Search Results (9)

Purple phototrophic bacteria (PPB) have great potential in treating nitrogen-contaminated wastewater. Unlike conventional heterotrophic denitrification, PPB-driven denitrification utilizes light-driven metabolism, concurrently improving nitrogen removal and carbon management efficiency. This work aimed to develop a PPB denitrification process for nitrogen removal, carbon emission mitigation, and resource recovery. The PPB growth was first optimized and the most desirable light and carbon sources (i.e., incandescent light and sodium acetate) were pinpointed. PPB denitrification could reach a nitrate removal rate of 0.68 mg N/L/h, while no nitrite was detected during the process, regardless of the amount of external electron donors. This was attributed to the fact that the true reduction rate of nitrite (4.42 mg N/gVSS/h) was significantly higher than that of nitrate (1.51 mg N/gVSS/h). In the presence of a sufficient carbon source, PPB denitrification was found to be a low-carbon process, with only ~0.17% of converted nitrate being emitted as nitrous oxide. Meanwhile, PPB biomass for denitrification was rich in value-added products (e.g., protein and pigment), which potentially generated additional benefits over the biomass valued at USD 17 kg⁻¹. These results provide a theoretical basis for implementing PPB denitrification for carbon-neutral and resource-efficient wastewater treatment. Full article

Purple phototrophic bacteria (PPB) offer a sustainable approach for biological wastewater treatment while simultaneously producing valuable by-products such as polyhydroxyalkanoates (PHAs). This study investigates the effects of continuous light wavelengths over a two-stage nutrient reduction setup on PHA accumulation in a mixed PPB culture grown on fuel synthesis wastewater (FSW). The first stage promoted biomass production under nutrient availability, while the second stage targeted the enhancement of PHA accumulation through nitrogen (N) or phosphorus (P) reduction. Biomass growth remained stable under P reduction but significantly increased under N reduction. The results showed that organics removal efficiency decreased under nutrient reduction, particularly under P reduction, while N reduction conditions enhanced P uptake from the media. Maximum PHA accumulation reached 12.6% CDW under N reduction and 10.0% CDW under P reduction. Light type played a dominant role, with a full-spectrum light that included ultraviolet (UV) and infrared (IR) promoting the highest PHA accumulation, whereas white light with far-red wavelengths (700–770 nm) enhanced biomass growth. These findings highlight the potential of optimizing light conditions and nutrient availability to enhance PHA biosynthesis, paving the way for improved bioplastic production from wastewater streams. Full article

Annually, the food industry generates large amounts of waste and by-products, causing serious problems in their management and final disposal. In particular, by-products are mainly recovered as livestock feed. A most appealing strategy to valorize them has herein been investigated, through polyhydroxyalkanoate (PHA) production. In this view, a stream rich in volatile fatty acids deriving from the acidogenic fermentation of reground pasta (RP), a farinaceous food-industry by-product, was used as a carbon source for PHA production with a phototrophic purple bacteria (PPB) consortium. PPB are very versatile organisms that present a unique metabolism allowing them to adapt to a variety of environmental conditions. The PPB-PHA enrichment phase was performed in a lab-scale semi-continuous photo-bioreactor under a permanent carbon feast regime, with organic loading rate (OLR) increments from 14 to 19 mmolC/Ld. The results showed that the fermented RP solution composition (with 23.4% of HV precursors on a COD basis) was suitable for the PHBHV copolymer production, with the PPB consortium being capable of reaching a very high content in the hydroxyvalerate (HV) monomer, with a maximum of 60% (gHV/gPHA). Regarding the PHA accumulation stage where the light intensity was increased up to 20.2 W/L, a further increase in the culture PHA content by 76% after 12 h was obtained. Overall, these results open the possibility of valorizing food-industry by-products through the development of a biocatalytic process for PHA production with PPB, thus making the overall approach more sustainable from a green perspective. Full article

This work shows the potential of a new way of co-treatment of domestic wastewater (DWW) and a liquid stream coming from the thermal hydrolysis of the organic fraction of municipal solid waste (OFMSW) mediated by a mixed culture of purple phototrophic bacteria (PPB) capable of assimilating carbon and nutrients from the medium. The biological system is an open single-step process operated under microaerophilic conditions at an oxidative reduction potential (ORP) < 0 mV with a photoperiod of 12/24 h and fed during the light stage only so the results can be extrapolated to outdoor open pond operations by monitoring the ORP. The effluent mostly complies with the discharge values of the Spanish legislation in COD and p-values (<125 mg/L; <2 mg/L), respectively, and punctually on values in N (<15 mg/L). Applying an HRT of 3 d and a ratio of 100:7 (COD:N), the presence of PPB in the mixed culture surpassed 50% of 16S rRNA gene copies, removing 78% of COD, 53% of N, and 66% of P. Furthermore, by increasing the HRT to 5 d, removal efficiencies of 83% of COD, 65% of N, and 91% of P were achieved. In addition, the reactors were further operated in a membrane bioreactor, thus separating the HRT from the SRT to increase the specific loading rate. Very satisfactory removal efficiencies were achieved by applying an HRT and SRT of 2.3 and 3 d, respectively: 84% of COD, 49% of N, and 93% of P despite the low presence of PPB due to more oxidative conditions, which step-by-step re-colonized the mixed culture until reaching >20% of 16S rRNA gene copies after 49 d of operation. These results open the door to scaling up the process in open photobioreactors capable of treating urban wastewater and municipal solid waste in a single stage and under microaerophilic conditions by controlling the ORP of the system. Full article

Wastewaters are mainly classified as domestic, industrial and agro-industrial based on their production source. Piggery wastewater (PWW) is a livestock wastewater characterized by its high concentrations of organic matter and ammonium, and by its odour nuisance. Traditionally, PWW has been treated in open anaerobic lagoons, anaerobic digesters and activated sludge systems, which exhibit high greenhouse gas emissions, a limited nutrients removal and a high energy consumption, respectively. Photosynthetic microorganisms can support a sustainable wastewater treatment in engineered photobioreactors at low operating costs and with an efficient recovery of carbon, nitrogen and phosphorous. These microorganisms are capable of absorbing solar irradiation through the photosynthesis process to obtain energy, which is used for their growth and associated carbon and nutrients assimilation. Purple phototrophic bacteria (PPB) represent the photosynthetic microorganisms with the most versatile metabolism in nature, whereas microalgae are the most-studied photosynthetic microorganisms in recent years. This review describes the fundamentals, symmetry and asymmetry of wastewater treatment using photosynthetic microorganisms such as PPB and microalgae. The main photobioreactor configurations along with the potential of PPB and microalgae biomass valorisation strategies are also discussed. Full article

Phototrophic mixed cultures (PMC) are versatile systems which can be applied for waste streams, valorisation and production of added-value compounds, such as polyhydroxyalkanoates (PHA). This work evaluates the influence of different operational conditions on the bacterial communities reported in PMC systems with PHA production capabilities. Eleven PMCs, fed either with acetate or fermented wastewater, and selected under either feast and famine (FF) or permanent feast (PF) regimes, were evaluated. Overall, results identified Chromatiaceae members as the main phototrophic PHA producers, along with Rhodopseudomonas, Rhodobacter and Rhizobium. The findings show that Chromatiaceae were favoured under operating conditions with high carbon concentrations, and particularly under the PF regime. In FF systems fed with fermented wastewater, the results indicate that increasing the organic loading rate enriches for Rhodopseudomonas, Rhizobium and Hyphomicrobiaceae, which together with Rhodobacter and Chromatiaceae, were likely responsible for PHA storage. In addition, high-sugar feedstock impairs PHA production under PF conditions (fermentative bacteria dominance), which does not occur under FF. This characterization of the communities responsible for PHA accumulation helps to define improved operational strategies for PHA production with PMC. Full article

Bioelectrochemical systems are a promising technology capable of reducing CO₂ emissions, a renewable carbon source, using electroactive microorganisms for this purpose. Purple Phototrophic Bacteria (PPB) use their versatile metabolism to uptake external electrons from an electrode to fix CO₂. In this work, the effect of the voltage (from −0.2 to −0.8 V vs. Ag/AgCl) on the metabolic CO₂ fixation of a mixed culture of PPB under photoheterotrophic conditions during the oxidation of a biodegradable carbon source is demonstrated. The minimum voltage to fix CO₂ was between −0.2 and −0.4 V. The Calvin–Benson–Bassham (CBB) cycle is the main electron sink at these voltages. However, lower voltages caused the decrease in the current intensity, reaching a minimum at −0.8 V (−4.75 mA). There was also a significant relationship between the soluble carbon uptake in terms of chemical oxygen demand and the electron consumption for the experiments performed at −0.6 and −0.8 V. These results indicate that the CBB cycle is not the only electron sink and some photoheterotrophic metabolic pathways are also being affected under electrochemical conditions. This behavior has not been tested before in photoheterotrophic conditions and paves the way for the future development of photobioelectrochemical systems under heterotrophic conditions. Full article

Domestic wastewater treatment by purple phototrophic bacteria (PPB) is based on the assimilative uptake of organics and nutrients into the bacterial biomass. Thereby, it strongly depends on the carbon/nutrients ratio of the wastewater. The physiological COD/N/P ratio for PPB growth in domestic wastewater makes the addition of an external organic carbon source necessary in order to allow for an efficient process. However, PPB need a source of alkalinity (as CO₂) to grow on reduced organics that serves as an electron acceptor since biohydrogen production (an alternative electron sink) is inhibited by ammonium. A preliminary experiment showed that high nutrients-loading wastewater was limited by CO₂ imbalance, leading to poor removal efficiencies. Subsequently, the effect of the oxidation state of the organics added as external organic carbon sources to PPB reactors treating low nutrients-loading domestic wastewater has been analyzed. Three organics were used as additives to PPB development in four consecutive batches: acetate (more oxidized), ethanol and butyrate (more reduced). The PPB population was settled and the general performance under the three situations, in terms of organics, N and P assimilation, and growth kinetics was not significantly different irrespective of the external organic carbon source. The reactors were dominated by PPB, though reduced organics allowed for dominance of Rhodopseudomonas palustris, whereas oxidized organics caused co-dominance of R. palustris and Rhodobacter capsulatus. Thereby, alkalinity (as bicarbonate), and not the oxidation state of the organics, is the key parameter for the efficient treatment of domestic wastewater by PPB. Full article

One of the current challenges in the treatment of wastewater is the recovery and/or transformation of their resources into high value-added products, such as biohydrogen. The aim of the present study was to optimize the production of hydrogen by mixed cultures of purple phototrophic bacteria (PPB), targeting in low CO₂ emission. Batch assays were conducted using different carbon (malic, butyric, acetic acid) and nitrogen (NH₄Cl, Na-glutamate, N₂ gas) sources by varying the chemical oxygen demand to nitrogen ratio (COD:N 100:3 to 100:44), under infrared radiation as sole energy source. Malate-glutamate (COD:N 100:5.5) and malate-NH₄-N (COD:N 100:3) fed cultures, exhibited high H₂ production rates of 2.3 and 2.5 mLH₂/Lh, respectively. It was observed that the use of glutamate decreased the CO₂ emission by 74% (13.4 mLCO₂/L) as compared to NH₄-N. The H₂ production efficiency achieved by organic carbon substrates in combination with glutamate, was in the order of malic (370 mLH₂/L) > butyric (145 mLH₂/L) > acetic acid (95 mLH₂/L). These substrates entailed partitioning of reducing power into biomass at 64%, 50% and 48%, respectively, whereas reductants were derived to biohydrogen at 5.8%, 6.1% and 2.1%, respectively. These results suggest that nitrogen source and carbon dioxide emissions play an important role in the optimization of hydrogen production by PPB. Full article