Date of Award


Degree Type


Degree Name

Master of Science in Agricultural and Biological Engineering


Agricultural and Biological Engineering

First Advisor

Jiqin Ni

Committee Chair

Jiqin Ni

Committee Member 1

Chi-hua Huang

Committee Member 2

Sara K. McMillan


There has been an increasing number of anaerobic digesters on livestock farms in the United States during the past two decades. Anaerobic digestion of manure allows production of renewable energy and generation of stabilized and nutrient-rich digestate that can be used as organic fertilizer. However, the majority of the existed studies using liquid digestate as fertilizer only focused on the effectiveness for crop yield, nutrient content and microorganism in soil. There is insufficient understanding in the environmental impact of digestate land-application. This laboratory study used six treatments including four different liquid digestate treatments, a chemical fertilizer treatment, and an unfertilized treatment with four replicates each. It was designed to investigate whether, when compared with chemical fertilizer, liquid digestate could reduce the volume, sediment, and nutrient (nitrate, ammonium, total Kjehldahl nitrogen, dissolved reactive phosphorus, and total phosphorus) losses from runoff and leachate after the first rainfall simulation (rainfall occurred within 24 hours after the treatments were made), and also the cumulative nutrient losses after nine rainfall simulations. The results showed that compared with chemical fertilizer, liquid digestate treatments did not cause higher losses of volume and sediment for both runoff and leachate. After the first rainfall simulation, except that the treatment with liquid digestate from digester 3 (D3) had higher ammonium and total Kjehldahl nitrogen losses than chemical fertilizer from runoff, application of other liquid digestate treatments did not cause more nutrient losses than chemical fertilizer from both runoff and leachate. And liquid digestate treatments even reduced the losses of phosphorus species from runoff (p ≤ 0.02). After nine rainfall simulations, except for the reduction of total Kjehldahl nitrogen, application of liquid digestate did not ameliorate the nutrient losses from leachate and even caused more losses for nitrate. None of the liquid digestate treatments caused higher losses of nitrogen species from runoff (apart from D3 for ammonium loss) compared with chemical fertilizer treatment. Application of liquid digestate significantly reduced the phosphorus losses for runoff (p ≤ 0.02) and this could better prevent eutrophication for watershed around farmland.