Comparison of organic matter concentration in wastewater between different drainage systems in districts affected by tidal river.

Investigation on concentrations of COD of different kinds wasterwater in a city affected by tidal river in the Pearl River Delta area was carried on. And COD of the wastewater in the city,272mg/L,was worked out. The COD Concentration of wastewater in separate system,191mg/L on average,was significantly higher than that in combined sewerage system,137mg/L on everage. COD concentration in combined sewerage system decreased as the river level increased,appearing significant negative correlation. The partial correlation coefficient was -0.8432. However,COD concentration in separate system appeared no correlation to the river level. In district affected by tidal river,separate system could prevent river water from backing up into the sewerage system more efficiently than combined sewerage system. On behave of the operation of wastewater treatment plants,separate system was more sutible than combined sewerage system for district affected by tidal river. References were provided for drainage systems choosing in the Pearl River Delta area.