Characterization and anaerobic biodegradability of grey water

Grey water consists of the discharges from kitchen sinks, showers, baths, washing machines and hand basins. Thorough characterization of 192 time proportional samples of grey water from 32 houses was conducted over a period of 14 months. COD concentrations were 724 ± 150 mg L− 1, of which 34% was present as suspended COD, 25% as colloidal COD and 38% as soluble COD. The maximum anaerobic biodegradability of grey water of 70 ± 5% indicates the possibility of recovering the COD as methane. However, the low hydrolysis constant makes the application of anaerobic treatment unsuitable. Surfactants accounted for 15% of the total COD. The concentrations of anionic, cationic and noninonic surfactants were 41.1 ± 12.1 mg L− 1, 1.7 ± 0.8 mg L− 1 and 11.3 ± 3.9 mg L− 1, respectively. Of the trace elements which were measured were present below limits suggested for irrigation. Only boron (0.53 ± 0.19 mg L− 1) in a few measurements exceeded the 0.75 mg L− 1 limit established for long term irrigation.

Research Highlights
► Grey water contains 724 mg L− 1 of total COD of which 34% was suspended, 25% colloidal and 38% soluble.
► The anaerobic degradability was 70 ± 5% with a hydrolysis rate constant of 0.02 ± 0.01 d− 1.
► Grey water contained 41 ± 12 mg L− 1of anionic surfactants, about 15% of the total COD.
► Concentrations of metals in grey water were below limits suggested for irrigation.