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Comment PDF Water Treatment

Wonderful wastewater

By Chemical Engineering |

Click here for full pdf version of this article – includes all graphs, charts, tables, and author information

 

Wastewater may not be exactly wonderful, but it is certainly fashionable. The global market for industrial water and wastewater equipment is growing at around 20% annually, according to a recent report from market research company BCC Research (Wellesley, Mass.; www.bccresearch.com). Sales are set to exceed $4.7 billion this year, up from $3.2 billion in 2005, and are forecast to reach over $10 billion by 2012.

Municipal water and wastewater treatment, which uses many of the same processes found in industrial plants, is even bigger business. BCC estimates this market at over $11 billion for 2007, not counting the money spent on water mains and sewers. China, India, Mexico, Egypt and Australia are the largest markets overall.

“I’ve been in the water and wastewater treatment business for more than 20 years, and this is probably the busiest I’ve ever seen it,” says Thomas Schultz, global sales and marketing manager for petroleum and chemical industries with Siemens Water Technologies (Erlangen, Germany; Palm Desert, Calif.; and Warrendale, Penn.). In the refining industry, record profits on the back of high oil prices are allowing companies to replace or upgrade wastewater treatment systems that may have received little investment since they were installed in the 1970s, Schultz says.

Siemens’ current wastewater projects span a wide range of technologies, from oil/water separators, through biological treatment, to polishing systems where strict effluent quality standards are in force. While most CPI companies take their effluent treatment responsibilities very seriously, Schultz says, new regulations for contaminants such as selenium, arsenic and copper are driving wastewater investment.

So too is the growing need to re-use and recycle water in dry areas such as the Middle East, Singapore, California and even Alberta, where extracting oil from tar sands uses large quantities of steam. Refineries around Los Angeles are already using treated municipal wastewater, Schultz points out, but re-using water within a petroleum facility is more challenging because of the dissolved oil and other “difficult” organic compounds that are often present. To protect ion-exchange resins and membranes for microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO) from contamination, it is often best to choose relatively clean streams such as cooling tower blowdown or stripped sour water for recycling. If it is essential to recycle general plant wastewater, more-complex treatment systems are needed to remove the organics — and that can be expensive, Schultz says.

Strong business areas for Siemens recently include oil-water separators and wet air oxidation systems, which are typically used to treat spent caustic from refineries and ethylene plants. OPTI Canada chose Siemens’ Zimpro wet air oxidation system to destroy soot in wastewater generated during the production of syngas at its Long Lake project, which will generate synthetic crude from Athabasca oil sands. Wet air oxidation will reduce the volume of soot by about 90%, cutting disposal costs and allowing the recovery of nickel and vanadium from the soot.

 

MBRs come of age

Membrane bioreactors (MBRs) are gaining interest in the CPI as companies look to improve effluent quality and possibly re-use wastewater. Though often more expensive to run than conventional biotreatment plants, MBRs have the advantages of guaranteeing complete disinfection of the treated effluent, according to Boris Lesjean of the Berlin Centre of Competence for Water (Berlin, Germany; www.kompetenz-wasser.de) and Simon Judd of Cranfield University (Cranfield, U.K.; www.cranfield.ac.uk). MBRs are also compact, thanks to their ability to operate at sludge concentrations up to 20 g/L, compared to 6 g/L for a conventional activated sludge process, Lesjean and Judd say.

Last year Siemens launched an MBR system, known as Petro MBR, specifically for the petroleum industry. The skid-mounted Petro MBR is suitable for applications including treating oily wastewater for use in cooling towers or boilers. It is based around Memcor low-pressure membranes, and features optimized crossflow for low fouling, as well as an automated cleaning cycle.

Another big name in water and wastewater treatment, Veolia Water Solutions & Technologies (Paris, France and Houston, Texas), is marketing its Neosep MBR process (known as Biosep outside the U.S. and Japan) for both municipal and industrial effluent. Available with both flat and hollow-fiber membranes, Neosep/Biosep provides typical COD levels below 30 mg/L.

“The new industrial high-rate water softening technologies that we are just introducing represent the most exciting recent development in wastewater treatment from my point of view,” says Chuck Blumenschein, vice president of Veolia subsidiary N.A. Water Systems (Pittsburgh, Penn.). “We have a patent pending for Turbomix, a reactor design based on research using computational fluid dynamics, and have combined that technology with two proven clarification technologies: Multiflo and Actiflo.”

“The complete mixing of the Turbomix enables us to perform enhanced chemical precipitation to accomplish water softening in a single treatment unit with a very small footprint. We have a mobile pilot system that can be delivered to industrial sites to determine which option — Multiflo or Actiflo — will perform better for specific applications.”

Wehrle Umwelt (Emmendingen, Germany) has been involved with MBR development since the 1980s and today is a leader in external MBR, in which the membrane cartridges are located outside the treatment basin. The company’s Biomembrat technology is suitable for concentrated wastewater from chemical plants, refineries and landfill sites. For maximum performance it can use pure oxygen instead of air.

Membrane specialist Microdyn-Nadir (Wiesbaden, Germany) has developed a membrane module for submerged MBR applications that it says combines the advantages of hollow-fiber and flat sheet modules (photo, p. 40). The BIO-CEL module uses a parallel array of large, self-supporting membrane sheets in a frameless configuration. At just 2 mm thick, the membrane sheets can be packed densely, and the elimination of a carrier plate makes the modules light in weight. The design avoids areas of laminar flow and so reduces sludge deposition, and is also optimized to prevent the braiding of hair and fibers on the membrane surface. Modules can be cleaned by backflushing without removing them from the plant.

For extreme operating conditions, Microdyn-Nadir has also expanded its Spira-Cel range of polyethersulfone (PES) membranes to cover the pH range 0–14 at temperatures up to 80°C. Spira-Cel OY (pH 0–12) and OX (pH 3–14) membranes are available for micro-, ultra- and nanofiltration.

GE Water & Process Technologies (Oakville, Ontario, Canada) markets MBRs as part of a wide range of membrane-based and other water treatment technologies. ZeeWeed hollow-fiber membranes manufactured by sister company Zenon Membrane Solutions are reinforced and self-healing, allowing them to withstand the rigors of use in commercial MBRs, the companies say. Multiple in-situ cleaning systems maintain long-term performance.

Tackling specific contaminants

While many biological processes provide broad-spectrum removal of organics, others are targeted at specific contaminants, both organic and inorganic. Paques B.V. (Balk, Netherlands) offers, as well as general-purpose anaerobic and aerobic treatment systems, a range of biological technologies to remove sulfur, nitrogen, metals and other substances. Earlier this year, the company demonstrated a commercial biological process to remove phosphate and ammonium along with COD (CE, July 2007, p.14). The Phospaq process uses magnesium oxide to precipitate phosphate and ammonium as struvite (MgNHâ‚„POâ‚„.6Hâ‚‚O), which can be used as fertilizer.

GE Water’s ABMet process uses micro-organisms to reduce and precipitate metals and other inorganics, such as selenium. The naturally-occurring, non-pathogenic microbes can remove more than 99% of selenium, arsenic, mercury, nitrate and other inorganics. ABMet is significantly less complex than conventional physical/chemical removal technologies, the company says. Other advantages include low power use, with no mixing or aeration needed; compact footprint; minimal sludge generation; and excellent cold-weather performance.

The ability to remove oil and organic solvents from wastewater is essential in many CPI applications. For high concentrations, API-type and dissolved air flotation (DAF) oil-water separators are often chosen. At lower concentrations, absorption on activated carbon or clays may be more appropriate.

Filtration and absorption specialist Biomin Inc. (Ferndale, Mich.) points out a potential problem when using activated carbon to remove mixtures of benzene, toluene and xylene. Depending on the relative concentrations of these compounds, toluene and xylene can cause benzene, which has a higher solubility, to become desorbed. This phenomenon of “roll-off” or “roll-over” can mean that at times, the concentration of benzene is higher in the treated water than in the influent. According to Biomin president George Alther, the company’s OilSorb organoclay material avoids this problem, as well as having a higher oil absorption capacity than carbon. OilSorb, a blend of anthracite with bentonite clay that has been impregnated with a quaternary amine, removes mechanically emulsified oil and grease, free oil, and high-molecular-weight organic molecules.

Dow Water Solutions (Midland, Mich.) supplies a wide range of technologies for desalination, contaminant removal and water reuse, including Filmtec reverse osmosis membranes, Dowex ion exchange resins, Adsorbsia GTO titanium-based arsenic removal media, ultrafiltration, and electrodeionization. Since August 1996, Black Canyon City, Ariz., has been using Dow’s Adsorbsia GTO medium to reduce arsenic in drinking water to non-detectable levels, from up to 22 ppb in the raw water, to comply with the EPA arsenic limit of 10 ppb. The non-regenerable Adsorbsia medium has faster kinetics than adsorbents based on iron oxide, Dow says, allowing the use of smaller vessels. The three treatment systems were supplied by Aquacell Water (Rancho Cucamonga, Calif.).

A versatile filter system that can handle sand, activated carbon, organoclay, and ion exchange resins has recently been launched by BakerCorp (Seal Beach, Calif.). Designed especially for rental use, the 10K filter system is said to be self-contained and quick to set up. Its twin vessels, each holding up to 10,000 lb of filtration medium, can be operated in series, in parallel or alternately. Maximum flowrate is 1,200 gal/min.

Amiad Filtration Systems (Oxnard, Calif.) has supplied six of its EBS self-cleaning filters for an expansion project at a municipal wastewater treatment plant in St. Cloud, Fla. (photo, p. 33). The 200-µm filters use a series of rotating suction nozzles to remove debris from the upstream face of the cylindrical filter mesh. This backflush arrangement provides effective cleaning while consuming typically less than 1% of the total flowrate, Amiad says.

 

 

 

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