Treatment method of ship maintenance wastewater

Abstract

The invention discloses a ship maintenance wastewater treatment method, which comprises: carrying out heating oil separation physicochemical treatment on heavy high-oil wastewater generated in a ship maintenance process, heating to dissolve the heavy high-oil wastewater, adding a chemical agent to convert the heavy high-oil wastewater into a separable floccule so as to obtain a first effluent; mixing the first effluent with light low-oil wastewater generated in the ship maintenance process to obtain mixed wastewater; the mixed wastewater is subjected to dosing air flotation treatment, light oil in the mixed wastewater is removed, and second effluent is obtained; the second effluent is introduced into a biochemical treatment system for deep purification treatment, and finally up-to-standard discharge water is obtained. According to the invention, the ship maintenance wastewater is subjected to classified treatment according to heavy high oil and light low oil, and is combined with heating oil separation physicochemical pretreatment, dosing air floatation and biochemical deep purification by adding a dominant microbial agent, so that the stability of the heavy oil is effectively broken, the system blockage and impact risks are remarkably reduced, and the construction and operation cost and the land use demand can be reduced at the same time.

Description

Technical Field

[0001] This invention relates to the field of water pollution treatment technology, and specifically to a method for treating ship maintenance wastewater. Background Technology

[0002] The shipbuilding industry generates a large amount of maintenance wastewater during daily production. This wastewater contains high levels of pollutants such as petroleum hydrocarbons, suspended solids, and grease. The grease in the wastewater is extremely viscous, making it ineffective for removal using ordinary physical oil-water separation methods. The grease in the wastewater needs to be removed during pretreatment. If the grease flows into the subsequent biological purification process, it will severely impact the bioreactor and affect the activity of microorganisms. Therefore, oily wastewater from the shipbuilding industry requires a pretreatment process before biological purification to remove pollutants such as petroleum hydrocarbons, smaller suspended particulate matter, and grease, thereby reducing the processing load on the subsequent biological system.

[0003] Currently, existing wastewater treatment methods typically combine wastewater treatment with domestic sewage treatment. While this reduces the concentration of pollutants in the wastewater, it also increases the design scale of the treatment facilities, raising investment and operating costs and occupying too much land. On the other hand, the timing of ship maintenance wastewater generation coincides with that of domestic sewage. If the two are treated together, the collection tank must be large enough to accommodate both streams of wastewater simultaneously, and the water concentration fluctuates significantly, seriously affecting the treatment effect and the quality of the effluent.

[0004] In existing technologies, the treatment of oily wastewater from ships often employs a combination of physical separation (such as oil separation and air flotation) and biochemical treatment. For example, patent CN119461738A discloses a "method and apparatus for deep treatment of oily wastewater from ships," which achieves deep oil-water separation through a three-stage physical treatment process involving precision filtration, coalescence separation, and ceramic ultrafiltration membranes, and incorporates concentrate reflux to improve recovery rates. This method is suitable for light oily wastewater such as bilge water generated during ship operation. However, for heavy oily wastewater (such as lubricating oil and hydraulic oil waste) with high viscosity, high concentration, and semi-solid or viscous state at room temperature generated during maintenance, its physical separation efficiency decreases significantly, the membrane system is prone to clogging, and operating costs are high.

[0005] Furthermore, traditional integrated treatment processes fail to differentiate between different types of maintenance wastewater, leading to excessive loads on the front-end treatment, vulnerability of the biological system, and unstable effluent quality. Additionally, existing solutions often neglect the compliant disposal of byproducts such as waste oil and sludge, posing a risk of secondary pollution.

[0006] Therefore, there is an urgent need to develop a wastewater treatment method that can specifically treat heavy oily components in ship maintenance wastewater and achieve efficient, stable, and compliant operation throughout the entire process. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention aims to provide a method for treating ship maintenance wastewater, solving the problems of low treatment efficiency, easy clogging, and unstable operation of existing technologies for heavy, oily wastewater, and achieving the integrated goal of wastewater classification treatment, resource recovery, and compliant discharge.

[0008] To achieve the above objectives, the present invention provides:

[0009] A method for treating ship maintenance wastewater, the method comprising the following steps:

[0010] Heavy, oily wastewater generated during ship repair is subjected to heat-oil separation physicochemical treatment. The heavy oil is dissolved by heating, and chemical agents are added to convert it into separable flocculent matter, resulting in the first effluent.

[0011] The first effluent is mixed with light, low-oil wastewater generated during ship repair to obtain mixed wastewater;

[0012] The mixed wastewater is subjected to chemical flotation treatment to remove light oils, resulting in a second effluent.

[0013] The second effluent is then fed into a biochemical treatment system for deep purification, ultimately yielding compliant discharge water.

[0014] Preferably, the heating and oil-separation physicochemical treatment specifically includes:

[0015] In the heating zone, the heavy, oily wastewater is heated to 35-40°C, causing the heavy oil to dissolve into low-quality, small-molecule oils.

[0016] In the chemical dosing area, demulsifiers, coagulants, and flocculants are added to the wastewater to cause the low-quality small-molecule oils to aggregate into flocculent precipitates.

[0017] Solid-liquid separation is carried out in the sedimentation zone. The supernatant flows out as the first effluent, while the separated floating oil is collected by overflow and the flocculent matter settles to form sludge.

[0018] Preferably, the demulsifier includes caustic soda flakes, the coagulant includes polyaluminum chloride, and the flocculant includes anionic polyacrylamide.

[0019] Preferably, during the heated oil-water separation physicochemical treatment process, the separated floating oil is collected in a waste oil collection tank, and the resulting sludge is discharged into a scum sludge thickening tank.

[0020] Preferably, the biochemical treatment system includes an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence.

[0021] Preferably, a dominant microbial agent is added to the biochemical treatment system, the dominant microbial agent including one or more of Bacillus, photosynthetic bacteria, filamentous fungi and microbial growth agents.

[0022] Preferably, the heating and oil-separation physicochemical treatment is operated in an intermittent mode of 8 to 10 hours, and the biochemical treatment system is operated in a continuous mode of 24 hours.

[0023] Preferably, the concentration of petroleum hydrocarbons in the compliant effluent is less than or equal to 15 mg / L, and the chemical oxygen demand is less than or equal to 350 mg / L.

[0024] Preferably, the heavy, oily wastewater originates from ship machining, equipment dismantling, or component cleaning processes, while the light, low-oily wastewater originates from ship deck washing or general cleaning processes.

[0025] Preferably, the method further includes collecting the waste oil and sludge generated during the heating and oil separation physicochemical treatment and the chemical flotation treatment, and treating them as hazardous waste.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. For the first time, it is proposed to classify and treat ship maintenance wastewater into "heavy and high-oil" and "light and low-oil" categories to avoid high-viscosity oils from directly entering the air flotation or biological treatment system, thereby significantly reducing the risk of system blockage and shock.

[0028] 2. Through the synergistic effect of heat treatment and chemical agents, the stability of heavy oil is effectively broken, transforming it into a separable form, with an oil removal rate of over 90%.

[0029] 3. Small-volume, heavy, and oily wastewater is effectively pretreated before being combined with large-volume, light, and low-oil wastewater for further treatment, which reduces construction and operating costs and also reduces land use requirements.

[0030] 4. Add dominant microbial agents to the biological treatment tank to deeply decompose and purify pollutants;

[0031] 5. After treatment using this method, the effluent quality meets the Class B requirements of the "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T 31962-2015), with typical indicators being: petroleum hydrocarbons ≤15 mg / L, and chemical oxygen demand (COD) ≤15 mg / L. Cr ≤350 mg / L, suspended solids (SS) ≤400 mg / L, ammonia nitrogen ≤45 mg / L, total phosphorus (TP) ≤8 mg / L, pH 6–9. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the process flow of the ship repair wastewater treatment method of the present invention. Detailed Implementation

[0033] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art should understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0034] like Figure 1 As shown, this application provides a method for treating ship maintenance wastewater, the method comprising the following steps:

[0035] Heavy, oily wastewater generated during ship repair is subjected to heat-oil separation physicochemical treatment. The heavy oil is dissolved by heating, and chemical agents are added to convert it into separable flocculent matter, resulting in the first effluent.

[0036] The first effluent is mixed with light, low-oil wastewater generated during ship repair to obtain mixed wastewater;

[0037] The mixed wastewater is subjected to chemical flotation treatment to remove light oils, resulting in a second effluent.

[0038] The second effluent is then fed into a biochemical treatment system for deep purification, ultimately yielding compliant discharge water.

[0039] The treatment method provided in this application addresses the differences in characteristics between the heavy, high-oil and light, low-oil components in maintenance wastewater by employing a segmented synergistic treatment strategy: First, the viscous, difficult-to-treat heavy, high-oil wastewater is heated to reduce viscosity, and demulsifiers, coagulants, and flocculants are added to transform it into settleable flocs, achieving efficient oil-water separation. Subsequently, the pretreated effluent is mixed with the light, low-oil wastewater, and residual light oil is further removed by chemical flotation. Finally, the wastewater undergoes deep degradation of organic matter, nitrogen, phosphorus, and other pollutants through an anaerobic-anoxic-aerobic biological system and dominant microbial agents. This method effectively avoids the impact and clogging of subsequent units by high-viscosity oil, significantly improves system stability and oil removal efficiency, has low operating energy consumption, and consistently meets municipal water quality standards, demonstrating both technical feasibility and engineering practicality.

[0040] It is understood that the heavy oily wastewater described in this invention refers to oily wastewater generated during ship maintenance processes such as machining, equipment dismantling, tank cleaning, or component rinsing. At room temperature (20°C), it is viscous or semi-fluid, with petroleum concentrations typically exceeding 2000 mg / L and dynamic viscosity greater than 50 mPa·s. It is difficult to effectively separate by conventional gravity separation and requires heating and chemical enhancement treatment to achieve effective oil-water separation.

[0041] It is understood that the heated oil-water separation physicochemical treatment described in this invention refers to an integrated pretreatment process that sequentially completes three functions—heating, chemical dosing reaction, and solid-liquid separation—within a continuous flow treatment unit: First, heavy, oily wastewater is heated to 35–40°C to reduce the viscosity of the oil phase and promote the dissolution of heavy oil; then, demulsifiers, coagulants, and flocculants are added to convert dissolved or emulsified oils into settleable flocs; finally, the supernatant is separated from the floating oil and sludge through a sedimentation zone. This treatment process combines physical (heating, gravity separation) and chemical (demulsification, coagulation, flocculation) effects, hence the name heated oil-water separation physicochemical treatment.

[0042] It is also understood that the light, low-oil wastewater described in this invention refers to wastewater generated during ship maintenance that has a low oil content, good oil fluidity, and is easy to float naturally or be removed by conventional air flotation. Typical sources include deck flushing water, cabin cleaning wastewater, or tool surface rinsing water, etc. Its petroleum concentration is generally below 500 mg / L, and it is clear or microemulsion at room temperature. It does not contain high-viscosity heavy oil components and can be directly treated in the chemical flotation unit.

[0043] Similarly, it can be understood that the chemical flotation treatment described in this invention refers to a physicochemical treatment process that, based on dissolved air flotation, adds chemical agents to wastewater to enhance the removal of oil and suspended solids. Specifically, it may include: first, adding coagulants (such as polyaluminum chloride) and flocculants (such as polyacrylamide) to the mixed wastewater to destabilize fine oil droplets and colloidal particles and aggregate them into larger flocs; then, generating micron-sized bubbles through a dissolved air release system, causing the flocs to adhere and float to the surface, forming scum, which is then removed by a scraper, resulting in clarified effluent. This treatment method combines the synergistic effects of chemical coagulation and physical flotation, hence the name chemical flotation treatment.

[0044] In one embodiment, the heated oil-separation physicochemical treatment specifically includes:

[0045] In the heating zone, the heavy, oily wastewater is heated to 35-40°C, causing the heavy oil to dissolve into low-quality, small-molecule oils.

[0046] In the chemical dosing area, demulsifiers, coagulants, and flocculants are added to the wastewater to cause the low-quality small-molecule oils to aggregate into flocculent precipitates.

[0047] Solid-liquid separation is carried out in the sedimentation zone. The supernatant flows out as the first effluent, while the separated floating oil is collected by overflow and the flocculent matter settles to form sludge.

[0048] In the above implementation method, the heating and oil-separation physicochemical treatment specifically includes: heating the heavy, oily wastewater to 35-40°C in the heating zone. This temperature range has been experimentally verified to effectively reduce the viscosity and surface tension of heavy, oily substances (such as lubricating oil and hydraulic oil), causing them to dissolve and disperse from a semi-solid or colloidal state into low-quality, small-molecule oils with better fluidity, thereby breaking their stable emulsion system with the aqueous phase; subsequently, the wastewater enters the chemical dosing zone, where demulsifiers (such as caustic soda flakes) and coagulants (such as polyaluminum chloride) are added. The process involves using flocculants (such as anionic polyacrylamide) to neutralize the surface charge of oil droplets through demulsification. The resulting micro-flocculations then bridge and grow into dense, easily settling flocculent precipitates. Finally, the wastewater flows into the sedimentation zone, where gravity facilitates efficient solid-liquid separation. The supernatant, as the first effluent, flows by gravity into the subsequent equalization tank. The less dense floating oil is collected in the waste oil recovery tank via a top overflow pipe, while the denser oily flocculents settle to the bottom, forming sludge which is periodically discharged into the sludge thickening tank. This treatment step, combining thermal decomposition with chemical conversion, effectively addresses the technical bottleneck of separating high-viscosity heavy oil from ship maintenance wastewater. It significantly improves pretreatment efficiency and avoids the problems of low heavy oil removal rates and clogging associated with traditional oil separation processes, providing a stable and reliable influent water quality guarantee for subsequent air flotation and biological treatment.

[0049] In one embodiment, the demulsifier comprises caustic soda flakes, the coagulant comprises polyaluminum chloride, and the flocculant comprises anionic polyacrylamide.

[0050] In the above embodiments, the demulsifier includes caustic soda (sodium hydroxide), which increases the pH of the wastewater to an alkaline range (usually 9-11), disrupting the emulsification stability of the oil-water interface and deactivating the surface-active substances coated on the oil droplets, thereby achieving effective separation of the oil and water phases. The coagulant includes polyaluminum chloride (PAC), which hydrolyzes in water to generate positively charged polynuclear hydroxyl complexes, neutralizing negatively charged colloidal particles and tiny oil droplets in the wastewater, destabilizing them and causing them to initially aggregate into micro-flocs. The flocculant includes anionic polyacrylamide (anionic PAM), whose long-chain polymer structure further connects and entangles the destabilized micro-flocs into dense flocculent precipitates with good settling properties through adsorption bridging. The synergistic addition of the above three types of agents in a specific order forms an integrated chemical enhancement pathway of "demulsification-destabilization-flocculation," which not only significantly improves the removal efficiency of oil and suspended solids in heavy, high-oil wastewater but also effectively improves the operation of subsequent sedimentation or flotation units. The proposed reagent combination scheme is optimized for the high viscosity and high emulsification characteristics of ship maintenance wastewater. It has the advantages of rapid reaction, fast floc formation, good settling performance, and low reagent consumption. It overcomes the technical obstacles of treating such complex wastewater with a single reagent or conventional ratio, and improves the adaptability and treatment efficiency of the present invention in terms of process.

[0051] Of course, the demulsifiers, coagulants, and flocculants mentioned in this application are not limited to caustic soda flakes, polyaluminum chloride (PAC), and anionic polyacrylamide (anionic PAM); these are merely specific examples in preferred embodiments. Based on the wastewater quality characteristics, treatment objectives, and cost considerations, those skilled in the art can reasonably select other alternative agents with the same or similar functions, which still fall within the scope of protection of this application.

[0052] In another embodiment, the demulsifier may also include inorganic alkalis, such as lime (Ca(OH)2) and sodium carbonate (Na2CO3), the coagulant may also include other aluminum salts, such as aluminum sulfate (Al2(SO4)3) and aluminum chloride (AlCl3), and the flocculant may also include natural polymeric flocculants, such as chitosan and starch modifiers.

[0053] It should be noted that, through experimental comparison, it is shown that when using a combination of caustic soda + PAC + anionic PAM, the petroleum removal rate of heavy, oily wastewater after heating and oil-water separation physicochemical treatment can reach over 92%. The resulting flocs are dense, settle rapidly (settling within 30 minutes), and the supernatant has low turbidity and good stability. However, if caustic soda is replaced with lime or sodium carbonate, although it has a certain demulsifying effect, it easily generates a large amount of calcium and magnesium precipitates, interfering with oil-water separation and increasing sludge volume. If PAC is replaced with aluminum sulfate or aluminum chloride, it easily forms colloidal hydroxides under alkaline conditions, resulting in loose flocs and poor settling performance. If natural high-molecular-weight flocculants such as chitosan or starch-modified materials are used to replace anionic PAM, the lower molecular weight and weak bridging ability make it difficult to effectively aggregate micro-flocs formed by high-viscosity oil droplets, leading to higher and more fluctuating oil content in the effluent.

[0054] In one embodiment, during the heated oil-water separation physicochemical treatment process, the separated floating oil is collected in a waste oil collection tank, and the resulting sludge is discharged into a scum sludge thickening tank.

[0055] In the above-described implementation method, during the heated oil-water separation physicochemical treatment process, as the wastewater completes solid-liquid separation in the sedimentation zone, the lighter, less dense floating oil rises and accumulates on the surface. It is continuously or periodically discharged through an overflow weir or oil collection pipe located at the top of the tank and then transported in a sealed manner to a waste oil collection tank for temporary storage. Simultaneously, the oily flocculent material formed through demulsification, coagulation, and flocculation settles to the bottom of the tank due to its higher density. This oily sludge is then discharged as oily sludge through a bottom sludge discharge valve or sludge pump into a scum sludge thickening tank for further concentration and volume reduction. On the one hand, timely removal of the floating oil prevents re-emulsification or back-mixing, ensuring the stability of the first effluent water quality. On the other hand, concentrating the high-moisture-content oily sludge in a dedicated thickening tank not only avoids toxic impacts on the subsequent biological treatment system but also provides a prerequisite for subsequent compliant disposal by qualified units (such as hazardous waste incineration or resource utilization).

[0056] In one embodiment, the biochemical treatment system includes an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence.

[0057] In the above-described implementation, the biochemical treatment system comprises an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence. In this system, the second effluent, after initial physicochemical treatment, first enters the anaerobic tank. During its residence in this tank, facultative and obligate anaerobic microorganisms hydrolyze large organic molecules into small organic acids and release phosphorus, creating conditions for subsequent biological phosphorus removal. Subsequently, the wastewater flows by gravity into the anoxic tank. In an environment without added dissolved oxygen but with the presence of nitrates, denitrifying bacteria utilize the organic carbon source in the influent to reduce nitrate nitrogen from the aerobic tank return liquid to nitrogen gas, achieving efficient nitrogen removal. Finally, the wastewater enters the aerobic tank, where sufficient dissolved oxygen (DO≥2 mg / L) is maintained through aeration. Aerobic heterotrophic bacteria further degrade residual organic matter, while polyphosphate-accumulating bacteria excessively absorb phosphorus, and nitrifying bacteria oxidize ammonia nitrogen to nitrate, completing multiple functions of organic matter removal, nitrification, and biological phosphorus removal. Through the three-stage (anaerobic, anoxic, and aerobic) biochemical treatment combined with the front-end heating and oil-water separation physicochemical pretreatment, not only can it effectively handle influent water with low oil and low suspended solids, but it also achieves the synergistic and efficient removal of carbon, nitrogen, and phosphorus pollutants through functional zoning, so that the effluent stably meets the requirements of the "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T 31962-2015).

[0058] In one embodiment, a dominant microbial agent is added to the biochemical treatment system, the dominant microbial agent including one or more of Bacillus, photosynthetic bacteria, filamentous fungi, and microbial growth agents.

[0059] In the above embodiments, a dominant microbial agent is added to the biochemical treatment system. This dominant microbial agent includes one or more of Bacillus, photosynthetic bacteria, filamentous fungi, and microbial growth agents. Preferably, the dominant microbial agent includes all four of the following: Bacillus, photosynthetic bacteria, filamentous fungi, and microbial growth agents. In this preferred embodiment, the agent is a functional complex of bacteria specifically constructed to target residual recalcitrant petroleum hydrocarbons, long-chain fatty acids, trace amounts of emulsified oil, and potentially biotoxic substances in ship maintenance wastewater. Among them, Bacillus species (such as Bacillus subtilis and Bacillus licheniformis) have a strong ability to secrete proteases and lipases, which can efficiently decompose oils and macromolecular organic matter, and their spore structure gives them excellent shock resistance and salt tolerance; photosynthetic bacteria (such as Rhodopseudomonas) can metabolize a variety of organic acids, aldehydes, ketones and other intermediate products under microaerobic or facultative conditions, while secreting growth-promoting substances to improve sludge settling properties; filamentous fungi (such as Aspergillus and Penicillium) adsorb and enrich hydrophobic pollutants through their well-developed hyphal networks, and work with bacteria to achieve deep mineralization of residual oils; while microbial growth agents (usually containing nitrogen, phosphorus, trace elements and biostimulants) provide essential nutrients for functional bacteria, accelerate their colonization and proliferation, shorten the system start-up cycle and maintain high activity.

[0060] Experiments show that when directly treating the effluent from the front-end physicochemical unit in a conventional activated sludge system, the COD... Cr Removal rates of petroleum hydrocarbons often fluctuate significantly due to microbial inhibition (COD). Cr The removal rate is approximately 70-80%; however, after adding the aforementioned compound microbial agent, the system can establish a highly efficient degrading bacterial community within 7-10 days, reducing COD. Cr The removal rate was steadily increased to over 90%, the petroleum concentration was further reduced to below 5 mg / L, and the sludge settling performance was significantly improved, with the SVI (sludge volume index) controlled below 80 mL / g. The aforementioned microbial agent combination, through multi-species synergistic metabolism, functional complementarity, and enhanced environmental adaptability, effectively overcomes the problems of slow start-up, low efficiency, and sludge bulking that are common in traditional biochemical processes for treating oily maintenance wastewater. It is a key technological guarantee for achieving stable and compliant wastewater discharge.

[0061] It is understood that the superior microbial agent described in this application refers to a compound functional microbial agent specifically formulated for the enhanced treatment of residual petroleum hydrocarbons and recalcitrant organic matter in ship maintenance wastewater. It comprises one or more of the following: Bacillus species (such as Bacillus subtilis), photosynthetic bacteria (such as Rhodopseudomonas), filamentous fungi (such as Aspergillus), and microbial growth agents (containing nitrogen, phosphorus, trace elements, and biostimulants). This microbial agent possesses characteristics of oil resistance, shock resistance, high-efficiency degradation, and promotion of sludge settling. It can rapidly colonize and synergistically metabolize within the biochemical system, significantly improving COD. Cr And the removal efficiency of petroleum-related substances.

[0062] In one embodiment, the heating and oil-separation physical and chemical treatment is operated in an intermittent mode of 8 to 10 hours, and the biochemical treatment system is operated in a continuous mode of 24 hours.

[0063] In the above implementation method, the heated oil-water separation physicochemical treatment operates in an intermittent mode of 8-10 hours, while the biological treatment system operates in a continuous mode of 24 hours. This operating strategy is based on the generation and discharge patterns and water quality characteristics of ship maintenance wastewater. Ship maintenance operations are usually concentrated during daytime working hours (e.g., 8:00–18:00), and heavy, oily wastewater is mainly generated during equipment cleaning, dismantling, and other processes, exhibiting obvious intermittent and peak characteristics. Therefore, designing the front-end heated oil-water separation physicochemical unit to operate for 8-10 hours per day can precisely meet the peak wastewater generation, avoid equipment idling, and significantly reduce energy consumption (especially the energy consumption of heating electrode rods) and reagent waste. At the same time, the biological treatment system is sensitive to hydraulic load and water quality fluctuations, and needs to maintain the stable activity of the microbial community. Therefore, a 24-hour continuous water intake and continuous aeration operating mode is adopted to ensure the ecological balance of the anaerobic-anoxic-aerobic functional zones.

[0064] More importantly, this application effectively buffers the impact of intermittent operation on water volume and quality by setting a sufficient retention time (typically 6-12 hours) in the integrated equalization tank to thoroughly homogenize and mix the intermittently generated first effluent with light, low-oil wastewater before pumping it at a stable flow rate to the subsequent chemical flotation and biological treatment systems. Actual operation data shows that compared to similar devices operating continuously around the clock, this solution can reduce daily power consumption by approximately 35%, reduce chemical dosage by more than 20%, and significantly improve the stability of effluent quality.

[0065] In one embodiment, the compliant effluent contains petroleum hydrocarbons at a concentration of less than or equal to 15 mg / L and chemical oxygen demand at a concentration of less than or equal to 350 mg / L.

[0066] For the above implementation method, the compliant effluent water has a petroleum concentration of less than or equal to 15 mg / L and a chemical oxygen demand (COD) of less than or equal to 15 mg / L. Cr The concentration of petroleum hydrocarbons must be less than or equal to 350 mg / L. Throughout the process, the front-end heating and oil-water separation physicochemical treatment removes over 90% of heavy oils, significantly reducing the oil load entering the mixing system. The chemical flotation unit further removes light oils and residual emulsified oils to below 30 mg / L. Finally, a biochemical system with added dominant microbial agents deeply mineralizes dissolved organic matter and trace amounts of petroleum hydrocarbons, ensuring that petroleum hydrocarbons are stably reduced to below 15 mg / L, and COD... CrSimultaneously reduced to below 350 mg / L. This effluent level not only meets the Class B limit requirements of the "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T 31962-2015) (petroleum ≤15 mg / L, COD ≤15 mg / L), but also... Cr ≤500 mg / L), and significantly better than the conventional effluent levels of similar ship repair wastewater treatment facilities (typically 20–50 mg / L for petroleum and COD). Cr (400–600 mg / L). It is particularly noteworthy that, even under conditions of drastic fluctuations in influent water quality (such as daily average oil content in heavy, oily wastewater varying between 2000–8000 mg / L), this application still maintains long-term stable compliance with effluent standards, demonstrating the system's excellent resistance to shock loads and operational stability.

[0067] In one embodiment, the heavy, oily wastewater originates from ship machining, equipment dismantling, or component cleaning processes, while the light, low-oily wastewater originates from ship deck washing or general cleaning processes.

[0068] In the above embodiments, the heavy, high-oil wastewater is usually generated during operations such as engine block boring, gearbox disassembly and cleaning, and hydraulic system maintenance. It contains a large amount of high-viscosity lubricating oil, cutting oil, rust-preventive oil, or accumulated sludge. It is viscous or even semi-solid at room temperature, and the concentration of petroleum is generally higher than 2000 mg / L. It is also often accompanied by metal particles, soaps, and strong emulsifiers, which are difficult to remove effectively by conventional oil separation or air flotation. On the other hand, the light, low-oil wastewater mainly comes from the washing process of areas such as the hull plating, deck, and cabin floors. The oil contained is mostly floating or slightly emulsified diesel and engine oil residues, which have good fluidity, and the concentration of petroleum is generally lower than 500 mg / L.

[0069] In one embodiment, the method further includes collecting the waste oil and sludge generated during the heating and oil separation physicochemical treatment and the chemical flotation treatment, and treating them as hazardous waste.

[0070] In the above-described implementation method, the method further includes the centralized collection of waste oil and sludge generated during the heating and oil-water separation physicochemical treatment and the chemical flotation treatment, and the disposal of these wastes to a unit with a hazardous waste management license for standardized hazardous waste disposal. This step effectively avoids the secondary pollution risk caused by the "heavy water, light sludge" approach in traditional treatment processes. If waste oil or oily sludge is discharged arbitrarily without proper management or mixed with ordinary sludge, it can easily cause soil and groundwater pollution and may violate the relevant provisions of the "National Hazardous Waste List" (HW08 category: waste mineral oil and mineral oil-containing waste). More importantly, the centralized recycling of waste oil also facilitates potential resource reuse, such as the refining of recycled base oils.

[0071] Example 1

[0072] Please refer to Figure 1 A shipyard generates approximately 80 m³ of maintenance wastewater daily, of which about 20 m³ is heavy, oily wastewater (originating from equipment dismantling and component cleaning in the machining workshop) and about 60 m³ is light, low-oily wastewater (originating from deck and cabin flushing). This embodiment employs the following treatment process:

[0073] 1. Pretreatment of heavy, oily wastewater

[0074] Heavy, oily wastewater first enters a heated oil-water separation physicochemical tank, which is divided into a heating zone, a chemical dosing zone, and a sedimentation zone.

[0075] in,

[0076] Heating zone: The volume corresponds to a hydraulic residence time of 30 minutes, and corrosion-resistant heating electrode rods are installed at the bottom; wastewater enters from the bottom of the pool and is gradually heated to 35-40°C during the ascent, which dissolves high-viscosity heavy oil into low-quality small-molecule oils with better fluidity; some light floating oil floats to the surface and is discharged through the top overflow pipe, and then transported to the waste oil collection tank through a closed pipeline.

[0077] In the chemical dosing area, the hydraulic retention time is 20 minutes. Demulsifier (caustic soda flakes, 50 ppm), coagulant (water purification type polyaluminum chloride PAC, 150 ppm) and flocculant (anionic polyacrylamide PAM, 50 ppm) are added sequentially. Through rapid stirring and slow flocculation, small molecule oils are destabilized and aggregated into dense flocculent precipitates.

[0078] Sedimentation zone: The surface loading rate is 0.8 m² / (m³·h), and it is equipped with inclined tube packing to enhance the sedimentation efficiency; the supernatant rises through the gaps between the inclined tubes to the top outlet channel and flows into the integrated equalization tank by gravity; the flocculent sediment settles to the bottom of the tank under gravity and is discharged into the scum thickening tank through the corrosion-resistant sludge discharge pipe.

[0079] 2. Mixing and flotation treatment of light, low-oil wastewater

[0080] Light, low-oil wastewater enters the integrated equalization tank directly through an independent collection network, where it is thoroughly mixed with the first effluent. The mixed wastewater is then pumped to a chemical flotation unit, where PAC (100 ppm) and PAM (30 ppm) are added. The dissolved air releases microbubbles, causing the light oil to adhere to and float to the surface, forming scum. After being skimmed off by a mechanical scum scraper, the clarified second effluent flows by gravity into the intermediate water tank.

[0081] 3. Advanced biochemical treatment and emission compliance

[0082] The effluent from the intermediate tank is metered and pumped to the biological treatment system, which consists of sequentially connected anaerobic, anoxic, and aerobic tanks, with a total hydraulic retention time of 24 hours. During operation, dominant microbial agents are continuously added to the aerobic tank. These agents consist of Bacillus, photosynthetic bacteria, filamentous fungi, and microbial growth promoters (effective viable count ≥ 1 × 10⁻⁶). 9 (CFU / g, dosage 50 mg / L) significantly enhances the degradation capacity of residual petroleum hydrocarbons, COD, and nitrogen and phosphorus pollutants. The effluent from the aerobic tank enters the secondary sedimentation tank for sludge-water separation, and the supernatant is discharged into the municipal sewage network as the final effluent.

[0083] 4. By-product disposal

[0084] Waste oil in the waste oil collection tank and oily sludge in the sludge thickening tank are temporarily stored in leak-proof containers and regularly handed over to units holding a "Hazardous Waste Management License" for compliant off-site disposal to prevent secondary pollution.

[0085] 5. Comparison of treatment effects

[0086] The system ran continuously for 30 days, and the water quality monitoring results are shown in the table below:

[0087]

[0088] Note: Except for pH, which is dimensionless, all other values ​​are in mg / L.

[0089] The removal efficiency data is as follows:

[0090]

[0091] The following is a comparison of the effects of treating heavy, high-oil materials alone versus traditional mixed treatment:

[0092]

[0093] The comparative example refers to the direct mixing of heavy, oily wastewater and light, low-oily wastewater, followed by only air flotation and biochemical treatment (without heated oil separation pretreatment).

[0094] The results show that the separate treatment process of "separate pretreatment of heavy, oily wastewater combined with mixed treatment of light, low-oily wastewater" adopted in this application is significantly better than the traditional mixed treatment method; the heated oil-water separator achieves a petroleum removal rate of 80% and a COD reduction of [missing information]. Cr With a removal rate of 37%, the load on subsequent units was effectively reduced; the overall system effluent consistently met standards (petroleum ≤15 mg / L, COD ≤15 mg / L). Cr The concentration of waste is ≤350 mg / L, and the equipment has high operational stability and strong shock resistance. Compared with traditional mixed treatment, this method has a smaller equipment footprint, lower investment, better treatment effect, and simpler waste composition, making it easier to dispose of.

[0095] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method of treating ship maintenance wastewater, characterized by, The method comprises the following steps: The heavy high-oil wastewater generated in the ship maintenance process is subjected to heating and oil separation physical treatment, the heavy high-oil is dissolved by heating, and chemical agents are added to convert it into separable flocculent, to obtain first effluent water; The first effluent water is mixed with light low-oil wastewater generated in the ship maintenance process to obtain mixed wastewater; The mixed wastewater is subjected to dosing air flotation treatment to remove light oil therein, to obtain second effluent water; The second effluent water is introduced into a biochemical treatment system for deep purification treatment, to finally obtain standard discharge water.

2. The method of treating ship maintenance wastewater according to claim 1, wherein, The heating and oil separation physical treatment specifically comprises: The heavy high-oil wastewater is heated to 35-40 DEG C in a heating zone, so that the heavy high-oil is dissolved into low-quality small-molecule oil; Demineralized water is added to the wastewater in a dosing zone, to add demulsifier, coagulant and flocculant, so that the low-quality small-molecule oil is gathered into flocculent precipitate; Solid-liquid separation is carried out in a precipitation zone, the supernatant is taken out as the first effluent water, the separated floating oil is collected by overflow, and the flocculent material is settled to form sludge.

3. The method of treating ship maintenance wastewater according to claim 2, wherein, The demulsifier comprises caustic soda, the coagulant comprises polyaluminum chloride, and the flocculant comprises anionic polyacrylamide.

4. The method of treating ship maintenance wastewater according to claim 2, wherein, In the heating and oil separation physical treatment process, the separated floating oil is collected into a waste oil collection tank, and the formed sludge is discharged into a scum sludge concentration tank.

5. The method of treating ship maintenance wastewater according to claim 1, wherein, The biochemical treatment system comprises an anaerobic tank, an anoxic tank and an aerobic tank which are sequentially communicated.

6. The method of treating ship maintenance wastewater according to claim 5, wherein, An advantage microbial agent is added in the biochemical treatment system, and the advantage microbial agent comprises one or more of bacillus, photosynthetic bacteria, filamentous fungi and microbial growth agent.

7. The method of treating ship maintenance wastewater according to claim 1, wherein, The heating and oil separation physical treatment is operated in an intermittent mode of 8-10 hours, and the biochemical treatment system is operated in a continuous mode of 24 hours.

8. The method of treating ship maintenance wastewater according to claim 1, wherein, In the standard discharge water, the concentration of petroleum is less than or equal to 15 mg / L, and the chemical oxygen demand is less than or equal to 350 mg / L.

9. The method of treating ship maintenance wastewater according to claim 1, wherein, The heavy high-oil wastewater is derived from ship machining, equipment disassembly or part cleaning process, and the light low-oil wastewater is derived from ship deck washing or general cleaning process.

10. The method of treating ship maintenance wastewater of claim 1, wherein, The method further comprises collecting and performing hazardous waste treatment on waste oil and sludge generated in the heating and oil separation physical treatment and the dosing air flotation treatment.

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