Treatment method of oily sewage of ship

Abstract

The invention discloses a method for treating ship oily sewage, which comprises the following steps: firstly, carrying out water quality analysis on inlet water of a ship oily sewage treatment plant, and then treating the oily sewage through the processes of coagulating sedimentation, dissolved air flotation, ozone pre-oxidation, secondary dosing sedimentation, ozone secondary oxidation and anaerobic / aerobic biochemical treatment. For the oily sewage which is difficult to treat, the link of adding calcium chloride to remove sulfite is added, so that the oily sewage is further treated, and the effluent is ensured to meet the discharge standard. The treatment method disclosed by the invention is simple and easy to operate, effectively solves the pollution problem existing in ship oily sewage treatment, and has wide application prospects and economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of ship oily wastewater treatment, and more specifically, relates to a method for treating ship oily wastewater. Background Art

[0002] The discharge of oily wastewater from ships can have serious impacts on the aquatic environment and ecosystems. Oily wastewater from ships can easily form a thin film on the surface of water bodies, causing short-term hypoxia and death to aquatic organisms. In the long term, it can cause chronic toxicity to the waters and aquatic life, weakening their self-purification capacity and damaging ecosystems such as wetlands, coral reefs, and mangroves. Toxic and hazardous substances accumulate in the food chain, posing a threat to human health. According to the International Maritime Organization (IMO), approximately 700,000 tons of petroleum pollutants enter the marine environment annually through oily wastewater from ships.

[0003] The treatment of ship oily wastewater faces complex technical challenges. Ship oily wastewater is characterized by complex composition, high oil content, large water volume fluctuations, and high salinity, placing high demands on both treatment technology and equipment. The oils in ship oily wastewater primarily include crude oil, heavy diesel, and lubricating oil, which are highly emulsifiable and difficult to treat. Furthermore, ship oily wastewater often contains high salt content and exhibits significant variability, further complicating treatment. In addition to oil and fat, ship oily wastewater may also contain various hazardous compounds, such as surfactants, tributyltin, and heavy metals (such as lead, zinc, copper, and cadmium), which pose potential risks to the environment and human health. Commonly used methods for treating ship oily wastewater include physical, chemical, and biochemical methods. Physical methods primarily remove oil and fat through gravity separation, coalescence separation, adsorption, filtration, flotation, and ultrasound. These methods are suitable for treating large oil particles in oily wastewater and are simple to operate, but may not completely remove fine oil droplets. Chemical methods, including coagulation separation, electrochemistry, and advanced oxidation technologies, can effectively improve treated water quality but may cause secondary pollution. Biochemical methods, such as activated sludge and biological contact oxidation, can effectively degrade organic matter, but they require longer treatment times and rely on the maintenance of biological activity.

[0004] At present, although a variety of technologies have been adopted internationally to treat ship oily wastewater, such as physical and chemical combined advanced oxidation, biochemical and membrane concentration and evaporation, it still faces problems such as huge investment, high operating costs and complex maintenance, and there is no widely applicable and efficient treatment solution yet. Summary of the Invention

[0005] In response to the problems of complex composition, high oil content, and large water volume fluctuations in ship oily wastewater, the purpose of the present invention is to provide a method for treating ship oily wastewater; by optimizing the treatment process, the present invention can effectively reduce the chemical oxygen demand (COD) and improve water quality.

[0006] The technical solution of the present invention is specifically described as follows.

[0007] The present invention provides a method for treating ship oily wastewater, which adopts the method of "dosing → flocculation precipitation → dissolved air flotation →

[0008] The specific steps of the "ozone pre-oxidation → ozone secondary oxygen → A / O biochemical" treatment process are as follows:

[0009] (1) Add flocculants to the raw water for flocculation and sedimentation to remove the particulate oil;

[0010] (2) Removal of emulsified oil from water by dissolved air flotation technology;

[0011] (3) Using ozone for pre-oxidation and secondary oxidation treatment. Pre-oxidation is used to improve water quality, reduce the concentration of refractory organic matter, and improve its biodegradability. Secondary oxidation is used to further destroy residual pollutants to enhance the effect of subsequent biochemical treatment.

[0012] (4) Use A / O biochemical treatment technology, i.e. anaerobic / aerobic treatment, to further degrade organic matter, thereby achieving a higher level of water purification.

[0013] In the present invention, in step (1), the chemical oxygen demand of the raw water is 1000-7000 mg / L, and the 5-day biochemical oxygen demand is 0-3000 mg / L.

[0014] In the present invention, in step (1), the flocculant is a mixture of polyacrylamide (PAM) and polyaluminium chloride (PAC), and the flocculation residence time is 2-4 hours.

[0015] In the present invention, the dosage of polyacrylamide (PAM) is 0.2-0.4% of the mass of the sewage, and the dosage of polyaluminium chloride (PAC) is 4-6% of the mass of the sewage; and the residence time after the addition of the drugs is 2-4 hours.

[0016] In the present invention, in step (3), when ozone is used for pre-oxidation and secondary oxidation, the ozone flow rate is 1-8Nm 3 / h, and the residence time is 6-10h respectively.

[0017] In the present invention, in step (1), calcium chloride is added in an amount of 0.001-0.015% of the mass of the sewage during the coagulation and sedimentation process. In step (3), a secondary dosing and precipitation step is added between the ozone pre-oxidation treatment and the ozone secondary oxidation treatment. In the secondary dosing and precipitation step, polyacrylamide (PAM) is added in an amount of 0.1-0.2% of the mass of the sewage, and polyaluminium chloride (PAC) is added in an amount of 1-2% of the mass of the sewage.

[0018] In the present invention, desulfurization tower drainage is mixed into the ship's oily wastewater.

[0019] In the present invention, in step (4), the dissolved oxygen in the aerobic tank is between 2-4 mg / L, the sedimentation ratio SV30 is between 25-30%, and the sludge contains thiobacillus, Thiogranum, NS9_marine_group and Thiobios genera, as well as organic matter metabolizing bacteria such as Flavobacterium, Flavobacterium, Pseudomonas, Xanthomarina, Thauera and Sphingosinicella.

[0020] In the present invention, the effluent water quality meets the municipal pipe network standard, that is, the chemical oxygen demand COD value is less than 500 mg / L.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention is not only suitable for treating oily wastewater from ships, but can also be widely applied to the treatment of other high-salt, high-oil, and complex wastewater. Through the technical transformation and optimization of the present invention, the efficiency and environmental protection of oily wastewater treatment can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of the method of Example 1 of the present invention.

[0024] Figure 2 This is a flow chart of the method of embodiment 2 of the present invention.

[0025] Figure 3 This is the SEM-EDS mapping result of the particles in the influent batch 02 sample.

[0026] Figure 4 This is the XRD result of the particulate matter produced after adding calcium chloride to the influent batch 02. DETAILED DESCRIPTION

[0027] In order to make those skilled in the art more clearly understand the technical solution of the present invention, the following examples are given for illustration. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] Unless otherwise specified, the raw materials, reagents or equipment used in the following steps can be obtained from conventional commercial sources or by existing known methods.

[0029] The chemical oxygen demand (COD) test method is as follows: Measure 2.5mL of a water sample and dilute it 10-fold. To avoid interference from chloride ions, use Lianhua COD reagent consumables, which contain a masking agent, mercuric sulfate, which can effectively eliminate this effect. Add 0.7mL of LH-D reagent and 4.8mL of LH-E reagent. Digest in a digester at 165°C for 10 minutes, cool with water for 2 minutes, then add 2.5mL of distilled water to mix. After air cooling for 2 minutes, place the test sample in a rapid chemical oxygen demand meter for reading.

[0030] The SEM scales for the sludge samples were set at 50 μm, 20 μm, and 5 μm. Experimental parameters were set at a voltage of 10 kV and a current of 10 μA. EDS point scanning and mapping tests were performed on the sludge samples to determine the content and distribution of elements such as carbon (C), oxygen (O), and iron (Fe).

[0031] XRD experimental parameters were set at 40 kV, 40 mA, a scan angle of 8°, a scan step of 0.02°, and a scan rate of 10° / min. Ion chromatography experiments used a METROSEPASUPP5–250 anion chromatography column with a length of 250 mm, a column diameter of 4 mm, and a particle size of 5 μm. The eluent was 3.2 mM Na₂CO₃ / 1.0 mM NaHCO₃, a flow rate of 0.7 mL / min, an injection volume of 20 μL, and a column temperature of 35°C.

[0032] The present invention aims to further explore and optimize the ship oily wastewater treatment process, and seek a more efficient treatment method through process design and transformation to solve the problems existing in the current ship oily wastewater treatment.

[0033] Example 1

[0034] Through preliminary testing of raw water quality, a treatment process of "dosing → flocculation and sedimentation → dissolved air flotation → ozone pre-oxidation → ozone secondary oxidation → A / O biochemical" was designed. The process flow is as follows: Figure 1 shown.

[0035] First, the raw water is treated with medication and flocculation sedimentation. The medication treatment involves adding polyacrylamide (PAM) and polyaluminum chloride (PAC) to aid in the aggregation of pollutants during the flocculation and sedimentation process. In a specific embodiment, both PAM and PAC are added simultaneously to the flocculation and sedimentation tank, with a PAM ratio of approximately 0.3% and a PAC ratio of approximately 5% for a retention time of 3 hours.

[0036] Next, dissolved air flotation (DAF) technology is used to remove floating matter and some grease from the water. In a specific embodiment, the DAF tank has dimensions of 6.1m x 4.1m x 2.7m and a maximum processing capacity of 15 cubic meters per hour.

[0037] Then, ozone is used for pre-oxidation treatment to improve water quality and reduce the concentration of refractory organic matter. In addition, the ozone secondary oxidation step further destroys residual pollutants and enhances the effect of subsequent biochemical treatment. In a specific embodiment, ozone is generated by an ozone generator with an ozone flow rate of 6Nm 3 / h. There are two ozone pre-oxidation towers connected in parallel, with a diameter of 1.8 meters and a height of 6 meters. There are two secondary oxidation tanks, measuring 6m×2.5m×3.2m, with a residence time of 8 hours.

[0038] Finally, A / O biochemical treatment technology, or anaerobic / aerobic treatment, is used to further degrade organic matter, thereby achieving a higher level of water purification. In a specific embodiment, the dissolved oxygen in the aerobic tank is between 2-4 mg / L, and the sedimentation ratio SV30 is approximately 25-30%. The aerobic tank measures 17.9m x 2.5m x 3.2m, with a packing installation spacing of 150mm x 150mm. The sludge contains Thiobacillus, Thiogranum, NS9_marine_group, and Thiobios, as well as organic matter metabolizing bacteria such as Flavobacterium, Flavobacterium, Pseudomonas, Xanthomarina, Thauera, and Sphingosinicella.

[0039] The design indicators of the inlet and outlet water quality of this process are shown in Table 1. Through the above process treatment, the effluent indicators can meet the municipal pipe network standards, that is, the chemical oxygen demand COD value is less than 500 mg / L, which meets the design indicator requirements.

[0040] Table 1 Designed inlet and outlet water quality

[0041]

[0042] Example 2

[0043] This embodiment relates to a method for treating oily wastewater from ships, and the specific implementation steps are as follows:

[0044] 1. Influent parameters: The influent parameters of the ship oily wastewater treatment system are shown in Table 2. Influent batch 01 is a typical easy-to-treat ship oily wastewater with good biodegradability (BOD / COD ratio is 0.43). After the operation process described in Example 1, the effluent can meet the standards, and the treatment of ship oily wastewater can be achieved. Influent batch 02 is a typical difficult-to-treat ship oily wastewater with poor biodegradability (BOD / COD ratio is 0.1). After the operation process described in Example 1, the effluent is also difficult to meet the standards (COD value is between 500-800 mg / L). Therefore, the influent batch 02 needs to improve the dosing type of coagulation and sedimentation, and add a secondary dosing step to achieve the treatment of ship oily wastewater.

[0045] Table 2 Water quality of different batches of influent

[0046]

[0047] 2. Wastewater analysis: In order to determine the specific components of oxidizable non-carbon substances in the influent batch 02, 1L of ship oily wastewater was filtered to obtain particulate matter, which was then dispersed in ethanol and analyzed using a scanning electron microscope and energy dispersive spectrometer (SEM-EDS mapping). The results are shown in the table. Figure 1 and Table 3.

[0048] The particulate matter in ship oily wastewater contains a variety of elements, and the contents of which exceed 0.3% include C, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Co, Ni, Zn, and I. Among them, C, O, Na, Mg, Si, P, Cl, K, Ca, and I are common elements in seawater, and S, Mn, Fe, Co, Ni, Cr, Zn, and Al may come from ship oily wastewater and desulfurization tower drainage. This result shows that ship oily wastewater is mixed with desulfurization tower drainage, and the oxidizable non-carbon substances contained in it may be in the form of SO3 2- exists in the form of .

[0049] Table 3 Content of each element in the particulate matter of the influent 02 batch sample

[0050]

[0051] 3. Technical treatment: Add calcium chloride (CaCl2) to the oily wastewater to react with SO3 2- The reaction generates calcium sulfite (CaSO3) and calcium sulfate (CaSO4), thereby effectively removing SO3 from oily wastewater 2- , thereby reducing the COD value in the sewage. The changes in COD value under different calcium chloride addition amounts are shown in Table 4; the XRD results of the generated particles are shown in Figure 2With the increase of calcium chloride addition, the COD value of influent 02 decreases continuously. When the addition amount of calcium chloride is 25g / m 3 When the amount of calcium chloride added reaches 150g / m 3 When COD drops to 1384 mg / L, SO3 2- The concentration is approximately 0 mg / L.

[0052] Table 4 COD values of influent 02 batch samples after adding different amounts of calcium chloride

[0053]

[0054] 4. System transformation and optimization: The oily wastewater treatment process after technical transformation is as follows Figure 3 As shown in the figure, calcium chloride is added to the coagulation and precipitation step in Example 1, and a secondary dosing precipitation step is added after ozone pretreatment. Calcium chloride promotes SO3 2- Converted into CaSO3 to remove SO3 generated in the system 2- The resulting sediment can be removed during the secondary dosing step. After the technical transformation, the effluent COD of batch 02 of wastewater was reduced to below 350mg / L, achieving standard piped discharge.

[0055] The present invention provides a method for treating sulfate in oily wastewater. To further optimize the treatment effect, the present invention adjusts the dosing type of the coagulation and sedimentation link in the process and introduces a secondary dosing and precipitation step. This improvement combines the strong oxidizing effect of ozone and achieves the reduction of oxidizable non-carbon substances (such as SO3 2- ) to effectively treat the oily wastewater, thereby significantly reducing the COD value of the oily wastewater and avoiding the oxidation of non-carbon substances (such as SO3 2- ) on the subsequent biochemical process. By adding calcium chloride in the coagulation and sedimentation process and adding a secondary dosing precipitation step, not only the removal rate of oil pollutants is improved, but also the oxidizable non-carbon substances (such as SO3 2- ), which also creates favorable conditions for subsequent biochemical treatment and provides an effective treatment strategy for ship oily wastewater treatment.

[0056] Through the technologies and treatment steps described above, this ship oily wastewater treatment system can effectively treat different types of wastewater, especially for difficult-to-remove oily wastewater, providing an environmentally friendly and economical solution.

Claims

1. A method for treating ship oily wastewater, characterized in that: It adopts the "dosing → flocculation precipitation → dissolved air flotation → ozone pre-oxidation → ozone secondary oxidation → A / O biochemical" treatment process, the specific steps are as follows: (1) Add flocculants to the raw water for flocculation and sedimentation to remove the particulate floating oil; (2) Removal of emulsified oil from water by dissolved air flotation technology; (3) Using ozone for pre-oxidation and secondary oxidation treatment. Pre-oxidation is used to improve water quality, reduce the concentration of refractory organic matter, and improve its biodegradability. Secondary oxidation is used to further destroy residual pollutants to enhance the effect of subsequent biochemical treatment. (4) Use A / O biochemical treatment technology, i.e. anaerobic / aerobic treatment, to further degrade organic matter, thereby achieving a higher level of water purification.

2. The processing method according to claim 1, characterized in that In step (1), the flocculant is a mixture of polyacrylamide (PAM) and polyaluminium chloride (PAC), and the flocculation residence time is 2-4 hours.

3. The processing method according to claim 2, characterized in that In step (1), the dosage of polyacrylamide (PAM) is 0.2-0.4% of the mass of the sewage, and the dosage of polyaluminium chloride (PAC) is 4-6% of the mass of the sewage.

4. The processing method according to claim 1, characterized in that In step (3), when ozone is used for pre-oxidation and secondary oxidation treatment, the ozone flow rate is 1-8 Nm³ / h, and the residence time is 6-10h.

5. The treatment method according to claim 1, wherein in step (1), calcium chloride is added simultaneously during the flocculation and sedimentation process, and the amount of calcium chloride added is 0.001-0.015% of the wastewater mass; and in step (3), a secondary flocculation and sedimentation step is added between the ozone pre-oxidation treatment and the ozone secondary oxidation treatment, the flocculant is a mixture of polyacrylamide (PAM) and polyaluminum chloride (PAC), and the flocculation residence time is 2-4 hours.

6. The treatment method according to claim 5, wherein in step (3), during the secondary flocculation sedimentation, the dosage of polyacrylamide (PAM) is 0.1-0.2% of the wastewater mass, and the dosage of polyaluminium chloride (PAC) is 1-2% of the wastewater mass.

7. The processing method according to claim 1, characterized in that In step (4), the dissolved oxygen in the aerobic tank is between 2-4 mg / L, the sedimentation ratio SV30 is between 25-30%, and the sludge contains Thiobacillus Thiobacillus Genus, Thiogranum Genus, NS9_ marine_group genus and Thiobios genus and organic matter metabolizing bacteria Flavobacterium Genus, Flavobacterium Genus, Pseudomonas Genus, Xanthomarina Genus, Thauera genus and Sphingosinicella Genus.

8. The processing method according to claim 1, wherein The effluent quality meets the municipal pipe network standards, that is, the chemical oxygen demand (COD) value is less than 500 mg / L.

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