Water mixing in reservoir and water age in the distribution network modelling

Abstract

The main role of reservoirs is to store the water for periods when consumption is higher then water production, thus increasing the reliability of system. However, the water storage can also lead to water aging, and its quality reduction. Preservation of water quality at the reservoir is a prerequisite for the preservation of water quality in the distribution network. Poor mixing in reservoirs can create pockets of older water that could have negative aesthetic and public health impacts. Time achieved by fully mixing in the tank during the charging cycle and the relationship between daily water turnover and the total volume of the reservoir are the most important factors that influence the water quality change in reservoirs, and consequently in the distribution network. Shortening the time required for complete mixing during the charging cycle and the change of relation between the daily water turnover and the total volume of the reservoir can be achieved by changing the level of shut on and shut off for pumps, changing the algorithm work of variable speed pumps, or by changing the mixing conditions in the reservoir. The overview of modelling methods for water mixing in reservoirs of different type, and water aging in distribution network, built in EPANet software is presented in this paper. The impact of changes in the model of mixing in the reservoir will be presented at the case study of gravitational water supply system in the town of Petrovac na Mlavi.

Rezervoari čiste vode u vodovodnom sistemu povećavaju sigurnost snabdevanja potrošača, ali mogu značajno da degradiraju kvalitet vode. Očuvanje kvaliteta vode po rezervoarskim prostorima je preduslov za očuvanje kvaliteta vode u distribucionoj mreži. Slabo mešanje po rezervoarima može dovesti do formiranja džepova sa vodom povećane starosti i negativnih posledica po zdravlje, kao i ukus i miris isporučene vode. Vreme za koje se postiže potpuno mešanje vode u rezervoaru tokom ciklusa njegovog punjenja i odnos dnevno promenjene i ukupne zapremine rezervoara su važni činioci koji utiču na promenu kvaliteta vode po rezervoarima, a samim tim i u distributivnoj mreži. Skraćivanje vremena potrebnog za potpuno mešanje tokom ciklusa punjenja i promena odnosa dnevno promenjene i ukupne zapremine rezervoara se može postići promenom nivoa uključivanja i isključivanja pumpi, promenom algoritma rada za pumpe sa promenljivim brojem obrtaja ili promenom uslova mešanja u samom rezervoaru. U ovom radu se daje pregled metoda za modeliranje mešanja vode u različitim rezervoarima i starosti vode u vodovodnoj mreži, koje su ugrađene u EPANet program. Kao primer, u radu je prikazan uticaj promene modela mešanja u rezervoarskom prostoru u gravitacionom vodovodu grada Petrovac na Mlavi.