Point of Entry/ Use Treatment for Delivery of Potable Water, Cooperative Research Centre for Water Quality and Treatment, 2007

Why do we have to have a centralized water treatment system or a point of entry system? Why can’t we take the best of both and combine them and reduce our infrastructure costs estimated in 2012 to be $13,813 per Canadian household? Click here or on the pdf file to read the full report or an excerpt below.

 

12 CONCLUSION AND RECOMMENDATIONS

The project investigated the possibility of providing safe drinking water with point of entry and point of use devices to small, remote communities. As part of the project, three POE MWTP were developed and tested on four different raw water sources throughout Victoria. In addition, two ultrafiltration units were trialled at two more locations. The trials showed that the POE units were able to reduce turbidity to values less than 1 NTU, which made the water suitable for UV disinfection and produced good quality safe drinking water. The sand filter operated reliably for at least four months. The UF units produced high quality water for turbidity, with treated water turbidity of less than 0.5 NTU. The trials showed, however, that the water entering the UF unit should have values less than 1 NTU in order to prevent rapid fouling. The water must, therefore, be prefiltered by sand filtration, a cartridge filter or sedimentation tank. The units are then able to produce high quality water for a very long period of time. Only the prefilter had to be replaced during the trials at Dadswells Bridge.

The colour reduction by the POE units was not very good in general with an average reduction of 50% at Timberline Road and Rupanyup and hardly any reduction at Avoca or Lexton. Recent developments in nanofiltration membranes has the potential to remove more than 90% of colour and dissolved organic carbon (DOC), however these units were not evaluated during this project. NF membrane performance should be evaluated for POE applications.

The MWTP also performed very well in removing disease-causing microorganisms. No E. coli or total coliform bacteria were found in treated water at any of the trials. The UV disinfection unit also removed HPC bacteria to very low values. Bacterial regrowth of HPC bacteria was, however, found inside the clear water tank at Avoca and Timberline Road. It is therefore recommended to disinfect the clear water tank once a month by adding a chlorine tablet. No regrowth of E. coli or total coliform bacteria was found. The UF unit at Dadswells Bridge completely removed even high concentrations of total coliform bacteria.

The POE treatment train at Lexton performed well in reducing electrical conductivity during the three months of testing. The average EC reduction by the Merlin RO unit at Avoca was 78% at the start and after the unit was replaced, producing treated water EC of less than 450 μS/cm. The Merlin RO did foul during the trials and if using one of these units for EC removal, it should be cleaned regularly. A six monthly cleaning frequency seemed suitable for the Avoca water which had EC levels of 3,000 μS/cm.

The trials at Rupanyup determined that activated carbon in the POE unit was able to remove THMs from the water. The activated carbon did not have to be replaced during the life of the trials (2 months). Where water is centrally disinfected, using activated carbon adsorption is sufficient to deliver better quality water to customers.

Water recovery for both the MWTP and the UF units was very satisfactory, except for the overall recovery when RO units were used. The overall water recoveries varied between 70% at Timberline Road and Dadswells Bridge to 97% at Rupanyup and could be increased by longer intervals between the backwash cycles.

The trials showed that the MWTP units produced potable quality drinking water over the life of the trials. The ultrafiltration units also produced high quality drinking water with very low turbidity.

When choosing to use POE treatment units to deliver potable water to a remote property, it is advised to use all the treatment units that were included in the MWTP unit and to ensure that the flow rate through the unit does not exceed the design flowrate of the disinfection unit to deliver microbiologically safe drinking water at all times. It may be possible to build in a fail safe system so that no water is processed when the UV lamp is not working. This could be achieved by detecting when there is no current flow in the UV lamp and then either activating a solenoid valve to prevent flow or deactivating the feed pump.

When using an ultrafiltration unit to produce high quality drinking water, it is recommended to prefilter the water with a sand filter, a cartridge filter or a sedimentation tank to reduce turbidity, thus preventing the unit from rapid fouling.

Consideration was also given to when it might be more cost effective to provide drinking water with POE/POU technologies to small, remote communities rather than provide potable water from a CTP. The calculations suggest that POE may be cheaper than building centralised treatment plants with widespread distribution systems for towns with less than 150 households. However, use of POE devices in a centralised mode (eg. manifolding of homespring units) may provide economic advantages when there are three or more households. Use of POE devices in this mode would also overcome issues associated with management of many individual units.

Five different models to manage onsite water treatment systems were introduced together with a case study. However, additional discussion is required to consider when specific models are appropriate to implement.

Performance monitoring and maintenance/replacement schedules are considered essential to ensure the production of safe drinking water is consistently and reliably delivered. Decentralised water production changes the performance monitoring paradigm and water regulators and proponents of this technology need to develop testing and monitoring schedules that have the capacity to ensure public health and safety. In conjunction with performance monitoring, hardware maintenance and replacement needs to be driven by the performance of the weakest element, not the average. So certification of operating life and replacement may be necessary. The water industry and consumers need to fully evaluate the merits of POE/POU in these terms as well as the financial imperatives.

Further work is required to:

1. develop management guidelines for POE/POU,

2. develop testing regime to protect public health and assist with developing costs for these systems,

3. develop maintenance schedules, and

4. integrate capital and management cost to develop lifecycle costs for direct comparison with other alternatives.

 

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