Narrow Results

Sludge-derived activated carbon (SDAC) is prepared from sewage sludge and can be used to treat pollutants. SDAC can also be used to dope catalytic materials to improve their pollutant degradation ability. However, there needs to be more research on doping TiO₂ with SDAC. In this study, TiO₂ was doped with SDAC by Ultraviolet light irradiation method under room temperature. The doping process saved a large amount of energy. The TiO₂ doped with SDAC had the ability to degrade dyes under visible light. The results showed that the removal rates of SDAC-doped TiO₂ for methyl orange (MO) and methylene blue (MB) were over 90% and 94% under visible light conditions. After five cycles, the removal rate of MO was 75%, while the removal rate of MB decreased to 45%. Molecular dynamics simulation results showed that the valence band and conduction band of SDAC-doped TiO₂ shifted downward, and three apparent impurity levels appeared near the Fermi level after SDAC doping.

An experimental PGNAA set-up using a 1 Ci Am–Be source has been developed and used for analysis of bulk sewage sludge samples issued from a wastewater treatment plant situated in an industrial area of Algiers. The sample dimensions were optimized using thermal neutron flux calculations carried out with the MCNP5 Monte Carlo Code. A methodology is then proposed to perform quantitative analysis using the absolute method. For this, average thermal neutron flux inside the sludge samples is deduced using average thermal neutron flux in reference water samples and thermal flux measurements with the aid of a ³He neutron detector. The average absolute gamma detection efficiency is determined using the prompt gammas emitted by chlorine dissolved in a water sample. The gamma detection efficiency is normalized for sludge samples using gamma attenuation factors calculated with the MCNP5 code for water and sludge. Wet and dehydrated sludge samples were analyzed. Nutritive elements (Ca, N, P, K) and heavy metals elements like Cr and Mn were determined. For some elements, the PGNAA values were compared to those obtained using Atomic Absorption Spectroscopy (AAS) and Inductively Coupled Plasma (ICP) methods. Good agreement is observed between the different values. Heavy element concentrations are very high compared to normal values; this is related to the fact that the wastewater treatment plant is treating not only domestic but also industrial wastewater that is probably rejected by industries without removal of pollutant elements. The detection limits for almost all elements of interest are sufficiently low for the method to be well suited for such analysis.

In this paper, the pyrolysis treatment of sewage sludge was studied in a laboratory fixed bed reactor at temperature range of 400~600 ⁰C. Meanwhile, the influences of the final pyrolysis temperature, the heating rate and ZnO additive on the characteristics of the resulting bio-oil were also investigated. The experimental results indicated that more than 35% bio-oil yield was achieved at a pyrolysis temperature range of 500~600 ⁰C and a heating rate of 5 ⁰C/min. Meanwhile, ZnO has some contributions to the vaporation of the volatile in the sewage sludge. Moreover, heavy oxygenated hydrocarbons in the bio-oil are as high as 90%, which should be updated and then reused as fuel.

The development of sewage sludge pyrolysis technology is helpful to achieve efficient, less cost and less polluting processing of sewage sludge, the output of which in China is very large. From the point of view of mass and energy balance, simulation of sewage sludge pyrolysis in equilibrium states was conducted. The effects of moisture and ash in sewage sludge and fixed carbon retention rate on reaction results were systematically discussed. The results were shown that yield and quality of gas and coke yield decreased with the increase of moisture in sewage sludge. With the increase of ash content, the coke yield increased the carbon content of coke decreased and the coke quality became poor. As the retention rate of fixed carbon increased from 50% to 100%, both coke yield and quality increased, the carbon content of coke rose from 11.69% to 20.93% and coke yield rose from 30.89% to 34.53%.

Excessive heavy metals contents in sewage sludge maybe hinder the recycling of the sludge and should be mitigated effectively using engineered processes such stabilization as reported. In this work, Sorel cement is used as additive to stablize heavy metals present in sewage sludge. It was found that the contents of Zn, Cu, As, Cr, and Pb in sewage sludge were stabilized as high as 96%, 87%, 84%, 99% and 92%, respectively in the leachability test. The sequential extraction procedure tests showed that the increase of immobile fractions of heavy metals in mixtures, e.g. organic or residual forms, inhibited the transferability of heavy metals to the solution. In addition, the SEM photos of the stabilized microstructures proved that hydration of Sorel cement was changed with various ratios. Therefore, the increase of pH towards highly alkaline value and the formation of ternary hydration in the mixtures appear to have developed to stable heavy metals in sewage sludge.

Biomasses such as woody waste and sewage sludge can be converted to renewable energy source by using carbonization process. Carbonization process is carried out to obtain energy characteristics of carbonization residue from the mixture of woody waste and sewage sludge. The effects of temperature, time, and sewage sludge content on carbonization process are estimated by energy characteristics of the residue such as heating, yield, and fuel ratio. From the results of energy characteristics of residue, the optimum content of sewage sludge in carbonization process can be decided by 30%. At the optimum content of sewage sludge in carbonization process, the carbonization residue of mixture of woody waste and sewage sludge can be deserved to use one of renewable energy sources from the results of fuel ratio and total heating value.