Nutrient Removal Structures Using Locally-Sourced Iron and Aluminum By-Products Reduce Nutrient Runoff from Broiler Production Facilities

A common issue with filters designed to remove nutrients from runoff is their reduced effectiveness in high-flow conditions. To overcome this challenge, it was determined that nutrient removal from broiler-house fan dust could be more effective if nutrient removal was conducted at the nutrient source. The objective of this study was to evaluate the effectiveness of containment trays (CTs) holding locally sourced by-products installed adjacent to broiler house fans at the University of Arkansas Savoy broiler production facility to capture nutrients released from dust during rainfall over four years (2013 to 2017). By-products used were locally sourced, iron-based red mud (RM) generated during the manufacture of steel belts for tires and alum-based drinking water treatment residual (WTR), where both materials have large phosphorus (P) sorption capacities. Four-year mean annual concentrations of dissolved P of through-flow from RM CTs were consistently below 0.7 mg·L-1 and below 1.6 mg·L-1 for WTR CT through-flow. This equated to an average 11- and 4-fold decrease for RM and WTR, relative to concentrations in runoff from same-sized plots adjacent to sidewall fans, demonstrating their potential to trap P at the source and decrease P runoff to nearby flowing waters. While there was no significant decline in RM or WTR effective-ness over the four-year study, further work needs to be conducted to determine the lifespan of CTs. Use of RM and WTR in CTs at poultry broiler production facilities, along with their subsequent land application, has the potential to reduce the amount of by-product materials that are currently landfilled.


Introduction
Accelerated cultural eutrophication continues to be a concern in the U.S. and globally [1], with agricultural production systems identified as a major contributor, for example in the Chesapeake Bay Watershed [2] [3], Mississippi River Basin [4], Florida's inland and coastal waters [5], Lake Erie Basin [6] [7] [8] and China [9]. Concerns have centered on regions with spatially concentrated livestock systems, where nutrients, particularly P, in manure produced exceed local crop requirements, leading to an increased risk of P runoff [10]. For broiler production systems, additional concerns were focused on nutrient runoff from dust deposit adjacent to broiler house ventilation fans [11] [12].
Accentuating the potential loss of nutrients is the fact that the water solubility of dust P was, on average, three times greater than that in the litter [11]. Strategies to reduce nutrient runoff now target nutrient sources, rather than treating receiving waters, to most effectively decrease impairment [13] [14] [15]. Thus, removing nutrients from runoff water prior to water leaving the production area is the most cost-effective, on-farm conservation practice (CP).
To be consistently effective, P-removal systems must able to treat and transmit large volumes of runoff. As runoff volumes from land around broiler production houses can easily overload available systems, P-removal systems would not be consistently effective. In addition, installation and maintenance of P-removal systems are expensive and labor intensive, making P-removal systems unrealistic as a permanent, on-farm solution. Removing P at the source avoids the issue of hydraulic overload, because it would no longer be necessary to treat large volumes of runoff.
Herron et al. [16] [17] reported RM and WTR could sorb 25 and 10 g•P•kg −1 of by-product, respectively, with hydraulic conductivities of 8.0 and 15.4 cm•cm −1 , prior to being used to sorb P from broiler-house ventilation dust. Further research by Herron et al. [17] [18] determined an optimal thickness of 8 cm for the RM and WTR by-products to retain P and at the same time allow infiltration of water for efficient P removal (96% to 99% of added P by WTR and RM, respectively).
To be most cost-effective, P retention media need to be locally sourced, readily available, and inexpensive. Industrial by-products with large P-retention capacities that are currently being landfilled are ideal candidates if the by-products do not contain hazardous materials. Two such byproducts are alum-based WTRs, generated where alum is used to flocculate suspended solids from municipal water supplies, and any of a group of by-products variously referred to as red muds or iron filter cakes, which consist primarily of iron oxides and oxyhy-Journal of Environmental Protection droxides. The effectiveness of a CT is not only a function of the design and placement, but is also a function of the capacity of the retention media to capture and retain the target nutrients [19] [20]. This paper describes a four-year study to test the hypothesis that CTs filled with P-sorbing materials and recessed into the ground adjacent to broiler house fan outlets, could sequester P from dust and decrease P runoff potential. Dust from broiler houses settles on top of the P-sorbing materials. During a rainfall event, rainfall first encounters the dust and leaches nutrients into the underlying P-sorbing materials where they are sequestered. In the research described in this paper, the bottom of CTs was enclosed by plastic so that through-flow could be collected and analyzed. If effective, on-farm CTs would not have enclosed bases, allowing through-flow to drain into underlying soil. Installed trays were recessed into the ground level, so rainfall would percolate through the dust and by-product evenly (Figure 1(c)). A 2.5-cm interior diameter PVC pipe was installed at one corner to allow access for a pump tube to collect the leachate, which was accomplished using a long, flexible tube connected to a peristaltic pump. Duplicate CTs were filled with RM or WTR, leaving 5 cm of the tray exposed to eliminate runoff or run on of water. Thus, CTs adjacent to fans 1 and 3 were filled with RM and those adjacent to fans 2 and 4 filled with WTR [16].

Containment Tray Design
Natural rain falling on the CTs leached the dust through the by-product, trapping particulate matter and sorbing P. A 10.2-cm free air space below the by-product allowed capture of the leachate, which was pumped out after each rainfall event and analyzed for P and nitrogen (N) (Figure 2

Containment Tray Leachate Collection and Analyses
Following storm events that generated runoff, leachate was pumped from the cavity beneath the CTs. Leachate was subsampled and 1 L was retained from each tray for analysis. Leachate was filtered through a 0.45-µm membrane filter Nitrate-N (NO 3 -N) and ammonium-N (NH 4 -N) were analyzed colorimetrically by flow-injection analysis (Lachat Instruments QuickChem 8500, Loveland, CO). One hundred twenty-five milliliters were acidified with 12 drops of concentrated sulfuric acid for sample preservation, and analyzed for TP and TN using persulfate/autoclave digestion [22]. Total P was determined by spectrophotometry (Beckman Coulter, Pasadena, CA), and total N (TN) was determined by flow-injection analysis (Lachat Instruments QuickChem 8500, Loveland, CO).
One hundred twenty-five milliliters were gravimetrically analyzed for total solids after oven drying at 105˚C for 12 hours.

Statistical Analyses
Statistical differences among mean concentrations of DP, TP, NH 4 -N, NO 3 -N, and TN of CT through-flow were determined by t-tests as a function of RM and WTR by-products and as a function of year for each CT using JMP Version 14.1 [23]. All relationships are reported as statistically significant at the p < 0.05 level.

Nutrients in Containment Tray Through-Flow
The concentration of DP measured in each through-flow event from the CTs is depicted in Figure 3 for RM CT1 and WRT CT2. The DP concentration of through-flow from the CTs decreased with consecutive rainfall events; however, with an extended dry period between rainfalls (i.e., > four weeks), DP concentration increased due to a buildup of sidewall fan dust on the CTs. Similar trends were observed from RM CT3 and WTR CT4 and for TP, NO 3 -N, NH 4 -N, and TN concentrations (data not shown).
The concentration of P in CT through-flow was consistently less for RM than WTR (p < 0.05; Table 1). For instance, mean annual DP concentration of through-flow for RM CTs was consistently below 0.7 mg•L −1 , and varied little (p > 0.05) among years and between duplicate trays (Table 1). For WTR, through-flow DP concentrations were below 1.6 mg•L −1 .
There was no difference in mean annual P and N concentrations, except for TN in the RM CT, of through-flow for RM or WTR CTs among study years (p < 0.05; Table 1). This was the case even though through-flow volume varied from year to year, indicating a consistency in performance of the by-products to remove P irrespective of through-flow volume.   (Table 1). However, the four-year average concentrations of DP, TP, NO 3 -N, and NH 4 -N, and TN were significantly lower in through-flow from RM than WTR CTs (p < 0.05; Table 1).

Efficacy of Nutrient Removal by Containment Trays
The concentrations of P and N released from poultry house dust were estimated as the mean concentration of P and N in runoff induced from simulated rainfall plots adjacent to the four sidewall fans of the poultry houses on the Savoy Farm, as reported in Herron et al. [16]. Mean concentrations of DP, TP, NO 3 -N, concentrations leached from house dust to a smaller extent than for P ( Figure 5).

Conclusions
Designed with PVC and vinyl-coated mesh, the CTs were resistant to environmental degradation from ultraviolet light, bacteria, and mold. The CTs also retained their structural integrity, despite being exposed to heavy rainfall (maximum of 9.3 cm in 24 h) and outdoor temperatures exceeding 38˚C and as low as −12˚C during the four-year study (2013 to 2017).
The trays functioned properly to trap broiler house dust and percolate rain and runoff water. Visual observations of the system during and directly following a rainfall event showed that dust accumulates on the surface and reduces infiltration of rainwater through the by-product, but does not pond and overtop the tray. The slowed infiltration rate increased contact time between through-flow and by-product in the CTs, which enhanced the effectiveness of P removal.
Once saturated with P or clogged, the by-product would be removed from the CT and land applied with broiler litter from house clean out, as evaluated and reported by Brennan et al. [24].  sequester P in house dust; thereby decreasing the quantity of P that could runoff and be transported to nearby flowing waters. In addition, use of RM and WTR in CTs at poultry-broiler production facilities has the potential to reduce the amount of the by-products that are currently landfilled.