WO1981002661A1

WO1981002661A1 - Mariculture filtering system

Info

Publication number: WO1981002661A1
Application number: PCT/AU1981/000035
Authority: WO
Inventors: K Lightburn
Original assignee: Aquaculture Int Ltd; K Lightburn
Priority date: 1980-03-26
Filing date: 1981-03-26
Publication date: 1981-10-01
Also published as: EP0048249A1; JPS57500458A; EP0048249A4

Abstract

A biological filtering system for water holding marine creatures having a plurality of separated chambers including biological filter segments in each and being connected in-line by an airlift arrangement providing transfer of water from one segment to the other, with an activated carbon filter in-line and subsequent to a first of the biological filter segments. Bypassing of each segment can be achieved in part or in whole by the height of a dividing barrier between successive segments.

Description

MARICULTURE FILTERING SYSTEM

This invention relates to a mariculture system using recirculation water.

The invention is specifically directed to a filtering system incorporated within such a mariculture system which uses biological filtering.

The problem t'o which this invention is directed relates to providing a more effective filtering than has hitherto been reasonably possible given a limit to cost or to size or to energy expenditure or any one of these.

As an example of the problem, an application for the invention relates to a tank for holding commercial varieties of fish or crustaceans in which the tank holding the water and the filters are one integral unit and are able to be located in a restaurant so that customers may select a fish or crustacean from the tank.

From a commercial point of view, it is essential firstly that the body of water can contain as many fish or crustaceans as possible and further that the filtering while being very efficient nonetheless will not take up an undue space which is considered extremely valuable in a restaurant location. Furthermore, both the cost in providing the equipment and the cost in providing repetitive upkeep must be kept to a minimum and finally the filters must be extremely reliable and furthermore not be subject to sudden breakdown so that an extremely valuable load of fish or crustaceans will not be put at sudden risk especially when the system is not being attended.

This invention therefore is directed toward provision of a mariculture system by which at least one of the above objects can be achieved in a way more effective than has hitherto been the case.

It is to emphasised that while the illustration of the problem has been given with respect to a specific application, clearly the invention is not intended to be limited to this specific application.

According one form of^{^}this invention, this can be said to reside in a mariculture system with re¬ circulating water including biological filters having a plurality of separate chambers, each chamber holding a separate biological filter segment, each chamber having an air lift arranged to effect transfer of water having passed through a first biological filter segment to a next biological filter segment and further arranged so that the water is then passed sequentially through each of the following biological filter segments and subsequent to or comprising- a second in line of the biological filter segments an acti-vated carbon filter. Preferably, the activated carbon filter is used subsequent to a second in-line biological filter segment and in a preferred instance comprises the last in-line of a series of biological filter segments.

The action of biological filters while understood to some extent nonetheless appears to operate in other ways which are not fully understood.

I have found that there is significant value in not only providing for separation of the biological filter into separate chambers and I have found that this promotes specialisation of bacterial action.

I have found that by transferring the water from a first such segment to a second segment by using an air lift ensures substantial oxygenation of the water and therefore promotes the development of aerobic bacteria which are preferred.

By providing this isolation however there has been a discovery that this promotes specialisation of the bacteria handling the conversions and this significantly improves the effectiveness of the bacterial conversion.

The provision of an air lift mechanism not only ensures oxygenation but can be used as the mechanism for transferring the water from one chamber to the next.

This promotes the growth of aerobic bacteria which is considered to be preferable and because of the segmentation of the treatment, the segments become specialised and migration between active portions of the specialist parts of the treatment system become much less inhibitory in the total working of the filter system.

The accidental discovery in relation to this invention is that byproviding a segmented biological filter system especially incorporating air lifts to promote the transfer of water from one segment

,aι_\ activated carbon filter to another and incorporating with this at least after the first segment, and preferably as the last or second to last segment that this gave a very significant and indeed surprising increase in the effectiveness of the filter.

Accordingly, even with the so called in-line segments, a slow flow rate of water through the segments and substantially high oxygenation, all of which significantly improved the effectiveness of the biological filter as a whole, in experimental cases it was found that such effectiveness was not sustainable for an extended period of time in a completely closed mariculture system but only in a partly opened system, that is a system in which a proportion of the water was being continually replaced.

As such a-"partially open system is not suitable in some applications and to be much less preferred in many instances, after significant research and in fact a quite accidental discovery, it was discovered that if a carbon filter be added subsequent to the first biological filter segment, so that the water being treated by the biological filter will also pass through a carboja filter and preferably this at the end of the treatment, this would appear to remove some chemical, the nature of which is not

C-.: known, which appears to have a quite inhibiting effect on bacterial activity or at least inhibits the effectiveness of the bacteria working in the remainder of the filter and a very significant improvement in efficiency is observed.

Moreover this improved efficiency is observable over a longer period than has hitherto been observable in similar filters.

The surprising result therefore has then been that by locating an activated carbon segment within a segmented or plurality of in-line biological filter segments has significantly improved the effectiveness of such a filter system.

The improvement in efficiency is very significant and in a typical example has improved an effectiveness and efficiency of a typical filter by a factor of some twenty times where the previous filter has a similar general size and was of a generally equivalent type.

As an illustration of the effectiveness experienced in a comparable filter in which a carbon filter segment is located as a first in-line segment, the effectiveness of the filter was reduced significantly after in a typical instance twelve days after which it has to be replaced.

In an arrangement of similar biological filtering capacity except that a activated carbon segment is located at the last stage of a segmented and air lift series of filters with three segments and a last being activated carbon, there was still effective operation of the biological filter given a similar handling load on a day to day basis after three months.

Part of this very significant improvement could be by reason of bacterial activity on the actual carbon segments themselves.

As stated previously, the reasons for the quite remarkable increase in efficiency is not known, although it is believed that the carbon filter would appear to remove by adsorption an organic or inorganic compound which does appear to inhibit the growth or activity of bacteria and particularly aerobic bacteria in the biological filter system. This becomes much more important where we have a much greater percentage of aerobic activity possible because of the. in-line filter system where perhaps previously there was a greater percentage of anaerobic bacterial activity.

It is noted that aerobic bacteria activity is to be preferred normally, because it will produce less toxic by-products. Perhaps another reason is that with the separation of the filter segments, there can be a greater degree of specialization.

To explain this further, it is known that perhaps a major activity at the first stage of any biological filter is to convert dissolved ammonia or ammonium compounds into nitrites. Further bacteria then convert the nitrites into nitrates and other by-products but the nitrite to nitrate conversion is inhibited so long as there is any significant level of ammonium compounds. It would seem therefore that the breaking

C:.; of the filtering into segments promotes this specialization perhaps keeping more separate the water with the ammonium compounds from the second or further segments where such compounds are either - less concentrated or negligibly in existence.

The conversion of the ammonium compounds to nitrites and then the conversion of these nitrites to nitrates taking place at the first filter segments then results in water having the more toxic compounds being largely removed and it is then perhaps appropriate when both these compounds and most suspended particles have been removed from the water. This therefore ensures that the carbon filter will be more efficiently used in the specialized removal of such organic compound that perhaps are causing the inhibition.

However, it would appear that provided there is a carbon filter effect, then this will significantly remove the inhibiting compounds and while it is more efficient at the end of the line segments of filter, nonetheless it would not appear to be essentially located in this location as more frequent replacement of the carbon in other locations will suffice.

According to a further form of this invention although this need not necessarily be the case, there is proposed a filter arrangement for filtering of waste including dissolved organic waste as well as suspended solids within a body of water resulting from fish or crustaceans retained within an enclosed body of water, the filter including at least two filter segments with at least part of each segment being adapted by reason of biological activity to break down ammonia, nitrites, nitrates and other organic compounds in the water and with the upper

c. r?ι 8 .

portion of the first segment or both segments or alternatively an additional prior segment being adapted to separate particles within the water.

In another form of this invention, although this also need not necessarily be the case, a portio of the first segment or alternatively an additional prior segment, is so arranged that there is a high flow rate through it and the remaining portions of the filter have a low flow rate through it.

The problem to which this invention and subseque features which will afterwards be described face, Is the difficulty of providing at minimal cost and preferably in a minimal volume a safe and effective filtration system for water in which fish or crustace at high density might survive for an extended period of time.

A number of problems exist which make it very difficult to provide a very safe filtering system for the purposes described which can at the same time be very economical in manufacture and servicing and at the same time be safe or at least provide with simple detection means adequate warning that some problem exists that may threaten the lives of the creatures within the water mass.

The first problem that has been referred to in general terms in relation to the answer given thus far, is the difficulty that In relation to biological removal of some of the organic compounds dissolved within the water, it is necessary to use biological filtering which of c_ ιrse means that a biological micro-flora will be necessary to take up compounds for biological purposes from the water as it passes any particular location.

It is also a necessary feature that there be means to provide some buffering to the water and this is achieved by providing calcareous dolomite or the like which will be slowly dissolved away providing the necessary return to a satisfactory level of alkalinity.

Agglutination and other effects cause an accumulation of detritus among the filter particles which, in combination with the micro-flora, reduces available sites for the calcareous material to dissolve and provide a necessary buffering effect.

Consequently, to maintain a limit to the detritus build up and thus to cause a sufficient buffering effect, it is essential we have discovered, that a selected flow rate exists past any such calcareous material.

In other words, by ensuring a flow rate over a given area of gravity held filtering material of the type described, this has a significant effect on keeping detritus cleared and at the same time providing adequate exposure of the liquid to the alkalinity providing calcareous gravel or like material.

The difficulty however, is that such conditions in relation to the water as compared to the filtering material are not beneficial to all of the biological actions of the filter.

From the point of view of economy of manufacture, and from a space point of view, it is considered to be of significant value to have separate filtering functions kept within one general container. This is not to say that they cannot be kept separate within the container but insofar that they are functiona blocks held together rather than separate blocks is the point made.

Accordingly there is provided the arrangement in which the flow of water In which the creatures such as fish or crustaceans are being held is supplied into the filtering apparatus and is first directed into a filter arranged to remove larger particles and to also provide by reason of some particle chemical activation with an alkaline agent such as calcareous gravel a buffering effect and perhaps but not necessaril also containing a carbon filter portion, this arrangemen being that a significant proportion- of the water first fed into this first filter is then returned directly into the body of water holding the edible creatures.

The remainder of the water is then fed into a series of biological filters.

A significant quantity of undissolved pieces will exist or precipitate out of the water in the first instance and it has been found firstly that it is an important feature that this material be removed but if a conventional filter Is used such as filter wool (Acrylic fibre) and or randomly sized and shaped particles within a gravity held mass, then there is a build-up which at first interferes and eventually will block the mechanical filtering action.

Q:. One of the significant problems with a filter especially when this is outside of the main body of the tank holding the creatures, is that if this fails for any reason for instance blocks, the fish or other creatures within the main body of water are in a life or death threatening situation.

In situations where very valuable animals, for instance a quantity of valuable fish or crustaceans are being held, this provides a significant problem.

According to a further feature of this Invention then, we have discovered that if we place two filters in-line and then provide that in the event of one of these filters blocking, or becoming ineffective, then especially in relation to the first in-line the water will continue to pass through the second of the filters while of course effecting a suitable alarm as necessary.

The point of this then is that there are at least two and in practice more than two filter segments in-line and each of the earlier filters in the line are arranged so that if there is a significant back-up pressure increase, then the water by reason of the arrangement will rise and effectively commence to and eventually fully by-pass the filter, but continue to be passed^"through the continuing other filters.

The result of this is that while a warning is effected that one of the filter segments is not active or not working, nonetheless, the position is no longer a life threatening problem and significant time can elapse such as many hours before any recovery situation is essential. While such an arrangement as has been described can be achieved in many mechanical ways, there has been achieved one very simple and in practice very effective way achieving this which does not require substantial mechanical parts and which therefore is not prone to a high degree of possible mechanical breakdown.

As a side discovery to the arrangement described, that is, of making the biological filter portion as two or more separate functional blocks in the arrangement described, there is the advantage especially by reducing the cross-sectional area of each as shown to provide significant improvement in the efficiency of the biological filter.

There are certain physical limitations to the way in which a biological filter can be arranged and insofar that the water must be kept flowing through these, there Is a general limitation to the height or depth to which a filter bed will be effective and insofar that there is a preferred flow rate per square foot of cross-sectional area then it is found that the higher retention time possible from segmenting the biological filter has effected a significant increase in efficiency of the filter over all.

That is to say, by having a biological filtering mass that is broken into segments so that the segments form biological filters in-line or in series that is the water flows in one and out of this into the next and out of this into the next in turn, has significantly improved the efficiency of the same mass as has hitherto been found feasible. 14.

Preferably, there are at least two such segments each containing particulate materials providing support for biologically active bacteria, the last in-line of the segments comprising or consisting of in the main activated carbon.

In a more generalized description of the features, it is to be noted that each chamber holding a biological filter segment is so arranged that if the water is being supplied into the chamber at a rate faster than that at which it is being extracted, it is arranged that the water level upon rising within the chamber may rise to an overflow level from whence it can bypass the said biological filter segment to a next in-line biological filter segment.

For a better understanding of this invention it will now be described in relation to a preferred embodiment which shall be described with the assistance of drawings In which:

FIG 1 illustrates in very simple form a flow diagram in a preferred Instance for a preferred filter system incorporating both a biological and mechanical filter,

FIG 2 is a side part cut-away of an arrangement according to a preferred embodiment incorporating the invention and

FIG 3 is a side elevation showing in more detail with the biological materials removed the holding structure for the filter once again according to the preferred embodiment. 13 .

Not only therefore is there provided a very safe means by which if the overflows of one segment are caused to flow into, the next upon blockage of that segment, but at the same time there appears to be a significant improvement in the efficiency of the system overall where the segments are biological filters.

It has been found to be of advantage in. an overall filter system to also provide a carbon absorbent also in-line and arranged so that the carbon can from time to time upon completion of its life, be removed and replaced with further carbon.

In a further form of this invention this can be said to reside in a mariculture system with re¬ circulating water including a tank with water therein holding aquatic creatures, and a filter for treatment of the water including a primary filter and a secondary filter, the primary filter being arranged to effect a mechanical filtering of the water, and being arranged so that a proportion of the water issuing from the said primary filter is directed into the secondary filter which comprises a biological filter constituted by a plurality of separate biologically active segments kept separate by being in separate chambers, the water being drawn through each In sequence by an air lift In each drawing water from an underneath of a first said segment to an upper part of a second said segment thereby transferring as well as aerating the water, and at or subsequent to a second sequentially in-line segment, an activated carbon filter, and overflow means providing for an overflow from any segment but the last in line to allow water being limited in flow through a segment to bypass the segment to a next in-line segment.

c::FI In this preferred instance of a filter arrangement, this of course is arranged to be coupled and is in an operative connection with respect to a body of water holding a significant loading of fish or Crustacea.

Accordingly, the filter described is intended therefore to effectively filter biological products existing in the water from the creatures so as to maintain these in a live and healthy state free of off flavours.

The filter is therefore arranged to take water from the water mass and direct this into the filter container 1, which has a first segment 2 including a significant area having therein filtering materials such as filter wool and below which are smaller rocks and other filtering agents that is particulate materials of random shape held under gravity upon a screen base 3 and including a significant proportion of calcareous dolomite.

Flow rate of water is such as to first provide rapid mechanical filtration, of the fish tank water and also to provide sufficient conversion of the calcareous material to maintain the buffering of the water and at the same time to cause sufficient removal of the detritus from time to time so as to keep the surfaces of the calcareous material exposed to the water flow. A proportion of this water, after it has been filtered in this first stage and approximately one third of the volume so filtered is then passed into the first of the biological filters 4 which in the preferred instance is in the lower portion of the first segment approximately one square foot in area and approximately four feet in depth and includes a number of rocks of a generally inert or again calcareous material held in gravity containment and adapted to provide firstly for a build-up of detritus between the adjacent faces of the rocks and at the same time to provide an adequate base for flora build-up of appropriate active bacteria.

In the preferred instance there are four such segments in-line noted as 5, 6, 7 and 4, that It is in the sense of a water connection and each is arranged with a conduit 8 passing up through the rocks with a screen base 9 and transfer of the water is effected by the passing of air at significant pressure from below the base into the conduit passing up between the rocks.

The second 5, third, 6, and fourth, 7, segments are of approximately one third of a square foot in area and four feet in depth.

In relation to this particular preferred arrange¬ ment, the height of the walls 10 defining the segment are such that when water overflows from the first, it will flow over the wall separating the first segment from the second segment and likewise the wall separating the second segment from the third segment is lower than that separating the first from the second and the wall separating the third from the fourth is lower again. These collectively are lower than the other walls limiting the water from the segment access to other parts of the filter and hence there is a very easily achieved overflow safeguard that if water from one of the segments is not passing through the segment then the water will automatically overflow into the next segment and hence without any difficulty, there is provided a-very safe and indeed a very cheap safety arrangement.

The arrangement of an overflow safeguard is of course the simplest of all methods and this can be achieved in other ways that is insofar that there is any unusual build-up of back pressure in the filter, then this will cause an overflow by passing that filter to some extent or perhaps finally to a total extent but the overflow then will pass to the next filter segment thereby as previously explained, not causing a life threatening situation to the creatures held -in the general water mass. In the fourth segment there is then provided a pack of carbon 11 and once again the water is drawn from above to below the carbon mass and caused to separate from this to the inert or calcareous material below 12 by an air lift 13 which then directs the water back to the main tank 14 holding the creatures

The upper portion of the first segment although designed to mechanically filter and buffer the water, also has a biological filtration effect. Separating the biological filter into four separate segments has achieved a significant improvement in efficiency of the biological activity possible.

By providing that each of the filters is arranged as a vertically orientated segment or effectively vertical segment and that there are vertical conduits with air lifts within each segment then, by providing the overflow so that if one is blocked, then when there is a water level rise with the resultant effective overflow as suggested into the next succeeding segment.

The arrangement of the filter bank or collection of segments at one end or side of the fish holding tank rather than under it, allows deeper and therefore more effective filter segments to be constructed whilst still allowing access and service to the top and it also allows the standard filter bank thus constructed to be attached to fish tanks of various sizes and shapes and can also be physically separated from it, provided the water is carried between the filter bank and the fish tank. Also provided is an airlift manifold 15 providing for the plurality of air at pressure conduit 16 which are inserted into each of the conduits providing for air to be introduced at a bottom of each of the conduits 8 for effective causation of the airlift effect.

The word "mariculture" throughout this specifi¬ cation is used to describe both a salt water and a fresh water system.

Claims

The claims defining this invention are as follows:-

1. A mariculture system with recirculation of water including a biological filter having a plurality of separate chambers, each chamber holding a separate biological filter segment, each chamber having an airlift arranged to effect transfer of water having passed through a first biological filter segment to a next biological filter segment and further arranged so that the water is passed sequentially through each of the biological filter segments, and subsequent to a first of the said biological filter segments an activated carbon filter.

2. A mariculture system with recirculating water including a tank with water contained therein for holding aquatic creatures, and a filter for treatment of the water including a primary filter and a secondary filter, the primary filter being arranged to effect a mechanical filtering of the water, and being arranged so that a proportion of the water issuing from the said primary filtering means is directed into a secondary filter which comprises a biological filter constituted by a plurality of separate biologically active segments kept separate by being kept in separate chambers, the water being drawn through each in sequence by an airlift, in each case drawing water from an underneath of a first of the segments to an upper part of the second of the segments thereby transferring as well as aerating the water and at or subsequent to a second sequentially located segment, an activated carbon filter and overflow means providing for an overflow from any segment but the last in-line whereby to allow water to pass from a forward in line to a subsequent in-line segment.

U -

3. A mariculture system with recirculating water as in Claim 2 further characterised in that there are at least four separate biologically active segments, each containing particulate materials providing support for biologically active bacteria for the purposes described and wherein a last or second to last of the segments comprises or consists of in the main activated carbon.

4. A mariculture system with recirculating water substantially as described in the specification with reference to and as illustrated by the accompanying drawings.

O PI