Performance evaluation of quick and compact package-type down-flow hanging sponge system for domestic sewage treatment

Wastewater treatment plants require long installation and start-up times. In this study, a compact package-type down-flow hanging sponge (DHS) operating system based on the trickling filter principle using polyurethane sponge media was designed and installed at a sewage treatment site in Thailand. The DHS system was installed within 14 d of material arrival and operated for 81 d without seed sludge inoculation. The T-BOD concentration of the DHS effluent reached 2.2 mg.L- 1 after 6 d of operation. High nitrification activity of the DHS reactor, when operated with a hydraulic retention time of 3.7 +/- 0.9 h, was observed after 13 d of operation. In addition, the DHS effluent achieved the discharge standard within 14 d of operation. The DHS reactor rapidly initiated the removal of organics and nitrogen and exhibited COD, TSS, and ammonia removal efficiencies of 58% +/- 10%, 76% +/- 21%, and 66% +/- 32%, respectively. Parallel 16S rRNA gene sequencing of sludge revealed the rapid growth of nitrifying bacteria. The abundance of ammonia-oxidizing bacteria Nitrosomonas spp. ranged from 0.1% to 1.8% on day 18, indicating that the DHS sponge media effectively retained slow-growth nitrifying bacteria that were affected by the rapid start-up process. Nitrite-oxidizing Nitrospira sp. was mainly detected at the bottom of the reactor. These results show that the compact package-type DHS system is a novel and practical easy contract sewage treatment method.

Automated summary

In this study, a compact package-type down-flow hanging sponge (DHS) operating system was designed and installed. The DHS system achieved the discharge standard quickly and showed high efficiencies in removing organics and nitrogen. The study also found that the DHS sponge media effectively retained slow-growth nitrifying bacteria.