• Energy Research

Abstract The growing production of non-recyclable urban wastes generates environmental problems that impose new alternatives for their energetic valorisation. Nonetheless, some of these wastes do not have adequate properties to be directly used in waste-to-energy technologies, thus requiring adequate pre-treatments to improve their fuel properties. This work aimed to evaluate dry and hydrothermal carbonisation (DC and HTC) as technologies to convert solid recovered fuel (SRF) from construction and municipal solid wastes to biochars or hydrochars with improved fuel quality. The operational parameters evaluated were temperature, mass ratio of SRF:water, and incorporation of a liquid additive (used cooking oil, UCO). The chars were characterised for chemical composition, calorific value, TGA profiles and surface functional groups. The chemical oxygen demand (COD), concentration of total phenols, pH, conductivity and the main components in process waters were determined. Results showed an improvement of fuel characteristics in terms of hydrophobicity and calorific value, enabling the use of chars for waste-to-energy technologies. HTC produced hydrochars with better fuel characteristics, presenting calorific values of 28–33 MJ/kg db, and lower average ash and chlorine contents (2.8 wt% db and 3.1 wt% db, respectively). The addition of UCO improved these fuel characteristics. However, the generation of an effluent that needs further decontamination and the lower amount of moisture present in SRF possibly made DC more attractive in terms of energy and costs requirements. A treatment at 350 °C during 30 min was recommended for a good compromise among process costs and char properties.

Abstract The growing production of non-recyclable urban wastes generates environmental problems that impose new alternatives for their energetic valorisation. Nonetheless, some of these wastes do not have adequate properties to be directly used in waste-to-energy technologies, thus requiring adequate pre-treatments to improve their fuel properties. This work aimed to evaluate dry and hydrothermal carbonisation (DC and HTC) as technologies to convert solid recovered fuel (SRF) from construction and municipal solid wastes to biochars or hydrochars with improved fuel quality. The operational parameters evaluated were temperature, mass ratio of SRF:water, and incorporation of a liquid additive (used cooking oil, UCO). The chars were characterised for chemical composition, calorific value, TGA profiles and surface functional groups. The chemical oxygen demand (COD), concentration of total phenols, pH, conductivity and the main components in process waters were determined. Results showed an improvement of fuel characteristics in terms of hydrophobicity and calorific value, enabling the use of chars for waste-to-energy technologies. HTC produced hydrochars with better fuel characteristics, presenting calorific values of 28–33 MJ/kg db, and lower average ash and chlorine contents (2.8 wt% db and 3.1 wt% db, respectively). The addition of UCO improved these fuel characteristics. However, the generation of an effluent that needs further decontamination and the lower amount of moisture present in SRF possibly made DC more attractive in terms of energy and costs requirements. A treatment at 350 °C during 30 min was recommended for a good compromise among process costs and char properties.

The use of microalgae to remediate raw effluent from brown crab aquaculture was evaluated by performing batch mode growth tests using separately the microalgae Chlorella vulgaris (Cv), Scenedesmus obliquus (Sc), Isochrysis galbana (Ig), Nannocloropsis salina (Ns), and Spirulina major (Sp). Removal efficiencies in batch growth were 100% for total nitrogen and total phosphorus for all microalgae. Chemical oxygen demand (COD) remediations were all above 72%. Biomass productivity varied from 20.9 mg L-1 day-1 (N. salina) to 146.4 mg L-1 day-1 (C. vulgaris). The two best performing algae were C. vulgaris and S. obliquus and they were tested in semi-continuous growth, reaching productivities of 879.8 mg L-1 day-1 and 811.7 mg L-1 day-1, respectively. The bioremediation of the effluent was tested with a transfer system consisting of three independent containers and compared with the use of a single container. The single container had the same capacity and received weekly the same volume of effluent as the three containers together. The remediation capacity of the 3 containers was much higher than the single one. The supplementation with NaNO3 was tested to improve the nutrient removal microalgae' capacity, with positive results. The removal efficiencies were 100% for total nitrogen and total phosphorus and higher than 96% for COD. The obtained C. vulgaris and S. obliquus biomass were composed of 31 and 35% proteins, 6 and 8% lipids, 39 and 30% carbohydrates, respectively. The composition of these biomass suggest that it can be used as novel and sustainable ingredients in aquaculture feeds. The algal biomass of Cv and Sc were used as biostimulants in the germination of wheat and watercress, and very promising results were attained, with increases in the germination index for Cv and Sc of 175% and 48% in watercress and 84% and 98% in wheat, respectively. The biomasses of Cv and Sc were also subjected to a torrefaction process with 72.5 ± 1.7% char yields. The obtained biochars were tested as biostimulants for germination seeds (wheat and watercress) and as bio-adsorbent of dye solutions.

The use of microalgae to remediate raw effluent from brown crab aquaculture was evaluated by performing batch mode growth tests using separately the microalgae Chlorella vulgaris (Cv), Scenedesmus obliquus (Sc), Isochrysis galbana (Ig), Nannocloropsis salina (Ns), and Spirulina major (Sp). Removal efficiencies in batch growth were 100% for total nitrogen and total phosphorus for all microalgae. Chemical oxygen demand (COD) remediations were all above 72%. Biomass productivity varied from 20.9 mg L-1 day-1 (N. salina) to 146.4 mg L-1 day-1 (C. vulgaris). The two best performing algae were C. vulgaris and S. obliquus and they were tested in semi-continuous growth, reaching productivities of 879.8 mg L-1 day-1 and 811.7 mg L-1 day-1, respectively. The bioremediation of the effluent was tested with a transfer system consisting of three independent containers and compared with the use of a single container. The single container had the same capacity and received weekly the same volume of effluent as the three containers together. The remediation capacity of the 3 containers was much higher than the single one. The supplementation with NaNO3 was tested to improve the nutrient removal microalgae' capacity, with positive results. The removal efficiencies were 100% for total nitrogen and total phosphorus and higher than 96% for COD. The obtained C. vulgaris and S. obliquus biomass were composed of 31 and 35% proteins, 6 and 8% lipids, 39 and 30% carbohydrates, respectively. The composition of these biomass suggest that it can be used as novel and sustainable ingredients in aquaculture feeds. The algal biomass of Cv and Sc were used as biostimulants in the germination of wheat and watercress, and very promising results were attained, with increases in the germination index for Cv and Sc of 175% and 48% in watercress and 84% and 98% in wheat, respectively. The biomasses of Cv and Sc were also subjected to a torrefaction process with 72.5 ± 1.7% char yields. The obtained biochars were tested as biostimulants for germination seeds (wheat and watercress) and as bio-adsorbent of dye solutions.

Studying the thermal decomposition of wood pellets is an important subject in order to understand the behavior of wood pellets during the combustion process. In fact, wood pellets have become an important fuel used in boiler combustion. The objective of this study is to investigate the mass loss and elemental analysis of pine wood pellets at various times and temperatures. Commercial pellets with a diameter of 6 mm were used. The experiment was conducted in the laboratory of the Engineering University of Minho. The pellets were burned in a small reactor of 1.36 kW with a maximum temperature range of 1150 °C. The data were observed at different temperatures: 264, 351, 444, 541, 650, and 734 °C, and at time intervals of 30, 60, 120, 180, 240, 300, 600, 900, 1200, and 3600 s. The results of the experiment revealed that the reaction rate increases with the temperature, and the higher the combustion temperature applied, the higher the mass loss of all substances observed. The remaining mass, as fixed carbon and ash or unburned substances, is about 3%. The residence time and temperature influence the species concentration of wood pellets.

Studying the thermal decomposition of wood pellets is an important subject in order to understand the behavior of wood pellets during the combustion process. In fact, wood pellets have become an important fuel used in boiler combustion. The objective of this study is to investigate the mass loss and elemental analysis of pine wood pellets at various times and temperatures. Commercial pellets with a diameter of 6 mm were used. The experiment was conducted in the laboratory of the Engineering University of Minho. The pellets were burned in a small reactor of 1.36 kW with a maximum temperature range of 1150 °C. The data were observed at different temperatures: 264, 351, 444, 541, 650, and 734 °C, and at time intervals of 30, 60, 120, 180, 240, 300, 600, 900, 1200, and 3600 s. The results of the experiment revealed that the reaction rate increases with the temperature, and the higher the combustion temperature applied, the higher the mass loss of all substances observed. The remaining mass, as fixed carbon and ash or unburned substances, is about 3%. The residence time and temperature influence the species concentration of wood pellets.

The main objective of this study was to assess the environmental risk of chars derived from the pyrolysis of mixtures of pine, plastics, and scrap tires, by studying their leaching potential and ecotoxicity. Relationships between chemical composition and ecotoxicity were established to identify contaminants responsible for toxicity. Since metallic contaminants were the focus of the present study, an EDTA washing step was applied to the chars to selectively remove metals that can be responsible for the observed toxicity. The results indicated that the introduction of biomass to the pyrolysis feedstock enhanced the acidity of chars and promote the mobilisation of inorganic compounds. Chars resulting from the pyrolysis of blends of pine and plastics did not produce ecotoxic eluates. A relationship between zinc concentrations in eluates and their ecotoxicity was found for chars obtained from mixtures with tires. A significant reduction in ecotoxicity was found when the chars were treated with EDTA, which was due to a significant reduction in zinc in chars after EDTA washing.