Dynamics of Nitrogen Transformation and Removal in a Pilot High Rate Pond

Abstract

The transformation and removal of nitrogen was studied in a pilot high rate pond with a surface area of 10.2 m 2 and water depth of 60 cm. The pilot unit received wastewater from an existing field scale primary facultative pond at the University of Dar es Salaam. Wastewater samples were collected from the influent and effluent of high rate pond and were analyzed for physical-chemical parameters in the laboratory and in situ. An appropriate model complexity was selected, from which a conceptual model was then developed to model various processes in the system using STELLA 6.0.1 software. The study demonstrated that dominant nitrogen transformation processes in HRP were nitrification and denitrification, which transformed 0.95 and 0.87 gN/m 2 •d, respectively. These were followed by mineralization (0.37 gN/m 2 •d), ammonia uptake by microorganisms (0.34 gN/m 2 •d), volatilization (0.30 gN/m 2 •d), sedimentation (0.24 gN/m 2 •d), and regeneration (0.15 gN/m 2 •d). Uptake of nitrate was not observed because of microorganisms preference for ammonia, which was abundant in the pond. The major nitrogen transformation mechanisms in high rate pond were denitrification, net sedimentation and volatilization, which accounted for 69.1%, 7.1% and 23.8% of the total permanent removal mechanisms of nitrogen in High Rate Pond.

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

“…The accuracy of predicted organic nitrogen concentration in effluent was improved by increasing the calibrated value of the sedimentation constant (Rs) to 0.050, instead of using the value reported in literature (0.015) [ 47 ]. K 1 , K 2 , and K 3 represent the Nitrosomonas half-saturation constant, ammonium half-saturation constant, and nitrate half-saturation constant, respectively [ 21 ]. K1 was increased from 0.15 to 1.26 to improve the simulation of ammonia and nitrate.…”

“…It was assumed that the study WSP is completely mixed and acts as a single continuous stirred tank reactor [ 46 ]. Mass balanced equations for organic nitrogen (ON-N), ammonia nitrogen (NH 3 -N), and nitrate nitrogen (NO 3 -N) concentrations are as follows [ 21 , 46 ]: where Q i and Q e are influent and effluent flow rate (m 3 /d), respectively; V is volume of the pond (m 3 ); r n is nitrification rate (mg/L.d); r d is denitrification rate (mg/L.d); r m is mineralization rate (mg/L.d), r s is net loss of Org-N (mg/L.d); r v is volatilization rate (mg/L.d); r 1 is uptake rate of NH 3 -N by microorganisms (mg/L.d); and r 2 is uptake rate of NO 3 -N by microorganisms (mg/L.d).…”

“…These include simulations of the rate of oxygen absorption incorporating interfacial oxygen by using a lumped parameter model [ 4 ], and mass balance equations using system dynamic modeling [ 11 , 19 ]. Recently, various types of models, such as mathematical, deterministic, stochastic, empirical, and dynamic models, have been developed to simulate the process of nitrogen removal and parameter calibration in waste stabilization and high rate algal ponds [ 13 , 16 , 17 , 20 , 21 , 22 ]. Process-based models have been widely used to examine the dynamics of nitrogen and represent the physical–chemical systems in WSP systems, which usually consist of major parameters that must be calibrated to account for environmental heterogeneity and variations [ 23 , 24 ].…”

Spatial variation of nutrients and primary productivity in the Rufiji Delta mangroves, Tanzania

“…Change in the pool size with time is governed by differential equations that are numerically integrated. The mass balance proposed by Mayo and Hanai (2014) was applied using Eqn 2 in the calculation. Thus:…”

“…However, it was assumed that nitrate would be consumed if all the NH 3 -N was depleted in the system. Eqn 11 was used to model the uptake of nitrate by microorganisms (mcruṕ), following Mayo and Hanai (2014):…”