Isolation of phosphorus-hyperaccumulating microalgae from revolving algal biofilm (RAB) wastewater treatment systems

Abstract

Excess phosphorus (P) in wastewater effluent poses a serious threat to aquatic ecosystems and can spur harmful algal blooms. Revolving algal biofilm (RAB) systems are an emerging technology to recover P from wastewater before discharge into aquatic ecosystems. In RAB systems, a community of microalgae take up and store wastewater P as polyphosphate as they grow in a partially submerged revolving biofilm, which may then be harvested and dried for use as fertilizer in lieu of mined phosphate rock. In this work, we isolated and characterized a total of 101 microalgae strains from active RAB systems across the US Midwest, including 82 green algae, 9 diatoms, and 10 cyanobacteria. Strains were identified by microscopy and 16S/18S ribosomal DNA sequencing, cryopreserved, and screened for elevated P content (as polyphosphate). Seven isolated strains possessed at least 50% more polyphosphate by cell dry weight than a microalgae consortium from a RAB system, with the top strain accumulating nearly threefold more polyphosphate. These top P-hyperaccumulating strains include the green alga Chlamydomonas pulvinata TCF-48 g and the diatoms Eolimna minima TCF-3d and Craticula molestiformis TCF-8d, possessing 11.4, 12.7, and 14.0% polyphosphate by cell dry weight, respectively. As a preliminary test of strain application for recovering P, Chlamydomonas pulvinata TCF-48 g was reinoculated into a bench-scale RAB system containing Bold basal medium. The strain successfully recolonized the system and recovered twofold more P from the medium than a microalgae consortium from a RAB system treating municipal wastewater. These isolated P-hyperaccumulating microalgae may have broad applications in resource recovery from various waste streams, including improving P removal from wastewater.

Intensive Microalgal Cultivation and Tertiary Phosphorus Recovery from Wastewaters via the EcoRecover Process

“…To explore alternative mechanisms for phosphorus recovery, the elemental composition of harvested biomass was characterized. The phosphorus content in algal biomass has been shown to vary across species , and also within species as a function of their physiological state. − The phosphorus content in microalgal cells is often around 1% of dry weight under limited phosphorus availability but may be as high as 3–10% dry weight when the microalgae achieve luxury uptake of phosphorus. ,,, The average phosphorus content of harvested biomass across the full focus period was 3.2 ± 0.7% (5/50/95th percentiles of 2.2/3.6/4.0%; n = 32; Figure S13), further suggesting partial phosphorus recovery via luxury uptake, surface adsorption, or precipitation of phosphorus.…”

“…43−47 The phosphorus content in microalgal cells is often around 1% of dry weight under limited phosphorus availability 48 but may be as high as 3−10% dry weight when the microalgae achieve luxury uptake of phosphorus. 14,19,49,50 The average phosphorus content of harvested biomass across the full focus period was 3.2 ± 0.7% (5/50/95th percentiles of 2.2/3.6/4.0%; n = 32; Figure S13), further suggesting partial phosphorus recovery via luxury uptake, surface adsorption, or precipitation of phosphorus. SEM-EDS was performed on a range of samples from the broader monitoring period (April 5, 2022 to February 13, 2023; Section S4.2 and Table S5), including samples with the highest and lowest phosphorus content, from periods with and without coagulant use, and start and end points of batch experiments.…”

“…Attached growth systems, such as the revolving algal biofilm (RAB) and the rotating algal biofilm reactor, grow mixed communities as biofilms and often cycle them between (i) submerged conditions for nutrient uptake and (ii) atmospheric conditions to support gas exchange (including CO 2 uptake) and exposure to light. Recent characterization of RAB systems across the Midwest U.S. has demonstrated the potential for luxury phosphorus uptake (as polyphosphate) in RAB communities . Polyphosphatealong with polyhydroxyalkanoates and glycogenis a key biopolymer in the rhythm of (chemotrophic) EBPR systems, helping polyphosphate-accumulating organisms to balance growth across cycling environmental conditions .…”

Recent advances and fundamentals of microalgae cultivation technology

“…used for wastewater treatment. [61] Table 4 summarizes gene engineering of phosphorus fixation and effects of phosphorus supplementation of microalgae growth and compound production…”

“…We categorized these findings according to the fundamental factors that regulate microalgae growth and properties including bioreactor type and supply of light and nutrients, [50][51][52] symbiotic microalgae-microbiotic interactions in which bacteria provide nitrogen fixation and nitrification as well as vitamins, whereas microalgae synthesize carbons, [53][54][55][56] CO 2 supplementation or genetic modifications of CO 2 fixation, [57][58][59][60] inorganic phosphate fixation, [61][62][63] adaptation to temperature. [64,65] Substantial research is focused on gene engineering and selection of microalga for food and pigment production.…”