The variations in the loading rates are mainly due to the dilutions done in the wastewater in order to attain the particular range of influent COD concentrations in different experiments. The experiments were operated in the same manner as described, for 10 days. After 10 days, the RCs, RWs and CCs were emptied and the second runs of the experiment were initiated with fresh untreated wastewater. The second run was operated for another 10 days in the same manner as explained above. Thus, in each run 20 l of wastewater was treated. At the end of first run (days 1–10), only the wastewater was changed while the plants remain in the raceways till the end of second run (days 11–20). At the termination of each experiment, plants were removed from the raceways, washed thoroughly with tap water, and their total number and mass (dry weight) were recorded. The first two experiments were conducted in the same manner as explained, while experiments III and IV were conducted with four runs in each experiment, that is, the wastewater was changed on every 5th day of the experiment. Therefore within the entire tenure of each experiment (20 days), the wastewater was changed fourtimes; however, the hydraulic loading and retention time were maintained same as in the case of experiments I and II.