Water mixing in rectangular storage tanks: small-scale versus field tests

ABSTRACT

Mixing and renewal processes are crucial for maintaining adequate drinking water quality in storage tanks. This paper studies the influence of baffle structures and of fill-and-draw cycles on water mixing and renewal in rectangular cross-section tanks through laboratory tracer tests carried out in two small-scale tanks (with and without baffles) and compares with results from a full-scale test. This study shows that the use of baffles inhibits water mixing and keeps older water pockets in small recirculation zones, though baffles allow faster water renewal than in open tanks for lower flow rates. High water volume variation in fill-and-draw cycles (between 50% to 80%) promotes water renewal, independently of the tank configuration (i.e. cross-section and the existence of baffles). Despite the existing baffle structure in the full-scale rectangular tank with 20% water volume variation, the high flow rates allowed a rapid renewal of the stored water.

Keywords:

• Mixing
• renewal
• residence time distribution
• turnover
• water storage tank

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Three configurations were analysed in circular storage tanks (Pinheiro et al., 2021), with Configuration A being similar to the one used in the rectangular tank, Configuration B with inlet and outlet pipes located in the same side of the tank wall and Configuration C corresponding to a tank with a baffle with a length of 75% of tank diameter.

Additional information

Funding

The authors would like to thank the Fundação para a Ciência e a Tecnologia (FCT) for funding the H2DOC doctoral programme for the PhD [grant PD/BD/135214/2017].