Although many aspects of the design and construction of aquatic facilities are governed by regulation other aspects are based on custom and practice based on many years of experience.
In order to address this situation in the USA the CDC (Centre for disease control) implemented the Model Aquatic Health Code (MAHC). The MAHC Code, through a Steering committee and a number of technical committees, has brought together a large group of experienced industry professionals in many diverse technologies. Wherever possible the language in the MAHC code has been based on peer reviewed science, data, and as a last resort custom and practice. The MAHC has been in development since 2005 and finally many of the various modules are available for public review.
Although a standard developed for use in the USA the collation and use of the latest science is expected to create a document that many aquatic facility regulators around the world will utilise as a reference for their own local regulations. One of the areas of the MAHC code is the application of UV disinfection, particularly for the control of cryptosporidium.
Ultraviolet Disinfection treatment
Ultraviolet disinfection is now an established method of water treatment for municipal pools, and has become the preferred treatment choice for a number leading international leisure brands and new-build or renovated swimming pools.
UV systems have a dual function in aquatic facilities. Firstly they are able to destroy chloramines. Chloramines are formed when free chlorine reacts with organics such as sweat, body fats and urea, brought into the pool environment by bathers. Trichloramines in particular are powerful irritants which are responsible for ‘burning red eyes’, itchy skin, respiratory complaints and the often over powering chlorine smell associated with indoor pools. Additionally chloramines are also the cause of corrosive condensation, which leads to the damage of pool buildings and structures such as ventilation ducts.
Secondly they are able to provide disinfection of chlorine resistant micro-organisms such as Cryptosporidium and Giardia, which have a thick outer membrane making them highly resistant to traditional Chlorine disinfection. It is this second benefit that is most significantly addressed in the MAHC. A number of Cryptosporidium outbreaks in aquatic facilities in the USA, from New York to Utah, has created considerable interest in the best practice method to apply this technology.
Type of Facility
As aquatic facilities with high bather loads of younger children are both more likely to result in outbreaks and to have occupants more susceptible to cryptosporidium the MAHC code requires that certain facilities meeting this criteria must include a method to kill or remove cryptosporidium quickly from the water. UV disinfection is one of the techniques that is accepted as having the required level of science to prove its performance. The MAHC code considered many aspects of UV disinfection and focused on the following key performance areas for application to swimming pools.
As any UV disinfection system is a physical not a chemical process, the performance depends on ensuring that all the water in the pool passes through the system in a reasonable amount of time. The MAHC technical committee utilised exponential decay models and additional CFD (computational fluid
dynamics) models to determine the turnover rate and also the disinfectionrate required to achieve a less than 1/100ml concentration of cryptosporidium within a few hours.
The simplest method to achieve this is to ensure that the filtration flow passes through the UV without any form of bypass or slip stream. Due to the requirement to add disinfection techniques to a wide range of indoor and outdoor aquatic facilities a mathematical equation is referenced in the code and the flow-rate
through the systems must be equal to or exceed this value.
Computational Fluid Dynamic models can theoretically track a Cryptosporidium outbreak, it’s spread, and subsequent control by a UV Disinfection system designed in accordance with the MAHC code.
The turnover rate needs to be combined with a disinfection rate in order to ensure speedy removal. The MAHC code requires a 3-log reduction of Cryptosporidium in EACH pass through the treatment system. A 3-log reduction is a 99.9% removal. This value is selected as the best compromise between treatment level and benefit.
Higher reductions than 3-log provided only marginal benefits in speed of reduction from any outbreak in the facility.
Validation of performance
Under the MAHC code it is notacceptable to utilise manufacturers claims as to performance. This is essential due to the difficulty for regulators to verify these claims, and the exagerations that have plagued this market in the past. In order to be accepted as having a ‘proven’ cryptosporidium performance any system must have undergone third party validation to an approved international UV performance standard. In the case of the MAHC code these are the USEPA, the DVGW (German) and the Onorm (Austrian).
Standard of the equipment
As expected, the MAHC code also addresses certain basic construction and manufacturing quality issues. As many of the states in the USA require the application of the NSF-50 standard, with its specific performance requirements and regular third party quality audits the MAHC code incorporates the NSF-50 standard into the code language.
The MAHC code and its UV specification provides an excellent scientifically based standard to provide the best method of control in swimming pools for chemically resistant pathogens. It is not possible to immediately remove such pathogens but the MAHC code provides a scientifically based risk management approach with appropriate quality controls and transparency for manufacturers. As such this can represent a best practice risk management tool for any aquatic facility managers.
With the Model Aquatic Health Code offering increased value for swimming pool operators in the form of guaranteed performance and reliability, a number of manufacturers such as atg UV Technology in the UK, and ETS in the USA are now standardising their swimming pool UV systems to be fully compliant with the MAHC regulation alongside offering pre-selected options tailored to the specific requirements of swimming pool operators.
Typical swimming pool UV units should include; 316L stainless steel chambers, UV monitoring, automatic wiper systems, strainer baskets and the option for half to full power for energy savings during periods of no/low use.
There are typically two types of UV systems available; traditional axial UV systems with inlets and outlets at either end of the chamber that offer swimming pool operators increased flexibility for retrofits or replacement of existing UV systems. For new modern facilities or where restricted plant room space is an issue, ultra efficient in-line UV systems are favoured. In-line UV systems can be installed directly into the pipe work and offer a much smaller foot printand increased efficiency and performance.