Disinfection and Antibiotic Resistance

**Chapter 8**

**Abstract**

Effects of UV-LED

Disinfection

photocatalytic disinfection.

**1. Introduction**

**159**

**Keywords:** UV-LED, disinfection, *E. coli*, water

Irradiation on *E. coli* in Water

*Paul Onkundi Nyangaresi, Baoping Zhang and Liang Shen*

with a potential of replacing the conventional chemical methods, mercury UV lamps and xenon lamps in water disinfection applications. In this chapter, we will first give a general description on the status of *E. coli* disinfection in water by UV-LEDs. Then the main text will concentrate on our experimental studies. We will discuss the effects of single and combined UV-LED irradiation on *E. coli* in water, including the inactivation efficiency, the recover percentage after the UV-LED irradiation, the optimal wavelength for low energy consumption, differences in pulsed and continuous operations of UV-LEDs, effect of UVA-LED followed by UVC-LED irradiation and vice versa, and finally the effect of TiO2-assisted

Ultraviolet light-emitting diode (UV-LED) is a newly emerging UV light source

Millions of people including children die every year from infectious diseases caused by various waterborne pathogens [1]. Among the pathogens, a group of bacteria called *Escherichia coli* (*E. coli*) is one of the known carrier of the diseases such as diarrhea, urinary tract infections, respiratory illness and pneumonia [2]. Since *E. coli* are typically found in the environment, foods and intestines of humans and animals, they have been widely used as fecal indicator bacteria in water quality analysis [3]. Numerous countries and world organizations put a limit count of zero per 100 ml *E. coli* for drinking water. Passing this limit, it is an indication of the presence of faecally related pathogens in water, and hence a potential risk of high level of microbial waterborne disease outbreak [4]. Therefore, different water disinfection methods have been employed using *E. coli* as an inactivation target either in laboratory tests or in water disinfection plants. Among the different methods, the

conventional use of chemicals such as chlorine can lead to introduction of

disinfectant-resistance to bacteria [5], change of water taste and production of odor [6] and harmful disinfection by-products (DBPs) such as trihalomethane (THM) compounds, and haloacetic acids (HAAs) that are carcinogenic, mutagenic and reproductive toxicants [7]. Ozone is reported as an effective alternative disinfectant to chlorine due to its ability of reducing microbiological challenge to downstream disinfection. However, the ozone is also known in forming DBPs, particularly

#### **Chapter 8**
