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

Abstract

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.