Modeling Nitrogen Dynamics in a Waste Stabilization Pond System Using Flexible Modeling Environment with MCMC

Superposition effect of floating and fixed beds in series for enhancing nitrogen and phosphorus removal in a multistage pond system

In order to improve the efficiency of nitrogen and phosphorus removal in a multistage pond system which receives polluted natural inflow and outflows to a landscape lake, ecological floating beds (EFBs) were installed along the flow-path of each pond and fixed beds (FBs) were embedded in between each pair of ponds. Such a simple modification of the MPS effectively enhanced the total nitrogen (TN) removal rate from 59.2% to 71.4% and the total phosphorus (TP) removal rate from 37.1% to 51.0%. It was identified that the EFBs mainly contributed to enhanced TN removal by the biomass growth in the stereo-elastic packing and attachment on the surface of ceramsite particles packed in the floating mat, while the FB filled with zeolites contributed to both TP adsorption and biological TN removal to certain extent, as indicated by the denitrification rate and adsorption function experimentally obtained for each part of the bed settings. The superposition effect of the installation of EFBs and FBs was estimated using a tank-in-series model. With a Nash-Sutcliffe efficiency higher than 0.75, calculation results of the model well fitted field measurements and showed that the EFBs (including plant uptake) contributed to the increase of TN and TP removal by 23.3% and 8.12%, respectively, and that contributed by FBs were 19.6% and 10.7%, respectively.

Assessing thermodynamic parameter sensitivity for simulating temperature responses of soil nitrification

Soil nitrification responses to temperature have major implications for the global nitrogen cycle. Temperature sensitivity of soil nitrification has been modeled using several mathematical models, yet the extent to which model-generated thermodynamic parameters are accurate and sensitive in describing temperature sensitivity is unclear. In this study, we performed global sensitivity analysis to identify the key thermodynamic parameters that are most influential when simulating the temperature response of the soil nitrification potential (NP) across two different temperature gradients (4-40 °C and 20-45 °C) which are imposed upon sixteen different soils with square root growth (SQRT) and macromolecular rate theory (MMRT) models. We found that two thermodynamic parameters stand out as moderately to highly sensitive, and are uniquely identifiable in each model, regardless of the temperature range. The minimum and maximum measured temperatures seem to have no impact on the list of sensitive parameters but do influence the parameter ranges, especially for the SQRT model. However, parameters that control the minimum temperature and curvature of the NP response curve (Tmin and ΔC‡P) were found to have little to no sensitivity to SQRT and MMRT model outputs, respectively. We show that the parameter sensitivity and range of measured temperatures influence the complementary model's ability to describe the temperature sensitivity of soil nitrification. Our proposed framework enhances the accurate interpretation of existing thermodynamic parameters that explain the temperature sensitivity of soil biochemical processes, and provides methodological recommendations for future temperature sensitivity studies.