Spray drifts have been studied by mathematical models and computer simulations as an essential complement to lab and field tests, among which are fluid dynamic approaches that help to understand the transport of spray droplets in a turbulent atmosphere and their potential impacts to the environment. From earlier fluid mechanical models to highly computational models, scientific advancement has led to a more realistic prediction of spray drift, but the current literature lacks reviews showing the trends and limitations of the existing approaches. This paper is to review the literature on fluid-mechanical-based modelling of spray drift resulting from ground spray applications. Consequently, it provides comprehensive understanding of the transition and development of fluid dynamic approaches and the future directions in this research field.

This study evaluates the performance of AERMOD, the current U.S. Environmental Protection Agency (EPA) regulatory model, in simulating particulate matter (PM₁₀ and PM_2.5) dispersion from a poultry pullet facility. At the source, the daily mean PM₁₀ and PM_2.5 concentrations with strong diurnal patterns were estimated to be 436.01 ± 166.77 μg m⁻³ and 291.09 ± 105.81 μg m⁻³, respectively. This corresponded to daily mean emission rates of PM₁₀ and PM_2.5 as 0.067–0.073 g sec⁻¹ and 0.044–0.047 g sec⁻¹, respectively. The modeled hourly PM concentration showed acceptable accuracy relative to the measured PM concentrations downwind of the source. Increasing the averaging period from hourly to daily resulted in improved prediction. The simulations revealed that PM concentrations at and beyond the property line of the poultry facility were within the National Ambient Air Quality Standards. This study suggested that AERMOD is effective in predicting and assessing the impacts of PM downwind of poultry facilities. Implications: Sampling and monitoring of PM emission around concentrated animal feeding operations (CAFOs) can be both time-consuming and costly. This makes dispersion modeling an alternative method for air quality assessment around CAFOs. The acceptable performance of the current EPA regulatory model, AERMOD, in modeling PM₁₀ and PM_2.5 dispersion around the pullet poultry facility suggested that this model can effectively predict PM downwind concentrations at and around CAFOs and can be used as a tool to assess the impacts of PM at downwind locations.

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

Particulate matter (PM) is a major air pollutant from animal production with significant impacts on human health and the environment. Abatement of PM emissions is imperative and effective PM control technologies are strongly needed. In this work, an electrostatic spray wet scrubber (ESWS) technology designed for removal of PM (PM₁₀ and PM_2.5) emissions from poultry facilities was evaluated under simulated laboratory conditions. Effects of primary operating parameters – including charging voltage (0–14 kV), air speed (0.5–3.5 ms⁻¹), droplet diameter (100–300 µm), and PM concentration (1–5 mg m⁻³) on the PM removal performance of the ESWS – were investigated. Predictive empirical models for PM₁₀ and PM_2.5 removal efficiencies were also developed. The preliminary results showed that the ESWS technology reduced emissions of PM₁₀ by 85–94% and PM_2.5 by 85–88% with a charging voltage of 7 kV, air speed of 0.5–0.75 m s⁻¹, and droplet diameter of 100–150 µm. The water consumption rate was approximately 2.35 L min⁻¹, while the total power consumed was 270 W. This study demonstrates that the ESWS could be a potentially effective and feasible tool in controlling PM emissions for commercial poultry facilities.

Droplet charging is an effective method to enhance dust removal efficiency using an electrostatic spray scrubber (ESS). However, effects of the materials and dimensions of different electrodes on droplet charging efficiency have not been studied systematically. In this study, ring-shaped electrodes were selected to test effects of three types of electrode materials (copper, stainless steel, and graphite) with various dimensions on droplet charging efficiency. A Faraday pail charge measurement device was used to measure the droplet charge generated by the electrodes. A reduced factorial design with four factors was used in this study to investigate the charging efficiency affected by the factors. The four factors tested were electrode material, electrode diameter, nozzle height, and applied voltage. A 304L stainless steel electrode was found to achieve higher droplet charge-to-mass ratio (CMR) values than identically shaped electrodes made from either copper or graphite. The optimal stainless steel electrode inner diameter was 100 mm. The 304L stainless-steel electrode with this optimal diameter and a height of 45 mm achieved the highest mean CMR of 0.435 ± 0.002 mC kg⁻¹ at an applied voltage of −11 kV with the bottom of the nozzle tip positioned 15 mm below the top of the electrode. Implications Currently, the low removal efficiency of submicron particles cannot meet the environmental control requirements of industrial applications that may have significant concentrations of particulate matter (PM) in this size range. As stricter environmental regulations are increasingly enforced, there is an urgent need to efficiently remove submicron dust particles from the air. Experiments show that the dust capture process is improved by charging droplets in the spray separator and reducing the secondary escape of dust particles in the electrostatic precipitator Although high-voltage charging of droplets has been investigated in many studies, the effect of electrode material and size on droplet CMR is still not fully understood. The purpose of this study was to (1) quantify the performance of 304L stainless steel (304L SS), copper, and high-purity graphite electrodes for spray droplet CMR, (2) evaluate effects of the applied voltage, nozzle height, electrode material and dimension on CMR, and (3) optimize the specific values of key design factors and operating parameters that lead to the highest CMR. The results of this study aim to optimize electrostatic spray scrubbers to achieve high droplet CMR values.