Patent Description:
These fluids may be used in production operations for many different purposes. For example, steel and other metals may be processed in hot strip or rolling mills that reduce a hot slab, bloom, or billet from a cast shape into thin coils, plates, rebar, or other structural shapes. A typical arrangement is a roughing mill, followed by finishing stands that continuously reduce the cast product into its desired dimensions for final use or additional processing in pickle lines, cold mills, and annealing and cut-to-length lines. The forces required to reduce a cast product to thinner shapes require roll stands with significant pressure requirements (><NUM> psi / <NUM> kPa). These pressures are maintained with hydraulic fluids.

From a hydraulics perspective, many industrial machines are designed to operate with fire-resistant hydraulic fluids, particularly water glycol-type hydraulic fluids, due to extremely high operating temperatures. Water glycol fluids usually contain glycols and about <NUM> to <NUM> wt% water (e.g., <NUM>-<NUM> wt% water, or <NUM>-<NUM> wt% water). Typical glycols used in such fluids include diethylene glycol, ethylene glycol, propylene glycol, and other polyalkylene glycols or combinations thereof. For example, the water glycol fluid can contain <NUM>-<NUM> wt% or <NUM>-<NUM> wt% diethylene glycol, and/or <NUM>-<NUM> wt% or <NUM>-<NUM> wt% other polyalkylene glycols.

While water is an important part of such water glycol fluids, its presence can also create performance issues for the fluid. Water, for example, does not exhibit the lubricating film strength of mineral oil or various synthetic lubricating base stocks and thus tends to limit the maximum operating pressure of the hydraulic system.

The high water solubility of water glycol fluids can present a range of difficulties in an industrial setting including, for example, establishing adequate control of wastewater discharges from industrial plants and facilities. Local municipalities, as well as state and federal agencies, may monitor water leaving an industrial site for contaminants such as phenol content, FOG (fats, oils, and grease), heavy metals, and CBOD (carbonaceous biological oxygen demand) and COD (chemical oxygen demand).

As noted above, water glycol fluids are used widely throughout various industrial and hydraulic operations and tend to be applied, under high pressures, for actuating various components or for circulating through operating equipment for controlling operating temperature. As a result, leaks or other inadvertent discharges of water glycols during industrial operations are not uncommon. For example, in a steel mill, the hydraulic fluid might be applied at a pressure of <NUM> to <NUM> kPa (<NUM>,<NUM> to <NUM>,<NUM> psi). At these high pressures, a leak can result in hundreds or thousands of gallons of the hydraulic fluid entering the wastewater stream.

Water glycol fluids that find their way into a wastewater stream are typically not removed during standard waste treatment methods and tend to contribute substantially to increased CBOD and COD levels in the effluent stream. The increased CBOD and COD levels can result in significant changes to the biodiversity of the effluent stream. Although anaerobic bacteria can survive-and perhaps thrive-in the presence of the water glycols, the rest of the ecosystem will be depleted as oxygen levels are diminished. As a result, many industrial operations are faced with treatment surcharges from their local wastewater treatment facilities or permit violations due to high levels of CBOD.

To address this, industrial operations have attempted to implement methods for suppressing the impact of inadvertent glycol discharges. However, the glycols are <NUM>% water soluble, and are therefore difficult to remove from water streams because the glycols will not float, cannot be filtered, and are generally not reactive. To date, ultrafiltration and reverse osmosis have been the only measures believed to be effective for removing glycols from wastewater streams. However, these processes are expensive and cumbersome, requiring wastewater to be collected and moved off-site for biological wastewater treatment.

There is a need for a more efficient method for quickly removing glycol contaminants from wastewater streams without requiring off-site treatment.

Document <CIT>, with its abstract, discloses methods for treating a fluid, particularly water, contaminated with organic compounds, organisms, toxic substances, hazardous substances, ammonia, or mixtures thereof, by adsorption with an adsorbent material and regeneration of the purified adsorbent material. The contaminants may be first adsorbed onto the adsorbent material, which is then regenerated by treatment with nanoparticles of at least one transition metal oxide catalyst and at least one oxidant; or the contaminants are adsorbed onto particles of the adsorbent material loaded with at least one transition metal oxide, which is then regenerated by treatment with an oxidant; or the contaminated fluid is treated with an oxidant first and then with particles of the adsorbent material loaded with at least one transition metal oxide. The adsorbed contaminants are converted into environmentally compatible products.

Document <CIT>, with its abstract, discloses a process for reducing the total organic carbon (TOC) in an aqueous mixture obtained as wastewater from a process for the preparation of an olefin oxide, the process for reducing the TOC comprising: (a) contacting the mixture M1 which contains at least one oxygenate having from <NUM> to <NUM> carbon atoms with an adsorbing agent and adsorbing at least a portion of an oxygenate at the adsorbing agent; (b) separating an aqueous mixture M2 from the adsorbing agent, the mixture M2 being depleted of the oxygenate adsorbed in (a); and (c) separating an oxygenate from the mixture M2 obtained in (b) by subjecting the mixture M2 to reverse osmosis in at least one reverse osmosis unit containing a reverse osmosis membrane obtaining an aqueous mixture M3 being depleted of this oxygenate.

In accordance with one aspect of this invention, it has been discovered that powder activated carbon (PAC), previously believed to be ineffective at removing water glycols from water streams, can efficiently reduce glycol-associated contaminants from water streams. The water can be treated on-site (e.g., at a steel mill) without requiring the water to be collected and transferred to an off-site treatment location. This allows for real-time evaluation and treatment of elevated total organic carbon (TOC) in order to ensure that industrial operations comply with regulations governing TOC levels.

According to the invention, there is provided a method for reducing an amount of total organic carbon (TOC) in water in a steel mill wastewater stream at a steel mill, the water containing <NUM> to <NUM> (<NUM> to <NUM> gallons) glycol / <NUM> (<NUM> lb) TOC and more than <NUM> TOC/L water, comprising the steps defined at claim <NUM>. The dependent claims <NUM>-<NUM> outline advantageous ways of carrying out the method.

The FIGURE is a chart illustrating the effectiveness of PAC on removing glycols (as measured by TOC) using varying concentrations of PAC in a laboratory trial.

It should be noted that this figure is intended to illustrate the general characteristics of methods with reference to certain example embodiments of the invention and thereby supplement the detailed written description below.

As described herein, methods are provided for reducing the amount of organic matter in a water stream.

The amount of organic matter in a water stream can be measured using various parameters. CBOD is a measurement of oxygen depletion in water as a result of biological activity facilitated by the carbonaceous organic matter in the sample. Higher concentrations of organic matter provide more "food" for microbes, resulting in greater microbial activity and thus greater oxygen depletion. Regulatory bodies generally monitor organic contaminants in industrial wastewater by evaluating CBOD. However, to monitor CBOD, effluent must first be collected and shipped to a treatment site (which can take about <NUM> days), and the CBOD test itself requires a <NUM>-day period to incubate the sample with microbes. Thus, a glycol leak could go undetected for <NUM> days before the industrial facility first becomes aware of the problem.

Also, because of the nature of the CBOD test, test results have a large standard deviation, and measurements can vary as much as from <NUM>% to <NUM>% of the actual CBOD. In order to ensure that effluent streams are found to be in compliance with regulations, CBOD must be minimized as much as possible (preferably eliminated) in order to ensure that CBOD tests do not report violating levels of organic matter.

TOC is a related parameter for measuring organic matter, and allows for substantially immediate feedback on amounts of organic matter in the waste stream. TOC provides a measure of the total amount of carbon in a sample through determination of CO<NUM> generation from an oxidation reaction. In other words, while CBOD measures the demand for oxygen, TOC measures the conversion of oxygen to CO<NUM>. TOC can be measured real-time, on-site, and with high accuracy. In a steel mill, for example, TOC levels can be monitored at different locations (e.g., caster, flume, scale pit) on a periodic basis. To ensure prompt feedback, measurements can be made every <NUM>-<NUM> minutes. Alternatively, the facility could continuously monitor TOC levels at one or more locations.

Because CBOD and TOC are related, either can be used to measure organic content in the water stream according to the disclosed methods. However, TOC is desirably used due to the ability to get immediate feedback on glycol levels with relatively high accuracy.

In methods of the disclosed embodiments, powder activated carbon (PAC) is introduced into a water stream and contacted with organic matter in the water stream in order to reduce the amount of the organic matter in the water stream. The effectiveness of organic matter (particularly glycol) removal can be determined by monitoring CBOD or TOC. For simplicity, the following discussion refers to monitoring TOC, but CBOD measurements may also be used.

Activated carbon is a highly porous, high-surface-area adsorptive material with a largely amorphous structure. It is composed primarily of carbon atoms joined by random cross-linkages. The randomized bonding creates a highly porous structure with numerous cracks, crevices, and voids between the carbon layers, resulting in a very large internal surface area.

Activated carbon may be in the form of powder activated carbon (PAC), such as powder having a particle size of <NUM> mesh (<NUM>) or smaller. For example, the PAC can have a particle size of <NUM> mesh (<NUM>) or smaller, <NUM> mesh (<NUM>) or smaller, <NUM> mesh (<NUM>) or smaller, <NUM> mesh (<NUM>) or smaller, <NUM> mesh (<NUM>) or smaller, or <NUM> mesh (<NUM>) or smaller. The PAC can be defined by a certain percentage of the particles passing through a given mesh size (e.g., at least <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%), or can be defined by a series of mesh sizes (e.g., a PAC in which <NUM>% of the particles pass through <NUM> mesh, <NUM>% pass through <NUM> mesh, and <NUM>% pass through <NUM> mesh).

PAC particles can have an average pore size of, for example, <NUM> or less, such as from <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>. Also, the PAC particles can have an iodine value of <NUM> to <NUM>, or even more than <NUM> (e.g., <NUM>-<NUM>). The iodine value is an indicator of porosity, and is defined according to ASTM D4607-<NUM> as the milligrams of iodine adsorbed by <NUM> of the carbon when the iodine concentration of the filtrate is <NUM> mol/L.

The apparent density of the PAC can range from <NUM> to <NUM>/m<NUM> (<NUM> to <NUM> lb/ft<NUM>), such as <NUM> to <NUM>/m<NUM> (<NUM> to <NUM> lb/ft<NUM>). For example, the PAC can have an apparent density of <NUM>/m<NUM> (<NUM> lb/ft<NUM>).

In embodiments of the invention, PAC can be injected into the water stream in either powder form or as a slurry. For example, the PAC can be mixed with water in a batch tank to form a slurry containing <NUM> to <NUM> PAC per liter water (<NUM> to <NUM> lbs PAC per gallon water). For example, the concentration of PAC in the slurry could be <NUM> to <NUM> PAC per liter water (<NUM> to <NUM> lbs PAC per gallon water), <NUM> to <NUM> PAC per liter water (<NUM> to <NUM> lbs PAC per gallon water), or <NUM> to <NUM> PAC per liter water (<NUM> to <NUM> lb PAC per gallon water). The slurry can be held in the tank, i.e., pre-made, or formed continuously and as needed. The PAC can then be injected into the system (either in powder form or as a slurry) in response to detected elevated TOC levels. This process of injecting the PAC in response to reaching a TOC threshold (e.g., <NUM> or <NUM> ppm) can be automated or performed manually.

Effective PAC dosing will depend on TOC levels. Treatment levels and dosing will vary depending on system configuration and CBOD permit limitations. Depending on system dynamics, the feed rate can be between <NUM> and <NUM> PAC per liter (<NUM> and <NUM> lbs of PAC per gallon) of glycol. A total treatment amount of <NUM> to <NUM> (<NUM> to <NUM>,<NUM> lbs) of PAC can be injected into the water stream for every <NUM> (<NUM> lb) of TOC introduced in the water stream. For example, <NUM> to <NUM> (<NUM> to <NUM> lbs) of PAC, <NUM> to <NUM> (<NUM> to <NUM> lbs) PAC, <NUM> to <NUM> (<NUM> to <NUM> lbs) PAC, or <NUM> to <NUM> (<NUM> to <NUM> lbs) PAC can be added for every <NUM> (<NUM> lb) of TOC. Depending on TOC levels and effluent flow rate, the PAC feed rate can be from <NUM> to <NUM>/min (<NUM> to <NUM> lb/min), from <NUM> to <NUM>/min (<NUM> to <NUM> lb/min), or from <NUM> to <NUM>/min (<NUM> to <NUM> lb/min).

In the case of a hydraulic fluid leak, glycol levels can range from <NUM> to <NUM> litres (<NUM> to <NUM> gallons) glycol / <NUM> (<NUM> lb) TOC (for example, <NUM> to <NUM> litres (<NUM> to <NUM> gallons) glycol / <NUM> (<NUM> lb) TOC, or <NUM> to <NUM> litres (<NUM> to <NUM> gallons) glycol / <NUM> (<NUM> lb) TOC). The amount of fluid leaked into the system can depend on different factors such as flow rate and how long the leak progressed until it was detected. For example, a leak can introduce <NUM>, <NUM>, <NUM> lb, <NUM>, <NUM>, <NUM> (<NUM> lb, <NUM> lb, <NUM> lb, <NUM> lb), or more TOC into the system. TOC levels at the time of initiating treatment can be lower if detected early (e.g., <NUM> or <NUM> TOC/L water), or can be as high as <NUM>/L, <NUM>/L, <NUM>/L, <NUM>/L or higher.

Average TOC levels after <NUM> hours of treatment should ideally be lower than <NUM>/L, and preferably lower than <NUM>/L or lower than <NUM>/L. Treatment could result in complete removal of TOC or a decrease in average amount of TOC over the course of <NUM> hours. For example, the detected amount can decrease by <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% over the course of treatment (e.g., within <NUM> hours from start of treatment).

The total treatment amount of PAC added with respect to glycol spilled into the system can be up to <NUM> PAC / litre glycol (<NUM> lb PAC / gallon glycol), e.g. from <NUM> to <NUM> PAC / litre glycol (<NUM> to <NUM> lb PAC / gallon glycol), from <NUM> to <NUM> PAC / litre glycol (<NUM> to <NUM> lb PAC / gallon glycol), from <NUM> to <NUM> PAC / litre glycol (<NUM> to <NUM> lb PAC / gallon glycol), or from <NUM> to <NUM> PAC / litre glycol (<NUM> to <NUM> lb PAC / gallon glycol). For example, the amount of PAC introduced can be about <NUM> PAC / litre glycol (<NUM> lb PAC/ gallon glycol).

In some aspects, to ensure sufficient interaction between the PAC and glycols, the PAC can be allowed to mix with the water containing organic matter (TOC) for a certain amount of time before being separated, such as for <NUM>-<NUM> minutes. For example, the PAC can be mixed into a water stream containing organic matter (where turbulent flow effectively mixes the PAC into the water stream) for at least <NUM> minutes, at least <NUM> minutes, at least <NUM> minutes, at least <NUM> minutes, or at least <NUM> minutes prior to being allowed to settle. Or the PAC can be mechanically mixed with water containing organic matter in a tank for any of these mixing times.

According to the invention, the PAC is added in the flume that leads to the scale pit or other clarification systems. The PAC is sufficiently mixed with the wastewater in the flume or other piping prior to the scale separating system, where it then settles together with the adsorbed glycols. In this case, the mixing time refers to the amount of time the PAC spends in the flume, mixing chamber, or piping before reaching the scale pit or other devices where it is allowed to settle. The settled PAC/glycols are removed from the scale pit, settler, dissolved air flotation (DAF) device, or other separation device, together with steel scale, and the clarified water can be recirculated.

The settled PAC/glycols can remain in the scale, which is removed and recycled or disposed per normal handling processes.

The following test was performed to demonstrate the effectiveness of the disclosed methods, and particularly to confirm the effect of various concentrations of PAC on treating TOC.

A control solution contained <NUM> ppm TOC (~ <NUM> ppm glycol) in water. The glycol product used was FR WG <NUM>-D from American Chemical Technologies, Inc. , and included <NUM>-<NUM> wt% diethylene glycol, <NUM>-<NUM> wt% water, <NUM>-<NUM> wt% polyalkylene glycol, <NUM>-1wt% morpholine, and <NUM>-<NUM> wt% diethanolamine. Test samples were prepared from the control solution by adding varying amounts of PAC, ranging from <NUM>,<NUM> ppm (<NUM> wt%) to <NUM>,<NUM> ppm (<NUM> wt%) PAC, and mixing the samples for <NUM>-<NUM> minutes. The samples were allowed to settle for approximately <NUM> minutes, and <NUM> of water was decanted from the top of each sample and analyzed using a Teledyne TOC analyzer. Minimal PAC was included in the <NUM> aliquots due to settling; however, any incidental amounts of PAC present in the samples is believed to have not affected the TOC analysis.

The results are summarized in the FIGURE. As shown, TOC levels decrease with increasing amounts of PAC. However, it becomes increasingly difficult to mitigate TOC levels below <NUM> ppm TOC. This demonstrates that PAC must be dosed carefully to ensure that TOC levels remain below regulated thresholds (which can require less than <NUM> or <NUM> ppm TOC).

Claim 1:
A method for reducing an amount of total organic carbon (TOC) in water in a steel mill wastewater stream at a steel mill, the water containing <NUM> to <NUM> (<NUM> to <NUM> gallons) glycol / <NUM> (<NUM> lb) TOC and more than <NUM> TOC/L water, the method comprising:
- adding powder activated carbon (PAC) to the flume leading to the scale pit or other clarification systems, upstream of a scale separating system of the steel mill;.
- mixing the powder activated carbon with the wastewater in the flume or other piping prior to the scale separating system and then settling the PAC with the adsorbed glycols;
- removing the settled PAC/glycols from the scale pit, settler, dissolved air flotation (DAF) or other separation device together with steel scale; and
- disposing of the settled PAC/glycol together with the scale.