Mechanical micromachining: a sustainable micro-device manufacturing approach?

The use of mechanical micromachining to produce micro-devices is a flexible approach that can use any material that can be machined. The energy consumption for micromachining was compared between a conventional CNC and a micro-milling facility and showed that the energy usage for conventional CNC is highly inefficient. An energy footprint that is two to three magnitudes smaller is possible with a custom built micro-milling facility. The rapid increase in the manufacture of micro-devices, which will more than double in the next five years, will require careful planning if a sustainable future is to be envisaged for the use of mechanical micromachining for mass manufacture.     

Parathion degradation and its intermediate formation by Fenton process in neutral environment

The purpose of this study is to investigate parathion degradation by Fenton process in neutral environment. The initial parathion concentration for all the degradation experiments was 20 ppm. For hydrogen ion effect on Fenton degradation, the pH varied from 2 to 8 at the [H₂O₂] to [Fe²⁺] ratio of 2-2 mM, and the result showed pH 3 as the most effective environment for parathion degradation by Fenton process. Apparent degradation was also observed at pH 7. The subsequent analysis for parathion degradation was conducted at pH 7 because most environmental parathion exists in the neutral environment. Comparing the parathion degradation results at various Fenton dosages revealed that at Fe²⁺ concentrations of 0.5, 1.0 and 1.5 mM, the Fenton reagent ratio ([H₂O₂]/[Fe²⁺]) for best-removing performance were found as 4, 3, and 2, resulting in the removal efficiencies of 19%, 48% and 36%, respectively. Further increase in Fe²⁺ concentration did not cause any increase of the optimum Fenton reagent ratio for the best parathion removal. The result from LC-MS also indicated that hydroxyl radicals might attack the PS double bond, the single bonds connecting nitro-group, nitrophenol, or the single bond within ethyl groups of parathion molecules forming paraoxons, nitrophenols, nitrate/nitrite, thiophosphates, and other smaller molecules. Lastly, the parathion degradation by Fenton process at the presence of humic acids was investigated, and the results showed that the presence of 10 mg L⁻¹ of humic acids in the aqueous solution enhanced the parathion removal by Fenton process twice as much as that without the presence of humic acids.     

Impact of polycyclic aromatic hydrocarbon emissions from medical waste incinerators on the urban atmosphere

In this study, polycyclic aromatic hydrocarbon (PAH) emissions from two batch-type medical waste incinerators (MWIs), one with a mechanical grate and the other with a fixed grate, both operated by a medical center, were assessed. Both MWIs shared the same air-pollution control devices (APCDs), with an electrostatic precipitator and a wet scrubber installed in series. Results show that when APCDs were used, total PAHs and total benzo[a]pyrene equivalent (total BaP(eq)) emission concentrations of both MWIs were reduced from 2220 to 1870 microg/m3 and 50 to 12.4 microg/m3, respectively. We used the Industrial Source Complex Short Term model (ISCST) to estimate the ground-level concentrations of the residential area and the traffic intersection located at the downwind side of the two MWIs. For the traffic intersection, we found both total PAHs and total BaP(eq) transported from MWIs to both studied areas were not significant. For the residential area, similar results were found when APCDs were used in MWIs. When APCDs were not included, we found that total PAHs transported from MWIs accounted for < 12%, but total BaP(eq) accounted for > 90%, of the on-site measured concentrations. These results suggest that the use of proper APCDs during incineration would significantly reduce the carcinogenic potencies associated with PAH emissions from MWIs to the residential area.     

Impact of Polycyclic Aromatic Hydrocarbon Emissions from Medical Waste Incinerators on the Urban Atmosphere

Abstract

In this study, polycyclic aromatic hydrocarbon (PAH) emissions from two batch-type medical waste incinerators (MWIs), one with a mechanical grate and the other with a fixed grate, both operated by a medical center, were assessed. Both MWIs shared the same air-pollution control devices (APCDs), with an electrostatic precipitator and a wet scrubber installed in series. Results show that when APCDs were used, total PAHs and total benzo- [a]pyrene equivalent (total BaP_eq) emission concentrations of both MWIs were reduced from 2220 to 1870 µg/m³ and 50 to 12.4 µg/m³, respectively. We used the Industrial Source Complex Short Term model (ISCST) to estimate the ground-level concentrations of the residential area and the traffic intersection located at the down-wind side of the two MWIs. For the traffic intersection, we found both total PAHs and total BaP_eq transported from MWIs to both studied areas were not significant. For the residential area, similar results were found when APCDs were used in MWIs. When APCDs were not included, we found that total PAHs transported from MWIs accounted for <12%, but total BaP_eq accounted for >90%, of the on-site measured concentrations. These results suggest that the use of proper APCDs during incineration would significantly reduce the carcinogenic potencies associated with PAH emissions from MWIs to the residential area.     

The need for global coordination in sustainable development

Natural resources are being depleted at faster rates than ever; this highlights the need for global audits and actions to reverse the depletion. Coordinated efforts by various organizations are essential to quantify reserves and demands in such audits in order to enable the development and implementation of strategies for sustainable recovery, usage, and recycling of natural resources. This paper discusses such audits in several industries and puts forward analytical and technical methods and policies for sustainable recovery, usage and recycling of resources in those industries. Scenario analysis can help to provide better future directions for industries whilst eco-industrial parks could improve the efficiency of usage of available resources and waste products through synergies among different industries on a regional basis. Sustainable manufacturing within industries such as micromachining, cement and leather could further reduce consumption of natural resources. New technologies in mineral recovery could help to recover valuable minerals present in concentrates generated by various processes such as reverse osmosis of sea water, chemical processing of minerals, and domestic and industrial wastewater treatments. These areas are discussed in this special issue of the Journal of Cleaner Production. It is imperative that the efforts by various organizations toward sustainable management of natural resources should compliment each other to minimize duplication; furthermore policy makers should play greater roles in developing and implementing policies and procedures to support such sustainable development oriented approaches simultaneously throughout the world in a coordinated and proactive manner for the short and long term future.