Coliforms, water disinfection

The EPA Surface Water Treatment Ruse (SWTR) requires public water supplies, under the direct influence of surface water, to be disinfected. Some disinfectants produce chemical by-products SWTR requires that their concentration remain within the MCL. Currently, one such by-product is trihalomethanes. Water disinfection is effective when combined with conventional treatment, such as coagulation, flocculation, sedimentation, and filtration. The latter is accomplished by sand or diatomaceous earth. The effectiveness of disinfection is evaluated by determining total coliform bacteria which are not pathogenic, but their presence suggests that certain pathogens may have survived. The various chemicals commonly used as disinfectants are presented below and some of their advantages and disadvantages are listed. 

Virus removal and inactivation have been reviewed by several authors [23, 25-27]. It is generally accepted that conventional water treatment practices can reduce viral levels by a factor of 10 to 10 in the finished water. Disinfection, mostly in the form of chlorination, has been the main method of virus inactivation in drinking water. Viruses seem to be considerably more resistant than coliforms, thus requiring higher doses and longer contact times (for ref. see [16]). 

For the past 50 years the determination of the sanitary quality of water has been based on the enumeration of indicator micro-organisms (e.g. coliform bacteria). The adequacy of coliform enumeration methods for this purpose has been questioned [21]. The current trend of year-round disinfection of waste water effluents and the increasing discharge of both toxic substances and heat from industrial outfalls cast further doubt on the accuracy of biological indicator systems [22]. 

Babineau D, Payment P, Chartray D, La-PORTE A, Fournier-Martin a (1999) Ultraviolet Disinfection of Municipal Waste-water Treatment Effluents Pilot Studies with a Low-Pressure System Using Ther-motolerant Coliforms and Clostridium per-fringens as Indicators, Vecteur Environ. 32, No. 6 34-43. 

Disinfection of municipal water contaminated with coliforms and fecal streptococci was the subject of a study by Patermarkis and Fountoukidis [31]. Disinfection was achieved using titanium electrodes and direct current. The polarity was alternated every minute to eliminate titanium oxide buildup. No additives or supporting electrolytes were used in this room-temperatures process. At a current density of 2.5 mA/cm and an applied voltage of 45 V, no microbial activity was detected after 30 min of operation. Noncontaminated, electrochemically treated water possessed a residual disinfection capacitiy addition of treated water to a contaminated sample destroyed the microbial life in the sample. 

At the well field adjacent to Terrieu Creek in southern France, a large proportion of fecal coliform bacteria was associated with suspended sediment, at times up to 90%. Bacterial concentrations associated with sediment in surface water and in the subsurface were very similar, indicating a close connection between the two. The association of bacteria with sediment has important implications for public health. The bacteria may be protected from predation, may be able to use the substrate as a food source, and are less susceptible to standard methods of disinfection. 

On June 29, 1989, the Surface Water Treatment Rules (SWTR) and the Coliform Rule were promulgated. According to the SWTR, all public water systems using surface water or groundwater under direct influence of surface water, must disinfect and may be required to filter if certain source water quality requirements and site-specific conditions are not met. The Maximum Contaminant Level Goals (MCLGs) established in the rule are ... 

Care should be taken to choose cleaning methods appropriate to the characteristics of the herbal materials being processed. Washing dried herbal materials with water is generally inappropriate. When it is necessary to clean them, an air duster or air shower should be employed. In cases when immersion of herbal materials in water or other appropriate agents (such as disinfectants) for cleaning is unavoidable (e.g. to eliminate suspected coliform bacteria), it should be kept to a minimum. 

Patel et al (1994) employed a combined process of coagulation and MF to avoid a disinfection posttreatment. The coagulation step was used to eliminate phosphorus, arsenic, and viruses, to avoid fouling, decrease particle accumulation on the membrane surface, and improve backflush characteristics. MF pilot plant studies in constant permeate flux mode showed that turbidity, particles, and faecal coliforms could be removed, but TOC removal was unreliable. Crossflow MF showed no difference to dead-end filtration, and both methods were similar to or better than sand filtration. Results with coagulation and MF improved phosphorous and turbidity removal, but the process was not optimised. The treatment lead to a reduction of chlorine demand in the product water. 

Implementation of the 1986 Amendments to SDWA led to the development of a number of important rules, including the Total Coliform Rule, the Surface Water Treatment Rule, the Lead and Copper Rule, and regulations for a large number of chemicals of public health concern. All public water systems using surface water sources were required to disinfect and provide specific levels of treatment for microbial pathogens most systems were required to filter their water. In addition, the best available technology was specified for the treatment of contaminants for which an MCL was established. 

The primary use of anhydrous ammonia (ammonia gas) in water treatment is to combine with chlorine to form chloramines. Chloramines are used both as primary and secondary disinfectants. Use as a secondary disinfectant (residual in the distribution system) is more common. A typical treatment strategy is to use free chlorine to satisfy the USE PA regulatory CT requirements as a primary disinfectant. Ammonia is then added to combine with the free chlorine residual to form chloramines for use as the secondary distribution system disinfectant. The ammonia added is carefully controlled to ensure that all the free chlorine is combined and little free ammonia remains. This control is necessary because the presence of free chlorine can form regulated by-products. Free ammonia can increase the growth of nitrifying bacteria, thus causing residual demand that could lead to conditions that could violate the Total Coliform Rule. 

In this work, u-Pd/u-WOs was synthesized and was applied as a photocatalytic agent for the disinfection of water from coliforms by using 355-nm pulsed UV laser radiations, generated from the third harmonic of an Nd YAG laser. The killing effect of w-Pd/w-WOs on coliform bacteria was characterized by means of selective culture media. 

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