Two of the fastest growing sectors of agriculture in the United States are horticulture and aquaculture. This preliminary study addresses key aspects of water use and effluent issues associated with both industries, namely the utilization of effluent discharges from one operation (aquaculture) to enhance the other (horticulture), thereby reducing water use and effluent discharge from both. This project builds upon results of previous research involving the use of constructed wetlands to improve water quality in finfish production ponds and reduce effluent discharges. Although these recirculating pond-wetland systems were shown to improve water quality in catfish ponds and reduce associated risk to production and discharges of effluent, the added costs associated with the use of wetlands could not be economically justified. One possible solution to this limitation is to find a filter system that includes plant products that could both contribute to the removal of nutrients from pond effluent and be harvested and sold to offset the added cost of the treatment systems.
Hydroponic System
A hydroponic filter system is a modified version of the pond-wetland system previously tested. The hydroponic filter was constructed adjacent to a bark-based (i.e. "bark-o-ponic") filter that shares an influent and effluent basin. Both filters are linked to a quarter-acre pond stocked with 2700 15g channel catfish (10,800 fish/acre). The one-foot deep hydroponic filter was originally planted with wetland plants to remove excess nutrients from pond effluents. Modifications removed the wetland plants and replaced them with vegetables and herbs grown on floating platforms divided by cells. Five cells were constructed to measure the filtering capabilities of a variety of food plants. Foam board was used to construct 48-inch by 48-inch floating platforms. Each cell contained three platforms. Three-inch square holes were cut into the foam boards on 6.5-inch centers in order to accommodate 25, four-inch pots per platform. These pots were filled with lava rocks and peat-o-pots containing plant seedlings. Three cells were planted in April 2002 with oregano, dill, and sweet basil. Oregano and dill did not germinate well in the peat-o-pots. Those that did germinate did not adjust well to the hydroponic filter and were discontinued in May. Sweet basil was grown and harvested bi-weekly beginning on May 28, 2002 and ending on August 27, 2002 after production had largely stopped.
Bark-O-Ponics System
A bark-based filter system (bark-o-ponics), a modified version of the pond-wetland system previously tested was linked to an intensive production catfish pond. The wetland was replaced with an effluent filter system that utilized a pine bark media to grow plants. Effluent from the pond flowed through the bark media where nutrients were removed through a combination of microbial degradation within the media and plant uptake before being returned to the pond. A series of cells were used to evaluate the flow rate potentials and filtering capabilities of various combinations of bark media. Nutrient-rich effluent from a quarter-acre pond stocked with 2700 15g channel catfish (10,800 fish/acre) was gravity fed into a settling basin. From the basin, water entered the cells through gate valves at the depth of twelve inches. These valves were used to maintain flow rates.
Four cells were used to evaluate the flow rate potentials and filtering capabilities of various combinations of bark media. Each were filled to a depth of twelve inches with one of the following media mixes: 100% Bark; 100% Peel; 90% Bark/10% Peel and 90% Bark/10% Sawdust. Landscape cloths were installed on top of these mixes. A layer of bark was then added until each cell reached a depth of twenty-four inches total. The cells were twenty-four feet long and three feet wide and were subdivided into three sections by sampling ports. Section A began at the settling basin wall and ended eight feet from the wall. Section B began at eight feet and ended sixteen feet from the wall. Section C began at sixteen feet and ended with the containment wall, twenty-four feet from the settling basin wall. These vertical porous ports were installed in order to obtain a water sample clean of media material from the bottom twelve inches of the cell.
PUBLICATIONS AND PRESENTATIONS
Walters, S. Christine, Benedict C. Posadas, Mark W. LaSalle, Cecil T. Pounders, Jr. and Mark A. Peterman. Use of a Constructed Filter to Improve Water Quality and Offset Production Costs in Finfish Pond Culture.
Walters, S. Christine, Benedict C. Posadas, Mark W. LaSalle, Cecil T. Pounders, Jr. and Mark A. Peterman. Use of a Hydroponic Filter to Improve Water Quality and Offset Production Costs in Finfish Pond Culture.