Study on restrictive water quality parameters for closed recycling water in the recycled fiber mills

Representative water quality parameters selection can provide scientific basis for monitoring the safe running of industrial water recycling. This paper investigated two recycled fiber mills with different closure degrees in Xi' an. According to the degree of pollutants accumulation in recycling water after closure, seven parameters TDS, CS, UV_DCS, conductivity, COD_t, and cationic demand, COD_col are selected and analyzed their correlation, the results revealed that CS and UV_dcs, TDS and electrical conductivity, TDS and cationic demand, UV_dcs and COD_t, electrical conductivity and cationic demand were highly correlated; the correlation coefficients were all above 0.85. Combining those not overlap restrictive water quality parameters, restrictive water quality parameter combination COD_t, CS TDS was determined as the optimum restrictive water quality parameters in term of indicating the pollutant content in the recycling water. CS and TDS contents of recycling water were predicted by UV_dcs and electrical conductivity based on the regression equation. The errors of most prediction results were within 20%. Because UV_dcs and electrical conductivity are easy to measure, combination of COD_t, UVdcs and electrical conductivity can be used for on-line monitoring of recycling-water quality.