Greywater treatment performance of a pilot-scale membrane bioreactor and characteristics of bacterial biofilm signatures in permeate effluent

Treated greywater has a high potential for water reuse. However, the post-treatment processes of reclaimed greywater may face biofouling problems due to biofilm formation. In the present study, the greywater treatment performance of a pilot-scale membrane bioreactor (MBR) was evaluated, and the effect of a dominant bacterial biofilm growing on the Pall ring media placed in the permeate pipeline was investigated. The MBR was operated for 125 days with a constant hydraulic retention time of 2 days under complete sludge retention. The treatment performance in terms of the levels of organic compounds, ammonium nitrogen, suspended solids, total coliforms, and Escherichia coli was >90 %. During the operation, a high relative abundance (>70 %) of the following bacterial phyla was observed within the MBR and the bacterial biofilm: Proteobacteria, Chloroflexi, Actinobacteria, and Planctomycetes. Furthermore, the following bacterial orders were predominantly observed in the biofilm: Sphingomonadales, Burkholderiales, and Planctomycetes. Acidovorax, Methylibium, Blastomonas, and Planctomyces were the important genera identified in the biofilm. Interestingly, the present study revealed that these bacterial species were predominant and well adapted in treated greywater containing various surfactant and detergent components. Knowledge of the predominant bacterial species in the biofilm could enable to select the appropriate disinfection method and prevent the biofouling of the reverse osmosis (RO) membrane, which can facilitate further application of the MBR-RO process for water reuse. [Display omitted] •Treatment performances and biofilm members by MBR for real greywater were explored.•MBR showed high treatment performance under HRT of 2 days without sludge discharge.•Acidovorax, Methylibium, Blastomonas, and Planctomyces were predominant biofilms in the effluent.