Review of Water Consumption and Water Conservation Technologies in the Algal Biofuel Process

Although water is one of the most critical factors affecting the sustainable development of algal biofuels, it is much less studied as compared to the extensive research on algal biofuel production technologies. This paper provides a review of the recent studies on water consumption of the algae biofuel process and presents the water conservation technologies applicable at different stages of the algal biofuel process. Open ponds tend to have much higher water consumption (216 to 2000 gal/gal) than photobioreactors (25 to 72 gal/gal). Algae growth accounts for the highest water consumption (165 to 2000 gal/gal) in the open pond system. Water consumption during harvesting, oil extraction, and biofuel conversion are much less compared with the growth stage. Potential water conservation opportunities include technology innovations and better management practices at different stages of algal biofuel production.

The deployment of carbon monoxide wireless sensor network (CO-WSN) for ambient air monitoring

Wireless sensor networks are becoming increasingly important as an alternative solution for environment monitoring because they can reduce cost and complexity. Also, they can improve reliability and data availability in places where traditional monitoring methods are difficult to site. In this study, a carbon monoxide wireless sensor network (CO-WSN) was developed to measure carbon monoxide concentrations at a major traffic intersection near the University of Cincinnati main campus. The system has been deployed over two weeks during Fall 2010, and Summer 2011–2012, traffic data was also recorded by using a manual traffic counter and a video camcorder to characterize vehicles at the intersection 24 h, particularly, during the morning and evening peak hour periods. According to the field test results, the 1 hr-average CO concentrations were found to range from 0.1–1.0 ppm which is lower than the National Ambient Air Quality Standards (NAAQS) 35 ppm on a one-hour averaging period. During rush hour periods, the traffic volume at the intersection varied from 2,067 to 3,076 vehicles per hour with 97% being passenger vehicles. Furthermore, the traffic volume based on a 1-h average showed good correlation (R² = 0.87) with the 1-h average CO-WSN concentrations for morning and evening peak time periods whereas CO-WSN results provided a moderate correlation (R² = 0.42) with 24 hours traffic volume due to fluctuated changes of meteorological conditions. It is concluded that the performance and the reliability of wireless ambient air monitoring networks can be used as an alternative method for real time air monitoring.

Dissolution kinetics of magnesium hydroxide for CO2 separation from coal-fired power plants

The dissolution of magnesium hydroxide in water for the release of magnesium and hydroxyl ions into the solution to maintain suitable alkalinity is a crucial step in the Mg(OH)2-based CO2 absorption process. In this study, the rate of dissolution of Mg(OH)2 was investigated under different operating conditions using a pH stat apparatus. The dissolution process was modeled using a shrinking core model and the overall Mg(OH)2 dissolution process was found to be controlled by the surface chemical reaction of Mg(OH)2 with H(+) ions. Under the chemical reaction control regime, the dissolution of Mg(OH)2 in alkaline conditions was found not to follow a first-order reaction, and the fractional order of reaction was estimated to lie between 0.20 and 0.31. This suggests that the dissolution reaction is a non-elementary reaction, consisting of a sequence of elementary reactions, via most likely forming a surface magnesium complex. The true activation energy value of 76 ± 11 kJ/gmol was found to be almost twice as much as the observed activation energy value of 42 ± 6 kJ/gmol determined at pH 8.6, and was comparable with the previously reported values. The particle sizes predicted from the intrinsic kinetics determined from the model were in good agreement with the experimentally measured particle sizes during the dissolution process.

Evaluation of a sustainable remediation option: beneficial reuse of petroleum-contaminated sediment as an energy source

The characteristics of petroleum-contaminated sediment (PCS) have been evaluated to assess whether the practice of its beneficial reuse as a sole or supplemental energy source is sustainable relative to other sediment remediation options such as monitored natural recovery (MNR), capping, or off-site disposal. Some of these remediation options for PCS are energy-intensive and/or require land utilization. The energy and compositional analysis results indicate a low carbon content (15-17%(wt)) and corresponding low energy values of 5,200 kJ/kg (2,200 Btu/lb) to 5,600 kJ/kg (2,400 Btu/lb). However, given other decision-making criteria, the sediment may contain enough value to be added as a supplemental fuel given that it is normally considered a waste product and is readily available. The thermogravimetric profiles obtained under both combustion and pyrolytic conditions showed that the sulfur contents were comparable to typical low sulfur bituminous or lignite coals found in the United States, and most of the volatiles could be vaporized below 750 degrees C. The heavy metal concentrations determined before and after combustion of the PCS indicated that further engineering controls may be required for mercury, arsenic, and lead. Due to the potential for reduction of public health and environmental threats, potential economic savings, and conservation of natural resources (petroleum and land), removal of PCS by dredging and beneficial reuse as a supplemental fuel clearly has merit to be considered as a sustainable remediation option.

Effects of activated carbon surface properties on the adsorption of volatile organic compounds

Physical and chemical properties of activated carbon (AC) were analyzed to investigate the effects of adsorbate properties on AC adsorption performance. Fixed-bed adsorption experiments were conducted with toluene, acetone, and xylene as adsorbates. From the results, the adsorption capacities of the three adsorbates had the following order: xylene > toluene > acetone. The correlation between experimental data and adsorbate properties was also analyzed. The results showed that different functional groups corresponding to the properties of adsorbates influenced the adsorptive properties of AC differently. The adsorption capacity of AC increased linearly as the molecular weight, dynamic diameter, boiling point, and density of the adsorbate increased. However, adsorption capacity decreased as the polarity index and vapor pressure of the adsorbate increased. For adsorption onto three types of AC, the adsorption energies of the three adsorbates had the following order: xylene > toluene > acetone.

IMPLICATIONS

This paper focused on the research on adsorption behavior of activated carbon based on adsorbate properties. Adsorption experiments were conducted under the same condition while the adsorbates were toluene, acetone, and xylene, respectively. Correlation analysis between experimental data and adsorbate properties was conducted. The different groups have different influence on the adsorptive properties of ACs. The adsorption capacity of activated carbon increases with the increase of adsorbate molecular weight, dynamic diameter, boiling point, and density, and that this relationship is linear. The relationship between adsorption capacity and the polarity index and vapor pressure of adsorbate shows an opposite trend, and the adsorption capacities and adsorption energies of three kinds of activated carbon for these three adsorbates had the following order: xylene > toluene > acetone.

Long-term wind speed variations for three midwestern U.S. cities

Long-term wind speed variations were investigated for three midwestern cities including Indianapolis, IN; Cincinnati, OH; and Little Rock, AR in the continental United States. These cities were chosen because their topography is relatively flat and unaffected by large mountain ranges or other topographical features, they represent important regional economic centers, and they have all undergone major air quality management efforts over the past 35 yr to attempt to meet the National Ambient Air Quality Standards. The hourly data were obtained from the National Climatic Data Center from 1943 to 2008 for Indianapolis and Little Rock and from 1948 to 2008 for Cincinnati. The analysis included calculating the frequency of calms and wind speeds over five different bins for the respective cities. The results indicate a significant increase in the frequency of calms (statistical significance > 99.999%) and a decrease in the overall frequency of other wind speeds for all three cities. Increasing trend in calms is more predominant during the ozone season (April through October). The results from regression analysis, significance testing, and spatial correlation analysis support the argument that a common "midwestern" large-scale atmospheric forcing is influencing surface wind speed in this area. It was found that for all three cities the Pacific North American (PNA) teleconnection pattern has the highest relative association with the trends in wind speed. The results support large-scale continental effects (like teleconnections) as a hypothesis to be examined more closely along with already established evidence of the influence of the Pacific and Atlantic teleconnection anomalies. Reduced wind speed may have implications on air quality management efforts in the region. Increases in the frequency of calms would affect ozone distribution patterns and may suggest a need to make changes to their ozone mitigation strategy. Weaker winds would ventilate pollutants from these areas less effectively, which could be problematic from a human health point of view, particularly for asthmatics.

Assessment of the ozone-nitrogen oxide-volatile organic compound sensitivity of Mexico City through an indicator-based approach: measurements and numerical simulations comparison

The ozone (O3) sensitivity to nitrogen oxides (NOx, or nitric oxide [NO] + nitrogen dioxide [NO2]) versus volatile organic compounds (VOCs) in the Mexico City metropolitan area (MCMA) is a current issue of scientific controversy. To shed light on this issue, we compared measurements of the indicator species O3/NOy (where NOy represents the sum of NO + NO2 + nitric acid [HNO3] + peroxyacetyl nitrate [PAN] + others), NOy, and the semiempirically derived O3/NOz(surrogate) (where NOz(surrogate) is the derived surrogate NOz, and NOz represents NOx reaction products, or NOy - NOx) with results of numerical predictions reproducing the transition regimes between NOx and VOC sensitivities. Ambient air concentrations of O3, NOx, and NOy were measured from April 14 to 25, 2004 in one downwind receptor site of photochemically aged air masses within Mexico City. MCMA-derived transition values for an episode day occurring during the same monitoring period were obtained through a series of photochemical simulations using the Multiscale Climate and Chemistry Model (MCCM). The comparison between the measured indicator species and the simulated spatial distribution of the indicators O3/ NOy, O3/NOz(surrogate), and NOy in MCMA suggest that O3 in this megacity is likely VOC-sensitive. This is in opposition to past studies that, on the basis of the observed morning VOC/NOx ratios, have concluded that O3 in Mexico City is NOx-sensitive. Simulated MCMA-derived sensitive transition values for O3/NOy, hydrogen peroxide (H2O2)/HNO3, and NOy were found to be in agreement with threshold criteria proposed for other regions in North America and Europe, although the transition crossover for O3/NOz and O3/HNO3 was not consistent with values reported elsewhere. An additional empirical evaluation of weekend/weekday differences in average maximum O3 concentrations and 6:00- to 9:00-a.m. NOx and NO levels registered at the same site in April 2004 indirectly confirmed the above results. A preliminary conclusion is that additional reductions in NOx emissions in MCMA might cause an increase in presently high O3 levels.

Investigation of a mercury speciation technique for flue gas desulfurization materials

Most of the synthetic gypsum generated from wet flue gas desulfurization (FGD) scrubbers is currently being used for wallboard production. Because oxidized mercury is readily captured by the wet FGD scrubber, and coal-fired power plants equipped with wet scrubbers desire to benefit from the partial mercury control that these systems provide, some mercury is likely to be bound in with the FGD gypsum and wallboard. In this study, the feasibility of identifying mercury species in the FGD gypsum and wallboard samples was investigated using a large sample size thermal desorption method. Potential candidates of pure mercury standards including mercuric chloride (HgCl2), mercurous chloride (Hg2Cl2), mercury oxide (HgO), mercury sulfide (HgS), and mercuric sulfate (HgSO4) were analyzed to compare their results with those obtained from FGD gypsum and dry wallboard samples. Although any of the thermal evolutionary curves obtained from these pure mercury standards did not exactly match with those of the FGD gypsum and wallboard samples, it was identified that Hg2Cl2 and HgCl2 could be candidates. An additional chlorine analysis from the gypsum and wallboard samples indicated that the chlorine concentrations were approximately 2 orders of magnitude higher than the mercury concentrations, suggesting possible chlorine association with mercury.

Potential flue gas impurities in carbon dioxide streams separated from coal-fired power plants

For geological sequestration of carbon dioxide (CO2) separated from pulverized coal combustion flue gas, it is necessary to adequately evaluate the potential impacts of flue gas impurities on groundwater aquifers in the case of the CO2 leakage from its storage sites. This study estimated the flue gas impurities to be included in the CO2 stream separated from a CO2 control unit for a different combination of air pollution control devices and different flue gas compositions. Specifically, the levels of acid gases and mercury vapor were estimated for the monoethanolamine (MEA)-based absorption process on the basis of published performance parameters of existing systems. Among the flue gas constituents considered, sulfur dioxide (SO2) is known to have the most adverse impact on MEA absorption. When a flue gas contains 3000 parts per million by volume (ppmv) SO2 and a wet flue gas desulfurization system achieves its 95% removal, approximately 2400 parts per million by weight (ppmw) SO2 could be included in the separated CO2 stream. In addition, the estimated concentration level was reduced to as low as 135 ppmw for the SO2 of less than 10 ppmv in the flue gas entering the MEA unit. Furthermore, heat-stable salt formation could further reduce the SO2 concentration below 40 ppmw in the separated CO2 stream. In this study, it is realized that the formation rates of heat-stable salts in MEA solution are not readily available in the literature and are critical to estimating the levels and compositions of flue gas impurities in sequestered CO2 streams. In addition to SO2, mercury, and other impurities in separated CO2 streams could vary depending on pollutant removal at the power plants and impose potential impacts on groundwater. Such a variation and related process control in the upstream management of carbon separation have implications for groundwater protection at carbon sequestration sites and warrant necessary considerations in overall sequestration planning, engineering, and management.

Bench-scale studies of in-duct mercury capture using cupric chloride-impregnated carbons

A brominated activated carbon (Darco Hg-LH) and cupric chloride-impregnated activated carbon (CuCl2-ACs) sorbent have been tested in a bench-scale entrained-flow reactor system which was developed for simulating in-flight mercury capture in ducts upstream of particulate matter control devices. The bench-scale experimental system has been operated with the conditions of a residence time of 0.75 s and a gas temperature of 140 degrees C to simulate typical conditions in the duct of coal-fired exhaust gas. In addition, sorbent deposition on walls which can occur in a laboratory-scale system more than in a full-scale system was significantly reduced so that additional mercury capture by the deposited sorbent was minimized. In the entrained-flow system, CuCl2-ACs demonstrated similar performance in Hg adsorption and better performance in Hg0 oxidation than Darco Hg-LH. In addition, the carbon content of those sorbents was found to determine their Hg adsorption capability in the entrained-flow system. The bench-scale entrained-flow system was able to demonstrate the important Hg adsorption and oxidation characteristics of the tested sorbents.

Performance of copper chloride-impregnated sorbents on mercury vapor control in an entrained-flow reactor system

An entrained-flow system has been designed and constructed to simulate in-flight mercury (Hg) capture by sorbent injection in ducts of coal-fired utility plants. The test conditions of 1.2-sec residence time, 140 degrees C gas temperature, 6.7 m/sec (22 ft/sec) gas velocity, and 0-0.24 g/m3 (0-15 lbs of sorbent per 1 million actual cubic feet of flue gas [lb/MMacf]) sorbent injection rates were chosen to simulate conditions in the ducts. Four kinds of sorbents were used in this study. Darco Hg-LH served as a benchmark sorbent with which Hg control capability of other sorbents could be compared. Also, Darco-FGD was used as a representative raw activated carbon sorbent. Two different copper chloride-impregnated sorbents were developed in our laboratory and tested in the entrained-flow system to examine the possibility of using these sorbents at coal-fired power plants. The test results showed that one of the copper chloride sorbents has remarkable elemental mercury (Hg(o)) oxidation capability, and the other sorbent demonstrated a better performance in Hg removal than Darco Hg-LH.

Control of diesel gaseous and particulate emissions with a tube-type wet electrostatic precipitator

In this study, experiments were performed with a bench-scale tube-type wet electrostatic precipitator (wESPs) to investigate its effectiveness for the removal of mass- and number-based diesel particulate matter (DPM), hydrocarbons (HCs), carbon monoxide (CO), and oxides of nitrogen (NOx) from diesel exhaust emissions. The concentration of ozone (O3) present in the exhaust that underwent a nonthermal plasma treatment process inside the wESP was also measured. A nonroad diesel generator operating at varying load conditions was used as a stationary diesel emission source. The DPM mass analysis was conducted by means of isokinetic sampling and the DPM mass concentration was determined by a gravimetric method. An electrical low-pressure impactor (ELPI) was used to quantify the DPM number concentration. The HC compounds, n-alkanes, and polycyclic aromatic hydrocarbons (PAHs) were collected on a moisture-free quartz filter together with a PUF/XAD/PUF cartridge and extracted in dichloromethane with sonication. Gas chromatography (GC)/mass spectroscopy (MS) was used to determine HC concentrations in the extracted solution. A calibrated gas combustion analyzer (Testo 350) and an O3 analyzer were used for quantifying the inlet and outlet concentrations of CO and NOx (nitric oxide [NO] + nitrogen dioxide [NO2]), and O3 in the diesel exhaust stream. The wESP was capable of removing approximately 67-86% of mass- and number-based DPM at a 100% exhaust volumetric flow rate generated from 0- to 75-kW engine loads. At 75-kW engine load, increasing gas residence time from approximately 0.1 to 0.4 sec led to a significant increase of DPM removal efficiency from approximately 67 to more than 90%. The removal of n-alkanes, 16 PAHs, and CO in the wESP ranged from 31 to 57% and 5 to 38%, respectively. The use of the wESP did not significantly affect NOx concentration in diesel exhaust. The O3 concentration in diesel exhaust was measured to be less than 1 ppm. The main mechanisms responsible for the removal of these pollutants from diesel exhaust are discussed.

Sex differences noted in mercury bioaccumulation in Magicicada cassini

This study focuses on quantitative differences in mercury bioaccumulation based on the sex of the specimen. The species of interest is an herbivorous, terrestrial insect. Male and female periodical cicadas (genus: Magicicada) analyzed using combustion atomic absorption spectrophotometry exhibit different levels of mercury bioaccumulation. The concentration of mercury in Magicicada cassini males was significantly higher than the concentration in females of the same species.

Collection of ultrafine diesel particulate matter (DPM) in cylindrical single-stage wet electrostatic precipitators

Long-term exposures to diesel particulate matter (DPM) emissions are linked to increasing adverse human health effects due to the potential association of DPM with carcinogenicity. Current diesel vehicular particulate emission regulations are based solely upon total mass concentration, albeit it is the submicrometer particles that are highly respirable and the most detrimental to human health. In this study, experiments were performed with a tubular single-stage wet electrostatic precipitator (wESP) to evaluate its performance for the removal of number-based DPM emissions. A nonroad diesel generator utilizing a low sulfur diesel fuel (500 ppmw) operating under varying load conditions was used as a stationary DPM emission source. An electrical low-pressure impactor (ELPI) was used to quantify the number concentration distributions of diesel particles in the diluted exhaust gas at each tested condition. The wESP was evaluated with respect to different operational control parameters such as applied voltage, gas residence time, etc., to determine their effect on overall collection efficiency, as well as particle size dependent collection efficiency. The results show that the total DPM number concentrations in the untreated diesel exhaust are in the magnitude of approximately108/cm(3) at all engine loads with the particle diameter modes between 20 and 40 nm. The measured collection efficiency of the wESP operating at 70 kV based on total particle numbers was 86% at 0 kW engine load and the efficiency decreased to 67% at 75 kW due to a decrease in gas residence time and an increase in particle concentrations. At a constant wESP voltage of 70 kV and at 75 kW engine load, the variation of gas residence time within the wESP from approximately 0.1 to approximately 0.4 s led to a substantial increase in the collection efficiency from 67% to 96%. In addition, collection efficiency was found to be directly related to the applied voltage, with increasing collection efficiency measured for increases in applied voltage. The collection efficiency based on particle size had a minimum for sizes between 20 and 50 nm, but at optimal wESP operating conditions it was possible to remove over 90% of all particle sizes. A comparison of measured and calculated collection efficiencies reveals that the measured values are significantly higher than the predicted values based on the well-known Deutsch equation.

The fate of chlorinated volatile organic compounds in aeration basins using recirculated aeration: a pilot-plant evaluation

The fate of chloroform, which was chosen to represent chlorinated volatile organic compounds sometimes found in publicly owned wastewater treatment works, has been followed in a pilot aeration basin utilizing aeration recirculation. Tests were conducted using real wastewaters spiked with two different concentration levels of chloroform and operated at conditions similar to those of a large-scale aeration basin of the Mill Creek Wastewater Treatment Plant in Cincinnati, Ohio. Aeration recirculation levels of 0, 25, 50, and 75% were used to evaluate the concept that aeration recirculation can be an effective method of reducing the release of these toxic compounds to the atmosphere. Data obtained demonstrated that the concentration of chloroform in the off-gas increased as the recirculation ratio increased, but that the total mass emission rate to the atmosphere decreased due to the decreased off-gas volumetric flow rate. Biodegradation in the pilot plant increased by 183% for the 75% recirculation level compared to 0% recirculation. Mass balance analysis results indicated that 60% of chloroform emissions could be reduced with 75% recirculation ratio with little or no effect of dissolved oxygen concentration.

Pyrolysis behavior of tire-derived fuels at different temperatures and heating rates

Pyrolytic product distribution rates and pyrolysis behavior of tire-derived fuels (TDF) were investigated using thermogravimetric analyzer (TGA) techniques. A TGA was designed and built to investigate the behavior and products of pyrolysis of typical TDF specimens. The fundamental knowledge of TGA analysis and principal fuel analysis are applied in this study. Thermogravimetry of the degradation temperature of the TDF confirms the overall decomposition rate of the volatile products during the depolymerization reaction. The principal fuel analysis (proximate and ultimate analysis) of the pyrolytic char products show the correlation of volatilization into the gas and liquid phases and the existence of fixed carbon and other compounds that remain as a solid char. The kinetic parameters were calculated using least square with minimizing sum of error square technique. The results show that the average kinetic parameters of TDF are the activation energy, E = 1322 +/- 244 kJ/mol, a pre-exponential constant of A = 2.06 +/- 3.47 x 10(10) min(-1), and a reaction order n = 1.62 +/- 0.31. The model-predicted rate equations agree with the experimental data. The overall TDF weight conversion represents the carbon weight conversion in the sample.

Determination of polycyclic aromatic sulfur heterocycles in diesel particulate matter and diesel fuel by gas chromatography with atomic emission detection

The sulfur content of diesel fuel is of environmental concern because sulfur can facilitate the formation of diesel particulate matter (DPM) and sulfur dioxide (SO2) in the exhaust can poison catalytic converters. The US Environmental Protection Agency (EPA) has established more stringent regulations to reduce the sulfur content of diesel fuels in the near future. In this study, various types of organosulfur compounds in DPM extracts and the corresponding fuels have been determined by gas chromatography with atomic emission detection. The diesel fuels used have sulfur contents of 2284 and 433 ppm, respectively, and are labeled as high-sulfur and low-sulfur diesel fuels. The compounds identified are mainly polycyclic aromatic sulfur heterocycles (PASHs). In the fuels tested, trimethylbenzothiophenes (TMBTs), dibenzothiophenes (DBTs), and 4-methyldibenzothiophene (4-MDBT) were the most abundant sulfur compounds, while larger PASH compounds were more abundant in DPM extracts. The high-sulfur diesel fuel contained a larger proportion of PASHs with one or two rings (lighter PASHs). In DPM, the concentrations of total organic sulfur and individual PASHs are higher for the high-sulfur diesel fuel, and the relative percentage of one or two-ring PASHs is higher as well. The influence of engine load on the DPM composition was also examined. With increasing load, the PASH concentration in DPM decreased for lighter PASHs, increased for heavier PASHs, and had a bell-shaped distribution for PASHs in between.

Development of cost-effective noncarbon sorbents for Hg(0) removal from coal-fired power plants

Noncarbonaceous materials or mineral oxides (silica gel, alumina, molecular sieves, zeolites, and montmorillonite) were modified with various functional groups such as amine, amide, thiol, urea, and active additives such as elemental sulfur, sodium sulfide, and sodium polysulfide to examine their potential as sorbents for the removal of elemental mercury (Hg(0)) vapor at coal-fired utility power plants. A number of sorbent candidates such as amine- silica gel, urea- silica gel, thiol- silica gel, amide-silica gel, sulfur-alumina, sulfur-molecular sieve, sulfur-montmorillonite, sodium sulfide-montmorillonite, and sodium polysulfide-montmorillonite, were synthesized and tested in a lab-scale fixed-bed system under an argon flow for screening purposes at 70 degrees C and/or 140 degrees C. Several functionalized silica materials reported in previous studies to effectively control heavy metals in the aqueous phase showed insignificant adsorption capacities for Hg(0) control in the gas phase, suggesting that mercury removal mechanisms in both phases are different. Among elemental sulfur-, sodium sulfide-, and sodium polysulfide-impregnated inorganic samples, sodium polysulfide-impregnated montmorillonite K 10 showed a moderate adsorption capacity at 70 degrees C, which can be used for sorbent injection prior to the wet FGD system.

Evaluation of ozone-nitrogen oxides-volatile organic compound sensitivity of Cincinnati, Ohio

Ambient concentrations of ozone (O3), nitrogen oxides (NOx), total reactive nitrogen (NOy), nitric acid (HNO3), and hydrogen peroxide (H2O2) were measured during September 2003 at an urban site of Cincinnati, OH. The aim of this study was two-fold: to investigate whether O3 formation in this population exposure-type site is NOx, sensitive or volatile organic compound (VOC) sensitive and to test the practicality of using two combined observational-based methods to identify the sensitivity of O3 formation in midlevel polluted locations. The evaluation of the indicator species: NOy, O3/NOy, O3/HNO3, H2O2/ HNO3, and O3/(estimated NOx reaction products), as well as the combined hypothesis testing analysis of the weekend/weekday (WE/WD) differences of 1-hr and 8-hr average maximum O3 and of the 6:00 a.m.-9:00 a.m. average nitric oxide and NOx concentrations, show evidence that Cincinnati is likely VOC sensitive. Average WE 1-hr and 8-hr maximum O3, as well as duration of WE O3 accumulation, were not lower than the corresponding WD levels in spite of the observed significant reduction in NO, emissions on WE, a typical situation in VOC-sensitive locations. The possibility that the seasonal transition from summer to autumn could have influenced the results was also investigated through an exploratory analysis of the afternoon O3 maximum/NOx measured and of the WE/WD differences of peak O3 and morning average NO and NO, concentrations observed at this site from June through September 2003. The results suggest that a VOC-sensitive chemistry regime dominated along the summer season. The findings of this study suggest that additional reductions in regional NO, emissions in Cincinnati, a potential nonattainment area under the 8-hr O3 standard, may cause an increase in local O3. Future strategies to reduce O3 in Southwest Ohio should be further evaluated carefully. The combination of observational-based methods might provide a consistent complementary approach in the identification of the NO,-VOC sensitive characteristics of mid-to-moderate polluted urban areas.

Biological phosphate uptake and release: effect of pH and magnesium ions

Enhanced biological phosphorus removal (EBPR) is based on poly-phosphate accumulating organisms' (PAOs) unique features of "luxury" phosphate uptake during aerobic conditions and phosphate release in anaerobic conditions. It is believed that poly-phosphate accumulation is accompanied by the uptake and accumulation of potassium ions (K+) and magnesium ions (Mg2+). The release of phosphate under anaerobic conditions is also accompanied by the release of both cations. The objective of this research was to evaluate the effect of pH and Mg2+ on the biological phosphate uptake and release behavior of activated sludge mixed liquor during aeration and sedimentation. Research results indicate that Mg2+, supplied either by magnesium chloride (MgCl2) or magnesium hydroxide [Mg(OH)2], stimulated phosphate uptake during the aeration period, while pH increase, caused by the application of Mg(OH)2, enhanced phosphate release during the sedimentation period. It is also noted in our experiments with MgCl2 that Mg2+ slightly inhibited anaerobic phosphate release.

Variations of the particulate carbon distribution from a nonroad diesel generator

The emissions of diesel particulate matter (DPM) from diesel engines are causing increasing health concerns due to their suspected carcinogenicity, especially the carbonaceous fractions. The total DPM emissions and the organic and elemental carbon (OC and EC) distributions of the DPM depend on many operating factors, such as load, engine design parameters, fuel sulfur content, fuel usage rate, and sampling conditions. Results of previous studies on the OC/EC variations with load for heavy-duty vehicles have been reported, but information is scarce for nonroad diesel generators. There is a clear need to better characterize nonroad DPM emissions, as studies have indicated that DPM emissions from nonroad diesel engines are significantly higher than those from on-road sources. The objective of the study is to provide a detailed account of the OC/EC distributions for a nonroad diesel generator operated with high and low sulfur fuels under different load conditions. DPM emissions were collected using an EPA Method 5 (Determination of Particulate Matter Emissions from Stationary Sources) sampling train. The OC and EC concentrations were quantified by NIOSH Method 5040. DPM concentrations and the relative contributions of OC, EC, and noncarbonaceous materials vary significantly with engine load, fuel sulfur content, and sample collection temperature. The fractions of EC over DPM increase with increasing load from 21% at OkW to 84% at 75 kW for the low sulfur fuel, while those of OC decrease from 62% to 9%. This is consistent with other studies, and the same trends exist regardless of the sulfur content and DPM collection temperature. The fractions of organic compounds range from 77% to 19% for the high sulfur fuel. Noncarbonaceous materials are from 27% to 18% in fraction from high sulfur DPM as opposed to the 17% to 7% in the low sulfur diesel emissions. At lower collection temperatures, more OC and noncarbonaceous materials are observed.

The effect of diesel fuel sulfur content on particulate matter emissions for a nonroad diesel generator

The effect of sulfur content on diesel particulate matter (DPM) emissions was studied using a diesel generator (Generac Model SD080, rated at 80 kW) as the emission source to simulate nonroad diesel emissions. A load simulator was used to apply loads to the generator at 0, 25, 50, and 75 kW, respectively. Three diesel fuels containing 500, 2100, and 3700 ppm sulfur by weight were selected as generator fuels. The U.S. Environmental Protection Agency sampling Method 5 "Determination of Particulate Matter Emissions from Stationary Sources" together with Method 1A "Sample and Velocity Traverses for Stationary Sources with Small Stacks or Ducts" was adopted as a reference method for measurement of the exhaust gas flow rate and DPM mass concentration. The effects of various parameters on DPM concentration have been studied, such as fuel sulfur contents, engine loads, and fuel usage rates. The increase of average DPM concentrations from 3.9 mg/Nm3 (n cubic meter) at 0 kW to 36.8 mg/Nm3 at 75 kW is strongly correlated with the increase of applied loads and sulfur content in the diesel fuel, whereas the fuel consumption rates are only a function of applied loads. An empirical correlation for estimating DPM concentration is obtained when fuel sulfur content and engine loads are known for these types of generators: Y = Zm(alphaX + beta), where Y is the DPM concentration, mg/m3, Z is the fuel sulfur content, ppm(w) (limited to 500-3700 ppm(w)), X is the applied load, kW, m is the constant, 0.407, alpha and beta are the numerical coefficients, 0.0118 +/- 0.0028 (95% confidence interval) and 0.4535 +/- 0.1288 (95% confidence interval), respectively.

Formation and biodegradation of toluene in the anaerobic sludge digestion process

The formation of toluene in municipal anaerobic primary and secondary sludge digestion processes was investigated. Experiments were carried out in a large laboratory-scale reactor using sludge from a primary settling tank of a municipal treatment plant. It was found that toluene was produced in the supernatant in relatively large concentrations for almost all cases tested. The concentration of toluene varied and was found to depend on the stage of the anaerobic process. During the acidity phase, which is the first stage of anaerobic digestion, an increase of toluene concentration was observed, while in the transition period, from the acidity phase to methanogenesis, the toluene concentration decreased. It was concluded that biosynthesis of toluene occurs in the acidogenic phase, while biodegradation was prevalent in the methanogenic stage. Depending on the type of experiments, an increase of toluene from a base value of approximately 200 microg/L up to 20,000 and 42,000 microg/L was measured in the first stage of anaerobic digestion. In the subsequent methane-production stage of digestion, the estimated rate of toluene decrease (biodegradation) varied from 400 to 900 microg/L-d.

A strategy for controlling deposition of struvite in municipal wastewater treatment plants

This paper presents strategies to reduce the risk of struvite deposition by controlling its location of formation. Two technical routes were investigated: (1) to fix the phosphate into the dewatered sludge cake, and (2) to remove phosphate from centrate or filtrate. Chemicals used include magnesium hydroxide [Mg(OH)2], both of reagent grade and reclaimed from a flue gas desulfurization system, magnesium chloride (MgCl2), calcium hydroxide [Ca(OH)2], ferric chloride (FeCl3) and aluminum sulfate [Al2(SO4)3]. Research results indicate that (1) for anaerobically well-digested sludge, Mg(OH)2 is effective in fixing phosphate into sludge cake and improving sludge dewaterability, and (2) adding Mg(OH)2 into a reactor, located between the sludge dewatering facilities and the centrate or filtrate discharge line, and using air for mixing and carbon dioxide stripping, proves feasible in reducing struvite deposition in centrate or filtrate discharge lines and can generate a potentially valuable plant fertilizer--struvite.

The organic composition of diesel particulate matter, diesel fuel and engine oil of a non-road diesel generator

Diesel-powered equipment is known to emit significant quantities of fine particulate matter to the atmosphere. Numerous organic compounds can be adsorbed onto the surfaces of these inhalable particles, among which polycyclic aromatic hydrocarbons (PAHs) are considered potential occupational carcinogens. Guidelines have been established by various agencies regarding diesel emissions and various control technologies are under development. The purpose of this study is to identify, quantify and compare the organic compounds in diesel particulate matter (DPM) with the diesel fuel and engine oil used in a non-road diesel generator. Approximately 90 organic compounds were quantified (with molecular weight ranging from 120 to 350), which include alkanes, PAHs, alkylated PAHs, alkylbenzenes and alkanoic acids. The low sulfur diesel fuel contains 61% alkanes and 7.1% of PAHs. The identifiable portion of the engine oil contains mainly the alkanoic and benzoic acids. The composition of DPM suggests that they may be originated from unburned diesel fuel, engine oil evaporation and combustion generated products. Compared with diesel fuel, DPM contains fewer fractions of alkanes and more PAH compounds, with the shift toward higher molecular weight ones. The enrichment of compounds with higher molecular weight in DPM may be combustion related (pyrogenic).

The ACCEND program: a combined BS and MS program in environmental engineering that includes co-operative work experience

Environmental engineering education has rapidly expanded in recent years and new teaching methods are needed. Many professionals and educators believe that a MS degree in environmental engineering should be the minimum in order to practice the profession, along with practical training. This paper describes an innovative program being offered at the University of Cincinnati that combines an integrated BS in civil engineering and an MS in environmental engineering with extensive practical co-operative education (co-op) experience, all within a five-year period. The program includes distance learning opportunities during the co-op periods. The result is a well-trained graduate who will receive higher pay and more challenging career opportunities, and who will have developed professionalism and maturity beyond that from traditional engineering programs.

Enhanced effect of in-situ generated ammonium salts aerosols on the removal of NOx from simulated flue gas

The combined removal of sulfur dioxide (SO2, up to 3,000 ppm) and nitrogen oxides (NO and NO2, up to 1,200 ppm) has been investigated in a bench-scale pulsed-corona enhanced wet electrostatic precipitator (wESP) with the optional injection of ammonia and/or ozone. The reaction of ammonia with SO2 produces submicron aerosols under certain conditions. Experiments have shown the feasibility of combined SO2 and NOx removal from simulated flue gases by the action of these in-situ generated aerosols. The mechanisms for NOx removal include oxidation of NO to NO2 and subsequent absorption of NO2 into the water wall of the wESP. The results have shown that injecting NH3 (NH3/NOx molar ratio 1) resulted in NOx removal of approximately 13% in a simulated combustion flue gas. Injecting 200 ppm ozone (no ammonia) increased NO conversion to 35% by oxidation, but total NOx removal increased to only 17%. Without the formation of ammonium salts aerosols (e.g., without SO2 in the gas), co-injection of ammonia and ozone increased NO conversion to 60% and NOx removal to 40%. However, high NOx removals were measured in simulated flue gas that contained NH3, SO2, and ozone. The total NOx removal efficiency was 79% when the ammonium salts aerosols were formed in the presence of 2400 ppm SO2, 312 ppm O3, and 2,900 ppm NH3. The energy efficiency of collection improved by approximately 250% for SO2 removal and more than 4700% for NOx removal under these conditions. It was determined that the ammonium salts aerosols produced from the reaction of ammonia and sulfur dioxide substantially enhanced total NOx removal.

Sludge digestion enhancement and nutrient removal from anaerobic supernatant by Mg(OH)2 application

Anaerobic sludge digestion is a widely adopted process for sludge stabilization. Phosphate removal from anaerobic supernatant is necessary to limit the phosphate returned to the head of the treatment plant, thereby improving the overall treatment efficiency. In this study, magnesium hydroxide (Mg(OH)2) was used to improve the sludge digestion efficiency and to remove phosphorus from anaerobic supernatant. The anaerobic sludge digestion experiment was conducted at a pilot scale, and the results showed that applying Mg(OH)2 to anaerobic sludge digester resulted in a larger reduction in SS and COD, a higher biogas production rate, a lower level of phosphate and ammonia nitrogen concentrations in the sludge supernatant and an improved sludge dewaterability. Research results at both lab scale and pilot scale on phosphorus removal from anaerobic supernatant using Mg(OH)2 showed that a high removal of phosphorus can be achieved through the addition of Mg(OH)2. The required reaction time depends on the initial phosphorus concentration and the Mg(OH)2 dosage.

Continuous Sorbent Reactions in a High-Temperature Fabric Filter Following Convective Pass Ca(OH)2 Injection for SO2 Removal

A specially designed two-stage reactor was used to study solid sorbent reactions in the filtration stage of a high-temperature fabric which follow convective pass Ca(OH)₂ injection. Solid conversions during the progress of the sorbent reactions were thoroughly analyzed. It was found that, unlike the sorbent reactions in the injection stage, which proceed extremely fast with strong carbonation under high temperatures, the subsequent sorbent reactions in the filtration stage are much slower and residual sorbent is mainly utilized in removing sulfur dioxide (SO₂). Two major reaction pathways are discovered in the filtration stage. The first route is through the decomposition of residual calcium hydroxide (Ca(OH)₂), which is critical in inducing further sorbent reactions when there is sufficient residual sorbent. The second route is the sulfation of the carbonation product, calcium carbonate (CaCO₃), which may become the principal reaction to remove SO₂ after the residual sorbent is consumed. The con-vective pass and the fabric filter are found to be equally important reaction sites in the combined process of convec-tive pass sorbent injection with high-temperature filtration. The overall SO₂ removal efficiency of the system is affected by both the sorbent injection and filtration conditions.

Temporal and Longitudinal Characteristics of Volatile Organic Compound Emissions from Aeration Units of Publicly Owned Treatment Works

The temporal and longitudinal characteristics of volatile organic compound (VOC) emissions from the aeration units of a publicly owned treatment works (POTWs) have been investigated by systematic monitoring and mathematical modeling. Field tests have been conducted at a 120-mgd wastewater treatment plant to investigate the hourly, weekly, and seasonal changes of VOC emissions. Variations of VOC emissions along the length of the aeration units have been tested and modeled. Most VOCs have decreasing concentration profiles. Henry's law coefficients and biodegradation constants for the detected compounds have been validated with the improved models and the field test data. More than one-half of the emissions were found to have been generated from the first one-third of the aeration unit length.