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In this study, the influence of Na2SO4 on electro-dewatering (EDW) of waste activated sludge (WAS) was investigated. The highest water removal efficiency of 42.5% was achieved at the optimum Na2SO4 dosage of 12.5 g kg−1 DS during EDW process at a constant voltage of 20 V. The migration and distribution of water, organic matters and Na+ at different Na2SO4 dosages were investigated through layered experiments. The results indicated the entire EDW process followed the S curve model, and it can be divided into three stages: (1) initial desalination stage: at the initial few min of EDW process, the rate of electroosmosis was extremely slow while electromigration of ions like Na+ was intense, and the electromigration was more obvious with increased Na2SO4 dosage; (2) dewatering stage: the dewatering efficiency increased dramatically via electroosmosis; (3) the dewaterability limit stage: the maximum value of dewatering efficiency has been achieved, while the water removal efficiency and dry solids content remained constant. During the EDW process, the possible electrolysis resulted in a pH gradient in the sludge cake. With the addition of Na2SO4 in the EDW, the pH gradient was intensified, and the migration rate of organic matters moving from cathode to anode increased while compared with the raw WAS. This study provided insights into the mechanism of EDW process at different dosages of Na2SO4.

Kinetic studies on the pyrolysis process for non-metallic fraction (NMF) of waste printed circuit boards (WPCBs) were conducted using both the isoconversional SKAS method and the discrete distributed activation energy model (discrete DAEM). The pyrolysis process of the NMF sample could be classified into three stages, and a large mass loss was observed from 98 to 570 °C, attributed to thermal degradation of epoxy resins in the NMF sample. The kinetic parameters, including activation energies (E i), pre-exponential factors (A i), and contributed fractions (f i,0), were determined. It indicated that the discrete DAEM could predict the pyrolysis process of the NMF more accurately and completely when compared with the isoconversional SKAS method. In the discrete DAEM, E i and A i values were evaluated at 99 equally spaced intervals of conversion. The E i and A i (in the form of lnA i) transformed with reaction progress, ranging from 80.9 to 240.5 kJ/mol and 19.07 to 39.55 s−1, respectively, with the conversion increased from 0.01 to 0.99. The pyrolysis of the NMF of WPCBs could be accurately characterized as 17 dominating reactions from f i,0 results.

Two types of deep-dewatered sewage sludge cakes were produced from pilot-scale experiments by using two composite conditioners: FeCl3 + quick lime (Fe–Lime) and Fenton's reagent + red mud (Fenton–RM). The feasibility of direct reuse without any solidifying agents of these two deep-dewatered cakes, with water content of about 60 wt%, as landfill cover materials was investigated. Geotechnical properties of these two sludge cakes were found appropriate for reuse as landfill covers. Their plasticity index values increased significantly from 11.6 (raw sludge) to 23.8 (Fe–Lime) and 35.4 (Fenton–RM). The unconfined compressive strength and direct shear strength of the two deep-dewatered sludge cakes could meet or exceed the requirement of landfill cover materials after a certain curing time. Microstructural analyses of scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that their microstructures were more porous than that of raw sludge since the skeleton builders played a role in building the rigorous framework. There was negligible leaching of Cu, Zn, Pb, Cd and Cr from the deep-dewatered sludge cake from the toxicity characteristic leaching procedure and column leaching test. Both deep-dewatered sludge cakes could be reused as effective landfill cover materials with a suitable curing time.

A liquid–gas two-phase computational fluid dynamics (CFD) model was developed to simulate flow field and gas hold-up in a pilot-scale oxidation ditch (OD). The volume of fluid (VOF) model and the mass flow inlet boundary condition for gas injection were introduced in this model. The simulated values of the flow velocities and the gas hold-up were verified by experimental measurements in the pilot-scale OD. The results showed that the gas hold-up at test-site 3, immediately downstream of the surface aerator, was the highest among all three test-sites. Most of the gas existed in the upper portion of the ditch and was close to the inner side of the channel. Based on the liquid–gas two-phase CFD model, three operating conditions with different setting height ratios of the submerged impellers were simulated. The simulated results suggested that the setting heights of the submerged impellers have significant impacts on the flow velocity distribution. Lowering the setting height could increase the flow velocity in the pilot-scale OD. An optimal setting height ratio of 0.273 was proposed, which would be beneficial for minimizing sludge sedimentation, especially near the inner side of the curve bend.

Non-metallic fractions (NMFs), which make up almost three fourths (by weight) of waste printed circuit boards, have become a matter of great concern for e-waste recyclers, because most of them contain hazardous substances with low utilization value. This study used an advanced Sales Obsolescence Model approach to quantify the generation and flows of non-metallic fractions in China, and to examine the potential environmental impacts associated with both the fractions themselves, and their end-of-life processing activities: disposal into landfills or incineration, and recycling via physical or chemical methods. The results show that approximately 201,000 tons (one time standard deviation: 67,000) of scrap non-metallic fractions were expected to be generated in 2015, and that this amount could increase to 279,000 tons by 2020. Both our own analysis and a systematic review of existing studies on the hazardous characterization of printed circuit boards waste, non-metallic fractions, and their recycling and disposal activities, indicate the threat of environmental pollution, from heavy metals, brominated flame retardants and secondary persistent organic pollutants, particularly dioxins.

This study investigated the pyrolytic performances of deep-dewatered sludge cakes which were previously conditioned with Fenton's reagent and red mud. The pyrolytic products, including fuel gas, tar and solid char, were characterized by GC, GC-MS and FTIR. The results showed that pyrolysis of sludge cakes conditioned with Fenton's reagent and red mud produced more gas, especially higher H2 yield, compared with pyrolysis of raw sludge. In addition, red mud promoted PAHs formation and tar re-formation through side-chain-cleaving, dehydrogenation, polycondensation and aromatization of hydrocarbon during the pyrolysis, resulting in enhancement of the H2 yield. The sharp decrease in the absorbance of C Haromatic group of chars from the conditioned cakes implied that red mud could intensify the cracking and re-formation of aromatics. The higher the iron oxide content in red mud was, the better catalytic efficiency in the decomposition of organics and tar re-formation was, which led to more H2 production.

Over the last decade, there has been much effort to promote the management of e-waste in China. Policies have been affected to prohibit imports and to control pollution. Research has been conducted in laboratories and on large-scale industrial operations. A subsidy system to support sound e-waste recycling has been put in place. However, the handling of e-waste is still a concern in China and the issue remains unresolved. There has been relatively little work to follow up this issue or to interpret continuing problems from the perspective of sustainable development. This paper first provides a brief overview of conventional and emerging environmental pollution in Chinese "famous" e-waste dismantling areas, including Guiyu in Guangdong and Wenling in Zhejiang. Environmentalists have repeatedly proven that these areas are significantly polluted. Importing and backyard recycling are decreasing but are ongoing. Most importantly, no work is being done to treat or remediate the contaminated environmental media. The situation is exacerbated by the rising tide of e-waste generated by domestic update of various electronics. This study, therefore, employs a Sales Obsolescence Model approach to predict the generation of e-waste. When accounting for weight, approximately 8 million tons of e-waste will be generated domestically in 2015, of which around 50% is ferrous metals, followed by miscellaneous plastic (30%), copper metal and cables (8%), aluminum (5%), and others (7%). Of this, 3.6% will come from scrap PCBs and 0.2% from lead CRT glass. While more and more end-of-life electronics have been collected and treated by formal or licensed recyclers in China in terms of our analysis, many of them only have dismantling and separation activities. Hazardous e-wastes, including those from PCBs, CRT glass, and brominated flame retardant (BFR) plastics, have become problematic and probably flow to small or backyard recyclers without environmentally sound management. Traditional technologies are still being used to recover precious metals--such as cyanide method of gold hydrometallurgy--from e-waste. While recovery rates of precious metals from e-waste are above 50%, it has encountered some challenges from environmental considerations. Worse, many critical metals contained in e-waste are lost because the recovery rates are less than 1%. On the other hand, this implies that there is opportunity to develop the urban mine of the critical metals from e-waste.

Waste printed circuit boards (WPCBs) are resource-rich but hazardous, demanding innovative strategies for post-consumer collection, recycling, and mining for economically precious constituents. A novel technology for disassembling electronic components from WPCBs is proposed, using hot air to melt solders and to separate the components and base boards. An automatic heated-air disassembling equipment was designed to operate at a heating source temperature at a maximum of 260 °C and an inlet pressure of 0.5 MPa. A total of 13 individual WPCBs were subjected to disassembling tests at different preheat temperatures in increments of 20 °C between 80 and 160 °C, heating source temperatures ranging from 220 to 300 °C in increments of 20 °C, and incubation periods of 1, 2, 4, 6, or 8 min. For each experimental treatment, the disassembly efficiency was calculated as the ratio of electronic components released from the board to the total number of its original components. The optimal preheat temperature, heating source temperature, and incubation period to disassemble intact components were 120 °C, 260 °C, and 2 min, respectively. The disassembly rate of small surface mount components (side length ≤ 3 mm) was 40-50% lower than that of other surface mount components and pin through hole components. On the basis of these results, a reproducible and sustainable industrial ecological protocol using steam produced by industrial exhaust heat coupled to electronic-waste recycling is proposed, providing an efficient, promising, and green method for both electronic component recovery and industrial exhaust heat reutilization. © 2013 American Chemical Society.