Impact of Storage Time on Characteristics of Synthetic Greywater for Two Different Pollutant Strengths to Be Treated or Recycled

Storage of greywater is controversial for environmental and health reasons. Artificial greywater was assessed after 2 and 7 days of storage time. Two different greywater pollutant strengths were statistically compared at each storage time. A negative significant (p < 0.05) correlation was evident with increasing storage time for the 5-day biochemical oxygen demand for more than 2 days. However, the concentrations of 5-day biochemical oxygen and chemical oxygen demands reduced significantly at 2 days of storage when compared with freshly prepared greywater. Biodegradability (5-day biochemical oxygen demand/chemical oxygen demand ratio) decreased significantly after storage to between 0.14 and 0.39. The nitrification process was improved significantly with increasing storage time concerning low strength greywater with a significant increase in the removal of ammonia-nitrogen and a non-significant decrease in the removal of nitrate-nitrogen. The correlation was significantly positive between ammonia-nitrogen and 5-day biochemical oxygen demand for stored greywater, while it was significantly negative between total suspended solids and both 5-day biochemical oxygen demand and dissolved oxygen. Significant reductions in colour, total suspended solids and turbidity were correlated positively with storage time. Precipitation of dissolved metals was suspected to occur in storing greywater by binding the inorganic components with the sediment and collide surfaces through adsorption, allowing a significant drop in concentrations of dissolved and undissolved metals with increasing storage time through sedimentation. Synthetic greywater of low mineral pollution had significantly higher removals for almost all concentrations compared with those for high concentrations. More advanced technologies for high trace element removal are required.