bioaugmented anaerobic cultures. These increases correlated to methanogen community structure above the 98% level (rs = 0.770) using Spearman’s Rank Correlation Coefficient (two-tailed). In the third project, a quantitative structure-activity relationship (QSAR) was established between methanogen community structure and two activities using multiple linear regression (MLR). Two different QSARs were predictive of SMA values with propionate (q2 = 0.52) and with glucose (q2 = 0.56), respectively. A MLR model may be applicable to other biological communities when trophic redundancy and a ubiquitous gene are present and when a linear model is appropriate. Greater understanding of anaerobic digester microbial communities is possible using these QSARs. This research serves as a template that can be used to construct additional QSARs for other complex microbial communities in engineered systems

Relating Anaerobic Digestion Microbial Community and Process Function

Anaerobic digestion (AD) involves a consortium of microorganisms that convert substrates into biogas containing methane for renewable energy. The technology has suffered from the perception of being periodically unstable due to limited understanding of the relationship between microbial community structure and function. The emphasis of this review is to describe microbial communities in digesters and quantitative and qualitative relationships between community structure and digester function. Progress has been made in the past few decades to identify key microorganisms influencing AD. Yet, more work is required to realize robust, quantitative relationships between microbial community structure and functions such as methane production rate and resilience after perturbations. Other promising areas of research for improved AD may include methods to increase/control (1) hydrolysis rate, (2) direct interspecies electron transfer to methanogens, (3) community structure–function relationships of methanogens, (4) methanogenesis via acetate oxidation, and (5) bioaugmentation to study community–activity relationships or improve engineered bioprocesses

Relating Methanogen Community Structure and Anaerobic Digester Function

Much remains unknown about the relationships between microbial community structure and anaerobic digester function. However, knowledge of links between community structure and function, such as specific methanogenic activity (SMA) and COD removal rate, are valuable to improve anaerobic bioprocesses. In this work, quantitative structure–activity relationships (QSARs) were developed using multiple linear regression (MLR) to predict SMA using methanogen community structure descriptors for 49 cultures. Community descriptors were DGGE demeaned standardized band intensities for amplicons of a methanogen functional gene (mcrA). First, predictive accuracy of MLR QSARs was assessed using cross validation with training (n = 30) and test sets (n = 19) for glucose and propionate SMA data. MLR equations correlating band intensities and SMA demonstrated good predictability for glucose (q2 = 0.54) and propionate (q2 = 0.53). Subsequently, data from all 49 cultures were used to develop QSARs to predict SMA values. Higher intensities of two bands were correlated with higher SMA values; high abundance of methanogens associated with these two bands should be encouraged to attain high SMA values. QSARs are helpful tools to identify key microorganisms or to study and improve many bioprocesses. Development of new, more robust QSARs is encouraged for anaerobic digestion or other bioprocesses, including nitrification, nitritation, denitrification, anaerobic ammonium oxidation, and enhanced biological phosphorus removal

Recent Biological Research in Greenland

The first two authors present a brief outline of research in plant taxonomy, geography and ecology; tree planting and future work. Dr. Dunbar reviews terrestrial and fresh-water faunistic studies: marine biological and fisheries investigations in West Greenland and its offshore waters

Bioaugmentation Can Increase Steady-State Methane Production and COD Reduction in Anaerobic Digestors

Bioaugmentation was investigated to improve anaerobic digesters at steady state. Two digester sets (Sets A and B), were seeded with different inocula and operated (HRT = 10 days, OLR = 4 g-COD/LR-day). Bioaugmented digesters received 50 mg-VSS/LR-day of an active culture enriched for H2/CO2 and propionate utilization. The bioaugmented Set-A digesters showed a significant increase in methane production and COD reduction, whereas Set-B digesters did not. The specific methanogenic activity (SMA) of seed used to start Set-A was lower than that used to start Set-B. In addition, initial SMA screening of each inocula mixed with enrichment culture indicated Set-A inoculum would benefit from bioaugmentation, whereas Set-B would not. Therefore, low SMA may indicate that bioaugmentation is beneficial and initial SMA screening can predict bioaugmentation outcomes. In conclusion, bioaugmentation can result in higher methane production and lower effluent COD at steady state; however, success depends on the initial digester methanogenic community