摘要:

Part of a study to assess the feasibility of coal tar site remediation by the injection and recovery of water‐miscible, biodegradable solvents is described. The overall objective of the study was to obtain estimates of cleanup times and solvent volumes required for a hypothetical contaminated site. We describe the results of column experiments, performed by passing solvent‐water solutions through glass bead‐packed columns contaminated with coal tar blobs at low volumetric saturation. This experimental design allowed the investigation of dissolution rate limitations at residual saturations similar to those observed in the field, albeit under more homogeneous conditions. The column effluent data were modeled with a modified advection‐dispersion equation that includes a mass‐transfer source term for coal tar dissolution. This source term empirically relates mass transfer to experimental variables such as coal tar saturation and solvent flow velocity using fitting parameters. Values of parameters in the mass‐transfer source term were estimated from experimental data. The modeling approach and the parameter values developed in this study have been used in simulations of thein situsolvent extraction process.

ISSN:1061-4303    

DOI:10.2175/106143095X131141

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

Subsurface contamination at many former manufactured gas plants (MGP) resulted from on‐site disposal in wells, pits, and lagoons of coal tar, a by product of the gasification process. Coal tar is difficult to pump from the ground because of its density and viscosity. A technique employed with success in enhanced oil recovery,in situsolvent extraction, may be useful for remediation of coal tar‐contaminated sites. A water‐miscible, biodegradable solvent would be injected into the subsurface to promote dissolution of coal tar for subsequent removal via recovery wells. This paper presents the results of process modeling done in conjunction with a project to assess in a preliminary way the feasibility ofin situsolvent extraction for remediation of coal tar sites. After evaluation of MGP site characteristics, possible injection‐recovery well schemes for the proposed process were developed. These comprised center injection and perimeter recovery patterns and patterns in which injection and recovery wells are placed on opposite sides of a contaminated area. A two‐dimensional model was then developed for simulating the proposedin situsolvent extraction process under simplified site conditions and applied to evaluate the performance of the various injection‐recovery schemes at a hypothetical MGP site. From model results it appears that anin situsolvent extraction process may be able to recover a significant mass of coal tar (more than 80%) from the subsurface within a time frame of 1 year or so, provided that site hydrogeologic conditions are conducive to process application. Pilot testing in the field is necessary to test the results of this preliminary assessment. There are also important implementation issues and some are discussed.

ISSN:1061-4303    

DOI:10.2175/106143095X131150

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

Upward curved (concave) filtration plots of the inverse filtrate flux as a function of filtrate volume have been investigated using a laboratory‐scale filtration device and different wastewater solids suspensions stored anaerobically in the laboratory. Using an empirical approach in which a polynomial expression of arbitrary order was applied for regression analysis on filtration data it was shown that a parabolic expression was able to fit adequately all concave filtration plots. Turbidity measurements on supernatant and filtrate evidenced that the concave behavior of the filtration plots could be explained by migration of small‐scale solids into the filter cake pores (blinding). The coefficients of the derived parabolic equation characterized the resistance attributed to blinding, basic cake filtration, and the filter medium, respectively. Based on the coefficients of the derived parabolic equation, a physically comprehensible parameter for characterizing the influence of blinding on filtration was defined.

ISSN:1061-4303    

DOI:10.2175/106143095X131169

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

Wastewaters from fish‐canning industries have a high concentration of organic polluting substances (10–50 g chemical oxygen demand L−1[COD]) and, in some cases, a high content of sea salts (Cl−: 8–19 g L−1, Na+: 5–12 g L−1, SO2−4: 0.6–2.7 g L−1). The presence of high sodium ion concentrations in wastewaters with high organic content traditionally is considered as a very negative factor for their anaerobic treatment. In fact, both the presence of Na+and SO2−4, transformed into H2S during the anaerobic degradation process, may cause toxicity and inhibition on the methanogenic process.
This work deals with the operation and treatment efficiency of two lab‐scale mesophilic and thermophilic anaerobic filters (MAF and TAF, respectively). So that the adaptation of anaerobic sludge to high saline concentrations is attained, a prolonged start‐up period of about nine months was necessary. After this, a stable operation and similar treatment efficiencies were reached, even when organic loading rate (OLR) as high as 9 kg COD m−3d−1(TAF) or 24 kg COD m−3d−1(MAF) were applied at chloride concentration of 13 g L−1. At these conditions, the COD removal reached 73% (TAF) and 64% (MAF), and the COD methanized reached 69% (TAF) and 66% (MAF). The sulphate in the influent was removed practically completely, leading to a H2S concentration in the biogas between 3–4%.
In spite of the lower specific activity of sludge from MAF (0.21 g COD g−1volatile suspended solids [VSS] d−1) than from TAF (0.66), the MAF reached a higher OLR than TAF. This fact can be explained because of the higher retention of sludge into MAF (72 g VSS L−1) than TAF (10 g VSS L−1). Two practical conclusions may be derived from this work: the thermophilic operation needs the use of a packing material with a higher capacity to retain biomass and the mesophilic operation requires a more frequent detachment of biomass from the support in order to avoid clogging problems.

ISSN:1061-4303    

DOI:10.2175/106143095X131178

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

The potential of the expanded bed Granular Activated Carbon (GAC) anaerobic reactor in treating a municipal wastewater containing Resource Conservation and Recovery Act (RCRA) volatile (VOC) and semivolatile organic compounds was studied. The GAC anaerobic reactor was followed by an aerobic nitrification tank. The GAC anaerobic reactor was operated at an empty bed residence time of 3.35 hours, whereas the nitrification tank was operated as a chemostat at a hydraulic residence time of 10 hours. A total of six VOCs (methylene chloride, chlorobenzene, carbon tetrachloride, chloroform, toluene, and tetrachloroethylene) and six semivolatiles (o‐chlorophenol, naphthalene, nitrobenzene,p‐nitrophenol, di‐n‐butyl phthalate, and lindane) were fed to the GAC anaerobic reactor each at a concentration of 1 mg/L. The VOCs and semivolatiles were fed to the reactor as a mixture along with primary effluent from a local sewage treatment plant. The GAC anaerobic reactor was found to achieve greater than 94% removal of all VOCs except chloroform, which was removed to an extent of 75%. The semivolatiles were removed in excess of 95%. The combined GAC anaerobic reactor‐aerobic nitrification system was able to achieve removal efficiencies for chemical oxygen demand and ammonia‐nitrogen in excess of 97%

ISSN:1061-4303    

DOI:10.2175/106143095X131187

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

The fate of semivolatile organic compounds was studied during heat drying of mixed primary and waste‐activated sludge. Selected organic compounds were spiked in the sludge collected from a wastewater treatment plant. The thickened sludge samples were heat dried in a tube furnace at different temperatures with a constant airflow rate. The exhaust air from the furnace was condensed in a glass condenser. Methanol was used as the solvent for extraction of compounds from both the dried sludge and the condensate. The concentrations of the organics were determined from high performance liquid chromatography (HPLC) analysis. The selected semivolatile organic compounds showed a high affinity to remain adsorbed in the thickened sludge. Drying sludge to more than 90% solids content caused complete removal of all of the organic compounds. The removal of organics took place in three distinct phases: a high removal in the initial phase, a sudden drop in the intermediate phase, and an increase in the final phase. Removal of phenol was approximately proportional to moisture removal from the sludge. For 4‐nitrophenol and nitrobenzene, the removal rate decreased as the amount remaining in sludge diminished. The removal pattern of the individual organics correlated with their respective Henry's law coefficients. At higher temperatures, a faster removal rate was observed for all the compounds.

ISSN:1061-4303    

DOI:10.2175/106143095X131196

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

A moving‐bed biofilm reactor has been developed, where the biofilm grows on small, free‐floating plastic elements with a large surface area and a density slightly less than 1.0 g/cm3. Nitrogen removal, based on nitrification and denitrification, was studied in a pilot plant with an active, specific biofilm surface area of approximately 310 m2/m3. Temperatures ranged from 7 to 18°C, and untreated wastewater had concentrations typically less than 100 mg soluble chemical oxygen demand (COD)/L and 25 mg total N/L. Both predenitrification, using untreated wastewater as carbon source, and post‐denitrification of pre‐precipitated wastewater, using acetate as an external carbon source, were examined. The predenitrification process was carbon limited, and only 50% to 70% total N removal was obtained, at a recirculation ratio of approximately 2.0 and a total empty bed hydraulic residence time of approximately 6 hours in the biofilm reactors. With post‐denitrification and an external carbon source, 80% to 90% total N removal could easily be reached at total empty bed hydraulic residence times less than 3 hours.

ISSN:1061-4303    

DOI:10.2175/106143095X131204

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

A moving‐bed biofilm reactor has been developed, where the biofilm grows on small, free‐floating plastic elements with a large surface area and a density slightly less than 1.0 g/cm3. Nitrification of preprecipitated wastewater in a once‐through system and raw wastewater in a recycled system with predenitrification has been studied in a pilot plant with an active, specific biofilm surface area of approximately 310 m2/m3. Maximum nitrification rates under comparable operating conditions were 20% to 25% higher with preprecipitated wastewater in the once‐through system than with raw wastewater in the recycled system. A temperature coefficient ofθ= 1.09 was found. However, under oxygen‐limited conditions, the apparent temperature effect was insignificant in the temperature range from 7 to 18°C because of increased dissolved oxygen levels at low temperatures. At 10°C volumetric nitrification rates from 300 to 400 g NH4‐N/m3·d can be expected.

ISSN:1061-4303    

DOI:10.2175/106143095X131213

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

Models of carbon‐limited algal biofilms have shown that the pH can increase significantly within the biofilm, and consequently, although the total inorganic carbon is not entirely depleted within the film, the amount of CO2available for substrate use is reduced. The presence of a buffer offsets this pH limitation and increases the flux of inorganic carbon into the film. A rigorous model is developed to investigate the role of a phosphate buffer, multiple background ions, and cell surface charge density on the flux of inorganic carbon into algal biofilms. The effects of the presence of a concentration boundary layer (CBL), light limitations, and activity corrections are included in the analysis. Results of the model establish that the phosphate buffer, the presence of a CBL, and light limitations have a significant impact on the predicted flux of inorganic carbon into algal biofilms, whereas the effects of background ions, activity corrections, and algal surface charges can be neglected.

ISSN:1061-4303    

DOI:10.2175/106143095X131222

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY

摘要:

An analysis of five sludge‐settling characteristics data sets is presented, representing data from 51 separate suspended growth biological wastewater treatment processes and including 214 separate runs and over 1 500 individual data points. The results indicate that the data can be characterized using a single relationship between the initial sludge settling velocity (Vi), the initial sludge concentration (Ci), and the sludge volume index (SVI). The predictive capability of this relationship is independently verified. These results suggest that this single relationship can be used to accurately characterize the settling characteristics of an activated sludge based only on the measured SVI. A comparison of alternate sludge‐settling indexes indicates that the predictive capability of the relationship can be further improved by use of the stirred SVI3.5analysis rather than the SVI. More data are required to refine relationships developed based on the SSVI3.5and the diluted SVI. Secondary clarifier‐operating diagrams based on the developed relationships are presented.

ISSN:1061-4303    

DOI:10.2175/106143095X131231

出版商:Water Environment Federation    

年代:1995

数据来源: WILEY