Analysis of water-using networks with multiple contaminants involving regeneration recycling

The introduction of regeneration recycling unit can significantly reduce freshwater consumption and consequently reduce wastewater discharge of water-using systems. In this paper, the influences of the regenerated concentrations of contaminants on regenerated stream consumption are investigated for the fixed mass-load water networks with multiple contaminants. The multi-contaminant water networks involving regeneration recycling are classified into simple ones and complex ones in this paper. Simple networks are similar to single-contaminant ones, in which only the key contaminant limits the usage of regenerated water. The regenerated stream consumption of simple networks can be predicted easily when the regenerated concentration of the key contaminant changes. The concentrations of other contaminants, if having influence on the regenerated stream consumption as well, should be reduced to their maximum allowable values. There is great difference between the features of complex networks of multiple contaminants and that of networks of single contaminant. The influence of the regenerated concentrations on regenerated stream consumption of complex networks is analyzed based on mass balances of the contaminants. The contaminant which has the most influence on regenerated stream consumption is identified. The methods proposed can contribute to evaluation of the appropriate regenerated concentrations for design or retrofit of the water networks with multiple contaminants.