Natural organic matter (NOM) is a complex matrix of organic substances present in various aquatic ecosystems through intricate geological, hydrological and biological cycles. Such variability, along with the important increase of its concentration in fresh waters and municipal wastewater effluents, makes the removal of NOM and its constituents from water sources a challenging issue, especially in the treated drinking water supplies. Hence, there is a need to develop robust and highly efficient water treatment processes targeting NOM removal.

Biofiltration is gaining attention in the drinking water treatment industry due to its ability to remove biodegradable organic matter and decrease disinfection by-product production by removing highly reactive Natural Organic Matter (NOM) species. The main removal mechanism of NOM in biofilters is biologically mediated through biodegradation and sorption to biofilms, although physical separation also occurs. When media with adsorption capacity (i.e., Granular Activated Carbon) are used over inert media types (e.g., sand, anthracite), NOM can also be removed through adsorption. GAC also demonstrates more stability under challenging operating conditions (e.g., under cold water temperature) compared to inert media types. Strategies such as preoxidation, pH control, filter media optimization, nutrient enhancement, and backwash optimization are used often to create an engineered environment within the filter media that will promote microbial growth and some studies have demonstrated their effectiveness in improving NOM removal. These parameters should be optimized on a site-specific basis to achieve maximum removal of NOM. In addition to conventional NOM metrics, tools such as photoelectrochemical oxygen demand, fluorescence spectroscopy (e.g., fluorescence excitation emission matrices) and liquid chromatography organic carbon detection (LC-OCD) have shown promise for monitoring the transformation and removal of NOM during biofiltration. Enzyme activity is also gaining attention as indicator for biodegradation and removal of NOM during biofiltration. This chapter provides an overview of biofiltration processes for NOM removal in drinking water treatment, as well as detailed information on types of biofiltration and their role in NOM removal, mechanisms for NOM removal in biofilters, operational aspects for targeting NOM removal, and various metrics for monitoring NOM removal biofilters.

Natural organic matter (NOM) is a complex matrix of organic materials and a key component in aquatic environments. As a result of the interactions between the hydrologic cycle and the biosphere and geosphere, the water sources of drinking water generally contain NOM. The amount, character, and properties of NOM vary considerably according to the origins of the waters and depend on the biogeochemical cycles of their surrounding environments. Also, the interrelation between NOM and climate change has attracted a great deal of attention in recent research. NOM has a significant impact on many aspects of water treatment, including the performance of unit processes, necessity for and application of water treatment chemicals, and the biological stability of the water. As a result, NOM affects potable water quality as a carrier of metals and hydrophobic organic chemicals and by contributing to undesirable color, taste, and odor problems. Moreover, NOM has been found to be the major contributor to disinfection by-product (DBP) formation. Changes in NOM quantity and quality have a significant influence on the selection, design, and operation of water treatment processes. These changes also cause operational difficulties in water utilities. High seasonal variability and the trend toward elevated levels of NOM concentration pose challenges to water treatment facilities in terms of operational optimization and proper process control. To improve and optimize these processes, it is vital to characterize and quantify NOM at various stages during the purification and treatment process. It is also essential to be able to understand and predict the reactivity of NOM or its fractions during different phases of the treatment. Once the composition and quantity of NOM in the water source has been examined, suitable methods for efficient NOM removal can be applied. No single process alone can be used to treat NOM due to its high variability.

Aquatic natural organic matter (NOM) is a heterogeneous mixture of biopolymers and their degradation products that cause harmful by-products during drinking water production. The great variability in NOM composition makes it difficult to remove from drinking water completely by conventional coagulation or by any single technique. This chapter reviews NOM removal by membranes—namely, micro-, ultra-, and nano-filtration, and also reverse osmosis.

Efficient methods for the removal of natural organic matter (NOM) in waters have emerged. Among these are advanced oxidation processes (AOPs). These processes include O3/H2O2, O3/UV, UV/H2O2, TiO2/UV, H2O2/catalyst, Fenton and photo-Fenton processes, and ultrasound. This chapter presents an overview of the recent research studies dealing with AOP methods for the removal of NOM and related compounds from drinking water.

Electrochemical techniques such as electrocoagulation (EC) and electrooxidation (EO) have proved their efficiency in the removal of humic acid (HA), coliform, and algae from surface waters. Many investigations have also been conducted with synthetic wastewaters. EC combined with membrane filtration hybrid systems can increase natural organic matter (NOM) removal rates remarkably. In EO technology, electrolysis efficiency is strongly linked to electrode composition. Efficiency could be increased by changing the reactor design, using commercial electrodes, and exploring the semiconducting properties of oxide mixtures. Electrochemical methods may present an attractive alternative to other NOM removal techniques, such as conventional coagulation and chemical oxidation methods, for natural waters. Surface water treatment with EC can produce high-quality water for either potable or industrial use. This technology appears to remove some toxic pollutants from wastewater and could be used as a pretreatment in combination with some other purification technology. Boron-doped diamond (BDD) anodes have proved effective in HA removal from aqueous solutions and potentially their total mineralization.

Integrating conventional coagulation with novel treatment methods is expected to enhance natural organic matter (NOM) removal in water treatment. The great variability in NOM composition makes it difficult to completely remove from drinking water by any single technique. This chapter discusses NOM removal by integrating coagulation with other treatment processes (ion exchange, oxidation, adsorption, and membrane technology) and hybrid processes combining membrane techniques with other unit processes (coagulation, adsorption, oxidation, and membrane bioreactors).

The presence of natural organic matter (NOM) in drinking water causes difficulties during conventional water treatment processes such as coagulation. Problems also arise when alternative treatment techniques for NOM removal, such as nanofiltration (NF), are applied. The most common problem with NF is membrane fouling. Ion exchange (IE) processes proved to be an efficient NOM removal technology, and are recommended for use at the beginning of the treatment process. This approach not only significantly decreases the concentration of NOM but also prevents the formation of disinfection by-products, such as trihalomethanes. This chapter reviews recent studies conducted on NOM removal from water by IE.

Worldwide reports over the last few decades have shown that the amount of natural organic matter (NOM) in surface water is continuously increasing, which has an adverse effect on drinking water purification. For many practical and hygienic reasons, the presence of NOM in drinking water is undesirable. Various technologies have been proposed for NOM removal with varying degrees of success. The properties and amount of NOM, however, can significantly affect the process efficiency. To improve and optimize these processes, it is essential to characterize and quantify NOM at various points during purification and treatment. It is also important to be able to understand and predict the reactivity of NOM or its fractions at different stages of the process. Methods used in the characterization of NOM include resin adsorption, size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, and fluorescence spectroscopy. The NOM in water has been quantified with parameters including ultraviolet and visible, total organic carbon, and specific UV-absorbance. More comprehensive analytical methods for determining NOM structures have been developed recently: liquid chromatography-mass spectrometry (LC-MS), pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), multidimensional NMR techniques, and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). This chapter focuses on the methods used for the characterization and quantification of NOM in relation to drinking water treatment.

For decades, there have been reported widespread increases in the concentration of natural organic matter (NOM) measured as dissolved organic carbon (DOC) throughout the Northern hemisphere, a phenomenon commonly referred to as brownification. Some of the main drivers of brownification are associated with anthropogenic pressures including the reversal of atmospheric acid (e.g., sulfate) deposition as a result of more stringent air emissions policies, and climate pressures (e.g., increasing frequency, intensity and duration of precipitation events, as well as warming temperature). Many studies have predicted that browning will continue considering climate pressures, even after sulfate deposition returns to background levels. Furthermore, browning of surface waters is expected to have a profound impact on drinking water treatment practices. For example, drinking water providers drawing from browning water supplies can expect to experience increased coagulant demand, reduced filter hydraulic performance and potential for elevated disinfection by-products (DBPs) if NOM removal is unoptimized. Inadequate removal of NOM during treatment may also result in elevated trace metal concentration in the distribution system, which can increase the ability of treated drinking water to transport contaminants such as lead. Drinking water treatment processes should be designed to accommodate for fluctuations in both NOM concentration and quality and a buffer between treated water quality and regulatory limits is critical.