Abstract:
Reverse osmosis (RO),is a system that purifies water by removing about 98% of total dissolved
solids, organics and heavy metals. However, it rejects large quantities of water with a raised
content of minerals normally called concentrate (reject water). At present, RO technology has the
actual producing water rate in the RO process as only about 50-75%, so it still faces serious
discharge problem of rejected water (Shahalam, Al-rashidi and Abusam,2010).
The main objective of this project was to design and simulate a recycling system for the reverse
osmosis reject water for Coca-Cola Century Bottling Company-Mbarara branch. The project
encompassed a review of literature about the reject water and recycling systems, characterizing
and quantifying this reject water, design of the recycling system components for reject water,
simulation of the recycling system and finally economic evaluation of the project.
The project was carried out using different engineering principles, methods and equations. The
reject water was characterized using laboratory tests; the quantity was got from primary data as an
average of several months. The system was designed per component where: water pump and
distribution pipes were obtained using Darcy-Welsbach and continuity equation, the storage tank
was sized using the peak discharge of reject water. The caustic soda dosing pump was obtained
using the chemical dosage equation. The simulation was done in Arduino and Proteus. Finally, the
economic evaluation was done using benefit cost ratio analysis and payback period method.
It was found out that the reject water parameters, total dissolved solids (121<500mg/l), electrical
conductivity, turbidity (O.2<10NTU) were within the required national standards of portable water
apart from PH0 which indicated acidity. A PH correction system was put to neutralize the reject
water with caustic soda. The average quantity of reject water discharged per day was 25M3 and
peak discharge as 40M3, so the storage tank had a volume of 40M3. The project was found to be
economically feasible since the benefit cost ratio was 2.58 greater than 1 and payback period of 2 years
The design once implemented, it will correct the PH of reject water to portable water standards
and eliminate the cases of corrosion in pipes and tank: hence very safe for floor cleaning, car
washing and toilet flushing. This will reduce on the mains water demand and costs for the plant.
