Reducing the natural color of membrane bioreactor permeate with activated carbon or ozone

Abstract

The suitability of two membrane bioreactors for on-site wastewater treatment and reuse in Switzerland was investigated. The treated wastewater was used for toilet flushing and gardening, with water recycling rates of 30% (single family house) and almost 100% (toilets in a cable car station) respectively. Due to the recycling, an increase in a natural yellowish-brown color was observed, leading to double flushing of the toilets, higher cleaning requirements and increased permeate production. Color removal with ozone, powdered (PAC) and granulated (GAC) activated carbon was assessed in laboratory and field experiments. PAC was added directly into the MBR, whereas ozonation and GAC were applied to the permeate. The dosage of ozone or activated carbon depended on the recycling rate and color intensity. If color removal is necessary, PAC is the option best suited to small treatment plants, with a requirement of 30–50 g m−3 for 30% and 100 g m−3 for 100% water recycling.