Waste to Resources

Waste to Resources

T. Maneerung, S. Kawi, C.H. Wang, “Biomass Gasification Bottom Ash as a Source of CaO Catalyst for Biodiesel Production via Transesterification of Palm Oil”, Energy Conversion and  Management, 92, 234-243 (2015).

The main aim of this research is to develop environmentally and economically benign heterogeneous catalysts for biodiesel production via transesterification of palm oil. For this propose, calcium oxide (CaO) catalyst has been developed from bottom ash waste arising from woody biomass gasification. Calcium carbonate was found to be the main component in bottom ash and can be transformed into the active CaO catalyst by simple calcination at 800 °C without any chemical treatment. The obtained CaO catalysts exhibit high biodiesel production activity, over 90% yield of methyl ester can be achieved at the optimized reaction condition. Experimental kinetic data fit well the pseudo-first order kinetic model. The activation energy (Ea) of the transesterification reaction was calculated to be 83.9 kJ mol-1. Moreover, the CaO catalysts derived from woody biomass gasification bottom ash can be reutilized up to four times, offering the efficient and low-cost CaO catalysts which could make biodiesel production process more economic and environmental friendly.

T. Maneerung, J. Liew 2, Y. Dai 3, S. Kawi, C. Chong, C.H. Wang, “Activated carbon derived from carbon residue from biomass gasification and its application for dye adsorption: kinetics, isotherms and thermodynamic studies”,  Bioresource Technology, 200, 350–359 (2016).

In this work, activated carbon (AC) as an effective and low-cost adsorbent was successfully prepared from carbon residue (or char, one of the by-products from woody biomass gasification) via physical activation. The surface area of char was significantly increased from 172.24 to 776.46 m2 g-1 after steam activation at 900 °C. The obtained activated carbons were then employed for the adsorption of dye (Rhodamine B) and it was found that activated carbon obtained from steam activation exhibited the highest adsorption capability, which is mainly attributed to the higher surface area and the abundance of hydroxyl (−OH) and carboxyl (−COOH) groups on the activated carbon surface. Moreover, it was also found that the adsorption capability significantly increased under the basic condition, which can be attributed to the increased electrostatic interaction between the deprotonated (negatively charged) activated carbon and dye molecules. Furthermore, the equilibrium data were fitted into different adsorption isotherms and found to fit well with Langmuir model (indicating that dye molecules form monolayer coverage on activated carbon) with a maximum monolayer adsorption capability of 189.83 mg/g, whereas the adsorption kinetics followed the pseudo-second-order kinetics.



L. Rong, T. Maneerung, J. C. Ng , K. G. Neoh, B. H. Bay, Y. W. Tong, Y. Dai, C.H. Wang, Co-Gasification of Sewage Sludge and Woody Biomass in a Fixed-bed Downdraft Gasifier: Toxicity Assessment of Solid Residues, Waste Management, 36, 241-255  (2015).

As the demand for fossil fuels and biofuels increases, the volume of ash generated will correspondingly increase. Even though ash disposal is now strictly regulated in many countries, the increasing volume of ash puts pressure on landfill sites with regard to cost, capacity and maintenance. In addition, the probability of environmental pollution from leakage of bottom ash leachate also increases. The main aim of this research is to investigate the toxicity of bottom ash, which is an unavoidable solid residue arising from biomass gasification, on human cells in vitro.  Two human cell lines i.e. HepG2 (liver cell) and MRC-5 (lung fibroblast) were used to study the toxicity of the bottom ash as the toxins in the bottom ash may enter blood circulation by drinking the contaminated water or eating the food grown in bottom ash-contaminated water/soil and the toxic compounds may be carried all over the human body including to important organs such as lung, liver, kidney, heart, etc. It was found that the bottom ash extract has a high basicity (pH = 9.8 – 12.2) and a high ionic strength, due to the presence of alkali and alkaline earth metals e.g. K, Na, Ca and Mg. Moreover, it also contains concentrations of heavy metals (e.g. Zn, Co, Cu, Fe, Mn, Ni and Mo) and non-toxic organic compounds. Although human beings require these trace elements, excessive levels can be damaging to the body. From the analyses of cell viability (using MTS assay) and morphology (using fluorescence microscope), the high toxicity of the gasification bottom ash extract could be related to effects of high ionic strength, heavy metals or a combination of these two effects. Therefore, our results suggest that the improper disposal of the bottom ash wastes arising from gasification can create potential risks to human health and, thus, it has become a matter of urgency to find alternative options for the disposal of bottom ash wastes.

Morphology of HepG2 cells at different time points (24 h, 48 h and 72 h) after exposure to extracts of bottom ash from 20% Sludge + 80% Wood Chips after the extracts was neutralized by nitric acid. The scale bar in each panel is 50 μm.


Z. Z. Yang, S.K. Koh, W.C. Ng, R.C.J. Lim, H.T.W. Tan, Y.W. Tong, Y. Dai, C. Chong, C.H. Wang, “Potential Application of Gasification to Recycle Food Waste and Rehabilitate Acidic Soil from Secondary Forests on Degraded Land in Southeast Asia”, Journal of Environmental Management, 172, 40-48 (2016).

Gasification is recognized as a green technology as it can harness energy from biomass in the form of syngas without causing severe environmental impacts, yet producing valuable solid residues that can be utilized in other applications. In this study, the feasibility of co-gasification of woody biomass and food waste in different proportions was investigated using a fixed-bed downdraft gasifier. Subsequently, the capability of biochar derived from gasification of woody biomass in the rehabilitation of soil from tropical secondary forests on degraded land (adinandra belukar) was also explored through a water spinach cultivation study using soil-biochar mixtures of different ratios. Gasification of a 60:40 wood waste-food waste mixture (w/w) produced syngas with the highest lower heating value (LHV) 5.29 MJ/m3—approximately 0.4-4.0% higher than gasification of 70:30 or 80:20 mixtures, or pure wood waste. Meanwhile, water spinach cultivated in a 2:1 soil-biochar mixture exhibited the best growth performance in terms of height (a 4-fold increment), weight (a 10-fold increment) and leaf surface area (a 5-fold increment) after 8 weeks of cultivation, owing to the high porosity, surface area, nutrient content and alkalinity of biochar. It is concluded that gasification may be an alternative technology to food waste disposal through co-gasification with woody biomass, and that gasification derived biochar is suitable for use as an amendment for the nutrient-poor, acidic soil of adinandra belukar.