Forecasting saltwater intrusion volume and sulfate content in a wastewater collection system. Case study: Barreiro/Moita WWTP, Portugal

A Figueiredo,L Amaral,J Pacheco

doi:10.2166/wcc.2021.375

Abstract

Abstract The presence of salt water from the Tagus Estuary has been identified in the influent at Barreiro/Moita Wastewater Treatment Plant (WWTP), Portugal. The intrusion occurs throughout damaged sections and direct vectors in the wastewater collection system, during high tide levels, changing the wastewater characteristics and impacting the WWTP process. This study designed models to quantify this problem, enabling more effective countermeasures within the right timing. The proposed models estimate the average volume of salt water and sulfate () load for each high tide period. The laboratory results show strong correlations between the influent electrical conductivity (EC) and percentage of salt water in WWTP inflow (0.9909), and between EC and concentration in WWTP influent (0.9797). The forecast models also show good correlation between the high tide levels with volume of salt water (0.9145) and load (0.9162) entering the system. Considering the total monthly inflow, the highest percentage of salt water registered in WWTP inflow was 3.6%. During high tide periods, critical situations have been assessed with up to 53.9% of salt water in the WWTP inflow, increasing energy consumption and costs in pumping stations.

Highlights

Around the globe most communities are located in coastal areas making their main wastewater treatment collection systems and treatment plants to preferably be located at the lowest areas, taking advantage of the gravity flow
The aim of this study is to develop a forecasting model based on high tide values, to provide measurable quantification of saltwater intrusion’s volume and SO24À load, to help Wastewater Treatment Plant (WWTP) management teams to apply better countermeasures within the right timing
Correlation between electrical conductivity (EC) and percentage of salt water in WWTP inflow The relationship determined in the laboratory tests between EC and the percentage of salt water in the WWTP inflow (%) is shown in Figure 8

Summary

Introduction

Around the globe most communities are located in coastal areas making their main wastewater treatment collection systems and treatment plants to preferably be located at the lowest areas, taking advantage of the gravity flow. At the Barreiro/Moita Wastewater Treatment Plant (WWTP), located in Portugal, the presence of salt water from the nearby Tagus Estuary has been identified in the wastewater inflow. Similar issues have been identified in other wastewater collection systems and WWTPs (Serrano 2014; Phillips et al 2015). This problem may occur throughout old and/or damaged sections, joints, manholes, emergency overflow weirs’ discharge sites from separated and/or combined wastewater and stormwater collection systems, and pumping stations’ emergency overflow weirs. Due to the unexpected and unwanted presence in the wastewater flow of saltwater volume, the saltwater intrusion in these wastewater collection systems is considered an undue inflow

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