A study of solubilization of sewage sludge by hydrothermal treatment.

The use of activated sludge process for biological treatment of domestic and industrial wastewaters generates large amounts of sewage sludge, which is regarded as problematic biowaste. Conventional waste treatment methods such as landfilling and ocean pumping have been used to dispose the unwanted sludge, but this practice is no longer recommended due to serious secondary pollution and strict environmental regulations. Hydrothermal treatment represents a promising alternative that has attracted attention in recent years. In this study, batch experiments of hydrothermal treatment of domestic sewage sludge were conducted under varying conditions (temperature of 150-300 °C, reaction time of 0.5-3.0 h, and sludge concentration of 5-30 g/L). A statistical study of the responses, including disintegration degree and concentration of dissolved compounds, was performed using a response surface methodology. Optimal conditions for hydrothermal treatment of sewage sludge were obtained through mathematical modeling.

Optimization and comparison of methane production and residual characteristics in mesophilic anaerobic digestion of sewage sludge by hydrothermal treatment.

Anaerobic digestion is the preferred method for treating sewage sludge because of its ability to reduce sludge volume and produce biogas. However, conventional anaerobic digestion has a long retention time and low degradation rate. In recent years, hydrothermal treatment has been used to improve the hydrolysis of sewage sludge and biogas production. This process tends to focus on maximizing biogas production. However, very little research has been done on anaerobic digestion residues. In this study, batch experiments were conducted to investigate the effect of hydrothermal temperature on methane production and the contents of liquid fraction after anaerobic digestion (centrate). Experimental conditions were designed using a response surface method and central composite model. A quadratic equation was used to interpret the individual and interactive effects of hydrothermal conditions on anaerobic digestion. Given the maximum biogas production and the minimum concentrate concentration, the optimal operating condition was determined by a 186 °C hydrothermal temperature and a reaction time of 106 min. Under these conditions, the following results could be obtained: methane production (200.5 ± 7.7 mL-CH4/gVSadded), TCOD (16,572 ± 348 mg/L), sCOD (1240 ± 65 mg/L), sTN (658.9 ± 8.0 mg/L) and ammonia (525 ± 27 mg/L).

Removal of anionic arsenate by a PEI-coated bacterial biosorbent prepared from fermentation biowaste.

As a problematic element in water systems, arsenic exists as As(III) and As(V). Adsorption techniques can be used to remove anionic As(V) as it is present as a polyatomic anion. In the case of As(III) which exists in zero-valent state under neutral pH, it can be also removed by adsorption after being converted into As(V). Many inorganic and organic materials have been examined as potential adsorbents for anionic As(V) removal. However, most exhibit relatively low adsorption capacities (<10 mg/g). The objective of this study is to examine As(V)-removal mechanism and practical potential of a PEI-coated bacterial biosorbent prepared from fermentation biowaste. The maximum As(V) uptake of the biosorbent was determined to be 62.99 mg/g by Langmuir model. The effects of various parameters including pH, biosorbent dosage, ionic strength and temperature were also examined. Kinetic and equilibrium models were used to interpret the experimental data mathematically. A 0.01 M NaOH solution was chosen as an effective As(V)-desorbing eluent for biosorbent regeneration. The adsorption capacity of the biosorbent remained above 85% over three successive cycles of adsorption and desorption. In conclusion, the biowaste-driven biosorbent is a promising anion adsorbent for treatment of As(V)-contaminated wasters.

A new efficient forest biowaste as biosorbent for removal of cationic heavy metals.

Among various forest biowastes, chestnut bur had the highest uptake values of Cd(II) and Pb(II), and these values were higher than those of agricultural biowastes used as comparable biosorbents. This study is the first report showing the high potential of chestnut bur as biosorbent for the removal of cationic heavy metals. Pseudo-second-order equation satisfactorily described the biosorption behaviors of both metals. Biosorption rate of Pb(II) was 3.12 times higher than that of Cd(II). Langmuir model could fit the equilibrium isotherm data better than Freundlich model. The maximum uptake capacities of Cd(II) and Pb(II) were determined to be 34.77mg/g and 74.35mg/g, respectively. FTIR study showed that carboxyl group on the biosorbent was involved in biosorbing the cationic metals. In conclusion, abundant and cheap forest biowastes, especially chestnut bur, is a potent candidate for efficient biosorbent capable of removing toxic heavy metals from aqueous solutions.