Curtis Miller

Biogas and CH4 productivity by co-digesting swine manure with three crop residues as an external carbon source

Co-digesting swine manure with three agricultural residues, i.e., corn stalks, oat straw, and wheat straw, to enhance biogas productivity was investigated in this study. A 3x3 experimental design with duplicates was adopted (3 crop residuesx3 carbon/nitrogen ratios) to examine the improvement of batch digestion in terms of biogas volume produced, CH(4) content in the biogas, and net CH(4) volume. The crop residues were first cut into small sections and then ground into fine particles smaller than 40 mesh size (0.422mm) before being added to digesters. All the digesters were run simultaneously under controlled temperature at 37+/-0.1 degrees C. The length of experiment was 25days. The results showed that all crop residues significantly increased biogas production and net CH(4) volume at all C/N ratios, among which corn stalks performed the best with increase in daily maximum biogas volume by 11.4-fold as compared to the control, followed by oat straw (8.45-fold) and wheat straw (6.12-fold) at the C/N ratio of 20/1, which was found to be the optimal C/N ratio for co-digestion in the present study. In addition, corn stalks achieved the highest CH(4) content in the biogas ( approximately 68%), which was about 11% higher than that of oat straw ( approximately 57%), whereas wheat straw and the control both had produced biogas with approximately 47% CH(4) content. Wheat straw demonstrated a lower biogas productivity than corn stalks and oat straw even it had a higher carbon content (46%) than the latter two residues (39%).

Swine manure fermentation for hydrogen production.

Biohydrogen fermentation using liquid swine manure as substrate supplemented with glucose was investigated in this project. Experiments were conducted using a semi-continuously-fed fermenter (8L in total volume and 4 L in working volume) with varying pHs from 4.7 through 5.9 under controlled temperature (35+/-1 degrees C). The hydraulic retention time (HRT) tested include 16, 20, and 24h; however, in two pH conditions (5.0 and 5.3), an additional HRT of 12h was also tried. The experimental design combining HRT and pH provided insight on the fermenter performance in terms of hydrogen generation. The results indicated that both HRT and pH had profound influences on fermentative hydrogen productivity. A rising HRT would lead to greater variation in hydrogen concentration in the offgas and the best HRT was found to be 16 h for the fermenter in this study. The best pH value in correspondence to the highest hydrogen generation was revealed to be 5.0 among all the pHs studied. There was no obvious inhibition on hydrogen production by methanogenesis when methane content in the offgas was lower than 2%. Otherwise, an inverse linear relationship between hydrogen and methane content was observed with a correlation coefficient of 0.9699. Therefore, to increase hydrogen content in the offgas, methane production has to be limited to below 2%.

Biohydrogen production through fermentation using liquid swine manure as substrate.

In this paper, continuous production of hydrogen through fermentation with liquid swine manure as substrate was researched using a semi-continuously fed fermenter (8 L in total volume and 4 L in working volume). The pH and temperature for the fermenter were controlled at 5.3 ± 0.1 and 35 ± 1°C, respectively, throughout the experiment. Three hydraulic retention times (16, 20, and 24 h) were investigated for their impact on the efficiency and performance of the fermenter in terms of hydrogen yields. The results indicate that hydraulic retention time (HRT) has a strong influence on the fermenter performance. An increasing HRT would increase the variation in hydrogen concentration in the offgas. To produce hydrogen with a fairly consistent concentration, the HRT of the fermenter should not exceed 16 h, which, however, did not appear to be short enough to control methanogenesis because the offgas still contained about 5% methane. When methane content in the offgas exceeded 2%, an inverse linear relationship between hydrogen and methane was observed with a correlation coefficient of 0.9699. To increase hydrogen content in the offgas, methane production has to be limited to below 2%. Also, keeping oxygen content in the fermenter below 1.5% would increase the hydrogen concentration to over 15%. The product to substrate ratio was found to be around 50% for the fermenter system studied, evidenced by the observation that for every 6 liters of manure fermented, 3 liters of pure hydrogen were produced, which was significant and encouraging.

A novel use of anaerobically digested liquid swine manure to potentially control soybean cyst nematode

Experiments were carried out in two steps to determine the effect of anaerobically digested swine manure on soybean cyst nematode (SCN) egg control. In the first step, liquid swine manure underwent anaerobic digestion to search for the best digestion time for both volatile fatty acids (VFA) and ammonium nitrogen (NH4 +) enrichment. The results showed that about 17 and 28 days of incubation were needed, respectively, to reach the maximal levels of VFA and NH4 + in the manure. In the second step, raw, VFA-enriched, and NH4 +-enriched manure were applied separately, at four different rates (25, 50, 100, and 200 mL/pot), to soil pots inoculated with nematode eggs in a greenhouse environment. Soil samples were collected 35 and 61 days after inoculation to determine the effect of such treated manure on SCN egg productivity. The data indicated that the SCN egg counts were inversely related to the manure application rates in a linear manner with correlation coefficients of 0.998, 0.967, and 0.900 for raw, NH4 +-enriched, and VFA-enriched manure for the 35-day samples. While no such relationships were found for the 61-day samples, implying that none of the treatments were still effective 61 days after application. At the four application rates, the VFA-enriched manure performed best in reducing SCN egg counts (by 18.1, 19.5, 34.3, and 18.6%) as compared to the raw manure treatment. In contrast, the NH4 +-enriched manure achieved mostly negative reductions. To achieve the best control of SCN egg growth, the VFA-enriched manure should be used and applied to soybean fields every 35 days.

In vitro enzymatic conversion of γ-aminobutyric acid immobilization of glutamate decarboxylase with bacterial cellulose membrane (BCM) and non-linear model establishment

The work investigated the properties and feasibility of using bacterial cellulose membrane (BCM) as a new and environmental friendly support carrier to immobilize glutamate decarboxylase (GAD) (a unique enzyme in the conversion of γ-aminobutyric acid (GABA) production). During cultivation, the porosities of BCM decreased successively with more extended fibrils piling above one another in a criss-crossing manner thus forming condensed and spatial structure. The BCM with this ultrafine network structure was found to immobilize GAD best via covalent binding because of the highest efficiency of immobilization (87.56% of the enzyme was bonded) and a good operational stability. And the covalent binding efficiency (amount of enzyme immobilized versus lost) was closely related to the porosity or the inner network of the BCM, not to the surface area. The capacity per surface area (mg/cm(2)) increased from 1.267mg/cm(2) to 3.683mg/cm(2) when the porosity of BCM ranged from 49% to 73.80%, while a declining trend of the loss of GAD specific activity (from 29.30%/cm(2) to 7.38%/cm(2)) was observed when the porosity increased from 49.9% to 72.30%. Two non-linear regression relationships, between the porosity and loading capacity and between porosity and enzyme activity loss, were empirically modeled with the determination of coefficient R(2) of 0.980 and 0.977, respectively. Finally, the established in vitro enzymatic conversion process demonstrated 6.03g/L of GABA at 0.10mol/L Glu, 60min of retention time and 160mL of suspension volume after the 1st run and a loss of 4.15% after the 4th run. The productivity of GABA was 6.03gL(-1)h(-1), higher than that from other reported processes.

Utilization of protein extract from dairy manure as a nitrogen source by Rhizopus oryzae NRRL-395 for l-lactic acid production.

Six levels of crude protein (0.21, 0.42, 0.84, 1.68, 2.52, and 3.36g/L) and six levels of protein hydrolysates from dairy manure, defined by degree of hydrolysis (DH, 6.9%, 17.2%, 25.9%, 33.8%, 36.1%, and 36.7%), were investigated as the nitrogen source for production of l-lactic acid by Rhizopus oryzae NRRL-395 with respect to the influence of nitrogen source on l-lactic acid yield and the correlation with biomass yield and mycelia morphology. Increases in crude protein from 0.21 to 1.68g/L led to an increase in l-lactic acid concentration in the culture media from 6.48 to 57.7g/L. However, further increases beyond 1.68g/L did not present continuing increases in l-lactic acid yields. The highest biomass yield was obtained at a crude protein nitrogen concentration of 2.52g/L. Hydrolysates with high DH resulted in high yields of l-lactic acid and biomass. At a nitrogen level of 0.42g/L (hydrolysates) with DH ranging from 33.8% to 36.7%, the l-lactic acid yield of 0.53-0.56g/g of glucose was achieved, coupled with a 13-14% yield of fungal biomass.

Kinetics study of fermentative hydrogen production from liquid swine manure supplemented with glucose under controlled pH

Kinetics of H2 production from liquid swine manure supplemented with glucose by mixed anaerobic cultures was investigated using batch experiments under four different pH conditions (4.4, 5.0, 5.6, and uncontrolled). The temperature for the experiments was controlled at 37 ± 1°C and the length of experiments varied between 50 and 120 hours, depending upon the time needed for completion of each individual experiment. The modified Gompertz model was evaluated for its suitability for describing the H2 production potential, H2 production rate, and substrate consumption rate for all the experiments. The results showed that the Gompertz model could adequately fit the experimental results. The effect of pH was significant on all kinetic parameters for H2 production including yield, production rate and lag time, and the substrate utilization rate. The optimal pH was found to be 5.0, at which a maximum H2 production rate (0.64 L H2/h) was obtained, and deviation from the optimal pH could result in substantial reductions in H2 production rate (0.32 L H2/h for pH 4.0 and 0.43 L H2/h for pH 5.6). The results also showed that if pH was not controlled for the batch fermentation process, the substrate utilization efficiency could steeply decrease from 98.8% to 33.7%.

Development and optimization of a culture medium for L-lactic acid production by Rhizopus oryzae using crude protein from dairy manure as a nitrogen source.

Experiments were conducted using the crude protein in fresh dairy manure as the nitrogen source in the culture media for Rhizopus oryzae to produce L-lactic acid. Two uniform design experiments were carried out with one for optimizing seed culture while the other for best percent L-lactic acid production. Multiple linear regression and ANOVA analyses were employed to determine the most significant media components. Data from the first uniform design U6 (62× 3), in which the experimental factors involved included nitrogen concentration (crude protein), spore concentration, and treatment duration, showed that the levels of these components in the optimal condition for the seed culture medium were 2.1 g/L nitrogen, 16 hour culture time, and 105 spore concentration. The biomass weight in the seed medium developed in this study reached 1.32 g/L, which was 48.3% higher than that of the control. The combination of culture time and nitrogen concentration was found to be most significant in influencing the biomass yield. In the second uniform design experiment, flask culture with five factors (glucose, nitrogen from dairy manure, ZnSO4, KH2PO4, and MgSO4) at eight levels was examined using the uniform design table U8 (85) with the content of L-lactic acid as the evaluating response Y. The results showed that ZnSO4 had the most influence on L-lactic acid yield, followed by nitrogen and KH2PO4. The optimum culture medium in terms of lactic acid production consisted of 240 g/L glucose, 1.26 g/L crude protein, 1.05 g/L KH2PO4, and 0.25 g/L MnSO4, which could achieve a yield of 59.57% (7.1% higher than the control).

Odor and Aeration Efficiency Affected by Solids in Swine Manure During Post-Aeration Storage

An extensive laboratory study followed by a limited field-scale investigation was carried out in this project with the goal of determining the relationship between manure solids levels and aeration times and rates as well as their effect on the length of odor-free storage after the combined separation and aeration treatment. In the laboratory study, three levels of aeration were examined (35 mV in oxidation-reduction potential [ORP], 1 and 3 mg L-1 in dissolved oxygen [DO]) in conjunction with three continuous aeration lengths (5, 15, and 30 days). All tests were performed on manure with solids levels of 0.5%, 1%, 2%, and 4% stored in PVC columns. The results showed that continuous aeration for 5, 15, and 30 days at 35 mV ORP, 1 and 3 mg L-1 DO levels was sufficient to keep the treated liquid odor-free for a storage period of up to 180 days if the manure solids levels were below 0.79%, 0.87%, and 0.96%; 0.82%, 1.0%, and 1.23%; and 1.02%, 1.11%, 1.52%, respectively. It turns out that in order to reduce aeration time and rates, the manure total solids content should not exceed 1%. The field experiment was conducted on a finishing farm located in Jackson County, Minnesota, where both solids-liquid separation and aeration were used by the producer in manure treatment. The site was composed of eight 600-head growing-finishing buildings equipped with shallow pits and a timer-controlled flushing system. With a 10 hp surface aerator, it would take about 83 and 74 days to reduce VFA and BOD to the respective levels, i.e., 230 and 171 mg L-1, under which offensive odors are not supposed to be produced.

Pilot-scale field study for ammonia removal from lagoon biogas using an acid wet scrubber.

The anaerobic activities in swine slurry storage and treatment generate biogas containing gaseous ammonia component which is a chemical agent that can cause adverse environmental impacts when released to the atmosphere. The aim of this pilot plant study was to remove ammonia from biogas generated in a covered lagoon, using a sulfuric acid wet scrubber. The data showed that, on average, the biogas contained 43.7 ppm of ammonia and its concentration was found to be exponentially related to the air temperature inside the lagoon. When the air temperature rose to 35°C and the biogas ammonia concentration reached 90 ppm, the mass transfer of ammonia/ammonium from the deeper liquid body to the interface between the air and liquid became a limiting factor. The biogas velocity was critical in affecting ammonia removal efficiency of the wet scrubber. A biogas flow velocity of 8 to 12 mm s−1 was recommended to achieve a removal efficiency of greater than 60%. Stepwise regression revealed that the biogas velocity and air temperature, not the inlet ammonia concentration in biogas, affected the ammonia removal efficiency. Overall, when 73 g L−1 (or 0.75 M) sulfuric acid solution was used as the scrubber solution, removal efficiencies varied from 0% to 100% with an average of 55% over a 40‐d measurement period. Mass balance calculation based on ammonium–nitrogen concentration in final scrubber liquid showed that about 21.3 g of ammonia was collected from a total volume of 1169 m3 of biogas, while the scrubber solution should still maintain its ammonia absorbing ability until its concentration reaches up to 1 M. These results showed promising use of sulfuric acid wet scrubber for ammonia removal in the digester biogas.