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“Nutritious” reactors turn hydrocarbon wastewater into fast food.
Black bilgewater, thick with diesel and fuel oils, makes for a costly disposal problem. A typical Navy cruiser yields about 5,000 gallons of it every day, and a big aircraft carrier, up to 10 times that, according to the US Naval Sea Systems Command. When in port, any ship’s oily wastewater is typically piped ashore to be separated, drummed, and hauled to a dumpsite, often at great cost.
Ships are not the only oily water dischargers, of course; hydrocarbons of assorted kinds often become semi-emulsified in wash-down water or other process wastestreams. As we all know, oil and water don’t mix, but millions of gallons of wastewater do carry it; and the question becomes that of how to treat or dispose of it economically.
“Petroleaginous” Diet Made Bug-Friendly
Traditional methods of dealing with oily bilge offer few options: either burning, re-refining, or hauling it away.
But a low-cost alternative is now emerging: bacterial treatment.
Microbes will eat oil, of course. This has long been known. In fact, says Battelle microbiologist Fred Getz, hydrocarbons are “a very good food source” for bacteria. What’s intriguing, says Getz, is that, in extracting petro-energy as a food, microbes “rearrange the molecules,” says Getz, into CO2, water, “and other environmentally friendly” elements. Meanwhile, the gorging bacteria multiply. Both outcomes, he adds, “are very desirable.”
Use of oil-eaters to combat oil spills, slicks, or ground contamination is well known. But dispatching bugs into high-molecular hydrocarbon-laced wastewater has remained, until recently, rather experimental and untapped. A chief barrier to advancement of this has been many wastestreams’ typically high pH and/or salinity—both potentially toxic to bugs.
However, for the past decade or so, Getz has been leading an effort to develop a process that first collects oily water in sequence batch reactors (SBRs), then adds appropriate ingredients to correct such problems so that microorganism can thrive. Under these conditions, even oily water that was otherwise “very inhospitable” may thus be treated and its oil effectively removed, Getz says.
And so far, the results of this cutting-edge method are proving that it’s clean, easy, and cheap.
The procedure itself is simple and straightforward. Step one is to provide some dilution or emulsification. Moderate thinning makes the oil palatable. When emulsified, in fact, it “becomes a perfect source of food, or is presented...in a form that’s really readily accessible.” Such dilution or emulsification has often occurred already if detergents were added in an oil washdown. In such cases, bacterial treatment become even more appropriate, he suggests, “since an oil-water separator won’t work anyway” at that point. On the other hand though, he adds, “If the oil is too dilute, the microbes can’t break it down.” So there’s some trick to knowing the right balance-point.
Food Nourishment
Bugs need nitrogen and phosphorous, so add these next. “You can use simple commercially available fertilizer for this,” Getz notes. Amino acids, yeast, enzymes, and vitamins accelerate bacterial growth and appetites—and, again, all of these can be purchased at lawn-and-garden shops or home-improvement stores. These ingredients will make microorganisms multiply like swarms of locusts. “All you have to do is promote their growth” with nutrients, he says.
Absent these appetite-enhancing additives, the microbes would still eat the oil diet—but would likely require a leisurely month to finish the meal, instead of a few days.
Better still, he adds, take note that this is not a two-step, “seed and feed” process: The necessary varieties of microorganisms naturally occur in oil. There’s no need to add exotic new strains (although many vendors have offered these, over the years, in assorted oil treatment regimens). Adding the correct nutrients alone will “promote what’s already present,” he says.
Mix it all in a big tank and keep it stirred, Getz advises. “Give them lots of oxygen... and the bacteria go to town.”
One key to fostering this famishment feat is that, shortly after the microbes get their nutrients, some of the food supply will be removed—thereby compelling them to adapt rapidly to a new menu, namely, the energy within the oil.
At this point, digestion of the petroleum proper (or mineral oil, etc.) begins. Rather than simply ingesting it, the bugs are actually “remodeling the hydrocarbons...into the kinds of molecules that are found in living organisms,” says Getz—again, like DNA, protein, carbohydrates and lipids.
“That’s pretty amazing when you think about it,” he adds.
Equally remarkable is the speed at which the hungry population accomplishes all this: Under optimal conditions, which are easily induced, he has cut the time to within just “one or two days,” after which, “the hydrocarbons are pretty much broken down.”
Finally, with the process complete, you switch-off the reactor to let the sludge settle. The clarified water can then be drawn off at the top—“oftentimes ready for sewer discharge or filtering for recovery and reuse,” he says.
And net cost?
“On the order of ten cents per pound” of oil content, he says. This is minuscule compared to competing methods, which range anywhere from five to 10 times higher.
Even the sludgy leftovers can potentially be harvested and processed to yield further commercial value, he adds, in the form of lactic acid, acrylates, and other byproducts. “Bacteria will produce a variety of polysaccharides that can be used as biodegradable polymers,” he says. “Polyhydroxic butyrate is one of those compounds that can be produced biologically and then polymerized to make a biodegradable polymer.”
Getz sums up: “These are really very simple systems. They’re easy to operate.” Too, they can respond to a wide range of hydrocarbon concentrations, from just a few thousand ppm up to 40,000 ppm. “And “they’re very robust.”
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| A US Navy cruiser can yield 5,000 gallons of bilge daily. |
Demo Versions for Navy, Army
To prove the concept, Getz recently treated thousands of gallons of bilge water microbially at Pearl Harbor, HI, enabling the Navy to replace what had been an extremely costly procedure of barreling and removal at dockside tanks. Getz’ bugs are now batch-treating water that is pumped ashore, where it’s feasted upon and easily discharged as environmentally safe.
Unfortunately, this first success also revealed that shipboard service for oily bilge at sea would probably be a much greater challenge, notes Tony Morales, who is the Navy’s chemical engineer overseeing this function for the fleet. As it turns out, he says, the requirement of adding nutrients to fairly large storage tanks—“which, in a Navy ship, you don’t have”—together the additional process-controls and monitoring that’s required, all render Getz’s system mostly suitable for onshore facilities. Finally, there’s a relatively greater sophistication need in running it, compared with the usual oil and water separators, which sailors are used to.
More positively, the Navy’s harbor-side version of biotreatment at least demonstrated its workability and a very promising start for other land-based service.
Thus, a commercial firm that manufactures wastewater treatment systems, Water Resources Inc., of Scottsdale, AZ, has now licensed Getz’s microbial process—which is currently patent-pending by the Navy—and has packaged and launched it as a product-line which the company calls the “Aquatex SBR.”
In the wake of the Navy success, WRI last year was awarded a contract, also with the Department of Defense, to install the oil-fest for a Pennsylvania facility owned by the Army.
In the course of forging their artillery shell casings, tens of thousands of gallons of water must be applied for cooling and rinsing. The runoff provides an ideal case of industrial oily wastewater: It departs the forge, thickened with graphite and sludgy casting oil. From the drainage area, sump pumps carry it “to a tank for gravity separation,” explains Stephen Cannizzaro, who is director of environmental management systems at the Scranton Army Ammunition Plant. SAAP, although Army-owned, is operated by Chamberlain Manufacturing Inc.
With such heavy oil in the wastestream, a major concern for Cannizzaro has been sewer discharge compliance. Although the oil-separation treatment method that he’d been using did enable him to remain within permitted levels, he says, “it wasn’t always optimal,” and he also found that “fluctuations in concentration and flow rates were greatly affecting the efficiency.”
Thus, a couple of years ago, Cannizzaro decided to experiment with bioremediation chemicals (i.e., adding “exotic” microbes that are custom-designed for oil treatment). He published a paper on his results. This led to a helpful contact from higher up, at the DoD’s Environmental Security Technology Certification Program (ESTCP); they passed-along to him a report on Getz’s new process and success with the Navy.
SAAP’s oily forge waste, which contains hydraulic and mineral oils, wasn’t very similar to the much more noxious ship bilge—and thus, Cannizzaro realized, the nutrient-enrichment SBR process which Getz had devised should obtain results at least as good as, if not better, than the Navy’s.
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| Oily water is collected in sequence batch reactors, with ingredients added for microorganisms to thrive. |
Simple System Construction
So in December 2005 Cannizzaro ordered and installed two storage tanks to be made of glass fused to steel in an inverted conical shape, with capacities of 41,000-gallons each. The Phillipsburg, NJ-based Northeast Aquastore Tank Co. did the manufacturing. Requiring a combined footprint of 40 feet by 100 feet and a height of about 18 feet, they’re sized to treat 100% of SAAP’s 80,000 weekly gallons of oily waste.
To provide a warm enclosure for them, SAAP also ordered a new metal prefab building (a provision that wasn’t needed in the moderate climate of Pearl Harbor).
Next, a few weeks passed as tank sludge was nurtured to grow to the point that both tanks now contain “all the needed bacteria” to eat lots and lots of oil, he says.
The two reactors now work independently as twin redundant systems. This enables nonstop operation. “As one is filling,” he explains, “the other one is treating; and when one is discharging, the other can be filling.”
Oily water enters via a common influent pipe and pump, bearing TPHs (“total petroleum hydrocarbons,” i.e., all oils and grease) at levels measured at up to 40,000 ppm.
Nutrients are added next. As previously noted, the system uses ordinary off-the-shelf garden supplies. “We’re using the same regular fertilizer that you can find at Lowe’s...to add some nutrients for the bacteria to help them get more acclimated... Since they are naturally occurring in our sludge,” he adds, “we give them the right fertilizer mix, and they’re really thriving on eating all the wastewater chains and the hydrocarbons.”
Nutrient-enrichment looks vaguely similar to the exotic or so-called “superbug” biotreatment that Cannizzaro had experimented with before, he points out. The big difference is that Getz’s cocktail of accelerants eliminates the need for nurturing the imported microbes. “We are just using the naturally occurring bacteria as are found in our wastewater,” he says. “And they’ve been doing a very good job.”
As the process extends over the next few days, a series of pipes, air manifolds, and big blowers aerates and circulates the contents. Control of both tanks via a PLC touch-screen enables either manual or fully automated operation. Fermentation starts to occur, yielding surprisingly high heat as a byproduct. This in itself actually keeps the operation room a comfortable 55°–60°F all winter long. Cannizzaro notes, however, that tank content temperatures should be maintained at 70°F or above for optimal processing, with pH kept at 7.5. Probes monitor pH conditions closely, with linkage to a pump, so that if pH dips, correction will be automatic.
For a simple readout, hour-by-hour, on how far along the process is, and how voraciously the bacteria are bingeing, you simply keep tabs on dissolved oxygen content. When indicators show that the “banquet” is finished, the tank’s decanting pipe draws the clarified outflow through a five-micron filter, and straight to the sewer.
Cycle time for each tank turns out to be “just three to four days,” he says.
Picked Clean
Oily water enters bearing tens of thousands of ppm of TPHs; it departs with only 20.
By comparison, the previous oil-water separation system at SAAP—based on gravity—had yielded clarity not nearly as good, but still within the permitted level of 100 ppm. Obviously, the new tanks improve on this considerably, and do so, he adds, “in a more reliable way.”
After the clarified water is drained off, left in the bottom tenth of the tank is thick biomass. This keeps thriving and enlarging, replenished with each cycle. Fresh portions are taken, Cannizzaro says, “to re-inoculate and use for treatment for the next wastewater loading.” This lively preservation necessitates constant mechanical recirculation.
Excess sludge also builds up, which must be removed to a filter press and formed into a biomass cake. Samplings verify that it meets landfill disposal standards under the Toxicity Characteristic Leachate Procedure.
Although the plant has only lately hit full stride, the bugs have performed, so far, consistently well, Cannizzaro reports. “We’ve been able, routinely, within a five-day period, to break everything down that we’ve sent to it... It’s very promising.”
Down the road, there’s an opportunity to expand beyond merely decomposing the TPHs, to full-fledged water recycling. When that comes, Cannizzaro says, instead of using fresh city water to flush the oily wash to the disposal troughs, “we can reuse processed water... recirculating it back through our pits.” To assess recycling feasibility, SAAP is now tracking and measuring outflow constituents.
As for cost-and-benefit calculations on the investment: this really isn’t a prime concern, he notes, as the military’s oil cleanup campaign is being driven and funded by ESTCP for environmental benefits.
However, Cannizzaro estimates that an industrial user of the SBR, seeking to de-oil its wastestream, might be able to retrofit nutrient-enrichment quite affordably. Assuming that suitable tanks are already in place, he says, merely by adding the necessary monitoring and control systems and recirculation pumps, a system could be installed at cost in the low six-figures.
He sums up: “Our basic premise is, this is a lot more efficient system. It gives us a more flexibility in our operations... If we ever have any kind of oil spill or mishap, we now have a very effective means of treating oily water and making sure that we can meet all our discharge requirements,” which, he adds, under Chamberlain’s ISO 14001 standards, are stringent.
SAAP is also a LEED-certified (Leadership in Energy and Environmental Design) facility. The microbial system thus “fell into the realm of pollution prevention... and this was where we wanted to go,” he says, as an expression of the company’s environmental commitment.
Blue Plate Special: Hazardous Paint
Back at Pearl Harbor, the Navy is now reportedly poised to take a second look at Getz’s famished microbes for an entirely different job—this time deploying the Aquatex on a mission to biodegrade many gallons of expired, oil-based toxic paints.
Under the current regimen for such procedures, hazmat disposal of old paint “has been costing the Navy $25,000 per month for drumming and hauling to sites” for environmentally safe destruction, says WRI president Randall Jones. Even for the Navy, that’s a lot of money. A much cheaper procedure—virtually identical to the one Cannizzaro used at SAAP—will soon be applied. First will come dilution of the paint epoxy and fixer; then, addition of nutrients to feed the already-present microbes; after this, the nutrients will be withdrawn to spur the bugs to gorge on waste media. Additional nutrient “cocktails” to encourage reproduction will complete the recipe.
Payback on the new system should come, Jones estimates, in “just about one year.”
A third installation, at an Alcoa Industries site in California, will treat oily process water there, disposal of which had been costing “about a dollar a gallon” to haul away and treat, Jones says. Microbes will slash this to a fraction.
Are there no downsides at all?
“There really are none,” answers Getz. “Regulators like it because it produces a clean stream. Companies like it because it reduces their waste liability more cost-effectively than the alternatives”—i.e., combustion, barreling, re-refining, “none of which is really satisfactory.”
If any practical limitation does exist, it’s probably just in the liquid volume, i.e., are there at least a few thousand gallons to be treated and to fill the tank daily? And secondly, as Morales had indicated pertaining to shipboard treatment: Is there adequate space at hand for siting tanks?
Finally, given the potential market of many thousands of industrial sites worldwide that are churning out oily wastewater in some form—forges, paint plants, refineries—the range and number of microbial applications is probably enormous; cumulatively, Getz suggests, somewhere in the “tens of millions of gallons” of industrial wastewater annually, in the US alone, “that contains, or may be contaminated with, 1%–2% oil by weight.”
As for market barriers and other obstacles, Getz points out that oily wastes in industry are usually being dealt with by some means already; thus, overcoming the legacy method may be tough unless (as at Alcoa) the method is a costly one.
Then too, there’s simply the novelty and inexperience hurdle—i.e., the idea of using biology in a field ruled by engineering. Getz reassures his colleagues, though, that, “There is no doubt this does work,” and fact, microbes “will handle emulsified oily waste that other physico-mechanical separators might not.”
La Mesa, CA-based writer David Engle specializes in construction-related topics.
OW - November/December 2006 |
