Date Published: March 6, 2015
Publisher: Public Library of Science
Author(s): Takashi Narihiro, Na-Kyung Kim, Ran Mei, Masaru K. Nobu, Wen-Tso Liu, Zhe-Xue Quan.
The anaerobic packed-bed (AP) and hybrid packed-bed (HP) reactors containing methanogenic microbial consortia were applied to treat synthetic soft drink wastewater, which contains polyethylene glycol (PEG) and fructose as the primary constituents. The AP and HP reactors achieved high COD removal efficiency (>95%) after 80 and 33 days of the operation, respectively, and operated stably over 2 years. 16S rRNA gene pyrotag analyses on a total of 25 biofilm samples generated 98,057 reads, which were clustered into 2,882 operational taxonomic units (OTUs). Both AP and HP communities were predominated by Bacteroidetes, Chloroflexi, Firmicutes, and candidate phylum KSB3 that may degrade organic compound in wastewater treatment processes. Other OTUs related to uncharacterized Geobacter and Spirochaetes clades and candidate phylum GN04 were also detected at high abundance; however, their relationship to wastewater treatment has remained unclear. In particular, KSB3, GN04, Bacteroidetes, and Chloroflexi are consistently associated with the organic loading rate (OLR) increase to 1.5 g COD/L-d. Interestingly, KSB3 and GN04 dramatically decrease in both reactors after further OLR increase to 2.0 g COD/L-d. These results indicate that OLR strongly influences microbial community composition. This suggests that specific uncultivated taxa may take central roles in COD removal from soft drink wastewater depending on OLR.
As the global consumption of soft drinks continues to grow, 687 billion liters in 2013, the global value reach 830 billion USD . However, this incurs copious production (up to 2.0 trillion liters per year) and discharge of wastewater  containing high concentrations of sugar [3–5] and polyethylene glycol (PEG; HO[CH2CH2O]nH), a detergent for bottle washing and equipment rinsing . As such, the wastewater stream is characterized by high organic content with the COD ranging from 1.2 to 8.0 g L−1 and BOD5 from 0.6 to 4.5 g L−1 , and required to be treated to reduce COD to prevent the occurrence of contamination in the natural environment. Previous studies report physicochemical treatment, including reverse osmosis , filtration [2, 7], ion-exchange [2, 7], and ozonation ; however, such approaches are relatively ineffective for removing soluble compounds (e.g., PEG and fructose) compared with biological methods [5, 9, 10]. While aerobic biological treatment systems have also been applied [11, 12], long hydraulic retention time (HRT), high aeration requirement, extensive land requirement, high sludge production, and poor biomass settling are significant drawbacks .