『Abstract
Two series of laboratory-scale vertical flow systems (flooded
and nonflooded columns) were designed to compare nitrogen removal
performance, nitrous oxide emission, and ammonia volatilization
under different water levels upon treating diluted digested livestock
liquid. In these systems, influent was supplied at three hydraulic
loading rates (HLRs of 1.25, 2.5, and 5 cm day-1) during
stage 1 and the rates doubled during stage 2 when the water levels
of nonflooded columns were elevated from zero to half the height
of the soil column. After hydraulic loading rates doubled, the
average removal rates of total nitrogen in flooded columns varied
from 1.27 to 2.94 g-2 day-1 and those in
nonflooded columns ranged from 1.23 to 3.88 g-2 day-1.
The T-N removal at an HLR of 10 cm day-1 in the nonflooded
column with an elevated water table level had higher efficiency
than that in the flooded column, suggesting T-N removal is enhanced
in the nonflooded column probably due to the improved coupled
nitrification-denitrification process under the elevated water
table level condition. On the other hand, there was a significant
correlation (r2 = 0.532, p＜0.001) between
the N2O flux and redox potential that mainly
corresponded to water levels and HLRs, suggesting anoxic or aerobic
conditions stimulate N2O emission by enhancing
the nitrification (nitrification-denitrification) process. In
contrast, NH3 volatilization had a high flux
in the anaerobic condition mainly because of flooding. Based on
the experimental results, it is hypothesized a nonflooded condition
with higher water table level (Eh range of -160 to +260 mV) would
be suitable to reduce N2O emission and NH3 volatilization peak value by at least half while
maintaining relatively efficient nitrogen removal performance.
Keywords: Ammonia volatilization; Digested livestock liquid; Nitrification-denitrification;
Nitrous oxide emission; Redox; Wastewater treatment』
1 Introduction
2 Materials and methods
2.1 Experimental equipment and materials
2.2 Water sampling and analysis
2.3 Gas sampling and analysis
2.4 Statistical analysis
3 Results and discussion
3.1 Evapotranspiration and Eh
3.2 Nitrogen removal
3.3 N2O emission and NH3
volatilization
4 Conclusions
Acknowledgements
References