Sulfur autotrophic denitrification biofilter for purifying mariculture tail water

Abstract

The invention relates to a sulfur autotrophic denitrification biological filter for purifying mariculture tail water, which comprises a cylindrical biological filter shell, and a zeolite layer, a first oyster shell layer, a sulfur filler layer, a second oyster shell layer and a cobblestone support layer are sequentially arranged in the biological filter shell from top to bottom, a water inlet pipe and a water inlet valve are arranged at the top of the biological filter shell, and a water outlet pipe and a water outlet valve are arranged at the bottom. The nitrification function layer and the denitrification function layer are vertically integrated, so that an independent nitrification tank, an independent middle water tank and an independent backflow system are omitted, and the occupied area and capital construction and operation energy consumption are remarkably reduced. The oyster shell layer is used for continuously and slowly releasing alkalinity and automatically neutralizing and denitrifying to produce acid, so that the problem of accurate control and secondary pollution caused by additional acid and alkali are avoided, and the pH value of the system is more stable. The denitrification efficiency is high and thorough, and no additional carbon source cost is needed.

Description

Technical Field This invention belongs to the field of water treatment technology, specifically relating to a biological denitrification system suitable for high-salinity, low-carbon-nitrogen ratio marine aquaculture wastewater, which is a sulfur autotrophic denitrification biological filter for purifying marine aquaculture wastewater. Background Technology Sulfur autotrophic denitrification is a biological process that uses elemental sulfur or reduced sulfur compounds as electron donors to reduce nitrates to nitrogen gas under anaerobic or anoxic conditions. A typical reaction is as follows: This process requires no external organic carbon source and is suitable for wastewater with a low carbon-to-nitrogen ratio. Existing technologies include fixed-bed bioreactors using sulfur packing as an electron donor for treating nitrate-containing wastewater. These reactors typically consist of a single packing layer (sulfur particles), with nitrate removal achieved through denitrifying bacteria attaching to the surface of the sulfur particles. To ensure reaction efficiency, a separate nitrification reactor is often required upstream to convert ammonia nitrogen into nitrate, or nitrate is supplied via reflux nitrification liquid. However, existing reactors are functionally limited to denitrification; treating ammonia-containing wastewater requires an additional nitrification unit, resulting in a complex system with a large footprint. The acidic substances generated during the reaction can easily cause a drop in system pH, typically necessitating an external alkalinity adjustment device. Furthermore, the sulfur-packed bed is prone to clogging during long-term operation, requiring frequent maintenance. For example, a representative existing technology, such as CN109942156B, discloses a "Seawater Aquaculture Wastewater Treatment System Based on Biological Filter and Its Application Method," which employs a structure of anaerobic biological filter + aerobic biological filter in series to remove nitrates through heterotrophic denitrification. Although this technology has a certain removal effect on conventional pollutants, it still has the following drawbacks: 1. Low system integration: Nitrification and denitrification are placed in two independent tanks, requiring an intermediate water tank and a return system, which occupies a large area and has high investment and operating energy consumption; 2. Reliance on external carbon sources: The denitrification process requires the addition of organic carbon sources such as glucose, which not only increases operating costs but also easily leads to fluctuations in effluent COD and accumulation of nitrite. 3. Lack of pH buffering capacity: The system does not have a built-in alkalinity replenishment layer, requiring the addition of additional agents such as sodium bicarbonate, which requires high control precision and poses a risk of secondary pollution. 4. Poor adaptability to low C / N ratio seawater tailwater: Heterotrophic denitrifying bacteria have limited activity in high-salt, low-carbon-source environments, resulting in unstable nitrate removal; 5. Insufficient anti-clogging ability: A single packing layer is prone to clogging due to excessive biofilm proliferation, requiring frequent backwashing. To address the aforementioned shortcomings, this invention aims to provide a highly integrated, high-salt-tolerant, and clogging-resistant sulfur autotrophic denitrification biological filter for purifying mariculture wastewater. Summary of the Invention In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a sulfur autotrophic denitrification biological filter for purifying effluent from marine aquaculture. To solve the above-mentioned technical problems, the technical solution of the present invention is: a sulfur autotrophic denitrification biological filter for purifying effluent from seawater aquaculture, comprising a cylindrical biological filter shell, wherein the interior of the biological filter shell is provided with, from top to bottom, a zeolite layer, a first oyster shell layer, a sulfur packing layer, a second oyster shell layer, and a pebble support layer; the top of the biological filter shell is provided with an inlet pipe and an inlet valve, and the bottom is provided with an outlet pipe and an outlet valve. Preferably, the zeolite layer is 25 cm thick and is composed of natural or modified zeolite particles to adsorb ammonia nitrogen in the influent and to serve as a biofilm carrier for nitrifying bacteria, forming an aerobic nitrification zone. Preferably, the first oyster shell layer is 5 cm thick and is composed of broken oyster shells to initially buffer the pH. Preferably, the sulfur filler layer is 25 cm thick and serves as the core reaction layer. It is composed of elemental sulfur particles or sulfur-containing composite materials and is used as an electron donor and attachment carrier for sulfur autotrophic denitrifying bacteria to form an anaerobic or hypoxic denitrification zone. Preferably, the second oyster shell layer is 15 cm thick and is composed of broken oyster shells, which is used to deeply neutralize the acidic substances produced by denitrification, maintain the pH stability of the system, and further assist in phosphorus removal through calcium precipitation. Preferably, the pebble support layer is composed of large-diameter pebbles, used to evenly distribute water, support the upper filler, and prevent filler loss. Preferably, an aeration system is provided in the upper middle part of the biofilter shell. Preferably, the bottom of the biological filter shell is also provided with a backwash inlet pipe and a backwash inlet valve, a drain pipe and a drain valve. Compared with the prior art, the present invention has the following beneficial effects: 1. High integration and simplified process flow: By vertically integrating the nitrification and denitrification functional layers into one, the separate nitrification tank, intermediate water tank and reflux system are eliminated, which significantly reduces the footprint, infrastructure and operating energy consumption. 2. Stable operation with inherent pH buffering capacity: It utilizes the continuous and slow release of alkalinity from the oyster shell to automatically neutralize the acid produced by denitrification, avoiding the problem of precise control of external acid and alkali and secondary pollution, and making the system pH more stable. 3. High and thorough nitrogen removal efficiency with no external carbon source cost: Based on the principle of sulfur autotrophic denitrification, it completely eliminates the need for external carbon sources such as methanol, resulting in extremely low operating costs and avoiding the accumulation of COD or nitrite in the effluent caused by excessive or insufficient carbon source addition. Experiments have shown that the nitrate nitrogen removal rate can reach up to 99.20%. 4. Strong resistance to salinity shock: The system has been specially acclimatized, and the functional microbial community formed inside has strong tolerance to high salinity environments, and its denitrification performance is stable when treating marine aquaculture wastewater. 5. Not prone to clogging and easy to maintain: The unique packing combination and regular backwashing design effectively alleviate the common clogging problems of biological filters, extend the operating cycle, and reduce maintenance intensity. The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description Figure 1 This is a schematic diagram illustrating the structure of an embodiment of the present invention. Figure 2 This is a diagram of the zeolite phylum-level microbial community in an embodiment of the present invention. Figure 3 This is a horizontal microbial community diagram of the genus Zeolite, as shown in an embodiment of the present invention. Figure 4 This is a diagram of the microbial community at the phylum Sulfur in an embodiment of the present invention. Figure 5 This is a horizontal microbial community diagram of the sulfur filler (Sulfur) in an embodiment of the present invention. Detailed Implementation The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. like Figures 1-5As shown, this embodiment provides a sulfur autotrophic denitrification biological filter for purifying effluent from seawater aquaculture, including a cylindrical biological filter shell 1, which adopts a continuous flow operation mode of top inlet and bottom outlet. The interior of the biological filter shell is arranged from top to bottom as follows: zeolite layer 2, first oyster shell layer 3, sulfur packing layer 4, second oyster shell layer 5, and pebble support layer 6. The top of the biological filter shell is provided with an inlet pipe 7 and an inlet valve, and the bottom is provided with an outlet pipe 8 and an outlet valve. In this embodiment of the invention, the zeolite layer is about 25 cm thick and is composed of natural or modified zeolite particles. It is used to adsorb ammonia nitrogen in the influent and to serve as a biofilm carrier for nitrifying bacteria, forming an aerobic nitrification zone. In this embodiment of the invention, the first oyster shell layer is about 5 cm thick and is composed of broken oyster shells, used to initially buffer the pH. In this embodiment of the invention, the sulfur filler layer is about 25 cm thick and is the core reaction layer. It is composed of elemental sulfur particles or sulfur-containing composite materials and is used as an electron donor and attachment carrier for sulfur autotrophic denitrifying bacteria to form an anaerobic or hypoxic denitrification zone. In this embodiment of the invention, the second oyster shell layer is about 15 cm thick and is composed of broken oyster shells. It is used to deeply neutralize the acidic substances produced by denitrification, maintain the pH stability of the system, and further assist in phosphorus removal through calcium precipitation. In this embodiment of the invention, the pebble support layer is composed of pebbles with a larger particle size, which is used to evenly distribute water, support the upper filler, and prevent the filler from being lost. In this embodiment of the invention, an aeration system is provided in the upper middle part of the biofilter shell. The aeration system is located within the zeolite layer area and is equipped with perforated aeration pipes that connect to an external air pump and air stones. By controlling the aeration rate, a high dissolved oxygen concentration can be maintained in the upper layer to ensure the nitrification reaction proceeds, while the lower layer, due to oxygen consumption and diffusion limitations, naturally forms an anaerobic environment, thereby achieving a vertical gradient distribution of dissolved oxygen and spatial coupling between nitrification and denitrification. In this embodiment of the invention, the bottom of the biofilter shell is further provided with a backwash inlet pipe 9 and a backwash inlet valve, a drain pipe 10 and a drain valve. Clean water or air can be periodically introduced for reverse flushing to remove suspended solids and excessively thick biofilm trapped in the packing layer, preventing clogging. In this embodiment of the invention, the working principle of the sulfur autotrophic denitrification biological filter for purifying mariculture wastewater is as follows: Simulated mariculture wastewater enters through the top inlet pipe and flows sequentially through each packing layer: In the aerobic zeolite layer, ammonia nitrogen is converted into nitrate by nitrifying bacteria. The water flows through the first oyster shell layer, where the pH is initially buffered. Entering the sulfur packing layer, under anaerobic conditions, sulfur autotrophic denitrifying bacteria use electrons provided by sulfur to reduce nitrate to nitrogen gas. The water then passes through the second oyster shell layer to further neutralize acidic products. The purified water is discharged through the bottom outlet pipe. Throughout the entire process, no external carbon source or pH adjuster needs to be added; the system achieves efficient conversion and removal of pollutants through its own structure. The embodiments of the present invention solve the following technical problems: 1. Simplified process flow: Nitrification, denitrification, pH buffering, and phosphorus removal functions are integrated into a single vertical filter, eliminating the need for separate nitrification tanks and reflux systems; 2. Achieve zero carbon source addition: Using sulfur autotrophic denitrification as the sole nitrogen removal pathway, completely eliminating the dependence of heterotrophic denitrification on organic carbon sources; 3. Built-in pH self-stabilizing mechanism: Utilizing the calcium dissolution characteristics of oyster shells, it simultaneously neutralizes the acid produced by denitrification, eliminating the need for external alkalinity; 4. Enhance high-salt adaptability: Construct salt- and sulfur-tolerant autotrophic denitrifying bacteria through functional layer spatial coupling and targeted microbial domestication; 5. Extended operating cycle: Through the synergy of packing gradation and backwashing system, clogging is effectively alleviated and maintenance frequency is reduced. Specific implementation process: Simulated aquaculture wastewater enters through the top inlet pipe and flows sequentially through each packing layer: In the aerobic zeolite layer, ammonia nitrogen is converted into nitrate by nitrifying bacteria. The water then flows through the first oyster shell layer, where the pH is initially buffered. Entering the sulfur packing layer, under anaerobic conditions, sulfur-autotrophic denitrifying bacteria use electrons provided by sulfur to reduce nitrate to nitrogen gas. Finally, the water passes through the second oyster shell layer to further neutralize acidic products. The purified water is discharged through the bottom outlet pipe. Throughout the entire process, no external carbon source or pH adjuster is required; the system achieves highly efficient conversion and removal of pollutants through its own structure. (1) System startup and film formation The experimental water was a simulated mariculture wastewater prepared from tap water, using ingredients such as cultured brown sugar, NH4Cl, KH2PO4, KNO3, and sea salt. The biofilm formation process consisted of three stages: The first stage was intermittent acclimatization and aeration. Sludge was mixed with acclimatization water and injected into the reactor. Every 24 hours, the entire sludge-water mixture was replaced, and sludge and fresh wastewater were added again. During this stage, the influent salinity was gradually increased, successively experiencing adaptation processes of 0-10‰, 10-20‰, and 20-35‰ salinity. The second stage was continuous flow start-up. The reactor operation was changed to a continuous influent / outfluent mode, initially with a low flow rate, which was then gradually increased to the design hydraulic load. The third stage was target water quality acclimatization. The prepared simulated mariculture wastewater was used for long-term acclimatization, allowing the microbial community to adapt to the actual wastewater's water quality characteristics. Biofilm formation was considered complete when the effluent water quality stabilized; this stage lasted a total of 20 days. (2) Formal operation The influent was simulated effluent from seawater aquaculture. The heating time (HRT) was controlled within the range of 3–12 h. The COD, TP, TIN, and NH3 levels in the upper layer (zeolite section) and the final effluent were monitored regularly. 4+ -N、NO 3- -N、NO 2- -N and other indicators. Backwash every 7–10 days to prevent clogging of the equipment.

[0001] Table 1. Main components of simulated wastewater during the biofilm formation period

[0002] Table 2. Main components of water quality during the acclimatization period

[0003] (3) Experimental results Table 3. Average removal rates of water quality indicators in the upper layer and effluent of the biological filter.

[0004] When the HRT is 12h, the metabolic cycle of sulfur-autotrophic denitrifying bacteria is sufficient, allowing for deep utilization of sulfur-containing substrates and nitrogenous materials, resulting in a TIN removal rate of 83.79% and NO removal rate of [missing information]. 3- -N removal rate reached 92.56%; even with HRT shortened to 3h, sulfur-autotrophic denitrifying bacteria could still rapidly utilize sulfur electron donors to complete NO removal. 3- The reduction of -N maintained a removal rate of 98.23%. The only slight decrease in TIN removal rate was due to insufficient substrate contact time. Simultaneously, the acidic substances produced by sulfur autotrophic metabolism were neutralized by the calcium-based buffer system of the upper and lower oyster shells, maintaining system pH stability and ensuring the activity of sulfur autotrophic denitrifying bacteria. The core innovation of this device lies in using sulfur autotrophic denitrification metabolism as the core driving force, combined with the spatial coupling design of the functional layer. It not only leverages the low-carbon and high-efficiency advantages of sulfur autotrophic denitrification, but also adapts to the low C / N characteristics of marine aquaculture wastewater. It is a dedicated and highly efficient technical equipment for denitrification of aquaculture wastewater. like Figure 2 , Figure 3 As shown, the dominant bacterial phylum in the zeolite group samples was Proteobacteria (…). Proteobacteria Bacteroidetes ( Bacteroidota ), Desulfobacteria ( Desulfobacterota ), Pneumatomycetes ( Planctomycetota Patellar Bacteria ( Patescibacteria The cumulative relative abundance reached 91.1%. Among them, Proteobacteria and Bacteroidota As a core phylum, its relative abundance totaled 73.3%. Proteobacteri It is the most metabolically diverse phylum of bacteria, widely involved in processes such as organic matter degradation, nitrogen and phosphorus removal, and is a typical phylum in wastewater treatment systems. Bacteroidota These are key bacterial groups that degrade large organic molecules such as proteins and polysaccharides. Planctomycetota This provides a species basis for potential anaerobic ammonia oxidation reactions. The dominant bacterial genus is *Venoglaskii* ( Winogradskella ), genus *Plasmodium* Epibacterium ), Unnamed genus ( PB19 ), Municardia ( Muricauada ), genus Halomonas ( Halomonas The cumulative relative abundance was 42.0%. Excluding unnamed genera... PB19 Apart from those whose functions are not yet clear, the other genera are typical groups found in marine or high-salt environments, for example, Muricauda and Winogradskyella It is a key genus of bacteria in marine ecosystems that degrade complex polysaccharides; Halomonas These bacteria are known for their broad salt tolerance and metabolic diversity, reflecting their good adaptability and ecological representativeness to the high-salinity habitat of marine aquaculture tailwater. like Figure 4 , Figure 5 As shown, the dominant bacterial phylum in the sulfur-filled sample group completely shifted to an ecological pattern dominated by the sulfur cycle, with Bacteroidetes being the dominant phylum in the water. Bacteroidota ), Desulfobacteria ( Desulfobacterota Proteobacteria ( Proteobacteria Campylobacteria ( Campylobacterota Patellar Bacteria ( Patescibacteria The cumulative relative abundance reached 93.3%. Desulfobacterota With an abundance of 23.6%, it belongs to the recognized core functional phylum of sulfur cycling bacteria, similar to other sulfur-oxidizing bacteria. CampylobacterotaThis collectively confirms that this layer has evolved into a highly characteristic anaerobic functional segment with the sulfur cycle as its core metabolic pathway. The dominant bacterial genera are highly synergistic sulfur-converting functional communities, mainly *Sulphurobacterium* (green sulfur bacteria). Chlorobaculum ), Desulfuric Vibrio spp. Desulfurivibrio ), Vibrio genus ( Vibrio Thiomonas spp. Sulfurimonas ), Longobacterium ( Prolixibacteraceae The cumulative relative abundance was 70.5%. Among them, Chlorobaculum (42.9%) is a representative genus of bacteria that performs photoautotrophic sulfur oxidation under strictly anaerobic conditions, and can fix CO2 using hydrogen sulfide and other substances as electron donors. Sulfurimonas They are chemoautotrophic sulfur-oxidizing bacteria and are often coupled with the denitrification process; Desulfurivibrio It is a typical sulfate-reducing bacterium, capable of reducing sulfate to hydrogen sulfide. Vibrio Some species also possess sulfur metabolism capabilities, such as those in the family Longobacteriaceae ( Prolixibacteraceae Some members of this genera have also been reported to participate in the sulfur reduction process. These bacteria constitute a complete cycle of sulfide production and chemooxidation, are highly adapted to and dominate the lower anaerobic, sulfur-rich environment, and form the microbial basis for sulfur-driven denitrification. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A sulfur-autotrophic denitrification biological filter for purifying effluent from seawater aquaculture, characterized in that: The biological filter includes a cylindrical shell, and the interior of the biological filter includes, from top to bottom, a zeolite layer, a first oyster shell layer, a sulfur packing layer, a second oyster shell layer, and a pebble support layer. The top of the biological filter is equipped with an inlet pipe and an inlet valve, and the bottom is equipped with an outlet pipe and an outlet valve.

2. The sulfur autotrophic denitrification biological filter for purifying effluent from marine aquaculture according to claim 1, characterized in that: The zeolite layer, 25 cm thick, is composed of natural or modified zeolite particles. It is used to adsorb ammonia nitrogen in the influent and serves as a biofilm carrier for nitrifying bacteria, forming an aerobic nitrification zone.

3. The sulfur autotrophic denitrification biological filter for purifying effluent from marine aquaculture according to claim 1, characterized in that: The first oyster shell layer is 5 cm thick and is composed of broken oyster shells, serving as a preliminary pH buffer.

4. The sulfur autotrophic denitrification biological filter for purifying effluent from marine aquaculture according to claim 1, characterized in that: The sulfur filler layer is 25 cm thick and serves as the core reaction layer. It is composed of elemental sulfur particles or sulfur-containing composite materials and is used as an electron donor and attachment carrier for sulfur autotrophic denitrifying bacteria to form an anaerobic or hypoxic denitrification zone.

5. The sulfur autotrophic denitrification biological filter for purifying effluent from marine aquaculture according to claim 1, characterized in that: The second oyster shell layer is 15 cm thick and is composed of broken oyster shells. It is used to deeply neutralize the acidic substances produced by denitrification, maintain the pH stability of the system, and further assist in phosphorus removal through calcium precipitation.

6. The sulfur autotrophic denitrification biological filter for purifying effluent from marine aquaculture according to claim 1, characterized in that: The pebble support layer is composed of large-diameter pebbles, which are used to distribute water evenly, support the upper filler, and prevent the filler from being lost.

7. The sulfur autotrophic denitrification biological filter for purifying effluent from marine aquaculture according to claim 1, characterized in that: An aeration system is installed in the upper middle part of the shell of the biological filter.

8. The sulfur autotrophic denitrification biological filter for purifying effluent from marine aquaculture according to claim 1, characterized in that: The bottom of the biological filter shell is also equipped with a backwash inlet pipe and a backwash inlet valve, as well as a drain pipe and a drain valve.

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