How Can We Make Pump and Treat Systems More Energetically Sustainable?

Rajandrea Sethi,Carlo Bianco,Arianna Bucci,Alessandro Casasso,Tiziana Tosco

doi:10.3390/w12010067

Abstract

Pump and treat (P&T) systems are still widely employed for the hydraulic containment of contaminated groundwater despite the fact that their usage is decreasing due to their high operational costs. A way to partially mitigate such costs, both in monetary and environmental terms, is to perform heat exchange (directly or with a heat pump) on the groundwater extracted by these systems, thus providing low-carbon and low-cost heating and/or cooling to buildings or industrial processes. This opportunity should be carefully evaluated in view of preserving (or even improving) the removal efficiency of the remediation process. Therefore, the heat exchange should be placed upstream or downstream of all treatments, or in an intermediate position, depending on the effect of water temperature change on the removal efficiency of each treatment step. This article provides an overview of such effects and is meant to serve as a starting reference for a case-by-case evaluation. Finally, the potentiality of geothermal use of P&T systems is assessed in the Italian contaminated Sites of National Interest (SIN), i.e., the 41 priority contaminated sites in Italy. At least 29 of these sites use pumping wells as hydraulic barriers or P&T systems. The total discharge rate treated by these plants exceeds 7000 m3/h and can potentially provide about 33 MW of heating and/or cooling power.

Highlights

The economic and environmental sustainability of subsurface remediation has largely become an acknowledged issue as most widely applied techniques, despite their efficacy, are far from being optimized in terms of energy demand and/or use of “green” chemicals [1]
We provide a preliminary evaluation of the potential of Pump and treat (P&T) systems for thermal exploitation, discussing the possible interactions with the most commonly adopted water treatment processes
We propose an overview of the 41 major contaminated sites in Italy, identifying active and foreseen P&T systems to assess their potential for renewable heat

Summary

Introduction

The economic and environmental sustainability of subsurface remediation has largely become an acknowledged issue as most widely applied techniques, despite their efficacy, are far from being optimized in terms of energy demand and/or use of “green” chemicals [1]. A direct heat exchange (Figure 1A) is possible only for cooling, and only with a hydraulic loop operating at a temperature sufficiently higher than the groundwater. Examples of these cases are radiant panels for building cooling (which generally operate at a minimum temperature of about 15–20 ◦ C to avoid the condensation of air moisture at typical indoor setpoints, i.e., 24–26 ◦ C) and industrial cooling processes (e.g., condensation of turbines). It is advised to use (Figure 1C) is recommended to preserve the heat pump and to ease maintenance operations (scaling such an intermediate heat exchange because of the variable quality of abstracted groundwater, and removal, cleaning, and replacement).

Possible

Expected Impacts on Water Treatment Processes

Conclusions

30 WG 090