Water Resources Research Act Program

Details for Project ID 2019AR008B

Utilization of Biodegradable Hydroponic Growth Media as a Carbon Source for Greenhouse Wastewater Denitrification

Institute: Arkansas
Year Established: 2019 Start Date: 2019-06-01 End Date: 2020-05-31
Total Federal Funds: $9,803 Total Non-Federal Funds: $20,333

Principal Investigators: Kristen E. Gibson

Abstract: In order to cultivate horticultural and food crops in hydroponic systems, nitrogen and phosphorus must be added in excess of what is needed. Hydroponic nutrient water cannot be used indefinitely due to risk of plant pathogen accumulation and nutrient depletion. As a result, spent hydroponic wastewater rich in nitrogen and phosphorus is often released directly into the environment. The nutrient levels in hydroponic wastewater can potentially be much higher even than that of typical agricultural wastewater, landfill leachate, and municipal sewage. Combined with other wastewater streams and non-point sources of pollution, the water quality of proximal waterbodies can become compromised. Many hydroponic systems use inorganic substrates such as rockwool, perlite, expanded clay, gravel, or simply suspend plant roots directly in nutrient water. However, some systems, particularly those that grow microgreens, will use fibrous mats made of biodegradable materials such as hemp, felt, or wood. While inorganic substrates can be washed and reused, organic substrates cannot be reused and present a significant disposal challenge, which undermines sustainability goals of these systems. We propose using spent organic growth substrate as a source of organic carbon for hydroponic wastewater treatment and to enhance reusability of the growth substrate waste stream. The objectives of the proposed study are to: 1) Characterize hydroponic wastewater from a large commercial hydroponics facility in Northwest Arkansas as well as two small research systems at University of Arkansas to determine volume and nitrogen concentrations to be treated; 2) Determine concentrations of bioavailable carbon that can be obtained from soaking or digesting several types of organic growth mats; 3)Compare nitrogen removal efficiency in both the commercial and the research system as well as a control “synthetic†wastewater mix using carbon from digested mats. Based on the proposed objectives, we hypothesize that extraction of bioavailable carbon from spent growth mats for treatment of hydroponic wastewater will reduce nitrogen concentrations to levels equivalent to currently utilized technologies. We also hypothesize that bioavailable carbon and time to extract the carbon will vary based on the material type.