Description:FIELD OF THE INVENTION
[0001] Embodiments of the present disclosure relates a compact, robust, and highly efficient and cost effective biofilter for nitrification in recirculating aquaculture systems.
BACKGROUND
[0002] Aquaculture is an important field of technology and is finding increasing importance in aquatic organism culture. A recirculating aquaculture system (RAS) is defined as an aquaculture system that incorporates the treatment and reuse of water with less than 10% of total water volume being replaced per day. The concept of RAS is to reuse the maximum possible volume of water through continual treatment and delivery to cultured organisms in the system. Therefore, water treatment components used in RAS need to accommodate the input of high amounts of feed required to sustain high rates of growth and high stocking densities typically required to meet financial outcomes. Generally, RAS consists of mechanical and biological filtration components, pumps, and holding tanks and may include several additional water treatment elements that improve water quality and provide disease control within the system. RAS can have more sustainable food production with higher yields and healthier fish, lower consumption of fresh water and land area, and shorter transport distances, as fish can be grown closer to the markets and reduce the cost of transportation significantly. By controlling the culture conditions, aquaculture production in a RAS facility can be established almost anywhere, regardless of local conditions. However, current RAS suffer from several disadvantages related to contamination, purification, stocking density, production output etc.
[0003] Ammonia is known to be a highly soluble gas that is often found also in drinking water due to environmental processes, water treatment, and industrial process wastes. Although ammonia toxicity through drinking water is rare, high ammonia levels may be detected in certain water sources. In RAS, ammonia is generated from excreta of the cultivated aquatic organism and uneaten feed. Ammonia’s toxicity primarily occurs due to the un-ionized ammonia, and generally, the higher the pH of water, the higher the likelihood of greater toxicity, which can cause severe harm to humans and animal life as well. It is therefore an object of the present disclosure to ameliorate one or more of these disadvantages with conventional RAS.
SUMMARY
[0004] Embodiments of the present disclosure relate to a method and system for efficient purification of water contaminated with ammonia (in recirculating aquaculture system). An embodiment includes receiving at a biofilter, which is typically a packed bed biofilm reactor, water contaminated with Ammonia from a source (hereinafter in the present disclosure reference to source may be a source tank or a culture tank), which typically is a culture tank, wherein aquatic organisms are cultured. A further embodiment includes treating the water contaminated with Ammonia in the biofilter wherein the ammonia from the water is converted to nitrate resulting in ammonia lean water, wherein the content of ammonia in the water is extremely low or negligible. A further embodiment includes recirculating the treated water to the source, wherein the treated water is ammonia lean. In an embodiment, though the above method and system describes removal of Ammonia from RAS, the same technique may be used to remove ammonia from other sources of water such as drinking water etc. Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The detailed description is described with reference to the accompanying figures. Features, aspects, and advantages of the subject matter of the present disclosure will be better understood with regard to the following description and the accompanying drawings. The figures are intended to be illustrative, not limiting, and are generally described in context of the embodiments, and it should be understood that it is not intended to limit the scope of the disclosure to these particular embodiments. In the figures, the same numbers may be used throughout the drawings to reference features and components. In order that the present disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages.
[0006] Figure 1 illustrates an exemplary system with a biofilter to provide ammonia lean water in accordance with embodiments of the present disclosure.
[0007] Figure 2 illustrates an exemplary method of providing ammonia lean water in accordance with embodiments of the present disclosure.
[0008] Figure 3 illustrates an exemplary case of results obtained from the biofilter using LECA balls and simulating rearing cycle in accordance with the embodiments of the present disclosure.
[0009] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical elements. The figures as disclosed herein are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings are meant to only be provided as examples and/or implementations consistent with the description, and the description may not be limited to the examples and/or implementations provided in the drawings.

DETAILED DESCRIPTION
[0010] The following describes technical solutions in exemplary embodiments of the subject matter of the present disclosure with reference to the accompanying drawings. In this application as disclosed herein, "at least one" means one or more, and "a plurality of" means two or more. The term "and/or" describes an association relationship for describing associated objects and represents that three relationships may exist. For example, A and/or B may represent the following cases: Only A exists, both A and B exist, and only B exists, where A and B may be singular or plural. The character "/" usually indicates an "or" relationship between the associated objects. "At least one item (piece) of the following" or a similar expression thereof means any combination of the items, including any combination of singular items (piece) or plural items (pieces). For example, at least one item (piece) of a, b, or c may represent a, b, c, a and b, a and c, b and c, or a, b, and c, where a, b, and c each may be singular or plural.
[0011] It should be noted that in this application articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”. Throughout this specification defined above, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of elements or steps but not the exclusion of any other element or step or group of elements or steps. The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably. In the structural formulae given herein and throughout the present disclosure, the following terms have been indicated meaning, unless specifically stated otherwise.
[0012] Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included for better understanding of the present disclosure. The term ‘about’ as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of ±10% or less, preferably ±5% or less, more preferably ±1% or less and still more preferably ±0.1% or less of and from the specified value, insofar such variations are appropriate to perform the present disclosure. It is to be understood that the value to which the modifier ‘about’ refers is itself also specifically, and preferably disclosed.
[0013] It should be noted that in this application, the term such as "example" or "for example" or “exemplary” is used to represent giving an example, an illustration, or descriptions. Any embodiment or design scheme described as an "example" or "for example" in this application should not be explained as being more preferable or having more advantages than another embodiment or design scheme. Exactly, use of the word such as "example" or "for example" is intended to present a related concept in only a specific manner.
[0014] It should be understood that in the embodiments of the present subject matter that "B corresponding to A" indicates that B is associated with A, and B can be determined based on A. However, it should be further understood that determining B based on A does not mean that B is determined based on only A. B may alternatively be determined based on A and/or other information.
[0015] In the embodiments of this application, "a plurality of" means two or more than two. Descriptions such as "first", "second" in the embodiments of this application are merely used for indicating and distinguishing between described objects, do not show a sequence, do not indicate a specific limitation on a quantity of devices in the embodiments of this application, and do not constitute any limitation on the embodiments of this application.
[0016] Though the embodiments of the present disclosure aim to provide ammonia lean water in RAS, it should be obvious to a person of ordinary skill in the art that the same technique may be used to purify any water source contaminated with ammonia and provide ammonia lean water at a highly efficient rate and a lower cost.
[0017] Generally, enhancing fish production multifold is in extremely high demand and this requires sustainable and responsible development in the fisheries sector. In some exemplary embodiment, recirculating aquaculture system (RAS) has been identified as a thrust area, which is an attractive and cost-efficient technique for achieving all-embracing sustainable fish farming, and RAS is considered to be a new and emerging technology that is sustainable in the long run.
[0018] In an exemplary case, RAS not only conserves water, through treatment and recirculation, but also reduces land area requirements, enhances production and quality of aquatic organisms. In the exemplary case, for treatment of water, RAS depends on mechanical filter for removing solids, and biological filter (biofilter) for removal of ammonia, which is highly toxic to aquatic organisms such as fish, by nitrification. In an exemplary case, maintaining low total ammonium nitrogen (TAN) concentration ideally to be less than 2 mg/L in a culture tank by ensuring high biofilter performance is considered to be the foremost challenge in RAS.
[0019] In an exemplary case, a compact, robust and efficient biofilter delivering high-rate nitrification up to 1900 g/(m³·d) vis-à-vis a nitrification rate of less than 100 g/(m³·d) , which is commonly achieved, and consistently maintaining a TAN of less than 1 mg/L at high stocking densities of about 45 kg/m³ was achieved by the embodiments of the present disclosure.
[0020] In an exemplary case, traditional aquaculture is characterized by a shallow stocking density in a very large volume of water. In an exemplary case, a catfish pond with an annual yield of 5600 kg/ha corresponds to a stocking density of only about 0.56 kg/m3 fish. There is therefore a need to increase aquaculture production, and such an increase leads to driving towards more intensive practices. In an exemplary case, factors affecting these trends are limitations in water quality and quantity, discharge of nitrogen-contaminated water and environmental norms and to add to these the cost and availability of land. Therefore, use of recirculating technologies helps in minimizing a large number of issues or disadvantages of the traditional system. In an exemplary case, a recirculating aquaculture system (RAS) facility reduces water demands and discharges by advantageously reconditioning of water, as better food conversions are achievable with a RAS, which means less waste is generated from the fish feed.
[0021] In an exemplary case, the RAS may be defined as an aquaculture system that incorporates the treatment and reuse of water with less than 10% of total water volume being replaced per day, which significantly finds importance as water wastage is minimized to a large extent. In an exemplary case, the concept of RAS may be primarily to reuse the maximum possible volume of water through continual treatment and delivery to cultured organisms, i.e. aquatic organisms. In an exemplary case, water treatment components used in RAS need to accommodate the input of high amounts of feed required to sustain high rates of growth and high stocking densities. In an exemplary case, generally, RAS consists of mechanical and biological filtration components, pumps, and holding tanks and may include several additional water treatment elements that improve water quality and provide disease control within the system. In an exemplary case, RAS advantageously provides more sustainable food production with healthier fish, lower consumption of fresh water, and shorter transport distances, as fish can be grown closer to the markets. In an exemplary case, by controlling the culture conditions, aquaculture production in a RAS facility can be established almost anywhere, regardless of local conditions.
[0022] In an exemplary case, an intensive recirculation system may be able to operate at stocking densities of 60 kg/m3, which is about 120 fish, each weighing about 500 g, and with oxygen supplementation at densities of 120 to 150 kg/m3. In an exemplary case, maintaining optimum water quality at these stocking densities while feeding a high protein diet at up to 15% of the biomass per day is a challenge. In an exemplary case, it has been estimated that every kilogram of feed generates about 300 grams of fecal matter, 30 grams of ammonia-nitrogen, 320 grams of carbon dioxide and consumes 250 grams of oxygen (biochemical oxygen demand). The numbers provided herein are only exemplary in nature and may vary depending on various conditions such as the fish being cultivated, the feed provided etc. In an exemplary case, critical water quality parameters that require an engineering system include the concentration of dissolved oxygen, un-ionized ammonia-nitrogen, nitrite-nitrogen, solids, and carbon dioxide. In an exemplary case, additionally nitrate-nitrogen, pH, and alkalinity are also important water quality parameters.
[0023] In an exemplary case, in RAS systems relatively large amounts of solids, that include typically uneaten feed and fecal matter are generated. In an exemplary case, technologies for solids removal are available and have been already commercialized, which have a relatively high efficiency. In an exemplary case, a much greater challenge in such types of recirculatory systems is ammonia removal from the water that is contaminated, wherein maintaining an ammonia-nitrogen at a relatively low level would be ideal from the point of sustainability. In an exemplary case, the total ammoniacal nitrogen, TAN at concentrations above 1.5 mg/L are generally known to be toxic to many aquatic organisms and removal of ammonia is a challenging step. In an exemplary case, the design of efficient and robust bioreactors for removal of ammonia, for example by nitrification plays an important role in these systems.
[0024] In an exemplary case, compared to suspended growth process, such as activated sludge and sequencing batch reactor, biofilm or attached growth reactors are more attractive and robust for nitrification, thereby also forming the preferred choice in RAS based systems. In an exemplary case, among the numerous biofilm reactors including trickling filter, moving bed biofilm reactor, and packed bed biofilm reactor PBBR, RAS has identified packed bed reactor to be the most advantageous in the process of ammonia removal by nitrification.
[0025] In an exemplary case, compared to other existing techniques on nitrification of RAS effluents using PBBR, embodiment of the present disclosure have been able demonstrated the possibility to achieve robust, stable and very high nitrification rate. In an exemplary case, while conventionally PBBRs in RAS have achieved nitrification rates less than 100 g N/(m³·d) only, the RAS implemented in accordance with the embodiments of the present disclosure PBBR achieved nitrification rate as high as 1900 g N/(m³·d), maintaining TAN concentration < 1.1 mg/L in the system.
[0026] In an exemplary case, genetically improved farmed tilapia (GIFT tilapia) and pangasius are the only two major species, which have been successfully cultivated in RAS in India, with stocking densities of about 18 kg/m³ only. In the exemplary case, both tilapia and pangasius are well known to be hardy fish species, meaning they can tolerate lower water qualities (including higher TAN concentrations). RAS in India is at its nascent stage and particularly challenged by maintenance of low TAN concentrations (in other words need for robust and efficient biofilters). Embodiment of the present disclosure delivers a compact, robust and efficient nitrifying biofilter, which will promote the success, profitability and acceptance of RAS.
[0027] Exemplary embodiments of the present disclosure relate to a system and method for efficient purification of water contaminated with ammonia in recirculating aquaculture system. In an exemplary case, high nitrification range from about 150 g /(m³·d) to about 1900 g /(m³·d) was achieved by the present disclosure via-a-vis that of less than 100 g /(m³·d) as in the prior art. In an exemplary case, the method includes receiving at a biofilter, which is packed bed biofilm reactor, water contaminated with Ammonia from a source (hereinafter in the present disclosure reference to source may be a source tank or a culture tank), preferably a source tank or a culture tank. In an exemplary case, the source may generally be a water storage tank or a culture pond or the likes. In an exemplary case, the method further includes treating the water contaminated with Ammonia in the biofilter wherein the ammonia from the water is converted to nitrate resulting in ammonia lean water. In the embodiment reference to lean mean negligible quantity of ammonia in the water. In an exemplary case, the method further includes recirculating the treated water back to the source, wherein the treated water is ammonia lean.
[0028] In an exemplary case, the biofilter includes naturally occurring nitrifying bacteria, which are autotrophic bacteria. In an exemplary case, the nitrifying bacteria perform nitrification by converting the ammonia in the water into a nitrate, when the ammonia rich water is passed through the biofilter. In an exemplary case, the water from source is sent to the biofilter for nitrification as a continuous feed or at predetermined time intervals or may be automated and controlled automatically. In an exemplary case, water from the source is sent to the biofilter for nitrification on detection that the ammonia content in the water has crossed a pre-determined threshold. In an exemplary case, detection may be performed by using sensors mounted in the source tank. It should be obvious to a person of ordinary skill in the art that other means may be used to determine the ammonia content in the water and all such method used to detect the ammonia content is the water and defining it to be above a pre-defined threshold level fall within the scope of the present disclosure.
[0029] In the exemplary case, volumetric nitrification rate in the biofilter is in the range of 100-2000 g N/(m³·d) as opposed to 100 g N/(m³·d) that has been currently reported and achieved in techniques currently available. In an exemplary case, the maximum surface specific nitrification rate in the biofilter is in the range of 1.2-2.2 g N/(m²·d). In an exemplary case, a pH between 7.0 to 8.0 and dissolved oxygen saturation between 70 to 95 % are maintained in the biofilter, and continuously monitored using sensors or other techniques. In an exemplary case, the total ammonia nitrogen concentration is maintained less than 2 mg/L in the source due to the nitrification and in a preferred embodiment can also be closer to 1 mg/L. In an exemplary case, the stocking density is in the range of 40 to 50 kg/m³, and preferably around 45 kg/m³. In an exemplary case, the ratio of biofilter volume to culture tank volume is between 0.01 to 0.04, wherein and tank exchange rate is between 45 to 360 minutes.
[0030] An exemplary embodiment includes a recirculating aquaculture system for purification of ammonia from water by nitrification. In the exemplary embodiment, the RAS includes a source tank, which may be a culture tank, containing water, wherein water in the source tank gets contaminated with ammonia over time due to the aquatic organisms being cultured in the tank by fecal matter (excreta) of the aquatic organisms and feed matter provided for the aquatic organisms. In an exemplary case, a biofilter reactor may be packed bed biofilm which is coupled to the source tank, wherein water is pumped from the source tank to the biofilter via a pump, and the biofilter on receiving the water which is contaminated with ammonia, is configured to convert the ammonia in the water to a nitrate resulting in ammonia lean water, wherein the ammonia lean water is recirculated back to the source tank. In an exemplary case, additional water may be added to the source tank, as make up water, as and when required, and is typically done when the quantity of water in the source tank becomes less due to losses, evaporation, etc.
[0031] Reference is now made to Figure 1, which illustrates an exemplary system 100 to provide ammonia lean water in accordance with embodiments of the present disclosure. System 100 contains source tank 110, which may also be referred to as a culture tank or a source, in which aquatic organisms may be cultured for production. Source tank contains water 112, wherein the aquatic organisms maybe cultured in water 112. Source tank 110 be fed with makeup water from feed reservoir 120, which contains clean water, at regular intervals when the water level in source tank 110 fall below a certain limit. If the water level on source tank 110 is above a predetermined level, water 112 is allowed to overflow so as to maintain the water level in the tank to be constant. Motor 115 may be used to pump the required amount of water from feed reservoir 120 to source tank 120. Alternate method may be used to refill water into source tank 110 and it should be obvious to a person of ordinary skill in the art that all such method to refill source tank 110 fall within the scope of the present disclosure.
[0032] As aquatic organisms are cultivated in source tank 110, due to faecal matter from the aquatic organisms and the feed that is provided to the aquatic organisms, water 112 in the source tank 110 get contaminated with ammonia. Accumulation of ammonia in source tank 110 make the water toxic for cultivation of aquatic organisms and hence water 112 in source tank 120 needs to be replaced frequently resulting in wastage of water or purified at regular intervals. Water 112 from source tank may be sent to a filter, such as a biofilter 130, wherein water 112 which is contaminated with ammonia is purified in biofilter 130 and recirculated back into source tank 110.
[0033] Water 112 that is contaminated with ammonia from source tank 110 may be sent to biofilter 130 as a continuous feed or at pre-determined time intervals, which may be periodic or sensors may be placed in source tank 110, wherein sensors (not shown in figure) are configured to continuously measure the level of ammonia in water 112, and when water 112 breaches a certain pre-determined threshold limit, sensors activate motor 125 to feed water contaminated with ammonia to biofilter 130 for purification. In biofilter 130, ammonia in the water received at biofilter 130 is converted to a nitrate and the water is then fed back to source tank. In the water treatment processes, which also including solids removal, nitrification etc small quantities of water may be lost during the purification process, and this may be replaced from feed reservoir 120 to maintain water 112 level in the source tank.
[0034] Importantly, naturally occurring nitrifying autotrophic bacteria may be used in biofilter 130 wherein the nitrifying bacteria perform nitrification by converting the ammonia present in the water into nitrate. Further, a check is maintained to ensure that in biofilter a pH between 7.0 to 8.0 and dissolved oxygen saturation between 70 to 95 % are maintained. Air is constantly supplied to biofilter 130. In an embodiment, the pH and oxygen saturation may be manually determined or alternatively sensors may be placed in biofilter 130 to indicate the pH level and oxygen saturation level of the water being purified in biofilter. In an embodiment, volumetric nitrification rate in biofilter 130 is in the range of 100-2000 g N/(m³·d). The large range has been tested with current biofilter 130 under laboratory conditions, and it should be obvious to a person of ordinary skill in the art that even at larger scale or industrial scales the laboratory conditions may be easily replicated. In an embodiment, maximum surface specific nitrification rate in biofilter 130 is in the range of 1.2-2.2 g N/(m²·d). In an embodiment, the total ammonia nitrogen concentration is maintained at around 1 mg/L and less than 2 mg/L in the source tank 110. In an embodiment, the stocking density is in the range of 40 to 50 kg/m³, and preferably around 45 kg/m³. In an embodiment, the ratio of biofilter volume to source/culture tank volume is between 0.01 to 0.04, wherein and tank exchange rate is between 45 to 360 minutes.
[0035] It should be obvious here to a person of ordinary skill in the art, that though the experimental setup in the laboratory has been demonstrated for aquatic organisms culture and production, the same technique may be used to remove ammonia in toxic form from other sources of water, for example drinking water sources, municipal and industrial wastewaters etc, and the same technique with a biofilter may be advantageously used to purify ammonia rich water from other sources, which may be not be culture and production sources for aquatic organisms. It should also be obvious to a person skilled in the art that though the laboratory demonstration was to scale, the entire apparatus may be implemented at an industrial scale or larger scale with the size of the biofilter being about 1-2 meter in size. In the exemplary embodiment the size of the biofilter was about a feet with a diameter of about 4 inches. Advantageously the efficiency of the process is much higher and the cost of making and using the system is lesser compared to already known system.
[0036] Reference is now made to Figure 2, which illustrates an exemplary method of providing ammonia lean water in accordance with embodiments of the present disclosure and may be implemented on a RAS system as illustrated in Figure 1. In step 210 water contaminated with ammonia is received at biofilter 130 from source tank 110, when water 112 in source tank 110 breaches a certain level predetermined level, or may be done at a continuous basis or may be done at pre-determined time intervals. Other feature has been described with respect to Figure 1 and will not be repeated. In step 220, ammonia rich water received from source tank 110, wherein the ammonia is converted to a nitrate by process of nitrification using microorganisms, as described with respect to Figure 1. In step 230, post nitrification in biofilter 130, the treated water is recirculated back to source tank 110 as described with respect to Figure 1. This ensures lesser wastage of water and higher reuse and less cost for achieving the nitrification process as described previously with respect to Figure 1.
[0037] Reference is now made to Figure 3, which illustrates an exemplary case of results obtained from the biofilter using LECA balls and simulating rearing cycle in accordance with the embodiments of the present disclosure. In accordance with the embodiment of the present disclosure, preliminary study and technology development was carried out using an imported commercial (standard) biocarrier. In an exemplary embodiment, in order to be able to make the process sustainable, the process was further validated using LECA balls (light expanded clay aggregate balls) under laboratory conditions, which is among the performant and economical biocarriers. In the exemplary embodiment, LECA balls were also enriched for 30 days in accordance with previously known techniques in the art. In an embodiment of the present disclosure, TAN concentration in feed water was increased over a period of 90 days (rearing cycle or duration) to simulate fish growth (and TAN generation) in source tank considering a stocking density of 45 kg/m³. The x axis shows time in days and various parameters on the y-axis. As illustrated TAN removal efficiency (X line) was very high around and was found to be close to about 100% over a period of 90 days. Stocking density (• line) had increased from close to 0 kg/m³ to about 45 kg/m³ over a period of 90 days, which depicts the growth of the aquatic organism in the rearing cycle. The total ammonia nitrogen concentration (triangles) is maintained < 1 mg/L. Ammonia loading rate showed an increase from 0 at day 0 to about 1800 g/(m³·d) around the 90- day mark.
[0038] It should also be noted here that the results illustrated in Figure 3 are of trials performed under laboratory conditions, which may be replicated over a larger scale. Ammonia was efficiently removed during the cycle, maintaining TAN concentrations less than 1 mg/L in the source tank. Stocking density of 45 kg/m³ and TAN less than 1 mg/L was maintained, which would permit cultivation of most of the fish species, and biofilter to source tank volume was only 0.02. Ammonia was efficiently removed during the cycle, enabling TAN concentrations < 1 mg/L in the culture tank. Stocking density of 45 kg/m³ is about 2.5 times higher than the current practice in India, yet maintaining TAN < 1 mg/L.
[0039] Table 1 below represents previously studied investigations of applications of PBBRs for nitrification in RAS using imported commercial biocarrier. In an exemplary case, stocking density was increased in steps from 10 to 46 kg/m³ using the biofilter with 3.9 L volume. The findings were validated, and it was also shown that nitrite build up does not occur in the biofilter (Table 1).
Table 1
Nominal ALR 200 400 600 800 900 g/(m³·d)
Stocking density 10.2 20.4 30.6 40.8 45.9 kg/m³
ALR applied 189 ± 11 384 ± 15 560 ± 31 802 ± 62 898 ± 43 g/(m³·d)
N-NH4+ in feed 126 ± 7 255 ± 10 372 ± 21 532 ± 41 595 ± 29 mg/L
N-NH4+ in CT 0.22 ± 0.07 0.43 ± 0.13 0.55 ± 0.11 0.73 ± 0.18 0.87 ± 0.12 mg/L
N-NO2- in CT 0.12 ± 0.03 0.18 ± 0.05 0.14 ± 0.05 0.17 ± 0.03 0.31 ± 0.07 mg/L
N-NH4+ removal 99.83 ± 0.05 99.83 ± 0.05 99.85 ± 0.03 99.85 ± 0.04 99.85 ± 0.02 %

[0040] Further, the effect of exchange rate (number of times the water inside the source tank is pumped to biofilter for treatment per day) and reactor volume, both of which need to be minimized, were evaluated as part of this phase. This was studied by reducing the exchange rate and reactor volume by maintaining the stocking density at about 46 kg/m³. The performance of the biofilter under these conditions is summarised in Tables 2 (reactor volume) and Table 3 (exchange rate).
Table 2
Stocking density 45.9 48.45 kg/m³
Reactor volume 3.8 1.9 L
Biofilter volume / CT volume 0.04 0.02 -
Nominal ALR 900 1900 g/(m³·d)
ALR applied 898 ± 43 1902 ± 35 g/(m³·d)
N-NH4+ in feed 595 ± 29 606 ± 11 mg/L
N-NH4+ in CT 0.87 ± 0.12 0.84 ± 0.17 mg/L
N-NO2- in CT 0.31 ± 0.07 0.55 ± 0.30 mg/L
N-NH4+ removal 99.85 ± 0.02 99.84 ± 0.08 %

Table 3
Stocking density 45.9 45.9 kg/m³
Reactor volume 3.8 3.8 L
Exchange rate 32 14.5 -
Nominal ALR 900 900 g/(m³·d)
ALR applied 924 ± 17 882 ± 69 g/(m³·d)
N-NH4+ in feed 613 ± 11 579 ± 55 mg/L
N-NH4+ in CT 0..72 ± 0.06 0.9 ± 0.11 mg/L
N-NO2- in CT 0.28 ± 0.06 0.35 ± .007 mg/L
N-NH4+ removal 99.89 ± 0.01 99.83 0.02 %

[0041] In accordance with the embodiments of the present disclosure. the process will facilitate robust, efficient and high-rate nitrification for RAS. In accordance with the present disclosure nitrification rates reported in prior art is < 100 g/(m³·d), whereas nitrification rates obtained using the current process has achieved as high as 1900 g/(m³·d). In accordance with the embodiment of the present disclosure, TAN removal efficiencies > 99 % and have been consistent, whereas stocking densities of only about 18 kg/m³ have been successfully achieved in RAS systems previously, the current process is capable of handling stocking densities up to 45 kg/m³, which is about a yield of 2.5 times higher. Even at high stocking densities, TAN concentration < 1 mg/L could be consistently maintained in the source tank, which would permit the cultivation of other fish species (other than tilapia and pangasius).
[0042] The present disclosure presents a compact, robust, and reliable process: which is influenced by several operating conditions and parameters. Numerous parameters such as media and bed properties, including specific surface area, roughness, bed porosity, operating conditions such as water velocity, loading rate, air velocity, water quality parameters such as pH, DO, temperature, salinity are all known to affect the performance of nitrifying biofilter. Additionally, parameters of RAS such as water exchange rate and freshwater replacement rate affect the nitrogen cycle in RAS.
[0043] Although the present disclosure has been described with reference to several preferred embodiments, it should be understood that the present disclosure is not limited to the preferred embodiments disclosed here. Embodiments of the present disclosure are intended to cover various modifications and equivalent arrangements within the spirit and scope of the appended claims. Although the foregoing disclosure has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practised within the scope of the appended claims. Examples of the present disclosure have been described in language specific to structural features and/or methods. It should be noted that there are many alternative ways of implementing both the process and apparatus of the present invention. Accordingly, embodiments of the present disclosure are to be considered illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope and equivalents of the appended claims. It should be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained as examples of the present disclosure.

, Claims:We Claim:
1. A method for efficient purification of water contaminated with ammonia, the method comprising:
- receiving at a biofilter 130, water contaminated with Ammonia from a source tank 110;
- treating the water contaminated with Ammonia in the biofilter 130 wherein the ammonia from the water is converted to nitrate resulting in ammonia lean water;
- recirculating the treated water to the source 110, wherein the treated water is ammonia lean.
2. The method as claimed in claim 1, wherein the biofilter 130 is a packed bed biofilm reactor.
3. The method as claimed in claim 1, wherein the biofilter 130 comprises naturally occurring nitrifying bacteria, wherein the nitrifying bacteria perform nitrification by converting the ammonia into a nitrate.
4. The method as claimed in claim 1, wherein the water from source tank 110 is sent to the biofilter 130 for nitrification as a continuous feed or at predetermined time intervals.
5. The method as claimed in claim 1, wherein the water from the source tank 110 is sent to the biofilter for nitrification on detection that the ammonia content in the water has crossed a pre-determined threshold, wherein sensors mounted in the source tank 110 are configured to detect the ammonia content in the water.
6. The method as claimed in claim 2, wherein volumetric nitrification rate in the biofilter 130 is in the range of 100-2000 g N/(m³·d).
7. The method as claimed in claim 2, wherein maximum surface specific nitrification rate in the biofilter 130 is in the range of 1.2-2.2 g N/(m²·d).
8. The method as claimed in claim 2, wherein a pH between 7.0 to 8.0 and a dissolved oxygen saturation between 70 to 95 % is maintained in the biofilter 130.
9. The method as claimed in claim 3, wherein the total ammonia nitrogen concentration is maintained less than 2 mg/L in the source 110.
10. The method as claimed in claim 1, wherein stocking density is in the range of 40 to 50 kg/m³.
11. The method as claimed in claim 1, wherein the ratio of biofilter volume to culture tank volume is between 0.01 to 0.04, wherein and tank exchange rate is between 45 to 360 minutes.
12. A system for recirculating aquaculture system, the system comprising:
- a source tank 110 containing water, wherein water in the source tank 110 is contaminated with ammonia;
- a biofilter 130, wherein the biofilter is packed bed biofilm reactor, the biofilter 130 coupled to the source tank 110, wherein water is pumped from the source tank 110 to the biofilter 130 via a pump 125, and the biofilter 130 on receiving the water contaminated with ammonia is configured to convert the ammonia to nitrate resulting in ammonia lean water, wherein the ammonia lean water is recirculated back to the source tank 110.
13. The system as claimed in claim 12, wherein the biofilter 130 comprises naturally occurring nitrifying bacteria, wherein the nitrifying bacteria perform nitrification by converting the ammonia into nitrate.
14. The system as claimed in claim 12, wherein the water from source 110 is sent to the biofilter 130 for nitrification as a continuous feed or at predetermined time intervals.
15. The system as claimed in claim 12, wherein the water from the source 110 is sent to the biofilter for nitrification on detection that the ammonia content in the water has crossed a pre-determined threshold, wherein sensors mounted in the source tank 110 are configured to detect the ammonia content in the water.
16. The system as claimed in claim 12, wherein volumetric nitrification rate in the biofilter 130 is in the range of 100-2000 g N/(m³·d).
17. The system as claimed in claim 12, wherein maximum surface specific nitrification rate in the biofilter 130 is in the range of 1.2-2.2 g N/(m²·d).
18. The system as claimed in claim 12, wherein pH between 7.0 to 8.0 and dissolved oxygen saturation between 70 to 95 % are maintained in the biofilter 130.
19. The system as claimed in claim 13, wherein the total ammonia nitrogen concentration is maintained less than 2 mg/L in the source 110.
20. The system as claimed in claim 11, wherein stocking density is in the range of 40 to 50 kg/m³.
21. The system as claimed in claim 11, wherein the ratio of biofilter volume to culture tank volume is between 0.01 to 0.04, wherein and tank exchange rate is between 45 to 360 minutes.

Dated this 20th day of March 2024 Indian Institute of Science
By their Agent & Attorney

Dr. Eric W B Dias/Reg No 1058
of Khaitan & Co