Chapter 7 - NOM removal by biofiltration

Abstract

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.