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The effect of bioaugmentation with different microorganisms on anaerobic digestion to mitigate the ammonia inhibition problem was investigated. Seven pure strains of microorganisms (including obligate aceticlastic methanogen, facultative aceticlastic methanogen, hydrogenotrophic methanogen, syntrophic acetate oxidizing bacteria (SAOB) were selected and thirteen bioaugmentation approaches were tested. Bioaugmentation with hydrogenotrophic methanogen Methanobrevibacter smithii (MBS) and SAOB Syntrophaceticu schinkii together was the optimal choice, methane production (MP) was 71.1% higher than that in Blank, the activity of hydrogenotrophic methanogenesis was greatly heightened according to specific methanogenic activity analysis. Bioaugmentation with facultative aceticlastic methanogen Methanosarcina barkeri (MSB) alone without SAOB addition was also proven efficient (MP was 59.7% higher than that in Blank), both aceticlastic and hydrogenotrophic methanogenesis were enhanced. Further evaluation with carbon isotope fractionations analysis indicated that balancing the activities of the aceticlastic and hydrogenotrophic methanogenic pathways is of great importance. 16s rRNA gene sequencing results showed that Methanobacterium spp. and Methanosaeta spp. were the dominant archaea in all 14 reactors. Nevertheless, bioaugmentation with Methanosaeta spp. did not result in a positive effect on MP. On the other hand, Methanobrevibacter spp. and Methanosarcina spp. were non-dominant archaea (even after bioaugmentation with MBS or MSB, the relative abundances were still poor (

Commercial digesters handling complex waste and organic overloading often encounter unbalanced conditions or failures. With limited studies on the digester recovery from an industry-based waste stream, a complex and high-strength digestate containing up to 79 g COD l

This study investigated methane production, long-chain fatty acids (LCFAs) profile, and predominant microorganisms in anaerobic digestion (AD) of lipid-rich swine slaughterhouse waste (SSW). The maximum methane yield was 999.2 mL/g VS. LCFAs, as inhibitory hydrolysis products, accumulated first to 1165 mg/L on day 3, and then decreased sharply to 125.7 mg/L on day 9, and finally were degraded to 20 mg/L on day 27. Linoleic acid (C18:2), oleic acid (C18:1) and palmitic acid (C16:0) were the dominant LCFAs. The easy conversion of C18:1 to C16:0 compared with difficult degradation of C16:0 resulted in an increase of C16:0 on day 4–6. Predominant microorganisms were Clostridium, Syntrophomonas and Methanospirillum. This study proved the high methane potential of lipid-rich SSW and gained insights into the degradation process by analysis of intermediates of LCFAs and predominant microorganisms. The results can provide valuable guidance for efficient utilization of this waste to produce methane in future.

Summarization: Municipal solid waste (MSW) contains a large fraction of biodegradable organic materials. When disposed in landfills, these materials can cause adverse environmental impact due to gaseous emissions and leachate generation. This study was performed with an aim of effectively separating the biodegradable materials from a Mechanical Biological Treatment (MBT) facility and treating them in well-controlled anaerobic digesters for biogas production. The rotary drum reactor (RDR) process (a sub-process of the MBT facilities studied in the present work) was evaluated as an MSW pretreatment technology for separating and preparing the biodegradable materials in MSW to be used as feedstock for anaerobic digestion. The RDR processes used in six commercial MSW treatment plants located in the USA were surveyed and sampled. The samples of the biodegradable materials produced by the RDR process were analyzed for chemical and physical characteristics as well as anaerobically digested in the laboratory using batch reactors under thermophilic conditions. The moisture content, TS, VS and C/N of the samples varied between 64.7 and 44.4%, 55.6 to 35.3%, 27.0 to 41.3% and 24.5 to 42.7, respectively. The biogas yield was measured to be between 533.0 and 675.6 mL g−1VS after 20 days of digestion. Approximately 90% of the biogas was produced during the first 13 days. The average methane content of the biogas was between 58.0 and 59.9%. The results indicated that the biodegradable materials separated from MSW using the RDR processes could be used as an excellent feedstock for anaerobic digestion. The digester residues may be further processed for compost production or further energy recovery by using thermal conversion processes such as combustion or gasification. Presented on: Journal of Environmental Management

Cage-free housing systems have attracted considerable attention in the United States recently as they provide more space and other resources (such as litter area, perches, and nest boxes) for hens and are considered to be more favorable from the standpoint of hen welfare. This study was carried out to quantify emissions of aerial ammonia (NH 3 ), carbon dioxide (CO 2 ) and particulate matter (PM 10 and PM 2.5 ) from cage-free layer houses in California and compare the values with those for other types of layer houses. Two commercial cage-free houses with 38,000 hens each were monitored from March 1, 2012 to April 1, 2013. Results show that NH 3 and CO 2 concentrations in the houses were affected by ventilation rate, which was largely influenced by ambient air temperature. The PM 10 and PM 2.5 concentrations in the houses depended on the activity of birds, ventilation rate and relative humidity of the ambient air. The average emission rates of NH 3 , CO 2 , PM 10 and PM 2.5 were 0.29, 89.9, 0.163 and 0.020 g d −1 hen −1 , respectively. The NH 3 emission rate determined in this study was higher than those of aviary houses. The PM 10 and PM 2.5 emission rates were higher than those reported for high-rise layer houses.

Anaerobic digestion (AD) is a widely applied technology for treating organic wastes to generate renewable energy in the form of biogas. The effectiveness of AD process depends on many factors, among which the most important is the presence of active and healthy microbial community in the anaerobic digesters, which needs to be explored. However, the deciphering of microbial populations and their functions during the AD process of different materials is still incomplete, which restricts the understanding of its long-term performance under different operational conditions. This review describes the type, morphology, functions, and specific growth conditions of commonly found hydrolytic, acidogenic, acetogenic bacteria, and archaea during the AD process. The effects of microbes on the performance and stability of the digestion process are also presented. Furthermore, the article offers a deep understanding of the AD management strategies for the enhancement of methane production and the efficiency of the energy conversion process of various organic wastes.

The methane production potential of kitchen waste (KW) obtained from different sources was compared through mesophilic and thermophilic anaerobic digestion. The methane yields (MYs) obtained with the same KW sample under different temperatures were similar, whereas the MYs obtained with different samples differed significantly. The highest MY obtained in S7 was 54%–60% higher than the lowest MY in S3. The modified Gompertz model was utilized to simulate the methane production process. The maximum production rate of methane under thermophilic conditions was 2%–86% higher than that under mesophilic conditions. The characteristics of different KW samples were studied. In the distribution of total chemical oxygen demand, the diversity of organic compounds of KW was the most dominant factor that affected the potential MYs of KW. The effect of the C/N and C/P ratios or the concentration of metal ions was insignificant. Two typical methods to calculate the theoretical MY (TMY) were compared, the organic composition method can simulate methane production more precisely than the elemental analysis method. Significant linear correlations were found between TMYorg and MYs under mesophilic and thermophilic conditions. The organic composition method can thus be utilized as a fast technique to predict the methane production potential of KW.

The effects of hydraulic retention time (HRT) and organic loading rate (OLR) were investigated during a continuous anaerobic digestion of Spirulina platensis . The continuous process operated with varying HRT (10–25 d) and OLR (1.0–4.0 [g VS] l −1 d −1 ) resulted in the biogas and methane yields in the range of 0.276–0.502 l [g VS] −1 and 0.163–0.342 l [g VS] −1 , respectively. The methane yield decreased with the increase in OLR and the reduction in HRT. Maximum methane yield of 0.342 l [g VS] −1 was produced when the digester was operated at OLR of 1.0 [g VS] l −1 d −1 and 25 d HRT. A mathematical model was developed from a kinetic study for predicting methane yield as the function of HRT during a continuous digestion. The model performed well at OLR lower than 2.0 [g VS] l −1 d −1 , at which the digestion was not limited by high ammonia levels or volatile fatty acid accumulation.

Biochar simply is the material produced when biomass undergoes any chemical processes under the conditions of pyrolysis. The variety of biomasses, including wood waste, agricultural crop leftover, organic waste, animal manure, and forestry residues, have been considered as raw material to produce biochar. Biochar is widely used for generation of heat and power and an addition to soils, in which it serves as a fertilizer and carbon sequestration agent. Also in the form of being activated, it finds significant role for various adsorption applications. The most beneficial use of a given char depends on its physical and chemical characteristics, even though the relationship of char properties to these applications is not well defined. Various widely used modern analytical techniques, which are applicable and crucial for biochar characterization, have been reviewed in the present work, such as solid state nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-rays photoelectron spectroscopy, X-rays diffraction, thermogravimetric analysis, near edge X-rays absorption fine structure spectroscopy, and gas chromatography-mass spectroscopy. Utilization of these modern techniques provides the quantitative as well as qualitative information, i.e., determining the sizes, shapes, and physicochemical characteristics of biochar, which is reliable to track changes in the carbon arrangement over reaction time and temperature, and will be useful for efficient production of biochar and application. It provides the useful information for the researchers in this area and is beneficial not only for the effective biochar production, but also for potential utilization/application, and not only for environment but also for agriculture.

Vinegar residue is the by-product in the vinegar production process. The large amount of vinegar residue has caused a serious environmental problem owing to its acidity and corrosiveness. Anaerobic digestion is an effective way to convert agricultural waste into bioenergy, and a previous study showed that vinegar residue could be treated by anaerobic digestion but still had room to improve digestion efficiency. In this study, steam explosion at pressure of 0.8, 1.2, and 1.5 MPa and residence time of 5, 10, 15, and 20 min were used to pretreat vinegar residue to improve methane production, respectively. Scanning electron microscopy and X-ray diffraction analyses were applied to validate structural changes of vinegar residue after steam explosion. Results showed that steam explosion pretreatment could destroy the structure of lignocellulose by removing the hemicellulose and lignin, and improve the methane yield effectively. Steam explosion-treated vinegar residue at 0.8 MPa for 5 min produced the highest methane yield of 153.58 mL gVS-1, which was 27.65% (significant, α VS-1). The analyses of pH, total ammonia-nitrogen, total alkalinity, and volatile fatty acids showed that steam explosion did not influence the stability of anaerobic digestion. This study suggested that steam explosion pretreatment on vinegar residue might be a promising approach and it is worth further study to improve the efficiency of vinegar residue waste utilisation.

Reducing the pretreatment cost of lignocellulosic biomass by utilizing alkali to alter its recalcitrant nature is an effective method for biofuel production. In this experiment, 1.5% KOH solution and its black liquor (spent liquor of KOH) (BL) were applied to pretreat corn stover (CS) at a temperature of 20 °C to enhance the digestibility for anaerobic digestion (AD). Results showed no significant difference in weighted average methane content on the basis of experimental methane and biogas yields between BL-treated and original KOH-treated CS after AD. The BL process significantly increased the overall methane yield by 52.4% compared with untreated CS (135.2 mL/gVS), whereas no significant difference between the overall methane yields of 1.5% KOH-treated and BL-treated CS was observed. In addition, the BL process significantly saved water and KOH consumption, by 56.2% and 57.4%, respectively, compared with the 1.5% KOH pretreatment. Overall methane production was well explained by the modified Gompertz model. The physiochemical changes to CS after BL pretreatment were confirmed by SEM, FTIR, and XRD analyses. Our findings collectively suggest that recycling and reuse of KOH black liquor might be an efficient method for lignocellulosic biomass treatment and have the capability to reduce input costs in future AD processes.

To improve the methane production of wheat straw (WS), the mono-pretreatment (MP) and co-pretreatment (CP) of WS with KOH and Ca(OH)2 were conducted in this study. The results showed that the MP with KOH presented better effects than the MP with Ca(OH)2. However, the CP with 2% KOH combined with 1% Ca(OH)2 displayed similar effects to those of the MP with 3% KOH, obtaining the cumulative methane yield of 239.8 mL gVS−1 and an improved biodegradability from 56.37% of raw WS to 66.10%. Methane production and kinetic analyses suggested that 2% KOH combined with 1% Ca(OH)2 was the ideal condition of alkaline pretreatment for anaerobic digestion of WS. The mechanism for the improvement in methane production was clearly described by biochemical component, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analyses. Moreover, preliminary economics and energy potential analyses also confirmed that alkaline co-pretreatment was a reasonable method, which not only gave important guidance for future utilization of WS waste but also showed useful reference for the efficient pretreatment of other lignocellulosic wastes.

This work firstly investigated the suitable organic loading (OL) and feed to inoculum (F/I) ratio of three kinds of tobacco stalks (TS116, TS99, and TS85) during anaerobic digestion (AD) via response surface methodology (RSM). The highest experimental methane yield (EMY) of 148.1 mL/g VS was achieved from TS116 at OL of 20.2 g VS/L and F/I ratio of 1.1. To further increase EMY, various pretreatments including alkaline hydrogen peroxide (AHP), NaOH, KOH, Ca(OH)2, HCl, and oxalic acid (H2C2O4) were implemented on TS116. Results showed that AHP was most effective, and the maximal EMY of 350.7 mL/g VS and biodegradability (Bd) of 81.4% were obtained from 7% AHP pretreated TS116, which increased by 105.6% than untreated. XRD, FTIR, and SEM analyses evidenced that the structure of AHP pretreated TS116 was strongly disrupted. This study lays the foundation for applying this waste into AD in future applications.

Thermophilic anaerobic sludge was processed to reduce the volume and moisture content in order to reduce costs for storing and transporting the sludge as microbial inoculum for anaerobic digester startup. The moisture content of the sludge was reduced from 98.7% to 82.0% via centrifugation and further to 71.5% via vacuum evaporation. The processed sludge was stored for 2 and 4 months and compared with the fresh sludge for the biogas and methane production using food waste and non-fat dry milk as substrates. It was found that fresh unprocessed sludge had the highest methane yield and the yields of both unprocessed and processed sludges decreased during storage by 1–34%, however processed sludges seemed to regain some activity after 4 months of storage as compared to samples stored for only 2 months. Maximum methane production rates obtained from modified Gompertz model application also increased between the 2-month and 4-month processed samples.

Anaerobic co-digestion of chicken manure and corn stover in batch and CSTR were investigated. The batch co-digestion tests were performed at an initial volatile solid (VS) concentration of 3 g VS/L, carbon-to-nitrogen (C/N) ratio of 20, and retention time of 30 d. The methane yield was determined to be 281 ± 12 mL/g VS added . Continuous reactor was carried out with feeding concentration of 12% total solids and C/N ratio of 20 at organic loading rates (OLRs) of 1–4 g VS/L/d. Results showed that at OLR of 4 g VS/L/d, stable and preferable methane yield of 223 ± 7 mL/g VS added was found, which was equal to energy yield (EY) of 8.0 ± 0.3 MJ/kg VS added . Post-digestion of digestate gave extra EY of 1.5–2.6 MJ/kg VS added . Pyrolysis of digestate provided additional EY of 6.1 MJ/kg VS added . Pyrolysis can be a promising technique to reduce biogas residues and to produce valuable gas products simultaneously.

X-ray diffraction (XRD) was used to understand the interactions of cellulose in lignocellulosic biomass with ionic liquids (ILs). The experiment was designed in such a way that the process of swelling and solubilization of crystalline cellulose in plant cell walls was followed by XRD. Three different feedstocks, switchgrass, corn stover and rice husk, were pretreated using 1-butyl-3-methylimidazolium acetate ([C4mim][OAc]) at temperatures of 50-130°C for 6h. At a 5 wt.% biomass loading, increasing pretreatment temperature led to a drop in biomass crystallinity index (CrI), which was due to swelling of crystalline cellulose. After most of the crystalline cellulose was swollen with IL molecules, a low-order structure was found in the pretreated samples. Upon further increasing temperature, cellulose II structure started to form in the pretreated biomass samples as a result of solubilization of cellulose in [C4mim][OAc] and subsequent regeneration.

The losses of total solids, moisture, nitrogen (N), phosphorus (P), potassium (K), carbon (C), and sulfur (S) were determined in two storage events of laying-hen manure immediately removed from three different housing systems in Iowa, USA. The three laying-hen houses were conventional cage (CC), enriched colony (EC), and aviary (AV). The houses held a nominal number of 200,000, 46,700, and 50,000 Lohmann LSL lite layers, respectively. The manure collected on belts in each house was cleaned out twice a week. A fraction of the cleaned out manure was transferred to designated storage rooms wherein losses of different components were determined in two storage events. Manure was loaded into the storage rooms over 171 days during the first storage event and over 185 days during the second storage event. The total storage periods were 202 and 245 days, respectively, for the first and second storage events. Manure was weighed, sampled, and analyzed before it was loaded into the storage rooms and at the end of each storage event. Mass balance calculations were used to determine the losses of different components. Statistical analyses show that the nutrient contents, on a wet basis, of manure loaded in CC, AV, and EC storage rooms were significantly different due to the differences in manure moisture contents. However, on a dry basis, they had no significant differences. The fresh manure cleaned out from the EC layer house was drier than that from the other two houses. Loaded-in nitrogen losses in the CC, AV, and EC storage rooms were 24.6, 12.9, and 20.8%, respectively. Nitrogen losses depended on house temperature, manure moisture, and pH. The average losses of loaded-in manure mass, moisture, and total solids during the two storage events were 27.6 ± 1.9, 33.8 ± 8.3, and 20.8 ± 7.0%, respectively. The losses of N, P, K, C, and S were 19.4 ± 13.4, 11.7 ± 5.6, 10.2 ± 6.8, 27.0 ± 6.5, and 8.3 ± 8.5% of their loaded-in amounts, respectively. The total loss of N, P, K, C, and S was 56% of the total loaded-in solids loss; thereof, the loss of N, P, and K was 7%, and C loss was 48%. The laying-hen-specific losses of N, P, K, C, and S were 0.34, 0.05, 0.08, 3.2 and 0.019 g day−1 hen−1, respectively. The results of this research are important for assessing impacts of stored manure on environment and nutrient losses. They can also be used to develop methodologies for the mitigation of the emissions from egg production facilities.

This study systematically investigated the anaerobic digestibility of durian shell and focused on maximizing the methane yield using response surface methodology. Results showed in the feedstock to inoculum (F/I) ratio range of 0.2-2, a lower value was preferred. Meanwhile the methane yield showed a sharp rise first followed by a decline as the organic loading (OL) increased from 3 to 27g VS/L. The highest experimental methane yield (EMY) was calculated to be 170.6ml/g VS at F/I ratio of 0.2 and organic loading of 20.45g VS/L. To make the combination of F/I ratio and OL more practical, 0.5 was set as the optimum F/I ratio, when the highest EMY was obtained to be 165.0ml/g VS at the OL of 20.45g VS/L. Characteristics of final effluent implied the anaerobic system was stable. This study is important to promote the application of durian shell into anaerobic digestion from theory to practice.

The effect of different sodium salt concentration on anaerobic digestion of kitchen waste was investigated. The methane production performance, the corresponding methane production model and sodium salt inhibition model were studied, and the degradation efficiency was analyzed. With the increase of sodium salt concentration, the methane yield and the maximal methane production rate decreased along with the increase of lag phase time. The highest methane yield of 594 mL/g-VSadded (VS: volatile solids) was found with no sodium salt addition while the lowest was obtained with addition of 16 g/L NaCl. The declines of the methane yield were negligible when the sodium salt concentration was below 8 g/L, which corresponded to 8 g/L NaCl (causing 17–80% inhibition). Five kinds of regression models were developed to describe the sodium salt inhibition efficiency, and the cubic regression model of y = 0.508 + 2.401x − 0.369x2 + 0.033x3 showed the best fitting. The volatile fatty acids/ethanol gradually accumulated along with the increase of the sodium salt concentration, and the volatile solid removal efficiency represented a gradual decline accordingly. It is recommended that the sodium salt concentration in the anaerobic digesters should be controlled below 8 g/L in order to avoid intense methane inhibition.

From the point of view of biogeochemistry, manure is a complex of organic matter containing minor minerals. When manure is excreted by animals, it undergoes a series of reactions such as decomposition, hydrolysis, ammonia volatilization, nitrification, denitrification, fermentation etc., from which carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) and ammonia (NH3) can be produced. Based on the principles of thermodynamics and reaction kinetics, these reactions are commonly controlled by a group of environmental factors such as temperature, moisture, redox potential, pH, substrate concentration gradient etc. The relations among the environmental factors, the reactions and the gas production have been incorporated in a process-based model, Manure-DNDC, to describe manure organic matter turnover and gas emissions. Using Manure-DNDC, the users can construct a virtual farm by selecting and integrating one or more of the candidate farm facilities (i.e., feedlot, compost, lagoon, anaerobic digester and cropping field) parameterized in the model. Manure-DNDC calculates variations of the environmental factors for each component facility based on its technical specifications, and then utilizes the environmental factors to drive the biogeochemical reactions. To verify the applicability of Manure-DNDC for livestock farms, seven datasets of air emissions measured from farms across the U.S. plus a Scotland pasture were utilized for model tests with encouraging results. A dairy farm in New York was used to assess the impacts of alternative management practices on the gas mitigation. The modeled results showed that a combination of changes in the feed quality, the lagoon coverage and the planted crop type could reduce greenhouse gas emission by 30 % and NH3 by 36 % at the farm scale.

Ammonia and hydrogen sulfide are hazardous substances that are regulated by the U.S. Environmental Protection Agency through community right-to-know legislation (EPCRA, EPA, 2011 ). The emissions of ammonia and hydrogen sulfide from large commercial layer facilities are of concern to legislators and nearby neighbors. Particulate matter (PM10 and PM2.5) released from layer houses are two of seven criteria pollutants for which EPA has set National Ambient Air Quality Standards as required by the Clean Air Act. Therefore, it is important to quantify the baseline emissions of these pollutants. The emissions of ammonia, hydrogen sulfide, carbon dioxide and PM from two California high-rise layer houses were monitored for two years from October 2007 to October 2009. Each house had 32,500 caged laying hens. The monitoring site was setup in compliance with a U.S. EPA-approved quality assurance project plan. The results showed the average daily mean emission rates of ammonia, hydrogen sulfide and carbon dioxide were 0.95 ± 0.67 (standard deviation) g d−1 bird−1, 1.27 ± 0.78 mg d−1 bird−1 and 91.4 ± 16.5 g d−1 bird−1, respectively. The average daily mean emission rates of PM2.5, PM10 and total suspended particulate (TSP) were 5.9 ± 12.6, 33.4 ± 27.4, and 78.0 ± 42.7 mg d−1 bird−1, respectively. It was observed that ammonia emission rates in summer were lower than in winter because the high airflow stabilized the manure by drying it. The reductions due to lower moisture content were greater than the increases due to higher temperature. However, PM10 emission rates in summer were higher than in winter because the drier conditions coupled with higher internal air velocities increased PM10 release from feathers, feed and manure.

Production of volatile fatty acids (VFAs), alcohols, and several other compounds in batch-stored dairy manure was experimentally studied. Test conditions included three initial total solids (TS) contents of dairy manure (2%, 4%, and 9%) and three storage temperatures (15°C, 25°C, and 35°C). Under each set of test conditions, the concentrations of methanol, ethanol, and VFAs in the manure and the amount and composition of biogas produced were measured over a one-month period. Results showed that the higher TS content of the manure resulted in more VFAs and less biogas production. Temperature had a positive effect on methanogenic activity, especially in the manure with 2% TS. At 35°C, the total VFAs reached 16,500 and 23,000 mg COD L-1 in the manures with 4% and 9% TS, respectively. Acetic acid represented over 42% of the total VFAs as COD. The highest methanol and ethanol concentrations (30 and 230 mg L-1, respectively) were found in the manure with 9% TS stored at 35°C. A mathematical model was applied to calculate the generation and emission rates and cumulative emissions of acetic acid from dairy manure stored under different temperatures and wind velocity conditions. Modeling results for a 1,000-cow dairy farm located in Davis, California, showed that the cumulative acetic acid emissions from a lagoon receiving the manure with 2% TS were about 4.8 and 11.2 g per cow per month under winter and summer conditions, respectively. More research is underway to calibrate and validate the emission model over a longer storage period.

The development of process-based models to estimate ammonia emissions from animal feeding operations (AFOSs) is sought to replace costly and time-consuming direct measurements. Critical to process-based model development is conducting sensitivity analysis to determine the input parameters and their interactions that contribute most to the variance of the model output. Global and relative sensitivity analyses were applied to a process-based model for predicting ammonia emissions from the surface of anaerobic lagoons for treating and storing manure. The objectives were to compare global sensitivity analysis (GSA) to relative (local) sensitivity analysis (RSA) on a process-based model for ammonia emissions. Based on the first-order coefficient, both GSA and RSA showed the model input parameters in order of importance in process model for ammonia emissions from lagoon surfaces were: (i) pH, (ii) lagoon liquid temperature, (iii) wind speed above the lagoon surface, and (iv) the concentration of ammoniacal nitrogen in the lagoon. The GSA revealed that interactions between model parameters accounted for over two-thirds of the model variance, a result that cannot be achieved using traditional RSA. Also, the GSA showed that parameter interactions involving liquid pH had more impact on the model output variance than the single parameters: (i) temperature, (ii) wind speed, or (iii) total ammoniacal nitrogen. This study demonstrates that GSA provides a more complete analysis of model input parameters and their interactions on the model output compared to RSA. A comprehensive tutorial regarding the application of GSA to a process model is presented.

Leaching was studied for its application in extracting inorganic and organic constituents from fresh fermented grape pomace, air-dried fermented grape pomace and air-dried sugar beet pulp. Samples of each feedstock were leached in water at ambient temperature for 30 or 120 min at dry solid-to-liquid ratios of 1/20 and 1/50 kg/L. Leaching removed 82% of sodium, 86% of potassium, and 76% of chlorine from sugar beet pulp, and reduced total ash concentration in air-dry fermented grape pomace from 8.2% to 2.9% of dry matter, 8.2% to 4.4% in fresh fermented grape pomace, and 12.5% to 5.4% in sugar beet pulp. Glycerol (7-11 mg/dry g), ethanol (131-158 mg/dry g), and acetic acid (24-31 mg/dry g) were also extracted from fermented grape pomace. These results indicate that leaching is a beneficial pretreatment step for improving the quality of food processing residues for thermochemical and biochemical conversion.

The effect of manure-screening on the biogas yield of dairy manure was evaluated in batch digesters under mesophilic conditions (35 degrees C). Moreover, the study determined the biogas production potential of different mixtures of unscreened dairy manure and food waste and compared them with the yield from manure or food waste alone. A first-order kinetics model was developed to calculate the methane yield from different mixtures of food waste and unscreened dairy manure. The methane yields of fine and coarse fractions of screened manure and unscreened manure after 30days were 302, 228, and 241L/kgVS, respectively. Approximately 93%, 87%, and 90% of the biogas yields could be obtained, respectively, after 20days of digestion. Average methane content of the biogas was 69%, 57%, and 66%, respectively. Based on mass balance calculations, separation of the coarse fraction of manure would sacrifice about 32% of the energy potential. The methane yield of the food waste was 353L/kgVS after 30days of digestion. Two mixtures of unscreened manure and food waste, 68/32% and 52/48%, produced methane yields of 282 and 311L/kgVS, respectively after 30days of digestion. After 20days, approximately 90% and 95% of the final biogas yield could be obtained, respectively. Therefore, a hydraulic retention time (HRT) of 20days could be recommended for a continuous digester. The average methane content was 62% and 59% for the first and second mixtures, respectively. The predicted results from the model showed that adding the food waste into a manure digester at levels up to 60% of the initial volatile solids significantly increased the methane yield for 20days of digestion.

A mass transfer model was developed and validated to predict ethanol emission from thin layers of corn silage. The model was developed using experimental data collected from silage placed in a wind tunnel under different temperatures and air velocities. Data from the wind tunnel experiments were used to derive a multiple regression equation that related the overall mass transfer coefficient of ethanol to temperature and air velocity. Evaluation of the model was done using data collected from experiments conducted in a controlled environmental chamber. Ethanol emission was determined from the ventilation rate of the environmental chamber and ethanol concentration in the chamber exhaust over a 24 h period, measured using a photoacoustic gas analyzer. Ethanol concentration in the silage was also monitored throughout the duration of each experiment. Predicted ethanol emission rates were strongly correlated (R 2 = 0.94) with values measured in the environmental chamber. A high correlation (R 2 = 0.96) was also found between predicted and measured ethanol concentrations in the silage. The model was used to estimate ethanol emission rates from thin layers of lightly packed silage on a dairy farm in California. Model predictions indicate that most of the ethanol contained in the silage could be emitted in the first 10 h after exposing the silage to ambient air temperature (18°C to 35°C) and air velocity (0.1 to 2.0 m s -1 ).

Biogas and methane yields of food and green wastes and their mixture were determined using batch anaerobic digesters at mesophilic (35+/-2 degrees C) and thermophilic (50+/-2 degrees C) temperatures. The mixture was composed of 50% food waste and 50% green waste, based on the volatile solids (VS) initially added to the reactors. The thermophilic digestion tests were performed with four different feed to inoculum (F/I) ratios (i.e., 1.6, 3.1, 4.0 and 5.0) and the mesophilic digestion was conducted at one F/I (3.1). The results showed that the F/I significantly affected the biogas production rate. At four F/Is tested, after 25 days of thermophilic digestion, the biogas yield was determined to be 778, 742, 784 and 396 mL/g VS for food waste, respectively; 631, 529, 524 and 407 mL/g VS for green waste, respectively; and 716, 613, 671 and 555 mL/g VS for the mixture, respectively. About 80% of the biogas production was obtained during the first 10 days of digestion. At the F/I of 3.1, the biogas and methane yields from mesophilic digestion of food waste, green waste and their mixture were lower than the yields obtained at thermophilic temperature. The biogas yields were 430, 372 and 358 mL/g VS, respectively, and the methane yields were 245, 206, and 185 mL/g VS, respectively.

The objective of this research was to develop an integrated process to produce biogas and high-quality particleboard using saline creeping wild ryegrass (CWR), Leymus triticoides through anaerobic digestion (AD). Besides producing biogas, AD also serves as a pretreatment method to remove the wax layer of CWR for improving binding capability and then the residue is used to produce high-quality particleboard. CWR was digested for three time periods, 15, 22, and 33 days with the volatile solid (VS) loading of 10 g-VS/L-sludge and the food to microorganism (F/M) ratio of 1.41. The highest biogas yield after digestion for 33 days was 251 mL/g-VS, which is corresponded to energy of 8419 BTU/kg-dry CWR. The highest methane content of biogas was 63%. Compared with particleboards manufactured from urea formaldehyde (UF) and untreated CWR, the mechanical and long-term (24 h) water resistance properties of particleboards made from UF and 33-day AD CWR residue were statistically significantly improved, except for modulus of elasticity (MOE). For example, the modulus of rupture (MOR) was increased by 39%. The results indicated that the integrated process could be a cost-effective and environmentally friendly method for producing bioenergy and particleboard with agricultural residues.

The co-digestion of onion juice and aerobic wastewater sludge produced from an onion processor using an anaerobic mixed biofilm reactor (AMBR) was investigated for biogas energy production potential and waste treatment. Two experiments were conducted to study the performance of an AMBR at different organic loading rates (OLRs) using different mixtures of onion juice and aerobic sludge. In the first experiment, the OLR was increased from 1.24 to 4.37 gVS/L/d by increasing the amount of onion juice in the feed mixture while maintaining a constant amount of aerobic sludge. When the OLR reached 4.37 gVS/L/d, the AMBR failed as indicated by decreased biogas production and pH. Increase of carbon to nitrogen ratio (C/N) from 13.7 to 20.3 and lack of proper alkalinity were suspected to be the causes for the failure. In the second experiment, the C/N of the feed mixture was maintained at about 15 while the OLR was increased from 1.40 to 3.60 gVS/L/d. The digester showed stable performance. The average biogas and methane yields of the two experiments were 0.62 +/- 0.05 L/gVS and 0.37 +/- 0.08 L/gVS, respectively. It was concluded that the C/N of about 15 was recommended for treating the mixture of onion juice and aerobic sludge.

The aim of this work was to investigate the effects of aeration rate, aeration method, moisture content, and manure age on the characteristics of dairy manure composting with rice straw in terms of composting temperature, oxygen consumption rate, emission of odorous gases, and final compost property. It was found that the aeration rate of 0.25 L/min-kg VS was capable of achieving the highest composting temperature, longest retention time of high temperature, and less emission of odor gases. Except for the composting temperature reached, there was no significant difference between bottom-forced and top-diffusion aerations in terms of final compost property. The higher initial moisture content (65%) was more favorable for its higher temperature, longer retention time of high temperature, and more stable end compost obtained. Fresh manure showed better composting performance than the aged manure for its higher temperature reached in less time and less ammonia emission. Oxygen consumption rates were basically similar to those of temperatures. Most emissions of the odorous gases occurred during the first week of composting, therefore, special attention should be paid to this period of time for effective odor control.

The objective of this research was to characterize the qualities (mechanical properties and water resistance) of particleboard made from saline Jose Tall Wheatgrass (JTW), Agropyron elongatum. For the JTW particleboards made with 4% polymeric methane dipherryl diisocyanate (PMDI), the mechanical properties and water resistance improved with the increase of particleboard density from 0.71 to 0.75 g/cm(3). The particleboards with density of 0.74g/cm(3) had similar mechanical properties of wood-based particleboards, except for lower internal bond strength. Among the particleboards made with particles of different initial moisture contents from 2% to 10%, the particleboard with the particles of 8% initial moisture content had the highest qualities. The pretreatment using NaOH solution to wash the JTW particles reduced the qualities of finished particleboards bonded with both PMDI and urea formaldehyde (UF) resins. Particle-boards made with PMDI showed superior qualities than those made with UF, as shown by the measured contact angle results between the adhesives and JTW.

Food waste collected in the City of San Francisco, California, was characterized for its potential for use as a feedstock for anaerobic digestion processes. The daily and weekly variations of food waste composition over a two-month period were measured. The anaerobic digestibility and biogas and methane yields of the food waste were evaluated using batch anaerobic digestion tests performed at 50 degrees C. The daily average moisture content (MC) and the ratio of volatile solids to total solids (VS/TS) determined from a week-long sampling were 70% and 83%, respectively, while the weekly average MC and VS/TS were 74% and 87%, respectively. The nutrient content analysis showed that the food waste contained well balanced nutrients for anaerobic microorganisms. The methane yield was determined to be 348 and 435 mL/gVS, respectively, after 10 and 28 days of digestion. The average methane content of biogas was 73%. The average VS destruction was 81% at the end of the 28-day digestion test. The results of this study indicate that the food waste is a highly desirable substrate for anaerobic digesters with regards to its high biodegradability and methane yield.

The pretreatment of wheat straw with potassium hydroxide (KOH) at ambient temperature (20 °C) was investigated. The pretreatment effects on chemical composition and physical structures, and subsequent enzymatic hydrolysis and anaerobic digestion were evaluated. Wheat straw at 10% total solids (TS) was treated with KOH solution for 24 h at a wide range of KOH loadings from 2% to 50% (w/w dry basis). Higher KOH loading resulted in higher lignin reduction from the straw and chemical oxygen demand (COD) in the resulting black liquor. Maximum lignin reduction of 54.7% was observed at 50% KOH loading. In comparison to untreated straw, specific hydrolysis yields achieved 14.0–92.3% over the range of 2–50% KOH loading, and methane yields increased 16.7–77.5% for KOH loadings of 10–50%, respectively. Accounting for losses during pretreatment, 20% KOH loading resulted in maximum overall reducing sugar yield and methane yield and therefore is the recommended loading for pretreatment under these conditions.

Anaerobic digestion (AD) of vinegar residue was investigated in continuously stirred tank reactor (CSTR). The influence of organic loading rate (OLR) and effluent recirculation on AD performance of vinegar residue was tested. Five OLRs, 1.0, 1.5, 2.0, 2.5, and 3.0 g(vs) L-1 d(-1), were used. The highest volumetric methane productivity of 581.88 mL L-1 was achieved at OLR of 2.5 g(vs) L-1 d(-1). Effluent reflux ratio was set as 50%, the results showed that effluent recirculation could effectively neutralize the acidity of vinegar residue, raise the pH of the feedstock, and enhance the buffering capacity of the AD system. Anaerobic digestion of vinegar residue could be a promising way not only for converting this waste into gas energy but also alleviating environmental pollution which might be useful for future industrial application. (C) 2015 Elsevier Ltd. All rights reserved.

Getting over recalcitrance of lignocellulose is effective way to fuel production from lignocellulosic biomass. In current work, different pretreatments were applied to enhance the digestibility of corn stover (CS). Results showed that steam explosion (SE)-treated CS produced maximal methane yield (223.2 mL/gvs) at 1.2 MPa for 10 min, which was 55.2% more than untreated (143.8 mL/gvs). Whereas 1.5% KOH-treated CS produced maximum methane yield of 208.6 mL/gvs, and significantly (α0.05) improved 45.1% with respect to untreated. Sequent pretreatment of potassium hydroxide and steam explosion (SPPE) (1.5% KOH-1.2 MPa, 10 min) achieved a very significant (α0.01) improvement (80.0%) of methane yield (258.8 mL/gvs) compared with untreated CS. Methane production could be well explained by the first-order and modified Gompertz models. Besides, SEM, FTIR, and XRD analyses validated structural changes of CS after SPPE. SPPE might be a promising method to pretreat CS in the future AD industry.

Rice straw was converted into biogas using a high-rate anaerobic digestion system, anaerobic-phased solids digester system (APS-digester system). The system was stable and, with proper design, could become a space-efficient, high-rate solids digestion system. Ammonia is used as a supplemental nitrogen source for rice straw digestion. The effects of different pretreatment methods, physical (mechanical), thermal and chemical (ammonia) treatment, on the digestion of rice straw were investigated at the mesophilic temperature of 35°C. A combination of grinding (10-mm length), heating (110°C), and ammonia treatment (2%) resulted in the highest biogas yield, 0.47 l g−1 VS−1 fed, which is 17.5% higher than the biogas yield of untreated whole straw. Pretreatment temperature has a significant effect on the digestibility of straw.

A two-stage anaerobic sequencing batch reactor (ASBR) system was studied in the laboratory to evaluate a temperature-phased anaerobic digestion process for dairy wastewater treatment. The temperature-phased anaerobic digestion system incorporates thermophilic digestion and mesophilic digestion processes into one system which has the potential to offer the benefits of high digestion rate, fecal bacteria destruction, process stability, and favorable economics for animal wastewater treatment. Two thermophilic (55°C)-mesophilic (35°C) systems (II and III) were evaluated against one mesophilic (35°C)-mesophilic (35°C) system (I) at two system hydraulic retention times (HRTs) (3 and 6 days) and five volatile solids (VS) loading rates (2, 3, 4, 6 and 8 g/l/day). The three systems were designed with different first- and second-stage volume ratios: 1:4 for systems I and II and 1:2 for system III. The effects of temperature configurations and volume ratios between the two stages, HRTs, and VS loading rates on the performance of the two-stage ASBR system were studied. A relatively high solid retention time (SRT) of 13–18 days was achieved at both 3- and 6-day HRTs for all three systems. The performance of each system depends on the HRT and the VS loading rate. All three systems at the 3-day HRT deteriorated when the VS loading rate reached 6 g/l/day. The total solids (TS) and volatile solids (VS) removals were similar for 3- and 6-day HRTs at the VS loading rates of 2, 3 and 4 g/l/d. For the same VS loading rate in the range of 2–4 g/l/day and the same first- to second-stage volume ratio (1:4), the VS removal and specific methane production rate of the thermophilic-mesophilic system (II) were 43.8–44.1% and 0.41–0.82 l/l/day for 3-day HRT, respectively, and 37.1–38.9% and 0.34–0.72 l/l/day for 6-day HRT, respectively, which are higher than the VS removal and specific methane production rate of the mesophilic-mesophilic system (I) (29.3–30.2% and 0.27–0.56 l/l/day for 3-day HRT, respectively; 26.1–29.1% and 0.27–0.48 l/l/day for 6-day HRT, respectively). With the thermophilic-mesophilic system, the 1:4 ratio for the first- and second-stage reactors yielded better solids removals and methane production rate than the 1:2 ratio. Both thermophilic-mesophilic systems were found to be more effective in destroying the total coliforms present in the wastewater than the mesophilic-mesophilic system. As far as solids removal, biogas production, and coliform bacteria destruction are concerned, thermophilic-mesophilic systems are recommended over the mesophilic-mesophilic systems. However, the increased heating energy requirement of the former system needs to be considered when comparing the economics of these two treatment systems.

The influence of particle size and an alkaline pretreatment on the anaerobic digestion of corn stover was studied. Four particle sizes, 0.075 to 0.25, 0.25 to 1.0, 1.0 to 5.0, and 5.0 to 20.0 mm, were used. The highest and lowest methane yields were obtained from untreated corn stover at particle sizes of 0.25 to 1.0 and 5.0 to 20.0 mm, respectively. 4% NaOH and 2% Ca(OH)2 (combined alkaline pretreatment, CAP) were then used together to pretreat corn stover at these two particle sizes, compared with 6% NaOH pretreatment (single alkaline pretreatment, SAP). The cumulative methane yields from particle sizes 0.25 to 1.0 mm after CAP, 0.25 to 1.0 mm after SAP, 5.0 to 20.0 mm after CAP, and 5.0 to 20.0 mm after SAP were 286.9, 287.0, 268.7, and 272.6 mLg-1 VS, respectively. The particle size barely influenced the final cumulative methane yield of alkali-treated corn stover. Moreover, the cumulative methane yield of the corn stover after CAP was comparable with that of the corn stover after the SAP under the same conditions. These results provide us with a promising substitute of NaOH pretreatment for corn stover bioconversion in the future.

Thermogravimetry (TG) was employed to understand the interactions between ionic liquids (ILs) and biomass components. The thermal decomposition profiles of several biomass samples with IL pretreatment at different temperatures were studied by TG. Samples of Avicel (PH101), xylan from beechwood and alkaline lignin as well as switchgrass and corn stover were pretreated using 1-butyl-3-methylimidazolium acetate ([C4mim][OAc]) at temperatures of 50–130 °C for 6 h. Analysis of TG data provided insight into the mode of degradation of xylan and lignin in [C4mim][OAc]. Pretreated Avicel samples exhibited higher decomposition temperatures due to transformation from cellulose I into cellulose II, while samples of switchgrass and corn stover showed an improved thermal stability as a result of removal of minerals by [C4mim][OAc]. More intensive pretreatment produced decreased thermal resistance due to degradation of biomass components and decrystallization.

The methane production potential, biodegradability, and kinetics of a wide range of organic substrates were determined using a unified and simple method. Results showed that feedstocks that contained high energy density and easily degradable substrates exhibited high methane production potential and biodegradability. Lignocellulosic biomass with high content of fibrous compositions had low methane yield and biodegradability. Feedstocks with high lignin content (≥ 15%, on a TS basis) had low first-order rate constant (0.05-0.06 1/d) compared to others. A negative linear correlation between lignin content and experimental methane yield (or biodegradability) was found for lignocellulosic and manure wastes. This could be used as a fast method to predict the methane production potential and biodegradability of fiber-rich substrates. The findings of this study provided a database for the conversion efficiency of different organic substrates and might be useful for applications of biomethane potential assay and anaerobic digestion in the future.

Corn stover (CS) and chicken manure (CM) are ubiquitous agricultural wastes at low cost and have the potential to achieve a nutrient-balance when mixed together to produce biomethane via anaerobic digestion (AD). The main objective of this work was to investigate methane production at different CS to CM ratios and to evaluate the process stability under wet (W-AD), hemi-solid state (HSS-AD) and solid state (SS-AD) conditions. Results showed that synergistic effects were found when mixing two substrates at CS:CM ratios of 3:1 and 1:1 (on volatile solid basis). The highest methane yield of 218.8 mL/g VS added was achieved in W-AD at CS:CM ratio of 3:1. In SS-AD, the highest volumetric methane productivity of 14.2L methane/L reactor volume was found at CS:CM of 1:1. The results of this work provide useful information to improve the efficiency and stability of co-digestion of CS and CM under different AD conditions.

Ensiling was investigated for the long-term storage of Sugar Beet Pulp (SBP). Eight strains of lactic acid bacteria (LAB) and a non-inoculated control were screened based on their ability to rapidly reduce pH, produce a large amount of lactic acid and inhibit undesirable fermentations. Lactobacillus brevis B-1836 (LAB #120), Lactobacillus fermentum NRRL B-4524 (LAB #137) and a non-inoculated control were selected for further research to determine the effects of LAB inoculation level and packing density on SBP silage quality and sugar yield upon enzymatic hydrolysis. Both SBP preservation and prevention of cellulose and hemicellulose loss were better when SBP was treated with LAB #137 compared to LAB #120 and the non-inoculated control. Additionally, the ensiling process was found to significantly improve the enzymatic digestibility of SBP by as much as 35%. The results suggest that ensiling may be a promising technology for SBP stabilization and pretreatment for bioconversion to products.

The ventilation and environmental control parameters of two broiler barns in California were measured and monitored as part of the National Air Emission Monitoring Study. This paper presents the ventilation measurement results from September 22 of 2007 to March 31 of 2009, which covers ten broiler production cycles. The duration of each cycle was about 45 d for raising the new chicks to 2.3-kg adults. The two broiler barns had identical structural design and ventilation, feeding and litter management practices. Each barn contained about 21,000 broilers in each production cycle and was mechanically ventilated with 11 fans, including one 91-cm fan and ten 122-cm fans. All the fans, heaters and evaporative cooling systems were automatically operated to control the house temperature from 32°C at the beginning to 20°C at the end of each production cycle. The environmental parameters that were monitored included temperature, relative humidity and static pressure inside the houses, and ambient temperature, relative humidity, wind speed and direction, and solar radiation outside the houses. The operational status and rotational speed of all ventilation fans were continuously monitored. The ventilation rate of each house was estimated by calculating the airflow rate through all the fans based on the depression of static pressure in the building, fan performance and operation status. The production cycle average daily mean ventilation rate was correlated with cycle average daily mean ambient temperature. The ventilation rate for any day within a cycle was influenced primarily by bird age and ambient temperature. The daily ventilation rate of a barn ranged from 0 to 75.8 m3/s with an average of 13 m3/s. The minimum and maximum ventilation rates occurred in January and July/August, respectively. Average ventilation volume per broiler during a growth cycle was 2341 m3, and ranged from 1161 to 5214 m3.

Summarization: This study was conducted to determine the characteristics and biogas production potential of organic materials separated from municipal solid wastes using a rotary drum reactor (RDR) process. Four different types of wastes were first pretreated with a commercial RDR system at different retention times (1, 2 and 3 d) and the organic fractions were tested with batch anaerobic digesters with 2.6 g VS L−1 initial loading. The four types of waste were: municipal solid waste (MSW), a mixture of MSW and paper waste, a mixture of MSW and biosolids, and a mixture of paper and biosolids. After 20 d of thermophilic digestion (50 ± 1 °C), it was found that the biogas yields of the above materials were in the range of 457–557 mL g VS−1 and the biogas contained 57.3–60.6% methane. The total solid and volatile solid reductions ranged from 50.2% to 65.0% and 51.8% to 66.8%, respectively. For each material, the change of retention time in the RDR from 1 to 3 d did not show significant (α = 0.05) influence on the biogas yields of the recovered organic materials. Further studies are needed to determine the minimum retention time requirements in the RDR system to achieve effective separation of organic from inorganic materials and produce suitable feedstock for anaerobic digesters. Presented on: Bioresource Technology

This study characterizes dynamic ammonia (NH3) and carbon dioxide (CO2) emissions associated with feeding and defecation activities of laying hens. Manure handling scheme used was reflective of commercial manure-belt house operation. Four dynamic emission chambers and measurement system was developed, featuring continuous measurement of the following variables for each chamber: (a) NH3 concentrations of inlet and outlet air, (b) air temperature and relative humidity, (c) airflow rate, (d) feeder weight and thus feeding activity, and (e) manure pan weight and thus defecation activity. Daily feed consumption of the hens averaged 103 g/hen-d and fresh manure production averaged 125 g/hen-d. Ammonia emission rate ranged from 1.26 mg/hen-hr on the first day of manure accumulation to 9.26 mg/hen-hr after 7 d of manure accumulation. CO2 emission rate averaged 3.41 and 2.47 g/hen-hr during light and dark hours of the day, respectively. Dynamic NH3 emissions tend to be inversely related to defecation events as manure accumulates. Results from this study will contribute to the development and/or validation of process-based farm emission model for predicting NH3 emissions from laying-hen houses. The dynamic nature of NH3 emissions vs. defecation may also provide insight concerning application timing of manure treatment agents to mitigate NH3 emissions from laying-hen houses.

The effects of the addition of enzyme products containing cellulase, hemicellulase, and beta-glucosidase to anaerobic digestion systems were studied using JoseTall Wheat Grass (wheat grass) as a model substrate. Anaerobic digestion tests were performed using batch reactors operated at 50 degrees C. The application of enzyme products in three digestion configurations were simulated and investigated: (1) enzyme addition to a single-stage digester, (2) pre-treatment of wheat grass with enzymes followed by a single-stage anaerobic digestion, and (3) enzyme addition to the first stage (hydrolysis and acidification) of a two-stage digestion system. The enzyme products showed positive effects on the solubilization of wheat grass when used alone to treat the wheat grass. However, no significant differences in biogas and methane yields, and volatile solids reduction resulted when the enzyme products were tested in the anaerobic digestion systems. This reveals that the microorganisms present in the inoculum were effective in carrying out the digestion of wheat grass. The types of microorganisms present in the inoculum were identified using 16S rRNA sequence analysis. A comparison of the sequences between the different inocula revealed that the prevalent operational taxonomic units were similar, but that the acidified inoculum contained a higher percentage of the species Thermotogae.

Six types of mechanical aerators were evaluated and compared for their capacities of transferring oxygen into water and their energy efficiencies. The standard method of American Society of Civil Engineers for testing aerators in clean water was used to determine the standard oxygen transfer rate (SOTR) and standard oxygenation efficiency (SOE) of each aerator. The aerators tested included four types that are typically used for dairy wastewater lagoons and two types that are being used for municipal wastewater lagoons. The names of the first four types were vortitech, black circulator, pond mill and vbttm and the latter two were aire-o2 aerator and aire-o2 triton. The SOTR was determined to be 0.20, 0.42, 0.15, 0.21, 2.66 and 2.93 kg o2/hr, respectively, and the SOE was 0.49, 0.35, 0.36, 0.10, 0.68 and 0.57 kg o2/kwh, respectively. all tested aerators showed lower SOTR and SOE than the published literature values for typical mechanical aerators. The results of this study pointed out the fact that the aerators currently used for dairy wastewater lagoons need significant improvement in their aeration performance in order to match their counterparts in municipal wastewater lagoons. The aerator testing results are important information for decision making with respect to the proper selection of aerators for performing the aeration of wastewater lagoons and estimating the energy requirement of operating the aerators.