Shaoqi Zhou

Modeling the oxidation kinetics of Fenton's process on the degradation of humic acid.

The degradation of humic acid (HA) was carried out in the presence of the Fenton reagent. The experiments demonstrated that HA was removed by oxidation and coagulation. Moreover, the oxidation occurred mainly at the first 60 min and predominated the HA removal efficiency. A new kinetic model was established according to the generally accepted mechanism of high active OH oxidation in order to well describe the Fenton oxidation reaction in HA aqueous solution. The model embraced two key operating factors affecting the HA degradation in Fenton process, including the dosages of hydrogen peroxide and ferrous ion. The experimental data were fitted by using the most commonly used first- and the second-order reaction models and the new model, respectively. The goodness of fittings demonstrated that the new model could better fit the experimental data than the other two models, which indicated that this analytical model could better describe the kinetics of Fenton reaction mathematically and chemically. Results indicated that the oxidation rate and removal efficiency were strongly dependent on initial pH, initial concentration of Fenton reagents, initial HA concentration and reaction temperature. The experiments demonstrated that hydrogen peroxide and ferrous ion would approach their saturated value with increasing dosage.

Utilization of municipal sewage sludge as additives for the production of eco-cement

The effects of using dried sewage sludge as additive on cement property in the process of clinker burning were investigated in this paper. The eco-cement samples were prepared by adding 0.50-15.0% of dried sewage sludge to unit raw meal, and then the mixtures were burned at 1450 °C for 2 h. The results indicated that the major components in the eco-cement clinkers were similar to those in ordinary Portland cement. Although the C(2)S phase formation increased with the increase of sewage sludge content, it was also found that the microstructure of the mixture containing 15.0% sewage sludge in raw meal was significantly different and that a larger amount of pores were distributed in the clinker. Moreover, all the eco-cement pastes had a longer initial setting time and final setting time than those of plain cement paste, which increased as the sewage sludge content in the raw meal increased. All the eco-cement pastes had lower early flexural strengths, which increased as the sewage sludge content increased, while the compressive strengths decreased slightly. However, this had no significant effect on all the strengths at later stages. Furthermore, the leaching concentrations of all the types of eco-cement clinkers met the standard of Chinese current regulatory thresholds.

Start-up of simultaneous removal of ammonium and sulfate from an anaerobic ammonium oxidation (anammox) process in an anaerobic up-flow bioreactor.

A laboratory testing of simultaneous removal of ammonium and sulfate (SRAS) was studied from an anammox process in an anaerobic bioreactor filled with granular activated carbon. Two different phases of experiment were investigated to start up the SRAS process, and final batch tests were performed to analyze the SRAS process. The experiment included an anammox process and an SRAS process. During the anammox process, the highest removal efficiency of ammonium and nitrite was up to 97 and 98%, respectively. After 160 days in the stationary phase of anammox process, the ratio of ammonium to nitrite consumption was approximately 1:1.15, which is much higher than 1:1.32 in the traditional anammox process. The extra electron acceptor, such as sulfate, was thought to react with ammonium by bacteria. Synthetic wastewater containing ammonium chlorine and sodium sulfate was used as the feed for the bioreactor in the second phase of experiment. During the SRAS process, the influent concentrations of ammonium and sulfate were controlled to be 50-60 and 210-240 mg L(-1) respectively. After start-up and acclimatization of this process for 60 days, the average effluent concentrations of ammonium and sulfate were 30 and 160 mg L(-1), respectively. The simultaneous ammonium and sulfate removal was detected in the reactor. In order to further validate the biochemical interaction between ammonium and sulfate, batch tests was carried out. Abiotic tests were carried out to demonstrate that the pure chemical action between ammonium and sulfate without microorganism was not possible. Biotic assays with different ammonium and sulfate concentrations were further investigated that high concentrations of ammonium and sulfate could promote simultaneous removal of ammonium and sulfate. And elemental sulfur and nitrogen gas as the products measured in the SRAS process helped to demonstrate the occurrence of new interaction between nitrogen and sulfur. The new process of SRAS in the inorganic condition, including simultaneous removal of ammonium and sulfate, and the appearance of elemental sulfur and nitrogen gas as the terminal products, widened the cycle approach between nitrogen and sulfur.

Combined treatment of domestic wastewater with landfill leachate by using A2/O process

A set of anaerobic-anoxic-aerobic (A(2)/O) bioreactor system was designed and used to treat domestic wastewater mixed with landfill leachate in Datansha Sewage Treatment Plant in Guangzhou, south China. The optimal mixing proportion of combined treatment of domestic wastewater with landfill leachate and the optimal operating conditions for the removal efficiencies of nitrogen by using Taguchi orthogonal array test was conducted to evaluate the influence of parameters. The results showed that: the optimal volume ratio of landfill leachate and domestic wastewater in the A(2)/O process was 1:500. The average removal efficiencies of NH(4)(+)-N, TN and COD was achieved to be 96.5%, 61.0% and 81.7%, respectively in the case of the hydraulic retention time (HRT) of 11h, dissolved oxygen (DO) of 3 mg L(-1), the mixed-liquid return ratio (r) of 200% and sludge return ratio (R) of 80% in the case of the confirmatory experiment. The pilot scale (3.8m(3)) investigation results were applied in the large-scale (220,000 m(3)/d) combined treatment of sewage wastewater with landfill leachate in Guangzhou Datansha Domestic Sewage Wastewater Treatment Plant. The removal efficiencies of COD, NH(4)(+)-N, T-N and T-P were 82.65%, 92.69%, 57.10% and 76.55%, respectively.

Mathematical model analysis of Fenton oxidation of landfill leachate

The treatment of concentrated landfill leachate rejected from reverse osmosis (RO) with Fenton process was studied, and the system model was developed through the examination of reaction kinetics. The leachate is typically non-biodegradable with low BOD(5)/COD ratio 0.01. The oxidation reactions of Fenton process was found to be a two-stage process, where a fast initial reaction (H(2)O(2)/Fe(2+)) was followed by a much slower one (H(2)O(2)/Fe(3+)). A simple and more accurate mathematics model based on COD and TOC removals has been derived successfully to describe the two-stage reaction kinetics. The two corresponding parameters involved in this model have been identified as the initial reaction rate and the maximum oxidation removal efficiency, respectively. It was found to be very useful for evaluating the performance of Fenton system and/or for process design using the two parameters under different experimental conditions.

Transformation of metals speciation in a combined landfill leachate treatment

Landfill leachate was treated by a combined sequential batch reactor (SBR), coagulation, Fenton oxidation and biological aerated filter (BAF) technology. The metals in treatment process were fractionated into three fractions: particulate and colloidal (size charge filtration), free ion/labile (cation exchange) and non-labile fractions. Fifty percent to 66% Cu, Ni, Zn, Mn, Pb and Cd were present as particulate/colloidal matter in raw leachate, whereas Cr was present 94.9% as non-labile complexes. The free ion/labile fractions of Ni, Zn, Mg, Mn, Pb and Cd increased significantly after treatment except Cr. Fifty-nine percent to 100% of Al was present mainly as particulate/colloidal matter >0.45 μm and the remaining portions were predicted as non-labile complexes except in coagulation effluent. The speciation of Fe varied significantly in various individual processes. Visual MINTEQ simulation showed that 95-100% colloidal species for Cu, Cd and Pb were present as metal-humic complexes even with the lower dissolved organic carbon. Optimum agreements for the free ion/labile species were within acidic solution, whereas under-estimated in alkaline effluents. Overestimated particulate/colloidal fraction consisted with the hypothesis that a portion of colloids in fraction <0.45 μm were considered as dissolved.