Effect of Ozonation on Trihalomethane and Haloacetic Acid Formation and Speciation in a Full-Scale Distribution System

Disinfection by-product (DBP) formation was evaluated before and after ozone implementation at two full-scale drinking water facilities in Las Vegas, NV USA. The two treatment plants used preozonation for primary disinfection followed by direct filtration with subsequent chlorination for secondary disinfection. DBP data was evaluated from the finished water of the two treatment plants along with six locations in the distribution system. Results showed that preozonation reduced the formation of total trihalomethanes (TTHM) by up to 10 μg/L and the sum of five haloacetic acids (HAA5) by up to 5 g/L. These reductions were primarily due to decreases in the di- and trichlorinated DBPs such as chloroform, bromodichloromethane, and trichloroacetic acid. Ozonation appeared to shift the speciation of TTHMs and HAA5 to favor increased formation of the di- and tribrominated species such as bromoform, chlorodibromomethane, and dibromoacteic acid. A bromide mass balance showed that <30% of the raw water bromide was accounted for by the formation of TTHMs (8–21%), HAAs (2–3%) and bromate (5%). Reducing the concentration of THMs and HAAs is often not the primary purpose of ozonation, but it can assist utilities in meeting regulatory requirements during drinking water treatment.     

Mathematical Modeling of Theoretical Cryptosporidium Inactivation in Full-Scale Ozonation Reactors

Conditions for theoretical inactivation of Cryptosporidium by ozone could be achieved at full-scale facilities if their design is appropriate. To perform this task correctly the chemical engineer's approach for process design must be applied. This paper discusses the basic equations the estimation of the disinfection efficiency of different ozone reacting systems. Available kinetic data have been integrated in a global model accounting for the hydrodynamics and mass transfer performances of the ozonation reactor. Thus the proposed method allows one to predict Cryptosporidium inactivation level in a given ozonation system. However, if a specified disinfection goal is to be achieved for Cryptosporidium with the developed model it is also possible to choose and optimize the design of the ozone reactor.     

Finite Element Analysis And T10 Optimization Of Ozone Contactors

A finite element analysis (FEA) computer program was used to model the hydraulic characteristics and to predict the corresponding residence time distribution (RTD) curves for four full-scale ozone contactors with hydraulic capacities ranging from 14.5 to 394 m³/min (5.5 to 150 mgd). On average, model predictions for contactor efficiency (T₁₀/HDT) were within 7.9% of actual test values. The Metropolitan Water District of Southern California (Metropolitan) is using the finite element program as a design tool to optimize the hydraulics of future ozone contactors. For one template model, results from several optimization runs are presented which confirm that T₁₀/HDT increases with increasing depth-to-length (D/L) ratio and which indicate that by adding two features, vanes or wall foils, the T₁₀/HDT is improved from 0.63 to 0.68 or to 0.66, respectively. Results from the template model also indicate that the T₁₀/HDT is unchanged with the addition of a single configuration of comer fillets.     

Application of Ozone in Full-Scale to Reduce Filamentous Bulking Sludge at Öresundsverket WWTP

The return sludge of one of the four treatment lines at Öresundsverket WWTP in Sweden was subjected to ozonation in full-scale to reduce filamentous bulking sludge. The biological nitrogen and phosphorus removal capacity along with effluent parameters were studied throughout the trial. Samples were also taken to track possible changes in microbial population due to ozone. 2.8–5.0 g O₃ kg^?1 treated SS^?1 reduced the DSVI of the ozone-treated line from 170 to 100 mL g^?1 and the reference line remained at 150 mL g^?1. No adverse effect on the biological nitrification- or the phosphorus removal rates could be detected. The microbial population of the two lines did not exhibit any substantial changes which can be correlated to ozone addition.     

Review of Ozone for Water Reuse Applications: Toxicity,Regulations, and Trace Organic Contaminant Oxidation

Increased public awareness, potential human health effects, and demonstrated impacts on aquatic ecosystems have stimulated recent interest in pharmaceuticals, personal care products (PPCPs), and endocrine-disrupting compounds (EDCs) in water and wastewater. Due to the potential public and environmental health implications, some agencies are taking a proactive approach to controlling trace organic contaminant (TOrC) concentrations in water supplies. This review describes some of the research related to the toxicity and estrogenicity of wastewater-derived TOrCs in addition to regulatory guidance from several international agencies. This review also evaluates pilot- and full-scale studies to characterize the efficacy of ozonation for TOrC mitigation in wastewater applications.     

Enhancement of Wastewater Disinfection Efficiency in Full-Scale Ozone Bubble-Diffuser Contactors

Tracer and disinfection tests were performed with the ozone bubble-diffuser contactors at the Belmont and Southport Advanced Wastewater Treatment Plants operated by the City of Indianapolis, Department of Public Works. The objective of the study was to develop a better understanding for the role of hydrodynamics and contactor design on the disinfection efficiency achieved in these contactors. Tracer tests were performed at varying gas and wastewater flow rates. The results indicated that high backmixing occurred within each chamber of the over-under ozone bubble-diffuser contactor trains. The addition of three baffles to one of the contactor trains resulted in a decrease in overall contactor backmixing. Low contactor backmixing was observed at high wastewater flow rates combined with high or medium gas flow rates for both the modified and original trains. Monitoring of effluent fecal coliform concentrations for both the original and modified contactor trains revealed lower average concentrations in the modified train effluent as compared to the original train.     

Efficacy of Ozone to Reduce Chlorinated Disinfection By-Products in Quebec (Canada) Drinking Water Facilities

The impact of ozonation on the reduction of chlorinated disinfection by-products formation was investigated in 15 full-scale and lab-scale drinking water facilities of Québec (Canada). Total trihalomethanes (TTHM) and the sum of six haloacetic acids (HAA6) were measured after chlorination under uniform formation conditions (UFC). Results showed that before ozonation TTHM and HAA6 average concentrations were 89.4 and 45.3 μg/L, respectively. In full-scale ozonation conditions TTHM-UFC and HAA6-UFC reductions averaged respectively 27 and 32%. After lab-scale ozonation at a O₃/C of 1:1, a decrease of only 9% of TTHM was calculated, while for HAA6, reduction was not significantly impacted (30%). For BDOC, average concentrations of 0.13, 0.46, and 0.69 mg C/L were measured before and after and lab-scale ozonation, respectively. Chlorine demand (Cl₂D) and immediate ozone demand (IOD) were found to be the most appropriate indicators to evaluate NOM reactivity after ozonation.     

Dynamic Response of Retrofitted Masonry Walls for Blast Loading

A full-scale blast test was conducted on eight masonry walls reinforced with two and four layers of carbon fibers and two types of polymer matrices. The walls were then subjected to a 0.45-kg pentolite booster suspended from the ceiling of a test structure. The pressure-time history caused by the blast and the resulting displacement response were measured during the test. This paper presents a summary of the test program and the corresponding results from a nonlinear single degree of freedom analysis. The results provide a basis for determining effective means of retrofitting existing masonry walls and designing new structures to withstand blast loads. The paper also outlines a fiber-reinforced polymer retrofit design procedure for walls subjected to blast loading.