Greywater treatment and recycling for toilet flushing: comparison of low and high tech treatment approaches

Abstract

Greywater (GW) from the showers of a sport club was treated following two approaches: adapted low-cost and advanced technologies. The low-cost unit consisted of a gravel-horizontal-flow constructed wetland planted with Phragmites followed by a vertical-flow-multilayer sand filter. For the comparison, two high-tech units were also used: a membrane bioreactor (MBR) with a net capacity of 550 L/d and a sequencing batch reactor (SBR) with a net capacity of 600 L/d and a built-in UV lamp. Performances of the low cost unit were satisfactory: turbidity was reduced from 28 to 2 NTU while removal efficiencies for COD and BOD5 were 75 and 80% respectively. Also, 50% of nitrogen was nitrified and 50% of phosphorus was removed. Anionic surfactants removal efficiency reached 90 %. On the contrary, FC removal did not exceed 1 Log Unit out of an initial concentration of 1.3 105 FC/100 mL. UV disinfection was necessary to bring the counts to 10 units/100 mL. On the other hand, the performance of the MBR and the SBR unit were excellent with effluent quality respecting recycling standards for toilet flushing. Helminth eggs found in the raw greywater were found at a concentration of 1 egg/6L of Hymenolepis sp. (rodent origin probably from the collection system) ; No eggs were found in 6L of the effluent of any of the treatment units tested. The effluent from the low-cost unit was recycled for toilet flushing for fifteen continuous months. We report the absence of any anaesthetic aspect and smell emanation and the acceptance of the approach by the toilet users.