Biotechniques for air pollution control

This paper gives an overview of present biological techniques for the treatment of off-gases and the techniques that are being developed at the moment. The characteristics, advantages, disadvantages, costs and application area are discussed and compared. Biological off-gas treatment is based on the absorption of volatile contaminants in an aqueous phase or biofilm followed by oxidation by the action of microorganisms. Biofilters, bioscrubbers and biotrickling filters are used for elimination of odour and bioconvertable volatile organic and inorganic compounds and are enjoying increasing popularity. This popularity is a result of the low investment and operational costs involved compared to physico-chemical techniques and the elimination efficiencies that can be obtained. The operational envelop is still extending to higher concentrations and gas flow rates (exceeding 200,000 m³ h^–1) and a broader spectrum of degradable compounds. Research and development on the use of membranes and the addition of activated carbon or a second liquid phase to the biological systems may lead to a more efficient elimination of hydrophobic compounds and buffering of fluctuating loads. Shorter adaptation periods can be obtained by inoculation with specialized microorganisms. Improved design and operation are made possible by the growing insights in the kinetics and microbiology and supported by the development of models describing biological off-gas treatment. In conclusion, biotechniques are efficient and cost effective in treating off-gases with concentrations of biodegradable contaminants up to 1–5 g/m³. They could play a justified and important role in air pollution control in the coming years.Abbreviations VOC volatile organic compound - NO _x gaseous oxides of nitrogen     

Allium test for air and water borne pollution control

An Allium cepa test was used to study the genotoxicity of the ecosystem. Elevated frequencies of chromosomal aberrations (CA) and root growth inhibition were observed in Allium as a result of exposure to genotoxicants investigated in rainfall, snowfall, a petrochemical polluted site and in aquarium water, compared with the relevant control. The Allium test has been shown to be a useful tool for the detection of potentially genotoxic substances in air and water screening programmes.     

Development of foamed emulsion bioreactor for air pollution control

A new type of bioreactor for air pollution control has been developed. The new process relies on an organic-phase emulsion and actively growing pollutant-degrading microorganisms, made into a foam with the air being treated. This new reactor is referred to as a foamed emulsion bioreactor (FEBR). As there is no packing in the reactor, the FEBR is not subject to clogging. Mathematical modeling of the process and proof of concept using a laboratory prototype revealed that the foamed emulsion bioreactor greatly surpasses the performance of existing gas-phase bioreactors. Experimental results showed a toluene elimination capacity as high as 285 g(toluene) m(-3) (reactor) h(-1) with a removal efficiency of 95% at a gas residence time of 15 s and a toluene inlet concentration of 1-1.3 g x m(-3). Oxygen limited the reactor performance at toluene concentration above about 0.7-1.0 g x m(-3); consequently, performance was significantly improved when pure oxygen was added to the contaminated air. The elimination capacity increased from 204 to 408 g x m(-3) h(-1) with >77% toluene removal at toluene inlet concentrations of 2-2.2 g x m(-3). Overall, the results show that the performance of the FEBR far exceeds that of currently used bioreactors for air pollution control.     

大气污染规制对城市空气污染的防治成效——基于准实验分析

以2003年实施的大气污染防治重点城市政策为准自然实验,运用双重差分模型从区域层面分析了大气污染规制对城市空气污染治理的影响,研究发现：（1）大气污染规制在1%的显著性水平下降低了重点城市的工业二氧化硫排放强度,工业二氧化硫排放量以及城市PM2.5年均浓度值。（2）大气污染防治重点城市政策实施后的9年时间内有效减少了12215.8万t城市工业二氧化硫排放量,并且使得城市PM2.5年均浓度改善2.97μg/m3,下降比分别达到了36.2%和8.5%,平均每年减少了3.7%的城市工业二氧化硫排放量并降低0.944%的城市PM2.5浓度值。（3）大气污染防治重点城市政策对于城市空气污染治理主要是通过减少能源消耗量、增加城市污染治理力度、促进规制地区产业结构转型升级和提升生产技术水平等渠道予以实现。     

The effect of air pollution on the mechanism of stomatal control

Summary A long-term field experiment permanently measuring gas exchange in the top of a 70-year-old spruce, continued for through the 1990 growing season. Two gas exchange chambers were run simultaneously under identical climatic conditions. One of two similar twigs was exposed to ambient air whereas the other received pure air. These experiments aimed to examine the ability of the stomata to control water balance, comparing pure and ambient air. This was done not only in natural climatic conditions but also in experimental, specifically maintained stress situations. Special care was taken to ensure that only steady state values of stomatal responses are related to the environmental stimuli. During a drought period lasting several weeks, overshooting transpiration values were documented for the ambient air. The two twigs do not merely differ in their control capacity, but the behaviour of the stomata in ambient air deviates from the norm. The increasingly uncontrolled water losses during the drought period have a negative effect on photosynthetic capacity. The influence of water deficit on stomatal response to other environmental factors (light, CO₂) is shown. Due to deficient control quality of the stomata lower stress tolerance in the face of drought is suggested in ambient air as compared with pure air. By tracing dysfunctions to structural changes in the cell walls of the stomatal apparatus, a mechanism is described explaining forest decline under the combined influence of air pollutants and drought stress.     

Toluene degradation in the recycle liquid of biotrickling filters for air pollution control

Pollutant degradation in biotrickling filters for waste air treatment is generally thought to occur only in the biofilm. In two experiments with toluene degrading biotrickling filters, we show that suspended microorganisms in the recycle liquid may substantially contribute to the overall pollutant removal. Two days after reactor start up, the overall toluene elimination capacity reached a maximum of 125 g m⁻³ h⁻¹, which was twice that found during prolonged operation. High biodegradation activity in the recycle liquid fully accounted for this short-term peak of pollutant elimination. During steady-state operation, the toluene degradation in the recycle liquid was 21% of the overall elimination capacity, although the amount of suspended biomass was only 1% of the amount of immobilized biomass. The results suggest that biotrickling filter performance may be improved by selecting operating conditions allowing for the development of an actively growing suspended culture. Received: 16 June 1999 / Received revision: 17 November 1999 / Accepted: 15 December 1999     

Perspectives in chronobiology of air pollution

In a series of experiments, male and female Sprague Dawley rats, kept in light (L) from 06(00) to 18(00) alternating with darkness (LD 12:12) inhaled different concentrations of carbon monoxide (50-1,700 ppm) at each of two test times, 12 h apart. A decrease in flow of CO2 (VCO2) resulting from CO inhalation was greater in the active dark (D) than resting light (L) span. Experimental hypoxic mortality of male and female mice also shows circadian variations, being greater in the D than in the L span. Moreover, a difference of mortality was observed betwen hypoxic exposures performed at 12(00) (in LD or DL) and hypoxic exposures performed at 00(00) (in LD or DL). Such results await tests of any extent to which they model responses of human beings to air pollution. In human beings any external environmental circadian, circaseptan and circannual variations in air pollution as such may serve to variable extent as socioeconomic synchronizers of innate rhythms with a corresponding frequency, rather than as solely generators of time patterns in any physiopathologic response to air pollution.     

External air pollution costs of telework

Background, Aims and Scope  Telework is associated with a number of costs and benefits, including reduced company overhead costs, need for office and parking space, office energy consumption, increased productivity, reduced absenteeism, retention of specialized employees, reduction in transportation-related fuel consumption and air pollution, and many others. This paper applies a systems model to telework and nontelework scenarios to quantify direct energy and fuel costs and external costs related to air emissions from transportation, heating, cooling, lighting, and electronic and electrical equipment use both at the company and the home office, including rebound effects. Methods  E-COMMUTair, a scalable web-based tool created by the authors and designed to assess the air pollution effects of individual or company telework programs versus nontelework is employed along with Monte Carlo simulation and sensitivity analysis. E-COMMUTair is using the latest available U.S. energy use and air emission factors. The external costs of air emissions are estimated. The role of telecommuting frequency is emphasized, and differences between various states are explored. The paper identifies the drivers of external costs, and presents an example breakeven analysis focused on CO₂ and key model parameters. Results and Discussion  Nontelework’s external costs are equal to or higher than telework’s costs for every model component, demonstrating that telework programs could provide benefits, including monetary benefits, to society. Transportation is the major contributor to the total costs, with home heating and cooling, and office cooling following. Most of the monetary costs associated with transportation are borne by individuals rather than society. Teleworking employees increase their home-related expenses but reduce their travel-related expenses, ending up with smaller total costs. Energy and fuel costs get reduced in the office space when telework programs are applied, resulting in benefits to companies. Energy and external costs decrease as telework frequency increases. When compared to not teleworking, 5-day telework scenarios on cooling days in California can have about 50–70% lower total costs. The probabilistic analysis confirms the results of the deterministic analysis. The sensitivity analysis reveals that for the nontelework scenario, transportation-related variables such as commuting distance and average number of passengers affect CO₂, CO, and NO_x emissions, while for the telework part, frequency and the number of roundtrips are the most relevant. Conclusions  Both analyses show that telework programs have the potential to lower both energy and external costs creating a favorable bottom line for society, employees, and companies by decreasing tailpipe emissions, lowering transportation costs, and decreasing energy costs at the company office. However, important parameters such as telecommuting frequency, characteristics of the office and home space, climate patterns, and rebound effects that determine external costs along with the price of gasoline, electricity and natural gas in the state where the program is implemented can greatly influence the final results, and should be carefully examined. Recommendations and Perspectives  The effects of telework programs on people’s daily lives are complex and difficult to predict and quantify. The current analysis showed that significant financial benefits can be expected from telework programs, but as seen often in environmental policy-making, the details of implementation will make or break the success of a program. formerly Postdoctoral Researcher, University of California, Berkeley ESS-Submission Editor: Dr. Gerald Rebitzer (Gerald.Rebitzer@alcan.com)