A syphon-downflow hanging sponge (DHS) reactor for improving the denitrification efficiency of sewage water treatment

The study focused on developing a low-cost down-flow hanging sponge (DHS) to enhance denitrification. The DHS reactor was modified by connecting with a syphon tube to maintain aerobic and anaerobic conditions. This method can simultaneously achieve nitrification and denitrification, requiring no extra energy for pumping. The study had two phases to evaluate the denitrification efficiency of the syphoned reactor at different reactor configurations. In the first phase, the syphon height was equal to the reactor height, and a water column was developed inside the DHS to create an anaerobic zone. The sCOD removal rates of syphon–DHS and conventional-DHS (control) were 75 ± 20% and 73 ± 19%, respectively, and the removal rates were almost similar in both reactors. However, the total nitrogen (TN) removal rate of syphon–DHS was 19 ± 3%, six folds greater than that of the conventional-reactor. In phase II, the syphon height of the developed DHS was changed to 3/5 of the DHS height. The sCOD and NH4+-N removal of syphon–DHS in the second phase were 62 ± 33% and 62 ± 31%, respectively, and approximately similar to the convectional DHSs’ performance. The anaerobic zone of the reactor facilitated enhancing the TN removal two folds than the conventional-reactor and was measured as 18 ± 16%. Nitrifiers, denitrifiers and anammox bacteria were present in the sludge samples of syphon–DHS as nitrogen-removing bacteria. The developed anaerobic conditions in the syphon–DHS enhanced denitrification without using extra energy for operation.