Using everything but the oink

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Regulation is re-defining the way industry manages its entire water cycle. Gord Cope explores the diverse opportunities for extracting value from wastewater streams.

There is an old saying in the pork processing industry: “We use everything but the oink.”

In the wastewater sector, that is not yet the case – every day, millions of dollars of valuable metals and organic compounds are literally flushed away. Fortunately, however, tight finances and even tighter regulation mean that this trend is changing.

Recently, a Japanese wastewater treatment plant in Nagano prefecture reported that it had recovered 66 ounces of gold per tonne from incinerated sludge (this compares to one ounce of gold per tonne recovered from Japan’s Hishikari Mine).

The high content is due to nearby precision equipment manufacturing plants that use the precious metal; the sewage treatment plant expects to receive over $150,000 per year for its reclamation efforts.

Marketable metals
Often, capturing valuable products from wastewater streams requires sophisticated technology. BioteQ Environmental Technologies Inc., listed on the Toronto Stock Exchange, has been working with mine sites for almost a decade to recover minerals that are found in dilute quantities in wastewater.

“The wastewater is fully regulated, and needs to be treated,” says Brad Marchant, CEO of BioteQ.

“The traditional method is lime treatment. You mix lime and the water in a stirred tank and lime combines with the metals to precipitate as a sludge. There are limitations to this process. The water quality doesn’t always meet discharge standards for dissolved metals, and the sludge is contaminated by the metals. Over time, you end up with an enormous quantity of sludge that requires storage, monitoring and management well beyond the life of the mine.”

Instead of the waste approach, BioteQ took a resource approach, and developed sulphide-based treatment processes to recover valuable metals from wastewater. “Our method introduces hydrogen sulphide, which can be generated using a biological process, into a contactor tank to precipitate metal sulphides selectively from the cocktail of metals and acid,” says Marchant.

“The water chemistry can be adjusted in order to remove individual base metals such as copper, nickel, zinc and cobalt. The metal precipitates as a fine particle that is then filtered to create a high-value by-product that can be sold to a refinery.”

The economics of each site differ, and plant capital costs can run from US$2-10 million, depending on treatment volumes, the availability of local labour, and material costs. Prior to construction, BioteQ conducts an analysis to determine the most appropriate technology and cost/benefit structure.

“Generally, capital costs are about the same for lime plants and our processes, but our operating costs are significantly lower, there is usually a revenue stream from recovered metals, and you don’t have to deal with sludge disposal,” says Marchant.

BioteQ has built eight plants in five countries, including one at the Raglan Mine in northern Québec. Raglan’s operator needed to remove nickel from contaminated water, but because the mine is located in the sensitive Arctic environment, discharge water quality standards are strict, and the costs of removing traditional lime sludge are high.

Under a build-own-operate agreement, BioteQ designed a 5,760m3/d plant that recovers 12,500 kg of nickel annually. BioteQ gives the mine the recovered nickel and charges a fee of Can$1.12 (US$0.91) per cubic metre of water treated – less than half the operating cost of a lime plant – and there is no sludge waste to ship out.

“We take what was a cost centre and turn it into a profit centre,” says Marchant. “The profitability depends on commodity prices. Obviously, it’s more attractive when copper is at US$3.75 per pound compared with US$1.50, but even at US$1.50 there’s a strong economic argument, both in terms of capital and operating costs, and reduced environmental liability.”

Catalytic conversion
Mining isn’t the only sector that produces wastewater laden with valuable metals. “In the automobile industry, manufacturers of catalytic converters use many expensive heavy metals such as rubidium, platinum and molybdenum, so every ounce counts,” says Josh Miller, spokesman for New Logic Research Inc., based in California. New Logic was founded in 1987 to market the Vibratory Shear Enhanced Process (VSEP), a membrane filtration system originally designed to separate plasma from blood.

Our technology is very versatile,” says Miller. “We now serve many different sectors, including mining, energy and manufacturing.”

VSEP is designed to overcome the tendency of membrane devices to foul under heavy loads. Solids build up gradually at the boundary layer, plugging pores and reducing the permeate level of the membrane.

In an effort to reduce boundary level build-up, membranes are often designed in spiral wound cartridge assemblies so that fluids can be injected at high-velocity crossflow, but this method has its own problems.

VSEP uses low-velocity crossflow and rapidly oscillating membranes to keep pores open and permeate levels high (visualize a North American-style agitating clothes washer stacked with album-sized membranes).

Using the VSEP system, the slurry can become highly concentrated without plugging the membrane. New Logic has several modular VSEP units that can be designed into systems that can handle from as little as 50 gallons per minute to millions of gpm, depending on the application.

Costs can range from US$200,000 to more than US$20 million. They have approximately 500 systems installed in over 20 countries, including a system to recapture precious metals from catalytic converter wastewater.

“The client actually has two systems, one that recovers 90% of alumina from discharge water, and another for precious metal recovery of platinum, rubidium and molybdenum,” says Miller.

Pricey process
For several years now, the pulp and paper sector has been recovering and reusing chemicals from its wastewater streams. The process begins with feedstock logs being chipped into small wood particles. The chips are then mixed with white cooking liquor (a brew of water, sodium hydroxide and sodium sulphide) in a digester tank.

The white liquor and wood chips are heated in the digester in order to break down and remove lignin, which holds the cellulose wood fibres together. Two phases emerge from the digester. The waste fluid sucked out of the top, known as black liquor, is a mix of lignin, processing chemicals, carbohydrates and resins.

The valuable porridge that emerges from the bottom is called brown stock, and is a mix of cellulose pulp and water. The brown stock is washed and bleached to remove the remaining lignin and other impurities, then pressed into various paper products.

Black liquor, the tarry waste from the digester, consists of 85% water and 15% chemicals. The fluid is sent to a recovery island, which consists of a series of fallingfilm evaporators. The evaporators contain bundles of heated two-inch tubes. As the black liquor runs through the evaporators, three streams of water emerge.

The first is called clean condensate; this can be directly recycled as process water. Middle condensate is used for secondary processes, such as cleaning. Foul condensate (a small fraction of water recovery), contains methanol in gas form, which is stripped off and used as fuel in the boiler. The solids from the black liquor are sent to a recovery furnace where they are burnt for their caloric content. The ash contains chloride and potassium compounds.

“Some mills dump the ash, but they lose valuable process chemicals,” says Tim Cornish, marketing manager for HPD, a subsidiary of Veolia. “We use a leaching technology to capture these process chemicals. It is called the chloride and potassium removal process. We’ve been selling a lot of these.”

The wood pulp sector has another waste stream that contains valuable products. In the US alone, about five million tonnes per year of paper is treated with high-value coatings to produce paper for magazines, books, stamps and catalogues.

Much of the coating (made of clay, titanium dioxide and carbonates) is lost during applications, and ends up in the plant’s wastewater stream.

New Logic has engineered a VSEP system for several paper plants that takes wastewater containing 1.5% total solids and produces clean permeate suitable for reuse or discharge. The remainder of the original liquid can then be run through a secondstage VSEP to produce clear permeate and concentrated coating. “The concentrate is recycled into the coating process,” says Miller.

Something fishy
When Bodø Sildoljefabrikk, a Norwegian fish processor, found itself in a financial squeeze, it came to GE for help. Formerly, the processor filleted 128,000 tonnes per year of fish, then used evaporators to process 70% of the fish waste (viscera and trimmings) into valuable fish meal. In 2005, after Norway reduced the company’s annual quota to 50,000 tpy to meet sustainable marine environment regulations, the company had to find a way to improve its fish meal recovery system.

GE designed a 7,925gpm Advanced Membrane Solution (AMS) that could handle not only their needs, but an additional 50,000 tpy of liquid waste from neighbouring fish processors. The AMS system separates 100% of the protein from the liquid stream, boosting Grade A meal recovery and adding almost US$2 million to their annual revenues. The new system has also lowered energy consumption by 54% and eliminated 50,000 tpy of waste being dumped into the ocean. “It’s a fish tail with a happy ending,” says GE spokesman Tony Kobilnyk.

GE was also asked by Straits Chemicals to design a US$220 million desalination plant that will produce 70,000m3/d for the Nelson Mandela metropolitan municipality of South Africa. The water, however, is a by-product; the primary function of the plant is to produce 1,700 tonnes of ultrapure salt each day for conversion into caustic soda and hydrochloric acid.

The desalination plant, which will be located in the Coega industrial zone of Port Elizabeth, is part of Straits Chemicals’ vision to supply chlor-alkali chemical products to the South African and world markets, and at the same time deliver pure water to 150,000 local residents.

The manufacturing process includes UF, RO and thermal steps to produce the salt feedstock. The removal of trace elements to reach 99.9% purity will be accomplished through a proprietary pure salt crystallization technology designed by a subsidiary of GE.

The future
Much of the future growth in terms of extracting value from wastewater streams is expected to come from the tightening of environmental regulations regarding such issues as acid mine drainage.

“Acid mine drainage occurs at 70% of the world’s mining sites,” says BioteQ’s Marchant. “It’s a natural process where water and oxygen react with bacteria and sulphide minerals to produce a weak acid solution that dissolves residual metals into water. Over time, you end up with a toxic cocktail of metals and acid that’s harmful to the environment.”

BioteQ is currently involved in a project with the US Environmental Protection Agency (EPA) in Breckenridge, Colorado. “There’s an old site there that was mined for over 100 years before finally closing down in the 1970s,” says Marchant. “But water from the mine was contaminating a fish-bearing stream. We were asked by the town and the EPA to build a water plant to treat the problem.”

The plant, which was commissioned in December 2008, has a capacity of 35m3/h [840m3/d], and is expected to remove approximately 50,000lb of zinc and cadmium annually.

Glycol recovery is another application with great potential. Every year, airports in North America use over half a billion gallons of the fluid to de-ice planes. The glycol then enters storm drains and is carried away from the tarmac. Because glycol consumes large quantities of oxygen during its degradation process, it cannot simply be released into storm sewers, and the EPA has established control requirements.

Typically, the runoff is treated in aerobic lagoons until glycol levels drop to acceptable levels, but this negates any opportunity to recover the valuable organic compound. New Logic has designed a two-stage system in which a 20,000gpd VSEP ultrafiltration membrane separates out 500gpd of suspended solids, emulsified oil and other impurities.

A second-stage VSEP RO receives 19,500gpd of water containing 1.5% glycol. 16,700gpd of clean water is discharged, and 2,800gpd of 10% glycol is recycled.

Selenium, an element that occurs in minute quantities in soil, plants and animals, is classified as a toxic hazard when concentrations rise above a certain level. “Selenium bubbled up in 2008 when the EPA said that they would like to lower discharge rates to less than five parts per billion,” says New Logic’s Miller. “Selenium has a mutagenic effect on wildlife such as ducks and fish, and discharge from refineries and coal-fired plants has to be controlled.”

But selenium is also a necessary ingredient in both manufactured products and food. It improves the machinability (i.e. the ease with which a metal can be machined to an acceptable surface finish) of steel alloys and is a vital vitamin supplement.

Most of the world production is a by-product of copper refining, but consumption is far outstripping supply. In the early 2000s, the price of selenium rose from US$3/lb to more than US$50/lb (it is now around US$33/lb). While coal contains up to 100 times the amount of selenium that copper sulphide deposits do, there has previously been no commercial way of concentrating it.

That may soon change. Environmental regulations control the amount of sulphur emitted from the flue gases of coal-fired power plants. Most coal-fired plants are now equipped with ending scrubbers that use water to remove sulphur from flue gases. The wastewater from the scrubber also ends up with relatively high concentrations of selenium, however, which is unacceptable to the EPA.

New Logic has installed a two-stage system at a coal-fired plant that takes a 700gpm feed with 500ppb selenium and runs it through a VSEP RO membrane that produces 693gpm of permeate with 36ppb of selenium.

A second stage spiral RO membrane then cleans up that permeate to 2ppb, (which is acceptable for surface discharge). The 7gpm concentrate from the first stage is sent to an evaporator which reduces the refuse to a stable solid containing 46,000ppb selenium; this compares to 120ppb in copper sulphides, offering an intriguing opportunity for producers.

In conclusion, recovering valuable products from wastewater is a wellestablished segment in the water treatment sector, with excellent future prospects. Despite the current economic crisis affecting all areas of the economy, participants are optimistic. “The rapid deflation in commodity prices has slowed the growth of the company, but environmental issues aren’t going to go away,” says BioteQ’s Marchant. “The potential is immense,” says New Logic’s Miller. “Our growth rate in 2008 was over 15%.”


Waste not, want not

Growth rates in the market for extracting value from wastewater can exceed 15%. There is a diverse range of applications.

* A Japanese sewage treatment plant in the Nagano prefecture reported that it had recovered 66 ounces of gold per tonne from incinerated sludge.

* Sulphide-based treatment processes recover valuable metals, including copper, nickel, zinc, and cobalt, from dilute mining wastewater. They can also be used to treat leachate pollution from old mines.

* Membrane filtration systems can recover metals such as platinum, rubidium and molybdenum from industrial processes.

* The pulp industry uses falling film evaporators and a leaching process to recover processing compounds.

* The paper sector uses membrane filtration technology to recover compounds used for coating highquality paper.

* The fishing industry relies on membrane filtration systems to recover liquid protein that is converted into feed pellets.

* Thousands of anaerobic digesters around the world convert liquid organic waste from sewage treatment plants, breweries and farms into methane biogas, which can then be converted into heat and electricity.

* RO membrane technology is used to recover selenium from wastewater at coal-fired power plants.

* Ultrafiltration technology can be used to recover ethylene glycol used to de-ice planes at airports.

 

Making money from miasma

Biogas generated from wastewater can help reduce a plant’s operating expenditure. The excess energy can be sold into the grid.

Biogas forms in wastewater treatment plants where organic matter is placed in specially designed anaerobic digesters, where it decomposes under controlled conditions into methane and CO2. About one third of biogas recovery is associated with municipal sewage treatment plants.

Suspended solids settle out in primary treatment tanks, and are then transferred to sludge tanks to be treated in anaerobic digesters for 25 days at 35°C. A wastewater treatment plant for a city of one million people can produce 17 million m3 of gas annually.

There are approximately 2,000 large-scale anaerobic digesters installed in breweries, food processors and pulp mills around the world. Industrial plants have fluid streams in which the BOD (biological oxygen demand) is dissolved; concentrations of BOD can often exceed 5,000ppm, 25 times that encountered in sewage.

A big brewery may generate up to five million gpd of wastewater with 3,000ppm of BOD. The fluid goes to a clarifier for pretreatment, and then into a continuous flow anaerobic digestion system.

A large digester/power system can cost US$10 million, but it can produce as much as US$2.5 million per year of power, as well as an 80% reduction in municipal sewage treatment surcharges.

Anaerobic digestion is also making major inroads into dairy farming. A 15,000-cow dairy operation produces about 180,000 lbs of solid waste a day, which is converted into 150,000 ft3/ day, or around $500,000 worth of gas annually.