Waste water disinfection systems utilizing ultraviolet (sometimes hereinafter "UV") treatment of waste water, such as industrial and municipal waste water, rely on complex systems presenting a wide variety of problems and challenges. The problems associated with such complex systems are enhanced in view of the wide span of engineering and scientific disciplines encountered, such as civil engineering, electrical engineering, computer hardware and software design, biology, chemistry and the like, in the design and construction of effective treatment systems. A representative example of some of the difficulties that have arisen in designing and constructing ultraviolet disinfection systems include a number of the items set forth below.
Radiation from ultraviolet light producing lamps utilized in UV disinfection systems decreases with time. There is typically a rapid drop in radiation during the first one hundred hours of operation. Following this initial period the decline in efficiency continues but at a much slower rate. After approximately 8800 hours of "on" service, or about one year of continuous operation, lamp efficiency drops to about 65% of its efficiency after the first 100 hours and typically no longer provides sufficient intensity to achieve the desired degree of disinfection. At this point to maintain operating efficiency of the system lamps are usually replaced.
Most UV installations replace lamps yearly to insure adequate waste water disinfection. Some lamps are replaced before they have been in "on" service a full year because not all lamp banks are in service during low flow periods. This typical mode of lamp replacement insures adequate disinfection but wastes the useful life of the lamps. This is an expensive and inefficient process in view of the many extra lamps purchased, the labor needed to monitor and change extra lamps and interrupted waste water treatment.
It is also known to employ relatively sophisticated control schemes to minimize electrical power consumption. In general, these schemes turn banks of lamps on and off in response to changes in waste water flow, which is constantly monitored. Using this mode of operation conserves both power and lamp life but, it introduces the additional factor of reduced filament life for the lamps because of the many "on-off" cycles. This is particularly true of plants fed by cycling pumps. A standard lamp has a filament life of 2000 to 3000 on-off cycles--after which time the lamp must be replaced.
The need to frequently replace lamps is further compounded by the problem that the lamps are submerged in a moving body of water, typically an open channel, which should remain continuously operational to maximize efficiency. Removing lamps or banks of lamps from the waste water flow can lead to significant efficiency losses due to water treatment stoppage, added personnel costs and the like.
It is also critical that the status of the UV lamps be continuously monitored to ensure that a proper dosage of ultraviolet radiation is produced for the waste water treatment process. Failure to maintain a proper dose of ultraviolet radiation can result in incomplete treatment, thereby permitting bacteria and other living organisms to escape in a live and active condition in the treated effluent. Of course, this is highly undesirable. It is therefore important that as much attention as possible be accorded to all ultraviolet radiation producing lamps to ensure proper dosage, while maintaining an efficient, low cost system.
Another aspect of maintaining proper ultraviolet radiation dosages relates to protective Jackets that typically surround the ultraviolet lamps. These protective jackets become covered with particulate matter over the course of time, which reduces the UV radiation dosage to the waste water. A number of methods of cleaning these protective Jackets are known. However, determining the frequency of the need for such cleaning and the efficiency of such cleaning is an important task that contributes to the total operating efficiency of the disinfection system.
Coordination of monitoring of the cleaning function with other operational functions such as waste water flow rate, waste water characteristics, ultraviolet radiation dosage, lamp life, lamp cycle life, electrical power requirements, personnel needs and the like, has proven to be a difficult task heretofore not completely mastered.
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