Volume 2, Issue 3

In a recent review, we surveyed a literature of about 70 papers between 1970 and 1994 in which some chemical oxidative pretreatment combined with a biological oxidation had been tried, usually at lab scale, in attempts to more efficiently degrade recalcitrant water contaminants. Since 1994, new reports have confirmed and expanded this integrated process concept. These recent, promising results collectively provide strong suggestions for further rapid developments of combining (A)OPs with biological oxidations. This paper updates our previous review by introducing new examples illustrative of important, and sometimes unexpected, phenomena. New areas of exploration include use of recycle streams within the combined process, scale-up to larger and to continuous systems, determination of optimal chemical reaction times, and the use of gross water quality measures (BOD, COD, DOC) within process engineering models.

An engineering study was performed to evaluate the use of ultraviolet light and hydrogen peroxide to destroy caustic-neutralized VX nerve agent in the U.S. chemical agent stockpile as an alternative to incineration. Whereas caustic neutralization completely destroys VX, (3-ethyl-S-2-(diisopropylamino)ethyl methylphosphonothiolate, the reaction leaves a complex two-phase mixture containing organic phosphates and organosulfur compounds which require treatment prior to ultimate disposal. Studies performed in laboratory-scale (320-mL), bench-scale (10-L) and pilot-scale (20-L) reactors demonstrated that the principal products of the caustic neutralization-ethyl methylphosphonic acid (EMPA), methylphosphonic acid (MPA), 2-(diisopropylamino)ethyl sulfide (RSR), disulfide (RSSR) and the other mixed sulfides-could be oxidized to inorganic sulfate, phosphate, ammonia and carbon dioxide. The reaction was zero order above 1000 mg/L and pseudo first order below. To mineralize 10,000 lb of VX per day to less than 10 mg/L organic carbon would require more than 1100 lamps of 30 kW each.

This paper presents experimental research to determine the affect of background natural organic material (NOM) on the conversion of five (5) VOC's: 1,1,1-trichloroethane (TCA), benzene (BNZ), trichloroethylene (TCE), 1,4-dichlorobenzene (DCB), and tetrachloroethylene (PCE). Experiments were conducted using DI water and Houston tap water ([TOC] = 3.6 mg/L) as solvents. In addition, the affects of buffer form and excess hydrogen peroxide were determined. Experimental runs were conducted in a photochemical-flow-stirred-tank reactor (pcfSTR), using a 450 W visible/ultraviolet radiation source. The data were analyzed using the Prengle- Shimoda reaction rate model, yielding the reaction rate constant ka (μmols A conv/min, Lr, photon flux) for comparison purposes. Analysis of the experimental data indicated the following conclusions: 1) At the concentrations used for bicarbonate or phosphate buffer, little or no affect was observed; 2) The presence of NOM surpressed the reaction rate for three of the compounds, TCA, BNZ, and PCE at the 95 % confidence level; and 3) Excess hydrogen peroxide, beyond the stoichiometric value, increased the reaction rate constant for all five compounds. The greatest increase was seen for DCB.

Photoinduced degradation of anthracene, perylene, phenanthrene, pyrene, and potassium ferricyanide in water were monitored spectroscopically. Three types of gas stream (ozone/nitrogen, oxygen/nitrogen, and ozoneoxygen/ nitrogen) were used to supply oxidants to the aqueous solutions. The use of an O 2 -free ozone/nitrogen gas stream allows the elucidation of the role of ozone in the degradation process without possible complications from oxygen. A light source of λ > 300 nm was employed to excite the aromatic compounds or ferricyanide exclusively without inducing photodecomposition of ozone. The relevance of the excited species of PAHs and ferricyanide in their own degradation thus can be examined. The measured degradation rate constants under these conditions support that the interaction between the excited states of PAHs or ferricyanide and ozone plays a role in their photoinduced decomposition.

Photooxidation of acetophenone (AP) in aerated dilute aqueous solution (4 × 10 -4 M) has been studied by means of direct photolysis at λ≥ 200 nm and TiO 2 photocatalysis at λ≥350 nm. Norrish-type I products were not observed from the direct photolysis of AP in water, and instead 2-hydroxyacetophenone (2HAP) and 3-hydroxy- acetophenone (3HAP) were identified. In the TiO 2 photocatalytic reaction, several primary intermediates were identified including 2HAP(major), 3HAP, phenol, and diacetylbiphenyl. In both cases, the oxidation is pH-depen- dent, faster at higher pH. The intermediates can be further oxidized, and HAPs are found to form dihydroxy- acetophenone as the main product. The observed rate of photooxidation follows the order of AP > 3HAP > 2HAP > 4HAP in direct photolysis, and the order of AP > 2HAP > 3HAP > 4HAP in TiO 2 photocatalysis.

Advanced oxidation processes (UWH 2 O 2 , UVZH 2 O 2 ZO 3 , and photo-Fenton) have been use to remove the organic carbon from aqueous-based fluids containing initial total organic carbon (TOC 0 ) levels up to 15000 ppm. Fluids containing ethylene glycol, polyethylene glycol (PEG200,average molecular weight 200 g mol -1 ) and sodium dodecylsulfate (SDS) were examined. All advanced oxidation processes investigated utilized initial H 2 O 2 levels of up to 9 %. Reactions were carried out in a stirred batch photoreactor and mass transfer through the photolytic zone was shown not to limit the efficiency of the photooxidation process. Carbon loss from the fluids was deter­mined to be a zero-order kinetic process and the rates of carbon loss were used to calculate the energy' equivalents per unit mass (EEZM) figure-of-merit for the process. The EEZM values w'ere determined to be a function of substrate structure with EG and PEG200 being removed from solution with approximately the same efficiency, while SDS was the most difficult substrate to oxidize. The energy costs for fluid treatment by each of the three AOP methodologies investigated were determined and the factors affecting fluid treatment are discussed.

The Advanced Oxidation Processes (AOPs) are powerful water treatment processes that utilize free radicals to destroy contaminants. The chemistry of these processes is sufficiently complicated that the correct route to process optimization is not always obvious. Examples of simple and complex applications of a competitionkinetic modeling method to the treatment of nitro compounds in water are described. The method used can provide a great deal of information that is useful in AOP optimization, while requiring a minimum amount of site data, making it an ideal tool for treatability assessments and rapid initial process optimization.

The use of stand-alone water treatment technologies such as UV/Oxidation, granular activated carbon (GAC), air stripping and sedimentation, has proven to be cost-effective in many cases. However, there are a substantial number of instances where a combination of treatment technologies integrated into a treatment train provides a more economical approach than would be obtained by using only one technology. This paper presents case studies of integrated systems where UV/Oxidation is combined with either GAC, air stripping, or precipitation. The benefits, including improved treatment costs, are described using data from actual installations.

The treatment of textile dyeing and finishing wastewaters by conventional methods, such as biological, physical and chemical processes or combinations thereof, are in common practice but have unique drawbacks, namely, a number of refractory chemicals in the effluents and difficulty in the complete removal of color. The study described herein is an investigation of an advanced oxidation treatment of a common azo dye, Remazol Black-B, widely used in textile dyeing and finishing operations. The investigation was focused on monitoring the degradation and toxicity reduction of an aqueous solution of the dye up to 30 min of treatment by a UV/H 2 O 2 oxidation system. The dye was completely decolorized and converted to colorless intermediates during this treatment, while only 44 % of the organic carbon was mineralized. The toxicity of the tested dye solution increased during the first few minutes of treatment and decreased rapidly thereafter, ending up in a 68 % reduction after 20 min of treatment. The influence of the initial H 2 O 2 concentration on the rate of dye removal was found to be inhibitory beyond the “effective” H 2 O 2 dose. The correlation was statistically modeled by a non-linear regression technique.