# Innovative Approaches for Minimizing Disinfection
## 4 DBP Minimization Approaches
### Alternative to Chlorine Disinfectants
#### 4.7.2 Ozonation  
Ozone water disinfection was initially introduced in France in 1886. Ozone is a highly versatile and efficient disinfectant due to its potent oxidative characteristics and ability to be utilized at different stages within the treatment process [23]. Ozone selectively and rapidly reacts with electron-rich compounds such as activated aromatic compounds, olefins, neutral amines, and reduced sulfur species. In natural waters and wastewater effluents, DOM typically acts as the primary consumer of ozone. During ozonation, hydroxyl radicals (\(\bullet\)OH) are generated in situ as secondary oxidants through ozone decomposition processes. These hydroxyl radicals exhibit less selectivity than ozone, with second-order rate constants generally ranging from 10\({}^{9}\) to 10\({}^{10}\) M\({}^{-1}\) s\({}^{-1}\), primarily through OH-addition or H-abstraction reactions. In environmental applications, the concentration of \(\bullet\)OH, either in steady-state or transient form, is controlled by its main scavengers, such as DOM, carbonate (CO\({}_{3}\)\({}^{-}\)), and bicarbonate (HCOO\({}_{3}\)\({}^{-}\)) [38]. Both ozone and sodium hypochlorite are powerful oxidizing agents that play vital roles in pre-oxidation and post-disinfection processes. These agents can degrade toxic organic compounds, algae, and microorganisms, thereby improving the treatment efficiency of WWTPs and DWTPs. However, their interactions with NOM and halogen anions, commonly found in natural waters, ultimately form oxidation/disinfection byproducts [39]. Ozone can chemically react with different substances in natural water through direct transformation. Another chemical process after ozonation is the indirect reaction of free radicals produced due to the breakdown of ozone molecules in water. The initial ozonation process can increase the average size of colloidal particles, converting dissolved organic matter into colloidal particles and improving the removal of organic matter or turbidity in sedimentation and filtration processes. Furthermore, the initial ozonation can modify the structure of organic compounds in the water, convert dissolved organic matter into colloidal particles, and enhance turbidity removal during sedimentation [24]. The dosage of ozone used in drinking water treatment can vary depending on the type of water, typically ranging from 2 to 5 mg L\({}^{-1}\). Due to its rapid decomposition under standard drinking water treatment conditions, ozone primarily acts as a primary disinfectant. Subsequently, following ozonation, chlorination or chloramination is commonly utilized as a secondary disinfection step. When ozone doses are at 1 or 2 mg L\({}^{-1}\), there is an observed increase in the formation of THMs, dihaloacetic acids, and trihaloacetic acids during subsequent chlorination, while higher ozone doses result in reduced formation. Additionally, chloral hydrate and trichlorontromethane formation potentials rise with higher ozone doses, ranging from 1 to 6 mg L\({}^{-1}\). In the case of subsequent chloramination, the concentrations of dihaloacetic acids, THMs, and HANs exhibit varying trends, with some DBPs decreasing and others increasing after ozonation. Moreover, in the presence of bromide in raw water, ozonation has been observed to modify the speciation of DBPs such as THMs, HAAs, and dihaloacetonitrile during subsequent chlor(am)ination, favoring the formation of more brominated compounds over chlorinated products [3]. Limited studies have been conducted to identify, quantify, and evaluate the toxicity of ozone DBPs (ODBPs) compared to those formed by chlorination. ODBPs are generally categorized into two main groups: (1) inorganic ODBPs, which primarily form based on the bromide levels in the raw water, and (2) organic ODBPs, which mainly form based on the characteristics of NOM, ozone dosage, and contact time. Various types of organic ODBPs have been recognized, including aldehydes, ketones, carboxylic acids (CA), hydroxy acids, alcohols, esters, ketoaldehydes, aldoacids, ketoads, and alkanes, [15; 27].