Influence of sodium hypochlorite on the anaerobic treatment of brown water

Effluent separation at the origin (brown water (BW), gray water and yellow water) improves sewage treatments. However, the BW can contain disinfectants such as sodium hypochlorite (NaOCl). This disinfectant has a high oxidant potential that could reduce the methane production and affect the granular sludge physiology. Therefore, the initial concentration of volatile solids (VS) from BW and the NaOCl effect on the anaerobic digestion (AD) were evaluated in this work. Variables analysed were specific methanogenic activity (SMA), structural morphology and mineral composition of granular sludge. A VS removal of 60% was obtained for 6, 9 and 14.6 g/L of VSo. At low concentrations of NaOCl (< 125 mg/L), a VSo removal of up to 55 % and methane production of 125 mLSTPCH4/L were observed. While at NaOCl high concentrations (>250 mg/L), the rupture of the granules was observed releasing exopolymeric substances (EPS), the SMA decreased to 0.004 gCODCH4/gVS.d. Our findings reveal that the NaOCl (> 125 mg / L) decreases the efficiency of BW treatments, and its effect must be considered to implement the anaerobic digestion of BW in low-flow toilet systems.

Keywords: anaerobic granules, brown water, sodium hypochlorite, specific methanogenic activity.