Aqueous Contamination

The ratio of BOD5 to COD varies according to the contamination. The ratio can vary between 0.05 and 0.8, depending on the chemical species2. Domestic sewage has a value of typically around 0.374. An average value across all types of contaminants is around 0.35. 

The relationship between BOD5, COD and TOD for the same organic waste is in the order, 

If the composition of the waste stream is known, then the theoretical oxygen demand (ThOD) can be calculated from the appropriate stoichiometric equations. As a first level of approximation, it can be assumed that the ThOD would be equal to the COD. The following example will help to clarify these relationships. 

Example 26.1 A process produces an aqueous waste stream containing 0.1 mol % acetone. Estimate the COD and BOD5 of the stream. 

Solution First, calculate the ThOD from the equation that represents the overall oxidation of the acetone  

---

Zitomer DH, Speece RH (1993) Sequential environments for enhanced biotransformation of aqueous contaminants. Environ Sci Technol 27 227... 

Cosolvent flushing is an in situ technology that enhances the remediation of contaminated soils and groundwater by injecting water and a cosolvent such as alcohol (e.g., ethanol, methanol, and isopropyl) into a contaminated area. Research has shown that an organic cosolvent can also accelerate the movement of metals through a soil matrix. The alcohol causes both an increase in aqueous contaminant solubility and lowering of non-aqueous-phase liquid (NAPL)-water interfacial tension. 

Terrapure Systems, L.L.C. (Terrapure), is currently developing palladized iron remediation technology (PIRT). The deposition of small amounts of palladium (approximately 0.05 wt%) on the surface of iron particles may result in a bimetallic surface that can cause the dechlorination of aqueous organic compounds. The developers claim that the technology can be used as an in situ or ex situ process and can be applied to aqueous contaminants and soil. PIRT has been evaluated in bench-scale tests and is not currently commercially available. 

Sorption of organic contaminants onto aquifer solids is frequently described as a partitioning process, where the hydrophobic organic compound partitions into natural organic material associated with the aquifer solids [8]. Sorption can be characterized as either an equilibrium or rate-limited phenomenon. Equilibrium sorption can be modeled as either a linear or non-linear process. Equilibrium sorption may be assumed when the flow of groundwater and other processes affecting contaminant transport are slow compared to the rate of sorption. In this event the sorption of the contaminant can be considered instantaneous. If we assume equilibrium sorption, the relationship between sorbed and aqueous contaminant concentrations may be described by a sorption isotherm. 

Unlike the linear model, the nonlinear model does not assume that sorbed concentrations are directly proportional to aqueous concentrations. While linear sorption is a good assumption when aqueous contaminant concentrations are relatively low, it may be necessary to use the nonlinear model when concentrations vary over a large range [20]. Nonlinear sorption is often modeled... 

R. Littlewood and E.J. Argent, The Effect of Aqueous Contaminants on the Redox Potential of Chloride Melts, Electrochim. Acta. 4 (1961) 114-128. 

Water sampling with a spiral hollow polydimethylsiloxane (PDMS) membrane was used with IMS for in situ sampling and analysis of trace chlorinated hydrocarbons in water in a single procedure. Aqueous contaminants permeate across the membrane into a gas flow, through the membrane tube, and into a specially made... 

Williams, of Dow Coming Corporation, discusses the properties of linear volatile methyl siloxanes, a class of mild solvents having an unusual combination of environmentally benign qualities, that have the potential to replace less benign solvents in applications such as coating formulations or the removal of particulates, oils, fluxes, and aqueous contaminants. The chapter details data showing that their solvency can be tailored to specific applications by using azeotropes, co-solvents and surfactants. 

Optrodes that provide trace-level detection of trichloroethylene and chloroform with high accuracy have been developed. High accuracy is obtained by providing an internal intensity reference. Also, a diode laser has been used to measure surface-enhanced Raman spectra (SERS) of low levels of fluorescent molecules. Near-infiared SERS is shown to be a useful technique for remote spectroscopic measurentents of aqueous contaminants. In addition, a temperature optrode has been used to obtain real-time temperature pioEles in a geothemoal well. 

Rate of dissolution of solid minerals increases by factor 1.5-2 with 10 °C increase. Supercritical carbon dioxide manage aqueous contamination or use alloys. 

The generation and treatment of aqueous contaminants is another aspect of coal liquefaction that must not be ignored. Major contaminants are hydrogen sulfide, anunonium sulfide, phenols, cresols, xylenols, and thiocyanates cyanides and solids (ash and char particles) may also be present. The gaseous contaminants (hydrogen sulfide and anunonia) are ranoved by steam-stripping. 

Fredenslund, F. C., Nendza, M. and Herbst, T. (1995) Cosolute interactions on aqueous contaminant concentrations. SAR QSAR Environ. Res., 3, 293-300. 

Dioxane proved to be the most suitable solvent for extracting the formazan formed in the nitroblue tetrazolium test (Muller et al. 1981). At 85 °C dioxane completely extracted nitroblue tetrazohum (absorption maximum at X, = 580 nm, absorption coefficient = 0.0256 ml X nmol X cm" ) from the cell pellet within 15 min, and nitroblue tetrazohum diluted in dioxane was sufficiently stable. As a possible aqueous contamination under conditions of an acid pH caused a slower decrease of the optical density of the extract than did pure water, 1 N HCl as washing agent to remove remaining nitroblue tetrazolium from the cell pellet is recommended. 

The most common reference electrode systems used in aqueous solutions are Ag/AgCl and the calomel electrode. If aqueous-based references are used in nonaqueous solution, however, large liquid junction is produced and often more serious, aqueous contamination of the nonaqueous cell occurs. Thus this combination is not recommended. The use of an Ag/Ag non-aqueous-based reference is suggested for nonaqueous electrochemistry. To avoid large junction potentials, the RE solvent should be as close in nature as possible to the cell solvent system. Often potentials are calibrated with a standard, such as ferrocene or cobaltocene. Suggested standards are listed in Table 2-2, along with reduction potentials and other properties. Construction of an Ag/Ag reference for nonaqueous use is shown in Figure 2-6. Reference electrodes can drift with time and must be carefully maintained. 

---