Measurement and modelling of quality changes in stored untreated grey water

This paper describes an investigation into stored untreated grey water quality processes and the development of a computer simulation for those processes. A laboratory study was carried out to investigate the changes in water quality with increasing residence time, and the results were used to calibrate and verify the model. Model results gave a good fit for dissolved oxygen (DO) concentrations, but only a reasonable fit for chemical oxygen demand (COD). Still, the main trends of model and laboratory COD data were broadly represented. Measurement and model results tend to confirm the initial hypothesis of four major processes in operation: settlement of suspended solids, aerobic microbial growth, anaerobic release of soluble COD from settled organic matter and atmospheric reaeration. Storing grey water for 24 h may significantly improve water quality through rapid settlement of organic particles, however, storage beyond 48 h leads to depleted DO levels and potential aesthetic problems. A more detailed model of COD fractions within grey water (with the relevant measured data) in conjunction with a characterisation of particulate settling velocities should lead to improvements in model predictions.