| 
|
By David Engle
It’s not your usual publicly owned treatment works-style waste. In fact it may pose the toughest wastewater challenge there is, at least technologically. Scores of “floating cities” of 5,000-plus people in multi-story palatial cruise ships ply the seas, and their continuous waste streams are collected, treated, and discharged, 24/7. Voyages last days and weeks—70% of the time, in coastal waters of the United States—yet, no sewers, drainage fields or ponds are around for doing the treatment work.
Ocean vessels have long solved the problem of shipboard wastewater, with holding tanks and marine sanitation devices (MSDs), retaining whatever is produced near ports, for later dumping out at sea. But, beginning a decade ago, environmentalists have charged this as inadequate, especially for cruise ships. In answer, the USEPA and its Coast Guard enforcement arm have issued hundreds of citations against oceangoing polluters, totaling many millions of dollars in fines, including some of the highest ever recorded
Meanwhile, effluent standards have been ratcheted upward, and soon will go even higher. No longer will MSDs suffice. On the immediate horizon, dozens of vessels will be needing to retrofit themselves with advanced wastewater treatment systems (AWTS) to comply.
Ship Waste “A Different Animal”
First, though, there have been multiple technical issues to solve. Conditions on high-occupancy ships pose extraordinary wastewater challenges. Randall Jones, chief executive officer of Navalis Environmental Systems in Scottsdale, AZ, explains, “Shipboard waste is a very different animal... having much higher organic loading” due to ships’ vacuum flush systems—meaning of course that the blackwater is very concentrated. A treatment approach that might succeed on land would be inadequate. Second, extreme load swings in waste elements follow one after another: galley water, followed by graywater from laundries (and from deck drains, showers, dishwashers, water fountains, equipment cooling, etc.), followed next by blackwater—all within a 24-hour “wastewater day” of perhaps 1,000 cubic meters. On a weekly basis that’s about 200,000 gallons of concentrated blackwater and a million of gray. It’s tons of treatment to compress in a day, every day, in the cramped confines of a ship’s hull, with no margin for error.
Such a spectrum of influents would strain any system, but in the nautical setting, difficulties multiply even more.
First, the option of using a large holding or equalization tank is pretty much eliminated: Within a ship’s hull, taking up so much space, along with the addition of relatively huge weight and ballast, creates untenable instabilities.
 |
Newer systems are set to treat any
blend of marine wastewater. |
Second, for the same reason, retention-times available for biological treatment must be curtailed, and the effluent must be quickly discharged.
A third complication arises here, though, in that the application of accelerants to hasten the treatment (e.g. polymers) and mechanical energy, both impose their own undesirable consequences: ballooning operational costs for the extra fuel, more tankage, and chemical resupply hassles, notes Steve DePoli , a vice president at shipboard wastewater system-maker Hydroxyl Marine Division (Victoria, B.C.) Illustrating his point: Five years ago his firm and several others competed for AWTS contracts to be awarded by Royal Caribbean Cruises Ltd. (Miami). In the resulting performance trials, he says, “The big shock was the annual energy consumption and cost of all the systems.” Totaling up operator’s time, chemical expenses, and the cost of electric power generation could easily double the up-front investment every few years. The energy portion alone requires between 100 kW and 400 kW, depending on the system, 24/7—adding hundreds of thousands in yearly fuel costs.
Hydroxyl adapted its AWTS to shipboard duty, but, says DePoli, “The trickiness in having land-based applications converted to marine,” comes in overcoming “vibration, list, roll, high temperatures, high humidity, and tougher fire codes”—atypical of the shoreside version. Meanwhile, AWTS must integrate seamlessly with existing electrical and plumbing systems and controls.
Another huge hurdle: Tight quarters below-decks make doing installations “a bear.” To accomplish them, blocks of cabins must be removed, the hull’s contents rearranged, and cabins replaced. Every day spent in dry dock means lost revenues, so there’s been a crunch to push working systems out the door.
A few years ago, in the early days of shipboard AWTS, such hastiness led to numerous emergency adjustments being necessitated at sea, and several ugly failures. First-generation AWTS efforts, “were very susceptible to the swings in the influent characteristics,” reports Jerome Daly of GE Water & Process Technologies, Ontario, describing the missteps of a vendor that eventually went bankrupt. Even when treatment systems work well in sea trials, they might easily fail in real-word conditions, due to the ever-changing crews’ inexperience.
As for doing maintenance “on the fly,” DePoli adds, “You can’t get on to do any maintenance work, because the ship is so jammed with passengers.” Consequently, the latest-generation AWTS are now largely automated, somewhat self-maintaining, and more reliable.
In sum, says DePoli, “It’s just a lot harder” to treat waste at sea. And more challenges lie ahead, particularly in improving food galley stream processing and in collection and handling of biosolids.
 |
| Converting land-based applications to
shipboard environments can be tricky. |
Push for Even Cleaner Seas
Meanwhile, the rules themselves are in flux as stricter effluent goals are being sought or are coming due; hence, there’s an element of uncertainty about precisely what effluent quality will apply, where. The toughest—the six-year-old Murkowski Act covering Alaska’s pristine waters—was proposed too as broader standard to extend to all US coastal waters. However, a bill introduced 2004 has so far not found sufficient support. Recently, Hawaii and California issued their own stricter requirements. A corporate standard set by Royal Caribbean Cruises Ltd. for its vessels’ effluents—15 ppm BOD, 15 ppm TSS, 10 ppm fecal coliform—is twice as tough as Murkowski. Royal plans to install AWTS fleetwide within the next couple of years. Moreover, two cruise industry groups, ICCO and ICCL, have stated a goal for member firms to meet Murkowski (30 BOD/ 30 TSS/ 20 fecal coliform) by 2010, notes Jones. The International Marine Organization (IMO) has set the year 2010 as the due-date for ships to comply with its forthcoming standard (50 BOD/50 TSS/200 fecal coliform), notes DePoli.
GE’s Daly, who is operations manager of marine and defense systems for Zenon Membrane Solutions, adds that “forward-thinking cruise line owners are ordering new ships with the best waste processing capabilities available,” just to be safe. DePoli points out similarly that owners “don’t want to be stuck with too many ships that they can’t use” in the lucrative Alaskan market.
Costs per system on big ships will probably come to between $2 million and $5 million each, according to Rich Pruitt, Royal Caribbean’s director of environmental programs, reporting to the Water Environment Federation. In August 2006, Royal announced a $9.2 million contract to Hydroxyl for four of dual black- and graywater “CleanSeas” systems.
All in all, this is adding up to perhaps a $5 billion market for retrofitting gray and blackwater AWTS, in fleets around the world, Jones suggests. His own firm, Navalis Environmental Systems, launched the latest technological innovation for gray- and blackwater treatment, and received Coast Guard certification for it, in summer 2006.
Globally, only a handful of manufacturers produce the new-generation AWTS meeting Murkowski, three of them in North America. Here’s a look at how each is approaching this extraordinary wastewater puzzle, in rather different ways.
ZeeWeed Filtration...
To tackle the aforementioned periodicity or “swing” in constituents and waste strengths, Holland American Lines is now using Zenon’s ship-optimized membrane bioreactors (MBRs). Zenon’s ZeeWeed system combines bio-oxidation and membrane immersed ultrafiltration (UF) into a single, simplified process step, making a small footprint and easing operation.
 |
| High-rate biological treatment can be
achieved through the use of ActiveCell
biofilm carriers. |
Zenon’s Daly notes that the shipboard ZeeWeed benefited from the company’s long prior experience with similar treatment issues: remote mining camps, oil exploration rigs, ski resorts, and overseas military sites demanding compact system efficiency. The key to making devices work and preventing the failures that earlier efforts suffered, he says, is to maintain “a very robust bioreactor with a very high concentration of biomass.”
Zenon achieves this with proprietary reinforced hollow-fiber membranes. These provide, says Daly, “a combination of ultrafiltration capability, while being able to operate in this extremely high-solids bioreactor environment.” Despite intense exposure to solids, the membranes “are not dependent on the use of chemicals, except for cleaning,” he says. Energy demand is at the low end compared with technologies that use dissolved air flotation (DAF).
ZeeWeed, introduced a half-dozen years ago, has steadily improve its effluent to attain Murkowski compliance. With that success came orders for six more gray- and blackwater ZeeWeed plants for Holland America; five now serve vessels in Alaskan waters; all consistently meet the standard for continuous discharge.
...And a CleanSea
A very different, multi-stage design powers Hydroxyl’s CleanSea, yet it, too, meets Murkowski. In the process, it also achieves, says Hydroxyl’s DePoli, perhaps “the lowest life- cycle cost in the industry” —about one-fourth that of high-end. A combination of proprietary technologies and selected add-on equipment reduces chemical consumption to “a very modest” level, he says, thereby saving on resupply and storage.
CleanSea can thus treat “any blend of marine wastewater streams, including graywater streams from accommodation, galley, food reject water, and laundry sources, as well as blackwater,” states Hydroxyl’s Web site.
First, automated influent collection and mixing of gray and blackwater occurs, to stabilize pH and provide consistency. Next comes mechanical separation of large and small primary solids via fine-screen rotating drums. Automatic sparging prevents the buildup of solids on surfaces. Solids descend for removal by diverter plates, are drained, and are discharged to a solid-handling subsystem.
Third, high-rate biological treatment is achieved using the ActiveCell biofilm carrier. Thousands of bacteria-containing protective polyethylene carriers move about within the aerated wastewater. Reliable high-rate biodegradation results, with minimal operator intervention. Response to load fluctuations is automatic. Space requirements are minimized, and no cleaning or backwashing is required. Hydroxyl claims that, by comparison, “...membrane bioreactor technology has proven unreliable in shipboard systems due to a requirement for frequent removal of membranes.” Hydroxyl’s biofilm carrier alternative requires no activated sludge, and experiences minimal downtime.
Following this biodegradation, removal of total suspended solids (TSS) occurs via another proprietary system, the ActiveFloat DAF (dissolved air flotation). Like the other components, this was adapted from land-based systems and was optimized for sea duty, in this case, by reducing the requirement for coagulant chemicals.
Tertiary filtration via gravity flow through fine-grain media yields effluent that meets the California Title 22 standard for water re-use and, of course, easily satisfies Murkowski.
As for solids, excess sludge is readily condensable. Unlike some land-based systems, the ActiveCell process uses no return activated sludge (RAS) line. Dewatering yields a cake for drying to a powdery form, ready for incineration or bagging and shore disposal.
Finally, one-pass ultraviolet (UV) disinfection destroys any remaining viruses, pathogens, and pharmaceutical residuals. Again, it’s automated.
Effluent can thus go overboard, having attained a Coast Guard certification significantly better than Murkowski. However, attaining this level was a lengthy and painstaking process requiring several years, DePoli notes.
Before getting its recent $9.2 million order for four, Hydroxyl had done three prototypes for Royal Caribbean, and, says DePoli, is now anticipating instructions for at least 15 more.
Navalis’ Poseidon And Orion
Newly emerging is a third design concept, “a whole new genre” consisting of ultrafiltration followed by advanced oxidation (AO) and UV disinfection, says systems co-designer Jones. The net result, he says, “takes the waste down to non-detectable BOD, suspended solids, and fecal coliform.”
 |
| In the Poseidon system, gray and black streams
remain separate. |
 |
| Large and small primary solids are separated by
rotating fine-screen drums. |
Unlike other shipboard AWTS, the Navalis was originally designed for cruise vessels, he says. Two version are offered: a large “Poseidon Graywater,” which treats 100 gpm to meet “California 22,” a graywater standard; a Blackwater Poseidon version treats 30 gpm to near-trace levels for BOD, TSS and fecal coliform, easily meeting all nautical standards.
Much smaller units of these two, designed for vessels with small passenger loads, are offered (dubbed the “Orion” system).
Poseidon’s co-designer is Steve Markle, a retired naval officer who chairs the sanitation device standards committee for the Society of Naval Architects and Marine Engineers. Markle introduced Navalis’ AO system in a recent SNAME white paper, from which the following description (and the discussion of discharge regulations elsewhere) are adapted.
Several facets of the Navalis differ considerably from the processes described. Above all: Gray and black waste streams remain separate, rather than mingling. The advantage, Jones explains, is that the two are very different waste problems, and thus should be treated with more tailored methods. For one thing, he says, concentrated blackwater “strains the membranes” and, over time, this will add wear and impair performance. UV disinfection will also suffer. Third, combining the two waters increases the need for costly chemicals, which, if misapplied, can also easily foul the membranes.
Graywater by itself, he goes one, “is much easier to treat,” and can even be reused afterwards, in the ship’s laundry, for wash-downs, and in toilets, saving the ship on some freshwater making (desalination) and reducing weight and tankage burdens.
Thus, in the Poseidon, about 85% of the graywater gets its own treatment, with the balance being mixed with black, for it’s process.
This “keep ‘em separated” philosophy naturally dictates a very different design approach. Nevertheless, the two processing streams share core component (stirred reactors, process tanks, pumps) to save on space and hardware cost, “taking turns” in processing.
With the blackwater, first (as in virtually any system) there’s solids separation. This occurs via a hydraulic separator; adding a fraction of the graywater thins this; then, it’s on to external plate-and-frame ultrafiltration.
Next, with the TSS strained out, comes the “breakthrough” technology, says Jones—the Poseidon’s use of ozone for AO. AO refers to the use of hydroxyl free compounds; these cannot be oxidized by conventional oxygen, ozone and chlorine. For processing, the stream is now diluted with some of the graywater; injected with dissolved ozone; and stirred in a couple of reactors, thus lowering the BOD and propelling disinfection to completion.
AO rapidly breaks down organic compounds, primarily into carbon dioxide and water.
Conventional biologic breakdown is thus avoided altogether, being replaced with what Markle reports is “a much faster-working and more efficient.. applied technology solution,” yielding a smaller footprint and quicker retention time.
AO also eliminates the MBR—“which,” says Jones, “is a little messy,” and operation of which, on ships, has proved to be relatively difficult, due to the previously mentioned constraints in space, pressure for high-volume processing, heavier loading, and swings.
Application of UV yields highly reactive oxygen; continued oxidation then consumes residual organics “in literally less than a second,” Markle reports.
Solids are directed to an incinerator or holding tank, or pumped via a macerating grinder to a clarifier, and the liquids then sent through for AO and UV; again, the outflow is clean enough to go overboard; Navalis’ AO earned Coast Guard certification in mid-2006, Jones reports.
On the separate graywater side, there’s initial screening via a resilient polyethylene shaker filter; ultrafiltration through ceramic membranes follows. At the back end, UV-disinfected effluent is clean enough for reused in various services (although not potable of course) or discharge.
Operation is automated by PLCs; monitoring and operational intervention can be done by shore-based specialists via an uplink.
 |
| The Orion units are designed for vessels
with small passenger loads. |
To save on installation expense, Jones and Markle designed the Poseidon as modular “building blocks.” These can pass through standards square and round ship hatches for assembly belowdecks. Blocks can be arranged to fit available deck space. Resulting space needs are thus much smaller, he asserts; similar productivity from a biologic-based system would “require ...10–20 times more arrangeable area and at least a half-man year of operator interaction,” he says.
Power requirements are also comparatively small—92 kW for the blackwater loop, and 66 kW for Poseidon Graywater on a 6,000 passenger vessel; the latter also potentially displaces some of the energy needed for desalination.
All told, operating costs, for both streams combined, should come to about $105,000 a year for 10 years (net present value using 5% discount rate), with only minimal operator intervention, Jones and Markle indicate.
Although no Poseidons or Orions are aboard any vessels yet, a land prototype is now busy reclaiming laundry graywater in Las Vegas, and a Poseidon Blackwater is treating city waste in Scottsdale, AZ, notes Jones.
The above technology sketch merely shows one aspect of a multifaceted global movement to protect the seas from ship wastes; besides the gray- and blackwater component, ships must now also meet tougher rules covering oily bilge water, and even ballast water handling.
And coming very soon will be a new line of “monster” cruise ships, the Genesis class at 220,000 gross tons and carrying 8,400 persons. This will nearly double the current size standard—and will surely multiply the operational challenges. Overall, four to six new cruise vessels are being built and christened each year; and obviously, as Hydroxyl’s DePoli notes, vessels of the future “are all going to be coming out with” the latest and greatest AWTS. “Rules are only going to get tougher,” he sums up. “They’re not going to ease up.”
Writer David Engle specializes in construction-related topics.
OW - January/February 2007 |
