A highway construction wastewater environmental protection treatment method

Abstract

The present application relates to the technical field of sewage treatment, and particularly relates to an environment-friendly treatment method for highway construction wastewater. The present application realizes three-stage weak flocculation through three-stage weak stirring intensity, the stirring intensity (expressed by the velocity gradient G value) during the flocculation reaction is gradually weakened from high to low, and the first flocculant PAC and the second flocculant PAM are respectively added before high-speed stirring flocculation and before medium-speed stirring flocculation, which is beneficial to forming stable large particle alum flowers, improving the sedimentation efficiency, and through different particle sizes and different characteristics of the materials, a multi-layer filter material layer is combined with physical screening and chemical adsorption to realize efficient SS and oil removal, and deep filtration is realized through precise particle size grading in a physical way.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to an environmentally friendly method for treating wastewater from highway construction. Background Technology

[0002] Highway construction generates a large amount of complex wastewater, mainly including washing water from concrete mixing plants, oily washing water from construction machinery, mud water from pile foundation construction, and surface runoff during the rainy season. This type of wastewater is typically characterized by extremely high suspended solids concentrations, large fluctuations in petroleum pollutant content, alkaline pH, and drastic changes in water quality and quantity. Direct discharge without treatment will severely pollute the surrounding soil and water environment.

[0003] Currently, the treatment of wastewater from highway construction often employs a simple, conventional process of "sedimentation-filtration-disinfection." However, in practical applications, these traditional methods have significant limitations:

[0004] Poor flocculation effect: Traditional single-stage or two-stage flocculation processes are difficult to adapt to water quality fluctuations. The resulting flocs (lumps) are uneven in size and not dense enough, resulting in low sedimentation efficiency and difficulty in achieving stable standards for suspended solids (SS) and turbidity in the effluent.

[0005] Limited oil removal efficiency: Conventional filter media (such as ordinary quartz sand and anthracite) have a weak ability to remove dissolved oil and emulsified oil, and the petroleum content in the effluent often exceeds the standard.

[0006] Therefore, developing a highway construction wastewater treatment process that can efficiently remove suspended solids and petroleum pollutants, adapt to water quality fluctuations, operate stably, and be environmentally friendly has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] Therefore, based on the above background, this invention provides an environmentally friendly treatment method for highway construction wastewater. Through the synergistic effect of three-stage gradually weakening flocculation and modified multi-layer filter media filtration, it can achieve highly efficient and deep removal of pollutants, enabling environmentally friendly wastewater recycling or direct discharge.

[0008] The technical solution provided by this invention is as follows:

[0009] An environmentally friendly treatment method for highway construction wastewater includes the following steps:

[0010] S1 adjusts the pH of the wastewater, after it has passed through a 3-5mm screen filter and an oil separator, to 6.5-8.0;

[0011] S2 performs a three-stage gradually weakening flocculation treatment on the wastewater after pH adjustment in step S1.

[0012] S2.1 Add the first flocculant to the wastewater after pH adjustment in step S1 and mix thoroughly;

[0013] S2.2 uses a paddle mixer, with the speed gradient G value controlled at 40-60s. -1 The flocculation reaction should proceed for 2-4 minutes.

[0014] After adding the second flocculant (S2.3), use a paddle mixer to control the velocity gradient G to be 20-40 s. -1 Perform flocculation reaction for 6-8 minutes;

[0015] S2.4 The wastewater from step S2.3, after flocculation, is subjected to a paddle agitator, with the velocity gradient G value controlled at 10-20 s. -1 Perform the flocculation reaction for 6-8 minutes;

[0016] S3 involves sedimentation of the wastewater after the three-stage weakened flocculation treatment in step S2.

[0017] S4 filters the wastewater after sedimentation and separation in step S3 using multi-layer filter media from top to bottom.

[0018] The multi-layer filter media consists of, from top to bottom, a ceramsite layer, a primary modified quartz sand layer, a secondary modified quartz sand layer, and a garnet layer. The ceramsite layer uses ceramsite with a particle size of 2.0-3.0 mm. The primary modified quartz sand layer uses quartz sand with a particle size of 1.0-1.6 mm after aminosilane modification. The secondary modified quartz sand layer uses quartz sand with a particle size of 0.6-0.8 mm after hydrophobic treatment. The garnet layer uses garnet with a particle size of 0.2-0.3 mm.

[0019] S5 will perform chlorine-free disinfection treatment on the wastewater that has been filtered in step S4.

[0020] Furthermore, the multi-layer filter media also includes a pebble support layer located below the garnet layer. The pebble support layer consists of an upper pebble support layer, a middle pebble support layer, and a lower pebble support layer from top to bottom. The upper pebble support layer uses pebbles with a particle size of 4-8 mm, the middle pebble support layer uses pebbles with a particle size of 8-16 mm, and the lower pebble support layer uses pebbles with a particle size of 16-32 mm.

[0021] Furthermore, the secondary modified quartz sand layer uses quartz sand that has undergone hydrophobic treatment with octylsilane.

[0022] Furthermore, the first flocculant is polyaluminum chloride with an alkalinity of 60-80%, and its dosage is 40-80 mg / L.

[0023] Furthermore, the second flocculant is anionic PAM with a molecular weight of 12-15 million and an addition amount of 1.0-2.0 mg / L.

[0024] Further, in step S2, a three-stage gradually weakening flocculation treatment is carried out in the flocculation tank (1). The flocculation tank (1) is provided with a first partition (2) and a second partition (3) in sequence. The first partition (2) and the second partition (3) divide the tank cavity of the flocculation tank from left to right into a first tank cavity, a second tank cavity and a third tank cavity, respectively. The first tank cavity, the second tank cavity and the third tank cavity are respectively provided with a stirrer.

[0025] Furthermore, the first partition (2) is provided with a first water outlet (21), the second partition (3) is provided with a second water outlet (31), and the flocculation tank (1) is provided with an overflow hole (41) on the tank wall 4 facing the second partition (3). The second water outlet (31) is located above the first water outlet (21), and the overflow hole (41) is located above the second water outlet (31).

[0026] The wastewater undergoes flocculation reaction sequentially through the first chamber, the second chamber, and the third chamber.

[0027] Furthermore, in step S5, the chlorine-free disinfection process primarily uses ultraviolet disinfection, supplemented by peracetic acid.

[0028] The beneficial effects achieved by this invention are as follows:

[0029] (1) This invention achieves three-stage gradually weakening flocculation through three stages of gradually weakening stirring intensity. The stirring intensity (expressed as the velocity gradient G value) during the flocculation reaction is controlled from high to low, with the velocity gradient ranging from 40-60 s. -1 (High-intensity stirring) First reduce to 20-40 seconds -1 (Stir at medium intensity), then reduce to 10-20 s -1 (Low-intensity stirring), with the first flocculant PAC and the second flocculant PAM added before high-intensity and medium-intensity stirring respectively, facilitates the formation of stable large floc particles, improving sedimentation efficiency. During the high-intensity stirring stage, PAC disperses rapidly and uniformly, neutralizing and destabilizing the colloidal particles to form micro-flocs. Subsequently, PAM is added during the medium-intensity stirring stage, providing more suitable kinetic conditions for the "adsorption bridging" of the micro-flocs, allowing them to gradually grow. The final low-intensity stirring stage further densifies and strengthens the flocs, effectively preventing breakage. This gradually weakening energy input results in flocs with large particle size (up to 3-5 mm), high density, and fast settling speed, significantly improving sedimentation efficiency. Compared to flocculation treatment with a single stirring intensity or the simultaneous addition of mixed flocculants, this method significantly improves SS removal efficiency. Furthermore, it exhibits stronger adaptability to fluctuations in the water quality of highway construction wastewater, ensuring stable treatment results.

[0030] (2) This invention uses materials with different particle sizes and properties to form a multi-layer filter media, combining physical sieving and chemical adsorption to achieve efficient removal of suspended solids (SS) and oil. Physically, it achieves deep filtration through precise particle size distribution: the filter media particle size ranges from coarse (2.0-3.0 mm) to fine (0.2-0.3 mm), which facilitates the penetration of suspended solids into the filter layer and their gradual interception, rather than just clogging the surface, thus improving the filtration cycle. Furthermore, the fine garnet particles in the lower layer have the smallest particle size, which may effectively capture the tiny particles that penetrate the upper layer. This ensures that the final effluent has extremely low and stable suspended solids (SS) and turbidity. Chemically, specific functional groups (amino and alkyl) are introduced through surface modification, transforming the passive retention of ordinary filter media into active adsorption. In particular, for difficult-to-treat emulsified oil, aminosilane modification makes the surface of quartz sand positively charged, enhancing the electro-adsorption of negatively charged colloidal particles and emulsified oil droplets. Octylsilane modification endows quartz sand with strong hydrophobic and oleophilic properties, enabling it to adsorb organic oil pollutants in water through physicochemical reactions. The two work synergistically to improve the oil removal efficiency of wastewater. Attached Figure Description

[0031] Appendix Figure 1 This is a system flowchart of Embodiment 1 of the present invention.

[0032] Appendix Figure 2 This is a schematic diagram of the flocculation tank in Embodiment 2 of the present invention.

[0033] Appendix Figure 3 This is a schematic diagram of the flocculation tank and sedimentation tank in Embodiment 2 of the present invention.

[0034] Appendix Figure 4 This is a cross-sectional view of the flocculation tank in Embodiment 2 of the present invention.

[0035] Appendix Figure 5 This is a schematic diagram of the structure of multi-layer filter media.

[0036] Appendix Figure 6 This is a schematic diagram of the flocculation tank and sedimentation tank in Embodiment 1 of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention provides an environmentally friendly treatment method for highway construction wastewater, comprising the following steps:

[0039] S1 adjusts the pH of the wastewater, after it has passed through a 3-5mm screen filter and an oil separator, to 6.5-8.0;

[0040] S2 performs a three-stage gradually weakening flocculation treatment on the wastewater after pH adjustment in step S1.

[0041] S2.1 Add the first flocculant to the wastewater after pH adjustment in step S1 and mix evenly; the first flocculant is polyaluminum chloride with an alkalinity of 60-80% and its dosage is 40-80 mg / L.

[0042] S2.2 uses a paddle mixer, with the speed gradient G value controlled at 40-60s. -1 The flocculation reaction should proceed for 2-4 minutes.

[0043] After adding the second flocculant (S2.3), use a paddle mixer to control the velocity gradient G to 20-40 s. -1 The flocculation reaction is carried out for 6-8 minutes; the second flocculant is anionic PAM with a molecular weight of 12-15 million and an addition amount of 1.0-2.0 mg / L.

[0044] S2.4 The wastewater from step S2.3, after flocculation, is subjected to a paddle mixer with a velocity gradient G value controlled at 10-20 s. -1 Perform the flocculation reaction for 6-8 minutes;

[0045] S3 involves sedimentation of the wastewater after the three-stage weakened flocculation treatment in step S2.

[0046] S4 filters the wastewater after sedimentation and separation in step S3 using multi-layer filter media from top to bottom.

[0047] The multi-layer filter media consists of, from top to bottom, a ceramsite layer, a primary modified quartz sand layer, a secondary modified quartz sand layer, and a garnet layer. The ceramsite layer uses ceramsite with a particle size of 2.0-3.0 mm. The primary modified quartz sand layer uses quartz sand with a particle size of 1.0-1.6 mm after aminosilane modification. The secondary modified quartz sand layer uses quartz sand with a particle size of 0.6-0.8 mm after hydrophobic treatment. The garnet layer uses garnet with a particle size of 0.2-0.3 mm.

[0048] Specifically, the thickness of the ceramsite layer is 295-300mm, mainly serving as a coarse filter to intercept large particles. The thickness of the primary modified quartz sand layer is controlled at 245-250mm. The quartz sand is modified with a silane coupling agent to increase its electro-adsorption capacity. The thickness of the secondary modified quartz sand layer is 245-250mm. The quartz sand is treated to be hydrophobic, enabling it to directly adsorb organic oil pollutants in the water through physicochemical processes. The thickness of the garnet layer is controlled at 145-150mm, serving both a supporting function and further fine filtration.

[0049] S5 will perform chlorine-free disinfection treatment on the wastewater that has been filtered in step S4.

[0050] The multi-layer filter media also includes a pebble support layer, which consists of an upper pebble support layer, a middle pebble support layer, and a lower pebble support layer from top to bottom. The upper pebble support layer uses pebbles with a particle size of 4-8 mm, the middle pebble support layer uses pebbles with a particle size of 8-16 mm, and the lower pebble support layer uses pebbles with a particle size of 16-32 mm. By forming a graded pebble support layer, it can effectively provide support. The upper pebble support layer has a thickness of 100-150mm, preferably 120-125mm, directly supporting the main filter media such as quartz sand and ceramsite above, preventing their loss during backwashing. The middle pebble support layer has a thickness of 100-150mm, preferably 120-125mm, serving as a transitional support. The lower pebble support layer has a thickness of 100-150mm, preferably 120-125mm, serving to evenly distribute the backwash water. This arrangement not only supports the main filter layer but also ensures effective backwashing. The layered pebbles create uniform pore channels, allowing backwash water or backwash air to rise evenly. If the support layer is not layered, water can easily pass through large gaps, leading to incomplete cleaning in certain areas. More specifically, the pebbles used are smooth and rounded. After laying one layer, it needs to be leveled with a wooden rake before laying the next layer.

[0051] The secondary modified quartz sand layer uses quartz sand that has undergone hydrophobic treatment with octylsilane.

[0052] The aminosilane-modified quartz sand is specifically modified with KH550 silane coupling agent, and the specific operation is as follows:

[0053] (1) Pretreatment

[0054] Pickling: Soak the quartz sand in 10% dilute hydrochloric acid to remove metal impurities, activate the surface, and increase the density of silanol groups.

[0055] Washing and drying: Wash with deionized water until neutral, and dry thoroughly at 115°C.

[0056] (2) Preparation of silane solution

[0057] KH-550 was dissolved at 2 wt% in a mixed solution of ethanol and water (90:10).

[0058] Adjust the pH to 4-5 with acetic acid to promote silane hydrolysis. Hydrolyze at room temperature and let stand for 30-60 minutes.

[0059] (3) Surface treatment

[0060] Immerse the dried hot sand (~80°C) in a silane solution and stir to ensure complete immersion.

[0061] (4) Curing

[0062] After draining, place the quartz sand in an oven at 125-130℃ for 1-2 hours to cure it, allowing the silane to bond with the sand surface.

[0063] (5) Post-processing

[0064] Cool, rinse with clean water to remove the physically adsorbed coupling agent, and then dry.

[0065] The preparation of the quartz sand after hydrophobic treatment with octylsilane is the same as above, modified with KH550 silane coupling agent. During the preparation of the silane solution, octylsilane is used to replace KH550 silane coupling agent.

[0066] The following are specific application examples. The highway wastewater used in the following examples or comparative examples is construction wastewater generated by a highway project. The wastewater contains approximately 3000 mg / L of suspended solids (SS), approximately 25 mg / L of organic oils, and approximately 11 pH.

[0067] Example 1: An environmentally friendly treatment method for highway construction wastewater, comprising the following steps:

[0068] S1 adjusts the pH of the wastewater, after it has passed through a 3-5mm screen filter and an oil separator, to 6.5-8.0;

[0069] S2 performs a three-stage gradually weakening flocculation treatment on the wastewater after pH adjustment in step S1.

[0070] S2.1 Add the first flocculant to the wastewater after pH adjustment in step S1 and mix evenly; the first flocculant is polyaluminum chloride with an alkalinity of 70% and its dosage is 60 mg / L.

[0071] S2.2 uses a paddle mixer, with a controlled speed gradient G value of 50s. -1 The flocculation reaction should proceed for 2-4 minutes.

[0072] After adding the second flocculant (S2.3), a paddle agitator is used to control the velocity gradient G to a value of 30 s. -1 The flocculation reaction is carried out for 6-8 minutes; the second flocculant is anionic PAM (polyacrylamide), the molecular weight of which is 13 million, and the dosage is 1.5 mg / L;

[0073] S2.4 The wastewater from step S2.3, after flocculation, is subjected to a paddle agitator with a velocity gradient G value controlled at 15s. -1 Perform the flocculation reaction for 6-8 minutes;

[0074] S3 involves sedimentation of the wastewater after the three-stage weakened flocculation treatment in step S2.

[0075] S4 filters the wastewater after sedimentation and separation in step S3 using multi-layer filter media from top to bottom.

[0076] The multi-layer filter media, from top to bottom, consists of a ceramsite layer 7, a primary modified quartz sand layer 8, a secondary modified quartz sand layer 9, and a garnet layer 100. The ceramsite layer uses ceramsite with a particle size of 2.0-3.0 mm. The primary modified quartz sand layer uses quartz sand with a particle size of 1.0-1.6 mm after aminosilane modification. The secondary modified quartz sand layer uses quartz sand with a particle size of 0.6-0.8 mm after hydrophobic treatment. The garnet layer uses garnet with a particle size of 0.2-0.3 mm.

[0077] Specifically, the thickness of the ceramsite layer is 295-300mm, mainly serving as a coarse filter to intercept large particles. The thickness of the primary modified quartz sand layer is controlled at 245-250mm. The quartz sand is modified with a silane coupling agent to increase its electro-adsorption capacity. The thickness of the secondary modified quartz sand layer is 245-250mm. The quartz sand is treated to be hydrophobic, enabling it to directly adsorb organic oil pollutants in the water through physicochemical processes. The thickness of the garnet layer is controlled at 145-150mm, serving both a supporting function and further fine filtration.

[0078] S5 will perform chlorine-free disinfection treatment on the wastewater that has been filtered in step S4.

[0079] The multi-layer filter media also includes a pebble support layer 110, which consists of an upper pebble support layer, a middle pebble support layer, and a lower pebble support layer from top to bottom. The upper pebble support layer uses pebbles with a particle size of 4-8 mm, the middle pebble support layer uses pebbles with a particle size of 8-16 mm, and the lower pebble support layer uses pebbles with a particle size of 16-32 mm. The upper pebble support layer has a thickness of 100-150mm, preferably 120-125mm, and directly supports the main filter media such as quartz sand and ceramsite above, preventing them from being lost during backwashing. The middle pebble support layer has a thickness of 100-150mm, preferably 120-125mm, and serves as a transitional support, preventing fine material from leaking into the gaps between the coarse material and the upper layer. The lower pebble support layer has a thickness of 100-150mm, preferably 120-125mm, and serves to evenly distribute the backwash water. This arrangement not only supports the main filter layer but also ensures effective backwashing. The layered pebbles create uniform pore channels, allowing backwash water or backwash air to rise evenly. If the support layer is not layered, water can easily pass through large gaps, leading to incomplete cleaning in certain areas. More specifically, the pebbles used are smooth and rounded. After laying one layer, it needs to be leveled with a wooden rake before laying the next layer.

[0080] Specifically, as shown in the attached document Figure 1 As shown, in this embodiment, the wastewater first undergoes 5mm grating filtration in a grating tank. As shown in the figure, the grating tank includes a tank body with a grating plate in the middle. The wastewater is pumped to one side of the grating plate in the tank body by a wastewater pump, and then pumped to an oil separator for oil removal through the other side of the tank body via the wastewater pump. The oil separator is a conventional technology and will not be described in detail here.

[0081] After oil removal from the grease trap, the wastewater is pumped to an intermediate buffer tank, where its pH is adjusted (using dilute sulfuric acid) to 7.5. Then, it is pumped to a flocculation tank for three-stage gradually weakening flocculation. The flocculation tank is equipped with a mixer, specifically a static mixer, between the intermediate buffer tanks. Specifically, the wastewater is mixed with a first flocculant through the static mixer. The first flocculant is a 0.1% aqueous solution of water, which is rapidly mixed with the wastewater through the static mixer and then fed into the flocculation tank for flocculation treatment.

[0082] This embodiment employs intermittent, three-stage, gradually weakening flocculation. The flocculation tank is a single unit equipped with a paddle agitator (variable frequency). After wastewater containing the first flocculant is transported to the flocculation tank, the paddle agitator is activated, and the velocity gradient G is controlled to 50 seconds. -1After flocculation for 2-4 minutes to form micro-flocculations, a second flocculant is added. The second flocculant is added to the wastewater as a 0.1% (w / w) aqueous solution. The speed gradient G value of the paddle agitator is then adjusted to 30 seconds. -1 Afterward, flocculation is carried out for 6-8 minutes, at which point the flocs will have grown significantly to 1-2 mm. Then, the speed gradient G value of the paddle agitator is adjusted to 15 seconds. -1 Afterwards, the flocs become significantly denser, with a particle size of 3-4 mm. The wastewater is then transported to a sedimentation tank for settling. This sedimentation tank is an inclined tube sedimentation tank (one of the walls of the flocculation tank has a pipe connected to the inclined tube sedimentation tank, allowing wastewater to be transported to the sedimentation tank via hydraulic differential pressure, avoiding the influence of external pumps on the flocs; more specifically, the flocculation tank is located above the inclined tube sedimentation tank, and the pipe is inclined downwards). The surface load is 1.2 m. 3 / (m 2 •h) The suspended solids (SS) of the supernatant wastewater after flocculation are measured and recorded as SS after sedimentation. The supernatant wastewater is then transported to a filter (via a transfer pump) for filtration. The filter includes a housing filled with multiple layers of filter media. The inlet of the housing is located at the top, and the outlet is located at the bottom. The wastewater passes through the multiple layers of filter media from top to bottom through the filter inlet. The filtered wastewater is then transported to a temporary storage tank for disinfection. The disinfection method is mainly ultraviolet disinfection, supplemented by peracetic acid. Specifically, it first passes through an ultraviolet disinfection channel (UV dose ≥30 mJ / cm). 2 As a backup, a peracetic acid dosing point is provided at the inlet of the temporary storage tank, which is only activated when the UV intensity is insufficient.

[0083] The suspended solids (SS) (referred to as final SS) and organic oils in the wastewater in the temporary storage tank were tested.

[0084] In practical applications, each corresponding treatment pool is equipped with a sewage pipe at the bottom of the pool. The sludge can be collected through the sewage pipe and then filtered by a plate and frame filter press until the water content is less than 60%. It can then be recycled as roadbed landfill material.

[0085] Example 2: An environmentally friendly treatment method for highway construction wastewater. Compared with Example 1, this example adopts continuous three-stage gradually weakening flocculation, that is, the structure of the flocculation tank for flocculation treatment is as follows: Figures 2 to 3As shown, the flocculation tank (1) is provided with a first partition (2) and a second partition (3) in sequence. The first partition (2) and the second partition (3) divide the tank cavity of the flocculation tank from left to right into a first tank cavity, a second tank cavity and a third tank cavity, respectively. The first tank cavity, the second tank cavity and the third tank cavity are respectively provided with a paddle agitator (frequency conversion). Specifically, the agitator is installed in the upper middle part of each tank cavity. The bottom of each tank cavity may be provided with a sludge discharge hopper or a perforated sludge discharge pipe with a slope of more than 5° towards the sludge discharge port. The first partition (2) is provided with a first water outlet (21), and the second partition (3) is provided with a second water outlet (31). The flocculation tank (1) is provided with an overflow hole (41) on the tank wall 4 facing the second partition (3). The second water outlet (31) is located above the first water outlet (21), and the overflow hole (41) is located above the second water outlet (31). The first water outlet, the second water outlet, and the overflow hole can be square with the same front and rear width as the tank cavity, or they can be multiple circles. More specifically, the circles can be connected to a connecting pipe, and the connecting pipe is provided with a control valve. Specifically, the first water outlet, the second water outlet, and the overflow hole are square. The wall height of the flocculation tank is 4.5m. The effective water depth of the first, second, and third tank chambers is 4.0m. The width and height of the first water outlet are 0.3×0.4m, and it is 0.5m from the bottom of the tank. The width and height of the second water outlet are 0.4×0.5m, and it is 2m from the bottom of the tank. The overflow hole is 0.5m from the top of the tank.

[0086] The wastewater undergoes flocculation in the first, second, and third chambers sequentially. Similar to Example 1, after the wastewater containing the first flocculant is transported to the first chamber, the velocity gradient G of the agitator corresponding to the first chamber is controlled to be 50 s. -1 The flocculation reaction is carried out for 2-4 minutes to form micro-flocculations; a second flocculant is added near the first partition. The second flocculant is added to the wastewater as a 0.1% aqueous solution. The velocity gradient G value of the corresponding agitator in the second chamber is 30s. -1 The wastewater undergoes flocculation in the second chamber for 6-8 minutes, while the velocity gradient G of the agitator in the third chamber is 15 seconds. -1 The wastewater undergoes a flocculation reaction for 6-8 minutes. After flocculation and preliminary sedimentation, the wastewater in the third chamber is then discharged through the overflow outlet to the sedimentation tank. Figure 3 As shown, the overflow outlet is equipped with an arc-shaped guide plate 6, which controls the slow delivery of wastewater to the sedimentation tank. The surface loading of the inclined tube sedimentation tank is 1.2 m. 3 / (m 2 ·h), the rest is the same as in Example 1.

[0087] Comparative Example 1: An environmentally friendly treatment method for highway construction wastewater. This invention is compared with Example 1. In step S2, PAC and PAM flocculants are prepared into aqueous solutions with a mass concentration of 0.1%. They are then mixed at a dosage of 60 mg / L for PAC and 1.5 mg / L for PAM. The mixture is then mixed with the wastewater in a static mixer before the flocculation tank. Then, intermittent three-stage gradually weakening flocculation treatment is performed. Other steps are the same as in Example 1.

[0088] Comparative Example 2: An environmentally friendly treatment method for highway construction wastewater. This invention is compared with Example 1. This comparative example uses the same stirring intensity for flocculation. Specifically, it uses the same flocculation tank as Example 1, i.e., the flocculation tank for flocculation treatment is a single tank, which is equipped with a paddle agitator. When the wastewater mixed with the first flocculant is transported to the flocculation tank, the paddle agitator is turned on, and the speed gradient G is controlled to be 50s. -1 Afterward, a flocculation reaction is carried out for 2-4 minutes to form micro-flocculations. Then, a second flocculant is added. The second flocculant is added to the wastewater as a 0.1% (w / w) aqueous solution, and the velocity gradient G is maintained at 50 s. -1 Continue the flocculation reaction for 12-16 minutes. Other procedures are the same as in Example 1.

[0089] Comparative Example 3: An environmentally friendly treatment method for highway construction wastewater. This invention is compared with Example 1. The multi-layer filter media consists of a ceramic aggregate layer, a secondary modified quartz sand layer, a primary modified quartz sand layer, and a garnet layer from top to bottom. The order of the secondary modified quartz sand layer and the primary modified quartz sand layer is reversed (the particle size is still larger at the top and smaller at the bottom). Other aspects are the same as in Example 1.

[0090] Comparative Example 4: An environmentally friendly treatment method for highway construction wastewater. This invention is compared with Example 1. The secondary modified quartz sand is replaced by a primary modified quartz sand layer (the two layers are still distinguished by particle size, with the upper layer having a particle size of 1.0-1.6 mm). Other aspects are the same as in Example 1.

[0091] Comparative Example 5: An environmentally friendly treatment method for highway construction wastewater. This invention is compared with Example 1. The primary modified quartz sand is replaced by a secondary modified quartz sand layer (the two layers are still distinguished by particle size, with the upper layer having a particle size of 1.0-1.6 mm). Other aspects are the same as in Example 1.

[0092] Comparative Example 6: An environmentally friendly treatment method for highway construction wastewater. This invention is compared with Example 1. The primary modified quartz sand and the secondary modified quartz sand are both replaced with unmodified quartz sand (the two layers are still distinguished by particle size, with the upper layer having a particle size of 1.0-1.6 mm). Other aspects are the same as in Example 1.

[0093] Comparative Example 7: An environmentally friendly treatment method for highway construction wastewater. This invention is compared with Example 1, which employs intermittent three-stage progressively stronger flocculation treatment. Specifically, after the wastewater mixed with the first flocculant is transported to the flocculation tank, the paddle agitator is turned on, and the speed gradient G is controlled to be 15s. -1 After flocculation for 6-8 minutes, a second flocculant is added. The second flocculant is added to the wastewater as a 0.1% aqueous solution. The speed gradient G of the paddle agitator is controlled at 30 seconds. -1 Afterward, the flocculation reaction is carried out for 6-8 minutes, and then the speed gradient G of the paddle agitator is controlled at 50 seconds. -1 After 2-4 minutes of flocculation reaction, the wastewater is transported to a sedimentation tank for settling.

[0094] The suspended solids (SS) in the supernatant after sedimentation in the sedimentation tank and the SS in the temporary storage tank of Examples 1, 2 and Comparative Examples 1 to 7 were tested, and the content of organic oil in the temporary storage tank was also tested. The test results are shown in Table 1.

[0095] Table 1: Wastewater Testing Results

[0096]

[0097] The SS content was determined according to GB 11901-89 (Chinese National Standard) "Determination of Suspended Solids in Water - Gravimetric Method", and the organic oil content was determined according to HJ 970-2018 "Determination of Petroleum in Water - Ultraviolet Spectrophotometry".

[0098] Comparing Example 1 with Comparative Examples 1 to 3, Comparative Example 1 involved a single addition of the reagent, Comparative Example 2 involved flocculation with uniform stirring intensity, and Comparative Example 7 involved a three-stage progressively stronger flocculation treatment. The SS content results after precipitation clearly show that the flocculation and precipitation effects of Example 1 are far superior to those of Comparative Examples 1 to 2. Among these, Comparative Example 7 showed the worst SS removal effect through flocculation and precipitation. This is likely because in the first stage, the stirring intensity was too weak, preventing most colloidal particles from destabilizing and leaving them dispersed in the water in a stable state. Effective collisions were minimal, resulting in the formation of very small, low-strength flocs. Since these micro-flocs were few in number and low in strength, increasing the stirring intensity at this stage did not allow the bridging effect of PAM to be fully utilized. The increased shear force would break up the low-strength flocs. Furthermore, further increasing the stirring intensity would completely break up all existing and forming flocs, turning them into a large number of even smaller, more difficult-to-remove flocs. The settled fragments demonstrate that the staged dosing of the reagent and the three-stage gradually weakening flocculation treatment in Example 1 are beneficial to improving the flocculation and sedimentation effect, and can significantly improve the removal effect of SS. Comparing Example 1 and Comparative Example 3, which uses modified quartz sand layers in different orders, the final SS content and organic oil content of Comparative Example 3 are significantly higher than those of Example 1, and even the final organic oil content is nearly 5 times that of Example 1. It can be seen that the filtration order of wastewater modified by K550 silane coupling agent and quartz sand treated with silane hydrophobicity will affect the retention of SS and organic oil. In Example 1, the first-stage modified quartz sand is used for demulsification by electro-adsorption, and then the second-stage modified quartz sand is used for deep oil removal by hydrophobic adsorption. However, if the order is reversed as in Comparative Example 3, the hydrophobic filter material will come into contact with the wastewater first and will be quickly blocked and ineffective by oil. The subsequent electro-adsorption layer will not be effective in treating the oil film that has already formed. Comparative Examples 4 and 5 used only one type of modified quartz sand. The final organic oil content of Examples 4 and 5 was significantly higher than that of Examples 1. It can be seen that the two different modified quartz sands in Example 1, with electro-adsorption on top and hydrophobic adsorption on the bottom, can play a synergistic role in the removal of emulsified oil and colloidal pollutants. Comparative Example 6 used unmodified quartz sand, and its final organic oil content was the highest, that is, its ability to remove emulsified oil and colloidal pollutants was the worst.

[0099] The embodiments shown are merely one implementation of the present invention, and the actual structure is not limited to this. In conclusion, if those skilled in the art, inspired by this invention, design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for environmentally friendly treatment of highway construction wastewater, characterized in that, Includes the following steps: S1 adjusts the pH of the wastewater, after it has passed through a 3-5mm screen filter and an oil separator, to 6.5-8.0; S2 performs a three-stage gradually weakening flocculation treatment on the wastewater after pH adjustment in step S1. S2.1 Add the first flocculant to the wastewater after pH adjustment in step S1 and mix thoroughly; S2.2 uses a paddle mixer, with the speed gradient G value controlled at 40-60s. -1 The flocculation reaction should proceed for 2-4 minutes. After adding the second flocculant (S2.3), use a paddle mixer to control the velocity gradient G to be 20-40 s. -1 Allow the flocculation reaction to proceed for 6-8 minutes; S2.4 The wastewater from step S2.3, after flocculation, is subjected to a paddle agitator, with the velocity gradient G value controlled at 10-20 s. -1 Allow the flocculation reaction to proceed for 6-8 minutes; S3 involves sedimentation of the wastewater after the three-stage weakened flocculation treatment in step S2. S4 filters the wastewater after sedimentation and separation in step S3 using multi-layer filter media from top to bottom. The multi-layer filter media consists of, from top to bottom, a ceramsite layer (7), a primary modified quartz sand layer (8), a secondary modified quartz sand layer (9), and a garnet layer (100). The ceramsite layer uses ceramsite with a particle size of 2.0-3.0 mm. The primary modified quartz sand layer uses quartz sand with a particle size of 1.0-1.6 mm after aminosilane modification. The secondary modified quartz sand layer uses quartz sand with a particle size of 0.6-0.8 mm after hydrophobic treatment. The garnet layer uses garnet with a particle size of 0.2-0.3 mm. S5 will perform chlorine-free disinfection treatment on the wastewater that has been filtered in step S4.

2. The environmental protection treatment method for highway construction wastewater according to claim 1, characterized in that, The multi-layer filter media also includes a pebble support layer (110) located below the garnet layer (100). The pebble support layer consists of an upper pebble support layer, a middle pebble support layer, and a lower pebble support layer from top to bottom. The upper pebble support layer uses pebbles with a particle size of 4-8 mm, the middle pebble support layer uses pebbles with a particle size of 8-16 mm, and the lower pebble support layer uses pebbles with a particle size of 16-32 mm.

3. The environmental protection treatment method for highway construction wastewater according to claim 1, characterized in that, The secondary modified quartz sand layer is made of quartz sand that has undergone hydrophobic treatment with octylsilane.

4. The environmental protection treatment method for highway construction wastewater according to claim 1, characterized in that, The first flocculant is polyaluminum chloride with an alkalinity of 60-80%, and its dosage is 40-80 mg / L.

5. The environmental protection treatment method for highway construction wastewater according to claim 4, characterized in that, The second flocculant is anionic PAM with a molecular weight of 12-15 million and an addition amount of 1.0-2.0 mg / L.

6. The environmental protection treatment method for highway construction wastewater according to claim 1, characterized in that, In step S2, a three-stage gradually weakening flocculation treatment is carried out in the flocculation tank (1). The flocculation tank (1) is provided with a first partition (2) and a second partition (3) in sequence. The first partition (2) and the second partition (3) divide the tank cavity of the flocculation tank from left to right into a first tank cavity, a second tank cavity and a third tank cavity, respectively. The first tank cavity, the second tank cavity and the third tank cavity are respectively provided with a stirrer.

7. The environmental protection treatment method for highway construction wastewater according to claim 6, characterized in that, The first partition (2) is provided with a first water outlet (21), the second partition (3) is provided with a second water outlet (31), and the flocculation tank (1) is provided with an overflow hole (41) on the tank wall 4 facing the second partition (3). The second water outlet (31) is located above the first water outlet (21), and the overflow hole (41) is located above the second water outlet (31).

8. The environmental protection treatment method for highway construction wastewater according to claim 1, characterized in that, In step S5, the chlorine-free disinfection process primarily uses ultraviolet disinfection, supplemented by peracetic acid.

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