![[BioMatNet Database - FAIR Program]](../images/Fair.gif) |
FAIR-CT96-3257
Waste water treatment by enhanced operation of separation and improved biological activity |
 |
Proposal No: | FAIR-CT96-3257 |
| Date Prepared: | July 2001, September 1999 | |
| Source: |
Final Report Periodic Report September 1998 |
Source: Final Report September 2000
Consortium: The project was co-ordinated by the Clausthaler Umwelttechnik-Institut GmbH, Clausthal-Zellerfeld (Germany) in partnership with SEPAREM S.p.A., Cossila-Biella (Italy), Slangerup (Denmark), the Department for Industrial Acoustics, Technical University of Denmark, Lyngby (Denmark), Valle Ballina y Fernadez S.A., La Espuncia S/N (Spain) and MELONI VINI s.r.l., Selargius (Italy).
Introduction
Bioreactors have as their main advantages adaptation to specific biochemical reactions and economical operation. They are widely applied in industrial sectors such as the food and pharmaceutical industries, in biotechnology and in municipal waste water treatment processes.
In waste water treatment, biological systems are usually the most cost efficient processes for reducing dissolved biodegradable organic components. The need and potential market for compact, cheaper and efficient process-water treatment systems based on bioreactors, was discovered from a market survey of the industry processing agro-products (especially wine and juice) in southern Europe.
To integrate a biological process-water treatment system into an industrial production system requires stringent safety measures and a stable operating system. The first step to develop such a process-water treatment plant that meets these requirements, was to activate the biomass by improving the solid-liquid interface of the sludge and thus increase the mass transfer rates of gas and nutrients. The concept adopted here was based on recent studies that showed that the use of low energy ultrasound wave irradiation could be used to increase the efficiency of bioreactors.
Activities
The project was carried out through co-operation between four companies and a university, resulting in the development of a new reliable method of biological waste water cleaning. The method, which combined a bioreactor and membrane filtration, enabled direct recycling of process water since the output was germ- free. The process also enables the waste water retention time to be de-coupled from the solids retention time. This has been achieved through use of a suitable membrane that forms the basis for a very safe operation.
As far as the bioreactor is concerned, increased biological activity has been achieved by treating the micro-organisms with ultrasound. To facilitate this the optimal shape for the bioreactor had to be established, as did the best position to connect the ultra-sound (US) transducer to the reactor. After working out the right frequency and power range, the biological plant has been scaled up and evaluated for integration into an industrial process water recycling system. For the membrane filtration, higher flux rates and a lower fouling were achieved by the integration of ultrasound in the membrane system. US-resistant membranes have been selected and integrated in spiral wound modules for industrial use. A finite-element calculation lead to a robust and efficient US-transducer, which has been adapted to the membrane modules in an optimal way.
Progress
In the first year of the project a small-scale ultrasound-bioreactor was developed and tested. The resistance to US of different membranes was tested and calculations were carried out in order to optimise the US-transducers.
In the second year of the project, an ultrasound bioreactor was constructed at pilot scale, designed on the basis of the results of the laboratory tests. This plant consists of a 600 l bioreactor and a separate US-reactor in a by-pass loop. The power and frequencies of the adapted transducers were also selected on the basis of the results of earlier laboratory tests and calculations made using the first phase of the project.
The main achievement of the third year of the project was construction of two different systems of US-spiral wound membrane elements. These systems have been developed in spite of significant difficulties experienced in calculating and constructing of US-tubes. This has led to a delay in and reduction of the demonstration phase. But in spite of this, the performance of these US- filter elements contributed to the success, since the new technology become available just in time to be integrated into industrial US-membrane filtration plants for the technical demonstration phase in combination with end-users.
The results, obtained from this demonstration phase, and the final environmental and economic evaluations of the new combined technology therefore, should be of particular industrial interest.
Achievements
Effect of ultrasound on the bioprocess The first test results with the US-bioreactor at laboratory scale showed a positive influence of the ultrasonic treatment on biological activity. Using fermentation as a model system, an increase in ethanol production by the process treated with ultrasound, over that without ultrasound, was recognisable. This increase in biological activity of the micro-organisms also led to an increase in the biomass concentration in the reactor.
The first test relating to the aerobic decomposition of organic compounds at the technical scale, using wastewater from the juice industry, was carried out initially with the ultrasound transducers switched off as a standard experiment. This was followed by a series of tests in which the power of the ultrasound transducers was varied between 350W and 1000W. During these experiments air was supplied at around 4m3/h. Data was recorded as a function of time at a constant power of ultrasound. The results obtained at 1000W were very different from the others, since the biological activity was strongly inhibited at this US-intensity.
In order to obtain a figure for the optimal power that benefiting the decomposition of waste water, the feed rate was normalised at 20g/l. Results showed that the micro-organisms benefited from an optimum power for the aerobic decomposition of the organic compounds, that lay between 350W and 500W.
Effect of ultrasound on membrane process Membrane material adequate to be used in combination with US has been selected. Methods for preventing fouling were investigated using US in filters, with selected US-resistant NTPS U002 membrane, for separation of biological sludge. This work was carried out using model solutions of pectin with and without the application of US as a function of the operating parameters (pressure, temperature, feed concentration and feed velocity).
The effect of US was positive over a wide whole concentration range. It was concluded from these pre-tests that the positive effect of the application of US on permeate flow rate of the tested NTPS U002 membrane increased at a higher concentration and reaches 44 % at 8 g/l pectin concentration. During membrane filtration experiments at pilot-scale, ultrasound was also shown to have positive effects on wine filtration. The permeate flux increased around 14 % due to the effect of the applied ultrasound. This positive effect of ultrasound on wine filtration rate was lower than that in the case of ultrafiltration of apple juice (38 - 41 %) with the same process parameters. If the process was operated without US, the permeate flow rate immediately decreased by around 25 %. When the US generator was switched on again, the permeate flow rate increased by about 20 %.
The effect of Ultrasound was significantly positive in both cases of wine and apple juice filtration, but the positive effect was higher when filtering apple juice.
Development and optimisation of the US-equipment
A new transducer construction for implementation into the pilot-plants was successfully developed.
Optimisation of the ultrasonic transducer (material, energy loss, transmission of the acoustic waves) and in particular scale-up was based on the Finite- Element methods (FE). This led to a strengthening of the ceramic elements and to an increased lifetime of the transducer. Based upon the results received during laboratory experiments, it was decided to use 25 kHz transducers (TC5003) for adaptation to the bioreactor and membrane filtration pilot- plants. This required 24 transducers in a closed-loop construction to be applied in the pilot-plants.
The development of a new power generator allowed the level of acoustical energy to be increased up to the maximum level permitted by transducer TC5003, at which point the intensity of the ultrasound field was around 1000W (1.7 W/cm2). 'Ibis value was exactly matched to the threshold for ultrasound cavitation, which was optimum in terms of experimental performance.
Evaluation
The evaluation of the results of membrane filtration of wine and apple juice confirmed the conclusions of cost calculations carried out on the basis of the flat membrane tests at SEPAREM with white wine from MELONI. The application of ultrasound does not decrease the operational costs of the membrane separation process when treating wine and apple juice. In each case it was found that the energy saving resulting from the application of ultrasound was less than the energy demand of the ultrasound generator, in each cases.
Concerning waste water treatment from juice industry, the activation of the bioprocess has been investigated and the industrial cost efficiency for the use of US has been calculated and compared with traditional process-water treatment plants. Applying US to the waste water treating plants investigated doubled the biological degradation rate. It was calculated that, in the case of waste water treatment, reactor system optimisation or doubling the volume of the reactor made of concrete should be more efficient, than the integration of US-equipment into the system. Only in some special cases e.g. if the ground for a new building is very expensive or in narrow situated plants, were it would not be possible to enlarge the reactor. Under these circumstances the use of US could be interesting even for waste water treatment plants. The main application of US bio-reactors should be seen in the biotechnology and pharmaceutical industries were the price of the product is high and bio-reactors made of stainless steel are very expensive. In such companies, the US-activation of biomass should give a very significant economical advantage.
Future actions
The results will now examined in terms of possible patent and industrial applications.
Summary
Objectives Based on the well known fact that biological systems usually are the most cost effective processes for reducing dissolved organic components, the general objective is to develop a more compact , efficient and reliable biological treatment system, which allows recycling of germ-free process water.
To integrate a biological process water treatment-system in industrial production, a high level of safety and stability in operation is necessary. A reliable reaction of the cleaning system after production breaks is needed. In addition, the process must be flexible in the case of varying load conditions and require only a small space. Conventional biological processes have to be designed as very large opperations or with a lot of control technology in order to guarantee a constant water quality. Moreover, this process is not germ-free, so that for process water recycling a further wastewater treatment is usually necessary.
Activities A new reliable method of biological cleaning of wastewater is being developed. The method, which combines a bioreactor and membrane filtration, enables direct process water recycling because the outflow is germ-free. Furthermore a decoupling of the waste water delay time from the substrate delay time can be achieved with a suitable membrane, which is a basis for a high safety in operation.
In the case of the bioreactor, an increased biological activity should be achieved by the treatment of the micro-organisms with ultrasound (US). To achieve this, the optimal shape of the bioreactor has to be found, as has the best position to connect the US-transducer to the reactor. After working out the right frequency and power range, the biological pilot plant will be scaled up and evaluated by integration into an industrial process water recycling system.
For the membrane filtration, higher flux rates and a lower fouling are expected by the integration of ultrasound in the membrane system. US resistant membranes have to be selected and integrated in spiral wound modules for industrial use. The FE calculation should lead to a robust and efficient US-transducer, which should be optimal adapted to the membrane modules.
Progress In the first phase of the project a small-scale ultrasound-bioreactor was developed and tested. The resistance to US of different membranes was tested and calculations were done for optimisation of the US-transducers. The developed pre-pilot plant including two bioreactors with US-units and membrane filtration-units were also developed and are availavble for more detailed tests. Three positions where the US-transducers may be fixed onto the membrane-housing have been discussed and are now to being investigated.
Achievements The test results with the bioreactor show a positive influence of the ultrasonic treatment on biological activity. An increase in ethanol production in a biological process treated with ultrasound was seen. This increase in biological activity of microorganisms also leads to an increase in the biomass concentration in the reactor. Membrane material suitable for use in combination with US has been selected. and will be used to manufacture spiral wound filters.
An optimisation of the ultrasonic transducer (material, energy loss, transmission of the acoustic waves) and in particular the scale-up has been evolved with the aid of Finite-Element methods (FE). This should lead to a strengthening of the sensible ceramic elements and to an increased lifetime of the transducer.
Future activities The main potential for optimisation is the enhancement of the biological activity by US-treatment and an improvement in the consistency of the quality of the cleaned waste water with varying waste water input. This process should be combined with the US-resistant spiral wound membrane modul system treated by progressive US-cleaning systems. A subsequent testing phase in industrial companies will verify the applicability and efficiency of this method.
© Copyright 2006 Policy Statements
Updated
by CPL Press:
03/07/2007
- biomatnet@biomatnet.org
 |
 |
 |
News |
 |
Events |
|
|