Investigation into the role of bacteria biofilms in the initial attachment and colonization stages of filamentous green algae in lab bench-scale algal turf scrubbers

Abstract

The design of reactor systems to cultivate filamentous green algae for remediation of nutrients from wastewater and for biomass production has long been pursued for various wastewater applications. The role of early colonization characteristics of algae on substrata in system performance has been poorly understood, however. In particular, the role of the overall background microbial community in contributing to attachment of filamentous green algae is not well known. Past research suggest that in mixed-community stream biofilms, bacteria, diatoms, and other microbes play an integral role in conditioning new surfaces through the exudation of extracellular polymeric substances (EPS), which forms an aggregate onto which algae cells settle and attach. This objective of this research was to investigate the role of a pre-existing bacteria biofilm in the colonization of polymer substrata in bench-scale floway systems by filamentous green algae (FGA). Specifically, it probes if the presence of microbial biofilms produced by communities sourced from FGA-favoring natural habitats results in faster and stronger attachment by the FGA Rhizoclonium spp, under varied flow, nutrient concentrations, bacteria community sources, and media types. For the studies described, novel lab-bench scale systems were constructed and tested for operation and parameter setting. The effect of three bacteria biofilms, formed by communities sourced from the Tallapoosa River (Tallasee, Alabama, USA) and Town Creek (Auburn, Alabama, USA) and from the two mixed together, was tested using different strengths of the synthetic media (freshwater-modified) Proline F/2 (1/4 and 2x) and dilutions of tilapia aquaculture wastewater (1/4, ½, and full-strength) with different floway channel slopes (1%, 2%, and 3%). The impact of bacteria biofilms on attachment was assessed as speed and strength of attachment, measured as amount of biomass and chlorophyll a over time, with the division of samples into two subsets for strength of attachment analysis. It was found that the presence of the Tallapoosa River bacteria biofilm resulted in significantly faster attachment of Rhizoclonium spp. cells in the ¼ dilution of F/2 and with a channel slope of 3.00 ± 0.100%. The presence of the mixed bacteria biofilm also had a significant impact on attachment when parameters of a ¼-dilution of unfiltered tilapia effluent and a channel slope of 2.00 ± 0.100% were used, as indicated through chl-a measures. While statistical significance was not detected for other trial conditions, based on effect sizes and wide confidence intervals, and the fact that the graphical trend remained consistent and visible, it can be argued there is a need for greater power in the experimental design. There is reason to believe that given sufficient replication, biofilms formed by the tested microbial communities would demonstrate a statistically significant impact on speed of attachment under these other constraints. From all results, it can be concluded that a microbial biofilm pioneer community can have impact on early colonization rates of FGA on virgin substrata. Also, it can be concluded that a lower nutrient concentration of the media results in a positive impact on speed of FGA attachment but altering the channel slope by 1% increments did not result in a noticeable effect. The research indicates that there is cause for further exploration of the microbial biofilm’s role in initial FGA colonization of ATS systems.