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Projeto de investigação
Utilization of photosynthetic mixed cultures PMC as new technology for biopolymer production sing agro-industrial residues as feedstock
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Nutrient removal by a microalgal-bacterial consortium as a means to reduce the aeration demand in wastewater treatment
Publication . Carvalho, Virgínia da Conceição Fernandes de; Fradinho, Joana; Reis, Maria d’Ascensão; Oehmen, Adrian
Nutrient runoff leads to serious environmental problems, such as eutrophication, that reduces water quality and unbalances aquatic habitats. Biological treatment of wastewaters reduces the need of the use of harmful and expensive chemicals and allows the recovery and upcycling of nutrients from wastewaters, consistent with the circular economy concept. Phos-phorus removal is normally performed by enhanced biological phosphorus removal systems (EBPR), while the simultaneous removal of phosphorus and nitrogen is performed using bio-logical nutrient removal (BNR) systems. Due to the need of aeration to promote nutrient re-moval, this treatment method requires huge energy costs. Microalgal-bacterial consortia are a sustainable alternative to BNR systems, as they are independent of mechanical aeration since the necessary oxygen for heterotrophic bacteria is photosynthetically produced.
A sludge enriched in Accumulibacter was subjected to dark (anaerobic) – light (aerobic) cycles and a microalgal-bacterial consortium was selected, with a capacity to remove up to 64 mg P/L. This photosynthetic EBPR system was capable of removing high amount of phospho-rus with no need of aeration and under low COD:P ratio (200:60).
To test the effect of seed sludge on the selection of the photosynthetic EBPR system, fresh activated sludge was used as a reactor inoculum that operated in the same dark (anaer-obic) – light (aerobic) conditions. This start-up strategy showed that a microalgal-bacterial consortium that performs photo-EBPR could be selected independently of the seed sludge. A higher enrichment of the biomass in Accumulibacter is correlated with faster selection: 14 days when Accumulibacter sludge was inoculated as opposed to 29 days with real activated sludge.
Since wastewater treatment plants require simultaneous phosphorus and nitrogen re-moval, a sequencing batch reactor was operated in dark (anaerobic) – light (aerobic) – dark (anoxic) conditions to promote nitrogen removal. The selected microalgal-bacterial consor-tium was able to remove 25 ± 9.2 mg P/L and 38 ± 0.92 mg N/L with a COD:N:P ratio of 300:40:60. The main mechanisms of nutrient removal were phosphorus accumulation as pol-yphosphate by polyphosphate accumulating organisms and nitrogen removal by biomass as-similation, since 33 ± 5% of ammonia was converted to nitrate through nitrification, which was further removed by denitrification during the dark anoxic phase. Raman spectrometry showed to be a potential tool for a real-time monitoring of the photo-BNR system, offering a faster alternative to laborious standard analytical methods.
To understand the key operational parameters of the photosynthetic BNR system, a re-actor was operated over 260 days, where the impact of light period duration and carbon di-oxide concentration were tested. Results indicated that the nutrient removal efficiencies of the microalgal-bacterial consortium were enhanced by higher periods of light exposition, rather than higher availability of CO2.
The photosynthetic biological nutrient removal system opens the possibility to reduce the costs of wastewater treatment and has the potential to be a more sustainable wastewater treatment alternative.
Long term operation of a phototrophic biological nutrient removal system
Publication . Carvalho, V. C. F.; Fradinho, J. C.; Oehmen, A.; Reis, M. A. M.; UCIBIO - Applied Molecular Biosciences Unit; DQ - Departamento de Química; Academic Press | Elsevier
The utilization of non-aerated microalgae-bacterial consortia for phototrophic biological nutrient removal (photo-BNR) has emerged as an alternative to conventional wastewater treatment. Photo-BNR systems are operated under transient illumination, with alternating dark-anaerobic, light-aerobic and dark-anoxic conditions. A deep understanding of the impact of operational parameters on the microbial consortium and respective nutrient removal efficiency in photo-BNR systems is required. The present study evaluates, for the first time, the long-term operation (260 days) of a photo-BNR system, fed with a COD:N:P mass ratio of 7.5:1:1, to understand its operational limitations. In particular, different CO2 concentrations in the feed (between 22 and 60 mg C/L of Na2CO3) and variations of light exposure (from 2.75 h to 5.25 h per 8 h cycle) were studied to determine their impact on key parameters, like oxygen production and availability of polyhydroxyalkanoates (PHA), on the performance of anoxic denitrification by polyphosphate accumulating organisms. Results indicate that oxygen production was more dependent on the light availability than on the CO2 concentration. Also, under operational conditions with a COD:Na2CO3 ratio of 8.3 mg COD/mg C and an average light availability of 5.4 ± 1.3 W h/g TSS, no internal PHA limitation was observed, and 95 ± 7%, 92 ± 5% and 86 ± 5% of removal efficiency could be achieved for phosphorus, ammonia and total nitrogen, respectively. 81 ± 1.7% of the ammonia was assimilated into the microbial biomass and 19 ± 1.7% was nitrified, showing that biomass assimilation was the main N removal mechanism taking place in the bioreactor. Overall, the photo-BNR system presented a good settling capacity (SVI ∼60 mL/g TSS) and was able to remove 38 ± 3.3 mg P/L and 33 ± 1.7 mg N/L, highlighting its potential for achieving wastewater treatment without the need of aeration.
The phototrophic metabolic behaviour of Candidatus accumulibacter
Publication . Carvalho, V. C.F.; Gan, A. Z.M.; Shon, A.; Kolakovic, S.; Freitas, E. B.; Reis, M. A.M.; Fradinho, J. C.; Oehmen, A.; UCIBIO - Applied Molecular Biosciences Unit; IWA Publishing | Elsevier
The phototrophic capability of Candidatus Accumulibacter (Accumulibacter), a common polyphosphate accumulating organism (PAO) in enhanced biological phosphorus removal (EBPR) systems, was investigated in this study. Accumulibacter is phylogenetically related to the purple bacteria Rhodocyclus from the family Rhodocyclaceae, which belongs to the class Betaproteobacteria. Rhodocyclus typically exhibits both chemoheterotrophic and phototrophic growth, however, limited studies have evaluated the phototrophic potential of Accumulibacter. To address this gap, short and extended light cycle tests were conducted using a highly enriched Accumulibacter culture (95%) to evaluate its responses to illumination. Results showed that, after an initial period of adaptation to light conditions (approximately 4–5 h), Accumulibacter exhibited complete phosphorus (P) uptake by utilising polyhydroxyalkanoates (PHA), and additionally by consuming glycogen, which contrasted with its typical aerobic metabolism. Mass, energy, and redox balance analyses demonstrated that Accumulibacter needed to employ phototrophic metabolism to meet its energy requirements. Calculations revealed that the light reactions contributed to the generation of, at least more than 67% of the ATP necessary for P uptake and growth. Extended light tests, spanning 21 days with dark/light cycles, suggested that Accumulibacter generated ATP through light during initial operation, however, it likely reverted to conventional anaerobic/aerobic metabolism under dark/light conditions due to microalgal growth in the mixed culture, contributing to oxygen production. In contrast, extended light tests with an enriched Tetrasphaera culture, lacking phototrophic genes in its genome, clearly demonstrated that phototrophic P uptake did not occur. These findings highlight the adaptive metabolic capabilities of Accumulibacter, enabling it to utilise phototrophic pathways for energy generation during oxygen deprivation, which holds the potential to advance phototrophic-EBPR technology development.
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Fundação para a Ciência e a Tecnologia
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OE
Número da atribuição
PD/BD/114574/2016