• Energy Research

The building of a sustainable society will require reduction of dependency on fossil fuels and lowering of the amount of pollution that is generated. Wastewater treatment is an area in which these two goals can be addressed simultaneously. As a result, there has been a paradigm shift recently, from disposing of waste to using it. There are several biological processing strategies that produce bioenergy or biochemicals while treating industrial and agricultural wastewater, including methanogenic anaerobic digestion, biological hydrogen production, microbial fuel cells and fermentation for production of valuable products. However, there are also scientific and technical barriers to the implementation of these strategies.

The biomethane potential and biodegradability of an array of substrates with highly heterogeneous characteristics, including mono- and co-digestion samples with dairy manure, was determined using the biochemical methane potential (BMP) assay. In addition, the ability of two theoretical methods to estimate the biomethane potential of substrates and the influence of biodegradability was evaluated. The results of about 175 individual BMP assays indicate that substrates rich in lipids and easily-degradable carbohydrates yield the highest methane potential, while more recalcitrant substrates with a high lignocellulosic fraction have the lowest. Co-digestion of dairy manure with easily-degradable substrates increases the specific methane yields when compared to manure-only digestion. Additionally, biomethane potential of some co-digestion mixtures suggested synergistic activity. Evaluated theoretical methods consistently over-estimated experimentally-obtained methane yields when substrate biodegradability was not accounted. Upon correcting the results of theoretical methods with observed biodegradability data, an agreement greater than 90% was achieved.

Multifunctional reactor microbiomes can elongate short-chain carboxylic acids (SCCAs) to medium-chain carboxylic acids (MCCAs), such as n-caproic acid. However, it is unclear whether this microbiome biotechnology platform is stable enough during long operating periods to consistently produce MCCAs. During a period of 550 days, we improved the operating conditions of an anaerobic bioreactor for the conversion of complex yeast-fermentation beer from the corn kernel-to-ethanol industry into primarily n-caproic acid. We incorporated and improved in-line, membrane liquid-liquid extraction to prevent inhibition due to undissociated MCCAs at a pH of 5.5 and circumvented the addition of methanogenic inhibitors. The microbiome accomplished several functions, including hydrolysis and acidogenesis of complex organic compounds and sugars into SCCAs, subsequent chain elongation with undistilled ethanol in beer, and hydrogenotrophic methanogenesis. The methane yield was 2.40 ± 0.52% based on COD and was limited by the availability of carbon dioxide. We achieved an average n-caproate production rate of 3.38 ± 0.42 g L(-1) d(-1) (7.52 ± 0.94 g COD L(-1) d(-1)) with an n-caproate yield of 70.3 ± 8.81% and an n-caproate/ethanol ratio of 1.19 ± 0.15 based on COD for a period of ∼55 days. The maximum production rate was achieved by increasing the organic loading rates in tandem with elevating the capacity of the extraction system and a change in the complex feedstock batch.

A bioprocess based on open-culture anaerobic biotechnology to elongate acetate and ethanol (C2) into primarilyn-caprylate (C8).

Anaerobic digestion of brewery wastewater solids in the form of primary sludge was investigated for its potential as a source of energy (methane). We operated a low-rate (hydraulic retention time (HRT)=solids retention time (SRT)) continuously stirred anaerobic digester (CSAD) and a high-rate (SRT>HRT) anaerobic sequencing batch reactor (ASBR) in parallel for 250 days. We found that high-rate anaerobic digestion was beneficial for solids-rich waste flows even during a long-term operating period that included a shock load of nonbiodegradable total solids. The ASBR biomass achieved a higher specific methanogenic activity compared to the CSAD biomass (0.257+/-0.043 vs. 0.088+/-0.008 g CH(4)-COD g(-1)VSS d(-1)), which aided in stability during the shock load with total solids. The methane yield for the ASBR was 40-34% higher than for the CSAD (0.306 vs. 0.219 l CH(4)g VS(-1) fed for days 1-183 and 0.174 vs. 0.130 l CH(4)g VS(-1) fed for days 184-250, respectively). Finally, we operated an ASBR for an additional 295 days to evaluate the effect of temperature variation on system stability. A stable performance was achieved between the operating temperatures of 22-41 degrees C.

A long-term comparative study using continuously-stirred anaerobic digesters (CSADs) operated at mesophilic and thermophilic temperatures was conducted to evaluate the influence of the organic loading rate (OLR) and chemical composition on process performance and stability. Cow manure was co-digested with dog food, a model substrate to simulate a generic, multi-component food-like waste and to produce non-substrate specific, composition-based results. Cow manure and dog food were mixed at a lower - and an upper co-digestion ratio to produce a low-fiber, high-strength substrate, and a more recalcitrant, lower-strength substrate, respectively. Three increasing OLRs were evaluated by decreasing the CSADs hydraulic retention time (HRT) from 20 to 10 days. At longer HRTs and lower manure-to-dog food ratio, the thermophilic CSAD was not stable and eventually failed as a result of long-chain fatty acid (LCFA) accumulation/degradation, which was triggered by the compounded effects of temperature on reaction rates, mixing intensity, and physical state of LCFAs. At shorter HRTs and upper manure-to-dog food ratio, the thermophilic CSAD marginally outperformed the biomethane production rates and substrate stabilization of the mesophilic CSAD. The increased fiber content relative to lipids at upper manure-to-dog food ratios improved the stability and performance of the thermophilic process by decreasing the concentration of LCFAs in solution, likely adsorbed onto the manure fibers. Overall, results of this study show that stability of the thermophilic co-digestion process is highly dependent on the influent substrate composition, and particularly for this study, on the proportion of manure to lipids in the influent stream. In contrast, mesophilic co-digestion provided a more robust and stable process regardless of the influent composition, only with marginally lower biomethane production rates (i.e., 7%) for HRTs as short as 10 days (OLR = 3 g VS/L-d).

Bioelectrochemical systems (BESs) employing mixed microbial communities as biocatalysts are gaining importance as potential renewable energy, bioremediation, or biosensing devices. While we are beginning to understand how individual microbial species interact with an electrode as electron donor, little is known about the interactions between different microbial species in a community: sugar fermenting bacteria can interact with current producing microbes in a fashion that is either neutral, positively enhancing, or even negatively affecting. Here, we compare the bioelectrochemical performance of Shewanella oneidensis in a pure-culture and in a co-culture with the homolactic acid fermenter Lactococcus lactis at conditions that are pertinent to conventional BES operation. While S. oneidensis alone can only use lactate as electron donor for current production, the co-culture is able to convert glucose into current with a comparable coulombic efficiency of ∼17%. With (electro)-chemical analysis and transcription profiling, we found that the BES performance and S. oneidensis physiology were not significantly different whether grown as a pure- or co-culture. Thus, the microbes worked together in a purely substrate based (neutral) relationship. These co-culture experiments represent an important step in understanding microbial interactions in BES communities with the goal to design complex microbial communities, which specifically convert target substrates into electricity.

Here, we studied the microbiome succession and time-scale variability of four mesophilic anaerobic reactors in a co-digestion study with the objective to find links between changing environmental conditions and the microbiome composition. The changing environmental conditions were ensured by gradual increases in loading rates and mixing ratios of three co-substrates with a constant manure-feeding scheme during an operating period longer than 900 days. Each co-substrate (i.e., alkaline hydrolysate, food waste, and glycerol) was co-digested separately. High throughput 16S rRNA gene sequencing was used to examine the microbiome succession. The alkaline hydrolysate reactor microbiome shifted and adapted to high concentrations of free ammonia, total volatile fatty acids, and potassium to maintain its function. The addition of food waste and glycerol as co-substrates also led to microbiome changes, but to a lesser extent, especially in the case of the glycerol reactor microbiome. The divergence of the food waste reactor microbiome was primarily linked to increasing free ammonia levels in the reactor; though, these levels remained below previously reported inhibitory levels for acclimated biomass. The glycerol reactor microbiome succession included an increase in Syntrophomonadaceae family members, which have previously been linked to long-chain fatty acid degradation. The glycerol reactor exhibited rapid failure and limited adaptation at the end of the study.

Abstract Anaerobic digestion systems on dairy farms in New York State rely on gate-fee revenues from co-digestion to ensure economic viability. Yet, because gate fees are paid on a volumetric (or weight) basis, farmers have been compelled to accept large waste volumes. When these wastes are co-digested at rates exceeding the design capacity of the digester, potentially significant technical, environmental, and economic consequences may arise. To better understand these trade-offs, we performed a combined environmental life-cycle and economic assessment with uncertainty analysis. We used the Anaerobic Digestion Model #1 to simulate the co-digestion process for 10 potential co-substrates that were hypothetically mixed with dairy manure throughout a range of loading rates. These simulation results demonstrated the need to include a robust anaerobic digestion model to capture complex process dynamics and loading limits. Results also showed that while higher loading rates were more economically favorable, they caused considerable reductions in the degree of waste stabilization during the digestion process, which dramatically increased downstream methane emissions (e.g., >450%) on the farm compared to manure-only digestion. Regardless, most co-digestion scenarios led to a net reduction in total life-cycle emissions compared to manure only and not digesting the co-substrate due mainly to greater electric power production and synthetic fertilizer replacement. Economically, gate-fee revenue was the most important contributor to profitability, substantially outweighing the revenue from electric power production, while also compensating for the increased handling costs of the added waste volume. Ultimately, the model clearly demonstrated the important environmental and economic implications arising from current anaerobic digestion implementation practices and policy in New York State. In addition, the model highlighted key stages in the system life-cycle, which was used to instruct and recommend immediately actionable policy changes.