Can a Wastewater Treatment Plant Power Itself? Results from a Novel Biokinetic-Thermodynamic Analysis

Mustafa Erguvan,David W Macphee

doi:10.3390/j4040045

Mustafa Erguvan, David W Macphee

Open Access

https://doi.org/10.3390/j4040045

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Abstract

The water–energy nexus (WEN) has become increasingly important due to differences in supply and demand of both commodities. At the center of the WEN is wastewater treatment plants (WWTP), which can consume a significant portion of total electricity usage in many developed countries. In this study, a novel multigeneration energy system has been developed to provide an energetically self-sufficient WWTP. This system consists of four major subsystems: an activated sludge process, an anerobic digester, a gas power (Brayton) cycle, and a steam power (Rankine) cycle. Furthermore, a novel secondary compressor has been attached to the Brayton cycle to power aeration in the activated sludge system in order to increase the efficiency of the overall system. The energy and exergy efficiencies have been investigated by varying several parameters in both WWTP and power cycles. The effect of these parameters (biological oxygen demand, dissolved oxygen level, turbine inlet temperature, compression ratio and preheater temperature) on the self-efficiency has also been investigated. It was found here that up to 109% of the wastewater treatment energy demand can be produced using the proposed system. The turbine inlet temperature of the Brayton cycle has the largest effect on self-sufficiency of the system. Energy and exergy efficiencies of the overall system varied from 35.7% to 46.0% and from 30.6% to 33.55%, respectively.

Highlights

Wastewater treatment has been important for humanity since the Bronze age (CA 3200–1100 BC) advanced technologies started in the early 1900s [1,2]
A base and a parametric study have been performed varying a significant number of variables in order to investigate the performance of the wastewater treatment plant, and combined gas-vapor cycle from the point of view of first and second law efficiencies
Whereas energy efficiency of the cogeneration system increased from 14% to 27%, it increased from 36% to 45% for the overall system when Turbine Inlet Temperature (TIT) varied from 700 to 1200 ◦ C

Summary

Introduction

The United Nations Educational, Scientific and Cultural Organization published a detailed report in 2020 to illustrate how climate change will affect water scarcity in the coming decades. More than 40% of mankind will suffer from water scarcity by 2050 due to climate change and a high increase in population [3]. The priority in wastewater treatment plants (WWTP) has historically been concerned with meeting certain effluent water standards with little concern for energy consumption [4]. Energy efficiency of WWTPs has been an important subject because of their high energy consumption. According to the US Environmental Protection Agency, 3–4% of total electricity use in the US is consumed by drinking water and wastewater systems [5,6]

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