Secondary Disinfection Research Articles

New disinfection method in RO seawater desalination systems

In general, in chlorine disinfection systems for RO seawater desalination a small amount of trihalomethane (THM) is formed in the seawater and then included in the RO permeate water [1–31]. The authors studied a new disinfection method where there is no formation of THM and where the chloramine is synthesized in seawater and is used effectively as a biocidal agent. At the seawater intake, ammonium chloride is injected and then sodium hypochlorite solution is added at optimal dosing conditions so that monochloramine, which is the best disinfectant among several chloramines can be produced at the rate of more than 90 %. From the seawater desalination test results, it was confirmed that there are no THMs in chloramine disinfected seawater and also in RO permeate water after secondary chlorine disinfection. This new chloramine disinfection method is worthy of note as it will be most useful in the strict quality control of drinking water.

Comparing Chlorination and Chloramination for Controlling Bacterial Regrowth

The Greater Vancouver (B.C.) Water District compared chlorine and chloramine as secondary disinfectants and their effects on bacterial regrowth in a distribution system supplied with disinfected, unfiltered surface water. The selected section of the distribution system was divided into three areas: a control area that received no secondary disinfectant, an area that received free chlorine as the secondary disinfectant, and an area that received chloramine. Water samples were analyzed for chlorine residual, coliform bacteria, heterotrophic plate count (HPC) bacteria, and turbidity. Although both chlorine and chloramine were effective in reducing bacterial growth in the distribution system, chloraminated water had a lower HPC, less taste and odor, fewer positive coliforms, and a more stable residual.

Secondary Disinfection of Service Reservoirs

ABSTRACTIn order to comply with the European Community Directive on the quality of water intended for human consumption', which was embodied in the 1989 Water Act, a number of problems need to be addressed. One such problem is to identify a reliable method of secondary disinfection for service reservoirs which have a history of bacteriological failures.This paper considers the advantages and disadvantages of ultraviolet (UV) and chemical disinfection techniques (both hypochlorite dosing and on‐site generation of chlorine), together with the basic design features, and presents a case study examining capital and revenue costs. The collated information suggests that UV disinfection is a cost‐effective secondary‐disinfection technique. This suggestion is supported not only by the cost benefits but also by the ease of operation, improved monitoring and control, and elimination of water quality problems associated with chemical techniques.

Comparing PEROXONE and Ozone for Controlling Taste and Odor Compounds, Disinfection By‐products, and Microorganisms

The Metropolitan Water District of Southern California is evaluating the hydrogen peroxide‐ozone (PEROXONE) advanced oxidation process (followed by secondary disinfection with chloramines) for removal of taste and odor compounds, control of disinfection byproducts (DBPs), and inactivation of microorganisms. This article reports the results of pilot‐scale testing designed to optimize the H2O2:O3 ratio and to compare ozone and PEROXONE at different contact times. The tests described represent one phase of a five‐phase PEROXONE pilot‐scale study for treating water from the California State Water Project and from the Colorado River. Results to date indicate that the PEROXONE process requires a significantly lower applied ozone dosage to oxidize 2‐methylisobomeol and geosmin as compared with ozone alone. The levels of DBPs formed when ozone or PEROXONE is used (followed by chloramines) are low, and PEROXONE (at H2O2:O3 ratios of ≤0.3) is comparable with ozone for the inactivation of microorganisms.

—Review Paper—Current State-Of-The-Art Measurements Of Ozone In The Gas Phase And In Solution

Abstract This paper is a critical review and summary of the analytical procedures currently used by operating water utilities to control ozone treatment processes, considering disinfection as well as the many oxidative applications of ozone in water treatment applications. The role of common interferences in the various methods is described. In operating U S., Canadian, European, and Japanese water treatment plants currently employing ozone as a primary disinfectant, ozone nearly always is followed by the addition of small quantities of chlorine, chlorine dioxide, or chloramine to provide the residual in the distribution system and to act as a secondary disinfectant. Clearly, the analytical procedures used must distinguish between the various species. This review critically presents these various factors and their implication with respect to “true values” of ozone determined under widely varying conditions.

Kinetics and products of the Reactions of Ozone with Various forms of Chlorine and Bromine in Water

Abstract Ozone reacts with various halogen compounds (chlorine, chloramines , bromine , and bromide) which may be present in water. Chlorine produces Cl− and ClO− 3; chloramines produce NO− 3 and Cl−. Bromide produces bromine , which acts as a secondary disinfectant, but can generate haloforms and interfere in O3 determinations. Brominepartly regenerates Br causing a catalytic destruction of O3. The kinetics of these reactions are described and interpreted with respect to their importance in water treatment.

Use of chlorine dioxide, chloramines, and short‐term free chlorination as alternative disinfectants

To limit the formation of trihalomethanes and to attain adequate disinfection in the distribution system, the Louisville Water Company investigated several disinfection processes using chlorine dioxide, chlorine dioxide and chloramines, and free chlorination–chloramination. From its study the utility concluded that the most effective process incorporates the use of a powerful disinfectant for the primary disinfection step, followed by a persistent secondary disinfectant that is carried into the distribution system.

The Photochemical Treatment of Wastewater by Ultraviolet Irradiation of Semiconductors

Abstract The primary photoefficiency of ten semiconductors to produce reactive oxidising species under ultraviolet (UV) illumination has been evaluated. TiO2 in the anatase phase was shown to be at least an order of magnitude more efficient than the other semiconductors so was chosen for further experimentation. While the anatase-UV treatment was shown not to be feasible for secondary effluent disinfection, the process did lead to substantial reduction in the toxicity to algae of PCB containing wastewater. Also, the process reduced the total organic chlorine content of a pulp and paper plant's chlorinated bleach-plant effluent and left lignin model compounds more amenable to biological degradation. In addition, the process destroyed cyanide in synthetic solutions and in gold and base metal mine effluents. Based on studies of model compounds, the reaction mechanisms for the process are discussed. Also, recommendations are made as to future research requirements for optimization of the process and for study of its economic viability.

Artificial Recharge of Treated Waste Waters and Rainfall Runoff into Deep Saline Aquifers of Peninsula of Florida: ABSTRACT

Fast-growing population centers of the state of Florida, mainly in coastal beaches, have imposed large demands on the sources of fresh water. They also threaten to deteriorate the esthetic and recreational value of the area with their waste waters. The largest of these population centers is on the southeastern end of the peninsula of Florida, commonly referred to as the Miami area. The second largest is on the central west coast of the peninsula in the Tampa-St. Petersburg area. The Florida peninsula is underlain by several thousand feet of carbonate rock, with only minor amounts of clastic sediments. Cavernous limestone and dolomite aquifers at relatively shallow depths constitute the principal source of fresh water in the area. Deeper cavernous zones, separated from the freshwater zones by practically impermeable limestone and dolomite, are uniquely suited to receiving injected fluids. Deep-well disposal of waste waters into deep saline aquifers, after secondary biologic treatment and disinfection, is feasible if (1) an aquifer exists that can accept treated waste waters without significant changes in its hydraulic and structural characteristics, and (2) if use of the water in that aquifer, adjacent ones, or from surficial sources is not impaired. Two large disposal wells have been constructed for a private utility in the Miami area of southeast Florida. They are approximately 3,000 ft in depth and recharge an artesian aquifer having chloride concentrations near that of seawater (19,000 mg/l). The receiving aquifer is overlain by a thick aquiclude, by another aquifer (saline but of lower chloride concentration), and then by a thick, impervious section separating the highly mineralized waters from the shallow and fresh groundwater. Three concentric steel casings, cemented at the proper depths, permit injection into the deeper aquifer with protection of the upper strata. Monitoring of the upper saline water-bearing stratum, where any possible leak from the deeper aquifer would normally be first detected, is performed through the annulus between the 2 inner well casings. An integrated water-quality aquisition system continuously monitors the injected waste and provides an alarm and pump shut down if established limitations are exceeded. Operation of the first well for over a year has proved fully reliable, and economically advantageous. Eight similar disposal wells are being considered in the area. On the basis of this experience, a new research program is being implemented to inject, store, and recover when needed, rainfall runoff into the deep saline aquifers of southern Florida. A test-prototype well is presently being constructed within the city of St. Petersburg to determine (1) the characteristics of the deep underground formations; (2) the quality of the deep groundwaters; (3) the injection rate capacity and associated increase in pressure; (4) the ratio of the amount of fresh water that could be subsequently recovered to that injected; and (5) the quality of the recovered water. End_of_Article - Last_Page 1595------------