Cationic and anionic dye adsorption by agricultural solid wastes: a comprehensive review

Recently many researchers have proved the capability of agricultural solid wastes as adsorbents to remove many types of pollutants including dyes. This review represents the use of agricultural solid wastes to remove two classes of dye, cationic and anionic dyes and makes a simple comparison among cationic and anionic dye adsorption by the same adsorbent, thus possibly opening the door for a better understanding of the dye-classified adsorption process. Both these classes of dyes are toxic and cause severe problems to aquatic environment. Some agricultural solid wastes can remove both dye classes, although they need activation. The dye adsorption capacities of agricultural waste adsorbents vary, depending on the pH of solution, initial dye concentration, adsorbent dosage and process temperature. The pH of solution is directly related to the dye-classified adsorption, where it affects the surface charge of the adsorbent and the degree of ionization of the adsorbate

Effect of washing pre-treatment of empty fruit bunch hydrogel biochar composite properties as potential adsorbent

Hydrogel biochar composite (HBC) showed a great potential as effective organic contaminant removal in various wastewater and gas treatment. The effectiveness is depending upon quality of biochar used during the preparation of the HBC. In this work, pre-treatment of the biochar samples (EFB in this case) through washing was investigated. The raw EFB biochar was prepared using microwave assisted pyrolysis under 1,000 W for 30 min under N2 flow with 150 mL/min. The prepared biochar is chemically treated using either acid solution (HCl) or oxidising agent (H2O2) to enlarge the pores and remove impurities. The biochar is then polymerised by using acrylamide (AAm) as monomer, N,N’-methylenebisacrylamide (MBA) as crosslinker and ammonium persulfate (APS) as initiator to form the treated hydrogel biochar composite (EFB-HBC). The H2O2 treated biochar [EFB-HBC (P100)] shows better porosity compared to HCl treated biochar [EFB-HBC (H100)] where EFB-HBC (P100) has higher surface area (1.5997 m2 /g) compared to EFB-HBC (H100) (1.2562 m2 /g). The HBC is porous and carbonaceous material with 21 % and 31 % of carbon content in EFB-HBC (P100) and EFB-HBC (H100) which have potential as an adsorbent in wastewater and gas treatment

Thermogravimetric study of Chlorella vulgaris for syngas production

The present study investigates the thermal degradation behavior of Chlorella vulgaris using a thermogravimetric analyzer (TGA) to explore application as feedstock for syngas production. The biomass was heated continuously from room temperature to 1000 °C at different heating rates (5, 10 and 20 °C min− 1) under N2/air conditions at a constant flow rate of 25 mL min− 1. Experimental results showed that the combustion process of C. vulgaris can be divided into three major phases; (1) moisture removal, (2) devolatilization of carbohydrates, protein and lipids and (3) degradation of carbonaceous material. A degradation rate of 80% was obtained at the second phase of the combustion process in the presence of air whilst a degradation rate of 60% was obtained under N2 atmosphere at the same phase. The biomass was further gasified for syngas production using a Temperature Programmed Gasifier (TPG). The effect of three different process variables, temperature, microalgal loading, and heating rate was investigated. The maximum H2 production was found at 800 °C temperature with a biomass loading of 0.5 g. No significant effect of heating rate was observed on H2 production. The activation energy values, based on the Kissinger method, were evaluated to be 45.38 ± 0.5 kJ mol− 1 (1st stage), 61.20 ± 0.5 kJ mol− 1 (2nd stage) and 97.22 ± 0.5 kJ mol− 1 (3rd stage). The results demonstrate a significant potential for the utilization of the microalgae biomass as feedstock for large-scale production of syngas via gasification

Thermochemical conversion of Napier Grass for production of renewable syngas

Fuel resource diversification is a global effort to deviate from non-renewable fossil fuels. Biomass has been identified as an alternative solid biofuel source due to its desirable properties and carbon neutrality. As reported in the literature, biomass can positively contribute towards combating climate change while providing alleviation for energy security issue. As part of efforts to diversify biomass resources, this work intends to explore the potential of Napier grass, one type of energy crop, for the production of renewable syngas via gasification. This energy crop is originally from Africa, which is highly productive with low cost (40 tonnes per year per hectare). Limited studies were conducted to analyze the potential of such an energy crop as a fuel source, which is the subject of this work. In order to analyze the full potential of such energy crop, the physical and chemical characteristics of this biomass was first analyzed. To determine the productivity of syngas from this biomass, fluidized bed gasifier was used in this work. The effects of gasification process parameters (i.e., equivalence ratio and temperature) on product yield and producer gas compositions were examined. Besides, the effects of equivalence ratio towards higher heating value of syngas and carbon conversion efficiency were analyzed. Based on the ultimate analysis results, the molecular formula of Napier gas was CH1.56O0.81N0.0043. Meanwhile, the higher heating value of such biomass was determined as 16.73 MJ/kg, which was comparable to other biomasses. It is noted that in this work, the volatile matter was determined as 85.52% and this promoted gasification process remarkably. The dynamics of the reactions involved were observed as a significant variation in product yield and biogas components were recorded at varying equivalence ratio and gasifier operating temperature

Thermogravimetric study of napier grass in inert and oxidative atmospheres conditions

Since the industrialisation of Malaysia, the energy demand which mainly relied on fossil fuels has risen continuously. Therefore, all parties including the government, academic society and communities have explored alternative fuel resources to improve the reliability and security of energy supply to meet the future energy. In recent years, biomass has been identified as one of the most promising renewable energy resources compared to hydro, solar, wind, etc. It is projected that energy crops could potentially supply around 200-400 EJ/year in Malaysia at a competitive cost by 2050. Perennial grass is one type of energy crop that could address the above mentioned challenge. In this work, Napier grass (NG) is chosen as the subject due to its desirable characteristics (availability, high growth rates, carbon neutrality and high volatility). In order to investigate the feasibility of NG for heat and power application, the thermal decomposition characteristics, reactivity, and kinetic of NG needed were tested via thermogravimetric analysis (TGA) under inert (nitrogen) and air atmosphere conditions, respectively. The results indicated that NG biomass has great potential as sustainable energy fuel source for energy generation via gasification process

Harvesting marine microalgae nannochloropsis sp. using Dissolved Air Flotation (DAF) technique

The production of high-value bioproducts from microalgae biomass has been widely investigated. However, their production is hindered by the expensive harvesting process. To date, flocculation followed by DAF process has been accepted as one of the affordable harvesting approaches. In this study, the use of DAF technique was attempted to harvest marine microalgae Nannochloropsis sp. Batch DAF harvesting was carried out using fabricated DAF unit equipped with several compartments including separation column, product collecting vessel and rotary skimmer. Tannin-based biopolymer flocculant, AFlok-BP1 at pH 5 with a concentration of 160 mg/L was used to facilitate the flocculation of particles. The effects of different saturator pressure at 1.8, 2, and 2.2 bar were then evaluated at a constant volume of 6 L microalgae culture. The effects of different microalgae culture volumes (6, 8 and 10 L) were also evaluated at a fixed saturator pressure of 2.2 bar. The highest pressure at 2.2 bar yielded the best result with the highest total solid of 3.19 ± 0.01% and a maximum yield of 1.70 ± 0.05 g/g (wet basis). The microalgae concentration was the lowest (0.027 g/L) when 6 L of culture volume was used. However, the values were significantly higher when the culture volume was increased to 8 and 10 L to approximately 0.035 and 0.050 g/L, respectively. As a conclusion, the study provided evidence for the feasibility of DAF technique in harvesting marine microalgae Nannochloropsis sp

Thermochemical conversion of microalgal biomass for biofuel production

Reliable and sustainable energy supply is critical to effective natural resource management, and it encompasses functioning efficiency of energy resources as well as socio-economic and environmental impact considerations. The complete reliance on fossil fuels is recognized as unsustainable throughout the world, and this is due to, amongst others, the rapid declining of fossil fuel reserves and the emission of significant quantities of greenhouse gases associated with their production and combustion. This has resulted in escalating interest in research activities aiming to develop alternative and somewhat carbon neutral energy sources. Algal biofuels, so called third generation biofuels, appear to be promising in delivering sustainable and complementary energy platforms essential to formulate a major component of the renewable and sustainable energy mix for the future. Algal biomass can be converted into various portfolios of biofuel products, such as bio-hydrogen, biodiesel, bioethanol and biogas, via two different pathways: biochemical and thermochemical pathways. Thermochemical conversion is considered as a viable method to overcome the existing problems related with biochemical conversion such as lengthy reaction time, low conversion efficiency by microbes and enzymes, and high production costs. This paper discusses process technologies for microalgae-to-biofuel production systems, focusing on thermochemical conversion technologies such as gasification, pyrolysis, and liquefaction. The benefits of exploiting upstream microalgal biomass development for bioremediation such as carbon dioxide mitigation and wastewater treatment are also discussed

Co-combustion of oil palm trunk biocoal / sub-bituminous coal fuel blends

Biomass is a promising alternative for the reduction of global dependency on fossil fuels. However, there are some issues with the direct application of raw biomass such as high moisture content, low heating value, and poor grindability. To alleviate the problems, biomass-derived biocoal is introduced and utilised as fuel in power plants. Oil palm trunk biocoal (OPTC) is produced from pyrolysis of oil palm trunk biomass (OPTB) in a top-lit, updraft reactor at a constant air flowrate of 4.63 L/min and maximum temperature of 550 °C. OPTC is co-combusted at temperatures between 600 and 900 °C with sub-bituminous coal (SBC). Pollutant emission and ash production from combustion of fuel blends containing 20% and 50% biocoal are analysed and compared with pure SBC, OPTB and OPTC. NOx and SO2 emission profiles from all tested fuel blends are well below the limits imposed under Environmental Quality (Clean Air) Regulation 2014 of 296 and 190 ppm respectively. Response surface methodology (RSM) analysis indicates that the operation of combustion is optimised with 92.16% efficiency at 774 °C and air flowrate of 16.6 SCFH to emit 16.38% CO2, and the findings are validated against experimental results. The optimised combustion process produces ash with 67.9% silicon compounds

Local practices for production of rice husk biochar and coconut shell biochar: production methods, product characteristics, nutrient and field water holding capacity

Application of biochar is widely reported to enhance soil quality and decrease leaching of nutrients. In this study, biochar from rice husk and coconut shells were used to determine physico-chemical characteristics, ability on nutrients and water holding capacity in soil. These biochars were produced using conventional processes of rotary husk (for rice husk) and kiln-drum furnaces (for coconut shells). It was found that coconut shell biochar (CSB) was very effective in retaining nitrogen compared to rice husk biochar (RHB). Leaching analysis over 19 days (100 ml each day) has identified 15 g/kg of CSB in Bungor series soil to consistently maintain a leaching rate of nitrogen at below 5 mg/litre as compared to other samples. Meanwhile, RHB was very effective in retaining water compared to CSB with highest water retention at 31.2%. Overall results indicate that conventionally made biochar has great potential to reduce nutrient leaching and improve water holding capacity in soil. CSB is more effective in reducing nutrient leaching, particularly nitrogen while RHB was most effective in increasing field water holding capacity. Further research is required to study its effectiveness on nutrient plant uptake

H2-Rich and Tar-Free downstream gasification reaction of EFB by using the Malaysian dolomite as a secondary catalyst

In this study, Malaysian dolomites as secondary catalysts are placed at the downstream of the fluidized-bed gasifier. Three types of Malaysian dolomites with different elemental ratios of CaO-MgO content denoted as P1, P2, and P3 are investigated with EFB gasification reaction at different cracking temperatures (700–900 °C). The performance of the catalysts with a variation of catalyst to biomass weight ratio (C/B) (0.05 to 0.30 w/w) is evaluated. The findings showed that the total gas yield increased by 20%, hydrogen increased by 66%, along with an almost 99% reduction in tar content with P1 catalyst with the following reaction conditions: gasification temperature of 850 °C, equivalence ratio (ER) of 0.25, and cracking temperature of 900 °C. Malaysia dolomite could be a secondary catalyst to provide a better alternative, tar-free hydrogen-rich gas with the possibility of regeneration and re-use