Enhanced anaerobic co-digestion of food waste and solid poultry slaughterhouse waste using fixed bed digester : Performance and energy recovery

This study investigated the effects of organic loading rate (OLR) for anaerobic co-digestion (AcoD) of food waste (FW) and solid poultry slaughterhouse waste (SPSW) was performed in a fixed bed digester (FBD) at controlled pH to improve the methane production not fully discovered. Anaerobic co-digestion FW and SPSW were started up for the first time by gradually increasing OLR. At steady state, the FBD-AcoD reactor at OLR of 23.5 g COD/L/d the methane production was 7.8 L/L/d. Which achieved the highest OLR of 23.5 g COD/L, on the other hand when at OLR of 25.5 to 27.5 g COD/L the digester appeared inhibited and showed low performance in methane yields due to the accumulation of volatile fatty acids (VFAs) and long chain fatty acids (LCFAs). Methanosaeta and Methanosarcina were dominant over the acidogenic in the digester boosting the FBD-AcoD system to counter the acid effect. The removals of TS and VS around 79% and 76% on a continuous basis with a waste mixing of SPSW 18.5% and OLR of up to 23.5 g COD/L could biogas production 81 g COD/L/d. The FBD-AcoD system produces bioenergy of 875.3 Kj/g COD and the total investment energy utilized in the system was 8.51 Kj/g COD respectively

Waste-derived activated carbons for control of nitrogen oxides

Activated carbons were produced from waste and investigated for their efficiency for the removal of mono-nitrogen oxides (NOx) in simulated flue gases at a low temperature. The wastes used were waste biomass (date seeds), processed municipal solid waste in the form of refuse-derived fuel and waste tyres. The morphology, porous texture and surface chemistry of the prepared activated carbons were evaluated by scanning electron microscopy, energy-dispersive X-ray spectrometry, nitrogen adsorption and Boehm titration, and were compared with several commercial activated carbons. The carbons were then investigated in terms of their use in adsorbing NOx at a low temperature. The waste-derived activated carbons had NOx adsorption efficiencies at 50°C which were between 50 and 70% of those achieved for the commercial activated carbons. Increasing the adsorption temperature from 25 to 100°C significantly reduced nitrogen oxide (NO) adsorption. It was also shown that the NO adsorption efficiency depends on the porous structure, particularly the presence of micropores in the activated carbon, but to a lesser extent on the surface area of the carbons and acid–base surface groups on the carbon surface

Thermal decomposition and gasification of biomass pyrolysis gases using a hot bed of waste derived pyrolysis char

Chars produced from the pyrolysis of different waste materials have been investigated in terms of their use as a catalyst for the catalytic cracking of biomass pyrolysis gases during the two-stage pyrolysis-gasification of biomass. The chars were produced from the pyrolysis of waste tyres, refused derived fuel and biomass in the form of date stones. The results showed that the hydrocarbon tar yields decreased significantly with all the char materials used in comparison to the non-char catalytic experiments. For example, at a cracking temperature of 800 °C, the total product hydrocarbon tar yield decreased by 70% with tyre char, 50% with RDF char and 9% with biomass date stones char compared to that without char. There was a consequent increase in total gas yield. Analysis of the tar composition showed that the content of phenolic compounds decreased and polycyclic aromatic hydrocarbons increased in the product tar at higher char temperatures

Production of activated carbons from waste tyres for low temperature NOx control

Waste tyres were pyrolysed in a bench scale reactor and the product chars were chemically activated with alkali chemical agents, KOH, K2CO3, NaOH and Na2CO3 to produce waste tyre derived activated carbons. The activated carbon products were then examined in terms of their ability to adsorb NOx (NO) at low temperature (25°C) from a simulated industrial process flue gas. This study investigates the influence of surface area and porosity of the carbons produced with the different alkali chemical activating agents on NO capture from the simulated flue gas. The influence of varying the chemical activation conditions on the porous texture and corresponding NO removal from the flue gas was studied. The activated carbon sorbents were characterized in relation to BET surface area, micropore and mesopore volumes and chemical composition. The highest NO removal efficiency for the waste tyre derived activated carbons was ∼75% which was obtained with the adsorbent treated with KOH which correlated with both the highest BET surface area and largest micropore volume. In contrast, the waste tyre derived activated carbons prepared using K2CO3, NaOH and Na2CO3 alkali activating agents appeared to have little influence on NO removal from the flue gases. The results suggest problematic waste tyres, have the potential to be converted to activated carbons with NOx removal efficiency comparable with conventionally produced carbons

Waste derived carbons for NOx control or syngas tar removal

The utilisation of waste materials as precursors for generating low-cost and effective carbonaceous materials, which can be used on a large scale, is very attractive and would help to solve the issues associated with waste disposal. In this work, scrap tyre, municipal solid waste in the form of refuse derived fuel (RDF) and date stones were selected for char and activated carbon production. The produced carbons were investigated as valuable adsorbent materials for control of (i) a problematic industrial nitric oxide (NO) gaseous pollutant or alternatively (ii) as a low-cost catalyst for tar cracking in relation to cleaning up the syngas produced from the gasification of biomass. The investigated carbonaceous materials were prepared using a fixed bed reactor. (i) The use of waste derived activated carbons as an adsorbent for NO removal under different test conditions at a low temperature of 50 ºC was investigated using a fixed bed reactor. The activated carbons were synthesised through carbonisation of the precursor at a temperature of 600 ºC, followed by subsequent physical activation with steam at 900 ºC. The NO removal efficiency of the waste-derived activated carbons was compared with different commercial carbons with varied porous texture and surface chemistry. Date stones activated carbon exhibited the highest NO removal efficiency of 40%, whereas a lower NO removal efficiency of 23% and 21% was obtained with RDF and tyre activated carbons respectively at 120 minutes time on stream. Commercially produced activated carbons had NO removal efficiencies of between 40% and 60%. The lower NO sorption of waste tyre and RDF activated carbons compared to those of commercial activated carbons or date stones was because of the difference in porous texture. Considering the Kinetic diameter of NO is 0.317 nm, effective adsorbents should exhibit a large volume of micropores. It was shown that the pores of the commercial activated carbons and date stones are mostly located in the micropore range of 1-2 nm (micropores), whereas RDF and waste tyre derived activated carbons have a much greater number of pores with diameters in the range of 2-10 nm (mesopores). Chemical activation can greatly alter the pore size and characteristics of the produced carbon. Therefore, surface modification of waste tyre was investigated via chemical activation to develop the porous texture and thereby enhance the NO adsorption capacity of tyre derived activated carbon. Thus, the influence of chemical activation of the waste tyre with KOH, K2CO3, NaOH and Na2CO3 on porosity development and the corresponding NO adsorption was investigated. It was shown that the activation of waste tyre with KOH favored the production of activated carbon with high micropore volume, which has been considered a key feature affecting NO adsorption at low temperature. Therefore, waste tyre activated with KOH at a char: KOH ratio of 1:3, with a total micropore volume of 0.437 cm3 g-1 and surface area of 621 m2 g-1 gave the highest NO adsorption capacity (17.23 mg g-1), which was double that of the physically activated tyre derived activated carbon. The results obtained in this study have shown that the adsorption capacity of carbonaceous sorbents relies greatly on the porous texture, in particular, the micropore structure of the carbon, as well as on the method of activation, but to a lesser extent on the BET surface area and acid-base surface groups on the carbon surface. (ii) Char materials derived from the pyrolysis of scrap tyre, RDF and date stones were also investigated in term of their use as a catalyst for the catalytic cracking of biomass pyrolysis gases during the two-stage pyrolysis/gasification of biomass. Biomass was used to generate a range of hydrocarbon gases typically found in biomass gasification tars through the pyrolysis of biomass. Among the investigated chars for bio-oil/tar decomposition, at a char cracking temperature of 800 ºC, tyre-derived pyrolysis char presented the highest activity resulting in a 70% reduction in bio-oil/tar yield compared to the non-char catalytic experiments. The results suggest that tar decomposition by char materials is mainly ascribed to the catalytic conversion of tar species, as the decrease of the hydrocarbon tar yields was accompanied with a consequent increase in total gas yield. Analysis of the tar composition showed the presence of naphthalene, fluorene and phenanthrene as the major polyaromatic hydrocarbon (PAH) components at the higher cracking temperature. To understand the tar decomposition mechanism and to further investigate the influence of porous texture and oxygen functional groups of char on tar decomposition process, the catalytic cracking of tar model (furfural, phenol, toluene, methylnaphthalene) over tyre char was investigated. The most reactive compound was furfural, followed by phenol and toluene, whereas methylnaphthalene presented the lowest reactivity. The results also indicated that both the porous texture and the oxygen functional groups of the carbonaceous materials had a marginal effect on tar decomposition. Additionally, tyre char was used as a sacrificial catalyst for the reforming/gasification of tars from the gasification of biomass to produce a hydrogen-rich syngas and also to contribute to the yield of biomass syngas through tyre char gasification reactions. The influence of tyre ash metals, catalyst bed temperature, steam to biomass ratio and reaction time were investigated. The metallic mineral content of tyre char has been shown to contribute significantly to the tar degradation. The maximum H2 content of the product syngas of 56 vol.% was obtained at a reforming temperature of 900 ºC and with steam to biomass ratio of 6 g g-1. Tyre char was also subjected to steam gasification during the process, whereby the tyre pyrolysis char catalyst is sacrificed to produce hydrogen and carbon monoxide to enhance the yield of the syngas. Overall, this research work shows that waste derived carbonaceous materials are low-cost promising adsorbents for NO control and tar removal from the syngas produced from biomass gasification