AquaCritox - Advanced Super Critical Water Oxidation

AquaCritox is proven to deliver 99.99%+ destruction of organic waste in a fast, safe, odourless process and is up to 100% more efficient than competing technologies. As well as reducing the carbon footprint of a plant, it will recover valuable by-products, such as phosphorus and CO₂ (which can be used for resale), and is the first technology to have a positive energy balance from processing wet waste.

Being a destruction (rather than reduction) technology, its most comparable method is incineration. However, AquaCritox offers greater destruction rates, is thermodynamically more efficient, provides a significant decrease in costs and produces none of the hazardous by-products. (please see Comparisons section below).

Whilst AquaCritox is especially suitable for the treatment of sewage and drinking water sludge, it is a multi-platform technology and is also effective for a number of other industries where the disposal of industrial liquid wastes and slurries is an issue (please see Applications section below).

AquaCritox is available in four sizes with hydraulic loads ranging from 1 to 20 tonnes per hour and a footprint of between 300m² and 1750m². These models are manufactured, assembled, pressure and wet-tested before arriving on site for integration. Prices include all of the standard equipment required to operate the plant including all of the basic kit such as reactor, heat exchangers, high-pressure pumps, oxygen feed points and low pressure pumping kits from feed tanks and all interconnections. The technology offers payback periods of approximately five years.

SCFI operates a 250 litre/hr AquaCritox demonstration plant in Cork, Ireland. The plant can be visited by appointment. Please email info@scfi.eu for further information.

AquaCritox uses super critical water oxidation, which is achieved when water temperature exceeds 374^oC and is pressurised to 221 bar. This moves water into a super critical condition or ‘fourth phase,’ where the water is neither a liquid nor a gas, but a homogenous dense fluid. In its super critical state, water becomes a universal solvent for gases and organic compounds, even those that are normally insoluble in water. By adding an oxygen supply, a very rapid and complete oxidation reaction takes place, which not only generates thermal energy, but also converts all organic materials in sewage sludge into CO_2, nitrogen and clean water. The nitrogen can be safely released into the atmosphere and the CO₂, (which is a short cycle carbon rather than greenhouse gas), may be sold on for industrial applications or dry ice production.

The unique physical properties of super critical water allow for a very rapid reaction rate and high efficiency destruction (99.99%+). The remaining water has a COD of less than 5ppm and the inorganic materials are easily separated and treated in a separate step to recover valuable by-products, such as phosphorus – or in the case of drinking water sludge, coagulants – which can then be reconstituted for re-use. Not only does this negate huge wastage levels, it also avoids the sociopolitical issues that surround sludge disposal, as all organic materials are converted into safe, inert gases and clean water.

The AquaCritox process will oxidise:

-      Organic Carbon to CO₂

-      Organic Nitrogen to N₂ with NOx formation

-      Organic sulphur to S0₄ with SOx formation

-      Soluble metals to their highest oxidation state

Using the super critical water oxidation process, AquaCritox is a net energy producer, generating significant amounts of excess heat, which can be recovered for heat applications or for the generation of electricity. This not only significantly reduces a plant’s carbon footprint but also presents an additional revenue stream for a wastewater treatment plant, generating electricity sales from a totally renewable source.

AquaCritox produces no odours, valuable resources are recovered and residual materials are non-hazardous. The technology is clean, creates no noise pollution and being a full destruction technology, requires no trucking off site. It also has a relatively small footprint compared to other technologies and planning concerns over height are void, as it is less than 15m tall. Its small footprint also allows it to fit into existing buildings, eliminating haulage movements. Operating availability is considered to be in excess of 7,500 hours per year. The technology is also fully automated and is an enclosed process, requiring minimum manpower and maintenance.

Following the recent banding review of DECC’s Renewables Obligation (RO),  AquaCritox technology has now been awarded the highest level of financial support available for waste to energy technologies. Under the definitions for the new ‘advanced conversion technologies’ RO band, between 2013 and 2015 the sustainable wet waste destruction technology is eligible to receive 2 ROCs per MWh of renewable electricity generated, which will later evolve to 1.9 ROCs in 2015/16 and 1.8 in 2016/17.

AquaCritox:

-      Reduces a plant’s footprint

-      Generates renewable electricity

-      Allows for phosphorous and coagulant recovery

-      Removes nutrient load from land

-      Produces no odour, hazardous by-products or emissions

-      Delivers 99.9999% conversion of contaminants

-      Uses a closed process

-      Generates carbon dioxide in a concentration and purity suitable for re-sale

-      Is not weather dependent

-      Does not rely on land bank availability

-      Eliminates truck movement

-      Provides a long-term solution (10-20 years)

-      Does not create any permit of licensing issues

-      Is not subject to incineration directives

AquaCritox offers a significant decrease in costs compared to current practices (e.g. landfill, incineration, drying), with payback periods of approximately five years. In addition to shipping and land spreading costs, AquaCritox also reduces the need for expensive dewatering and eliminates drying, incinerating and trucking off site.

AquaCritox offers greater destruction rates than incineration or wet air oxidation in one single, straightforward step. The technology is:

-      Thermodynamically more efficient than incineration: it avoids the large unrecoverable loss of potential energy used to heat/dry wastes prior to incineration

-      Commercially more attractive than anaerobic digestion or wet air oxidation: its faster reaction rates (under its near-critical and super critical conditions) result in a smaller plant footprint/lower capital cost

-      Environmentally more sustainable, allowing for easy recovery/recycling of valuable by-products (including commercial/food grade CO₂ and thermal energy)

AquaCritox is a particularly attractive alternative to incineration when it comes to lean liquid waste streams. Until now, waste with more than 60 grams per litre of chemical oxygen demand (COD) has been traditionally destructed using incineration. However, this high water content and low energy value means incinerators need to use a primary fuel to ensure the kiln temperature is maintained, which leads to subsequent high costs. AquaCritox presents a cost-effective and sustainable alternative. Whilst incinerators typically require at least 600 grams per litre of COD to be auto-thermal, with AquaCritox there is no need to evaporate water and it can be auto-thermal at just 60 gram/litre.

Although it is especially suitable for the treatment of biosolids, AquaCritox also has potential for multiple applications across a range of industries. Examples include:

Destruction of organics in:

o    Drinking water sludge

o    Fermentation broths

o    Paper sludges

o    Pharma/chemical waste streams

o    Pharmaceuticals

o    Petrochemical waste streams

  Destruction of ammonia in:

o    Refinery streams

o    Spent industrial refrigerants

o    Wastewater applications

Destruction of proteins and prions

• Destruction of the carbon backbone of heterogeneous catalyst (to allow for effective precious metal recovery)

• Decontamination and reactivation of absorbents and catalysts

• Treatment of refinery spent caustics

Billions of pounds are being spent globally each year on the disposal of sewage sludge alone. This, matched with the serious economical and commercial barriers facing current disposal methods means there is increasing pressure to find a sustainable alternative. AquaCritox presents an attractive solution that not only eliminates any onerous licensing issues and liability risks associated with sludge disposal, but also significantly cuts costs, reduces a plant’s overall footprint and generates renewable energy.

With AquaCritox the route to disposal is fully secure, as is the amount of energy that is generated in the process. Whilst other methods, such as application on land, face the continual threat of being banned due to potential disease outbreaks, AquaCritox allows for total control of the waste disposal process as well as the costs involved - leaving it far less exposed. It also delivers energy security, as the technology continues to generate more energy than it actually requires, creating a steady source of electricity or steam and hot water.

With destruction efficiencies of 99.99%+, trials show that AquaCritox is up to 100% more efficient than competing technologies and provides faster payback periods.  Both raw and digested sludge can be treated at 6–18% dry solids, providing the option of reducing dewatering requirements earlier in the treatment process.

For every dry tonne of organic wet waste processed, AquaCritox delivers up to:

• A volume reduction of 97%
• 3.6MWh of thermal energy / 1MWh of renewable electricity
• Totally inert byproducts

Therefore a plant designed to process 20,000 metric tons of dry solids per year can generate between 15,000 and 20,500MWh of electricity gross. 

The treatment of drinking water using alum (aluminium sulphate) or ferric sulphate produces large quantities of sludge – the disposal of which creates a mammoth, costly task. This alum sludge cannot be processed through traditional methods of sewage sludge disposal (such as land spreading or incineration) and therefore, hazardous landfill is considered the only safe option.

The shortage of landfill sites, and rising landfill taxes, mean that drinking water treatment plants are faced with heavy cost burdens to collect, transport and dispose of the waste, not to mention the loss of valuable coagulant (alum).

AquaCritox provides a unique solution – fully recycling the coagulant in a sustainable way and providing complete organic waste destruction in a fast, safe and odourless process that eliminates the need for landfill. Not only does this negate the huge wastage levels associated with disposing of used coagulants, it also avoids the wider issues that surround sludge disposal, as all organic materials are converted into safe, inert gases and clean water.

Calculations undertaken as part of extensive trials at SCFI’s testing facility in Cork show that for every tonne of alum sludge received, 50% is organic and 50% inorganic (with typical dry solid content at 17%). When subjected to the AquaCritox process, the organic matter is fully destructed, while the inorganic will recover approximately 85 kilos of aluminium hydroxide.

The by-products of industrial refining processes, both ethylene and refinery spent caustics are hazardous wastewaters – and as such, require specialist handling and disposal in line with necessary regulatory frameworks. Made up of a mixture of either sodium hydroxide or potassium hydroxide, water and a variety of contaminants, spent caustic typically has to be trucked off site for incineration or pre-treated before disposal.

Trials carried out by SCFI show that AquaCritox’s super critical water oxidation (SCWO) process delivers a higher oxidation rate than conventional wet air oxidation (which requires treated waste to be transferred to a biological treatment plant for disposal). The result is a rapid oxidation of contaminants (e.g. sulphides, mercaptans and napthenic acids) to give an odourless, non-toxic treated effluent.

Processing undiluted spent caustic for the trials consistently produced the following results:

•   > 94 percent reduction in COD. Typical oxygen consumption of no more than 120 percent of COD demand

•   Operation in auto-thermal mode is possible when spent caustic contains a COD concentration of 24,000 mg/ltr or greater

The trials also show that once treated by AquaCritox, spent caustics were safe for disposal through a conventional wastewater treatment plant or sewer, meeting environmental discharge quality and permit requirements.

The pharmaceutical and biopharma industries produce organic liquid wastewater sludge. These high-strength industrial waste streams typically have high COD values, contain recalcitrant organic compounds and are often difficult to break down using conventional wastewater treatment processes.

AquaCritox provides a unique solution to this disposal problem. Trials carried out at SCFI’s testing facility in Cork indicate that the technology delivers complete destruction of high-strength (50–350 g/l COD) industrial waste. As well as complete destruction of organics, AquaCritox produces an inert ash and liquid stream.

AquaCritox uses super critical water oxidation to deliver rapid and total oxidation of all of all organic compounds present in the waste. Furthermore, as the reaction occurs in the water phase, the process does not generate the hazardous emissions associated with incineration of high-strength organic wastewater streams. The process is autothermal, heating itself using the energy within the wastewater, and in many cases can produce excess thermal energy. This can be converted into steam for reuse elsewhere in the plant.

Precious metals are used extensively as catalysts in a wide range of industrial chemical processes. They can be used in a homogeneous form, but more commonly they are heterogeneous, i.e. fixed to a solid support for ease of handling. In many applications only a precious metal catalyst can provide the necessary speed or selectivity for the reaction. In others, the long lifespan of a precious metal catalyst makes it the most cost-effective choice. Precious metals, such as platinum, palladium, rhenium and rhodium constitute a huge investment. Because of this, a key factor in the economics of these processes is the ability to recover the precious metal content from the catalyst quickly and efficiently once it is spent.

AquaCritox uses the unique properties of supercritical water to completely oxidise the organic backbone in spent catalyst. The precious metal is oxidised and removed as pure particulate or soluble salt ready to be refined. The process is totally enclosed, preventing release of harmful substances and ensuring 100% recovery of precious metals.

The AquaCritox process is suitable for use on both heterogeneous and homogenous precious metal catalysts. Trials using SCFI’s testing facility have been carried out for several international catalyst users and suppliers. The results for materials such as rhenium, platinum and a number of other rare earth metal catalysts have proven the technical and economic viability of the AquaCritox process for these applications. Tests also indicate that the process enables activated carbon regeneration and activated carbon catalyst recovery.

SCFI is actively seeking companies with catalysts containing precious metal who are interested in discussing catalyst recovery. For further information please email info@scfi.eu.