Abstract

Climate change has often caused failure in water treatment operations. In this study, we report a real case study at a major surface water treatment plant in Alabama, USA. Following a severe winter storm, the effluent water turbidity surged to >15.00 Nephelometric Turbidity Units (NTU), far exceeding the 0.30 NTU standard. As a result, the plant operation had to be shut down for three days, causing millions of dollars of losses and affecting tens of thousands of people. Systematic jar tests were carried out with sediment samples from 22 upstream locations. The coagulation and settleability of sediment particles were tested under simulated storm weather conditions, i.e., low temperature (7 °C) and in the presence of various types and concentrations of natural organic matter (NOM) that was extracted from the local sediments. Experimental results proved that elevated NOM (6.14 mg·L−1 as Total Organic Carbon, TOC) in raw water was the root cause for the failure of the plant while the low temperature played a minor but significant role. Pre-oxidation with permanganate and/or elevated coagulant dosage were found effective to remove TOC in raw water and to prevent similar treatment failure. Moreover, we recommend that chemical dosages should be adjusted based on the TOC level in raw water, and a reference dosage of 0.29 kg-NaMnO4/kg-TOC and 19 kg- polyaluminum chloride (PACl) /kg-TOC would be appropriate to cope with future storm water impacts. To facilitate timely adjustment of the chemical dosages, the real time key water quality parameters should be monitored, such as turbidity, TOC, Ultraviolet (UV) absorbance, pH, and color. The findings can guide other treatment operators to deal with shock changes in the raw water quality resulting from severe weather or other operating conditions.

Highlights

  • Over the last several decades, extreme weather events associated with climate change have been gaining a surging momentum in frequency, latitude and impact [1,2,3]

  • Experimental results indicated that polyaluminum chloride (PACl) was an effective coagulant to remove the turbidity produced by these sediment samples under normal conditions

  • The results indicate that raw water Total Organic Carbon (TOC) level is a key factor in turbidity removal, and a very practical and effective measure to cope with the sudden rise of influent TOC is to increase the coagulant dosage

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Summary

Introduction

Over the last several decades, extreme weather events associated with climate change have been gaining a surging momentum in frequency, latitude and impact [1,2,3]. Impacts of climate change on water treatment facilities have elicited growing attention [4]. Safe drinking water supply has been frequently challenged by extreme weather events such as storms and abrupt temperature fluctuation, which often cause sharp variation in raw water quality such as elevated. Res. Public Health 2019, 16, 2808; doi:10.3390/ijerph16152808 www.mdpi.com/journal/ijerph

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