Ultraviolet Water Treatment Applied

Novel Solutions for Ballast Water & Oil Recovery Applications

By Jon McClean

Compact, high-power ultraviolet (UV) treatment systems are now being used to prevent the transit of a wide variety of organisms across the globe in ballast water carried by ships. Ballast water is taken on board in ports of call to maintain stability when the vessel is not laden, and it is discharged as the vessel takes on cargo. The discharge, often thousands of miles from the port of embarkation, can relocate microscopic plants, mussels, crabs, and, recently, the fish pathogen VHS.(1) Between 3-4 billion metric tons of ballast water moves across the oceans annually.

UV systems are being incorporated in packages that use separation technology to prepare the ballast water to be disinfected using UV light prior to discharge. The UV systems are compact, use high-power polychromatic lamps, have automatic wiping mechanisms, and are generally configured with the lamps at right angles to the flow. This orientation eliminates bends before and after the UV chambers, thus preserving flow profile and saving space. Medium pressure lamps are most often used in this application, as their compact size permits a small treatment footprint, allowing skid mounting and safe lamp removal.

Understanding the Issue of Ballast Water

More than 46,000(2) commercial vessels – tankers, cruise liners, bulk carriers, ferries, container ships and barges – travel across the oceans carrying cargo and passengers for transport, leisure and commerce. Seventy-five percent of these vessels are involved in intercontinental trade, and the often-asymmetric nature of this trade means that, occasionally, container vessels arrive, for example, in U.S. ports laden with cargo from China, and they embark empty, ballasted with water taken on board in the United States.

Likewise, coal and iron-ore carriers arrive empty into Australian or South American ports fully ballasted with water and discharge this ballast water prior to taking on raw material for transport.

It is estimated that 7,000(3) species are transported in ships’ ballast water. The majority of these species do not survive the ballasting/de-ballasting cycle, as the environment within the ballast tanks is quite hostile. Those that do survive, however, are hardy and frequently out-compete the indigenous species to establish a reproductive population.

Ballast water is often used as a trim aid in port when loading or unloading cargo. Over 100(4) species of marine organisms are known to have been introduced by ballast water. While some appear benign, others are a threat to biodiversity, fisheries and aquaculture. The U.S. National Oceanic and Atmospheric Administration views the invasion of such species as “the greatest immediate threat to most coastal state ecosystems.”(5) Some introduced species severely deplete native populations or deprive them of food. Others form colonies, which can damage other existing fauna.

Introduced toxic dinoflagellates cause red tides and algal blooms that can affect or even kill shellfish, fish, seabirds, and, when eaten by humans, these contaminated shellfish can cause paralysis or even fatality. In southern Australia and along the west coast of the United States, for example, the Asian kelp Undaria pinnatifida is invading new areas, rapidly displacing native seabed communities. Shipments of the European oyster (Ostrea edulis) were brought from Washington to France to supplement a low native stock. The virus Bonamia ostrea accompanied these shipments and ended up destroying the remaining native stock of the European oyster in France.

In the Black Sea, the filter-feeding North American jellyfish Mnemiopsis leidyi has on occasion reached densities of two pounds of biomass per nine square feet. It has depleted native zooplankton stocks to such an extent that it contributed to the collapse of entire Black Sea commercial fisheries in the 1990s. Salt marsh cordgrass (Spartina alterniflora), once used as packing material for Atlantic oysters (Crassostrea virginica), has been introduced into Oregon, and the cordgrass continues to spread along the Oregon coast, taking over mudflats and disrupting bird migrations.

The fish pathogen, Viral Haemorrhagic Septicemia (VHS), was reported in the Great Lakes in 2003(6), and the virus has spread rapidly through all of the waterways frequented by vessels dumping ballast.

The Chinese mitten crab (Eriocheir sinensis) was banned for importation and aquaculture in the United States in the late 1980s. However, the crab was discovered in San Francisco Bay in 1994. The crab burrows into river banks, dykes and levees, causing erosion and siltation. It is believed that mitten crabs were introduced into San Francisco Bay by ballast water.

Addressing Ballast Water Issues With Technology

The United Nations’ International Maritime Organization (IMO) has a number of initiatives underway at this time to address the issue of nonindigenous species transit and invasion, and to address pollution of the oceans generally. The Ballast Water Management (BWM) convention was published in 2004 and has a target implementation date of 2009. The MARPOL 73/78 guidelines cover the discharge of sewage at sea and came into enforcement in 2003.

Two methods are proposed to mitigate the threat of species transfer – Ballast Water Treatment [BWT] or Ballast Water Exchange [BWE]. BWE is available only to those noncoastal vessels that can exchange ballast water mid-ocean. This is a time-consuming and potentially hazardous exercise, as it involves the vessel stopping or slowing considerably and exposes the hull structure to stress. A number of ship designers are now developing “no stop” BWE systems, or vessel designs that eliminate the need for ballast water altogether. For BWE regimes, a 95 percent volumetric exchange of ballast water, or three times the volume of the ballast tank exchange, is required.

From the date of implementation (2009), ships have been required to treat their ballast water discharge to achieve less than 100 Colony Forming Units (cfu)/100ml of Intestinal Enterococci, less than 250cfu/100ml Escherichia Coli, and Vibrio Cholerae (O1 and O139) less than 1 CFU/100ml or less than 1 CFU per 1 gram (wet weight) zooplankton samples. In 2016, all vessels will be required to treat their ballast water to comply with these microbial levels.

MARPOL 73/78 has been in enforcement since 2003, and by 2006 113 countries, or 75 percent of active tonnage, had signed the convention. In April 2008, the U.S. House of Representatives approved regulations that all saltwater ships entering U.S. ports treat their ballast water by 2016. The bill, HR 2830, sets a more demanding disinfection standard than the IMO requirement and requires the number of organisms greater than 50 microns in minimum dimension to be reduced to fewer than 10 living organisms per cubic meter of water in the discharged ballast water.

Chemical- or biocide-based methods of disinfecting ballast water are unattractive from a number of perspectives – the proximity of bulk chemicals poses handling and storage risks to the ship’s crew, and often a de-chlorination process is required to ensure no active substance or residual is discharged.

A number of innovative suppliers are enhancing the production of hydroxyl radicals with the exposure of an accelerant such as Titanium Dioxide to UV light. A dedicated Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection [GESAMP](7) now has a ballast water technical Work Group. A key focus of this group is to determine what risk is posed by the discharge of a variety of active substances. Hydroxyl species are a novel addition to th usual list of chemical residuals to investigate. These reactive species are very short-lived, and the ballast water has a high hydroxyl demand.

The ballast water is prepared for UV disinfection using a variety of filters or cyclonic separators. The systems are usually skid-mounted and automated; the UV systems have automatic wiping and the filters have automatic backwashing.

A Closer Look at Ultraviolet Water Treatment
UV works by permanently damaging the DNA of all living organisms. The damaged (or dimerized) DNA is no longer able to support normal cell function, and the organism is rendered nonviable. The sizing of the UV system is determined by flowrate, transmittance of the fluid to ultraviolet light, and the dose requirement. The method is nonintrusive and does not alter the chemistry, color or physical property of the ballast water.

No organism has demonstrated resistance to UV; however, a growing number of organisms are demonstrating advanced resistance to chlorine. These emerging pathogens can be effectively disinfected using UV.

UV dose is expressed in m J cm-2. Most of the leading UV manufacturers use CFD models to predict the performance of the UV system, and then, working in partnership with BWT system providers, use a variety of validation techniques to determine the actual UV system performance. Preparation of the ballast water is very important, as color, suspended solids and particulates would render the UV system ineffective.

Computational Fluid Dynamics (CFD) modeling has advanced significantly in the last five years, and the leading UV system manufacturers use a similar approach. The flow profile is produced from the chamber geometry, flowrate and particular turbulence model selected. The radiation profile is developed from inputs, such as water quality, lamp type (power, germicidal efficiency, spectral output, arc length), and the transmittance and dimension of the quartz sleeve in use.

Proprietary CFD software simulates both the flow and radiation profiles. Once the 3-D model of the chamber is built, it is populated with a grid or mesh that comprises of thousands of small cubes. Points of interest, such as at a bend, on the quartz sleeve surface, or around the wiper mechanism, use a higher-resolution mesh, while other areas within the reactor use a coarse mesh. Once the mesh is produced, hundreds of thousands of virtual particles are fired through the chamber. Each particle has several variables of interest associated with it, and the particles are harvested after the reactor. Discrete phase modeling produces the delivered dose, headloss, and other chamber-specific parameters.

For system approval, onshore and ship-based process validation is conducted to ensure the overall system is capable of performing as required. Hyde Marine is a supplier of marine-based treatment packages, and its Guardian system was tested extensively aboard the Coral Princess cruise ship during a 17-day voyage in 2004. The system is also being evaluated as part of the US Coast Guard STEP(8) program in the United States and is undergoing IMO Type Approval through the United Kingdom’s Maritime and Coastguard Agency (MCA) in cooperation with Lloyd’s Register.

Fouling of quartz sleeves can occur and prevent the UV light from penetrating into the water; iron is often present in ballast/bilge water, as the marine environment is aggressive and materials coming into contact with it need to be carefully selected. In addition to iron, ballast water can often contain oils and lubricants and have a high oxygen demand. Effective wipers are critical to the UV system’s long-term performance.

Downhole Injection for Enhanced Oil Recovery
One of the oldest and most widespread techniques for enhanced oil recovery is well flooding by injecting water down into the reservoir hole. Water is injected into the reservoir to pressurize and displace hydrocarbons toward the producing wells. Injection water is also used in water-storage operations in offshore and remote locations.

The quality of the injection water is critical, as the displaced oil needs to flow through porous rock structures. The treatment of injection water is multi-stage, with filtration to remove solids and deaeration, or oxygen-stripping processes, to reduce the oxygen content of the water. Ultraviolet light is used as a penultimate stage to ensure the water sent downhole is free from microbial contamination without the use of chemicals.

The seawater used for offshore well injection contains a variety of micro-organisms. Some of these species lead to corrosion and scale downhole, while others are slime-forming. Many species can survive in oxygen-rich (aerobic) seawater or in the oxygen-starved (anaerobic) environment below ground.

Aerobic bacteria can convert iron from the ferrous (Fe²⁺) to the ferric (Fe³⁺) state, and produce ferric hydroxide (Fe [OH]₃), which is highly insoluble and causes formation damage. Iron-oxidizing bacteria can be slime-forming species that form mats of high-density slime that cover surfaces. If allowed into the well, they shield corrosion-forming bacteria colonies from chemical bactericides and plug the pores of the matrix holding the oil.

Anaerobic species, such as Sulphate Reducing Bacteria (SRBs), can convert sulfate or sulphite that is naturally occurring or present in a variety of drilling muds into hydrogen sulphite (H₂S). When combined with iron, iron sulphide, a scale that is very costly to remove, is formed. In addition, SRB species can cause pitting corrosion of steel, and elevated H₂S increases the corrosiveness of the water, which increases the possibility of hydrogen blistering, sulfide stress cracking, and can lead to costly sweetening of sour oil.

Eldfisk is an oilfield located near Ekofisk in the North Sea, in sea depths of 200-225 feet. The original Eldfisk development consisted of three facilities: Eldfisk B is a combined drilling, wellhead, and process facility; Eldfisk A and FTP are wellhead and process facilities. In 1999, a new water-injection facility, Eldfisk E, was installed. The facility also supplies injection water to the Ekofisk K. The facility uses horizontal injection wells, injecting into a reservoir between 8,000 and 8,700 feet (2,900 meters).

The UV plant treats 4,000m³/hr, or 25 million gallons per day, and is the largest downhole injection facility in operation. The system is comprised of duty and standby units, and was supplied by atg in the United Kingdom. It is modular and has been in active operation for more than 10 years.

The Troll platform, a condeep (concrete deep water structure) offshore natural gas platform in the Troll gas field, is the tallest construction that has ever been moved to another position, relative to the surface of the Earth, and is among the largest and most complex engineering projects in human history.

Standing at a height of 1,400 feet (472 meters) and weighing over 1.2 million tons, the troll platform depends on a crew of over 350 engineers to draw natural gas from over 40 gas fields on the sea floor.

In order to keep the Troll crew safe from infectious waterborne diseases, such as Legionella and Cryptosporidium, the Troll relies on two high-specification, duty-standby, ATEX-certified systems for operation in the Zone I & II Hazardous Areas found on the platform. The unit is configured as duty/standby and ensures the crew of the Troll platform has safe drinking water.

The Future of UV Water Treatment
UV systems are rapidly gaining acceptance as part of offshore water treatment process. The performance of the UV systems can be validated and many operators have now adopted this nonchemical process barrier.

Using UV to provide nonchemical disinfection for water being used for downhole injection is now gaining widespread adoption among operators in some of the most difficult oilfield applications in the world.

Meanwhile, much damage has been done by the inadvertent transit of so many nuisance species in ballast water; however it does seem this area is finally getting the attention it deserves, as UV treatment systems are gaining momentum for ballast applications as well.

Ratification and implementation of the IMO Ballast Water Management Convention will soon make it a criminal act to discharge untreated ballast water. No longer will the international nature of the shipping business, nor the intense competitive pressures caused by high and rising fuel costs, nor the lack of a global regulation be acceptable reasons for noncompliance.

Jon McClean is president of Engineered Treatment Systems (ETS) LLC. Prior to joining ETS, he was managing director of Hanovia Ltd in Great Britain. He presents papers at conferences and frequently publishes articles about UV disinfection and photolysis. Mr. McClean can be reached at jon.mcclean@ets-uv.com.

www.ets-uv.com

References
1. Viral Hemorrhagic Septicemia (VHS)
2. CRS Report for Congress “Cruise Ship Pollution” Claudia Copeland, www.ncseonline.org (RL 32450)
3. Hutchins P Australian Museum, 2003 (www.australianmuseum.net.au)
4. Hutchins P Australian Museum, 2003
5. NOAA Fact Sheet (www.oar.noaa.gov)
6. Whelan G VHS Briefing Paper, Michigan Dept. Natural Resources, www.michigan.gov (2/6/2009)
7. Working Group 34 (www.gesamp.org)
8. US Coast Guard Shipboard Technology Evaluation Program (www.uscg.mil/STEP)

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