Abstract
A considerable amount of ablution greywater (AGW) is being produced at mosques for cleaning certain parts of the body before performing prayers. In this study, alum coagulation followed by batch and continuous AC adsorption tests was conducted to examine the removal efficiency of turbidity, COD, and BOD to evaluate the recycling potential of AGW. In coagulation experiments, optimal overall removals of turbidity (95.8%), COD (31.6%) and BOD (50.0%) were achieved at 20 mg/L of alum dose. Further, the overall removal efficiencies were enhanced by AC adsorption for COD up to 70.8% and BOD up to 57.2% at 20 min adsorption equilibrium time with 0.2 g/L of optimal AC dose. The adsorption data was well fitted to the pseudo-second-order kinetics model. Both the Langmuir and Freundlich isotherm models were found suitable to characterize the adsorption of COD and BOD on AC. Maximum adsorption capacities were calculated 175 mg/g for COD and 88 mg/g for BOD. Continuous experiments of the AGW treatment process resulted in residual turbidity less than 1 NTU and both the COD and BOD values less than 10 mg/L. Treated AGW was found suitable for unrestricted irrigation, toilet flushing, and firefighting. The estimated cost for a full-scale treatment process (1.02 US$/
m
3
)
came out to be less than the existing cost of water production (1.09 US$/
m
3
)
in Saudi Arabia. The study revealed that the combination of alum coagulation and AC adsorption is a sustainable treatment option for recycling of AGW in arid and semiarid regions.