Rundong Li

Heavy metal removal and speciation transformation through the calcination treatment of phosphorus-enriched sewage sludge ash

On the basis of the heavy metal (Cd, As, Pb, Zn, Cu, Cr, and Ni) control problem during the thermochemical recovery of phosphorus (P) from sewage sludge (SS), P-enriched sewage sludge ash (PSSA) was calcined at 1100°C. The effect of organic chlorinating agent (PVC) and inorganic chlorinating agent (MgCl2) on the fixed rate of P removal and the speciation transformation of heavy metal was studied. The removal of heavy metals Cd, Pb, As, Zn, and Cr exhibited an increasing tendency with the addition of chlorinating agent (PVC). However, an obvious peak under 100gCl/kg of PSSA appeared for Cu, owing to the presence of carbon and hydrogen in PVC. MgCl2 was found to be more effective than PVC in the removal of most heavy metals, such that up to 98.9% of Cu and 97.3% of Zn was effectively removed. Analyses of heavy metal forms showed that Pb and Zn occurred in the residue fraction after calcination. Meanwhile, the residue fraction of Cr, Ni, Cd, and Cu exhibited a decreasing tendency with the increase in the added chlorinating agent (MgCl2). Losses of P from PSSA were around 16.6% without the addition of chlorinating agent, which were greatly reduced to around 7.7% (PVC) and to only 1.7% (MgCl2).

Transformation of phosphorus during drying and roasting of sewage sludge.

Sewage sludge (SS), a by-product of wastewater treatment, consists of highly concentrated organic and inorganic pollutants, including phosphorus (P). In this study, P with different chemical fractions in SS under different drying and roasting temperatures was investigated with the use of appropriate standards, measurements, and testing protocol. The drying and roasting treatment of SS was conducted in a laboratory-scale furnace. Two types of SS samples under different treatment temperatures were analyzed by (31)P NMR spectroscopy. These samples were dried by a vacuum freeze dryer at -50°C and a thermoelectric thermostat drying box at 105°C. Results show that the inorganic P (IP) content increased as the organic P content decreased, and the bio-availability of P increased because IP is a form of phosphorousthat can be directly absorbed by plants. (31)P NMR analysis results indicate the change in P fractions at different temperatures. Non-apatite P was the dominant form of P under low-temperature drying and roasting, whereas apatite P was the major one under high-temperature drying and roasting. Results indicate that temperature affects the transformation of P.

Transformation of apatite phosphorus and non-apatite inorganic phosphorus during incineration of sewage sludge.

The recovery of phosphorus from incinerated sewage sludge ash (SSA) is assumed to be economical. Transformation from non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP), which has a higher bioavailability and more extensive industrial applications, was studied at 750-950°C by sewage sludge incineration and model compound incineration with a calcium oxide (CaO) additive. Thermogravimetric differential scanning calorimetry analysis and X-ray diffraction measurements were used to analyze the reactions between NAIP with CaO and crystallized phases in SSA. High temperatures stimulated the volatilization of NAIP instead of AP. Sewage sludge incineration with CaO transformed NAIP into AP, and the percentage of AP from the total phosphorus reached 99% at 950°C. Aluminum phosphate reacted with CaO, forming Ca2P2O7 and Ca3(PO4)2 at 750-950°C. Reactions between iron phosphate and CaO occurred at lower temperatures, forming Ca(PO3)2 before reaching 850°C.

A new integrated evaluation method of heavy metals pollution control during melting and sintering of MSWI fly ash

Evaluations of technologies for heavy metal control mainly examine the residual and leaching rates of a single heavy metal, such that developed evaluation method have no coordination or uniqueness and are therefore unsuitable for hazard control effect evaluation. An overall pollution toxicity index (OPTI) was established in this paper, based on the developed index, an integrated evaluation method of heavy metal pollution control was established. Application of this method in the melting and sintering of fly ash revealed the following results: The integrated control efficiency of the melting process was higher in all instances than that of the sintering process. The lowest integrated control efficiency of melting was 56.2%, and the highest integrated control efficiency of sintering was 46.6%. Using the same technology, higher integrated control efficiency conditions were all achieved with lower temperatures and shorter times. This study demonstrated the unification and consistency of this method.

Geochemical modeling and assessment of leaching from carbonated municipal solid waste incinerator (MSWI) fly ash

Municipal solid waste incinerator (MSWI) fly ashes are characterized by high calcium oxide (CaO) content. Carbon dioxide (CO2) adsorption by MSWI fly ash was discussed based on thermogravimetry (TG)/differential thermal analysis (DTA), minerology analysis, and adapting the Stenoir equation. TG/DTA analysis showed that the weight gain of the fly ash below 440xa0°C was as high as 5.70xa0%. An adapted Stenoir equation for MSWI fly ash was discussed. The chloride in MSWI fly ash has a major impact on CO2 adsorption by MSWI fly ash or air pollution control (APC) residues. Geochemical modeling of the critical trace elements copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb), and antimony (Sb) before and after carbonation was performed using a thermodynamic equilibrium model for solubility and a surface complexation model for metal sorption. Leaching of critical trace elements was generally found to be strongly dependent on the degree of carbonation attained, and their solubility appeared to be controlled by several minerals. Adsorption on ferrum (Fe) and aluminum (Al) colloids was also responsible for removal of the trace elements Cd, Pb, and Sb. We used Hakanson’s potential ecological risk index (HPERI) to evaluate the risk of trace element leaching in general. The results demonstrate that the ecological risk showed a V-shaped dependency on pH; the optimum pH of the carbonated fly ash was found to be 10.3–11, resulting from the optimum carbonation (liquid-to-solid (L/S) ratiou2009=u20090.25, carbonation durationu2009=u2009∼30–48xa0h). The dataset and modeling results presented here provide a contribution to assessing the leaching behavior of MSWI fly ash under a wide range of conditions.

Behaviors of rice straw two-step liquefaction with sub/supercritical ethanol in carbon dioxide atmosphere

This study extended previous work investigating two-step liquefaction by supercritical ethanol of rice straw under CO2 atmosphere at temperatures of 270-345u202f°C. Subcritical CO2-subcritical ethanol (SubCO2-SubEtOH) pretreatment decreased the content of lignin in the rice stalk from 22.94 to 21.43u202fwt%. The results showed that although oxygen-transfer reaction, transesterification, carbonylation, and other reactions may occur with the supercritical CO2-supercritical ethanol (ScCO2-ScEtOH) liquefaction reactions, transesterification was the main reaction. The de-oxygen-transfer reaction mainly comprised de-oxygenation and decarboxylation. For temperatures exceeding 320u202f°C, the bio-oil yield decreased because the effects of esters decreased. The residence time affected the H/C and O/C ratios to a minor extent. It was shown that the nucleophilic and hydrolytic functions of ethanol might be strengthened, generating higher amounts of ester, phenolic, acidic, and hydrocarbon derivatives in the bio-oil fraction.

Kinetic study of heavy metals Cu and Zn removal during sewage sludge ash calcination in air and N 2 atmospheres

Heavy metal control is essential during the thermochemical recovery of phosphorus (P) from sewage sludge ash (SSA). For medium volatile heavy metals, i.e. Cu and Zn, the effect of chlorine additive was complicated and more sensitive to temperature variation. So, in the in-depth study on the removal kinetics of Cu and Zn was necessary. Thus, the studies described in this paper considered the experiments and kinetic models of Cu and Zn removal in SSA through calcination under different atmospheres and temperatures. The results showed that within 15u202fmin, the removal of Cu and Zn was more effective at the same temperature in air than in N2. The result is consistent with kinetic analysis: Reaction activation energy of both Cu and Zn in an air atmosphere is lower than in N2. In addition, the reaction orders, energy and frequency factors of Cu and Zn removal reaction during SSA calcination at high temperature with air and N2 atmosphere were calculated.

Real-time recovery strategies for volatile fatty acid-inhibited anaerobic digestion of food waste for methane production

This study investigated effects of real-time recovery strategies on VFA (volatile fatty acid)-inhibited anaerobic system of FW (food waste) and identified key driver of process recovery. The long-term anaerobic system of FW encountered serious VFA (mainly propionate) inhibition. The pH adjustment (PA) strategy could not reverse process imbalance but only delayed the process failure. The short-term effect of reinoculation (RI) strategy was greatly effective, but its long-term effect was non-sustainable. Trace elements were key drivers of process recovery owing to their indispensable roles in activating methanogenesis and therefore stimulating propionate conversion. From the viewpoint of economic feasibility, the single strategy of trace elements supplementation (TE) and the combinational strategy of PAu202f+u202fTE were respectively recommended in the initial and medium VFA-inhibition stages. The three-in-one strategy of PAu202f+u202fTEu202f+u202fRI was always effective but was costly. This study provided practical guidance on real-time recovery of VFA-inhibited anaerobic system of FW.

Accelerated Carbonation of Municipal Solid Waste Incineration Fly Ash Using CO2 as an Acidic Agent for Clinker Production

Because of the high Ca and amphoteric heavy metals content of the municipal solid waste incineration (MSWI) fly ash, accelerated carbonation at high liquid to solid ratio of 10:1 was investigated to improve its physical and chemistry properties. Carbonation and heavy metals (Pb, Cu, Zn, Cd, Ni, Cr) mobility were studied by applying mineral analysis, morphology analysis, porosity analysis and leaching assays. XRD analysis showed the disappearance of the CaClOH peak and the appearance of CaCO3 in the accelerated carbonated fly ash were showed. Treatment through carbonation reduced the pH of the fly ash from 12.4 to 7, and reduced the leaching concentration of Pb Cu, Zn and Ni by 99.7%, 93.9%, 90.6% and 27.8%, respectively. However, the leaching concentration of Cr increased 29.7%.