Andrew G. Hashimoto

Modeling and optimization of the dilute-sulfuric-acid pretreatment of corn stover, poplar and switchgrass

Lignocellulosic biomass may be used as a potential renewable feedstock for biochemical production of ethanol as an alternative transportation fuel. However, cellulose, which is the major source of fermentable sugars in these materials, is protected by a network of lignin and hemicellulose. The dilute-sulfuric-acid pretreatment removes this protecting shield and makes the cellulose more susceptible to enzymatic digestion. In this study, three lignocellulosic feedstocks (i.e. corn stover, poplar and switchgrass) were pretreated with dilute sulfuric acid (0.6, 0.9 and 1.2% w/w) at relatively high temperatures (140, 160 and 180°C) in a Parr batch reactor. The hydrolysis of hemicellulose to its monomeric constituents and possible degradation of these monomers were modeled by a series of first-order reactions. The kinetic parameters of two mathematical models for predicting the percentage of xylan remaining in the substrate after pretreatment and the net xylose yield in the liquid stream were determined using the actual acid concentration in the reactor after accounting for the neutralization effect of the substrates.

Ammonia inhibition of methanogenesis from cattle wastes

Ammonia inhibition of methanogenesis from cattle wastes was studied using laboratory scale, mesophilic and thermophilic fermentors fed beef-catle manure (40 kg Volatile Solids per cubic metre) and various levels of 5N NH4Cl. Results showed that ammonia inhibition began at about 2·5 kg Nm−3 for both thermophilic and mesophilic fermentations that were not previously acclimated to high ammonia concentrations and about 4 kg Nm−3 for thermophilic fermentors previously acclimated to ammonia concentrations between 1·4 and 3·3 kg Nm−3. This study also showed that assuming ‘steady state’ after three to four volume turnovers may lead to erroneous conclusions when inhibitory substances are present in the substrate.

Ultimate methane yield from beef cattle manure: Effect of temperature, ration constituents, antibiotics and manure age

The effects of temperature, ration constituents, antibiotics and manure age on the ultimate methane yield B0, litre CH4/g volatile solids fed (VSf)) were investigated using 4-litre batch fermenters. The average B0 for fermenters maintained at 30–60°C (at 5°C intervals) was 0·328 litre CH4/g VSf. The B0 at 65°C averaged 0·118 litre CH4/g VSf, but this low yield was attributed to unstable fermentation rather than decreased substrate availability at that temperature. These results agreed well with B0 values estimated from daily-fed fermenters. Chlortetracycline and monensin did not affect B0; however, monensin did delay the start of active fermentation in batch fermenters. The average B0 of manure from cattle fed 91·5, 40 and 7% corn silage were 0·173, 0·132 and 0·290 litre CH4/g VSf, respectively. The average B0 for 6–8 week old manure from a dirt feedlot was 0·210 litre CH4/g VSf.

Effect of inoculum/substrate ratio on methane yield and production rate from straw

Abstract This study evaluated the effect of inoculum/substrate ration on methane yield and production rate in small-batch fermentors. Four trials were conducted with substrate concentrations of 10, 20, 30 or 40 g ball-milled straw diluted with tap water to a total weight of 1 kg. Inoculum concentrations were: 100 (control), 90, 70, 50, 30 and 20 or 10% by volume. Results showed that the ultimate methane yield was drastically lower at inoculum/substrate ratios (on a volatile solids basis) below 0·25. Methane production rate increased at a decreasing rate up to an inoculum/substrate ratio of two, after which it remained relatively constant.

Thermophilic and mesophilic anaerobic fermentation of swine manure

The effects of temperature (35° and 55°C), influent Volatile Solids (VS) concentration (So = 50·4 and 62·5 kg VS m−3) and hydraulic retention time (HRT = 5, 10, 15 and 25 days) on methane (CH4) production from swine manure were evaluated using 3-dm3 laboratory scale fermentors. The highest CH4 production rate achieved was 3·12 m3 CH4 per m3 fermentor per day at 55°C, 5-day HRT and So = 50·4 kg VS m−3. Batch fermentations showed an ultimate CH4 yield (B0) of 0·49 m3 CH4 kg VS fed. Extreme fermentation instability was experienced by the thermophilic (55°C) fermentors at 25-day HRT and S0 = 62·5 kg VS m−3. This instability was attributed to free-ammonia and influent-substrate inhibitions. After a significant period for adaptation (over 170 days), the thermophilic fermentors adapted to the high free-ammonia concentrations and operated satisfactorily.

Methane emissions from typical manure management systems

Abstract Methane is the most abundant organic chemical in the earths atmosphere, and its abundance is increasing with time and has reached levels not seen in recent geological history. Methane is produced both naturally and anthropogenically. One of teh sources of anthropogenic methane is manure from domesticated animals. A methodology has previously been developed to estimate the amount of methane generated from this source. This was done by estimating the methane conversion factor (MCF) typically achieved by various waste management systems. The present study was conducted to evaluate these MCF assumptions using dairy manure as the representative livestock manure. The MCFs for the most dominant of disposal methods, rangeland/pasture disposal, were much lower than the earlier estimates. Other waste management systems, such as solid storage and liquid slurry storage had much higher MCFs, at 20 and 30°C. However, these waste management methods are more prevalent in parts of the world where the average annual temperature is closer to 10°C. At that temperature, the MCF is negligible in all waste management systems. This study showed that the previously reported estimates of MCF for some waste management systems were higher than was actually the case. Consequently earlier estimates of the amount of methane generated globally from manures were higher than those found in this study.

Effects of pH and substrate:inoculum ratio on batch methane fermentation

Batch digestion experiments were conducted to determine the effects of inoculum:substrate ratio and initial medium pH on methane production from glucose. A ratio between the chemical oxygen demands (COD) of the substrate and inoculum solids (SISR) was used to quantify the food to microorganisms (F/M) ratio. Two periods of active methane production, separated by a period of inactivity, characterized the fermentation. The duration of inactivity was affected by both SISR and the initial medium pH. It decreased as SISR was decreased or when a higher initial pH was used. With a SISR of 4.8 and a pH of 7.2 or 7.0, the inactive period was eliminated, indicating satisfactory coupling of the acid- and methane-forming phases. Ultimate methane yield at a SISR of 4.8 was higher than at a SISR of 38.5.

Methane from swine manure: Effect of temperature and influent substrate concentration on kinetic parameter (K)☆

The effects of temperature (35 and 55° C) and influent Volatile Solids (VS) concentration (S0 = 33·5, 43·6, 54·3, 61·8 and 77·1 kg VS m−3) on the kinetic parameter K (an increase in K indicates inhibition of fermentation) of swine manure were evaluated using 3-dm3 laboratory-scale fermentors. Ultimate methane (CH4) yield (B0) of the swine manure was 0·48 ± 0·02m3 CH4 (kg VS fed)−1 as determined by 109-day batch fermentations. K increased exponentially as S0 increased, and was described by: K = 0·6 + 0·0206 exp (0·051 × S0) Temperature had no significant (P > 0·05) effect on K for S0 between 33·5 and 61·8 kg VS m−3.

Thermophilic and mesophilic methane production from anaerobic degradation of the cyanobacterium Spirulina maxima

Abstract Methane production from fermentation of the cyanobacterium, Spirulina maxima, as the sole substrate was investigated in 200 mL working-volume anaerobic digesters maintained at 35 and 55°C. Digesters were fed once-per-day with a feed concentration (St0) of 22.5 g volatile solids (VS) per liter, at retention times (θ) of 8, 12, and 16 days. Digester contents were mixed for one min before and after feeding. After 3 volume turnovers, effluent samples were obtained on four consecutive days. Methane production rate (L CH4/L-day) and methane yield (B) (L/g of COD fed) at 35°C were 0.47 and 0.09, 0.41 and 0.15, and 0.31 and 0.15 at the respective θ of 8, 12, and 16 days; at 55°C they were 0.20 and 0.05, 0.31 and 0.11, and 0.19 and 0.09, respectively. The ultimate methane yield (B0) after 105 days of batch fermentation was 0.22 L CH4 per g COD fed (0.33 L CH4/g VS fed). COD degradation at these retention times and temperatures was between 23 and 40%, ammonia nitrogen between 1.12 and 1.86 g/L, and alkalinity between 7.0 and 7.8 g CaCO3/L. The concentration of total volatile acids at 35°C was 4.07, 2.58 and 3.13 at θ = 8, 12, and 16 days, respectively; at 55°C they were 6.78, 4.18, and 4.07, respectively. These results indicate that the biomass of S. maxima can be used as a sole nutrient for methane production at mesophilic and thermophilic temperatures. However, the methane production rates at these retention times are higher at the mesophilic temperature. These rates are significantly lower than those obtainable with cattle or swine wastes because greater maximum loading rates can be obtained with these wastes before digester failure occurs.

Performance of a pilot-scale, thermophilic, anaerobic fermenter treating cattle waste

Abstract Start-up and steady-state operation of a pilot-scale, thermophilic, anaerobic fermenter is described. The fermenter was operated at: temperatures of 45, 50 and 55°C; hydraulic retention times (HRT) ranging from 4 to 12 days; mixed continuously or for 2 h/day; and fed once/day or 22 times/day. No difference in methane (CH 4 ) production rate was observed when the fermenter was mixed 2 h/day versus continuously. CH 4 production rate was about 10% higher when the fermenter was fed the same loading rate 22 times/day compared to once/day. The highest CH 4 production rate achieved by the fermenter was 4.7 m 3 CH 4 /m 3 fermenter·day. This is the highest rate reported in the literature for fermentation of livestock waste and about four times higher than other pilot- or full-scale systems fermenting livestock waste. Performance of the pilot-scale fermenter was predicted using a previously reported kinetic equation. The mean ratio of predicted to experimental CH 4 production rates was 0.99 with a standard deviation of 0.10.