The Carnival Fantasy steamed into port recently, returning from a seven-day trip to the eastern Caribbean with 2,188 passengers aboard. Just before reaching port, while the ship cruised some 48 miles east of Beaufort and 22 miles southeast of Folly Beach, the crew flipped a switch and the sewage dumping stopped.

That's no small thing. A ship the size of the Fantasy can flush 15,000 to 30,000 gallons of treated sewage per day behind it, along with eight times that much untreated "gray water."

That's the drainage from sinks, showers, kitchens, laundries and shipboard cleaning. The ship also produces and periodically discharges tons of oily bilge water per day after removing some oil.

In port, sewage gets diverted into bilge tanks to be held until the ship sails away again.

About 90 cruise ships are expected to dock in Charleston in 2011. S.C. Portsí planned facility will allow two ships per week to dock, according to Byron Miller, S.C. Ports public relations director.

In Charleston, sewage disposal is the concern getting the most attention in the debate over the environmental impact of the ships.

How thoroughly treated should waste be before it's discharged? How far from shore should the ship be allowed to dump to give the ocean enough water to absorb the discharge? Should local, state and federal governments toughen the rules and enforcement?

The answers are anything but clear.

Nobody really knows how nasty the discharge is. It isn't monitored or tested. Sewage aboard the boats gets primary, chlorine-based treatment that wouldn't meet federal requirements on land. Gray water gets none.

Nobody really knows what impact the discharge has on shallow offshore waters; not enough study has been done.

Nobody really knows if 12 nautical miles offshore -- the point where Carnival Cruise Lines officials say their boats quit dumping -- is far enough to keep the residue of that mess from washing up on Lowcountry beaches.

Add to that the impact of four diesel engines burning as the ship comes into port spewing exhaust into the air from diesel fuel that is dirtier than the fuel used in land-based vehicles. And the single engine that keeps burning to supply power while docked. And the ton of garbage and recyclables off-loaded.

Nobody knows the cumulative environmental cost of doing business with cruise ships.

Little or nothing is being done about it. Unlike in other states, where environmental regulations are gradually being tightened around the ships, South Carolina legislators and local officials have kept hands off, saying federal laws are good enough. Much of what the industry does is self-regulation.

"At the end of the day (being environmentally responsible) is good business procedure because we have to be accepted by the community if we're going to succeed," said Tom Dow, Carnival's vice president of public relations.

Critics say that isn't good enough.

Dana Beach, head of the Coastal Conservation League, said "Every single business that operates here operates under enforceable standards. (The cruise industry says) they're not going to discharge within 12 miles of the coast, and they're only going to discharge treated effluent. All we say is, put it in writing. An enforceable, verifiable document."

Treated enough?

The environmental officer aboard the Fantasy is Irfan Bate, 34, of Mumbai, India. Mumbai is a western port city on the Arabian Sea, maybe best recognized in the United States as a tourist destination to see tigers. Asked if there are tigers in Mumbai, Bate smiled. "Yes," he said. "Lots."

After the Fantasy landed on that recent stop, Bate showed a reporter how waste is handled aboard a huge ship that is a virtual small city. He was escorted by officials from Carnival Corp. and the State Ports Authority. They did not allow photographs, citing security concerns.

For the tour, Bate was dressed in his cruise ship uniform and was a little flattered to be singled out. He spends much of his time in the three decks below the 10 passenger decks.

He works behind locked doors, where getting around means clambering up a maze of portals and ladders, where the engine's rumble is loud enough that crew members wear ear plugs.

Bate has been with Carnival for 10 years. Asked what he likes about the job, he said, "I like to do something challenging all the time."

The warrens that lead to the sanitation center of the ship look like something out of a science fiction movie.

Big-bellied pipes and lines run along the walls and ceiling. The machines are huge. The engines themselves look like an outsize version of a wall of World War II submarine torpedo tubes. The control room for the works has the feel of a 1960s NASA mission control -- all dials and switches and screens.

A few portals down, the group is led into a narrow room where a Marine Sanitation Device sits. The device is the core of sewage treatment on the ship. It looks like a big shipping container with pipes coming out of it, gauges and buttons under signs such as "Aeration," "Setting" and "Chlorination."

It doesn't look big enough to handle the flush of toilets from more than 2,000 people, and it isn't. The device is one of three aboard the Fantasy.

A half-dozen or more empty barrels sit near the device. Asked about them, Bate said the drums are used to dump oily rags and trash from working on the device.

The Marine Sanitation Device does some of the same work as a municipal sewage treatment plant, and there's a little of that smell around it. The devices are the crux of the sewage debate over cruise-ship impact.

These devices aboard the Fantasy are in the middle range of three types. Critics say the Fantasy, and every other cruise ship, should be using advanced treatment devices that more closely match the sort of treatment the law requires on land.

Cruise ships are expressly exempted from those regulations. A Marine Sanitation Device can cost thousands of dollars; an advanced device costs 100 times more.

Carnival Corp. posted net earnings of $1.3 billion among its 98 ships for the 2010 summer season, according to the company's report.

Alaska and Washington state now require cruise ships to have advanced sanitation devices, as well as treatment for gray water, in order to discharge in state waters.

"We're letting cruise ships set the agenda for Charleston rather than the other way around," Beach said. "Charleston needs to establish standards that don't put us at the bottom of the barrel."

Far enough out?

The mess that sewage and gray-water discharge leaves in the water is largely fecal coliform, the bacteria that leads to beach and shellfish closings along the coast. But there can be any number of other nasty things present, including diseases, viruses, intestinal parasites, soaps, oils, grease and metals.

Cruise ships have a spotty record of environmental compliance. Carnival is among the companies that have been fined for illegal dumping and falsifying records to hide it.

In 2004, the EPA sampled wastewater discharge from four cruise ships in Alaska and found Marine Sanitation Devices "unable to effectively treat black water (sewage). In addition, untreated shower and galley water contained bacteria and suspended solids concentrations equal to or exceeding treated black water."

The report went on to note that treatment equipment since had been updated to meet tougher federal requirements.

None of the four was a Carnival ship.

The Coast Guard is the agency in charge of inspecting sewage treatment on cruise ships. The inspection is part of a larger, eight-point protocol that focuses on safety equipment and the seaworthiness of the vessel.

A team of five to eight personnel disperse through the 14 decks of the ship. For sanitation, they inspect the equipment and operations, do an operational test of the oily water separator and review the records.

The Marine Sanitation Device gets a look over. On land, a sewage treatment plant is required to have its discharge tested regularly for pollutants by staff and by state inspectors.

Since January, all eight cruise ships that called on the Port of Charleston have been inspected -- two of them here, six at other ports of call, said Cmdr. Christopher Marcy, prevention chief of the Coast Guard Sector Charleston. The Fantasy was one of two ships inspected locally.

"No pollution-related deficiencies were issued," he said.

A 2000 federal General Accounting Office report on cruise ships said Coast Guard inspectors "rarely have time during scheduled ship examinations to inspect sewage treatment equipment or filters to see if they are working properly."

That finding was noted in a 2008 report by the Congressional Research Service. Its report went on to say that since the 9/11 terror attacks, the Coast Guard has taken on more homeland security duties, leaving less time for environmental inspections.

Two factors make it uncertain whether 12 miles out is far enough to begin dumping: Charleston sits in the relatively shallow South Atlantic Bight, where the ocean doesn't reach 100 feet deep until nearly 50 miles offshore; the Gulf Stream flows some 60 miles out, kicking up eddies that circulate shoreward.

Pam McCarthy's "Cruise Line Wastewater Discharge in the Caribbean Region" is one of the few studies done on impacts of shallow-water dumping on the East Coast.

McCarthy, an environmental manager who studied at Duke Marine Lab, wrote the paper working with Conservation International, an environmental advocate.

Conservation International is working with the Cruise Lines International Association to plot out safe dumping zones in the Caribbean, using depth as the indicator. Using distance out to sea isn't adequate where waters are shallow, said Kate Olson, the organization's corporate communications manager.

In the paper, McCarthy used 65 feet as the depth where the water would be considered safe for dumping. Off Charleston, that depth is reached about 15 nautical miles out.

"The big concern, I think, is the cumulative impact on the local area. Really, if the cruise lines worked to be very environmentally responsible, that would be the way to go," McCarthy said.

Whether a not-fully-diluted waste stream could work its way in from 20 miles offshore depends on the Gulf Stream eddies, prevailing winds, density of the discharge and salinity, said Jack DiTullio, a College of Charleston oceanographer who studies ocean currents.

Northerly winds would tend to push it in, but they're not so common here. The eddies are frequent, however, and range from a few miles wide to much bigger and can last a few weeks to several months.

More concerning to DiTullio is the possibility of algal blooms. The blooms are an explosion of algae growth in the water that can be caused by nutrients from sewage discharge. The blooms, in turn, kill sea life, creating "dead zones" in the water.

Researchers in the past few years found an alarming tendency for the blooms to occur just offshore at Myrtle Beach.

"I'm not trying to make a cause for alarm," DiTullio said. "But we always worry for algal blooms."

Reach Bo Petersen at 937-5744.