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To maximize the production of carboxylic acids with open cultures of microbial consortia (reactor microbiomes), we performed experiments to understand which factors affect the community dynamics and performance parameters. We operated six thermophilic (55 °C) bioreactors to test how the factors: (i) biomass pretreatment; (ii) bioreactor operating conditions; and (iii) bioreactor history (after perturbations during the operating period) affected total fermentation product and n-butyrate performance parameters with corn fiber as the cellulosic biomass waste. We observed a maximum total fermentation product yield of 39%, a n-butyrate yield of 23% (both on a COD basis), a maximum total fermentation production rate of 0.74 g COD l-1 d-1 and n-butyrate production rate of 0.47 g COD l-1 d-1 in bioreactors that were fed with dilute-acid pretreated corn fiber at a pH of 5.5. Pyrosequencing of 16S rRNA genes with constrained ordination and other statistical methods showed that changes in operating conditions to enable dilution of toxic carboxylic acid products, which lead to these maximum performance parameters, also altered the composition of the microbiome, and that the microbiome, in turn, affected the performance. Operating conditions are an important factor (tool for operators) to shape reactor microbiomes, but other factors, such as substrate composition after biomass pretreatment and bioreactor history are also important. Further optimization of operating conditions must relieve the toxicity of carboxylic acids at acidic bioreactor pH levels even more, and this can, for example, be accomplished by extracting the product from the bioreactor solutions. [ABSTRACT FROM AUTHOR]

Abstract: 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 250days. 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±0.008g CH4-CODg−1 VSSd−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. 0.219l CH4 gVS−1 fed for days 1–183 and 0.174 vs. 0.130l CH4 gVS−1 fed for days 184–250, respectively). Finally, we operated an ASBR for an additional 295days to evaluate the effect of temperature variation on system stability. A stable performance was achieved between the operating temperatures of 22–41°C. [Copyright &y& Elsevier]

Many beer breweries use high-rate anaerobic digestion (AD) systems to treat their soluble high-strength wastewater. Biogas from these AD systems is used to offset nonrenewable energy utilization in the brewery. With increasing nonrenewable energy costs, interest has mounted to also digest secondary residuals from the high-rate digester effluent, which consists of yeast cells, bacteria, methanogens, and small (hemi)cellulosic particles. Mesophilic (37 °C) and thermophilic (55 °C) lab-scale, low-rate continuously-stirred anaerobic digestion (CSAD) bioreactors were operated for 258 days by feeding secondary residuals at a volatile solids (VS) concentration of ∼40 g l−1. At a hydraulic retention time (HRT) of 15 days and a VS loading rate of 2.7 g VS l−1 day−1, the mesophilic bioreactor showed an average specific volumetric biogas production rate of 0.88 l CH4 l−1 day−1 and an effluent VS concentration of 22.2 g VS l−1 (43.0% VS removal efficiency) while the thermophilic bioreactor displayed similar performances. The overall methane yield for both systems was 0.21 l CH4 g−1 VS fed and 0.47–0.48 l CH4 g−1 VS removed. A primary limitation of thermophilic digestion of this protein-rich waste is the inhibition of methanogens due to higher nondissociated (free) ammonia (NH3) concentrations under similar total ammonium (NH4 +) concentrations at equilibrium. Since thermophilic AD did not result in advantageous methane production rates or yields, mesophilic AD was, therefore, superior in treating secondary residuals from high-rate AD effluent. An additional digester to convert secondary residuals to methane may increase the total biogas generation at the brewery by 8% compared to just conventional high-rate digestion of brewery wastewater alone. [ABSTRACT FROM AUTHOR]