Diversity of thermophilic populations during thermophilic aerobic digestion of potato peel slurry

Aims:  To study the diversity of thermophiles during thermophilic aerobic digestion (TAD) of agro-food waste slurries under conditions similar to full-scale processes.
Methods and Results:  Population diversity and development in TAD were studied by standard microbiological techniques and the processes monitored by standard fermentation procedures. Facultative thermophiles were identified as Bacillus coagulans and B. licheniformis, while obligate thermophiles were identified as B. stearothermophilus . They developed rapidly to peaks of 10⁷ to 10⁸ in ≤48 h. Stability of obligate thermophiles increased with process temperatures. Thermophiles were unstable at process pH above or below neutral, but developed rapidly at all aeration rates. Peak populations were higher in the median than at extremes of aeration rates. Obligate thermophiles were unstable at low aeration rates. Process self-heating was higher at lower than at higher aeration rate. Beyond 96 h most thermophiles were present as spores.
Conclusions:  Limited range of indigenous thermophiles drives TAD of slurry. They develop rapidly and are stable at most digestion conditions.
Significance and Impact of the Study:  Development and stability of thermophiles in TAD suggest that the process may be operated in a wide range of conditions; and even at short HRT in continuous processes without compromising efficiency.     

Enzyme research and applications in biotechnological intensification of biogas production

Biogas technology provides an alternative source of energy to fossil fuels in many parts of the world. Using local resources such as agricultural crop remains, municipal solid wastes, market wastes and animal waste, energy (biogas), and manure are derived by anaerobic digestion. The hydrolysis process, where the complex insoluble organic materials are hydrolysed by extracellular enzymes, is a rate-limiting step for anaerobic digestion of high-solid organic solid wastes. Biomass pretreatment and hydrolysis are areas in need of drastic improvement for economic production of biogas from complex organic matter such as lignocellulosic material and sewage sludge. Despite development of pretreatment techniques, sugar release from complex biomass still remains an expensive and slow step, perhaps the most critical in the overall process. This paper gives an updated review of the biotechnological advances to improve biogas production by microbial enzymatic hydrolysis of different complex organic matter for converting them into fermentable structures. A number of authors have reported significant improvement in biogas production when crude and commercial enzymes are used in the pretreatment of complex organic matter. There have been studies on the improvement of biogas production from lignocellulolytic materials, one of the largest and renewable sources of energy on earth, after pretreatment with cellulases and cellulase-producing microorganisms. Lipids (characterised as oil, grease, fat, and free long chain fatty acids, LCFA) are a major organic compound in wastewater generated from the food processing industries and have been considered very difficult to convert into biogas. Improved methane yield has been reported in the literature when these lipid-rich wastewaters are pretreated with lipases and lipase-producing microorganisms. The enzymatic treatment of mixed sludge by added enzymes prior to anaerobic digestion has been shown to result in improved degradation of the sludge and an increase in methane production. Strategies for enzyme dosing to enhance anaerobic digestion of the different complex organic rich materials have been investigated. This review also highlights the various challenges and opportunities that exist to improve enzymatic hydrolysis of complex organic matter for biogas production. The arguments in favor of enzymes to pretreat complex biomass are compelling. The high cost of commercial enzyme production, however, still limits application of enzymatic hydrolysis in full-scale biogas production plants, although production of low-cost enzymes and genetic engineering are addressing this issue.     

Rheology of enzyme liquefied corn stover slurries: The effect of solids concentration on yielding and flow behavior

The measurement of yield stress and shear thinning flow behavior of slurries formed from unpretreated corn stover at solids loadings of 100–300 g/L provides a key metric for the ability to move, pump, and mix this lignocellulosic slurry, particularly since corn stover slurries represent a major potential feedstock for biorefineries. This study compared static yield stress values and flow hysteresis of corn stover slurries of 100, 150, 200, 250, and 300 g/L, after these slurries were formed by adding pellets to a cellulase enzyme solution (Celluclast 1.5 L) in a fed-batch manner. A rotational rheometer was used to quantitate relative yield stress and its dependence on processing history at insoluble solids concentrations of 4%–21% (wt/vol). Key findings confirmed previous observations that yield stress increases with solids loadings and reaches ~3000 Pa at 25% (wt/vol) solids concentration compared to ~200 Pa after enzyme liquefaction. While optimization of slurry forming (i.e., liquefaction) conditions remains to be done, metrics for quantifying liquefaction extent are needed. The method for obtaining comparative metrics is demonstrated here and shows that the yield stress, shear thinning and shear thickening flow behaviors of enzyme liquefied corn stover slurries can be analyzed using a wide-gap rheometry setup with relative measuring geometries to mimic the conditions that may exist in a mixing vessel of a bioreactor while applying controlled and precise levels of strain.     

Anaerobic digestion of microalgal biomass for bioenergy production,removal of nutrients and microcystin: current status

Using renewable microalgal biomass as active feedstocks for biofuels and bioproducts is explored to substitute petroleum-based fuels and chemicals. In the last few years, the importance of microalgae biomass has been realized as a renewable feedstock due to several positive attributes associated with it. Biorefinery via anaerobic digestion (AD) of microalgal biomass is a promising and sustainable method to produce value-added chemicals, edible products and biofuels. Microalgal biomass pretreatment is a significant process to enhance methane production by AD. Findings on the AD microbial community’s variety and organization can give novel in turn on digester steadiness and presentation. This review presents a vital study of the existing facts on the AD microbial community and AD production. Co-digestion of microalgal biomass with different co-substrates was used in AD to enhance biogas production, and the process was economically viable with improved biodegradability. Microcystins, which are produced by toxic cyanobacterial blooms, create a severe hazard to environmental health. Anaerobic biodegradation is an effective method to degrade the microcystins and convert into nontoxic products. However, for the cost-effective conversion of biomass to energy and other beneficial byproducts, additional highly developed research is still required for large-scale AD of microalgal biomass.     

Long-term nitrogen fertilizer replacement value of cattle manures applied to cut grassland

Manures supply nitrogen (N) to crops beyond the year of application. This N must be taken into account for agronomic and environmental reasons. From 2002 to 2006 we conducted a field experiment on a sandy soil in The Netherlands (52°03″N, 6°18″E) to better quantify this residual N effect. Treatments comprised different time series of mineral fertilizer N or cattle manures of different compositions, all applied at a rate of 300 kg total N ha⁻¹ year⁻¹, whilst compensating for differences in available potassium and phosphorus. Dry matter and N yields of cut grassland responded positively (P < 0.05) to both current manure applications and applications in previous years, whereas mineral fertilizer N affected yields in the year of application only. N yields could be reasonably well predicted with a simple N model, adopting an annual relative decomposition rate of the organic N in manure of 0.10–0.33 year⁻¹ during the year of application and 0.10 year⁻¹ in the following years. Subsequent model calculations indicated that the N fertilizer value (NFRV) of injected undigested cattle slurry rises from an observed 51–53% when slurry is applied for the first time, to approximately 70% after 7–10 yearly applications, whereas it took two to four decades of yearly applications to raise the NFRV of surface applied farm yard manure to a similar level from an initial value of 31%. Manures with a relatively high first year NFRV (e.g. anaerobically digested slurry) had a relatively small residual N effect, whereas manures with a low first year NFRV (e.g. farm yard manure) partly compensated for this by showing larger residual effects. Given the long manuring history of most agricultural systems, rethinking the fertilizer value of manure seems justified. The results also imply that the long term consequences of reduced N application rates may be underestimated if manuring histories are insufficiently taken into account.     

Give them credit‐the greenhouse gas performance of regional biogas systems

Anaerobic digestion to produce biogas is an important decentralised renewable energy technology. Production varies extensively between different countries and within countries, as biogas production is heavily dependent on local and regional feedstocks. In Germany, distinct regional differences can be observed. Therefore, understanding the kinds of biogas systems operating within a region is crucial to determine their greenhouse gas (GHG) mitigation potential and carbon neutrality. This is the first study to conduct an integrated life cycle assessment of biogas configurations in the landscape (biogas plants and their biomass catchments) for an entire region. RELCA a ‘REgional Life Cycle inventory Assessment’ approach was used to model the GHG mitigation potential of 425 biogas plants in the region of Central Germany (CG), aggregated to nine biogas clusters, based on feedstock mix (e.g. animal manures and energy crops) and installed capacity. GHG emission profiles were generated to compare and to identify the role of GHG credits and size of installed capacity on the mitigation performance of the regional biogas clusters. We found that smaller scaled slurry dominant clusters had significantly better GHG mitigation performance (?0.1 to ?0.2 kg CO_2eq kWh_el^?1), than larger energy crop dominant (EC_dom) clusters (0.04–0.16 kg CO_2eq kWh_el^?1), due to lower cultivation emissions and larger credits for avoided slurry storage. Thus, for the CG region larger EC_dom clusters should be targeted first, to support GHG mitigation improvements to the overall future electricity supplied by the regional biogas systems. With the addition of GHG credits, the CG region is producing biogas with GHG savings (?0.15 kg CO_2eq kWh_el^?1, interquartile range: 0.095 kg CO_2eq kWh_el^?1). This infers that biogas production, as a waste management strategy for animal manures, could have important ramifications for future policy setting and national inventory accounting.     

Methanogenic population dynamics during semi‐continuous biogas fermentation and acidification by overloading

Aims: This study was to investigate the methanogenic community in a biogas reactor from start‐up to acidification conditions. Furthermore, reliability and accuracy of the applied quantitative real‐time PCR method (Q‐PCR) was briefly evaluated. Methods and Results: A mesophilic (37°C), maize silage fed, continuously stirred tank reactor was surveyed. It was operated semi‐continuously with increasing daily organic loading rates (OLRs) to reach acidification. Gas production and organic acid composition were measured. Methanogenic community structure was determined by 16S rDNA‐based Q‐PCR to estimate the abundance of key methanogenic micro‐organisms. 16S rDNA of hydrogenotrophic Methanobacteriales was most abundant at OLRs of ≥3·7 g dry organic matter (DOM) l^?1 day^?1. By contrast, that of aceticlastic Methanosaetaceae predominated at lower OLRs but disappeared at OLRs of ≥4·1 g DOM l^?1 day^?1. At the same OLR, the propionate concentration increased dramatically indicating the acidification of the digester. Application of internal standards to examine Q‐PCR’s accuracy revealed that the detected amount of 16S rDNA may vary within one log cycle. Conclusions: These results suggest that the absence of Methanosaetaceae might be taken as biological indicator for process’ instability. Inhibitory effects on Q‐PCR analyses could not be determined based on the spiking experiments. Significance and Impact of the Study: In this study, reactors’ microbiology was observed over time using Q‐PCR. Insights into the abundance of different methanogens might be used to improve the performance of biogas reactors.     

Estimation of nutrients and organic matter in Korean swine slurry using multiple regression analysis of physical and chemical properties

Swine waste land application has increased due to organic fertilization, but excess application in an arable system can cause environmental risk. Therefore, in situ characterizations of such resources are important prior to application. To explore this, 41 swine slurry samples were collected from Korea, and wide differences were observed in the physico-biochemical properties. However, significant (P < 0.001) multiple property correlations (R²) were obtained between nutrients with specific gravity (SG), electrical conductivity (EC), total solids (TS) and pH. The different combinations of hydrometer, EC meter, drying oven and pH meter were found useful to estimate Mn, Fe, Ca, K, Al, Na, N and 5-day biochemical oxygen demands (BOD₅) at improved R² values of 0.83, 0.82, 0.77, 0.75, 0.67, 0.47, 0.88 and 0.70, respectively. The results from this study suggest that multiple property regressions can facilitate the prediction of micronutrients and organic matter much better than a single property regression for livestock waste.     

Characterization of a mobile and multiple resistance plasmid isolated from swine manure and its detection in soil after manure application

Aims: To isolate and characterize multiple antibiotic resistance plasmids found in swine manure and test for plasmid‐associated genetic markers in soil following manure application to an agricultural field. Methods and Results: Plasmids were isolated from an erythromycin enrichment culture that used liquid swine manure as an inoculant. Plasmids were transformed into Escherichia coli DH10β for subsequent characterization. We isolated and DNA sequenced a 22 102‐bp plasmid (pMC2) that confers macrolide, and tetracycline resistances, and carries genes predicted to code for mercury and chromium resistance. Conjugation experiments using an pRP4 derivative as a helper plasmid confirm that pMC2 has a functional mobilization unit. PCR was used to detect genetic elements found on pMC2 in DNA extracted from manure amended soil. Conclusions: The pMC2 plasmid has a tetracycline‐resistant core and has acquired additional resistance genes by insertion of an accessory region (12 762 bp) containing macrolide, mercury and chromium resistance genes, which was inserted between the truncated DDE motifs within the Tn903/IS102 mobile element. Significance and Impact of the Study: Liquid swine manure used for manure spreading contains multiple antibiotic resistance plasmids that can be detected in soil following manure application.     

Factors influencing the presence and concentration of E. coli O157 and E. coli in farm waste on six cattle farms in North-West England

Aims:  To investigate the factors influencing the presence and burden of Escherichia coli O157 in farm wastes.
Methods and Results:  Wastes from six cattle farms were screened for the presence and concentration of E. coli O157 and E. coli on three occasions over a year and waste management data were collected. Sixty-three of 878 (7·1%) samples were positive for verocytotoxigenic Escherichia coli O157 and 664/875 (75·9%) for E. coli with detectable levels greater in fresh waste than in stored waste, pasture or dirty water.
Conclusions:  The turning/stirring of stored waste and the use of more than one store (allowing longer storage times) reduced the proportion of E. coli O157 positive samples. The presence of E. coli O157 significantly reduced from a high prevalence found in fresh faeces and stored waste to lower proportions in dirty water and pasture samples. Escherichia coli O157 was only detected on pasture when waste was spread from contaminated stores the day before sampling. A high prevalence of positive E. coli O157 samples were detected when cattle were re-housed.
Significance and Impact of the Study:  These findings help to support the importance of treating and storing farm waste, as well as providing evidence for the level of dilution of E. coli O157 from fresh waste to recently spread pastures.