Removal of nutrients and other pollutants from agricultural drainage
ditch water, ponds, and other surface waters.
Some of this work is funded by a nearly 1 million dollar NRCS CIG (conservation innovation grant), conducted in collaboration with the University of Maryland (Principal investigator Dr. Joshua McGrath), University of Maryland Eastern Shore (Dr. Arthur Allen), and USDA-ARS Pasture Systems Management and Watershed Research Unit (Dr. Ray Bryant).
Objectives:
- To identify waste products that can be used as phosphorus sorbing materials (PSMs) in surface water bodies
- To design structures containing PSMs for optimal removal of nutrients from water bodies
Introduction/Benefits
- Excessive nutrients in surface waters can result in algae growth, fish kills, eutrophication, and overall poor water quality.
- Many waste products that are typically land-filled, including materials produced during drinking water treatment, power generation, paper production, mining and metal casting may have a beneficial re-use in improving surface water quality.
Removal of phosphorus
Chemical mechanisms. Phosphorus “sorption” is the combined process of adsorption and precipitation of phosphorus from dissolved to solid forms. Materials containing the elements aluminum, iron, calcium and magnesium can potentially react with phosphorus and other contaminants, depending on several factors. Properties of the materials that affect the capacity and rate of phosphorus and contaminant removal include: pH, surface area, mineralogy, and particle size/hydraulic conductivity. While there are numerous benefits to using waste materials, it is critical that materials and targeted surface waters be thoroughly characterized to estimate the potential removal capacity and determine if any negative environmental effects may occur from the use of these materials.
Schematic of ditch flow-through treatment structure
The main benefit of the structure is for the containment of the PSMs. Many studies have been conducted on the addition of PSMs to waterways, irrigation water or direct application to soil or manure, but do not allow for ultimate removal. Containment of the PSMs allows for the removal of “spent” material, effectively removing the contaminants from the water body and watershed. Other methods only affect the availability/solubility of the phosphorus with long-term solubility unknown. Structures may be designed using active or passive systems. An active system utilizes gravity or a mechanical pump to facilitate the flow of water through the PSMs. A passive structure utilizes concentration gradients to allow for phosphorus in the water to come in contact with the PSMs. Many aspects need to be considered in the design of a phosphorus removal structure including: phosphorus concentrations in water, amount of material needed, hydraulic head or water pressure, retention time necessary (kinetics), available space, and access to PSMs for removal. The following is a schematic and picture of a ditch flow-through structure currently in operation on the Eastern Shore of Maryland.
Current investigations
Agricultural uses. Dr. Penn is currently working with researchers at the University of Maryland and the USDA-ARS to implement the use of PSMs in ditch structures in the Chesapeake Bay watershed. This research is being conducted with a grant from the USDA-NRCS and will be conducted over the next three years. Previous research and pilot studies have demonstrated that this technology is effective at removing phosphorus and other contaminants from agricultural drainage ditches.
Urban uses. The OSU Soil Chemistry Laboratory is in the process of investigating locally-available waste materials for use in phosphorus removal structures. Structure designs will also be evaluated for use in ponds, water retention systems and drains. Studies will examine the effectiveness of PSMs to removal other contaminants including heavy metals, pesticides and nitrogen. The pond at the turf farm will serve as the first “test plot” for removing phosphorus from surface waters in an urban/suburban setting. For more information see the August issue (2007) of the Journal of Soil and Water Conservation (pg 269-276; see “publications”).
Gypsum Bed Ditch Filtration Structure
AMDR Ditch Box Filtration Structure (acid mine drainage treatment residuals)
In addition, the Soil Chemistry Group at Oklahoma State University is currently developing a filtration unit for suburban, golf course, and farm ponds for removal of phosphorus, heavy metals, and nitrogen. A small scale filter will be installed on a pond located at the Oklahoma State University Botanical Gardens this spring (08).
