WO1996038386A1 - Concentration technique - Google Patents

Abstract

In a bio-reactor utilising a floc to form a biomass in a liquid medium, an alternating attached/suspended floc process including a fibre or fibres to the surface of which said floc is attracted and against which the floc is retained; said process further including means to agitate said floc in said liquid medium so as to cause said floc to be dislodged from said surface; said process comprising periodically actuating and deactuating said means to agitate whereby said floc is correspondingly caused to alternate between a suspended and attached state.

Description

CONCENTRATION TECHNIQUE

The present invention relates to concentration techniques applicable to any kind of process where removal or concentration or immobilisation of a suspension or a colloid or a precipitate is desired in a fluid environment; more particularly but not exclusively in a liquid environment. The technique is particularly described in relation to wastewater treatment, but it can be used in several other applications as well, which are described later in this document. BACKGROUND ART

The major application which will be described first is "Upgrading Activated Sludge Wastewater Treatment Systems". This technique applies to both existing plants and the design of new plants. All biological wastewater treatment processes are devices which speed up naturally occurring waste decomposition processes. They do this by controlling the population and environment of active micro organisms.

The most widely used system in biological wastewater treatment is the activated sludge system which is a suspended growth process. It can be described as one of the major process developments in wastewater treatment.

Efficiency of a biological treatment system greatly depends on maintaining the highest possible biomass concentration within the reactor. Of the many factors which limit the maximum concentration of suspended biomass in an activated sludge reactor poor settling characteristics of biomass is the most important. In recent years many researchers have attempted to replace the troublesome settling part of the system with membrane filtration. Using this technique it is possible to achieve higher operating biomass concentrations and hence higher performance, several times that of the original system. Unfortunately membrane filtration is still a high cost process and is hardly used commercially. Growing a great amount of biomass in a fixed film has been attempted by devising rotating biological contactor processes, but because of the significant increase in the complexity of the hardware, such systems are not popular.

In other systems, attempts have been made to grow biomass as a fixed film on a stationary medium in the reactor, in addition to the suspended biomass, in order to intensify the process by increasing the total biomass in the activated sludge reactors. Such hybrid systems provide advantages not only by increasing carbon removal, but also by providing opportunity for nitrification and denitrification as well. This technology is evolving by producing better media to provide greater surface area for growing the biomass to solve clogging problems and to solve handling problems of the media. It is an object of the present invention to provide a technique which improves the efficiency of separation relative to volume of apparatus, and applicable in a number of varying separation / filtration / coagulation environments. SUMMARY OF INVENTION In one broad form of the invention there is provided in a vessel utilising a floe in a fluid medium, an alternating attached/suspended floe process including a fibre or fibres to the surface of which said floe is attracted and against which the floe is retained; said process further including means to agitate said floe in said medium so as to cause said floe to be dislodged from said surface; said process comprising periodically actuating and deactuating said means to agitate whereby said floe is correspondingly caused to alternate between a suspended and attached state.

In a further broad form of the invention, there is provided in a bio-reactor utilising a floe to form a biomass in a liquid medium, an alternating attached/suspended floe process including a fibre or fibres to the surface of which said floe is attracted and against which the floe is retained; said process further including means to agitate said floe in said liquid medium so as to cause said floe to be dislodged from said surface; said process comprising periodically actuating and deactuating said means to agitate whereby said floe is correspondingly caused to alternate between a suspended and attached state. In a particular preferred form said bioreactor is any one of batch type, continuous type or intermittent type and wherein biochemical transformations or synthesis are done using suspended microorganisms, said microorganisms including bacteria, yeasts or fungi or any combination thereof.

Preferably said bioreactor operates any one of aerobic process anoxic process anaerobic process combined aerobic, anoxic and anaerobic processes pond process. In a further form of the invention there is provided a concentration technique comprising the application of alternate immobilisation of particles on or around fibres or like material in the form of floes and mobilisation of the floes back into suspension.

The immobilisation may be carried out with or without chemical enhancement, by transporting / circulating biomass through fibres of any diameter or length, arranged in any feasible way with any distance between each other, in any packing density, with controlled shear stress which is bearable for growing floes to stay stable on or around fibres, by aeration or mixed liquor circulation or mechanical agitation or similar.

Mobilising (suspending) the floe may be carried out alternately with immobilisation at any frequency, by increasing shear stress on the attached floes to an unbearable level, enough to destabilise the attached floes using aeration or gas recirculation or mixed liquor recirculation or mechanical agitation of fluid surrounding the floes or mechanical shaking or vibrating of the fibres, or by using waves like ultrasound or by temperature variation or by changing the chemical nature of the surroundings of floes or any similar action to the above described, which leads to floe detachment, or leaving the floe undisturbed. The particles involved in this process may be microbial biomass or any other kind of suspension or emulsion or colloid or precipitate.

All the biological wastewater treatment systems in use can be categorised under three major groups: suspended-growth, attached-growth, and combinations thereof. The new process is an intermediate between suspended-growth processes and attached-growth processes which uses significant properties of both processes. It may be called an "Alternating Attached/suspended-floc (AASF) process". This AASF process is started as a suspended-growth process. The suspended biomass is then entrapped rapidly on to a stationary medium in the form of natural floes. The most suitable medium is fibres (but other like material may be used). Enough circulation is essential to initiate the attachment and also for the rapid growth of the floes. The formation of attached floes starts within seconds and they grow quickly to form fully grown attached floes. The time taken for the full growth may vary from a few minutes to a few hours, depending on the efficiency of the method or technique used to circulate or transport biomass to the surface of the fibres, biomass concentration, attachment properties of the biomass, strength of the shear forces acting on the growing floes, and diameter, packing density and arrangement of fibres. In fixed film processes, available specific surface area of the medium for biomass to grow on is a critical factor but for the AASF process, diameter, spacing, and total length of fibres are more critical than the available surface area. In fact the AASF process requires much less total surface area of media than an equivalently loaded fixed film process. It is observed that this type of floe formation is enhanced by addition of ferric chloride and calcium hydroxide rnixture. This flocculant mixture is normally used together with suspended biomass in activated sludge systems where Phosphorous removal is done. Although this floe formation occurs to an extent on the surface of any medium, fibres may be the best in structure, holding the growing floes against prevailing shear forces. It was observed that on most other surfaces such floes do not exist, because the floes detach before they grow to maturity. It has been discovered that fibres and like materials provide surface properties which allow for initial attachment and retaining the growing floes.

The fibres may be either natural or synthetic and the length and diameter may vary from material to material or fibre to fibre. Arrangement of fibres has no restrictions; they and can be arranged in any feasible way which provides suitable distance between fibres (which leaves a gap between fully grown floes under operating conditions for effective circulation of liquid phase) and a stable structure to the packing.

This AASF process is very flexible in nature as the attached floes can either be allowed to continue to a long term entrapment or can be detached to get a completely suspended biomass which can be redeposited, depending on the requirement of the application. The resuspended biomass shows comparatively better settling properties than the original suspension.

In one particular form of the invention alternate agitation zones can be provided both in time and space within the one vessel or tank. In particular forms, there must be enough room between the fibres or like materials so that bridging of floes does not occur. In particular forms, a typical distance between fibres might be between

1mm and 100mm, more typically between 1mm and 10mm. Mass efficiency dictates a preference for relatively narrow diameter fibres as the preferred geometry.

BRIEF DESCRIPTION OF DRAWINGS In the drawings :

Fig.l is a schematic of a reactor illustrating the basic steps of immobilisation of biomass on fibres.

Fig.2 is a detailed schematic of a fibre inside a reactor and its surroundings, with respect to the steps of fig.l.

Fig 3 is a side section view of a reactor tank to which the alternative attached / suspended floe process according to a first embodiment of the invention can be applied.

Fig 4 is a side section view of a reactor to which the method of the invention can be applied in an alternating manner separately in various portions of the tank according to a second embodiment of the invention.

Fig 5 illustrates a particular, portable application of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to step A of fig.1 and 2, the reactor is loosely packed with fibres (1). Suspended biomass

(2) in the reactor is transported to the surface of the fibres by internal eddy currents formed due to circulatory action of aeration or gas recirculation or mixed liquor recirculation or mechanical mixing or any other form of such action (3). As seen in step B of fig.1 and 2, transported biomass (2x) then starts to attach to the surface of fibres similarly to the attachment mechanism of filtration processes. Attachment begins with single particles and continues as further particles attach, resulting in rapid formation of floes around the fibre (2y), step C of fig 1 and 2. Size of the floes obviously has a limitation, as attachment and detachment reach equilibrium at the surface of a grown floe (2z). As seen in step D of fig.1 and 2, if the concentration of biomass is not enough to form floes of equilibrium size for the prevailing conditions, the liquid phase will quickly become very clear (4), similar to filtered water. In upgrading existing treatment systems fibre or like material can be arranged inside the existing reactor in any feasible configuration. The described form of floes will be formed on fibres except in the areas subjected to direct impingement of air.

In systems where diffused air is used, aeration may be set to alternate between different sections of the reactor over a certain time interval (as seen in fig.4). This alternating aeration will result in alternating periods of suspension and deposition of the formed floe. Hence the biomass will be alternately suspended and immobilised, giving the opportunity for the floes to experience alternating aerobic conditions (when suspended), and anoxic/anaerobic conditions (when immobilised) offering the possibility of nutrient removal.

In continuous flow systems of this type, a certain amount of suspended biomass will pass through to the settling tank, where they can be settled and recycled to the reactor or wasted out of the system to maintain required sludge age of the system. The concentration of the biomass passing through to the settling tank will be much less than that of actual operating concentration of biomass in the reactor. The biomass concentration passing to the settling tank can be controlled, by adjusting the frequency of alternation of aeration, so that overall performance of the settling tanks is superior to that of conventionally configured activated sludge systems. Compared with traditional fixed film systems, the AASF process requires much less total media and hence much less total volume is occupied by the media, so that the effective volume of a reactor which is upgraded by AASF process will be much higher than that of a reactor upgraded by traditional fixed film processes. AASF process overcomes also the media clogging problem which is inherent with traditional fixed film processes. In addition AASF process holds paniculate or emulsified wastes for a longer time period by entrapping them together with the biomass during alternate floe formation period, allowing them time for proper degradation and allowing them to be used in denitrification as the carbon source. By having these advantages, the AASF process is more cost effective than traditional fixed film processes in at least some applications. Treatment of Special Wastewater:

Treatment of special wastewater which contains problematic substances such as toxins and other non-degradable material is traditionally attempted by using special microorganisms which have special affinity for particular substances. Microorganisms may be a pure culture of a bacteria, yeast or fungi, or a mixed culture. Separation of microorganisms involved is again troublesome. Growing such special microorganisms in a fixed film is also difficult, so that use of the AASF technique will result in higher efficiency in carrying out such special treatment processes. Bioreactors Producing Biochemicals: The AASF technique can be used in bioreactors which produce biochemicals such as enzymes, amino acids, pharmaceuticals, and fermentation products. In traditional bioreactors procedures and problems allied with those procedures are more or less similar to those of treatment of special wastewater, described in the above paragraph. Filtration; Using this technique, a long tank or pipe filled with fibre-like material and suitably aerated or agitated by other means, can be adapted to operate as a high rate continuous tertiary filter (fig 5). Operation time before backwash will be long, as particle holding capacity of this kind of filter is high. Back wash will be easier than with conventional filters.

Furthermore, if a suspended growth aerobic reactor is operated at high biomass concentration, which typically results in poor settling of the biomass, the liquid phase or supernatant can be polished by using this proposed type of filtration.

These filters can be used in separation of non-settleable precipitates from chemical treatment of wastewater; for example chromium in tannery waste can be easily precipitated as its hydroxide, but the settleability of it is not good, so it can be separated by using the said filters. This type of filter can be used in primary treatment of problematic wastes such as wastes from raw rubber factories, and wastes from paint industry. Traditionally simple primary treatment of such wastes is problematic as the contained particles do not either settle or float properly and when filtered they clog the filter by irreversibly sticking to the filter medium. But the filters based on the new technique provide much greater particle holding capacity before clogging and filter medium from the clogged filter would become a by-product of the main industry. MAIN APPLICATIONS

1.) Bioreactor processes generally

The AASF technique can be used in any kind of bioreactors whether batch type or continuous type or intermittent type, or any combination thereof where biochemical transformations or syntheses are done using suspended microorganisms whether bacteria or yeasts or fiingi or any combination thereof.

Bio-reactor processes of wastewater treatment:

According to Metcalf & Eddy (third edition, 1991, pg 378) five major groups of treatment processes are identified and documented as follows; " aerobic processes, anoxic processes, anaerobic processes, combined aerobic, anoxic, and anaerobic process, and pond processes."

In general it can be stated that AASF technique can be used to enhance the efficiency in any of the above mentioned processes by maintaining higher than normal active biomass concentrations in the system, with or without settling section. Although anaerobic treatment is included in the above general statement, it is noteworthy that the AASF technique overcomes several major drawbacks of anaerobic treatment.

In anaerobic treatment, settling is troublesome even with degasification, so that it is desirable to have the biomass in a sort of immobilised form. Traditionally immobilising of the biomass is attempted either by forming and growing it as granules (UASBR), or growing it as a fixed film on a stationary or fluidised medium. But formation of granules or developing a fixed film is not easy, and also usually takes a long time.

In addition when such immobilisation is disturbed due to an operational problem, such as accidental shock load, it again takes a long time to regain the immobilisation.

Transportation of paniculate or emulsified compounds, or those with larger molecules, into the fixed film biomass is a limiting factor to the reactor performance. The invention claimed herein overcomes many of these classic difficulties inherent to anaerobic treatment systems.

As immobilisation of biomass by the new technique is rapid, start up of a reactor with anaerobic immobilised biomass is also rapid. If enough suspended biomass is available, an AASF reactor can be started up and reach its design loading rate in a very short time; possibly the same day. Basically AASF overcomes the typical disadvantage of delay in starting up anaerobic immobilised biomass processes. In case of accidental disturbance of bacterial immobilisation such as by accidental shock load, the biomass of AASF reactors will regain the immobilisation quickly, while conventional reactors take a long time to regain the immobilised biomass.

Transportation of problematic substrates such as paniculate or emulsified compounds, or those with larger molecules, into the biomass is automatically done during the alternate floe formation period, by entrapping such substrates inside the floes together with biomass and hence a more efficient degradation results.

AASF also overcomes clogging problems by providing an opportunity for removal of excess anaerobic biomass (while suspended). Bioreactors producing biochemicals:

AASF technique can be used in bioreactors which produces biochemicals such as enzymes, amino acids, pharmaceuticals, and fermentation products.

2.) Filtration

Using this technique, a long tank or pipe filled with fibre-like material and suitably aerated or agitated by other means, can be adapted to operate as a high rate continuous tertiary filter (fig.5).

Operation time before backwash will be long, as particle holding capacity of this kind of filter is high. Back wash will be easier than with conventional filters.

Furthermore if a suspended growth aerobic reactor is operated at high biomass concentration, which typically results in poor settling of the biomass, the liquid phase or supernatant can be polished by using this proposed type of filtration.

This type of filter can be used in primary treatment of problematic wastes such as wastes from raw rubber factories and wastes from paint industry. Traditionally simple primary treatment of such wastes is problematic as the contained particles does not either settle or float properly and when filtered they clog the filter by sticking to filter medium irreversibly. But the filters based on the new technique provide much greater particle holding capacity before clogging and filter medium from clogged filter would become a byproduct of the main industry.

3.) Chemical synthesis

In chemical synthesis, it is necessary to separate, concentrate and purify end products or intermediate products. In some cases separation is done by precipitating the product. In such cases the new technique described can be used to separate and or concentrate the product.

4.) Sludge concentration

Using the same technique, sludges with poor dewaterability can be concentrated. In this case addition of polyelectrolyte may give enhanced effect. 5.) Cleaning already polluted waterways

This technique can be adapted to clear already polluted waterways, for example, waterways contaminated with bluegreen algae.

A floating device (fig.5) fitted with submerged fibre medium, suitably aerated or agitated by other means, slowly moved or towed, may entrap the algal particles. Addition of polyelectrolyte flocculant in front of the moving device may enhance the entrapment. By covering with a collapsible plastic tank, entrapped algae can be disturbed and pumped out. 6.) Concentrating low grade mineral ores The same technique can be used alone or together with a flocculant to concentrate low grade but high value mineral ores such as colloidal gold or uranium. 7.) Oil and grease removal

Using the same technique it is possible to remove oily or greasy material from water or wastewater, for example, waters polluted with petroleum waste, wastewater from edible oil factories such as oil- palm, wastewater from abattoirs, and wastewater from food processing factories using frying processes.

In conclusion, applications of this technique can be summarised in one sentence; 'This invention can be used in any kind of process where removal or concentration or immobilisation of a suspension or a colloid or a precipitate is necessary or advantageous.' The above describes only some embodiments of the present invention and modifications obvious to those skilled in the art can be made thereto without departing from the scope and spirit of the present invention.

Claims

1. In a bio-reactor utilising a floe to form a biomass in a liquid medium, an alternating attached/suspended floe process including a fibre or fibres to the surface of which said floe is attracted and against which the floe is retained; said process further including means to agitate said floe in said liquid medium so as to cause said floe to be dislodged from said surface; said process comprising periodically actuating and deactuating said means to agitate whereby said floe is correspondingly caused to alternate between a suspended and attached state.

2. The process of claim 1 wherein said bio-reactor is any one of batch type, continuous type or intermittent type and wherein biochemical transformations or synthesis are done using suspended microorganisms, said microorganisms including bacteria, yeasts or fungi or any combination thereof.

3. The process of claim 1 or claim 2 wherein said bio-reactor operates any one of aerobic process anoxic process anaerobic process combined aerobic, anoxic and anaerobic processes pond process.

4. A concentration technique comprising the application of alternate immobilisation of particles on or around fibres or like material in the form of floes and mobilisation of the floes back into suspension.

5. The technique of claim 4 wherein the immobilisation is carried out.

6. The technique of claim 4 or claim 5 wherein mobilising of the floes is carried out by increasing shear stress on the attached floes to a level sufficient to destabilise the attached floes, for example using aeration or gas recirculation or mixed liquor recirculation or mechanical agitation of fluid surrounding the floes or mechanical shaking or vibrating of the fibres

7. The technique of claim 4 or claim 5 wherein mobilising of the floes is carried out by using waves like ultrasound or by temperature variation or by changing the chemical nature of the surroundings of the floe or any similar action to the above described, which leads to floe detachment.

8. The technique of any one of claims 4, 5, 6 or 7 where in the particles are a microbial biomass or any other kind of suspension or emulsion or colloid or precipitate.

9. In a vessel utilising a floe in a fluid medium, an alternating attached/suspended floe process including a fibre or fibres to the surface of which said floe is attracted and against which the floe is retained; said process further including means to agitate said floe in said medium so as to cause said floe to be dislodged from said surface; said process comprising periodically actuating and deactuating said means to agitate whereby said floe is conespondingly caused to alternate between a suspended and attached state.