- Email: [email protected]
Memtec's success with NSW sewage
ISSN 0958-2118 I
June 1991
An International Newsletter
Number 14
Membrane Technology Memtec's success with NSW sewage Memtec's membrane technology solution to the effluent problems of Sydney, New South Wales, Australia (see News, Membrane Technology Nos 5 and 7), has now undergone successful trials, delegates at a desalination symposium held in Valetta, Malta, in April were told. Tony Fane from the Centre for Membrane & Separation Technology at the University of New South Wales revealed results of the full scale trials at the 5th World Congress and 12th European Symposium of Desalination and Water Re-use, which was held in Valetta 15-20 April this year. The Memtec pilot plant has processed municipal effluent, containing both industrial and domestic wastes, in one-tenth of the residence times used in conventional sewage treatment, and produced a clean water product comparable to that obtained by conventional tertiary sewage treatment, Fane said. The plant, which generated very little smell, was able to produce a water quality superior to conventional secondary treatment plus disinfection.
Novel bioreactor
ELSEVIER ADVANCED TEC HNOLOGY
The successful system is a combination of biological reactors and membrane filtration. The key is in the design of the new type of bioreactor employed. Conventional bioreactors used in sewage treatment (methane digestion) are of the "activated sludge" type, in which the anaerobic bacteria that degrade and decompose the constituents of the sewage are held in large reaction tanks. The digestion cycle normally takes around 5 hours and then the digested slurry passes to a settling tank so that sludge separates from the treated water. In the Memtec reactor, similar bacteria are used, but they are immobilised on solid support particles. The digestion process is therefore more efficient and there is no need for a subsequent settling stage to separate the solids from the water phase. Thus the treated effluent passes through to the next stage in one-tenth of the time taken by a conventional sludge digester system, and it is much clearer of solid matter, according to Fane.
.........
]
News and Views .
After the bioreactor step, microfiltration is used to polish the quality of the treated water further. Hollow fibre bundles used in the filtration cartridges have pore size less than 1 micron. They incorporate a patented self-cleaning process in which air is blown backwards through the system to clear any obstructions and blockages caused by solids buildup. A further advantage of the Memtec system over conventional sewage treatment is that the absence of settling areas means that the process has a much smaller "footprint". At the Cronulla sewage works where the trials were made, the full-scale plant occupies only one-third of the space of the conventional treatment facility. Fane's belief is that this would allow many industrial plants to build on-site treatment facilities rather than discharge raw effluent into municipal systems.
II
I
Membranes in space A report published in April by the European Space Agency says that in future space stations will be able to recycle 98% of their water supplies, prolonging the period between services. The ESA report says that 97-100% of all impurities can be filtered from waste water by their process; however, no guarantees are given that the water will be palatable. In a space station, all urine, washing water, flush water, laundry water and dishwashing water will have to be purified. The report says "Only experimental evidence on real waste waters can show whether, in all cases, unpleasant odour can be removed?~ Rud Madsen and Jasper Thomassen of the Danish company Danisco, Denis Vial of Lyonnaise des Eaux and Roger Binot of the ESA research centre in the Netherlands propose a multistage purifying and recycle system for the Columbus module, due to be launched towards the end of the century. "Kitchen sink" water would first be prefiltered using a purpose built lightweight membrane to remove solids as a "cake". Acidification is also required to kill bacteria, and limit the breakdown of urea into carbon dioxide and ammonia - gases which would pose problems in an enclosed environment. The permeate from the pre-filter - still containing many undesirable substances (detergents, amino acids, salts, sugars etc) - would then be subjected to reverse osmosis. The proposal is that three RO units would be required for Columbus to deal solely with hygiene and washing water. The permeate from the RO units would then be neutralised, oxidised with hydrogen peroxide, and subjected to ultraviolet radiation. Neutralisation with magnesium oxide produces formates and acetates which can be filtered out at high efficiency, up to
.
.
.
.
.
.
.
.
.
.
.
i
Because urea can only be rejected at about 85% efficiency by RO, reverse osmosis is not proposed for dealing with liquid lavatory waste. Rather it will be mixed under acid conditions with the concentrated residues from reverse osmosis and then distilled to recover water as condensate. The concentrated residue from this operation would be stored for collection. The authors stress that even with this level of processing, the system would not be sterile, and a sterilant is also recommended.
Painting by membranes A pipe-shaped ion exchanger has been developed in Japan by Tokuyama Soda Co, to be marketed in the form of a round diaphragm electrode device, mainly for use in electro-deposition in the automotive and metal finishing industries. An ion-exchange membrane within the pipeshaped electrode is both small and lightweight and virtually wrinkle free. Up to now the problems encountered with fiat devices is the size and weight (often 1 or 2 metres in dimension) and the deterioration caused by wrinkling of the membrane over time. The Tokoyama product is light enough that replacement is easy, but the smooth membrane means that paint hardly adheres to it at all. The device can be used in deep painting tanks and is only 60mm in diameter and 1-3 m in length. For electrodeposition of car bodies, the paint compound is dissolved in a neutralizer solution and put in a tank with the electrode device. The paint is then deposited onto the metal by ion exchange. In conventional systems, the electrode device removes surplus neutraliser containing negative ions, and this can result in deterioration of the membrane if the paint adheres to it. Pipe-shaped ion exchanger
i~~."
~'~
~:.~!:~:~::~:~:~:~:~.ff....~i~ii~i!~!~!:!:!:i!!:!~!:~:k*.~:~:~:~:~..
====================================================
~.:}}i}}{i}i}{}i}{i{}i~:{}}}{i}{}}}i{i:j
~
.~
' ' ':'[::~'
~".":.{i:
}i}!i]}{{}}{!:{}i~ i{:
.,i~ii}i!il}!{i:i;i!iii!i{2i!!!i i i!i
98%.
2
Membrane Technology
June 1991
An International Newsletter
Number 14
Membrane Technology Memtec's success with NSW sewage Memtec's membrane technology solution to the effluent problems of Sydney, New South Wales, Australia (see News, Membrane Technology Nos 5 and 7), has now undergone successful trials, delegates at a desalination symposium held in Valetta, Malta, in April were told. Tony Fane from the Centre for Membrane & Separation Technology at the University of New South Wales revealed results of the full scale trials at the 5th World Congress and 12th European Symposium of Desalination and Water Re-use, which was held in Valetta 15-20 April this year. The Memtec pilot plant has processed municipal effluent, containing both industrial and domestic wastes, in one-tenth of the residence times used in conventional sewage treatment, and produced a clean water product comparable to that obtained by conventional tertiary sewage treatment, Fane said. The plant, which generated very little smell, was able to produce a water quality superior to conventional secondary treatment plus disinfection.
Novel bioreactor
ELSEVIER ADVANCED TEC HNOLOGY
The successful system is a combination of biological reactors and membrane filtration. The key is in the design of the new type of bioreactor employed. Conventional bioreactors used in sewage treatment (methane digestion) are of the "activated sludge" type, in which the anaerobic bacteria that degrade and decompose the constituents of the sewage are held in large reaction tanks. The digestion cycle normally takes around 5 hours and then the digested slurry passes to a settling tank so that sludge separates from the treated water. In the Memtec reactor, similar bacteria are used, but they are immobilised on solid support particles. The digestion process is therefore more efficient and there is no need for a subsequent settling stage to separate the solids from the water phase. Thus the treated effluent passes through to the next stage in one-tenth of the time taken by a conventional sludge digester system, and it is much clearer of solid matter, according to Fane.
.........
]
News and Views .
After the bioreactor step, microfiltration is used to polish the quality of the treated water further. Hollow fibre bundles used in the filtration cartridges have pore size less than 1 micron. They incorporate a patented self-cleaning process in which air is blown backwards through the system to clear any obstructions and blockages caused by solids buildup. A further advantage of the Memtec system over conventional sewage treatment is that the absence of settling areas means that the process has a much smaller "footprint". At the Cronulla sewage works where the trials were made, the full-scale plant occupies only one-third of the space of the conventional treatment facility. Fane's belief is that this would allow many industrial plants to build on-site treatment facilities rather than discharge raw effluent into municipal systems.
II
I
Membranes in space A report published in April by the European Space Agency says that in future space stations will be able to recycle 98% of their water supplies, prolonging the period between services. The ESA report says that 97-100% of all impurities can be filtered from waste water by their process; however, no guarantees are given that the water will be palatable. In a space station, all urine, washing water, flush water, laundry water and dishwashing water will have to be purified. The report says "Only experimental evidence on real waste waters can show whether, in all cases, unpleasant odour can be removed?~ Rud Madsen and Jasper Thomassen of the Danish company Danisco, Denis Vial of Lyonnaise des Eaux and Roger Binot of the ESA research centre in the Netherlands propose a multistage purifying and recycle system for the Columbus module, due to be launched towards the end of the century. "Kitchen sink" water would first be prefiltered using a purpose built lightweight membrane to remove solids as a "cake". Acidification is also required to kill bacteria, and limit the breakdown of urea into carbon dioxide and ammonia - gases which would pose problems in an enclosed environment. The permeate from the pre-filter - still containing many undesirable substances (detergents, amino acids, salts, sugars etc) - would then be subjected to reverse osmosis. The proposal is that three RO units would be required for Columbus to deal solely with hygiene and washing water. The permeate from the RO units would then be neutralised, oxidised with hydrogen peroxide, and subjected to ultraviolet radiation. Neutralisation with magnesium oxide produces formates and acetates which can be filtered out at high efficiency, up to
.
.
.
.
.
.
.
.
.
.
.
i
Because urea can only be rejected at about 85% efficiency by RO, reverse osmosis is not proposed for dealing with liquid lavatory waste. Rather it will be mixed under acid conditions with the concentrated residues from reverse osmosis and then distilled to recover water as condensate. The concentrated residue from this operation would be stored for collection. The authors stress that even with this level of processing, the system would not be sterile, and a sterilant is also recommended.
Painting by membranes A pipe-shaped ion exchanger has been developed in Japan by Tokuyama Soda Co, to be marketed in the form of a round diaphragm electrode device, mainly for use in electro-deposition in the automotive and metal finishing industries. An ion-exchange membrane within the pipeshaped electrode is both small and lightweight and virtually wrinkle free. Up to now the problems encountered with fiat devices is the size and weight (often 1 or 2 metres in dimension) and the deterioration caused by wrinkling of the membrane over time. The Tokoyama product is light enough that replacement is easy, but the smooth membrane means that paint hardly adheres to it at all. The device can be used in deep painting tanks and is only 60mm in diameter and 1-3 m in length. For electrodeposition of car bodies, the paint compound is dissolved in a neutralizer solution and put in a tank with the electrode device. The paint is then deposited onto the metal by ion exchange. In conventional systems, the electrode device removes surplus neutraliser containing negative ions, and this can result in deterioration of the membrane if the paint adheres to it. Pipe-shaped ion exchanger
i~~."
~'~
~:.~!:~:~::~:~:~:~:~.ff....~i~ii~i!~!~!:!:!:i!!:!~!:~:k*.~:~:~:~:~..
====================================================
~.:}}i}}{i}i}{}i}{i{}i~:{}}}{i}{}}}i{i:j
~
.~
' ' ':'[::~'
~".":.{i:
}i}!i]}{{}}{!:{}i~ i{:
.,i~ii}i!il}!{i:i;i!iii!i{2i!!!i i i!i
98%.
2
Membrane Technology