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Sludge to energy - supercritical water oxidation
Paul O Callaghan
Posted: Thursday, December 17, 2009 2:23 AM
Joined: 10/18/2009
Posts: 2

Hi, I am wondering if anyone has heard anything about the Supercritical water oxidation sludge to energy plant which was proposed for the Ironbridge WWTP in Orlando, Florida?

There is a demo plant for the Aquacritox supercritical water oxidation process in Cork, Ireland currently operating on sewage sludge, but the Florida project was going to be using a different supercritical process. If I find out any more about it, I will post the info here as well.

Paul O Callaghan
Posted: Tuesday, January 5, 2010 4:00 AM
Joined: 10/18/2009
Posts: 2

I found out a few things about the Ironbridge Supercritical water oxidation (SCWO) sludge destruction project. Its quite a large demonstration facility, with a capacity of 5 dry tonnes of sludge per day. This will be capable of taking about 25% of the sludge from the 40MGD Wastewater treatment plant. Interestingly there is no primary treatment at the plant, everything just goes straight to secondary, so the SCWO plant will be fed WAS at 10% dry solids directly. So far, the plant has been run using alternative feedstocks during trial runs and its expected that it will be fed sludge in the next 6-8 weeks. The goal after that is to  run the plant contiuously for a period of 90 days to demonstrate reliability of the technology.

For those of you not familiar with supercritical water oxidation, the basic premise is that once water goes above 370 Deg C and 220 Bar of pressure, it enters a fourth state, referred to as supercritical. If you introduce oxygen into supercritical water, you can completely oxidise organic material. This releases energy which can be used in a CHP plant and produces an inert ash-like material and water (supernatant) with a COD of less than 5mg/l. It has a number of advantages over alternative thermal treatment processes. Firstly, sludge does not have to be dewatered. This eliminates mechanical dewatering and thermal drying. Secondly, as the oxidation occurs in the water phase, it does not have the air emissions issues associated with sludge incineration. Supercritical processes are not new in and of themselves, but the treatment of sewage sludge, is a new application of the technology. The US military use supercritical water oxidation, (I think provided by General Atomics) to destroy military waste. The Aquacritox process, which was originally developed by Chematur, has been used for Catalyst recovery in the past and is currently being used on sewage sludge. The Ironbridge SCWO plant will not incorporate energy generation or carbon dioxide capture immediately, but the goal would be to add these things on and to include them in future plants. The technology also lends itself to phosphorus recovery, as all soluble phosphorus present in the sludge, will be present in the supernatant and could be recovered using struvite fluidised bed crystallisers.


It will be interesting to see how the Ironbridge and other SCWO projects progress. Gasification and Pyrolysis are receiving considerable attention with demonstration plants in California (Rentech in Rialto), Stamford Connecticut (Nexterra) and Florida (MaxWest). The WERF  State of Science Report: Energy and Resource Recovery from Sludge, provided pretty good coverage on a number of these options as did Water Technology Markets, though I have to state an interest in the latter as I was an author.  I would take the view that the future of sludge handling will involve a) moving away from aerobic secondary treatment process which will eliminate WAS, and b) complete energy recovery in one step, possibly eliminating need for anaerobic digestion as an intermediary step.

If hear any more on above, I will post it.

Posted: Tuesday, February 9, 2010 7:24 AM
Joined: 2/9/2010
Posts: 1



It is good to see that people are returning to this process but you should be aware that it is certainly not as new as you think.

For those of you who can remember the developments at Longmont Colorado and the Sub-critical water Treatment demonstration plant that became the fully operational VerTech Aqueous Phase Oxidation process. You might be aware that this facility (in its original operation) used a water-cooled Gravity Pressure Vessel and was a continuous procedure working at 5 tonnes dry weight of sewage sludge per day. When it was taken over in the late 1980s it was refined further and then transferred totally to the Netherlands under the Van Wijnan Construction company umbrella and operated at over 22,000 tonnes dry weight of sewage sludge per year (60+ tonnes per day) minimum. During its operational time this was successfully increased such that it could treat over 32,000 tonnes dry weight of sewage sludge per year (88+ tonnes per day.) As a finance design build and operate programme it was one of the first of its kind. The capital cost was minimal as was the operations and maintenance costs.

Although this facility had just one Gravity Pressure Vessel it remained operational over 96% of its working time. In fact when we went there with various people from within the UK and French and Asian area to view the site and its operations in the 1996, 1999 and 200/2002 it was certainly an impressive facility and very compact. So much so that my colleague Dr Wu Jin Lee is promoting it in our territory (as you will see later.)

At the point of renewing the contract (after 14 years of operations) the owners of the Apeldoorn sewage treatment facility decided that they could better the treatment costs for disposing of the sludge by diverting it (the sludge) to East Germany, for what is now known to be 'illegal,' dumping of the sludge down mine shafts. (As this was a direct infringement of European Union Laws and Statutes we now hear that the European Union will be prosecuting the Water Board for this and levy exemplary fines to it as a result.) With the sludge supply gone the plant was declared redundant and it was sold off and it is now being rebuilt in Arnhem (Netherlands) in an updated form in an important development.

It be borne in mind that Genesyst International Incorporated through its subsidiaries in the USA and through the development of its entrepreneurs (particularly from) the UK has expanded to develop the process further and is in deep discussions in the Asian Far East and South East to develop a series of major programmes for treating 1,600 tonnes dry weight of sewage and animal sludge per day. If as this programme gets the go-ahead from the Governments and Metropolitan City Areas involved and the Investors who have confirmed interest reach an agreement then this programme embracing five Metropolitan Cities should be finally commissioned in the later part of this decade. 

The Genesyst programme looks at using its proprietary and Internationally World Patented Gravity Pressure Vessel for this procedure as it offers a free energy pumping system that uses gravity and heat derived from the thermodynamics of the process as the driver rather than pumping as described in this process. The site of reference to this can be seen in www.genesyst.com for which their contacts in the USA and in the UK are given.

The other area where Genesyst though is working and which provides even more benefit to the Waste Industry is in the conversion of biomass to the biofuels ethanol/butanol. Here again the company uses its patented Gravity Pressure Vessel in a continuous procedure again for a process called Dilute Acid Hydrolysis of Biomass. By using a continuous method of operation in Dilute Acid hydrolysis to rupture and hydrolyze the Ligno-Cellulose in the Biomass this updating of the process extends a technique (originally developed in the 1800s) which hitherto had been a batch process and barely 35% efficient to one that can attain over 70% efficiency. This means that its use can be used in turning Biomass derived from municipal solid waste as well as from other areas to the biofuel ethanol economically (at less than a third of the equivalence of incineration and gasification programmes) and without the detractors of the air-borne emissions (odours dust particulates etc.) commonly found there. And it will produce a valued fuel for transport without using food crops with the added advantage that even the carbon dioxide produced can be captured and diverted from the atmosphere. This is the ultimate development in the process which is now being built in the West Yorkshire project for Mytum and Selby, in Ho Chi Minh City Viet Nam in Kentucky and Virginia and is also proposed elsewhere in Europe Asia and beyond.

Thus by observation the industry has now moved beyond using super-critical water alone to the next generation of processes where valuable products are to be made from the biomass raw material. This is real innovation and should be considered by all.


Posted: Wednesday, February 10, 2010 6:00 PM

Hi, isn't it wonderful what this site opens up.


The article referred to here on SCWO and SubCWO should both be welcomed as this solution to a pressing sludge issue was also raised by Sludge Watch earlier this week.


Now you are saying go one better and combine the sludge and biomass from waste sources in one as you report is happening in this Genesyst procedure in places as widely apart as Yorkshire Kentucky Virginia and overseas in VietNam Malta and Israel and beyond. Let's hope that the whole world follows suit as this is worth following


This sounds like a programme which is worth following and I hope is seen positively for investors.


Making use of biomass in waste to make fuels at a fraction the cost of the alternative of incineration is a far better option. And we should commend it.




Posted: Friday, February 12, 2010 4:41 AM

That's interesting.  Never heard of the VietNam and Malta projects.  Are these in operation?



Jerry Hunter
Posted: Friday, February 12, 2010 8:42 AM
Joined: 10/2/2009
Posts: 1

Sounds to me to be a lot like the old Zimpro Process.

Posted: Thursday, February 18, 2010 6:09 PM

It is good to see people talking about SCWO and WAO.

We operate the Aqua Critox scwo plant in Cork and are actively promoting the technology as a sustainable solution to sewage sludge.

we have been operating the plant in Cork,Ireland since early 2008.

We believe that the key to making the aqua Critox technology a success is offering it to the market as a pre-engineered product. this takes all of the guess work out of capital cost, foot print, energy and mass balance, operating cost etc.

Oxygen is the largest consumable and it typically takes 800kg of oxygen to process one ton of dry solids. Bulk liquid oxygen is currently priced at $80-$100 per ton LOX.


Posted: Saturday, February 20, 2010 12:25 PM

Interesting that the process in Cork is a revamped Zimpro system and a batch one at that. We in Asia have tried this batch system and it causeed us so much of a hassle stabilising the process. We are looking at a continuous one as per the previous discussion and that rules out this one. The Genesyst proposal to go further and make ethanol out of sludge and msw is to us more beneficial as it makes for us a proper useful product which has a real commercial value rather than spent gases going up in to the atmosphere.

John O'Regan
Posted: Monday, March 1, 2010 6:57 AM
Joined: 3/1/2010
Posts: 1

The Aqua Critox process is not a revamp of the old Zimpro process.

Zimpro is based on sub critical water oxidation and had a retention time on 15 - 30 minutes. Typically the effluent still contains significant residual organic acids and ammonia.

power generation is not an option for Zimpro.

Aqua Critox is based on super critical water oxidation and has a reactor retention time of 60 seconds. effleunt contains no orgaincs or ammonia.

aqua Critox is a continuous process and has the potential to generate up to 1 MWh of electricity per ton of sludge processed.

If you want to learn more please visit www.aquacritox.com

Posted: Thursday, March 11, 2010 6:14 AM

For those interested in the Ironbridge Sludge Supercritical Water Oxidation project,, the following is a link to the agreement with the City Of Orlando for the demonstration scale project. Its an interesting agreement in that it tries to get around the 'valley of death' syndrome for new technologies by providing an incentive for the City to host and support the project.


In general Municipalities appear to be getting more creative in how they engage with sludge to energy projects.  

Posted: Monday, February 14, 2011 12:04 AM

Hi there, a couple of years ago at my University in Australia I undertook a group undergraduate design project (theory only) for which my focus was the SCWO reactor of a wastewater treatment plant. With the limited infomation (just research papers compared to design manuals), my design followed something similar to the Aqua critox (i.e tubular reactor). Sizing of the reactor was based on research papers reaction rates for carbon (assumed basic first order, fully insulated reaction), however I did find that it seemed that ammonia and some nitrogen based compounds took alot longer too react, and this vastly increase the sizing of the reactor (to reach our very strict disposal requirements). Of course, we were treading new ground, so it was hard to get advice about these reactors. Just wonder what Aqua critox thoughts are and are there currently any other problems or issues which are still being ironed out?

Posted: Tuesday, April 17, 2012 9:57 PM
Joined: 4/17/2012
Posts: 1

That's interesting.Vitnam is near China,we have belt filter press for sludge dewatering,if you're interested in ,you guys can come to China to see .Any query you can contact me.