Browsing by Author "Ometto, Francesco"

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    Data for the paper "Influence of light regime on the performance of an immobilised microalgae reactor for wastewater nutrient removal"
    (Cranfield University, 2019-10-31 18:14) Whitton, Rachel; Ometto, Francesco; Villa, Raffaella; Pidou, Marc; Jefferson, Bruce
    Wastewater nutrient remediation data using immobilised microalgae under differing light regimes including wavelength (nm), duty cycles and photoperiods (on:off cycles), light transmittance and attenuation depths.
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    Impacts of microalgae pre-treatments for improved anaerobic digestion: Thermal treatment, thermal hydrolysis, ultrasound and enzymatic hydrolysis
    (IWA Publishing, 2014-08-06) Ometto, Francesco; Quiroga, Gerardo; Psenǐckǎ, Pavel; Whitton, Rachel; Jefferson, Bruce; Villa, Raffaella
    Anaerobic digestion (AD) of microalgae is primarily inhibited by the chemical composition of their cell walls containing biopolymers able to resist bacterial degradation. Adoption of pre-treatments such as thermal, thermal hydrolysis, ultrasound and enzymatic hydrolysis have the potential to remove these inhibitory compounds and enhance biogas yields by degrading the cell wall, and releasing the intracellular algogenic organic matter (AOM). This work investigated the effect of four pre-treatments on three microalgae species, and their impact on the quantity of soluble biomass released in the media and thus on the digestion process yields. The analysis of the composition of the soluble COD released and of the TEM images of the cells showed two main degradation actions associated with the processes: (1) cell wall damage with the release of intracellular AOM (thermal, thermal hydrolysis and ultrasound) and (2) degradation of the cell wall constituents with the release of intracellular AOM and the solubilisation of the cell wall biopolymers (enzymatic hydrolysis). As a result of this, enzymatic hydrolysis showed the greatest biogas yield increments (>270%) followed by thermal hydrolysis (60–100%) and ultrasounds (30–60%).
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    The impacts of replacing air bubbles with microspheres for the clarification of algae from low cell-density culture
    (Elsevier, 2014-02-24) Ometto, Francesco; Pozza, Carlo; Whitton, Rachel; Smyth, Beatrice; Gonzalez Torres, Andrea; Henderson, Rita K.; Jarvis, Peter; Jefferson, Bruce; Villa, Raffaella
    Dissolved Air Flotation (DAF) is a well-known coagulation–flotation system applied at large scale for microalgae harvesting. Compared to conventional harvesting technologies DAF allows high cell recovery at lower energy demand. By replacing microbubbles with microspheres, the innovative Ballasted Dissolved Air Flotation (BDAF) technique has been reported to achieve the same algae cell removal efficiency, while saving up to 80% of the energy required for the conventional DAF unit. Using three different algae cultures (Scenedesmus obliquus, Chlorella vulgaris and Arthrospira maxima), the present work investigated the practical, economic and environmental advantages of the BDAF system compared to the DAF system. 99% cells separation was achieved with both systems, nevertheless, the BDAF technology allowed up to 95% coagulant reduction depending on the algae species and the pH conditions adopted. In terms of floc structure and strength, the inclusion of microspheres in the algae floc generated a looser aggregate, showing a more compact structure within single cell alga, than large and filamentous cells. Overall, BDAF appeared to be a more reliable and sustainable harvesting system than DAF, as it allowed equal cells recovery reducing energy inputs, coagulant demand and carbon emissions.
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    Improving the energy balance of an integrated microalgal wastewater treatment process
    (2014-04-01T00:00:00Z) Ometto, Francesco; Whitton, Rachel; Coulon, Frederic; Jefferson, Bruce; Villa, Raffaella
    The inclusion of a microalgal system in a wastewater treatment flowsheet for residual nutrient uptake can be justified by processing the waste biomass for energy recovery. Low energy harvesting technologies and pre-treatment of the algal biomass are required to improve the overall energy balance of this integrated system. Scenedesmus obliquus and Chlorella sp., achieving nitrogen and phosphorus removal rates higher than 90 %, were used to compare cells recovery efficiency and energy requirements of two energy efficient harvesting systems: dissolved air flotation (DAF) and ballasted dissolved air flotation (BDAF). In addition, thermal hydrolysis was used as a pre-treatment to improve biogas production during anaerobic digestion. The energy required for both systems was then considered to estimate the daily energy demand and efficiency of two microalgae wastewater treatment plants with a capacity of 25,000 and 230,000 p.e., respectively. Overall, a high algal cells recovery efficiency (99 %) was achieved using low energy demand (0.04 kWh m-3 for BDAF) and a coagulant dose reduction between 42 and 50 % depending on the algal strain. Anaerobic digestion of pre-treated S. obliquus showed a threefold increase in methane yield. Compared to a traditional activated sludge process, the additional tertiary microalgal treatment generates an integrated process potentially able to achieve up to 76 % energy efficiency.
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    Influence of light regime on the performance of an immobilised microalgae reactor for wastewater nutrient removal
    (Elsevier, 2019-10-23) Whitton, Rachel; Ometto, Francesco; Villa, Raffaella; Pidou, Marc; Jefferson, Bruce
    Microalgae immobilised within a resin shaped into beads have demonstrated the ability to remediate nutrients from wastewater effluents within hydraulic retention times as low as 3 h. Methods to further optimise performance consider parameters relating to the bead with the impact of external conditions seldom investigated. Light is an essential parameter for microalgal growth with its effect on suspended cultures well documented. This work explores the influence of light on nutrient remediation by immobilised microalgae in order to recommend an optimal lighting solution for an immobilised microalgae technology based on Scenedesmus obliquus encapsulated within calcium-alginate beads. White light (400–700 nm) at a photon flux density (PFD) of 200 μmol∙m−2∙s−1 was determined optimal when illuminating a packed bed configuration. When considering phosphate, these conditions supported a remediation rate of 10.7 (± 0.01) mgP∙h−1∙106 beads−1 in comparison to 10.2 (± 0.01) and 10.1 (± 0.01) mgP∙h−1∙106 beads−1 for the blue (465 nm) and red (660 nm) spectra respectively. Although similar performance was demonstrated, light transmission trials determined white light to penetrate to greater bed depths resulting in a larger photoactive zone. A PFD of 200 μmol∙m−2∙s−1 was regarded as optimal when considering performance, attenuation depth and effective use of total supplied light. In addition, photoperiods trials determined lighting periods <12 h extended the overall treatment time.
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    Influence of microalgal N and P composition on wastewater nutrient remediation
    (IWA Publishing, 2016-01-04) Whitton, Rachel; Le Mevel, Amandine; Pidou, Marc; Ometto, Francesco; Villa, Raffaella; Jefferson, Bruce
    Microalgae have demonstrated the ability to remediate wastewater nutrients efficiently, with methods to further enhance performance through species selection and biomass concentration. This work evaluates a freshwater species remediation characteristics through analysis of internal biomass N:P (nitrogen:phosphorus) and presents a relationship between composition and nutrient uptake ability to assist in species selection. Findings are then translated to an optimal biomass concentration, achieved through immobilisation enabling biomass intensification by modifying bead concentration, for wastewaters of differing nutrient concentrations at hydraulic retention times (HRT) from 3 h to 10 d. A HRT <20 h was found suitable for the remediation of secondary effluent by immobilised Scenedesmus obliquus and Chlorella vulgaris at bead concentrations as low as 3.2 and 4.4 bead·mL−1. Increasing bead concentrations were required for shorter HRTs with 3 h possible at influent concentrations <5 mgP L−1.
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    Microalgae for municipal wastewater nutrient remediation: mechanisms, reactors and outlook for tertiary treatment
    (Taylor and Francis, 2015-11-03) Whitton, Rachel; Ometto, Francesco; Pidou, Marc; Jarvis, Peter; Villa, Raffaella; Jefferson, Bruce
    This review explores the use of microalgae for nutrient removal in municipal wastewater treatment, considering recent improvements in the understanding of removal mechanisms and developments of both suspended and non-suspended systems. Nutrient removal is associated to both direct and indirect uptake, with the former associated to the biomass concentration and growth environment (reactor). Importantly, direct uptake is influenced by the Nitrogen:Phosphorus content in both the cells and the surrounding wastewater, with opposite trends observed for N and P. Comparison of suspended and non-suspended systems revealed that whilst all were capable of achieving high levels of nutrient removal, only non-suspended immobilized systems could do so with reduced hydraulic retention times of less than 1 day. As microalgae are photosynthetic organisms, the metabolic processes associated with nutrient assimilation are driven by light. Optimization of light delivery remains a key area of development with examples of improved mixing in suspended systems and the use of pulsating lights to enhance light utilization and reduce costs. Recent data provide increased confidence in the use of microalgae for nutrient removal in municipal wastewater treatment, enabling effluent discharges below 1 mg L−1 to be met whilst generating added value in terms of bioproducts for energy production or nutrient recovery. Ultimately, the review suggests that future research should focus on non-suspended systems and the determination of the added value potential. In so doing, it is predicted that microalgae systems will be significant in the delivery of the circular economy.
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    Microalgae to energy: biomass recovery and pre-treatments optimisation for biogas production integrated with wastewater nutrients removal
    (Cranfield University, 2014-01) Ometto, Francesco; Villa, Raffaella; Jefferson, Bruce
    The increasing concern about water quality and energy demand promotes the development of innovative and low-cost processes to improve the nutrient uptake and energy efficiency of existing wastewater treatments (WWT). In this context, the inclusion of a microalgae system (MAS) in the flowsheet of a WWT plant represents a sustainable alternative to conventional technologies, as it combines a low-cost nutrient uptake system with the production of biomass suitable for biofuel production. However, at present, the energy required to cultivate and process the algae cells is often too high to justify their use. The adoption of a low energy harvesting system and an efficient energy conversion process are the sine qua non requirements to guarantee the sustainability of the process. In this thesis, current and innovative harvesting technologies for large scale applications have been reviewed to identify the optimal working conditions of each system and their link to the main characteristics of the algae suspension. In particular, the performance of the Ballasted Dissolved Air Flotation (BDAF) system was investigated using different algae and compared to the conventional Dissolved Air Flotation (DAF). BDAF was demonstrably a very viable harvesting method where the use of floating microspheres as ballasting agents allowed significant coagulant savings, reduced the level of energy dissipation within the flotation chamber, and lowered the overall carbon emissions and the process costs. Cont/d.
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    Tertiary nutrient removal from wastewater by immobilised microalgae: impact of wastewater nutrient characteristics and hydraulic retention time (HRT)
    (IWA Publishing, 2018-03-15) Whitton, Rachel; Santinelli, Martina; Pidou, Marc; Ometto, Francesco; Henderson, Rita; Roddick, Felicity; Jarvis, Peter; Villa, Raffaella; Jefferson, Bruce
    Immobilising microalgal cells has been proposed as a process solution to overcome the barriers associated with the implementation of microalgae for wastewater remediation. This work evaluated the performance and remediation mechanisms of immobilised microalgae for continuous wastewater treatment under varying hydraulic retention times (HRT). Three domestic secondary wastewaters with differing concentrations of orthophosphate (PO4-P), ammonium (NH4-N) and nitrate (NO3-N) were treated by Scenedesmus obliquus immobilised within 2% calcium alginate. Trials were run in continuous operation at HRTs of 3, 6, 12 and 20 h. Removal rates for PO4-P improved with increasing HRT, with minimum residual concentrations of 0.3–3.1 mg·L−1 observed at 3 h and 0.01–0.2 mg·L−1 at 20 h. Ammonium remediation was not linked to HRT or NH4+ concentration with minimum residual concentrations of <0.001 mg·L−1. Reduction in NO3-N improved with increasing HRT, with minimum residual concentrations of ≤19.3 at 3 h and ≤0.4 mg·L−1 at 20 h. Remediation was achieved through a combination of mechanisms including biological uptake and precipitation as a by-product of photosynthesis and nutrient metabolism. As such, immobilised microalgae have been proven to be an effective alternative solution for PO43− and NH4+ remediation of wastewater effluents at HRTs of 6–12 h.