DEP48 - Artículos de revista

Influence of biomilking on methanotrophs cultivation during biogas conversion into ectoines

Thu, 01 Jan 2026 00:00:00 GMT

Ectoine is one of the most profitable value chains for biogas valorisation. This study assessed the long-term effects of biomilking for ectoine (Ect) and hydroxyectoine (Hy) extraction on upstream methane bioconversion into ectoines using a halotolerant methanotrophic consortium cultivated in a Taylor-Flow bioreactor. After a control stage (S-I), fractions of the culture broth volume of 10 %, 50 %, 30 % and 60 % (S-II to S-VI) were subjected to biomilking before a final control (S-VII). No adverse effects were observed at 10 %, while higher fractions led to salt depletion, a ∼10 % reduction in CH4 bioconversion efficiency, and a loss of dominant ectoine producers, mainly Methylomicrobium. A decrease in intracellular Ect was also observed. Restoring salt levels (S-VI) recovered Methylomicrobium dominance and Ect content in the culture broth. Enhanced biomilking yielded up to 27.2 g-Ect + Hy per inlet kg of CH4, supporting its feasibility for sustainable biogas valorisation at a commercial scale.

Influence of design and operational parameters of a Taylor flow reactor on the bioconversion of methane to ectoines

Mon, 01 Jan 2024 00:00:00 GMT

Ectoine is one of the most attractive bioproducts due to its high market price and applications. Methanotrophic bacteria can synthesize ectoine from biogas. In this work, key design and operating parameters were optimised to maximise the bioconversion of methane to ectoine in a novel Taylor Flow bioreactor. This bioreactor configuration is characterized by higher gas-liquid mass transfer coefficients compared to conventional bubble column bioreactors. Thus, the influence of the internal gas recirculation flow rate (1.0 L·min−1, 2.5 L·min−1, 4.0 L·min−1, 5.5 L·min−1) at 60 and 120 min of gas residence time (GRT), the liquid recirculation flow rate (0 L·h−1, 141 L·h−1, 165 L·h−1, 395 L·h−1, 434 L·h−1) and the capillary length (1.50 and 0.75 m) was evaluated using a mixed methanotrophic consortium. Process operation at 120 min of GRT and 5.5 L·min−1 of gas recirculation flow rate enhanced methane bioconversion, resulting in a maximum efficiency of 83.8 ± 2.7 %. The decrease in capillary length from 1.5 to 0.75 m did not enhance methane bioconversion. Intracellular ectoine and hydroxyectoine reached maximum contents of 105.1 ± 8.6 mgEC·gTSS−1 and 33.4 ± 11.7 mgHE·gTSS−1, respectively. Nitratireductor was the dominant genus, while Methylomicrobium and Methylophaga were the main methanotrophic bacteria detected in the consortium. This study confirmed the feasibility of bioconverting novel renewable feedstocks such biogas into high-added value bio-products, boosting the circular and carbon neutral economy in bio-based industries.

Thermally self-sufficient process for single-step coproduction of methanol and dimethyl ether by CO2 hydrogenation

Mon, 01 Jan 2024 00:00:00 GMT

Methanol and DME are highly efficient fuels and relevant building blocks that can be synthesized by CO2 hydrogenation. While several alternatives for methanol production by CO2 hydrogenation have already been developed at a commercial scale, DME production is still based on methanol dehydration. In this sense, the development of bifunctional methanol synthesis/dehydration catalysts is a clear opportunity for the simultaneous coproduction of methanol and DME in a single-step process. Although a few alternatives for DMEmethanol coproduction have been proposed, either they need external fuels or refrigerants, or part of the CO2 used as raw material is purged, resulting in a loss of methanol and DME yields. This work presents a novel thermally self-sufficient process that hydrogenates CO2 into methanol and DME in a single reactor at 100 % yield (only water as a byproduct at 0.94 kgwater/kgproduct), that only consumes air, cooling water (0.006 m3 water/kgproducts) and electricity (net CO2 emissions of − 1.20 or 0.64 kgCO2eq/kgproducts when the plant is operated with green or grey electricity, respectively). The innovative design, based on the combination of a top-divided wall column, an integrated heat network, and limited pressure drop in the reaction-separation loop, results in a thermally self-sufficient process that uses only 0.76 kWh per kg products.

Thermally self-sufficient process for cleaner production of e-methanol by CO2 hydrogenation

Sun, 01 Jan 2023 00:00:00 GMT

The hydrogenation of CO2 to methanol is a technology that converts a greenhouse gas into a valuable chemical compound that efficiently stores energy. Several alternatives to perform this process have been proposed, but they are either not thermally self-sufficient and depend on using external fuel, or the power usage per ton of methanol is insufficiently optimized, or part of the raw materials must be purged and therefore there is a loss of methanol yield. This original study aims to develop a novel thermally self-sufficient process for e-methanol production (at practically 100% yield along with water by-product of 0.37 kgwater/kgproduct) that only uses green lectricity. The main innovation of the process is an effective thermally self-sufficient heat-integration scheme that only needs 0.0059 m3 water/kgmethanol combined with using a dividing wall column to recover the unreacted CO2 and obtain high purity methanol. In addition, the pressure reduction in the reaction-separation loop is limited to the pressure drop of the circuit to minimize the overall green electricity use to only 656 kWh per ton methanol, resulting in net CO2 emissions of − 1.13 gCO2/kgMeOH or 0.78 kgCO2/kgMeOH when the plant operates with green or grey hydrogen and electricity, respectively. Finally, the operating pressure in the reactor is optimized at 65 bar to minimize the total annualized cost.

Net-zero sustainable aviation fuel (SAF) production via CO2 hydrogenation in low-temperature Fischer-Tropsch synthesis: Process design and alternatives

Wed, 01 Jan 2025 00:00:00 GMT

Sustainable Aviation Fuel (SAF) is fundamental for decarbonizing the aviation sector, which remains one of the hardest industries to electrify. Among the available production routes, SAF derived from indirect CO₂ hydrogenation stands out as a promising alternative, delivering drop-in fuels compatible with existing infrastructure. This work presents and compares three thermally self-sufficient process alternatives for SAF production from captured CO₂, green hydrogen, and renewable electricity. The base case follows a conventional configuration consisting of Reverse Water Gas Shift (RWGS), Fischer-Tropsch (FT), hydrocracker, and Auto-Thermal Reformer (ATR) reactors. The first alternative replaces the ATR with two furnaces and substitutes the PSA-based CO₂ separation with an amine absorption unit. It also includes an isomerization bed to reduce SAF’s freezing point, a Dividing Wall Column (DWC) for efficient separation, and a steam turbine to recover part of the plant’s power demand. The second alternative retains the ATR while integrating CO₂ capture, the isomerization bed, and the DWC. The analysis shows that maintaining the ATR reactor reduces hydrogen consumption (0.52 kg H₂ per kg of products in the second alternative), being economically more favorable (3.65 €/L of SAF) than minimizing power consumption (716 kWh per ton of products in the first alternative), given the high cost of electrolytic hydrogen. In addition, the DWC proves to be the most efficient separation option, requiring the lowest reboiler duty and the fewest trays. All process configurations produce water as the only byproduct (approximately 3.3 kg H₂O/kg products), and achieve net-negative greenhouse gas emissions of up to − 2 kg CO₂eq per kg of product.

Water‐Energy Nexus: Benchmarking the Energy Efficiency of Drinking Water Treatment Plants Accounting for Heterogeneity

Thu, 01 Jan 2026 00:00:00 GMT

The assessment of energy efficiency in water facilities is receiving increasing attention as a key strategy in the transition toward an energy-neutral urban water cycle. This study evaluates the energy efficiency of 146 drinking water treatment plants (DWTPs) in Chile by applying a latent class stochastic frontier analysis (LCSFA) to account for both observable and unobservable sources of heterogeneity. Unlike traditional models that assume homogeneity across units, the LCSFA approach identified two distinct groups of DWTPs with significantly different operational characteristics, pollutant loads, and efficiency profiles. Group 1 exhibited an average energy efficiency score of 0.534, while Group 2 showed a significantly higher average of 0.737. In Group 1, efficiency scores estimated under the pooled frontier are higher than those obtained from the latent class model for 73% of DWTPs, whereas in Group 2 the pooled frontier yields lower efficiency scores for 58% of plants. The analysis also revealed substantial energy-saving opportunities. Group 1 facilities could reduce energy use by an average of 0.112 kWh/m3, compared to 0.044 kWh/m3 in Group 2. These findings demonstrate the importance of adopting heterogeneity-aware methods for fair and accurate benchmarking. The study offers methodological innovation and practical insights for regulators and utility managers aiming to design targeted energy efficiency interventions and performance-based incentives in the water sector.

Assessing Eco‐Efficiency in Municipal Solid Waste Management Integrating Heterogeneity: A Latent Class Stochastic Frontier Analysis

Thu, 01 Jan 2026 00:00:00 GMT

The measurement of eco-efficiency in the municipal solid waste (MSW) sector has garnered significant attention due to the substantial environmental impacts of unsustainable MSW management and the high operational costs associated with public service provision. Given the heterogeneous nature of municipalities providing MSW services, a robust method is necessary to account for technological differences when assessing eco-efficiency. This allows for consistent comparisons and reliable policy recommendations. In this study, we applied a latent class Stochastic Frontier Analysis (SFA) model that accommodates technological heterogeneity without requiring predefined groups of municipalities. A case study of 297 Chilean municipalities that collect, dispose of, and recycle MSW was conducted. The analysis identified two distinct groups of municipalities based on operational scale and waste management patterns. Group 1, composed of larger municipalities, exhibited lower eco-efficiency scores, with an average eco-efficiency score of 0.595. In contrast, Group 2, consisting of smaller municipalities, achieved a higher eco-efficiency score of 0.862. While population density influenced eco-efficiency in both groups, its effect was more pronounced in smaller municipalities. These findings underscore the need for targeted policies aimed at improving eco-efficiency in the MSW sector.

Assessment of a deep, LED-enhanced high-rate algal pond for the treatment of digestate

Fri, 01 Jan 2021 00:00:00 GMT

High Rate Algal Ponds (HRAP) are a sustainable alternative for wastewater treatment. However, HRAPs must be shallow (h = 0.2–0.3 m) for adequate sunlight penetration and require relatively long hydraulic retention times (HRT, >5 d) for effective pollutant removal, which results in high area footprints. In this context, a deep HRAP (h = 1.2 m) was equipped with red light-emitting diodes (LED, 660 nm) to provide photosynthetic active radiation in the aphotic zone. A conventional HRAP (HRAP1) and the LED-enhanced HRAP (HRAP2) were operated with identical working volumes (1.25 m3) and HRT (10 d), treating digestate dilutions of 5% (Stages S-0, S-I), 25% (S-II, S-III) and 50% (v/v) (S-IV to S-VI). The HRAP2 used only 25% of the area needed by the HRAP1 but LEDs used 1.4 (S-0 to S-II), 2.3 (S-III, S-IV) and 3.4 (S-V) times the energy consumed in HRAP1. HRAP2 presented similar performance to HRAP1 during the treatment of 5% and 25%-digestate, achieving removals above 75% for TSS, COD, TAN, and TKN. However, HRAP1 showed better treatment performance at 50%-digestate, likely due to more intense light radiation induced by its shallow depth, resulting in higher microalgal activity. Biomass productivity decreased with increasing digestate concentration, showing averages in HRAP1 and HRAP2 of 9 and 3 gVSS·m−2d−1, respectively, during feeding with 5%-digestate. With 25%, average productivities ranged from 2 to 5 and 2 to 6 gVSS·m−2d−1, and from 0 to 6 and 0 to 4 gVSS·m−2d−1 with 50%-digestate, respectively. Both systems showed reasonable nitrogen and phosphorus recoveries in the biomass (TN: 8–17% and 6–34%; TP: 10–45% and 5–48% for HRAP1 and HRAP2, respectively). Nitrogen volatilization, likely as NH3, N2O, and N2, was caused by stripping and nitrification-denitrification in both systems. Our data suggest that using LED-lighting to complement sunlight in deeper HRAPs is a promising alternative for enhancing microalgae-based reactors for digestate treatment.

Assessment of the performance of an anoxic-aerobic microalgal-bacterial system treating digestate

Fri, 01 Jan 2021 00:00:00 GMT

he performance of an anoxic-aerobic microalgal-bacterial system treating synthetic food waste digestate at 10 days of hydraulic retention time via nitrification-denitrification under increasing digestate concentrations of 25%, 50%, and 100% (v/v) was assessed during Stages I, II and III, respectively. The system supported adequate treatment without external CO2 supplementation since sufficient inorganic carbon in the digestate was available for autotrophic growth. High steady-state Total Organic Carbon (TOC) and Total Nitrogen (TN) removal efficiencies of 85–96% and 73–84% were achieved in Stages I and II. Similarly, -P removals of 81 ± 15% and 58 ± 4% were recorded during these stages. During Stage III, the average influent concentrations of 815 ± 35 mg TOC·L−1, 610 ± 23 mg TN·L−1, and 46 ± 11 mg -P·L−1 induced O2 limiting conditions, resulting in TOC, TN and -P removals of 85 ± 3%, 73 ± 3%, and 28 ± 16%, respectively. Digestate concentrations of 25% and 50% favored nitrification-denitrification mechanisms, whereas the treatment of undiluted digestate resulted in higher ammonia volatilization and hampered nitrification-denitrification. In Stages I and II, the microalgal community was dominated by Chlorella vulgaris and Cryptomonas sp., whereas Pseudoanabaena sp. was more abundant during Stage III. Illumina sequencing revealed the presence of carbon and nitrogen transforming bacteria, with dominances of the genera Gemmata, Azospirillum, and Psychrobacter during Stage I, II, and III, respectively. Finally, the high settleability of the biomass (98% of suspended solids removal in the settler) and average C (42%), N (7%), P (0.2%), and S (0.4%) contents recovered in the biomass confirmed its potential for agricultural applications, contributing to a closed-cycle management of food waste.

Physicochemical and diatom trophic state indexes: A complementary approach for improving water sustainability in a high Andean urban stream

Tue, 01 Jan 2019 00:00:00 GMT

Discharge of untreated wastewater into freshwater ecosystems increases nutrient concentrations, causing eutrophication and demanding more intensive monitoring and control activities, particularly in developing areas. Two approaches are commonly used for assessing trophic states of rivers: (1) physicochemical trophic state indexes (TSIs), and (2) trophic indexes based on bioindicators, mainly periphytic diatoms (TDIs). Even when these two approaches seem to be very different, they can be complementary under certain circumstances. This is the case with Río Chili (Arequipa, Peru), a shallow regulated river used for multi-purpose activities, but which is highly polluted due to the discharge of municipal wastewater. The present study assessed the suitability of different TSIs and TDIs by processing data from historical water quality registers and recent monitoring, including periphytic diatom sampling. TDIs were compared with TSIs applied to both recent and historical records. Results indicated that TSIs can be easily obtained from measurements of phosphorus concentrations, but they are less sensitive and resulted in a high degree of homogeneity among the classification of trophic conditions along the urban path of the river. Alternatively, TDIs showed higher precision and sensitivity, reporting detailed classifications of the sampling points. TDIs suggested that Río Chili presented conditions that varied from mesotrophic to eutrophic as consequence of wastewater discharges and soil occupation. A routine use of TDIs with occasional assessment by physicochemical TSIs may contribute to water quality sustainability by informing managers of the effects of organic and phosphorus pollution on eutrophication at a lower cost.

Viability of SARS-CoV-2 in river water and wastewater at different temperatures and solids content

Fri, 01 Jan 2021 00:00:00 GMT

COVID-19 patients can excrete viable SARS-CoV-2 virus via urine and faeces, which has raised concerns over the possibility of COVID-19 transmission via aerosolized contaminated water or via the faecal-oral route. These concerns are especially exacerbated in many low- and middle-income countries, where untreated sewage is frequently discharged to surface waters. SARS-CoV-2 RNA has been detected in river water (RW) and raw wastewater (WW) samples. However, little is known about SARS-CoV-2 viability in these environmental matrices. Determining the persistence of SARS-CoV-2 in water under different environmental conditions is of great importance for basic assumptions in quantitative microbial risk assessment (QMRA). In this study, the persistence of SARS-CoV-2 was assessed using plaque assays following spiking of RW and WW samples with infectious SARS-CoV-2 that was previously isolated from a COVID-19 patient. These assays were carried out on autoclaved RW and WW samples, filtered (0.22 µm) and unfiltered, at 4 °C and 24 °C. Linear and nonlinear regression models were adjusted to the data. The Weibull regression model achieved the lowest root mean square error (RMSE) and was hence chosen to estimate T90 and T99 (time required for 1 log and 2 log reductions, respectively). SARS-CoV-2 remained viable longer in filtered compared with unfiltered samples. RW and WW showed T90 values of 1.9 and 1.2 day and T99 values of 6.4 and 4.0 days, respectively. When samples were filtered through 0.22 µm pore size membranes, T90 values increased to 3.3 and 1.5 days, and T99 increased to 8.5 and 4.5 days, for RW and WW samples, respectively. Remarkable increases in SARS-CoV-2 persistence were observed in assays at 4 °C, which showed T90 values of 7.7 and 5.5 days, and T99 values of 18.7 and 17.5 days for RW and WW, respectively. These results highlight the variability of SARS-CoV-2 persistence in water and wastewater matrices and can be highly relevant to efforts aimed at quantifying water-related risks, which could be valuable for understanding and controlling the pandemic.

Treatment of food waste digestate using microalgae-based systems with low-intensity light-emitting diodes

Mon, 01 Jan 2018 00:00:00 GMT

Anaerobic digestion of food wastes coupled with digestate post-treatment using microalgae-based systems could recover large amounts of energy and nutrients worldwide. However microalgae inhibition by high ammonia concentrations and low light transmittances affecting photosynthesis should be overcome to develop full scale implementations. This study evaluated the potential of microalgae-based reactors supplied with red LEDs at low intensity (660 nm and 15 μmol·m-2·s-1) to treat food waste digestate. LED reactors were compared with control reactors exposed to natural solar radiation. From a range of species in the inoculum, Chlorella vulgaris showed high adaptation to both lighting regimes and digestate environmental conditions, characterized by a C:N:P ratio of 74:74:1. Removal efficiencies for control and LED reactors were 84.0% and 95.8 % for soluble COD and 89.4% and 53.0 % for ammonia, respectively. Approximately 50% of ammonia in control reactor and 15% in LED reactor was lost mainly through volatilization, whereas 17% and 36% of ammonia was transformed in organic nitrogen in control and LED reactors, respectively. Low-intensity LEDs maintained microalgae growth in levels similar to solar radiation and supported efficient digestate treatment, showing a potential for further application in optimization of full scale reactors at a relatively low energy cost.

Long-term influence of high alkalinity on the performance of photosynthetic biogas upgrading

Wed, 01 Jan 2020 00:00:00 GMT

The alkalinity of the cultivation medium plays a key role on photosynthetic biogas upgrading, exerting impact not only on the mass-transfer of CO2 and H2S in the biogas scrubbing column but also on the subsequent CO2 uptake or stripping to the atmosphere. The long-term performance of algal-bacterial processes devoted to the concomitant removal of CO2 and H2S from biogas in a 180 L open pond interconnected to a 2.5 L biogas scrubbing column via an external liquid recirculation of supernatant from a 8 L conical settler under process operation at high inorganic carbon (IC) concentrations was assessed. The influence of biomass concentration in the cultivation medium on process performance was also evaluated. CO2 concentrations in the upgraded biogas fluctuated between 1.5 and 4.4% at IC concentrations in the cultivation medium of 1200 mg C/L, and remained almost constant (0.7 ± 0.1%) at IC concentrations > 2400 mg C/L. However, the increase in the IC concentration from 1203 to 3476 mg C/L entailed an increase in C-CO2 stripping from 14.5 to 33.4% of the IC input to the system. The increase in biomass concentration from 0.33 to 1.38 g SSV/L entailed a reduction in CO2 removal of 1.1% even under process operation at high alkalinity. H2S removal efficiencies of 100% were achieved regardless the IC or biomass concentration.

Development of a control strategy to cope with biogas flowrate variations during photosynthetic biogas upgrading

Tue, 01 Jan 2019 00:00:00 GMT

The design and evaluation of a control system for a photosynthetic biogas upgrading unit was successfully carried out in this study. This control system ensured a specific biomethane quality under any disturbance in the biogas flowrate. The recycling liquid flowrate, and indirectly the liquid to biogas (L/G) ratio, was selected as the manipulated variable in order to maintain the CO2 and O2 content of biomethane, and therefore comply with the requirements for its use as natural gas substitute (<2.5% and <1.0%, respectively). The control system was able to maintain the biomethane CO2 content below the set point value under a stepwise increase in the biogas flowrate from 60 to 150 ml/min, together with negligible H2S concentrations and an O2 stripping from the recycling liquid to the biomethane lower than 1%, thus obtaining a consistent biomethane quality over time. On the contrary, the biomethane CO2 content increased up to 13.2% under this stepwise increase in the biogas flowrate without control system. Successful results were also obtained when the control system was challenged with stepwise surges in the biogas flowrate between 60 and 120 ml/min under different temperatures (15 and 35 ºC) and inorganic carbon concentrations (1500, 500 and 100 mg/L) when the recycling liquid entering the absorption column presented a pH 10. However, the high liquid flowrates required at a cultivation broth pH of 8.5 as a result of the low CO2 mass transfer led to an excessive O2 desorption to the biomethane, resulting in biomethane O2 contents >1%.

Influence of alkalinity and temperature on photosynthetic biogas upgrading efficiency in high rate algal ponds

Mon, 01 Jan 2018 00:00:00 GMT

Algal-bacterial photobioreactors have emerged as a cost-effective platform for biogas upgrading. The influence on biomethane quality of the inorganic carbon concentration (1500, 500 and 100 mg L−1) and temperature (12 and 35 °C) of the cultivation broth was evaluated in a 180 L high rate algal pond (HRAP) interconnected to a 2.5 L absorption column via settled broth recirculation. The highest CO2 and H2S removal efficiencies (REs) from biogas were recorded at the highest alkalinity (CO2-REs of 99.3 ± 0.1 and 97.8 ± 0.8% and H2S-REs of 96.4 ± 2.9 and 100 ± 0% at 12 and 35 °C, respectively), which resulted in CH4 concentrations of 98.9 ± 0.2 and 98.2 ± 1.0% at 12 and 35 °C, respectively, in the upgraded biogas. At the lowest alkalinity, the best upgrading performance was observed at 12 °C (CO2 and H2S-REs of 41.5 ± 2.0 and 80.3 ± 3.9%, respectively). The low recycling liquid to biogas ratio applied (0.5) resulted in a negligible O2 stripping regardless of the alkalinity and temperature, which entailed a biomethane O2 content ranging from 0 to 0.2 ± 0.3%.

The Influence of Environmental Variables on the Carbon Performance of Water Companies Across Time

Wed, 01 Jan 2025 00:00:00 GMT

One of the main challenges that water companies face is to reduce carbon footprint in their transition to carbon neutrality. Past research assessing carbon performance of water companies has mostly ignored heterogeneity among the water companies evaluated. To overcome this limitation, this study employed a parametric metafrontier approach to assess and compare carbon performance of a sample of English and Welsh water companies, embracing water and sewerage companies (WaSCs) and water-only companies (WoCs). This method allows for a comparison of the carbon performance of these two types of companies and analyses the impact of environmental variables on their performance. It was evidenced that water treatment complexity, main source of raw water, and population density significantly influence carbon performance of water companies. The average carbon efficiency for WaSCs was 0.816, indicating marginally superior performance compared to WoSCs, which had an average carbon efficiency of 0.803. Regarding carbon productivity between 2011 and 2020, WoSCs demonstrated an annual improvement in carbon performance of 2.9%, while WaSCs showed an annual decrease in carbon productivity of 4.2%. The insights gained from this study are highly significant for policymakers focused on transitioning the water industry toward net-zero carbon emissions.