The Southeastern Aerosol Research and Characterization Study: Part 1—Overview

Abstract

This paper presents an overview of a major, long-term program for tropospheric gas and aerosol research in the southeastern United States. Building on three existing ozone (O₃)-focused research sites begun in mid-1992, the Southeastern Aerosol Research and Characterization Study (SEARCH) was initiated in mid-1998 as a 7-year observation and research program with a broader focus including aerosols and an expanded geographical coverage in the Southeast. The monitoring network comprises four urban-rural (or urban-suburban) site pairs at locations along the coast of the Gulf of Mexico and inland, including two moderately sized and two major urban areas (Pensacola, FL; Gulfport, MS; Atlanta, GA; and Birmingham, AL). The sites are equipped with an extensive suite of instruments for measuring particulate matter (PM), gases relevant to secondary O₃ and the production of secondary aerosol particles, and surface meteorology. The measurements taken to date have added substantially to the knowledge about the temporal behavior and geographic variability of tropospheric aerosols in the Southeast. Details are presented in four papers to follow.     

The Southeastern Aerosol Research and Characterization Study: part 1--Overview

This paper presents an overview of a major, long-term program for tropospheric gas and aerosol research in the southeastern United States. Building on three existing ozone (O3)-focused research sites begun in mid-1992, the Southeastern Aerosol Research and Characterization Study (SEARCH) was initiated in mid-1998 as a 7-year observation and research program with a broader focus including aerosols and an expanded geographical coverage in the Southeast. The monitoring network comprises four urban-rural (or urban-suburban) site pairs at locations along the coast of the Gulf of Mexico and inland, including two moderately sized and two major urban areas (Pensacola, FL; Gulfport, MS; Atlanta, GA; and Birmingham, AL). The sites are equipped with an extensive suite of instruments for measuring particulate matter (PM), gases relevant to secondary O3 and the production of secondary aerosol particles, and surface meteorology. The measurements taken to date have added substantially to the knowledge about the temporal behavior and geographic variability of tropospheric aerosols in the Southeast. Details are presented in four papers to follow.     

Effects of untreated hospital effluents on the accumulation of toxic metals in sediments of receiving system under tropical conditions: Case of South India and Democratic Republic of Congo

Physicochemical and ecotoxicological analyses have been performed to assess the quality of sediments receiving untreated hospital effluents from Indian and Democratic Republic of Congo (DRC) hospitals. The sediments were collected monthly and characterized for grain size, organic matter, total organic carbon, total carbon, nitrogen, phosphorus, toxic metals and ecotoxicity. The results highlight the high concentration of toxic metals from the Indian hospital effluent receiving systems, especially for Cr, Cu, As, Zn and Hg. On the other hand, the metal concentrations in the sediment receiving system from DRC are low (e.g. maximum Hg and Zn concentration were 0.46 and 48.84 mg kg⁻¹ respectively). Ostracods exposed to sediment samples H2 (September month sample) and H3 (June and September month samples) were found dead after 6 d of exposure whereas the higher mortality rate for Congo sediments was 23% but was accompanied with 33 ± 7% of growth inhibition. The results of this study show the variation of sediment composition on toxic metal levels as well as toxicity related to both, the type of hospitals and the sampling period. Additionally, hospital effluent disposal practices at the study sites can lead to the pollution of water resources and may generate risks for aquatic organisms and human health.     

Case study of testing heavy‐particle concentrator‐aided remediation of lead‐contaminated rifle shooting range soil

Trials were conducted to optimize the parameters of a heavy‐particle concentrator (HPC) for the remediation of soil stockpiles contaminated by metallic lead at the Mount Stuart training area in Townsville, Queensland, Australia. A range of treatment methods, including orbital screen, HPC, and a combination of orbital screen and HPC were evaluated. The treatment efficiency, as well as reductions in Pb and Australian Standard Teaching Procedure values, was ranked: Orbital screen + HPC < HPC < 2nd run through HPC. The combination of orbital screening, HPC, and phosphate‐aided immobilization completely remediated the stockpiled material by reducing total lead to below the Australian National Environmental Protection Measure Health Investigation Level for Soil Contaminant (Recreational; < 600 milligrams lead per kilogram). The optimized parameters of HPC at 4 tonnes per hour of the < 40 millimeter (mm) orbital screen feed fraction were: inclination angle 4°, trommel speed 1,860 revolutions per minute (rpm), HPC belt speed 3.5 rpm, material distribution chute extension 100 mm and water flow 480 liters per minute.     

Low-Cost Filtration System to Treat First-Flush Stormwater

The aim of this paper is to evaluate the performance of the low-flow filtration system (LFFS) that Kogarah Municipal Council developed for treating and reusing the highly polluted first-flush stormwater (FFSW) while allowing the cleaner subsequent major stormwater flows to be directed to the major street drainage. The LFFS was evaluated through laboratory investigations using columns packed with different filter media to test the removal efficiency of pollutants such as zinc (Zn), total phosphorus (TP), total nitrogen (TN), total organic content, total petroleum hydrocarbons (TPH), and turbidity. The findings from this study demonstrate the effectiveness of the LFFS to largely reduce turbidity, TPH, and trace metals from the FFSW. The LFFS also partially removes dissolved organics, TP and TN. These pollutants are more commonly and effectively removed in subsequent processes of a stormwater treatment train. Further this paper highlights the importance of regular maintenance of the LFFS especially as it is only associated in removing the high pollutant loads during a storm event. Due to this first flush, a thick oily crust-formed layer requires monthly removal, and an entire replacement of the exhausted filter media is required quarterly. However considering the labor required to service the crust formed layer within the LFFS, it is more cost effective to replace the entire depth of filter media monthly.     

Treatment of Stormwater using Fibre Filter Media

In this study, a high-rate fibre filter was used as a pre-treatment to stormwater in conjunction with in-line flocculation. The effect of operating the fibre filter with different packing densities (105, 115 and 125 kg/m³) and filtration velocities (20, 40, 60 m/h) with and without in-line flocculation was investigated. In-line flocculation was provided using 5, 10 and 15 mg/L of ferric chloride (FeCl₃·6H₂O). The filter performance was studied in terms of pressure drop (ΔP), solids removal efficiency, heavy metals (total) removal efficiency and total organic carbon (TOC) removal efficiency. It is found that the use of in-line flocculation at a dose of 15 mg/L improved the performance of fibre filter as measured by turbidity removal (95%), total suspended solids reduction (98%), colour removal efficiency (99%), TOC removal (reduced by 30–40 %) and total coliform removal (93%). The modified fouling index reduced from 750–950 to 12 s/L² proving that fibre filter can be an excellent pre-treatment to membrane filtration that may be consider as post-treatment. The removal efficiency of heavy metal was variable as their concentration in raw water was small. Even though the concentration of some of these metals such as iron, aluminium, copper and zinc were reduced, others like nickel, chromium and cadmium showed lower removal rates.     

Submerged Membrane System with Biofilter as a Treatment to Rainwater

Rainwater has been used as drinking water in Thailand for centuries especially in the rural parts and is accepted as an important water resource. From past to present, the quality of rainwater has changed with the landuse of the landscape, and its water quality is influenced by a diverse range of conditions such as the management of pollutant sources, the catchment condition, wind and meteorological conditions, and the location of rainwater collection points. In this study, the quality of rainwater collected off roofs at several locations was examined. Granular activated carbon (GAC) filtration was used as a pretreatment to microfiltration (MF) to remove the dissolved organic matter (DOC). After an initial adsorption period, the biofilm that formed on the GAC (biofilter) was found to remove DOC by up to 40%, 35%, and 15% for bed filter depths of 15, 10, and 5 cm, respectively. Biofilters also removed nitrate and phosphate by more than 80% and 35%. The hollow fiber membrane microfiltration with pore size of 0.1 μm was used to treat the effluent from biofiltration to remove the microorganisms/pathogens in the rainwater. Although there was no significant additional removal of DOC by MF, the biofilter removed all microorganisms. The use of biofilters as pretreatment to MF/UF could remove a higher amount of DOC, remove microorganisms, increase the membrane treatment efficiency, and reduce membrane fouling.     

Conversion of chromium-containing solid wastes into value-added products through a plasma-assisted aluminothermic process

Chromium-containing solid wastes have been generated by chemical and leather/tanning industries, and the management and proper disposal of the same wastes have been challenging tasks. A significant fraction of these wastes contains chromium compounds with chromium present in the hexavalent (Cr⁺⁶) form, which is hazardous to human beings, animals, and ecosystems. Since these wastes are discarded largely without proper treatments, soil and groundwater get contaminated and they can cause several health issues to human beings. Conventional methods developed to convert hazardous Cr⁶⁺ to Cr³⁺/Cr metal either generate secondary toxic wastes and unwanted by-products and/or are time-consuming processes. In this work, a plasma-assisted aluminothermic process is developed to convert the toxic waste into non-toxic products. The waste was mixed with aluminium powder and subjected to transferred arc plasma treatment in a controlled air atmosphere. Chemical analysis and Cr leachability studies of the waste material prior to plasma treatment have shown that it is highly toxic. Analysis of the products obtained from the plasma treatment showed that Cr and Fe present in the waste could be recovered as a metallic mixture as well as oxide slag, which were found to be non-toxic. Easy separation of the metallic fraction and the slag from the treated product is one of the merits of this process. Besides converting chromium-containing toxic waste to non-toxic materials, the process is rapid and recovers the metals from the waste completely.