Secondary wastewater effluent treatment by microalgal-bacterial membrane photobioreactor at long solid retention times

Abstract

Microalgal-bacterial membrane photobioreactors (MPBRs) have recently emerged as a new sustainable tech- nology in wastewater treatment. For advanced treatment of domestic secondary effluents, selecting long solids retention times (SRTs) may be crucial to achieve optimal community structure and therefore, process perfor- mance. This study assesses the effects of operating conditions on nutrient removal, biomass productivity, sus- pension characteristics and membrane fouling. A lab-scale MPBR was run during long-term tests to assess process stability. Indigenous microalgae-bacteria consortia were developed for each condition. Conventional membrane bioreactor was used for tested control condition. Experimental results showed the crucial role of extending SRT to 80 d to enhance bioflocculation, avoid biopolymer clusters accumulation and minimize membrane fouling rates. Despite influent fluctuations, optimal hydraulic retention time value between 2 and 5 d was necessary to achieve moderate nutrient removal (40.6–48.7 % and 18.5–34.7 % for nitrogen and phosphorus, respectively). A mixed microalgal structure of green microalgae, cyanobacteria and diatoms was also achieved