Print

Weber, David L.

Plant and Soil Science

2006

MS

Eutrophication of fresh water lakes and streams ranks among the highest water quality issues in the United States. Phosphorous (P) removal from agricultural wastewater is a regional topic of concern in the Lake Champlain Basin (LCB), and current dairy production in Vermont has been associated with P rich waters entering the basin. Constructed wetlands are an alternative nutrient management approach for barn yard runoff and parlor waste on small to medium sized dairy farms. In 2003, a subsurface flow constructed wetland (SSF-CW) system was built adjacent to the UVM's Paul Miller Research Center, and designed to treat barn yard runoff and milk house wash water generated during milk production. Given the increasing importance of phosphorus (P) pollution in the LCB, a new slag based P-removal filter technology (PFT) was established (2004) at the UVM CW site with two major objectives: i) to test the filters efficiency as an upgrade unit for improving P removal performance via constructed wetlands ii) to investigate the capacity of filters technology to remove P as a "stand alone" unit. Columns experiments previously conducted under laboratory conditions using synthetic P solution have demonstrated that electric arc furnace (EAF) slag has an extremely high P retention capacity (3.65 g kg-1) over extended periods of time. There were six individual filters tested. Filters F1-F4 were fed with water that had gone through one of the CW cells, with filter influent concentration ranging between 8.3 - 59.9 (average 31.5 mg L⁻¹). Filters F1 & F2 were fed with a vertical upward flow (VUF) regime and filters F3 & F4 were fed with a vertical downward flow regime (VDF). Filters F1-F4 received approximately 2.17 g DRP kg⁻¹ EAF steel slag (244.8 g DRP in total) during the 259 day feeding period. Filters F1 & F2 retained 1.7 g DRP/kg EAF steel slag (199.1 g DRP in total), representing 78% of the total DRP added. Filters F3 & F4 retained 1.67 g DRP kg⁻¹ EAF steel slag (193.75 g DRP total), representing 77% of the total DRP added over the life span of the filters. Two filters (F5 & F6) were fed untreated barn yard and milk house waste that was diverted to the filters before passing through a CW cell. Filters F5 & F6 were fed under a VDF flow regime, and influent concentration ranged between 7.6 - 80.4 (average 41.0 mg L⁻¹) over the 180 day life span of the filters. Filters F5 & F6 received 1.96 g DRP kg⁻¹ EAF steel slag (220.7 g DRP in total) over the life span of the filter, and retained 1.52 g DRP kg⁻¹ EAF steel slag (180g DRP in total), representing 72% of the DRP added. Further analysis on heavy metals, oxi-redox and pH were also performed during the course of the study. The establishment of the EAF slag based PFT represents the first in-field evaluation of this technologies potential to reduce P concentrations from dairy farm wastewater in Vermont.