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Introduction

Overview Of TEXOX Process

What Are Spent Caustics?

How Are Spent Caustics Generated?

Properties Of Spent Caustics

Disposal Characteristics Of Spent Caustics

Disposal Alternatives For Spent Caustics

Results Following Treatment

Case History

Tragedy In The Ivory Coast - What Not To Do

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Introduction:

          The TEXOX^TM Processes utilize technologies developed by Texas Technology over the past two decades.  The founder of Texas Technology has received several US and Worldwide patents for treating spent caustics and the chemicals used to oxidize these troublesome waste streams, effectively and economically.

            The handling and disposal of spent caustics is a paramount problem to the refining, petrochemical, and LPG industries.  Spent caustics produce noxious odors, toxicity, and high loading effects when attempting disposal in typical wastewater treatment plants without pretreatment.  Spent caustics contain sulfides, mercaptans, disulfides, phenolics, cresylics, and naphthenic compounds in endless combinations in sodium or potassium hydroxide "spent caustic" solutions.  All of which are hazardous materials and often classified as hazardous wastes.  All types of spent caustics are amenable to treatment using the TEXOX Process.

 

            The TEXOX^TM Processes were developed especially for the effective treatment and environmentally friendly disposal of these troublesome wastewaters.  Furthermore, the family of TEXOX Processes can also transform a wide variety of other toxic and hazardous wastes into biodegradable products.  

 
Scope Of Process:

          The TEXOX Processes utilize chemical oxidation technologies operating at low pressures and moderate temperatures extending equipment life for many years.  Compared to "Wet Air Oxidation" (WAO) technologies, extremely high pressures and temperatures have high O&M costs and short equipment life expectations.  To meet  environmentally green practices, the products of the oxidation must be compatible with the natural environment in the receiving watershed.  To meet this challenge, it is preferred to use hydrogen peroxide, ozone, oxygen, or potassium permanganate as the primary oxidant.  In some instances, natural catalysts are used to enhance the performance and economics of the reactions.  However, the TEXOX Processes can easily adapt to virtually any other oxidizer, if preferred by the customer.

          These oxidizers and catalysts breakdown into water, oxygen, and naturally occurring compounds found throughout our planet.  No adverse effects result from these environmentally perfect reactants.

          Using either of these oxidizer pathways, with or without catalyst, at controlled pH, temperature, and pressure ultimately results in an economical and competitive process compared to any other technology offered today.  Furthermore, the TEXOX family of processes have shown to be cost competitive with the costs of the least expensive disposal practices, off-site Deepwell disposal.  After all, what could be cheaper than disposing of spent caustics down a hole in the ground with Deepwell technology?  There, the spent caustics will remain unabated until poisoning our biosphere and potable water ground water supplies for millennium.

Spent Caustics Characteristics:

            Spent caustics exhibit similar characteristics, however, each is unique and requires process development to determine the most cost effective TEXOX program.  Typical concentration ranges of the major substrates are depicted in the following Figure showing the various categories including Sulfidic, Disulfide, Mercaptanic, Cresylic, Phenolic, and lastly Naphthenic spent caustics:
 
 

 
Waste Minimization:

            The USEPA and local environmental regulations promulgated in the reauthorization of the Solid Waste Disposal Act of 1984 is a strong driving force to implement alternative processing and disposal methods.  The TEXOX Process utilizes commercialized chemical oxidation pathways to effectively destroy noxious odors, toxicity, and reduce the loading impact in downstream processes.  Downstream processes most often benefited include sensitive biological wastewater treatment plants prone to odor emissions and upsets.
 

Wastewater Loading Effects:

            The following Figure shows typical results from a TEXOX Process comparing increasing oxidizer dosage with standard wastewater treatment parameters used to determine oxidation performance.  The plot evaluated BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), and TOC (Total Organic Carbon) against oxidizer dosage to pre-determine the impact in a typical downstream wastewater treatment plant for final disposal.  Notice the intermediate increase in BOD where toxic phenolic compounds were transformed into biological food while the COD and TOC continued to decrease.

            The principal goals were to eliminate both the odors and the toxicity impact in the downstream biological wastewater treatment plant.  A secondary goal was also to significantly reduce the carbon loading to the final treatment plant.

One Process Destroys Many Hazardous Compounds:

            The order of destruction of selected substrates is depicted in the following Figure with respect to increasing oxidizer dosages.  For example, inorganic sulfides (i.e. hydrogen sulfide) are the easiest and fastest reacting compounds compared to un-substituted phenol (carbolic acid), however, substituted phenols (i.e. cresols) react easier.  The concentrations were determined during treatability studies using typical spent caustics and further supported during field applications.
 
 

Toxicity Assessment:

            The destruction of toxic and inhibitory compounds commonly found in spent caustics is imperative to the health and overall performance during final treatment in the receiving wastewater treatment plant (WWTP).  Toxicity effects are quantified using biological respirometry to measure the rate of oxygen uptake in the mixed liquor.  The oxygen uptake rate of the mixed liquor is proportional to the rate at which the chemical compounds are digested and also determine the retention time necessary for complete destruction.

            Compounds easily digested (e.g. carboxylic acids) stimulate the microorganisms and consume oxygen at a high rate; whereas, toxic compounds (e.g. phenolics) inhibit or kill the microorganisms resulting in a low rate.  When the oxygen uptake rate is decreased, the time for effective biological assimilation may exceed the hydraulic retention time in the WWTP and result in a poor discharge quality and breakthrough.  If the uptake rate falls to zero, the microorganisms are dead and a reseeding program is necessary to rebuild the population.

            To demonstrate the effectiveness of the TEXOX Process for toxicity abatement, samples of both the raw spent caustic and the TEXOX Process effluent were placed into separate biological respirometers (e.g. Warburg Apparatus) containing the same biological mixed liquor seed.  To determine the specific toxicity effects, the sample volumes were adjusted to reflect the same TOC loading used in the operation of the WWTP.  The results are shown in the Figure below where the oxygen uptake rates clearly show that the TEXOX Process eliminated the toxicity effects compared to the raw untreated spent caustic.
 
 

            Notice in the above Figure that a typical WWTP retention time of 24 to 48 hours resulted in complete assimilation of the pre-treated spent caustic.  This result is evidenced by the oxygen uptake rate reaching endogenous respiration within 24 hours.  The raw un-treated spent caustic resulted in a toxicity upset and inhibited the microbes respiration well beyond the maximum 48 hour period.
 

Wastewater Treatment Plant Performance:

           The TEXOX Process was also applied at a chemical plant in Freeport, Texas, during a remedial response action to treat over a million gallons collected in an interim containment pond.  The remedial action was to eliminate both the foul odor emanating from the pond and blowing downwind into a nearby residential neighborhood and to eliminate the toxicity effects when initially attempted to dispose of in the plant's wastewater treatment plant.

           The foul odor recognition was determined by a team of plant personnel walking around the containment pond and downwind from the pond and plant.  Once the foul odor was eliminated, being transformed to an "earthy" or "dirt" like odor, then the task was to dispose of the pond water in the plant's WWTP without toxic effects. 

            Samples of the pond water were tested in a biological respirometer (referenced above) and found not to exhibit toxic properties.  The pond water then began pumping into the WWTP, cautiously at first at a low flow rate to allow acclimation with the microbes.  After a few hours the pumping rate reached its capacity and samples of the mixed liquor were tested in the respirometer.  In the figure below, the oxygen uptake rates showed that the new influent matrix was easily assimilated by the microbes with no inhibitory or toxic effects.  Actually, the effects with the new influent demonstrated a higher oxygen uptake over the Control suggesting that the once toxic pond water had been transformed into a biological food (conversion of indigestible COD into digestible BOD).
 

Epilogue:

           The TEXOX^TM Process solves spent caustic handling and disposal concerns.  TEXOX destroys all odor and toxicity precursors thus allowing final disposal in conventional wastewater treatment plants without the otherwise adverse effects without TEXOX.  The treated spent caustics are highly amenable to biological assimilation, improve the wastewater treatment plant's primary and secondary clarification, and produce less biological sludge than without TEXOX.  While using the TEXOX Process, environmental discharge quality and permit requirements are easily met.