Municipal solid waste landfill age and refuse-derived fuel.

Landfill sites are hard to obtain in Taiwan. Municipal solid waste (MSW) in the closed landfill sites has high combustible content and calorific value (CV). Therefore, activating the closed landfill sites as municipal mine sites to prolong their service life will promote a sustainable environment. This study transforms combustibles from the closed municipal landfill sites of different landfill ages (LAs) into refuse-derived fuel (RDF) through pretreatment and squeeze forming equipment, so to investigate the characteristics of the MSW of different LAs, and the manufacturing conditions and firing behaviour of RDF. The results indicate that the proportion of the combustibles in MSW declines as the LA grows, and therefore the proportions of both incombustible materials and soil and debris correspondingly increased. The LA of the MSW is thus negatively correlated with the CV. The MSW at the LA of 10 years still has high potential as fuel material. The fixed carbon initiation temperatures (i.e. ignition temperatures) of combustibles of the MSW at the LAs of 1 year, 5 years and 10 years are 259°C, 256°C and 245°C, respectively. The CV and flame temperature of the RDF increase slightly with the increasing squeeze temperature (ST) at 100-120°C, but it will decrease when the ST reaches 130°C. Therefore, this study recommends the squeeze pressure of the RDF as 41.65 ± 8.24 kg cm-2, ST 110°C and combustible size 10-20 mm.

Evaluating the manufacturability and combustion behaviors of sludge-derived fuel briquettes.

Based on the physical and chemical properties as well as calorific values of pulp sludge and textile sludge, this study investigates the differences between manufacturability, relationship between extrusion pressure and formability, as well as stability and combustion behaviors of extruded sludge-derived fuel briquettes (ESBB) and cemented sludge-derived fuel blocks (CSBB). The optimum proportion and relevant usage ESBB policies are proposed as well. Experimental results indicate that a large amount of water can be saved during the ESBB manufacturing process. Additionally, energy consumption decreases during the drying process. ESBB also has a more compact structure than that of CSBB, and its mean penetration loading is approximately 18.7 times higher as well. Moreover, the flame temperature of ESBB (624-968°C) is significantly higher than that of CSBB (393-517°C). Also, the dry bulk density and moisture regain of ESBB is significantly related to the penetration loading. Furthermore, the optimum mix proportion of ESBB is co-determined by the formability of pulp sludge and the calorific values of textile sludge. While considering the specific conditions (including formability, stability and calorific values), the recommended mix proportion for ESBB is PS50TS50.

Enhancing performance and durability of slag made from incinerator bottom ash and fly ash.

This work presents a method capable of melting the incinerator bottom ash and fly ash in a plasma furnace. The performance of slag and the strategies for recycling of bottom ash and fly ash are improved by adjusting chemical components of bottom ash and fly ash. Ashes are separated by a magnetic process to improve the performance of slag. Analytical results indicate that the air-cooled slag (ACS) and magnetic-separated slag (MSS) have hardness levels below 590 MPa, indicating fragility. Additionally, the hardness of crystallized slag (RTS) is between 655 and 686 MPa, indicating toughness. The leached concentrations of heavy metals for these three slags are all below the regulatory limits. ACS appears to have better chemical stability than MSS, and is not significantly different from RTS. In the potential alkali-silica reactivity of slag, MSS falls on the border between the harmless zone and the potentially harmful zone. ACS and RTS fall in the harmless zone. Hence, the magnetic separation procedure of ashes does not significantly improve the quality of slag. However, RTS appears to improve its quality.

Distribution of chloride ion in MSWI bottom ash and de-chlorination performance.

When recycling bottom ash from municipal solid waste incinerators (MSWIs), salts and heavy metals contents must be considered; in particular, chloride ions must be addressed because they cause serious corrosion in metals. Therefore, only limited amounts of bottom ash can be utilized as a substitution for material or the bottom ash must be treated at high temperatures prior to use. These factors markedly decrease the applications of bottom ash. In addition to the distribution characteristics of chloride ions, this study also investigates the characteristics change before and after de-chlorination using a counter-flow pipe column and three different flow fluxes for different refuse incinerators as the experiment variables. Thus, this study attempts to determine the appropriate conditions for de-chlorination and an appropriate policy for use of bottom ash as concrete aggregate. The experimental results show that a negative correlation exists between the natural logarithm of the chloride ion concentration and particle size in bottom ash. Characteristics of de-chlorinated bottom ash, such as pH value, mud content, loss on ignition, chloride ion concentration, turbidity, and species intensity, all decrease, meaning that de-chlorination decreased chloride ion content and generates a cleaning effect. The per-unit-time efficiency of de-chlorination is highest in the high flux flow. When flow flux is 80 mL/min, the de-chlorination efficiency is >0.3%/h. However, the shortest time required for bottom ash de-chlorination does not reduce in proportion to the legally prescribed concentration of chloride ion.

Effect of SiO2-Al2O3-flux ratio change on the bloating characteristics of lightweight aggregate material produced from recycled sewage sludge.

This study investigates the characteristics of lightweight aggregates sintered from sewage sludge ash by modifying the proportion of the main components (SiO(2)-Al(2)O(3)-flux). The ash of incinerated sludge from a municipal sewage treatment plant (STP) was used as the tested material and sintering temperature ranged from 1050 to 1100 degrees C within a time span of 10-30min. The sludge ash appeared to have a high proportion of SiO(2) (44.89%), Al(2)O(3) (11.62%) and Fe(2)O(3) (6.81%) resembling the dilatable shale. When the sintering temperature was raised to above 1060 degrees C, the blowing phenomenon appeared. The aggregates become lighter in weight by prolonging the sintering time and raising the temperature. Cullet powder (amorphous SiO(2)), Al(2)O(3), and fly ash were added to sludge ash to analyse the characteristic changes of the aggregates. The results showed that amorphous SiO(2) lowered the melting point and increased foaming; Al(2)O(3) raised the compression resistance; fly ash lowered the sintering temperature required. However, the composition of fly ash can vary dramatically, resulting in a less predictable characteristic of aggregates.

Lightweight aggregate made from sewage sludge and incinerated ash.

In this study, sewage sludge ash (SSA), with similar characteristics to expansive clay, was used as the principal material and sewage sludge (SS) as the admixture to sinter lightweight aggregate and to study the influences of raw material composition on pelletising, sintering effect and aggregate properties. Results showed that both SS and SSA could be sintered to produce synthetic aggregates individually or mixed. Increasing the amount of SS would decrease the pelletising ratio. Under the consideration of energy saving, the mixture of SSA was better for sintering normal weight aggregate. On the contrary, the mixture that added 20-30% of SS was more adequate to make lightweight aggregates. Adding SS would enhance the oxidation-reduction reaction and lower the bulk density and sintering temperature of aggregates to save energy. Sintering temperature affected the properties of sewage sludge ash lightweight aggregate (SSALA) more than retention period did. Prolonging the retention period could improve bloating effect.

Foamed lightweight materials made from mixed scrap metal waste powder and sewage sludge ash.

The porous properties and pozzolanic effects of sewage sludge ash (SSA) make it possible to produce lightweight materials. This study explored the effects of different metallic foaming agents, made from waste aluminium products, on the foaming behaviours and engineering characteristics, as well as the microstructure of sewage sludge ash foamed lightweight materials. The results indicated that aluminium powder and mixed scrap metal waste powder possessed similar chemical compositions. After proper pre-treatment, waste aluminium products proved to be ideal substitutes for metallic foaming agents. Increasing the amount of mixed scrap metal waste by 10-15% compared with aluminium powder would produce a similar foaming ratio and compressive strength. The reaction of the metallic foaming agents mainly produced pores larger than 10 microm, different from the hydration reaction of cement that produced pores smaller than 1 microm mostly. To meet the requirements of the lightweight materials characteristics and the compressive strength, the amount of SSA could be up to 60-80% of the total solids. An adequate amount of aluminium powder is 0.5-0.9% of the total solids. Increasing the fineness of the mixed scrap metal waste powder could effectively reduce the amount required and improve the foaming ratio.