Managing Municipal Wastewater Treatment to Control Nitrous Oxide Emissions from Tidal Rivers

Chandra Sekhar Akella,S. Murty Bhallamudi

doi:10.3390/w11061255

Abstract

Waste load allocation management models were developed for controlling nitrous oxide emissions from a tidal river. The decision variables were treatment levels at wastewater discharging stations and the rate of upstream water release. The simulation model for N2O emissions from the river was embedded in the optimization model and the problem was solved using the simulated annealing technique. In two of the models, the total cost was minimized, while in the third model, emissions from the river were minimized for a specified constraint on the available money. Proof-of-concept studies, with hypothetical scenarios for contaminant loading but realistic flow conditions corresponding to the Tyne River, UK, were carried out. It was found that the treatment cost could be reduced by 36% by treating wastewater discharges in the upper reaches more during the high tide as compared to during low tide. For the same level of N2O emissions, approximately 16.7% lesser costs could be achieved by not only treating the wastewater but also inducing dilution by releasing more water from the upstream side. It was also found that beyond a limit, N2O emissions cannot be reduced significantly by spending more money on treatment and water release.

Highlights

Nitrous oxide is one of the most significant greenhouse gases (GHG), with a 10% share of total net anthropogenic radiative forcing with a Global Warming Potential (GWP) ~300 [1]
The present study aims at developing management models to control N2O emissions in a tidal river by determining optimal levels of wastewater treatment at different sewage treatment plant (STP) discharging treated wastewater into the river, and optimal releases from an upstream environmental reservoir for specified channel characteristics and tidal variation at the downstream end (Figure 3)
This model suggests the extent of treatment for NH4 + in various STPs located along the banks of the river and discharging treated domestic wastewater into the river

Summary

Introduction

Nitrous oxide is one of the most significant greenhouse gases (GHG), with a 10% share of total net anthropogenic radiative forcing with a Global Warming Potential (GWP) ~300 [1]. With a sizable fraction of domestic wastewater, is known to contain significant amounts of dissolved organic and inorganic nitrogen and discharge of such wastewater into rivers without treatment may result in significant N2 O emission [7]. Vertical velocity variations and DO (dissolved oxygen) consumption by various sources may induce different oxygenated conditions in rivers and estuaries. These conditions favour ammonium oxidation (aerobic) and reduction of nitrate, NO3 − (anoxic), which result in N2 O emission. Many past studies have shown rivers and estuaries to be major GHG sources [10,11,12,13,14,15]. Nitrous oxide from estuaries and rivers are predicted to increase by a factor of 3 and 4 respectively by 2050, with rivers becoming the principal contributor

Methods

Results

Conclusion