Yu-Yang Long

Behavior of dibutyl phthalate in a simulated landfill bioreactor

In this study, the behavior of dibutyl phthalate (DBP) from municipal solid waste (MSW) in the leachate and refuse of two simulated landfill bioreactors was compared. In one reactor, the leachate was circulated between a landfill and a methanogenic reactor, while the other reactor was operated using direct recirculation of the leachate. The results revealed that the original concentration of DBP in the refuse was approximately 18.5 microg/g, and that this concentration decreased greatly during decomposition of the waste for both reactors. Furthermore, the major loss of DBP from the landfill occurred in an active methanogenic environment in the later period, while the environment was acidic due to a high concentration of volatile fatty acids (VFA) and contained a large volume of biologically degradable material (BDM) during the early stage. Circulating the leachate between the landfill and a methanogenic reactor resulted in an increase in the biodegradability of MSW and a high degree of waste stabilization. Furthermore, DBP degraded more rapidly in the landfill that was operated in conjunction with the methanogenic reactor when compared to the landfill in which there was direct leachate recirculation.

A comparative study on stabilization of available As in highly contaminated hazardous solid waste.

The stabilization of available As was conducted by chemical fixation after Fenton process in a solid waste residual (SWR) from organic arsenic industry. Single as well as combined fixation treatments by using ferric sulfate (FS), magnesium chloride (MC) and calcium hydroxide (CH) were carried out to assess and to evaluate the fixation effect through toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP) and sequential extraction procedure (SEP). The effect of aging treatment on the fixation of available As in SWR was also investigated. Experimental result showed that the optimal molar ratios for Fe:As, Mg:As and Ca:As were 2:1, 3:1 and 2:1, respectively, and the combination fixation FS+MC+CH was found to be the optimal fixation treatment. With respect to the leaching behavior and the speciation migration of As in SWR after stabilization, TCLP, SPLP and SEP represent a pertinent and inseparable system for the fixation effect evaluation. The fixation treatment of available As in SWR could be evaluated directly after 3 days and the aging treatment is not needed though it can further enhance the fixation effect.

Evaluation of a novel ‘semi-solid’ Fenton process: Case study on a kinetic model of o-nitroaniline degradation in hazardous solid waste

A ‘semi-solid’ Fenton process (SSFP), in which the Fenton process (FP) takes place in a matrix with a low liquid-to-solid ratio (≤ 5:1), was conducted on the degradation of o-nitroaniline (ONA) in hazardous solid waste. Based on the assumption of a first order reaction between ONA and the hydroxyl radical (·OH), an SSFP kinetic model was developed to accurately describe the kinetics of ONA degradation and to quantitatively investigate the effect of operating conditions. Half-life prediction model was also proposed and compared with the half-life calculated from pseudo first order equation to prove the effect of operating conditions. It showed that the degradation of ONA proceeded rapidly at pH 3.5. The kinetic rate constant, k, for ONA degradation increased with the initial ferrous ion concentration, but decreased with the liquid-to-solid ratio. With respect to the lowest residual ONA concentration, the optimal ferrous ion concentration and liquid-to-solid ratio were 0.062 mol/kg dry weight and 1.8, respectively.

Effect of liquid-to-solid ratio on semi-solid Fenton process in hazardous solid waste detoxication

The liquid-to-solid ratio (L/S) of semi-solid Fenton process (SSFP) designated for hazardous solid waste detoxication was investigated. The removal and minimization effects of o-nitroaniline (ONA) in simulate solid waste residue (SSWR) from organic arsenic industry was evaluated by total organic carbon (TOC) and ONA removal efficiency, respectively. Initially, Box-Behnken design (BBD) and response surface methodology (RSM) were used to optimize the key factors of SSFP. Results showed that the removal rates of TOC and ONA decreased as L/S increased. Subsequently, four target initial ONA concentrations including 100 mg kg(-1), 1 g kg(-1), 10 g kg(-1), and 100 gk g(-1) on a dry basis were evaluated for the effect of L/S. A significant cubic empirical model between the initial ONA concentration and L/S was successfully developed to predict the optimal L/S for given initial ONA concentration for SSFP. Moreover, an optimized operation strategy of multi-SSFP for different cases was determined based on the residual target pollutant concentration and the corresponding environmental conditions. It showed that the total L/S of multi-SSFP in all tested scenarios was no greater than 3.8, which is lower than the conventional slurry systems (L/S ≥ 5). The multi-SSFP is environment-friendly when it used for detoxication of hazardous solid waste contaminated by ONA and provides a potential method for the detoxication of hazardous solid waste contaminated by organics.