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Cr(III) dynamic removal in a fixed-bed column by using a co-gasification char

Publication . Dias, Diogo; Bernardo, Maria; Pinto, Filomena; Fonseca, Isabel Maria; Lapa, Nuno

ABSTRACT: A char (GC) obtained from the co-gasification of rice husk and polyethylene was used in a fixed-bed column with continuous flow for Cr(III) removal assays from synthetic and industrial wastewaters. For comparison purposes, a commercial activated carbon (CAC) was also used. The best experimental conditions in the continuous removal assays were the following ones: Cr(III) inflow concentration = 5 mg L-1, feed flow rate = 3 mL min(-1), mass of adsorbent in the column = 0.8 g, and inflow temperature = 50 degrees C. Under these conditions, the highest uptake capacities were 1.60 and 2.14 mg g(-1) in the synthetic solution, and 3.25 and 7.83 mg g(-1) in the industrial wastewater, for GC and CAC, respectively. These results are different from those obtained under batch conditions in which GC performed better than CAC. Cr(III) removal by both adsorbents occurred due to precipitation, but CAC presented a slightly higher amount of Cr(III) removed due to its highest porosity. The regeneration of GC and CAC was also studied, but both adsorbents showed no capacity to be used in more than one cycle. This study highlighted the importance of studying Cr(III) removal under continuous conditions, as the removal mechanisms may be completely different from the batch assays, affecting the adsorbents' performance.

2021-10Journal article

Open access

Cr(III) removal from synthetic and industrial wastewaters by using co-gasification chars of rice waste streams

Publication . Dias, Diogo; Lapa, Nuno; Bernardo, Maria; Ribeiro, W.; Matos, Inês; Fonseca, Isabel Maria; Pinto, Filomena

ABSTRACT: Blends of rice waste streams were submitted to co-gasification assays. The resulting chars (G1C and G2C) were characterized and used in Cr(III) removal assays from a synthetic solution. A Commercial Activated Carbon (CAC) was used for comparison purposes. The chars were non-porous materials mainly composed by ashes (68.3-92.6% w/w). The influences of adsorbent loading (solid/liquid ratio - S/L) and initial pH in Cr(III) removal were tested. G2C at a S/L of 5 mg L-1 and an initial pH of 4.50 presented an uptake capacity significantly higher than CAC (7.29 and 2.59 mg g(-1), respectively). G2C was used in Cr(III) removal assays from an industrial wastewater with Cr(III) concentrations of 50, 100 and 200 mg L-1. Cr(III) removal by precipitation (uptake capacity ranging from 11.1 to 14.9mg g(-1)) was more effective in G2C, while adsorption (uptake capacity of 16.1 mg g(-1)) was the main removal mechanism in CAC.

2018Journal article

Open access

Activated carbons from the co-pyrolysis of rice wastes for Cr(III) removal

Publication . Dias, Diogo; Bernardo, Maria; Lapa, Nuno; Pinto, Filomena; Matos, Inês; Fonseca, Isabel Maria

ABSTRACT: Rice husk and polyethylene were mixed (50 % w/w each) and submitted to a pyrolysis assay. Four physical activations with CO2 were performed on the resulting co-pyrolysis char (PC). The activation at 800 °C, for 4h, generated the activated carbon (PAC3) with the best textural properties. PC, PAC3 and a commercial activated carbon (CAC) were characterized and submitted to Cr(III) removal assays. PC had a high percentage of volatile matter that was removed after the physical activation, resulting in more available pores in the final material (PAC). In the Cr(III) removal assays, two S/L ratios were tested: 5 and 10 g L-1. PC did not remove any Cr(III) from the solutions, but PAC presented similar results to CAC. At the S/L of 5 g L-1, Cr(III) removal was of 58.5 % for PAC and 62.5 % for CAC, both by adsorption mechanism; at the S/L of 10 g L-1, Cr(III) removal was almost complete due to precipitation caused by pH increase. The highest uptake capacities were of 7.92 mg g-1 for PAC and 8.71 mg g-1 for CAC, at the S/L of 5 g L-1. The results indicated that PAC3 may be a viable alternative to CAC on Cr(III) removal from aqueous media.

2018Journal article

Open access

Comparison of co-gasification of wastes mixtures obtained from rice production wastes using air or oxygen

Publication . Pinto, Filomena; Andre, Rui N.; Lopes, Helena; Neves, Diogo; Varela, Francisco; Santos, João Navalho; Miranda, Miguel

The world annual production of rice is higher than 700.7 million tons, which generates rice husk and straw wastes. Rice culture also produces big amounts of polyethylene (PE) bags used in rice packs and for seeds and fertilizer storage that usually end up in landfills, due to their degree of contamination. The energetic valorisation of these wastes may be accomplished by different processes, co-gasification is one of the most viable, as it leads to the production of a synthetic gaseous mixture (bio-syngas) that can be used for energy production to be used during rice milling processes. Gasification of rice husks has some challenges, due to these wastes high content of silica and alkali metals that lead to the formation of solids with lower melting point, thus, leading to bed agglomeration that causes reactor erosion and serious damage. PE has lower ash content and much higher energetic content than rice husks. However, PE polymeric structure may lead to the formation of higher tar contents, which compromise most gasification gas utilisations. Co-gasification of PE and rice husks allows taking advantages of each waste favourable characteristic, diluting the unsuitable features. Co-gasification of these wastes was done in presence of steam blended with air or oxygen. Steam promoted the gasification reactions and favoured H2 production. Air or oxygen promoted the partial oxidation of the feedstocks to be co-gasified and supplied the energy necessary for the endothermic gasification reactions. The use of air has a low cost, but has the great disadvantage of diluting the bio-syngas produced, thus lowering its energetic content. On the other hand, the use of oxygen solves the problems related to gas dilution with nitrogen, but increases the operating cost. Bio-syngas composition obtained by co-gasification trials done with air enriched with different oxygen contents was compared with those obtained with air or pure oxygen to determine the best approach considering both the technical and economical sustainability.

2015Journal article

Open access

Co-pyrolysis of wastes mixtures obtained from rice production: upgrading of produced liquids

Publication . Pinto, Filomena; Miranda, Miguel; Costa, Paula

The increasing need to find alternative fuels to decrease the dependency on fossil fuels and to reduce the negative environmental impact of wastes accumulation has led to the idea of studying the energetic valorisation of different types of wastes by co-pyrolysis. Rice production process generates rice husk together with polyethylene (PE) bags that are used for rice packaging and to transport seeds and fertilizers used for rice culture. In Portugal, most of these plastic bags waste usually end up in landfills, since the amount of dirt and dust does not allow their recycling. Bio-oils produced by rice wastes pyrolysis present some undesirable properties: chemical instability, high solids content, ashes, oxygenated compounds and water, which prevent its direct use in conventional engines. On the other hand, PE pyrolysis produces around 80% w/w of liquid hydrocarbons (bio-oils) composed by a complex mixture of hydrocarbons from C5 to C20 (without the mentioned undesirable properties), 10% w/w of gases and almost no solids. Co-pyrolysis of rice husk blended with plastic wastes leads to the production of bio-oils that may be used as bio-fuels or as raw materials. These bio-oils quality can be improved by the optimisation of co-pyrolysis experimental conditions, including the use of suitable catalysts. Otherwise, liquids may be thermally upgraded to convert heavier liquid molecules into smaller ones with lower molecular weight and better fuel properties. The capability of these bio-fuels for energy production to be used during rice milling processes was analysed. Different approaches: pyrolysis, hydrogenation and pyrolysis followed by hydrogenation were analysed, considering the technical, economical and environmental viability of each process.

2015Journal article

Open access