Gerald L. Riskowski

Thermochemical conversion of swine manure: an alternative process for waste treatment and renewable energy production.

A thermochemical conversion (TCC) process was applied to the treatment of swine manure slurry for oil production and waste reduction. The objectives of the first stage study were to explore the feasibility of oil production from swine manure and to determine the waste reduction rates through the TCC process. A bench TCC reactor was developed and tested at operating temperatures of 275°C to 350°C. The corresponding operating pressures ranged from 5.5 to 18 MPa. Carbon monoxide was used as a reducing agent at pressures from 0.34 to 2.76 MPa. The oil product was evaluated by element analysis, heating value, and benzene solubility. The waste reduction rate was evaluated in terms of chemical oxygen demand (COD) before and after the TCC process. The highest oil yield was 76.2% of the total volatile solids of the feedstock. The hydrogen to carbon molar ratio was 1.53. The TCC oil product had a similar quality as that of pyrolysis oils from liquefaction of other biomass such as wood sludge and newspaper waste. The average heating value of the oil product was estimated at 34 940 kJ/kg. The COD in the post-processed water after the TCC process was reduced as much as 75.4%. Carbon dioxide was the sole detected gaseous by-product. The solid by-product of the TCC process was only 3.3% of the total solids input by weight.

Volatile fatty acids as odor indicators in swine manure: A critical review

Determination of odor indicators in swine manure is critical for many aspects of developing effective odor control techniques. Past research has used volatile fatty acids (VFAs) as an odor indicator; however, using all VFAs can still be misleading. This article presents the available information regarding the mechanisms in microbiology and biochemistry of producing volatile fatty acids in swine manure and an extensive discussion on using VFAs as odor indicators. Long chain and branching VFAs (C4-C9) may represent the offensiveness of malodors in swine manure better than short and straight chain acids and thus should receive further research to correlate them with odor indicators. Two bacterial genera, Eubacterium and Clostridium, appear to be the most likely major contributors to the production of odorous compounds, such as volatile fatty acids, in swine manure. More research is needed to identify the species within these two genera to determine the types and quantities of odorous compounds produced by different species.

OPERATING TEMPERATURE AND RETENTION TIME EFFECTS ON THE THERMOCHEMICAL CONVERSION PROCESS OF SWINE MANURE

A thermochemical conversion (TCC) reactor was developed to process swine manure for waste reduction and energy production. The operating temperature and retention time are the two key parameters affecting the process. Carbon monoxide (CO) was employed as the reductive reagent. The investigated ranges of the operating temperature and retention time were 275°C ~ 350°C (corresponding operating pressures were 7 ~ 18 MPa) and 5 ~ 120 min, respectively. The pH value of the fresh swine manure (pH= 6.1), CO to VS ratio (CO:VS = 0.07 by weight or CO initial pressure p ini = 690 kPa), and total solids content (TS = 20%) were kept constant for all the experiments in this study. No extra catalyst was added in the experiments because of the presence of plentiful minerals and carbonates. The operating temperature was the most important factor affecting the TCC process. No substantial oil product yield was achieved unless the temperature reached 285°C or above. Temperature higher than 335°C led to solid char formation. Retention time affected the completeness of the TCC process. The retention time for achieving high oil yield and quality was largely dependent upon the operating temperature levels. The suggested operating temperature and retention time for the TCC process are 295°C to 305°C and 15 to 30 min, respectively. Keywords. Swine manure, Manure utilization, Biomass energy, Thermochemical conversion, Direct liquefaction.

Hydrogen sulfide production from stored liquid swine manure : A laboratory study

The production of hydrogen sulfide from stored liquid swine manure as influenced by the manure settling characteristics and the initial sulfate concentration was studied in the laboratory. The manure was settled in a 30-cm diameter ×120-cm high column for 24 h and then divided into three layers based on the solids content. The manure from different layers were placed in separate closed jars and stored for 30 days at 22 ± 2°C. The total sulfide, total solids, volatile solids, pH in the manure, and the hydrogen sulfide in the effluent gas stream were measured. The sulfide production rate was highest for all three manure layers during the first 5-10 days of storage. The top manure layer had the lowest solids content and the highest sulfide concentration. However, because of the lower pH levels in the bottom layer, the concentration of molecular H2S is higher in the bottom layer compared with the top layer. Mathematical equations for predicting hydrogen sulfide concentration and production rates in the different manure layers were derived. Three levels of initial sulfate concentration (5.89, 110, and 275 mg/L as SO4 2–) were used to test the effect of initial sulfate concentration in the liquid manure on sulfide production. Higher initial sulfate concentration in the manure resulted in higher sulfide concentration during the storage period. From the observations made, it was confirmed that reducing the sulfate concentration in the water supply would help reduce the sulfide production in the pit.

MASS TRANSFER COEFFICIENT FOR HYDROGEN SULFIDE EMISSION FROM AQUEOUS SOLUTIONS AND LIQUID SWINE MANURE

Mass transfer coefficient for hydrogen sulfide emission from an aqueous solution and liquid manure into the air was determined using a convective emission chamber where air temperature, velocity, turbulence, and relative humidity were precisely controlled. The mass transfer coefficient was determined from experimental data and correlated to liquid temperature, air temperature, and air velocity using a dimensional analysis method. Typical values of air temperature (15-35°C), air velocity (0.1-0.5 m/s), and liquid manure temperature (15-35°C) found in under-floor manure storage pits were used. The mass transfer coefficient increased as liquid temperature increased and decreased as the air velocity and air temperature increased. When the liquid temperature was higher than the air temperature, the mass transfer coefficient increased as the difference between the two temperatures increased. This result implies that higher emission rate of H2S is likely to occur in a situation where the liquid temperature is higher than the air temperature. Sensitivity analysis showed that the mass transfer coefficient is more sensitive to changes in liquid and air temperature than to air velocity above the liquid.

EFFECT OF VENTILATION RATE ON DUST SPATIAL DISTRIBUTION IN A MECHANICALLY VENTILATED AIRSPACE

Dust spatial distribution is an important variable to understand the nature of dust transportation and to implement appropriate control strategies. There is a lack of data on dust spatial distribution in mechanically ventilated airspaces because of lack of adequate sampling techniques. In this project, a multi-point sampler was used to measure the dust spatial distribution at different ventilation rates in a mechanically ventilated airspace, which was an isothermal and two-dimensional flow empty room. Dust mass concentration varied as much as 30-fold between the lowest and the highest within the mechanically ventilated airspace. Ventilation rate had a large effect on the dust spatial distribution. Increasing the ventilation rate reduced the overall mean dust concentration when ventilation rates were lower than 56 air changes/h (ACH). When ventilation rates were higher than 56 ACH in this study, the overall mean dust concentration did not change much (<4%) as the ventilation rate increased by 18%. The spatial gradients of dust concentration become relatively lower as the ventilation rate increases. There is a high dust concentration zone in the ventilated airspace, which is important for selecting proper locations for air cleaning devices.

Ascorbic acid, nitrate, and nitrite concentration relationship to the 24hour light/dark cycle for spinach grown in different conditions.

Nitrate, nitrite and ascorbic acid (vitamin C) concentrations were determined for spinach (Spinacia oleracea L.) over a 24 h period to determine if light intensity (including dark periods) at time of harvest impacts concentrations in raw vegetables. Nitrate, nitrate and ascorbic acid concentrations varied significantly over the 24 h period and appeared to be related to changes in light intensity. Light intensity at the time an experimental sample is collected may affect the concentration of some constituents that a researcher is studying. Also, nitrate and nitrite concentrations in raw spinach can be reduced by harvesting at the best time of day. The highest nitrate concentrations in spinach occurred in the dark just prior to an increase in light intensity. Ascorbic acid was near its highest level for the 24 h period when the light intensity initially increased, then decreased to its lowest level around 3-6 h later.

Changes in nitrate and nitrite concentrations over 24 h for sweet basil and scallions

Nitrate and nitrite concentrations were determined for sweet basil and scallions over 24h to determine if time of sampling or harvest impacts concentrations in raw vegetables. Also, nitrate and nitrite concentrations were determined separately for various edible parts of these plants. Basil had significant changes in nitrate and nitrite concentrations over a 24h period. Nitrate was correlated to changes in light intensity with a 3h lag time. The highest nitrate concentrations in basil (2777 ppm) occurred around 3h after the light intensity peaked and had low values (165-574 ppm) during the dark period. The scallion nitrate and nitrite concentrations were always low but nitrate showed a peak a few hours before sunrise. Nitrate and nitrite concentrations in some raw vegetables may be reduced by harvesting at the best time of day for each type of plant. Nitrate concentrations were different in the edible plant parts tested.

QUANTIFYING VENTILATION EFFECTIVENESS FOR AIR QUALITY CONTROL

The term “ventilation effectiveness” has been widely used to evaluate ventilation systems for air quality control. The application of the term is often either qualitative, rather than quantitative, or difficult for field application. This paper presents the results of quantification of ventilation effectiveness for specific ventilation systems by using a ventilation effectiveness factor (VEF) and a ventilation effectiveness map (VEM). The VEF and VEM are defined mathematically so they can be used to quantify the ventilation effectiveness of a ventilation system. The application of the VEF and VEM was illustrated using a full–scale room case study, which involves comparison of two different ventilation systems: one had a slot air outlet at the opposite wall to the air inlet (Case A), and the other had a air outlet at the same wall as the air inlet (Case B). It is commonly assumed that the locations of air outlets or exhaust fans have little effect on the ventilation effectiveness for livestock buildings. The case studies show that the outlet location had a substantial effect on the ventilation effectiveness for the room airspace as a whole and for specific locations in the room. The differences in ventilation effectiveness for these two systems were quantified in terms of VEF. Ventilation in Case B is three times as effective at dust removal as in Case A. Ventilation effectiveness factors at specific locations within the airspace were also plotted on a VEM. One of advantages of VEF is that a ventilation system can be its own control for comparison of ventilation effectiveness, instead of requiring a control and a treatment. This feature is particularly useful in system evaluation or troubleshooting because it is often very difficult and expensive to have an identical system to compare.

EFFECTS OF ROOM OZONATION ON AIR QUALITY AND PIG PERFORMANCE

Reducing odor emissions from swine farms to avoid complaints about odor nuisance is a major issue. Ozonation has been used to reduce odor in swine buildings, but little research exists on its benefits. A swine-finishing building was divided into two identical rooms and two treatments, ozonation and the control, were applied in a cross-over design. The treatments were switched between rooms every three weeks. The overall experimental period was 12 weeks, during which there were four trials. Pig growth performance, dust mass and size concentration, odor intensity, total sulfur compounds, hydrogen sulfide concentration, ammonia concentration, and total heterotrophic bacterial counts were measured and analyzed during the test period. Sulfur-containing compounds detected included dimethyldisulfide, dimethylsulfide (methanethiol), and dimethyltrisulfide. Ozone application to a swine building at the maximum safe concentration of 0.1 ppm did not have any statistically significant effects on dust mass concentration, odor concentration and emission rate, sulfur compound concentrations, and bacteria counts. However, it did increase ammonia concentration and decrease pig average daily gain. The ozonation effects on hydrogen sulfide concentration could not be evaluated by the gas tube method used during this study.