Oily wastewater treatment methods

Abstract

This invention provides a method for treating oily wastewater, comprising the following steps: a wastewater input step, a pressurized flotation step, an oily sludge collection step, a floc formation step, and a dewatering and pressing step. In the wastewater input step, oily wastewater is provided and introduced into a flotation tank. In the pressurized flotation step, air bubbles ejected from the flotation tank cause impurities in the oily wastewater to float to the surface. In the oily sludge collection step, a scraping mechanism scrapes away impurities floating on the surface of the oily wastewater, collecting them to form oily sludge, which is then sent to an oily sludge drainage channel. In the floc formation step, a coagulant is added to the oily sludge to cause it to flocculate and form flocs. In the dewatering and pressing step, the oily sludge is squeezed to filter out excess water, causing the flocs to form a sludge cake. The coagulant comprises a conditioning agent and a polymeric flocculant. The conditioning agent, derived from shellfish waste, alters the boundary potential of the oily sludge to increase the flocculation effect and increases the alkalinity of the oily sludge to inhibit the formation of rancid odors.

Description

Technical Field

[0001] A field relating to the treatment of oily wastewater, particularly a process for treating oily wastewater without stirring chemical agents before flotation. Prior Technology

[0002] To conserve water resources and promote recycling, the treatment of wastewater generated from domestic and industrial activities has become crucial. Depending on its intended use, wastewater often contains various types of impurities, with oily wastewater being the most common. Unlike solid impurities, oil in wastewater cannot be removed by simple physical filtration; chemical agents such as flocculation or demulsifiers must be added to separate the oil and water, forming a floc. Subsequent processes remove impurities from the water and collect the floc to form oil sludge, which is then sent to a dewatering machine to reduce the impurity content of the wastewater to meet sewer discharge standards.

[0003] Without the addition of coagulants to flocculate the gel, the dewatering effect of the oil sludge is extremely poor, and it is impossible to effectively form the oil sludge into a cake, making subsequent recycling and reuse difficult.

[0004] The effectiveness of added chemical agents varies depending on the quality of the wastewater. Currently, most wastewater treatment methods utilize both inorganic and organic chemical agents simultaneously. Inorganic chemical agents include polyaluminum chloride (PAC), aluminum sulfate, sodium aluminate, or iron salts as coagulants. Among these, polyaluminum chloride is the most widely used due to its broad applicability across a wide range of water pH levels and temperatures. Organic chemical agents are high molecular weight organic polymers, typically copolymerized with acrylamide as the monomer and other ionic monomers. They are further classified into anionic, nonionic, and cationic types based on the electrical properties of their functional groups.

[0005] The conventional process for treating oily wastewater is as follows: wastewater addition, reagent addition and stirring, pressure flotation, oil sludge collection, oil sludge dewatering, and recovery. Because PAC hydrolyzes rapidly, the prepared PAC solution needs to be rapidly stirred when added to the wastewater to ensure even distribution and prevent clumping, which would reduce flocculation effectiveness. Therefore, wastewater treatment facilities using PAC as a reagent require an additional stirring step to enhance its coagulation effect. If PAC is added after oil sludge collection, the higher viscosity of the sludge compared to the wastewater makes it more difficult to evenly distribute the PAC through stirring, thus affecting the treatment's effectiveness.

[0006] Furthermore, the sludge formed from wastewater treatment using PAC contains aluminum ions, requiring further treatment before it can be recycled. Additionally, the added PAC depletes the alkalinity of the wastewater; therefore, increasing the dosage of PAC will correspondingly increase the acidity of both the wastewater and the sludge.

[0007] The inventors of this case, recognizing the shortcomings of conventional methods for treating oily wastewater, such as the need for rapid mixing processes to introduce chemical reagents, leading to increased equipment costs and process time; and the increased acidity of the water and oily sludge, which easily results in rancidity and odor during subsequent treatment, have actively and continuously developed inventions that can solve the above problems. Summary of the Invention

[0008] The main objective of this invention is to provide an improved method for treating conventional oily wastewater by using shellfish waste as a coagulant to replace traditional inorganic chemical agents, thereby eliminating the need for rapid mixing processes and equipment and improving wastewater purification efficiency.

[0009] Another objective of this invention is to use a pressurized flotation device to attach microbubbles to particles in wastewater and carry them to the surface of the wastewater for centralized transport to a dewatering device.

[0010] Another objective of this invention is to utilize the chemical properties of shellfish waste to make the oil sludge and dehydrated mud cake slightly alkaline, thereby inhibiting the generation of rancid odors during subsequent stacking, storage, and transportation.

[0011] To achieve the aforementioned objectives, the present invention provides an embodiment of a method for treating oily wastewater, comprising the following steps: Wastewater input procedure: Provide oily wastewater and input it into the flotation tank; In the pressurized flotation step, pressure is applied to the oily wastewater to dissolve air into it. When the oily wastewater is discharged into the flotation tank, the air is released to form microbubbles that adhere to the impurities in the oily wastewater, carrying the impurities to the surface of the oily wastewater. The oil sludge collection step involves using a scraping mechanism to scrape the impurities from the surface of the oily wastewater, collecting them to form oil sludge, and then sending it to the oil sludge drainage channel; In the floc formation step, a coagulant is added to the sludge to form a flocculent floc; and The dehydration and pressing step involves squeezing the oily sludge to filter out the water, causing the colloid to form a sludge cake.

[0012] In a preferred embodiment of the present invention, the coagulant comprises a conditioning agent and a polymeric flocculant, wherein the conditioning agent is prepared from shellfish waste and water, and the concentration of the conditioning agent is 0.5 to 2.5% by weight.

[0013] Preferably, the polymeric flocculant is prepared by mixing a polymer with water, and the concentration of the polymeric flocculant is 0.05 to 0.15% by weight.

[0014] In a preferred embodiment of the present invention, the flotation tank is equipped with an air dissolving device. Oily wastewater is first fed into the air dissolving device, where pressurization causes air to dissolve into the wastewater. When the oily wastewater is discharged into the flotation tank, the external pressure decreases, causing the gas in the wastewater to dissolve and form microbubbles, which adhere to impurity particles in the wastewater. The buoyancy of these bubbles carries the impurities to the surface of the oily wastewater.

[0015] Preferably, the volume ratio of oily wastewater to conditioner is 7:1 to 7:2.

[0016] Preferably, the volume ratio of oily wastewater to polymeric flocculant is 7:1.5 to 7:2.

[0017] Preferably, the acid value of the oily wastewater is in the range of 6.5 to 7.5.

[0018] Preferably, the shellfish waste is a mixture of calcium carbonate and calcium oxide. Simple Explanation of the Diagram

[0019] Figure 1 shows the sequence of steps in the method for treating oily wastewater according to an embodiment of the present invention. Implementation

[0020] To facilitate understanding of the present invention, a detailed description of the invention is provided below with reference to the accompanying drawings and embodiments. The drawings show only a portion, not all, of the embodiments of the invention. The invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any inventive effort are within the scope of protection of the present invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0022] As shown in the step sequence of the embodiment of the present invention in Figure 1, the method for treating oily wastewater of the present invention includes the following steps: Wastewater input step S1: Provide oily wastewater and input it into the flotation tank; In the pressurized flotation step S2, pressure is applied to the oily wastewater to dissolve air into it. When the oily wastewater is discharged into the flotation tank, air is released to form microbubbles that adhere to the impurities in the oily wastewater, carrying the impurities to the surface of the oily wastewater. In step S3, the impurities are scraped off from the surface of the oily wastewater using a scraping mechanism to form oily sludge, which is then sent to the oily sludge drainage channel. Step S4, flocculant formation, involves adding a coagulant to the sludge to form flocculant flocs; and In the dewatering and pressing step S5, the oily sludge is squeezed to filter out the water, and the colloid is formed into a sludge cake.

[0023] In a preferred embodiment of the present invention, the coagulant comprises a conditioning agent and a polymeric flocculant, wherein the conditioning agent contains shellfish waste. The shellfish waste may be oyster shells that have undergone high-temperature calcination.

[0024] Specifically, conventional methods for treating oily wastewater utilize inorganic chemical agents to alter the zeta potential and destabilization of microparticles in the wastewater. The coagulation groups released from the hydrolysis of the inorganic chemical agents combine with the microparticles in the water, thus destabilizing them; the metal ions in the agents neutralize the particles to form microfluids. During this process, the microfluids collide with the destabilized particles and other colloids, forming larger particles that settle. This is further enhanced by the use of polymeric flocculants to create bridging between the larger particles, increasing the settling velocity.

[0025] In detail, oyster shells calcined at high temperatures have increased alkalinity and adsorption capacity, and contain calcium carbonate and calcium oxide. When dissolved in water, they dissociate into calcium ions, which can replace the positively charged particles in traditional inorganic chemical agents to adsorb negatively charged particles in water. At the same time, oyster shells dissolved in water also generate antibacterial substances and increase the alkalinity of the sludge, inhibiting the formation of rancid odors during the stacking, storage, and transportation of the sludge.

[0026] In a preferred embodiment of the present invention, the flotation tank is equipped with an air dissolving device for pressurizing the oily wastewater to dissolve air. The air dissolving device includes a pressurizing tank, a pressurizing inlet valve, a pressurizing regulating valve, and a pump. The pressurizing tank receives both the oily wastewater and air; the pressurizing inlet valve is connected to the pressurizing tank to introduce the oily wastewater; the pump is connected to the pressurizing tank to introduce air, increasing the pressure inside the pressurizing tank to dissolve the air into the oily wastewater; and the pressurizing regulating valve connects the pressurizing tank to the interior of the flotation tank, discharging the pressurized oily wastewater into the flotation tank. The pressure inside the pressurizing tank can be controlled by the pressurizing regulating valve.

[0027] In optimal application, after the oily wastewater enters the pressurization tank, air is pressurized by a pump to increase the pressure inside the tank and increase the dissolved air volume. When the oily wastewater is discharged into the flotation tank, the decrease in external pressure causes air in the oily wastewater to begin to precipitate, forming microbubbles that attach to the impurity particles in the oily wastewater, carrying them to the surface where they are scraped off and collected by the scraping mechanism to form oil sludge.

[0028] Specifically, pressurized flotation can effectively bring impurities in oily wastewater to the water surface, where they are collected by a scraping mechanism to form oily sludge. However, the dewatering effect of oily sludge that has not yet flocculated and produced flocs is not good, and it cannot form a sludge cake. Therefore, in the floc formation step S4, a coagulant is added to the oily sludge to form flocs, which is used to improve the dewatering efficiency in the dewatering and pressing step S5.

[0029] Preferably, the concentration of the conditioner is 0.5 to 2.5% by weight, more preferably 1.0 or 2.0% by weight.

[0030] Preferably, the concentration of the polymeric flocculant is 0.05 to 0.15% by weight, more preferably 0.1% by weight.

[0031] Preferably, the volume ratio of the oily wastewater to the conditioner is 7:1 to 7:2.

[0032] Preferably, the volume ratio of the oily wastewater to the polymeric flocculant is 7:1.5 to 7:2.

[0033] Preferably, the acid value of the oily wastewater is in the range of 6.5 to 7.5, and more preferably 6.8 or 7.1.

[0034] In a preferred embodiment of the present invention, the shellfish waste is a mixture of calcium carbonate and calcium oxide.

[0035] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various changes and modifications without departing from the inventive concept, and these all fall within the scope of protection of the present invention.

[0036] S1: Wastewater Discharge Procedure S2: Pressure Flotation Step S3: Oil Sludge Collection Steps S4: Feather Formation Steps S5: Dewatering and pressing steps

Claims

1. A method for treating oily wastewater, comprising the following steps: a wastewater input step, providing oily wastewater and inputting it into a flotation tank; a pressurized flotation step, applying pressure to the oily wastewater and dissolving air into it, wherein when the oily wastewater is discharged into the flotation tank, the air is released to form microbubbles, which adhere to impurities in the oily wastewater and carry the impurities to the surface of the oily wastewater; an oil sludge collection step, using a scraping mechanism to scrape the impurities from the surface of the oily wastewater and collect them to form oil sludge, which is then sent to an oil sludge drainage channel; a flocculant formation step, adding a coagulant to the oil sludge to form flocculants; and a dewatering and pressing step, squeezing the oil sludge to filter out water, causing the flocculants to form a sludge cake; wherein... The coagulant comprises a conditioning agent and a polymeric flocculant. The conditioning agent contains shellfish waste after high-temperature calcination, and the shellfish waste is a mixture of calcium carbonate and calcium oxide. The coagulant is added after the sludge collection step, thereby eliminating the rapid mixing step and increasing the overall process efficiency.

2. The method for treating oily wastewater as described in claim 1, wherein, The concentration of this conditioner is 0.5 to 2.5% by weight.

3. The method for treating oily wastewater as described in claim 1, wherein, The concentration of this polymeric flocculant is 0.05~0.15% by weight.

4. The method for treating oily wastewater as described in any one of claims 1 to 3, wherein, The flotation tank is equipped with an air dissolving device; wherein, the air dissolving device is used to dissolve the air into the oily wastewater, and when the oily wastewater is discharged into the flotation tank, the air is precipitated to form microbubbles.

5. The method for treating oily wastewater as described in claim 4, wherein, The volume ratio of the oily wastewater to the conditioner is 7:1~2.

6. The method for treating oily wastewater as described in claim 4, wherein, The volume ratio of the oily wastewater to the polymeric flocculant is 7:1.5~2.

7. The method for treating oily wastewater as described in claim 4, wherein, The acid value of this oily wastewater ranges from 6.5 to 7.5.

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