Swimming pools are traditionally disinfected with a residual disinfectant such as sodium hypochlorite. Nowadays, swimming water without a residual disinfectant is increasingly popular, as can be seen by the growing number of (natural) swimming ponds (Weilandt 2015), but health risks for bathers do raise concerns for these type of pools, so some form of disinfection is needed (Giampaoli et al. 2014). The combination of ultra-filtration and UV-disinfection for pool water treatment, without a residual disinfectant might be an interesting alternative. The Dutch Innovative Pool project (DIPool) was initiated to explore this new treatment concept, to study its applicability for swimming pools and to verify first system design specifications. The goals of this study were to compare the microbial water quality during treatment without disinfection, treatment with ultra-filtration, treatment with UV-disinfection, treatment with chlorination, and the influence of single treatment steps. Methods All treatment concepts were studied in a pilot plant equipped with a pool basin and simulated bathing load, containing only chemical components. Adenosine triphosphate (ATP) and intact cell count measurements were used to monitor the microbial water quality before and after each treatment step at regular intervals in several experiments during 23 days of operation. High pollutant/nutrient conditions without recirculation were used to study the effect of single treatment steps, and recirculation conditions were used to study the effect of accumulation of pollutants/nutrients. A chlorinated pilot plant was used as reference for the alternative disinfection. The influence of a biological activated carbon filtration during chlorinated conditions was also investigated. Both pilot plants were operated at 1 m3/h, with a turnover time of 30 minutes during the recirculation conditions. Results The results showed that the microbial quality of pool water with UV-disinfection was similar to that of chlorinated pool water, while pool water treatment without disinfection resulted in a higher microbial number. After 23 days, most of the results during chlorination and UV-disinfection experiments with recirculation were within 103-105 intact cells/mL and 0.2-13 ng intracellular ATP /L which is similar to both bottled and tap water. Treatment steps with the highest reduction in microbial quality were ultrafiltration (UF) in the treatment setup with UV-disinfection and chlorination in the treatment setup with chlorination. The largest increase in microbial quality was observed during residence in the pool basin, which was obvious, and during biological activated carbon filtration. Most important conclusions were that i) the microbial water quality of pool water with a UV-based treatment can be similar to that of pool water with chlorination ii) UF plays an important role in maintaining a low number of micro-organisms during UV-based treatment and iii) P-limitation is an additional method to limit microbial growth in swimming pool water. @en

In the context of the present work it is hypothesized that the condition of a PVC push-fit joint can be obtained from the analysis of the joint's gap width. A perfectly jointed and aligned pipe, for example, should have a constant gap for the complete pipe diameter while a bent joint should show variations of the gap width with the diameter. Therefore, laboratory tests were performed to test the applicability of ultrasound in the assessment of PVC push-fit joints which are ubiquitously used in the Netherlands. In those tests the potential of ultrasound to detect changes in geometrical alignment of PVC pipes was evaluated using a specially built metallic loading frame. This frame supported two 2-meters ø315 mm PVC pipes connected with a push-fit joint. This pipe could be kept in horizontal position or be bent up to an angle ofca. 5 degrees in 11 uniform steps. Results show that when two pipes have a perfect alignment (zero degrees angle between the pipes) the tested ultrasound tool describes quite adequately the real situation and gives good information about the joint's real condition. However, when an angle is imposed on a PVC joint the ultrasound results are not consistent with reality. This discrepancy is probably due to both longitudinal and shear ultrasound waves echoing back to the transducer from the PVC wall. The creation of both longitudinal and shear waves occurs when an angle between the ultrasound transducer and the object being studied exists. This factor is known to complicate the resulting ultrasound scans and the interpretation of the results. In conclusion, for this application ultrasound inspection is vulnerable to changes in geometrical alignment of assessed pipes. Even being unanimously considered as a potential technique for the inspection of polymeric pipes, ultrasound tool is not capable of giving results that permit accurate detection of all known failure mechanism of joints.

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