Technical Field

[0001] The present invention relates to methods for remediating stored liquid wastes under anaerobic conditions. In some forms, the present invention relates to methods for remediating holding lagoons containing industrial wastewaters produced by alumina refineries.

Background Art

[0002] The Bayer Process, invented by Carl Josef Bayer in 1887, has become the primary industrial method to produce aluminium oxide (AI2O3) from bauxite ore. The Bayer Process starts with the bauxite ore being crushed, washed and then dried. Post drying, the crushed ore is dissolved in caustic soda at high temperature and then filtered to remove impurities.

[0003] The resultant sodium aluminate (NaAl(OH) ₄ ) solution is transferred into a precipitator tank where aluminium hydroxide (Al(OH) ₃ ) seeds stimulate the formation of aluminium hydroxide crystals as the hot solution cools down. The aluminium hydroxide crystals collect at the bottom of the precipitator tank where they are removed. The crystals are washed to ensure the complete removal of any residual caustic soda. Lastly, the aluminium oxide product is obtained by heating the aluminium hydroxide at very high temperatures.

[0004] Bauxite ore typically contains high levels of organic material. During the high temperature caustic soda dissolution of the ore, this complex organic material is broken down into smaller and simpler compounds. These compounds include sodium oxalate (Na ₂ C ₂ 0 ₄ ) and sodium salts of succinic, oxalic and acetic acids, with sodium oxalate being the most prevalent. The compounds listed above are considered impurities that must be removed in order to avoid diminishing the quality of the product and disrupting process operations.

[0005] To prevent the production of low grade aluminium oxide, the impurities are typically precipitated out of the Bayer process stream as part of an oxalate cake. The cake can then either be thermally destroyed or stored in a holding lagoon/storage facility for further specialised treatment.

[0006] Destruction of the oxalate cake using thermal methods has, however, shown to be very costly and environmentally unacceptable. Oxalate has the potential to be treated biologically, through both aerobic and anaerobic pathways. Aerobic bioreactor treatment plants have been utilised by industry to treat separated dissolved oxalate waste streams, but have experienced many challenges, including the frequent breakdown of mechanical components due to deposition of aluminium hydrate particles, destruction of sealing of pumps, accumulation of aluminium hydrates and other material in the mechanical diffusers and aerators, deposition of aluminium hydrate on the reactor floor which requires extensive maintenance for removal, and dealing with aluminium hydrate rich biomass. These limitations prohibit the widespread use of aerobic pathway for oxalate degradation from alumina refineries. Anaerobic biodegradation has been used to treat some types of wastewaters, but the characteristics of the wastewater in storage lagoons containing oxalate are too harsh for biological activity, primarily because of their high (typically >13) pH.

[0007] Indeed, due to the specialist treatments required to remediate oxalate containing effluent, and the problems associated with such treatments, large quantities of the separated oxalate cake have been stockpiled by alumina refineries throughout Australia and elsewhere in holding lagoons.

Summary of Invention

[0008] In a first aspect, the present invention provides a method for remediating a stored liquid waste by reducing a content of a species capable of being bacterially degraded under anaerobic conditions, the stored liquid waste having bulk properties incompatible with anaerobic biodegradation. The method comprises the steps (a) and (b) set out below, which are repeated until the stored liquid waste has bulk properties compatible with anaerobic biodegradation and contains an amount of the microorganism effective to sustain biodegradation of the species in the stored liquid waste:

(a) removing an aliquot of the liquid waste and treating the aliquot by exposing to

conditions whereby the species is anaerobically biodegraded by a microorganism capable of biodegrading the species; and

(b) returning the treated aliquot back to the stored liquid waste, whereby the bulk

properties of the stored liquid waste become more conducive to anaerobic biodegradation.

[0009] The present invention can advantageously be used to remediate many stored liquid wastes, including oxalate-containing wastes. The invention thus provides a solution to the problem of legacy oxalate-containing storage lagoons at alumina refineries, and potentially for a range of other metallurgical and mineral processing industries. As noted above, oxalate is a by product of processing organic rich ores that reduces the quality of the mineral product produced, and the Bayer Process is a key example where oxalate management is a significant economic and environmental consideration. To the best of the inventor’s knowledge, no process currently exists for treating oxalate cake/liquor under storage conditions within a holding lagoon/storage facility. The present invention therefore provides a novel anaerobic treatment solution that enables treatment of oxalate wastewater within a holding lagoon, particularly in the case of legacy wastewater which is difficult to treat using conventional methods due to its bulk properties being wholly incompatible with existing treatment methods.

[0010] To enable biological treatment of a species three fundamental conditions must be met:

1. a population of bacteria in sufficient concentration that can utilise the species to mediate biological reactions;

2. the correct pH and temperature range for that bacteria to survive and operate; and

3. sufficient nutrients and trace elements to ensure cell function.

[0011] The present invention works by treating aliquots taken from the stored liquid waste and releasing the treated aliquots back into the stored liquid waste, gradually fulfilling the conditions required to enable anaerobic biodegradation of the species within the stored liquid waste. The conditions to which the relatively small aliquots are exposed can be controlled independent of the main body of stored liquid waste. Adjusting these conditions to effectively treat the aliquot is far more manageable when treating the aliquot than for the bulk waste.

[0012] In some embodiments, the stored liquid waste may be a legacy waste from an industrial process. In some embodiments, the stored a liquid waste may be a holding lagoon containing industrial waste. In some embodiments, the stored liquid waste may be a legacy waste from an alumina refinery, as described above, although it is to be appreciated that the present invention had broader applicability than just remediating oxalate-containing effluent produced via the Bayer Process.

[0013] In some embodiments, the stored liquid waste may have a pH incompatible with anaerobic biodegradation. The pH of the stored a liquid waste may, for example, have a pH of 12 or greater. Very few microorganisms are capable of surviving such high pH and direct addition of the microorganism into the lagoon would therefore not be effective.

[0014] In embodiments of the present invention in which the species capable of being bacterially degraded under anaerobic conditions is oxalate, the microorganism capable of biodegrading the oxalate may comprise Oxalobacter formigenes . In some embodiments, the microorganism capable of biodegrading the oxalate (or other species, in embodiments where the stored liquid waste does not contain oxalate) may further comprise (or comprise only) bacterial species obtained from an environmental source close to the stored liquid waste (e.g. a microorganism that has developed in an existing anaerobic bioreactor or which has naturally developed).

[0015] In some embodiments, the aliquot may be taken from close to the bottom of the stored liquid waste, where the oxalate concentration is likely to be relatively high.

[0016] In some embodiments, the aliquot may be diluted before being exposed to the conditions whereby the species is anaerobically biodegraded. Such dilution may result in the species within the aliquot being more susceptible to biodegradation. In such embodiments, the aliquot may be diluted with liquid taken from close to the surface of the stored liquid waste or with effluent from another source of wastewater. Such water is less likely to be as contaminated as that located deeper in the stored liquid waste.

[0017] In some embodiments, once the stored liquid waste has bulk properties compatible with anaerobic biodegradation, then it can be used to degrade the species without the need for continual aliquots to be taken (or such aliquots may be taken less frequently). In effect, the stored liquid waste becomes“self-sustaining”, in that it has bulk conditions (e.g. pH and a biomass) capable of sustaining biodegradation of the species. Once such conditions are reached, the present invention may further comprise adding additional components, such as additional microorganisms and/or additional nutrients for the microorganisms in order to further increase the biomass in the stored liquid waste. The present invention may further comprise adding additional liquid waste that contains the species for remediation (i.e. a storage lagoon can itself, once in the appropriate condition, be used to biodegrade fresh oxalate, for example).

[0018] In some embodiments, the stored liquid waste may be partitioned before the first aliquot of the liquid waste is removed and treated. Such partitioning would define a smaller volume of the stored liquid for remediation, which may be beneficial in circumstances where the stored liquid waste is of a volume or has conditions especially incompatible with anaerobic

biodegradation. The stored liquid waste may, for example, by partitioned by physically isolating a portion of the stored liquid waste from the remainder of the stored liquid waste.

[0019] In such embodiments, once the partitioned stored liquid waste has bulk properties compatible with anaerobic biodegradation (when it may also contain an amount of the microorganism which is capable of sustaining biodegradation of the species), the partition may be moved to increase the portion of the stored liquid waste that is partitioned. As will be described in further detail below, such embodiments may facilitate a faster overall remediation of the stored liquid waste). [0020] In some embodiments, the method of the present invention may further comprise separating substances from the treated aliquot (or indeed, the stored liquid waste, e.g. produced as its bulk properties change) for beneficial reuse. For example, methane gas and carbonate produced when treating the aliquot may be collected for beneficial reuse (e.g. for generating electricity or heat, or for resale). In some embodiments, the method of the present invention may further comprise separating substances from the treated aliquot which may adversely affect downstream processes. For example, species that precipitate during treatment of the aliquot may be separated for further treatment or disposal.

[0021] Other aspects, features and advantages of the present invention will be described below.

Brief Description of Drawings

[0022] Embodiments of the present invention will be described in further detail below with reference to the following drawings, in which:

[0023] Figure 1 is a flowchart depicting a method in accordance with an embodiment of the present invention;

[0024] Figure 2 shows a side view of bioreactors for use in an embodiment of the present invention;

[0025] Figure 3 shows a plan view of a lagoon and bioreactors for use in an embodiment of the present invention;

[0026] Figure 4 shows a side view of a lagoon and bioreactors for use in an embodiment of the present invention;

[0027] Figure 5 shows a cross sectional schematic of an oxalate treatment bioreactor for use in an embodiment of the present invention;

[0028] Figure 6 shows a simplified cross sectional schematic of a bioreactor for use in an embodiment of the present invention;

[0029] Figure 7 depicts the aliquot inlets and treated aliquot outlet in a lagoon in accordance with an embodiment of the present invention;

[0030] Figure 8 shows a plan view of a lagoon, balance tank and bioreactors for use in another embodiment of the present invention;

[0031] Figure 9 depicts a progressive treatment of a lagoon using an engineered barrier to partition the lagoon; [0032] Figure 10 is a graph showing the results of modelling of the pH of a partitioned portion of a lagoon as a function of time during operation of an embodiment of the present invention; and

[0033] Figure 11 is a graph showing the results of modelling of the pH of the lagoon (as an indicator of the lagoon’s remediation) as a function of time during operation of an embodiment of the present invention

Detailed Description of the Invention

[0034] The overarching purpose of the present invention is to remediate a stored liquid waste under anaerobic biodegradation conditions (which do not suffer from the disadvantages of aerobic digestion, discussed above, or the environmental cost of thermal methods of destruction), despite the stored liquid waste having bulk properties that are (at least initially) incompatible with anaerobic biodegradation. In specific embodiments, the present invention may

advantageously be used to enable treatment of legacy oxalate-containing wastewater in storage lagoons by facilitating the controlled introduction of seed oxalate consuming bacteria to the lagoon, and systematically lowering the pH of the lagoon to a level that is conducive to a continuous biological oxalate degradation within the lagoon via the effluent of a number of separately maintained bioreactors.

[0035] The present invention thus provides a method for remediating a stored liquid waste by reducing a content of a species capable of being bacterially degraded under anaerobic conditions, the stored liquid waste having bulk properties incompatible with anaerobic biodegradation. The method comprises the steps (a) and (b) set out below, which are repeated until the stored liquid waste has bulk properties compatible with anaerobic biodegradation and contains an amount of a microorganism effective to sustain biodegradation of the species in the stored liquid waste:

(a) removing an aliquot of the liquid waste and treating the aliquot by exposing to

conditions whereby the species is anaerobically biodegraded by the microorganism capable of biodegrading the species; and

(b) returning the treated aliquot back to the stored liquid waste, whereby the bulk

properties of the stored liquid waste become more conducive to anaerobic biodegradation.

[0036] The method of the present invention may be used to remediate any stored liquid waste containing species capable of being bacterially degraded under anaerobic conditions, but which cannot presently be bacterially degraded because the stored liquid waste has bulk properties incompatible with anaerobic biodegradation. Whilst described herein primarily in the context of treating oxalate-containing wastewater from alumina refineries, it is within the ability of a person skilled in the art, based on the teachings contained herein and using routine trial and

experimentation, to determine whether the invention is effective to remediate any given stored liquid waste.

[0037] Typically, the stored liquid waste is a legacy waste from an industrial process. The stored liquid waste may, for example, present in the form of a holding lagoon or pond containing a significant volume of industrial waste, and which may have been held for some time.

[0038] As will be appreciated by persons skilled in the art, stored liquid wastes from sources such as industrial processes will likely be a complex mixture of chemical species, with those species being present in both solid and liquid forms. It is to be understood in the context of the present invention that the phrase“stored liquid waste” does not necessitate that the waste material in need of remediation be a solution containing only dissolved species and containing only the species capable of being bacterially degraded under anaerobic conditions. Indeed, the stored liquid waste for remediation using the method of the present invention may contain significant amounts of non-dissolved and dissolved species in addition to the species capable of being bacterially degraded under anaerobic conditions, provided that those other substances do not adversely affect operation of the method.

[0039] It is also to be understood that, in the context of the present invention, the term “remediation” does not mean that all of the species present in the stored liquid waste necessarily needs to be biodegraded in order for the method to have been completed. Provided that the stored liquid waste has a content of the species the same as or lower than that expected of a remediated waste by the relevant industry, the present invention is to be deemed as having run to completion.

[0040] As will also be appreciated by persons skilled in the art, stored liquid wastes can often become stratified, with different portions (usually depths) of the liquid having slightly different chemical and physical properties. As used herein, the phrase“bulk properties” is to be understood to mean the properties of the majority of the stored liquid waste, accepting that properties at other parts of the stored liquid waste may differ slightly.

[0041] In embodiments described in more detail below, the stored liquid waste may, for example, be a legacy waste from an alumina refinery, containing oxalate formed during the Bayer Process, as described above. The present invention will be described below primarily in this context, but it will be appreciated that the invention has broader applicability than just remediating legacy oxalate-containing effluent produced via the Bayer Process. For example, with appropriate adaptation, the present invention may be useful in treating fresh oxalate waste generated by an alumina refinery, oxalate wastes from rare earth minerals, as well as from other carbon-rich waste streams emanating from mineral processing plants.

[0042] Any property of the stored liquid waste may render its bulk properties incompatible with anaerobic biodegradation. For example, microorganisms can be sensitive to pH, and will not survive at extremes of pH, as may be found, for example, in highly acidic or highly alkaline effluent. In such embodiments therefore, the stored liquid waste may have a pH incompatible with anaerobic biodegradation. The bulk pH of the stored liquid may, for example, be above about 12 or below about 4, where microorganisms either cannot survive or cannot survive to such an extent that they can anaerobically digest a sufficient quantity of the species effective to provide remediation.

[0043] Other properties of the stored liquid waste that may render its bulk properties incompatible with anaerobic biodegradation include nutrient content, stratification, salinity, temperature and/or the presence of contaminants that adversely affect anaerobic bacteria (e.g. waxes, ammonia and oxygen).

[0044] The method of the present invention remediates a stored liquid waste by reducing the amount of a species capable of being bacterially degraded under anaerobic conditions. The species may be any species that is capable of being bacterially degraded under anaerobic conditions, and which a reduction in the quantity of in the stored liquid waste would be considered to be a remediation of the liquid.

[0045] In the embodiments described in further detail below, the species capable of being bacterially degraded under anaerobic conditions is oxalate, a well-known and problematic by product of the alumina industry (and other industries). In other embodiments, however, the method of the present invention may be used to remediate stored liquid wastes containing other appropriate species.

[0046] The microorganism capable of anaerobically biodegrading the species may be any microorganism that is effective to biodegrade the relevant species under the relevant conditions. Suitable microorganisms may be specifically cultured for a given purpose, or may be obtained from natural sources (e.g. microorganisms within or close to the stored liquid waste may naturally have become adapted to biodegrade the species). Typically, the microorganism would be specific to a particular species, although the same microorganism may be capable of biodegrading a number of species, to a greater or lesser extent. [0047] In embodiments where the contaminant species is oxalate, for example, the microorganism may comprise Oxalobacter formigenes . In some embodiments, the oxalate consuming bacteria may include Oxalobacter formigenes amongst other species native to the local environment.

[0048] The aliquot of the liquid waste for treating may be removed at any location (or locations) of the stored liquid waste. The aliquot may, for example, be taken from close to the bottom of the stored liquid waste, as this is where the concentration of species such as oxalate is likely to be at its highest. Care would need to be taken, however, not to draw the aliquot from a location where significant amounts of sediment incompatible with the treatment process or with the apparatus used in the treatment process may be present.

[0049] The aliquot may be pumped into and subsequently treated in a bioreactor or bioreactors, typically located adjacent to the stored liquid waste in order to minimise energy requirements and to contain the waste. Specific bioreactors suitable for this purpose will be described below, and it is within the ability of persons skilled in the art to design bioreactors appropriate for use in the method of the present invention.

[0050] The aliquot may be treated as is, or may be pre-treated before, during or after being introduced into the bioreactor (in such embodiments) in order to make it more conducive to anaerobic biodegradation. The aliquot may, for example, be diluted before being exposed to the conditions whereby the species is anaerobically biodegraded by the microorganism capable of biodegrading the species. Such dilution may, for example, have the effect of lowering the pH (i.e. compared to that of the stored liquid waste from which the aliquot was drawn) or reducing the concentration of the species in the aliquot, both of which may help to enhance anaerobic biodegradation.

[0051] Where such dilution takes place, the aliquot may be diluted with any suitable liquid, including with liquid taken from close to the surface of the stored liquid waste (which is likely to be relatively less contaminated) or with effluent from another source of wastewater (e.g. cooling towers, or the like, used elsewhere on site).

[0052] The volume of the aliquot taken for treatment will depend on factors such as the total volume of the stored liquid waste requiring remediation and the available time to affect remediation, the types of species it contains, its pH and other physical characteristics, as well as the biodegradation capacity of the method (e.g. the number and capacity of bioreactors that are available and the biodegradation efficiency of the microorganism). Each aliquot may, for example, have a volume of between about 10 to l,000m ³ , e.g. between about 50 to 800m ³ between about 100 to 600m ³ between about 200 to 500m ³ between about 250 to 400m ³ .

[0053] Similarly, the frequency at which the aliquots are taken will depend on factors such as those described above. The aliquot of the liquid waste will be deemed to be sufficiently treated after exposure to the conditions whereby the species is anaerobically biodegraded to a degree when the treated aliquot (i.e. for returning to the lagoon) will affect the bulk properties of the stored liquid waste such that it become more conducive to anaerobic biodegradation (even if only very slightly, as would be the case at the start of the process). In some embodiments, for example, the aliquot may be treated for between about 1 and 10 days before being returned to the stored liquid waste.

[0054] The treated aliquot may, for example, have a pH of between about 8-11 (e.g. a pH of about 10). This pH should be lower than that of the stored liquid waste such that there is a corresponding reduction in the bulk pH of the stored liquid waste. Although the effect of adding a relatively small volume having a lower pH that that of the stored liquid waste may not be immediate, the cumulative effects of adding multiple treated aliquots would, over time, cause the pH of the stored liquid waste to itself reduce, whereupon it becomes more conducive to sustaining anaerobic biodegradation.

[0055] In embodiments where an oxalate-containing stored liquid waste is being remediated, for example, the treated aliquot would comprise carbonate species and at least a small amount of a biomass comprising the microorganism. Repeated additions of such to the stored liquid waste will eventually beneficially affect its bulk properties whereby biodegradation of the oxalate- containing stored liquid waste may become self-sustaining.

[0056] The conditions at which the aliquot is treated (e.g. inside the bioreactors) may be any conditions effective to promote microbial activity and corresponding anaerobic biodegradation of the species. In some embodiments, for example, the bioreactor(s) may be designed to enable anaerobic species degradation and operate over a pH range from 7-12. The bioreactor(s) may also (or instead) be acclimatised with seed bacteria before treatment commences. The bioreactors may also include sensors for monitoring conditions such as the pH, temperature and flow rates within the reactor, and controlling these as necessary.

[0057] The conditions to which species in the aliquot are exposed (e.g. inside the bioreactors) can be primed and controlled independently of the stored liquid waste and adjusting these conditions is much more manageable, given the far smaller volume (e.g. 30-50 m ³ for a bioreactor versus 65,000 m ³ for a lagoon). For example, the pH, active biomass concentration and nutrient concentration is the bioreactor can be primed before introduction of the aliquot.

[0058] If the bioreactors are operated within a pH range of 9-10, the oxalate degradation process produces enough carbonate to maintain the pH at this range, even with the introduction of aliquots from the lagoon having a pH as high as 13. The pH of the reactors is self-sustaining provided consistent biological oxalate degradation is maintained through adequate supervision and control. This is manageable in the external controlled environments of the bioreactors.

[0059] To start up the system, the bioreactors would be seeded with significant concentrations of appropriate biomass from a local environmental or an external source. The pH in the reactor is then initially controlled through acid addition (e.g. using a mineral acid), carbonation, or other dilution factors to maintain a reactor pH of 9-10 while the biomass acclimatises to oxalate degradation as limited oxalate lagoon feed is introduced to the reactor. Acclimatisation is completed through a gradual lagoon oxalate feeding process. Once completed, the conditions of the reactor continue to be monitored, and further pH lowering or biomass addition can be carried out in order to maintain oxalate degradation if required

[0060] The steps (a) and (b) in the method of the present invention are repeated until the stored liquid waste has bulk properties compatible with anaerobic biodegradation and contains an amount of a microorganism which is capable of sustaining biodegradation of the species (i.e. after which biodegradation of the species will continue to occur in the stored liquid waste (e.g. storage pond), without requiring further aliquots to be treated. It would be within the ability of a person skilled in the art to determine when this result has been achieved, using routine measurements of bacterial content/activity and/or rate of degradation of the species, for example.

[0061] Other measurable indications that such conditions have been reached may include the pH of the liquid waste. For example, steps (a) and (b) may be repeated until such time as the volume of the liquid waste has a pH of between about 9 and 11. Alternatively, it may not be necessary to use measured parameters to determine when the method has become self-sustaining. For example, steps (a) and (b) may repeated for a specific period of time, such as between about 6 to 12 months, which has been found by previous treatment processes to have been sufficient.

[0062] Once the method of the present invention has been performed for a time sufficient for the stored liquid waste to achieve the self-sustaining condition described above, it may beneficially be used to biodegrade any remaining species in the stored liquid waste. In such embodiments, the method may further comprise adding additional microorganisms to the stored liquid waste (e.g. a bulk addition form the bioreactor(s)) once it has bulk properties compatible with anaerobic biodegradation. The method may also (or instead) further comprise adding additional nutrients for the microorganisms to the stored liquid waste once it has bulk properties compatible with anaerobic biodegradation. Such nutrients would promote further microbial activity and likely increase the efficiency of species biodegradation.

[0063] Furthermore, once in its self-sustaining condition, the stored liquid waste may itself be used to remediate fresh industrial effluent by biodegrading additional species added thereto. In such embodiments, the method of the present invention may further comprise adding to the stored liquid waste additional liquid waste that contains the species capable of being bacterially degraded under anaerobic conditions. Thus, it is envisaged that the method of the present invention may be operable in a manner compatible with a continual biodegradation of the species and hence remediation of the effluent.

[0064] In some embodiments, advantages may be obtained by reducing the volume of the stored liquid waste to be remediated, even if only temporarily. Reducing the effective volume may help to speed up the rate at which the bulk properties become compatible with anaerobic

biodegradation, due to the treated aliquots returned to the partitioned volume being more effective at changing the conditions in the smaller volume. In some embodiment therefore, the stored liquid waste may be partitioned before the first aliquot of the liquid waste is removed and treated. Such partitioning may be effected in any suitable manner. The stored liquid waste may, for example, be partitioned by physically isolating a portion of the stored liquid waste from the remainder of the stored liquid waste.

[0065] Once the partitioned stored liquid waste has bulk properties compatible with anaerobic biodegradation (at which time it may also contain an amount of the microorganism which is capable of sustaining biodegradation of the species, although this could be added if needs be), the partition may then be moved (or removed) to increase the portion of the stored liquid waste that is partitioned.

[0066] In some embodiments, the method may also include separation steps, where various substances may be recovered for reuse (e.g. for a beneficial reuse such as for to generating heat or electricity, for reuse in an industrial process or for sale in order to offset operation costs). Substances may also be removed if there is a risk of them adversely affecting downstream processes.

[0067] In some embodiments, for example, the method may further comprise separating substances (such as methane gas and/or carbonate produced when treating the aliquot) from the treated aliquot for beneficial reuse. Methane generated from the bioreactors may, for example, be used for power generation or heating the reactor to operate it in thermophilic range where the ambient temperature is low. If methane needs to be captured or required by regulatory authorities, then the lagoons can be covered using technologies such as self -regulating suspended biogas capturing technology.

[0068] In some embodiments, for example, the method may further comprise separating any species that precipitate during treatment of the aliquot. Aluminium hydroxide (hydrate) solids precipitated during treatment of oxalate cake in the bioreactor may, for example, be prevented from returning to the lagoon by being collected from the base of the bioreactors.

[0069] The present invention will now be described in further detail with reference to embodiments in which the stored liquid waste for remediation is a legacy oxalate-containing storage lagoon containing effluent from an alumina refinery. It will be appreciated that the methods and apparatus described below could readily be adapted by those skilled in the art for remediating other kinds of stored liquid wastes.

[0070] In these embodiments, the present invention provides a novel anaerobic process that enables treatment of oxalate cake directly within a holding lagoon and avoids the technical problems faced by an aerobic reactor system. The process enables treatment of oxalate in storage facilities such as lagoons by facilitating the controlled introduction of seed oxalate consuming bacteria to the lagoon, whilst systematically lowering the pH of the lagoon to a level that is conducive to continuous biological oxalate degradation within the lagoon.

[0071] This may be achieved by using a system of anaerobic oxalate bioreactors external to the lagoon to treat oxalate in a closed loop series configuration to“kick-start” the process. The highly alkaline oxalate rich wastewater is fed into the acclimatised bioreactor series for anaerobic treatment. The resultant treated effluent, along with biomass and nutrients, is then discharged back to the lagoon/storage system which primes the system to auto-start the anaerobic process. This process is technically, environmentally and economically superior compared to the current treatment methods of oxalate streams, and has the potential to provide significant savings for the metallurgy industry.

[0072] The present invention is, to the best of the inventor’s knowledge, a novel solution because it enables treatment of the oxalate directly within the holding lagoon after the engineered“kick-starting” process. Anaerobic lagoons and stabilisation ponds have been used to treat wastewater for decades, however the technology has not been utilised for the treatment of oxalate, possibly because the anaerobic pathway for oxalate removal has had limited exploration in the art and the conditions of these waste lagoons is too harsh for biological activity owing to the high (typically >13) pH.

[0073] The significant advantage of anaerobic treatment is that the pond is already under anaerobic conditions due to limited oxygen exchange at the surface and high loading of organic material in the pond. It would be prohibitively expensive to aerate the entire lagoon to remove the oxygen under aerobic conditions, and the aluminium hydrates could easily block the diffusors and cause a myriad of operations issues.

Priming the lagoon

[0074] The lagoon would originally have a pH of up to 13 (due to high sodium hydroxide), which does not support biological treatment. Adding sludge to the lagoon would thus result in bacteria die-off and no oxalate treatment. The pH must be lowered (to a pH of 10 or slightly more) to enable oxalate consuming bacteria to function.

[0075] The inventor noted that anaerobic biological degradation of oxalate at a pH of 10 generates bicarbonate and carbonate by-products and that, by increasing the carbonate and bicarbonate species concentrations, the pH of a system can be regulated. In effect, by adding carbonate/bicarbonate a series of acid/base equilibrium reactions are introduced that regulate the system’s pH.

[0076] The distribution of the carbonate species (carbonate, bicarbonate and carbonic acid) are dependent on the pH conditions. At lagoon conditions, the biodegradation of oxalate creates products that actively consume free hydroxide and lower the pH.

Bioreactors

[0077] The bioreactors are external to the lagoon, where their operating conditions (including pH, active biomass concentration, and nutrient concentration) can be primed and controlled independent of the lagoon. Altering these parameters are much more manageable in an external reactor than the whole lagoon given the far smaller volume (in the order of 30 - 50 m ³ of the reactor versus 65,000 m ³ for the lagoon).

[0078] At the reactor operating pH of 9-10 the oxalate degradation process produces enough carbonate products to keep the pH within this range, even if the introduction of aliquots having the pH of the lagoon, which may be as high as pH 13. The pH of the bioreactors is self- sustaining provided that a consistent biological oxalate degradation is maintained through adequate supervision and control. [0079] To start up the system, the bioreactors are seeded with significant concentrations of appropriate biomass from a local environmental or an external source. The pH in the reactor is then initially controlled through acid addition, carbonation, or other dilution factors to maintain a reactor pH of 9-10 while the biomass acclimatises to oxalate degradation as limited oxalate lagoon feed is introduced to the reactor. Acclimatisation is then completed through a gradual lagoon oxalate feeding process. Once completed, the conditions of the reactor continue to be monitored, and further pH lowering or biomass addition can be carried out in order to maintain an optimum efficiency of oxalate degradation as required.

Introduction of Biomass to the lagoon

[0080] Once the pH of the lagoon (or portioned segment thereof) is within a range that is conducive to biological activity for the oxalate degrading bacteria (e.g. between 10 - 11) the lagoon in now primed for biological remediation. The biomass initially built up in the external bioreactors is released in a controlled manner to the targeted segment. The rate of biological degradation in the lagoon segment is dependent on the biomass concentration (MLVSS) in the segment.

[0081] Once a sufficient‘critical’ biomass concentration has been reached, oxalate degradation in the segment becomes self-sustaining and the next segment is targeted. This is achieved by gradual mixing of the surrounding area with the initial primed segment or complete isolation of a new segment area and repeating the initial process.

End Products

[0082] Aside from the treatment of waste oxalate (which is an environmental condition to continue operating) the biological treatment of oxalate also generates valuable by-products that can be re-used in the process. As the lagoon can operate at a higher pH than a conventional aeration system more of the carbonate species generated will be in carbonate form (as opposed to bicarbonate). The carbonate can be used to generate sodium hydroxide for the process more efficiently. Recausticisation of the sodium with slaked lime generates 2 moles of NaOH per mole of lime as opposed to 1 mole from bicarbonate. This is not unique to the present invention, but offers a benefit over conventional aerobic bioreactors.

[0083] Specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0084] Figure 1 shows a process flowchart for a method in accordance with an embodiment of the present invention referred to herein as the“SPORE Process” (Smart Priming Oxalate Removal Enabler). The SPORE Process provides a solution to the issue of legacy oxalate waste treatment in mineral processing industries such as alumina refineries. Also described herein is the SPORE System, which is the apparatus used to carry out the embodiments of the SPORE Process.

[0085] A central influent feed, originating from a legacy oxalate-containing storage lagoon containing waste from an alumina refinery would be used to supply aliquots of the feed oxalate wastewater (with or without dilution) to one or more bioreactors that have been primed with oxalate-biodegrading microorganisms. The central influent feed will branch off into separate influent sub-feeds using metal connectors and pipes, with these sub-feeds being fed to a corresponding number of bioreactors. Volume regulatory valves will be installed between the central influent feed line and the individual influent sub-feeds. The number of bioreactors used will be dependent on the size, volume of the reactors, total volume of oxalate stream to be treated and the residence time, as well as other parameters such as time allowed for priming of the storage lagoon for anaerobic process, and the overall economics.

[0086] The treated bioreactors effluent stream containing oxalate degrading biomass and sodium carbonate species, which is a by-product of the process will be fed into out-flow sub connectors. The bioreactor effluent stream will have a lower pH than the original storage area influent stream due to the presence of carbonate and bicarbonate generated as a result of chemical reaction between hydroxide ions and carbon dioxide produced during the anaerobic biodegradation process. The outflow sub connectors will be connected to a central out-flow line, for feeding back into the lagoon, with pumps ensuring a sufficient feed rate between the lagoon and the bioreactors.

[0087] The pH of the lagoon will reduce as the bioreactor treatment continues, due to the effects of recycling the bioreactor effluent stream (having a relatively lower pH than that of the lagoon) and, after some time, the bacteria added via the bioreactor effluent stream will start treating the storage area/lagoon as a large bioreactor whereupon the system will become near self-sustaining. To ensure this continues, nutrient feeds may need to be added to ensure a healthy culture.

[0088] This process enables an oxalate storage lagoon to be converted to an anaerobic treatment lagoon of oxalate, with or without covering the lagoons.

[0089] Figure 2 shows a side view of an embodiment of the SPORE System and which is configured to operate the SPORE Process. In Figure 2, the following numerals are used to refer to the recited features: (1) Influent feed, (2) Effluent output, (3) Bottom influent sub-feed, (4)

Top influent sub-feed, (5) Oxalate bioreactor, (6) Biogas output line, (7) Top effluent sub-output, (8) Bottom effluent sub-output, (9) Sludge removal tap. Please note, this schematic is a basic layout of the SPORE process and does not represent all the components of the reactors. These Features will be described in further detail below, with respect to Figures 4 and 5.

[0090] Figure 3 shows a plan view of another embodiment of the SPORE System. In Figure 3, the following numerals are used to refer to the recited features: (i) Effluent Feed Valve, (ii) Effluent Feed Pump, (iii) Effluent Sub-Feed Flow Gauge, (iv) Effluent Feed Fine, (v)Effluent Sub-Feed, (vi) Effluent Sub-Feed Valve, (vii) Oxalate Bioreactor, (viii) Reactor Seed Port, (ix) Out Flow Valve, (x) Out Flow Gauge, (xi) Out Flow Sub Reactor Fine, (xii) Out Flow Fine and (xiii) Out Flow Fine Valve, (xiv) Oxalate Fagoon. These Features will be described in further detail below, with respect to Figures 4 and 5.

[0091] An embodiment of the SPORE Process and System will now be described in specific detail with reference to Figures 4 and 5. Figure 4 is a visual representation of an embodiment of the SPORE process the inventor expects would be effective to perform the method of the present invention. The full description of the process that has been given (below) is an interpretation of this diagram.

[0092] Figure 4 shows a side view of the SPORE System 10, where bioreactors A, B and C are located next to an oxalate storage lagoon 12. Oxalate-containing liquid is drawn from lagoon 12 via Influent feed 14 and fed to a top influent feed gauge 16 and, via a top influent sub-feed 18, into the bioreactor A. Bioreactors A, B and C each have a biogas out-put line (shown generally as 22), a biogas barometer (shown generally as 24) and a biogas valve (shown generally as 26) for regulating the flow of biogases produced in the bioreactors. Bioreactors A, B and C also each have a top effluent sub-output (shown generally as 28), a top effluent sub-output gauge and valve (shown generally as 30).

[0093] An effluent output 32 is provided for returning the combined effluents from bioreactors A, B and C to the lagoon 12. Each bioreactor A, B and C has a bottom effluent sub-output gauge (shown generally as 34), support legs (shown generally as 36), a bottom effluent sub output (shown generally as 38), a bottom effluent sub-output valve (shown generally as 40) a sludge removal outlet (shown generally as 42), as well as bottom influent sub-feed valves (shown generally as 42) and bottom influent sub-feeds (shown generally as 46).

[0094] The oxalate lagoon 12, also known as an oxalate residue storage pond, is one of the most common types of oxalate storage technologies implemented in the mineral processing industry. The oxalate is stored in an outdoor onsite pond, in a solubilised state. The untreated oxalate resides at a very high pH, usually having a pH value of 13. [0095] The SPORE process involves the aqueous oxalate residue being removed from the storage lagoon 12 using a main large diameter feed pipe as the influent feed stream 14 to the bioreactors A, B and C. It is important to note that this pipe should be resistant to the corrosive nature of the oxalate. A liquid pump (not shown) is placed along this line to ensure a constant flow rate of residue to the oxalate reactors. The influent feed stream then diverges into influent sub feeds 18, that are attached via a flange connection. This ensures a watertight, secure and strong connection, while allowing easy dismantling of the system.

[0096] The influent sub feed streams are then connected to the high rate bioreactors A, B and C. Emergency cut-off valves and flow-rate gauges are placed along this line to the sub feed stream before the feed streams are attached to the bioreactors. This ensures that each bioreactor can be independently isolated, and that the concentration and volume of the influent feed streams can be controlled to achieve the exact chemical and biophysical conditions for optimum operation of the bioreactors.

[0097] The treated oxalate is then removed from the oxalate bioreactor via an output sub stream line after a hydraulic retention time of two to five days. The output sub stream is then connected to a main output stream 32 in a similar fashion to the connection made between the influent sub feed stream and the influent feed stream, with an outflow flowrate gauge and valve connected to the sub out-put stream. The out-put stream is then fed back into the oxalate lagoon 12. A pump may be installed along the out-put stream to provide the necessary pressure to transport the effluent back into the lagoon, if needed.

[0098] The SPORE treatment process begins with oxalate being transferred from a legacy oxalate storage pond 12, via an influent feed stream 14. The feed stream is separated to a distribution feed line 46 which is then further divided into two smaller influent sub-feed streams 18, 44. The sub feed streams supply both the top and bottom of the reaction vessel A, B or C, allowing oxalate to be fed into the reactor through the top or the bottom. Each sub-feed stream can be independently isolated using a series of valves 16, 42. Flow meters located near the valves allow easy determination of the rate of flow of oxalate into the reactor vessel. The oxalate is then treated in the reaction vessel A, B or C via a biological anaerobic process. The 7-10 pH range of the reactor is maintained due to the retention of dissolved carbon dioxide in the system generated from the anaerobic degradation of oxalate. The treated water is then removed through, either a top effluent output sub-stream 28 or a bottom output sub-stream 38. Similar to the influent sub-feed streams, each output sub-stream can be independently isolated using a series of valves 30, 40. Flow meters located near the valves allows easy determination of the rate of flow of oxalate into the reactor vessel. The sub-feeds then merge to form the main effluent output stream 32, where it is then returned into the legacy wastewater pond.

[0099] The receiving legacy oxalate storage pond/lagoon 12 will be primed by way of return treated wastewater from the bioreactors, which will supply the required biomass, nutrients and in addition, enable the pH conditions of the storage facility to commence anaerobic process within the facility. The storage facility may be covered with either fixed or floating anaerobic covers, or operated without covering the surface. The process modelling described below indicates that the process should not cause any hydrogen sulphide odour generation.

[0100] By using a system of smaller anaerobic oxalate bioreactors, the SPORE process treats oxalate in a low volume, continuous, closed loop configuration. The highly alkaline, oxalate rich water is fed into the acclimatised bioreactors for biological anaerobic treatment. The oxalate found in these lagoons generally has a pH value of approximately 13, whereas the bioreactors sustain a pH of between about 7-10. The acclimatisation process at the start-up of the process will facilitate rapid multiplication of special anaerobic oxalate degrading seed bacteria that can function in a high alkaline environment. The resultant treated effluent, along with a certain percentage of active anaerobic biomass is then discharged back to the lagoon/storage area, systematically lowering the pH of the storage lagoon. This enables the bacteria present in the lagoon (from both the local environment and the contained in treated effluent from the bioreactors) to establish anaerobic degradation of oxalate within the lagoon.

[0101] The addition of nutrients may be required to maintain the bacterial biomass. The biomass will break down the oxalate until it is completely removed or reaches an acceptable

concentration. Due to net positive energy generation of this system (from the produced methane during anaerobic treatment of oxalate in the bioreactors), the SPORE treatment technology will result in significant savings for the metallurgy industry and reduce the impact that aluminium processing has on the environment.

[0102] Referring now to Figure 5, shown is a cross sectional schematic of an oxalate treatment bioreactor A for use in the method described above with respect to Figure 4. Bioreactor A includes biogas outlet 22, biogas valve 26 and biogas barometer 24, which link the bioreactor A to the biogas output line 22 shown in Figure 4. Bioreactor A also includes top outlet sub- stream 28, having an outlet sub-stream flowmeter 30 and outlet sub-stream valve 31 incorporated therein. The influent can be fed either from the top or bottom of the tank A, similarly the effluent can be withdrawn either from the top of bottom. A pipe fitting 33 joins the top 28 and bottom 38 outlet sub-streams and feeds them into outlet stream 32. Sludge may be removed from the bioreactor A via sludge removal outlet 42 by operating sludge removal valve 43, for the benefits described below.

[0103] Bioreactor A also includes a bottom inlet sub-stream 46, having an inlet sub-stream valve 16 and inlet sub- stream flowmeter 17, and a top inlet sub- stream 18, which are fed by liquid from the lagoon 12 (not shown in Figure 5) via inlet feed stream 14.

[0104] The oxalate treatment anaerobic reactors can use a myriad of processes including but not limited to suspended growth, attached growth, completely mixed, plug flow with either up or down flow mechanism, up flow anaerobic sludge blanket, moving bed biomedia, up flow or down flow filters. There may be additional mechanism such as recycled biogas for stirring or crust breaking, recycling of sludge or treated oxalate wastewater for pH adjustment or bacterial activation. The general mechanism of the reactor design is provided in the following paragraphs.

[0105] Referring again to Figure 5, a single influent pipe from the oxalate legacy wastewater pond is fed to the bioreactor via the influent feed pipe 14, where it splits into two separate sub feed streams 18 and 46. One feed stream supplies influent oxalate wastewater into the top of the bioreactor 18, while the other, feeds oxalate via the bottom of the reactor 46. These two sub feeds can be independently isolated and separated via valves and flowrate gauges to help maintain the influent flowrates of the influent sub-feeds. The upper sub-feed stream contains a U-Bend, to prevent backflow of biogas into the influent feed stream. The reactor contains a valved 43, sludge removal outlet 42 to allow easy analysis and removal of sludge samples. The bioreactor A also has a biogas outlet pipe 22, located at the top of the reaction vessel, which is controlled by an airtight valve 26 and measured using a pressure barometer 24. In addition, similar to the influent streams, the bioreactor contains two outlets, the top 28 and bottom 38 effluent removal outlets. These outlets merge to form a single oxalate removal outlet 32, and like the influent sub-feed pipes, can be independently controlled and measured using outflow valves 30, 31 and flowrate meters 31. The entire reactor sits on a series of legs/platforms 36to ensure stability.

[0106] As the SPORE process utilises natural processes to break down the oxalate, it is significantly more environmentally conscious than current combustion, aerobic treatment or storage techniques. It also treats the oxalate at a much faster rate than if it was simply left in the storage pond. The method of the present invention is expected to be capable of removing substantially all of the sodium oxalate on average from a 20 to 25 g/L Na ₂ C ₂ 0 ₄ feed, operate over a large pH range, and treat additional oxalate being added into the feed stream, resulting in a greater cost effectiveness for industry. [0107] Figure 6 is a simplified schematic of SPORE reactor internals. In Figure 6 the following numerals are used to refer to the recited features: (51) Feed inlet, (52) Treated Effluent Outlet, (53) Sludge Outlet, and (54) Hydrate Outlet. As discussed above, the presence of aluminium hydrates within the oxalate waste has the potential to cause significant operational issues for aerobic bioreactors operated. As the pH decreases in the bioreactor, however, there is less available hydroxide, and Al(OH) ₄ (aluminium hydrate) species begin to precipitate out as aluminium hydroxide. The SPORE reactors may therefore have a cone base to separate and recover hydrates from the biomass

[0108] Referring now to Figure 7, shown is a cross section of the targeted segment of a lagoon L. The lagoon surface is shown at 61, and the dotted line is indicative of likely oxalate concentration with depth. Low dissolved oxalate concentration (expected 0-10 g/L) would be likely to be found in the upper region 62 of the lagoon L (above the line 63), with increasing concentrations of dissolved oxalate likely to be found below the depth of line 63. An average oxalate concentration (approximately 20 g/L) would likely be found at the depth of line 63. Cemented oxalate solids 67 would be likely to be found at the bottom of the lagoon L.

[0109] In use, a combination of light and heavy oxalate concentration feeds may be drawn via inlets 64 and 66 into the SPORE reactors described above, with the feed from inlet 54 diluting the feed from inlet 56. Return treated effluent from the SPORE reactors may be returned to the lagoon’s mid depth, via outlet 65, where it can mix in either direction in order to alter the bulk properties of the lagoon L.

[0110] Referring now to Figure 8, the lagoon fluid flow of an embodiment of the SPORE Process is schematically shown. In the Figure, the aliquots drawn from different depths of the oxalate holding lagoon L are combined (optionally with mixing) in the balance tank 70 before being transferred to the SPORE 72, connected in series or parallel.

[0111] The concentration of oxalate in the lagoon typically varies with depth as a stratified system. Following profiling of the oxalate concentration with depth, layers of low and high oxalate concentration may be drawn from the appropriate lagoon depth for input to the balance tank and subsequently feed the SPORE reactors (See Figures 7 and 8) to a consistent 15-30 g/L dissolved oxalate concentration. This mixing may advantageously reduce the need to add fresh water to the balance tank in order to lower the oxalate concentration to the target band (although fresh water may be added if required).

[0112] The treated effluent from the SPORE reactors may subsequently be released to the lagoon midpoint (see Figure 7) to aid in oxalate concentration distribution. [0113] Figure 9 schematically depicts a progressive treatment of a lagoon. In the Figure, (L) is the oxalate holding lagoon, and (2a - d) represent the engineered barrier being progressively moved such that it initially defines just enclosed segment 2a to the entire lagoon

[0114] Given the large volume of many storage lagoons (typically -65,000 m ³ ), isolating a smaller targeted volume of the lagoon for initial remediation may be an efficient means of“kick starting” the oxalate degradation process in the lagoon. This isolation is achieved by specific placement of the influent and effluent pipes to draw from the lagoon to the SPORE unit and release the carbonate rich treated effluent back to the lagoon. Physical barriers may also be implemented depending on the flow conditions in the pond.

[0115] Segmentation may be achieved, for example, using an engineered barrier of HD PE material or equivalent that can be moved along the edge of the lagoon, as depicted in Figure 9. Monitoring of the lagoon conditions through sensors or sampling and chemical testing will determine whether the target pH (-11) and biomass concentration (-5% by volume) have been achieved for the segment Once the targets have been met, the segment may be extended by adjustment of the barrier position to include additional untreated lagoon area

[0116] The initial segment can be remediated for anaerobic oxalate degradation much faster than the entire lagoon and, once so remediated, the acclimatised segment can help to increase the remediation rate of the remainder of the lagoon as in situ oxalate degradation commences, adding additional biomass and carbonate products to the lagoon. To the best of the inventor’s knowledge, this approach is unique to the SPORE process for oxalate removal and is not used in other anaerobic lagoon applications.

[0117] Remediation of the lagoon with effluent from the SPORE Reactors will now be described with reference to Figures 10 and 11. Figure 10 is a graph showing the change in pH of the targeted lagoon segment with time. Figure 11 is a graph showing the gradual remediation of the entire lagoon following movement of the target segment.

[0118] As described previously, successful anaerobic biological degradation of oxalate at a pH of 10 generates bicarbonate and carbonate by-products. By increasing the carbonate and bicarbonate species concentrations the pH of a system can be regulated.

Eqn 1. 4NCI2C2O4 (aq) + 5H2O (I) ^® Na ₂ C0 ₃ (aq) + 6NaHC03 (aq) + CH4 (g)

[0119] Carbonate species influence the pH through a series of acid/base equilibrium reactions: Eqn

Eqn 3.

Eqn 4. H ₂ 0 _(l) ¾ 0/T _(b<ϊ) + H _aq> K _w = [H ⁺ ] [OH ^~ ]

[0120] K _ai , K _a2 and K _w are the equilibrium constants that govern the species concentrations at the lagoon conditions.

[0121] A charge balance, mass balance on ion types present in the system, and the equilibrium concentration balance at the process conditions outlined above must be undertaken to predict pH changes in the targeted lagoon segment.

[0122] The rate of pH change in the target segment will depend on:

• Initial pH and alkalinity of the lagoon

• Volume of the lagoon or targeted segment

• Oxalate and other organic loading in the lagoon and chosen feed concentration

• The total volume of the SPORE reactors and hydraulic retention time (HRT) of the process

• The SPORE reactor operating pH

[0123] The inventor has modelled the rate of pH change for a typical oxalate holding lagoon of 65,000 m ³ volume being treated through the SPORE Process. In this modelling process, the targeted segment (3.7% of total lagoon volume) had three times the external SPORE reactor volume and the SPORE reactors were operating at a pH of ~ 9.5 with a hydraulic retention time of 5 days. As can be seen from Figure 10, the pH of the targeted segment reached the acceptable range within 68 days.

[0124] As the segments are progressively remediated (i.e. as depicted in Figure 9), the in-situ oxalate degradation within the lagoon greatly increases the rate of pH decline for each successive segment. The total modelled pH remediation time for this scenario is 140 days as shown in Figure 11. pH remediation is the biggest limiting factor early in the remediation, with longer times required than for biomass generation.

[0125] The inventor has also modelled the rate of biomass accumulation for a typical oxalate holding lagoon of 65,000 m ³ volume being treated through the SPORE Process. To enable biological treatment of the oxalate in-situ, sufficient oxalate degrading biomass must be transferred to the lagoon. In the inventor’s experience, biomass should be added until the target segment contains at about 5 to 10% biomass by volume. However, adding biomass to a segment while the pH is greater than 11 will lead to significant die-off of the added biomass. The SPORE reactors would therefore typically retain the majority of the biomass while the pH is remediated, with only small quantities of the biomass being released with the treated aliquot.

[0126] From previous oxalate degradation experience, approximately 10% of oxalate carbon by mass is used to maintain and grow the oxalate degradation culture. Using the sludge density, SPORE reactor biomass retention factor and mass of oxalate degraded the oxalate feed required for biomass generation can be calculated. Environmental factors, acclimatisation periods and die-off events beyond the direct control of the process will affect the biomass accumulation time required.

[0127] For the previously described 65,000 m ³ oxalate holding lagoon scenario, the biomass accumulation time required to kick start the first target segment (3.7% of total lagoon volume) was found by the inventor’s modelling to be about 30 days. Once the target segment is remediated it can generate more biomass that can be transferred to the next segment through flow effects and mixing. As can be seen, the biomass accumulation time factors are less important than pH factors for lagoon kick start, pH stabilisation is therefore the limiting factor of the process. This time might be reduced through additional pH reduction methods such as carbonation of the feed.

[0128] It may also be beneficial to the method if additional nutrients are added to promote biomass growth. Such nutrient addition requirements will be dependent on the condition of the holding lagoon. Addition of nitrogen, phosphorus and trace elements may, for example, be required to support biomass growth

[0129] As described herein, the present invention provides a method for remediating a stored liquid waste by reducing a content of a species capable of being bacterially degraded under anaerobic conditions, even though the stored liquid waste has bulk properties incompatible with anaerobic biodegradation. Embodiments of the present invention provide a number of advantages over existing therapies, some of which are summarised below:

• Enables anaerobic remediation of lagoons/holding ponds containing oxalate, providing a solution to a long-standing problem in the industry; • Use of compact and mobile external bioreactor’s effluent to prime the anaerobic lagoon in a controlled manner (segment by segment) with, after a time, the lagoons becoming capable of sustain biodegradation;

• Transformation of the waste storage area to continuous oxalate removal infrastructure (oxalate from the plant can be sent to the lagoon for treatment after existing oxalate destroyed).

[0130] It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention. All such

modifications are intended to fall within the scope of the following claims.

[0131] It will be also understood that while the preceding description refers to specific forms of the microspheres, pharmaceutical compositions and methods of treatment, such detail is provided for illustrative purposes only and is not intended to limit the scope of the present invention in any way.

[0132] It is to be understood that any prior art publication referred to herein does not constitute an admission that the publication forms part of the common general knowledge in the art.

[0133] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as“comprises” or“comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.