Pesticide Removal by Combined Ozonation and Granular Activated Carbon Filtration

Ervin Orlandini

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9789054104148
• eBook ISBN: 9781351425292
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

This research aimed to identify and understand mechanisms thar underlie the beneficial effect of ozonation on removal of pesticides and other micropollutants by Granular Activated Carbon (GAC) filtration. This allows optimization of the combination of these two processes, termed Biological Activated Carbon filtration. The study concluded that ozonation significantly improves removal of atrazine by GAC filtration not only due to the wellknown effect of oxidation of atrazine, but also due to the effect of partical oxidation of Background Organic Matter (BOM) present in water. Ozone-induced oxidation of BOM was found to improve adsorption of atrazine in GAC filters. Biodegradation of atrazine in these filters wasnot demonstrated. Higher GAC's adsorption capacity for atrazine and faster atrazine's mass transfer in filters with ozonated rather than non-ozonated influent were explained as due to ozonated BOM. Both can be attributed to enhanced biodegradability and reduced adsorbsbility of partially ozidated BOM compounds, resulting in their increased biodegradation and decreased adsorption in GAC filters.

Chapter 1

General Introduction

ABSTRACT—Disinfection and removal of organic micropollutants are the two aspects of the production of drinking water from surface water that are currently of particular importance. They are important issues because conventional water treatment processes are not always able to cope with them. This was first realized when chlorine, a commonly used disinfectant, was found to result in the formation of trihalomethanes, and when various micropollutants were detected in drinking water at concentrations far exceeding acceptable levels. Thus, new, advanced water treatment processes are needed.

Amsterdam Water Supply (AWS) introduced two new integral concepts for the treatment of surface water. They include conventional pretreatment of Rhine River water by coagulation, sedimentation and rapid sand filtration, followed either by slow sand filtration and reverse osmosis or by ozonation, Granular Activated Carbon (GAC) filtration, slow sand filtration and reverse osmosis. The performances of these two concepts were tested and evaluated by AWS. The mechanisms playing a role were studied in the context of the research project conducted jointly by IHE, NORIT NV, Kiwa NV and AWS. In particular, attention was paid to the following aspects: removal of pesticides, metabolites and other organic micropollutants by combined ozonation and GAC filtration, and by reverse osmosis; disinfection by ozonation and by reverse osmosis; and control of the fouling and scaling of reverse osmosis membranes. The research presented in this thesis was conducted within the framework of this project. Its focus is on the removal of pesticides by Biological Activated Carbon filtration, which is a combination of ozonation and GAC filtration.

1.1 TREATMENT OF SURFACE WATER

1.1.1 History

The earliest recorded knowledge of water treatment can be found in Sus’ruta Samhita, a collection of Sanskrit medical lore thought to date from 2000 B.C. It declares that impure water should be purified by boiling, or by exposing to sunlight, or by filtering through sand and coarse gravel and allowing to cool. Other ancient civilizations also left behind some evidence of their water treatment practices. Egyptians siphoning off water (or wine!) clarified by sedimentation were pictured on the wall of a tomb built at Thebes in 1450 B.C. A somewhat less sophisticated method was the drinking cup devised by the Spartan ruler Lycurgus (ninth century B.C.), which hid badly colored water from the sight of the drinker and allowed mud to stick to its side. Cyrus the Great, King of Persia in the sixth century B.C., was known to take boiled water in silver flagons along with him when going to war. In this way, water sterilized by boiling was kept sterile through the germicidal action of silver. The simile in Plato’s Symposium (fourth century B.C.) suggests that Greeks commonly used wick siphons to clarify water. In this simile, Socrates says that it would be a good thing if wisdom could flow from a person full of it to a person less wise, just as water flows through a thread of wool from a fuller to an emptier vessel (Baker, 1949).

The first reference to public water supply was made by the Roman engineer Sextus Julius Frontinus, who in 97 A.D. became water commissioner of Rome. One year after his appointment as water commissioner, he wrote the first known detailed description of water works systems: De Aquis Urbis Romae Libri II. Among others things, these two books describe the piscanae or pebble catchers built into most aqueducts to serve the double purpose of storing and of clarifying the water (Baker, 1949).

Thus, throughout history, the greatest concern regarding the use of surface water as a source of drinking water was to ensure its clarity and microbiological integrity. Water was clarified by sedimentation and/or filtration, neither of which was quite satisfactory. While easy to operate, settling basins result in an effluent of rather low clarity. Better clarity of water is obtained by filtering it over a coarse material like gravel; however, over time, clogging occurs and filters need to be cleaned. Until one and a half centuries ago, cleaning of the filter was laborious and time-consuming: filter material had to be taken out from the filter, washed, and then put back into the filter. A new way of ensuring the clarity of surface water, superior to either sedimentation or filtration, came into use in England in the first decade of the 19^th century. The new process, termed “slow sand filtration”, combined the use of fine filtering material and low filtration rates. The fine material limited clogging to the initial few centimeters of the filter bed, which can be easily scraped away, while the low filtration rates extended the interval between two scrapings to a few months. In 1829, James Simpson built the first slow sand filters used for a public water supply, the Chelsea Water Company in London.

The biological/physical process of slow sand filtration improves not only the clarity but also the microbiological quality of water. This was first indicated in 1849, when much higher incidences of cholera were noted in the districts of London where water was clarified by sedimentation than in the districts where slow sand filtration was used. The final and clear evidence was provided in 1892, when Hamburg experienced a massive outbreak of cholera, while there were only a few cholera cases in the neighboring city of Altona. Both cities used the Elbe River water as a source of drinking water. In Hamburg, however, it was treated by sedimentation, while in Altona it was treated by slow sand filtration (Huisman, 1990).

Due to the simplicity of its design and operation, and the quality of the water produced, slow sand filtration is still used in both industrialized and developing countries. Over time, it has been extended by coagulation, sedimentation and rapid sand filtration as a pretreatment for the removal of suspended matter and algae, and with post-chlorination for additional disinfection.

After World War II, many water supply companies set up a purely physicochemical system for the treatment of surface water. The new concept required less space than the one based on slow sand filtration, and consisted of pre-chlorination, coagulation, sedimentation, rapid sand filtration and post-chlorination. These basic concepts are frequently extended with the storage of raw water in reservoirs or in the underground. This is done to improve the quality of water by self-purification and equalization, and to allow no intake when the quality or the quantity of raw water is exceptionally low. The abstraction of bank filtered water, and the addition of powdered activated carbon to remove taste and odor, are also frequently applied.

By the end of the sixties, these conventional water treatment processes¹ seemed to suffice for the treatment of surface water. Opinion changed drastically with the finding that chlorine reacts with humic substances present in surface water to form trihalomethanes (Rook, 1974). In addition, at around the same time, there was growing awareness that many surface waters were polluted with potentially hazardous organic chemicals of industrial origin that could not be effectively removed. This started the ongoing discussion about the ability of water treatment processes to provide adequate disinfection of surface water, and a sufficient barrier against organic micropollutants present in this water (Sontheimer, 1979; Kruithof et al., 1991; Schippers, 1993; Degrémont, 1994a-c; Schippers and Kruithof, 1997).

This discussion, especially the part on pesticide removal, is currently most intense in the countries of the European Union (EU). This is not because of exceptionally poor quality of the raw water in these countries, but rather because their standards are more stringent than those promulgated by the World Health Organization (WHO), or those applied in other developed countries such as the USA and Japan. Based on the principle that pesticides must not be present in drinking water, the EU set the standard for any pesticide at 0.1 μg/l and the standard for the sum of all pesticides at 0.5 μg/l (ECC, 1980). In contrast, the WHO and the United States Environmental Protection Agency (USEPA) apply standards based on the acceptance of a certain health risk and, usually, allow much higher pesticide concentrations. For instance, they allow 2 μg/l and 3 μg/l of atrazine, respectively (WHO, 1993; Pontius, 1995).

1.1.2 Disinfection

The findings of Rook in 1974 initiated wide-scale research on chlorination by-products formation and control (Kruithof, 1986). The list of compounds eventually identified was long and frightening: besides trihalomethanes there was a whole host of other compounds including haloaceticacids, haloacetonitrils, halogenated ketones, chloropicrin, chloralhydrat, chlorophenols and MX (Kruithof et al, 1991). Furthermore, the alternatives for chlorine, chlorine-dioxide and chlo...

Table of contents

• Cover Page
• Half Title
• Title Page
• Copyright Page
• Contents
• Acknowledgments
• Abstract
• 1. General introduction
• 2. Ozonation and atrazine removal by GAC filtration: process analysis and research scope
• 3. Ozonation vs. disinfection and formation of biodegradable organic matter and bromate
• 4. Biodegradation and atrazine removal by GAC filtration
• 5. Ozonation and competitive adsorption of background organic matter
• 6. Ozonation and preloading of background organic matter
• 7. Predicting atrazine removal by ozone-induced biological activated carbon filtration
• 8. Summary
• Samenvatting (abstract in Dutch)
• Curriculum vitae