Lingying Zhao

A Prototype Acid Spray Scrubber for Absorbing Ammonia Emissions from Exhaust Fans of Animal Buildings

Mitigation of ammonia (NH3) emissions from animal production buildings has been a challenge because of the large volume of low NH3 concentration laden air being released. Among emission mitigation technologies for concentrated animal feeding operations, acid spray scrubbers have the greatest potential for adaptation to the existing large animal facilities because of their lower fan airflow reduction, ability to simultaneously remove particulate and gaseous pollutants, and viability for zero or less waste generation by recycling effluents as liquid fertilizer. A multi-stage wet scrubber prototype that can be operated with a maximum of three stages was developed and optimized for reducing NH3 emissions using simulated conditions typically encountered at an animal building exhaust. The parameters optimized for a single-stage wet scrubber include nozzle type, nozzle operating pressure, sulfuric acid concentration, spray coverage, and air retention time. The optimized single-stage wet scrubber settings can remove emissions from 60% ±1% at 5 ppmv inlet NH3 concentration (IAC) to 27% ±2% at 100 ppmv IAC at a normal exhaust superficial air velocity (SAV) of 6.6 m s -1 . A high concentration of droplets inside the contact chamber increased the rate of inter-collision between droplets, which led to high droplet coagulation and decreased surface area for gas-liquid contact. These phenomena were prevented by operating the nozzles in the higher stages co-current to the airflow and by using fewer nozzles in higher stage. The two-stage and three-stage wet scrubbers were therefore optimized by determining the least number of nozzles in each stage that provided the most effective NH3 removal. The optimized two-stage scrubber could remove NH3 emissions from 60% ±0% at 5 ppmv IAC and 35% ±1% at 100 ppmv IAC. The optimized three-stage scrubber could remove emissions from 63% ±3% at 5 ppmv IAC and 36% ±3% at 100 ppmv IAC. Airflow retention time was found to significantly affect NH3 absorption. Reducing the superficial air velocity to 3.3 m s -1 from 6.6 m s -1 , which increased the air retention time from 0.2 s to 0.4 s, improved NH3 removal efficiencies to 98% ±3% at 5 ppmv IAC and 46% ±2% at 100 ppmv IAC for the single-stage scrubber. Similarly, the performance of the two-stage scrubber at a SAV of 3.3 m s -1 improved to 77% ±0% at 20 ppmv IAC and 57% ±1% at 100 ppm IAC. Lastly, the performance of the three-stage scrubber at a SAV of 3.3 m s -1 improved to 70% ±1% at 30 ppmv IAC and 64% ±1% at 100 ppmv IAC. It was observed that the three-stage wet scrubber did not increase the overall wet scrubber performance, as predicted theoretically. Further studies are needed so that the application of these scrubber designs becomes feasible for treating air emissions from animal buildings. The wet scrubber caused an additional backpressure of 27.5 Pa, resulting in about 8% airflow reduction for a fan operating at 12.5 Pa.

Dietary protein effects on hen performance and nitrogen excretion

Because dietary nitrogen intake affects nitrogen content in manure, diet management has been recognized as a means to reduce ammonia emissions from poultry operations. The objectives of the present research were 1) to determine the extent to which the CP content of laying diets can be reduced, based on performance criteria, and 2) to determine how ash:nitrogen ratios of manure, eggs, and hens are affected by dietary protein changes. Egg-type hens were fed equal daily amounts of essential amino acids in diets that provided 13, 15, or 17 g of protein/d. Each diet was fed to 20 hens, with 2 hens/cage. The planned digestible lysine intake was 0.71 g/hen per day. Ratios of other digestible amino acids to lysine were methionine plus cysteine, 0.83; threonine, 0.68; and isoleucine, 0.94. The experiment began when hens were 29 wk old and continued until they were 57 wk old. Egg production averaged approximately 90%, and daily protein intake caused no effects on egg production or grams of egg per hen per day. Feed intake was higher for hens fed 13 g of protein than for hens in the other 2 treatments (P < 0.01). Average feed intake for the experiment was approximately 95 g/d. Composition of the eggs was not affected by protein intake. Average values were DM, 30.5%; ash, 31.0% of DM; and nitrogen, 6.31% of DM. The average manure DM production was 25.9 g/hen per day, with an ash content of 25.5% of DM. Manure nitrogen content ranged from 3.98% of DM for hens fed 13 g of protein to 5.68% for those fed 17 g of protein (P < 0.01). A method is outlined that uses the analysis of fresh manure and manure leaving the poultry operation to estimate the loss of nitrogen as ammonia.

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.

Development and evaluation of a full-scale spray scrubber for ammonia recovery and production of nitrogen fertilizer at poultry facilities.

Significant ammonia emissions from animal facilities need to be controlled due to its negative impacts on human health and the environment. The use of acid spray scrubber is promising, as it simultaneously mitigates and recovers ammonia emission for fertilizer. Its low pressure drop contribution on axial fans makes it applicable on US farms. This study develops a full-scale acid spray scrubber to recover ammonia emissions from commercial poultry facilities and produce nitrogen fertilizer. The scrubber performance and economic feasibility were evaluated at a commercial poultry manure composting facility that released ammonia from exhaust fans with concentrations of 66–278 ppmv and total emission rate of 96,143 kg yr−1. The scrubber consisted of 15 spray scrubber modules, each equipped with three full-cone nozzles that used dilute sulphuric acid as the medium. Each nozzle was operated at 0.59 MPa with a droplet size of 113 μm and liquid flow rate of 1.8 L min−1. The scrubber was installed with a 1.3-m exhaust fan and field tested in four seasons. Results showed that the scrubber achieved high NH3 removal efficiencies (71–81%) and low pressure drop (<25 Pa). Estimated water and acid losses are 0.9 and 0.04 ml m−3 air treated, respectively. Power consumption rate was between 89.48 and 107.48 kWh d−1. The scrubber effluents containing 22–36% (m/v) ammonium sulphate are comparable to the commercial-grade nitrogen fertilizer. Preliminary economic analysis indicated that the break-even time is one year. This study demonstrates that acid spray scrubbers can economically and effectively recover NH3 from animal facilities for fertilizer. GRAPHICAL ABSTRACT

A Wireless Data Acquisition System for Monitoring Temperature Variations in Swine Barns

Increasing interest in monitoring the spatial variation of temperature at the animal level in swine finishing barns has led to the development of a new wireless data acquisition system. Previous studies used individual commercial data loggers placed in a protective container, then lowered into the animal pens. These traditional systems required significant effort to download each logger individually and to post-process the data into a time-synchronized file with all measurement points. The newly developed wireless system allows all measurement points to be simultaneously collected and logged to a single external data file. The specific project objectives include (1) develop a wireless sensor node capable of meeting the data transfer and sensor interface requirements of a swine finishing barn and (2) evaluate the performance of the wireless node through experimental testing. Each wireless node is preset with a specific ID which is logged with the sensor data to provide a definite indicator for the data’s source location within the barn. The individual nodes use a high accuracy thermistor for temperature sensing and are capable of transmitting one additional analog signal and eight digital signals to the data logger. The digital inputs were commonly used to collect fan activity data for ventilation monitoring. The additional analog channel can be used for other environmental sensing or for monitoring static pressure. When powered from a single 3.6 volt, 1200 mAhr battery, the wireless nodes have a usable life of 3.5 years when transmitting at a 5-minute sampling interval. This system was successfully developed and implemented for a 4-year study of swine finishing barns.

Variations in Air Quality of New Ohio Dairy Facilities with Natural Ventilation Systems

As dairy operations evolve towards larger, concentrated facilities, air quality on and around the dairy farms becomes a concern. Data on air quality in and around large dairy facilities are insufficient and therefore very much needed. In this study, preliminary data on air quality spatial distribution and temporal variations on two new large dairy facilities with naturally ventilated free stall barns and outside manure storage were collected. Concentration of hydrogen sulfide (H2S) and ammonia (NH3) at 12 to 14 locations on each farm were measured in three seasons using portable gas analyzers. Odor samples were collected at odor sources, upwind and downwind locations. Dust was measured using a portable dust mass concentration meter. Gas levels inside the dairy buildings at one leeward location were continuously monitored for three days in two seasons. In addition, indoor and outdoor temperature, relative humidity, and air velocity were measured to determine effects of these parameters on air quality.

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.

Longitudinal study to evaluate the association between thermal environment and Salmonella shedding in a midwestern US swine farm

The objective of this study was to document the association between the thermal environment in the barn and Salmonella shedding in finishing pigs. For this purpose, individual fecal samples from 900 finishing pigs (8 collections per pig) were repeatedly collected from 18 cohorts (50 pigs per cohort) on 3 sites of a multi-site farrow-to-finish production system in a longitudinal study. Pen temperature and humidity were measured every 2 min during the study period. The thermal parameters of interest were: hourly average temperature, minimum and maximum temperature, hourly temperature variation, temperature humidity index (THI) and cumulative number of hours/degree above and below the thermal neutral zone at the pen level prior to fecal sampling for 6 time periods (12h, 24h, 48 h, 72 h, 1 week and 1 month). Additional potential risk factors at the individual (e.g., sex, health events), cohort (e.g., mortality, morbidity, Salmonella status of the nursery) and pen level (e.g., type of pen) were also evaluated. Multilevel logistic models using generalized linear models, with random intercepts at pig, pen and cohort levels to account for clustering (individual samples nested within pigs, pigs nested within pens, pens within cohorts) were constructed. Site (A, B, C) was considered as a fixed effect in order to control for clustering within site. The outcome variable was Salmonella fecal status of the individual sample. Cold exposure (temperatures below the thermal neutral zone) and exposure to a THI>72 were both positively associated with risk Salmonella shedding. Nursery Salmonella status was positively associated with Salmonella shedding and pig age was negatively associated with Salmonella shedding. In the multilevel intercept-only model the largest proportion of model variance was associated with the individual fecal sample (44.8%) followed by cohort (24.5%), pen (20.5%) and pig (10.2%). The present study allowed the investigation of the association of time-variant thermal factors and Salmonella shedding. Interventions that target the thermal environment may have an effect on reducing Salmonella shedding in swine and also improve pig well-being and production efficiency. Alternatively, thermal parameters may be used to identify groups of pigs at high risk for Salmonella shedding. Future studies should be performed to investigate the cost-efficacy of interventions to improve the thermal environment of swine.

Comparison of six CFD models for room airflow study with PIV measurement data

Indoor airflow significantly influences the spatial distribution of indoor contaminants, and thus the health and comport of room occupants. Numerical simulation based on computational fluid dynamics (CFD) is considered a relatively convenient method in room airflow research. Several numerical models have been developed for different applications. There is little agreement that has been reached yet on a more acceptable CFD model due to the multitude and variability of variables affecting the room airflow. A lack of experimental data for CFD model development is another bottleneck in this area. In this paper, airflow in a full-scale room was modeled using six different CFD models and the results were compared with experimental data obtained using particle image velocimetry technology. The results indicated that the RNG k-a model would be preferred for predicting the airflow in a full-scale room over the other models.

A ROBUST SENSOR FOR MONITORING THE OPERATIONAL STATUS OF AGRICULTURAL VENTILATION FANS

A new vibration sensor for monitoring the operational status of exhaust fans in confined animal feeding operations (CAFOs) and other ventilated structures was developed and tested. The sensor utilizes integrated Micro Electro Mechanical Systems (iMEMS) technology to accurately and reliably detect the vibration of agricultural fans, an indicator of fan operating status. When coupled with a sensor to measure pressure drop across the fan and an appropriate fan performance curve, the vibration sensor can enable the collection of real-time building ventilation airflow data. The sensor integrated an iMEMS accelerometer along with signal conditioning components to convert the cyclic acceleration signal into a filtered TTL digital signal appropriate for a wide variety of data acquisition equipment. Sensor current draw was 0.9 mA, which allowed multiple devices to operate from a single power bus. Laboratory and field testing has shown that the sensor is 99% effective in determining the total on-time of agricultural fans when compared with existing methods. Testing has also shown that the sensor response is not affected by changes in operating environment temperature. Sensor installation takes only a few minutes and requires only a single hole placed in the existing fan mounting structure. Furthermore, by encapsulating the sensor in a potting compound, all critical electronic components can be sealed from the corrosive effects of moisture and gases common to CAFOs and other ventilated structures.