lux research technologies turn waste to profit

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©2009 Lux Research Inc.

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Technologies turn waste to profit

Once considered a negative cost center, wastewater – specifically, sewage sludge – can now be

a valuable resource, mitigating wastewater treatment facilities operating and disposal costs.

Wastewater Treatment Facilities Are Turning Waste into Profit

Globally, about 171 km3 of wastewater is produced annually from homes, businesses, industries, as well as storm water runoff. The byproduct of the treatment process is sludge (or solids) that must be further treated before disposal. Overall, treatment and handling of sludge can represent anywhere from 20% to 50% of a wastewater treatment facility’s costs. Treating wastewater to higher and higher standards results in increased sludge volumes that must be managed at higher and higher costs. However, new technologies can now provide an opportunity to turn a costly waste stream into a valuable product that could actually offset the treatment facility’s other costs.

Overall, there are three drivers prompting increased interest in extracting value from sludge:

Tightening global regulations. Legislation around the world sets requirements for wastewater treatment and sludge disposal. For instance, the European Union’s Landfill Directive limits the organic content in landfills, preventing sludge from being disposed in landfills; its Sewage Sludge Directive permits the use of sewage sludge in agriculture instead, but requires additional treatment before application. In the U.S., landfilling is an acceptable disposal option under Environmental Protection Agency (EPA) regulations, along with land application and incineration, but several states have more stringent requirements limiting the quality of sludge disposed.

Rising energy costs. Energy makes up a significant share of the operations and maintenance costs for a wastewater treatment facility, accounting for 40% to 60% of a facility’s budget.1 On average, about 0.48 kWh is needed to treat 1 m3 of wastewater (which includes sludge treatment), and with a global average electricity rate of $0.12/kWh, the global total electricity cost for wastewater treatment is about $10 billion annually. However, many of the emerging technologies for wastewater recovery use the sludge to produce energy. With the uncertainty of electricity pricing – in some countries it’s as high as $0.19/kWh – it’s not surprising that interest is shifting towards technologies that can provide a favorable energy balance while reducing the volume of sludge to be disposed.

Depleted phosphorus supplies. Phosphorus occurs in wastewater because of human waste, as well as from detergents and soaps, and needs to be removed from wastewater because it causes surface water to become choked with plankton and algae. However, phosphorus is also a valuable mineral to the fertilizer industry. About 7 billion tons of phosphate rocks are remaining in reserves that can be economically mined, and the human population currently consumes 40 million tons of phosphorus per year, so current phosphate rock reserve could last anywhere from 100 years to 250 years depending on how steeply consumption increases.2 Recovery of phosphorus from sludge in the form of struvite, a phosphate mineral, could potentially reduce phosphate rock mining and make phosphorus production more sustainable.

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By taking a major cost from the process and turning into a profitable revenue stream, recovery can improve the bottom line of a treatment facility, generating tens of billions in value worldwide. As such, recovery technologies can be fertile hunting grounds for executives and investors looking for opportunities in the hydrocosm.

Technologies Focused on Resource Recovery Face Many Challenges

Recovering value from sludge is not a new concept, but, despite its clear appeal, many different types of technologies have been tested and deployed, only to fail. Challenges facing companies interested in deploying technologies that extract value from sludge include:

Producing a valuable end product. The composition of sludge can vary significantly, which can make it difficult for a company to develop a technology that can consistently generate a valuable product. Case in point is the struggle that Environmental Solutions Inc. (ESI) – now known as Environmental Clean Technologies – faced with its defunct Enersludge process. The only full-scale installation of the Enersludge process was shut-down after four months of operation because the oil product it created from the processed sludge was deemed unsuitable for diesel engines – it contained high levels of water and solids. Environmental Clean Technologies is no longer pursuing the technology.

Reducing land and carbon and carbon footprint. Extracting energy, phosphorus, or other nutrients from sludge is not a valuable process if it requires a significant amount of space, making it difficult to integrate into existing treatment plants, or if it requires significant energy inputs, offsetting any value extracted from the product. Such was the fate that befell the Sludge-to-Oil-Reactor System (STORS), which was originally developed by Battelle Memorial Institute and licensed to ThermoEnergy through a licensing agreement. Even though pilot testing provided some successful results, the process was complex, requiring many process vessels – and the energy input needed was also substantial, requiring 1.3 MWh to 1.4 MWh per dry metric ton of sludge. In the end, ThermoEnergy was unable to capitalize on the success of the pilot and has since dropped the product from its technology portfolio.

Keeping costs down. To be attractive, technologies focused on resource recovery must be cost effective: Projects will fail if capital and/or operating costs are too high. Utilities in Japan made attempts to repurpose their sludge into valuable products such as brick, lightweight aggregates, and molten slag using thermal solidification processes. While a number of large wastewater treatment plants adopted these processes, in the end the manufacturing costs were too high, with the “sewage” bricks three times the retail price of a traditional brick. The bottom line is that manufacturing costs need to be less than the value of the product created – easier said than done with emerging technologies.

Understanding Sewage Sludge Facilitates Technology Deployment

In order to understand the technical opportunities for energy and resource recovery of sewage sludge, it’s important to first understand what sewage sludge is, how much is produced annually, and current disposal strategies. These three characteristics define the issues driving sludge production and disposal and the potential for extracting value:

Sludge Mixtures Are an Inconsistent Soup of Many Different Components

Sewage consists of wastewater from domestic, commercial, and industrial sources, as well as rainfall and potentially, surface water. At a wastewater treatment facility, the waste stream at a minimum goes through primary treatment, which involves both screening and passing the waste stream through large settling tanks. It’s at this point that some 70% of the materials in the water sink to the bottom, becoming sewage sludge. The

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sludge is pulled from the tank and treated by: 1) dewatering or thickening, which reduces the water content of the sludge through centrifugal treatment or filter pressing; and/or 2) digestion, which breaks down the organic matter using bacteria resulting in the formation of methane gas, which can be used for energy production. The composition of untreated sewage sludge varies from treatment plant to treatment plant and from country to country, but can be composed of 6% dry solids (which means about 94% of the sludge is water). The dry solids typically have the following characteristics:3

Volatile solids (material that can be burned off when ignited at about 500 ºC) – mostly organic (carbon-based) compounds comprising about 65% of the total dry solids

Total nitrogen (organic nitrogen, ammonia nitrogen, nitrate, and nitrite) – typically 2.5% of total dry solids

Phosphorous as phosphorus pentoxide (PO5) – typically about 1.6% of total dry solids Potassium as potassium carbonate (K2CO3)– typically about 0.4% of total dry solids Grease and fats – ranging anywhere from 6% to 35% of total dry solids Silica, also known as silicon dioxide (SiO2) – about 15% to 20% of total dry solids Heavy metals – can include arsenic, iron, lead, mercury, and zinc, with concentrations ranging widely

from 6 mg of mercury per kg of dry solids (0.6%) to 17,000 mg of iron per kg of dry solids

The challenge with sewage sludge is that all of these compounds can be present in the mixture. Organic compounds, phosphorus- and nitrogen-based compounds, as well as inorganic compounds are viewed as valuable components in sludge, which many new technologies are trying to extract/recover. However, the amount of any compound present in the sludge mixture is dependent on the source of the wastewater, as well as the type of treatment processes employed and the chemicals used in treatment, and this variability affects the market opportunity for various recovery technologies. In the case of phosphorus, on average there is about 10 milligrams of phosphorus per liter of wastewater with effluent standards typically requiring less than 1 mg/L. For instance, with a total world wastewater volume of 171.3 km2, and a market value of phosphorus as struvite of $400 per kg, the potential market for phosphorus recovery is about $685 million annually. However, the actual market opportunity for any given wastewater treatment plant will vary with the concentration of phosphorus in the wastewater stream – as well as the percent recovery achieved, which can also be affected by the type of phosphorus compounds, as well as the other components of the stream.

Sludge Production Volumes Will Continue to Grow with Increasing Population and Country Wealth

Sludge production volume is important both because the sludge needs to be treated and disposed of, which adds cost to the overall wastewater treatment process, and of course because sludge production volumes define the total opportunity for wastewater recovery. The volume of sludge produced can vary for many reasons, but tends to correlate primarily with population and wealth.

Data from municipal wastewater treatment plants shows a direct correlation between sewage sludge production and population, averaging about 60 grams of sludge per person per day (see Figure 1).4 Not surprisingly, as populations continue to grow, the volume of sludge produced annually will rise as well. However, sludge production also depends on the wealth of the country. Many high-income countries – such as the U.S., Finland, Germany, Hungary, Japan, and the Netherlands – provide 100% treatment, meaning that no untreated sewage is discharged to rivers, lakes, or seas. As a result of these higher standards of treatment, sludge production volumes are high in these countries. For example, Denmark produces 99 grams of sewage sludge per person per day, compared to low-income or even middle-income countries, such as China, which generates only 6.2 grams per person per day of sludge – in large part because 30% of the population has no wastewater treatment. And of course, for countries that are lacking basic wastewater treatment facilities for the majority of the population – such as Ethiopia and Columbia – little or no wastewater treatment facilities means little or no sludge produced.

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Fig. 1: Annual Sewage Sludge Production by Country5

Country type Annual sludge production (dry metric ton)

Population Sewage sludge production rate (in grams per person per day)

Austria High income 196,000 8,210,281 65.4

Australia High income 360,000 21,007,310 47.0

Belgium High income 113,000 10,414,336 29.7

Brazil Middle income 372,000 188,078,000 5.4

Canada High income 550,000 33,100,000 45.5

China Middle income 2,996,000 1,313,974,000 6.2

Czech Republic High income 200,000 10,235,000 53.5

Denmark High income 200,000 5,500,510 99.6

Finland High income 150,000 5,231,000 78.6

France High income 878,000 64,057,792 37.6

Germany High income 2,000,000 82,422,000 66.5

Hungary High income 120,000 9,981,000 32.9

Ireland High income 100,000 4,203,200 65.2

Italy High income 1,000,000 58,134,000 47.1

Japan High income 2,000,000 127,464,000 43.0

Jordan Middle income 14,000 3,400,000 11.3

Netherlands High income 1,500,000 16,491,000 249.2

Norway High income 86,500 4,611,000 51.4

Portugal High income 236,700 10,606,000 61.1

Russia Middle income 3,000,000 140,702,096 58.4

Slovakia High income 55,000 5,439,000 27.7

Slovenia High income 57,000 2,010,000 77.7

Spain High income 1,069,000 40,525,002 72.3

Turkey Middle income 580,000 70,414,000 22.6

United Kingdom High income 1,500,000 60,609,000 67.8

United States High income 6,514,000 298,444,000 59.8

Thus, sludge volumes will grow as countries grow in population and become wealthier. For example, if Brazil and China, which are both middle-income countries, were to attain the same level of wastewater service

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coverage as high-income countries, the annual sludge production could theoretically increase from 372,000 metric tons to over 4 million metric tons per year for Brazil and from 2.9 million metric tons per year to 28.4 million metric tons per year for China. As a result of this growth, sludge management will continue to be a growing concern for countries around the world. We estimate that the annual global volume of sewage sludge is about 46 billion metric tons, representing a total treatment and disposal cost of about $17 billion – and current population and GDP growth trends suggest it could reach a volume of 54 billion metric tons and disposal costs of $31 billion in 2020.

Current Sludge Disposal Options All Have Their Drawbacks

Sewage sludge must be treated before it’s disposed. Treatment includes removal of moisture from solids via thickening, conditioning, dewatering, and drying and stabilization of the organic material through composting or digestion. The remaining product is typically called “biosolids,” which can be disposed of one of three ways: landfilling, incineration, or recycling to the soil (see Figure 2).

Fig. 2: Sludge Disposal Practices in the United States and the European Union Are Heavily Focused on Agricultural Land Application.

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Fig. 2-1: Current sludge disposal practices in the United States

Fig. 2-2: Current sludge disposal practices in the European Union

Landfilling is a common option, but one that is on the decline. Despite the simplicity of dumping sludge in municipal landfills, it’s not a viable long-term solution. Modern landfills are complex and costly facilities to build and operate – and in many locations, accessible, long-term landfill capacity is limited. The allure of landfilling solids is also tainted by tipping fees, which can range anywhere from $25 to $75 per metric ton, and transportation costs to haul the sludge to the landfill.

55%

15%

28%

2%

Agriculture Incineration

Landfill Surface disposal

46%

20%

21%

13%

Agriculture Incineration

Landfill Other

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Incineration creates environmental issues of its own. Incineration of sludge is another limited disposal option because the ash produced in the incineration process must be treated as a hazardous waste since it contains high levels of heavy metals. While incineration is practiced quite frequently in the Netherlands and Germany, it’s unlikely to catch on worldwide due to these pollution worries.

Land application is the predominant disposal route for sludge. Applying sludge to farms and fields sounds like a win-win: A disposal route applicable to high volumes of sludge for treatment plants; a source of fertilizer for farmers. However, increasing public awareness of contaminants in water and the concern about toxic pollutants present in the sludge leaching into the soil and groundwater limits the long-term viability of this option without extensive treatment to ensure that the sludge is safe to use.

Wastewater treatment facilities must take all of these factors into consideration when determining the best disposal option for its treated sludge. Reducing disposal costs – such as transportation, tipping fees, or energy fees – is a goal for all wastewater treatment facilities. As energy and fuel prices climb, treatment plants will be looking for ways to reduce sludge disposal costs, and resource recovery technologies can do just that by reducing sludge volume while providing a valuable end product that can offset some of the plant’s operating costs.

A Myriad of Technologies Extract Value from Sewage Sludge

New technologies are in development or are commercially available that recover and reuse valuable components from sludge, and these processes can be integrated into the existing sludge treatment process. These technologies can be grouped into two categories – those that recover energy and those that recover chemicals and materials (see Figure 3).

Fig. 3: Summary of Technologies for Recovering Value from Sewage Sludge

Description End product Beneficial use Companies

Anaerobic digestion Utilizes microbes to breakdown sewage

Biogas Thermal or electrical energy

Shaw Group, Veolia Water

Thermal hydrolysis Cell lysing at high temperatures and pressure; pretreatment for anaerobic digestion


Cambi, Veolia Water

Ultrasonic cavitation Cell lysing using acoustical frequencies; pretreatment for anaerobic digestion


Ultrawaves, Eimco Water Technologies, Kotobuki, Royce Water Technologies

Mechanical/chemical disintegration

Cell lysing through chemical or mechanical means; pretreatment for anaerobic digestion


Biogest, MicroSludge, Eco-Solids

Ozonation Ozone gas oxidizes cell walls; pretreatment for anaerobic digestion


Praxair, ITT-Wedeco

Gasification Heating sludge to form a char that reacts with

Syngas Fuel that can generate electricity and heat

KOPF, PrimeEnergy, EBARA, Nexterra

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water and oxygen

Pyrolysis Heating sludge to form a char, which is vaporized

Biodiesel/oil Oil product used as fuel in boilers or combusted to produce electricity

Enertech, Splainex, US Centrifuge

Supercritical water oxidation

Exposes sludge to high heat and pressure resulting in carbon dioxide, nitrogen, and an inert material

Thermal heat; phosphorus

Thermal heat, potentially electricity, fertilizer

Veolia Water, SCFI, Feralco

Microbial fuel cells Producing electricity directly from wastewater or sludge

Electricity Thermal or electrical energy

Emefcy, InTact Labs, Hy-Syence

Grease to biodiesel Chemical process that converts grease into biodiesel

Biodiesel Heating, engine combustion

Biofuel Box, BlackGold Biofuels

Crystallization Chemical precipitation of phosphorus using a seed material

Struvite or calcium phosphate

Fertilizer DHV Water, Ostara Nutrient Recovery Technologies, Unitika

Physical-chemical technologies

Precipitation, incineration or separation of phosphorus from sludge

Phosphorus compounds including struvite, phosphoric acid or iron phosphate

Fertilizer Kemira, Seaborne

Vitrification Combustion of sludge to form a building material

Glass Construction materials Minergy (formerly)

Thermal solidification Ash from sludge incineration converted to building materials

Building materials Construction materials None

Energy Recovery Technologies Can Convert Sludge into Biofuel or Electricity

Recovering energy from sludge is a relatively new business, though the basic technology has long been available in the form of anaerobic digesters. The process feeds the sludge to anaerobic bacteria (those that can live and eat without oxygen present,) in a closed vessel called a digester; as the bacteria consume the sludge, they produce a “biogas” that consists of approximately 60% methane (CH4) and 40% carbon dioxide (CO2). This biogas is now recognized as a significant source of useful energy, as thermal electrical or mechanical energy can be recovered from the biogas through the use of turbines, fuel cells, or boilers. New, innovative technologies are finding a way to recover energy from sludge in the form of biogas itself, or other products that can be made from sludge, such as syngas – a mixture of hydrogen (H2) and carbon monoxide (CO) – thermal energy, diesel fuel or oil, and electricity. Technologies that extract energy from sludge include:

Enhanced anaerobic digestion. Anaerobic digestion is a well established technology with about 3,500 installations at wastewater treatment plants worldwide. While anaerobic digestion is a fairly mature technology, new technologies are in development, making slight changes to the technology, such as the Shaw Group’s modified anaerobic baffled reactor, which enables the system to process the sludge in 24 hours, instead of the 12 days to 25 days that conventional anaerobic digesters require. Companies providing enhanced anaerobic digestion technologies include the Shaw Group and Veolia Water.

Thermal hydrolysis.

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Thermal hydrolysis technologies are designed to work with anaerobic digesters to enhance biogas production. The process destroys microbial cell walls in the sludge, releasing a more easily digestible organic compound by heating sludge to a high temperature, about 150 °C to 180 °C, and high pressure, between 6 bar and 10 bar, for a period of 30 minutes to 60 minutes. Thermal hydrolysis processes from companies such as Veolia Water, and Cambi can produce about 1.5 times more biogas than conventional anaerobic digestion.

Ultrasonic cavitation. Like thermal hydrolysis, ultrasonic cavitation is a complimentary technology to anaerobic digestion that enhances cell destruction to boost yields. The process uses acoustical frequencies, ranging from 20 kHz to about 100 kHz, to create microscopically small cavities filled with water vapor or gas. These bubbles implode, a process known as cavitation, producing powerful shear forces that break up cellular matter, resulting in increased biogas production of up to 50%. Ultrawaves has licensed its ultrasonic technology to companies such as Eimco Water Technologies, Kotobuki, and Royce Water Technologies.

Mechanical or chemical disintegration. Disintegration systems are anaerobic digestion enhancers that can potentially yield 30% more biogas. The process weakens the cell wall by either chemical means (for instance, by adding caustic soda) or mechanical means (such as a macerator) before the sludge is sent to a mixer to ensure a homogenous suspension. The homogenized sludge is then mechanically disintegrated, which causes the cell structures to collapse and release their contents, before the sludge is sent to an anaerobic digester. Companies offering mechanical disintegration technologies include Biogest, Microsludge, and Eco-Solids.

Ozonation. Ozone technology is already used at treatment facilities around the world because the ozone gas generated acts as an effective oxidant as well as disinfectant. However, another valuable use for ozone is for lysing cellular matter in sewage sludge. The use of ozone to enhance anaerobic digestion biogas production is still relatively new and under evaluation, but companies such as Praxair and ITT-Wedeco have preliminary results indicating yield improvements of up to 40%.

Gasification. Unlike the above processes, which enhance biogas production, gasification produces a different energy product from sludge – syngas. Gasification takes place in two steps. In the first step, sludge is heated to about 600 °C in the absence of air to form a carbon-rich substance called char. The char is then heated in the presence of oxygen or air, and water, producing syngas. Gasification is employed around the world for treatment of a wide variety of materials, including coal, biomass, and municipal solid waste (MSW). Examples of companies providing gasification technologies for sewage sludge applications include KOPF, PrimeEnergy, and EBARA.

Pyrolysis. The conversion of sewage sludge to oil relies on pyrolysis, which is the conversion of sludge to char in the absence of air. The char vaporizes at elevated temperatures, 425 °C to 538 °C, and rapid cooling and condensation of the vapor results in the oil that can be used as a fuel in boilers or combusted in an engine to produce electricity. Pyrolysis can also operate at temperatures below 325 °C, producing not oil, but rather a char that can be burned as fuel, with an energy density of 13,960 kJ/kg, roughly the same value as lignite coal. Pyrolysis technologies can process a wide range of inputs, including municipal solid waste, process manure, and agricultural waste, but companies providing pyrolysis technologies for sewage sludge treatment include Enertech, Splainex, and US Centrifuge.

Supercritical water oxidation.

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Supercritical water oxidation (SCWO) operates by heating water to 374° C and pressurizing it to 221 bars to create a phase of water called supercritical water, which exhibits characteristics of both a liquid and a gas. Sludge in supercritical water oxidizes rapidly in the presence of oxygen, converting all carbon present in the sludge to carbon dioxide and nitrogen compounds into nitrogen (N2). When the pressure is then lowered to less than 10 bars, the carbon dioxide, nitrogen, and any residual oxygen can be removed from the waste stream, leaving an inert material that can be landfilled or treated further for recovery of phosphorus. Depending on the size of the SCWO unit, the process can produce waste heat for recovery, potentially as electricity. However, smaller plants will only have the option to recover low-grade heat, which can be used for heating options in earlier treatment processes or for district heating. Companies providing SCWO technologies include Veolia Water, SCFI, and Feralco.

Microbial fuel cells. Microbial fuel cells can process the wastewater liquid itself or sludge, removing organic matter and reducing sludge output while producing energy. The process captures electrons released by the oxidation of dissolved organic material in wastewater by bacterial strains that are growing on electrodes (called the anode and cathode) with the fuel cell. The bacteria release electrons, free protons (H+ ions), and carbon dioxide as part of their metabolic process; the electrons are captured by the anode while the protons are released into the water, diffusing to the cathode, where they recombine with the electrons after the latter have been used to do useful work. Microbial fuel cells are still in the early stage of development and the goal of one company, Emefcy, is to generate 0.5 kWh of free electrical energy per kilogram of dissolved organic matter (dissolved organic matter in wastewater has an energy density of about 4 kWh per kilogram). Companies investigating microbial fuel cells include Emefcy, InTact Labs, and Hy-Syence.

Grease to biodiesel technology. Wastewater treatment facilities must also deal with oils and greases collected from commercial or industrial businesses – materials that can be harvested for energy, but which otherwise would contribute to sludge production. A grease trap captures grease that has gone down a drain and prevents it from going deeper into sewer pipes, where it can clog the pipes, causing a sewer overflow. On a regular basis, the grease is vacuumed out of the trap and hauled to a local wastewater treatment facility, which is paid a tipping fee to dispose of the grease, usually around $18 to $52 per cubic meter of grease. Typically, wastewater treatment plants then transfer the grease to an incinerator or landfill, but another option is converting grease into biodiesel through dewatering, filtration, and a chemical conversion. Companies developing such an approach include BioFuelBox and BlackGold Biofuels.

Chemical and Material Recovery Technologies Are Still in the Early Stages of Development

The concept of recovering phosphorus or other useful chemicals and materials from sludge is newer than energy recovery, and technologies in this area are still in the early stages of development. Methods for recovering valuable products from sludge include:

Crystallization. Crystallization processes typically use a seed material, such as sand, to encourage crystals of phosphorus-containing materials to develop in the sludge, where they can be collected. Activated sludge is sent to a reactor filled with the seed material, and a chemical such as lime – calcium oxide (CaO) – is added to adjust the pH and to create optimal conditions for precipitation of calcium phosphate (CaPO4). Over time, calcium phosphate pellets form, and as they increase in size and weight, the larger, denser pellets sink to the bottom of the reactor, where they can be pulled off and used as a fertilizer raw material.

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Depending on the seed material, chemical addition may not be needed. One seed material under development is tobermorite, which is composed of calcium silicate hydrates (CaSiO5·xH2O), that stimulates precipitation of calcium phosphate while also increasing the reactor pH. Another variation of the crystallization process is to use magnesium chloride (MgCl2), which is added to the activated sludge and pumped into a fluidized bed reactor, forming crystals of struvite – ammonium magnesium phosphate ((NH4)MgPO4) – that can be resold as fertilizer. Companies providing crystallization technologies include DHV Water, Ostara Nutrient Recovery Technologies, and Unitika.

Physical-chemical technologies. Many emerging technologies are turning to physical-chemical means to dissolve phosphorus and then separating it from heavy metals or other sludge components via precipitation. Some technologies utilize only chemicals to dissolve and precipitate phosphorus, while others turn to incineration or ion exchange. The final product – which can be struvite, phosphoric acid (H3PO4), or iron (III) phosphate (FePO4) – depends on the chemical used in the precipitation step. Companies offering physical-chemical technologies for phosphorus recovery include Kemira and Seaborne.

Vitrification. Vitrification can turn sewage sludge into construction materials by injecting the sludge along with air into a chamber where it combusts, releasing a significant amount of heat energy, and raising the temperature to about 1,300 °C to 1,500 °C. The sludge melts at these temperatures into molten glass as

the organic materials combust, leaving behind silica and other inorganic materials. The gases (combustion

products) are exhausted from the melting unit to a heat recovery system, and the glass is drained into a

quenching tank. Only one company has sold a vitrification system, Minergy, but the firm recently went

through reorganization and no longer sells this system.

Thermal solidification. Thermal solidification uses ash from sewage sludge incineration to create building materials such as artificial lightweight aggregates, brick, slag, ceramic, glass, and interlocking tile, by melting and solidifying the ash in a process analogous to sludge vitrification. Currently, there are no companies selling thermal solidification systems, and the process remains very energy intensive.

Landscape Conclusions

From our review of sewage sludge characteristics, treatment, and disposal, we conclude the following:

Sludge production volumes will continue to grow with increasing population and country wealth.

Current sludge disposal methods have their drawbacks.

There are a variety of technologies available to extract value from sludge – in the form of energy, nutrients, or building materials.

1 Source: Wastewater Engineering: Treatment and Reuse, 4th Edition, Metcalf & Eddy, Inc.

2 Source: “An Economic Evaluation of Phosphorus Recovery as Struvite from Digester Supernatant”, L.Shu, P.Schneider, V. Jegatheesan, and J. Johnson, Bioresource Technology, vol. 97, 2006.

3 Source: Wastewater Engineering: Treatment and Reuse, 4th Edition, Metcalf & Eddy, Inc.

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4 Industries either treat wastewater on-site or discharge it to a municipal wastewater facility for treatment. It’s estimated that about 80% of all industrial wastewater is eventually treated at a publically owned wastewater treatment facility.

5 Sources:

State of Science Report: Energy and Resource Recovery from Sludge, Y. Kalogo and H. Monteith, Global Water Research Coalition, 2008.

Global Atlas of Excreta, Wastewater, Sludge, and Biosolids Management: Moving Forward the Sustainable and Welcome Uses of a Global Resource, United Nations Human Settlements Programme (UN-Habitat), 2008.

6 Source: Global Atlas of Excreta, Wastewater, Sludge, and Biosolids Management: Moving Forward the Sustainable and Welcome Uses of a Global Resource, United Nations Human Settlements Programme (UN-Habitat), 2008.

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