Enriching and aggregating purple non-sulfur bacteria in an anaerobic sequencing-batch photobioreactor for nutrient capture from wastewater

Abstract

25Purple non-sulfur bacteria (PNSB), a guild of anoxygenic photomixotrophic organisms, rise 26 interest to capture nutrients from wastewater in mixed-culture bioprocesses. One challenge 27 targets the aggregation of PNSB biomass through gravitational separation from the treated 28 water to facilitate its retention and accumulation, while avoiding the need for membranes. We 29 aimed to produce an enriched, concentrated, well-settling, nutrient-removing PNSB biomass 30 using sequencing batch regimes (SBR) in an anaerobic photobioreactor. The stirred tank was 31 fed with a synthetic influent mimicking loaded municipal wastewater (430-860 mg CODAc LInf -32 1 , COD:N:P ratio of 100:36:4-100:11:2 m/m/m), operated at 30°C and pH 7, and continuously 33 irradiated with infrared (IR) light (>700 nm) at 375 W m -2 . After inoculation with activated 34 sludge at 0.1 g VSS L -1 , PNSB were rapidly enriched in a first batch of 24 h: the genus 35Rhodobacter reached 54% of amplicon sequencing read counts. SBR operations at volume 36 exchange ratio of 50% with decreasing hydraulic retention times (48 to 16 h; 1 to 3 cycles d -1 ) 37 and increasing volumetric organic loading rates (0.2 to 1.3 kg COD m -3 d -1 ) stimulated the 38 aggregation (compact granules of 50-150 μm), settling (sedimentation G-flux of 4.7 kg h -1 m -39 2 ), and accumulation (as high as 3.8 g VSS L -1 ) of biomass. The sludge retention time (SRT) 40 increased freely from 2.5 to 11 d without controlled sludge wasting. Acetate, ammonium, and 41 orthophosphate were removed simultaneously (up to 96% at a rate of 1.1 kg COD m -3 d -1 , 77% 42 at 113 g N m -3 d -1 , and 73% at 15 g P m -3 d -1 ) with a COD:N:P assimilation ratio of 100:6.7:0.9 43 (m/m/m). Competition for substrate and photons occurred in the PNSB guild. SBR regime shifts 44 sequentially selected for Rhodobacter (90%) under shorter SRT and non-limiting acetate 45 concentrations during reaction phases, Rhodopseudomonas (70%) under longer SRT and 46 acetate limitation, and Blastochloris (10%) under higher biomass concentrations. We 47 Highlights 56• PNSB were highly enriched (90%) in an anaerobic stirred-tank photobioreactor. 57• The mixed-culture SBR process fostered PNSB biomass aggregation and accumulation. 58• PNSB sludge reached 3.8 g VSS L -1 and a sedimentation G-flux of 4.7 kg h -1 m -2 . 59

Control tools to selectively produce purple bacteria for microbial protein in raceway reactors

“…A further cost reduction of 27-40% can be possible if ultrafiltration is replaced by gravitational settling (€0.9-2.4 kg -1 DW). Currently, there is no published literature studying the settleability of PNSB except for Cerruti, et al 2020 DOI: https://doi.org/10.1101/2020.01.08.899062 38 . Further research should explore this closely, as it will be an important cost saver.…”

Syntrophy between fermentative and purple phototrophic bacteria for carbohydrate-based wastewater treatment

“…DNA was extracted from 0.5-7 mg biomass using DNeasy Powersoil microbial extraction kit (Qiagen, Hilden, Germany) accordingly to manufacturer's instructions and stored at -20°C. The compositions of the bacterial communities of the mixed liquors were characterized from the samples collected by V3-V4 16S rRNA gene-based amplicon sequencing as in (Cerruti, Stevens, et al, 2020).…”

Effects of light / dark diel cycles on the photoorganoheterotrophic metabolism ofRhodopseudomonas palustrisfor differential electron allocation to PHAs and H2

“…The Rhodopseudomonas strain was isolated with dilution series in agar from an in-house PNSB enrichment culture designed for nutrient removal from synthetic wastewater (30) (31), and sequenced for phylogenetic identification using a Sanger sequencing (Baseclear, NL).…”

“…Here, we aimed to elucidate the effects of diel light / dark cycles on the physiology and electron allocation in Rhodopseudomonas palustris, isolated from an in-house PNSB enrichment culture for nutrient removal from wastewater (30). The dynamic conditions were hypothesized to influence the physiology of purple bacteria, as the energy source is intermittently provided.…”