Abstract
[Author declined to make full text available]Cheese making and vegetable processing are global food production industries generating immense wastewater volumes with elevated nitrogen (N) that must be managed. Many facilities utilise nature-based, low-cost land application systems that match loading rates with the soil microbial community capacity to denitrify wastewater while remaining protective of local water resources. This research used the state of Wisconsin (USA) as a case study to assess the fate and impact of food industry land applied wastewater nitrogen discharges to inform facility management and regulation.
Wisconsin is the United States’ largest producer of cheese and second for processed vegetables. Wisconsin wastewater land application statute allows N discharges equal to system cover crop uptake (readily measured) and “demonstrable” denitrification (to-date not directly quantified). This research endeavored to develop complete nitrogen budgets for vegetable processing spray field and cheese making ridge and furrow wastewater land disposal systems. Field studies utilised an automated four-chamber array with integrated photoacoustic infrared analyzer to measure denitrification via the acetylene inhibition technique. Laboratory incubation studies were used to estimate field denitrification measurement underestimation. Study results indicate that, broadly, the systems which received 113-1,744 kg N ha-1 a-1 and were managed to keep groundwater nitrate-N concentrations below 10 mg L-1 are operating as designed with plant uptake at 76-256 kg N ha-1 a-1 and estimated denitrification at 99-1,111 kg N ha-1 a-1.
Calculations show that on average 4.6% of spray field and 1.6% of ridge and furrow N remains unaccounted but with wide individual system variation. The utilization of 15N in-situ denitrification measurement methods, a more comprehensive analysis of cheese making systems in winter, and deeper vadose zone measurements in future studies would allow further N budget refinement. A first ever soil microbial population analysis of these systems indicated that future combined stable isotope and microbial studies could elucidate denitrification pathways active at different times thereby allowing for system management changes to optimize nitrogen wastewater removal.
| Date of Award | 18 Jul 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Fay Couceiro (Supervisor) & John Williams (Supervisor) |