Multi-stage filtration-chemical precipitation cyclic utilization treatment method for slurry wastewater

Abstract

The invention discloses a multistage filtration-chemical precipitation cyclic utilization treatment method for slurry wastewater, and belongs to the field of industrial wastewater treatment. The problems that the turbidity of reuse water exceeds the standard and the yield of chemical sludge is too large are solved. According to the technical scheme, waste water with the solid content of 15%-35% is subjected to impurity removal through a grating and then enters a quartz sand filtering tank; the primary filtrate is subjected to microfiltration and ultrafiltration treatment, and 1-3 mg / L of sodium hypochlorite is added into an ultrafiltration water inlet end in a pulse mode according to the transmembrane pressure difference larger than or equal to 0.25 MPa or the produced water turbidity larger than 0.5 NTU; adding 60-100mg / L of aluminum ion polyaluminum chloride and 0.3-0.8 mg / L of polyacrylamide into the ultrafiltration concentrated water in a sedimentation tank; supernatant of the sedimentation tank flows back to the quartz sand filtering tank, and 10%-30% of sludge flows back to the sedimentation tank; dividing 3%-20% of ultrafiltration produced water into a quartz sand filtering tank, and recycling the balance; and periodically discharging sludge and dehydrating. The method is used for sludge wastewater resource utilization and sludge reduction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of industrial wastewater treatment. More particularly, the present application relates to a multi-stage filtration-chemical precipitation recycling treatment method for slurry wastewater. BACKGROUND

[0002] In the field of slurry wastewater treatment, the existing technology generally adopts a combination route of grid impurity removal, sedimentation separation and filtration process for treatment. However, in long-term engineering practice, this technical route still has several technical problems that have not been properly solved.

[0003] The problem of turbidity exceeding the standard of recycled water caused by insufficient removal efficiency of micro-fine colloids. The colloidal substances with a particle size of 1 μm to 5 μm (mainly composed of clay minerals and organic humus) in the slurry wastewater are difficult to be effectively intercepted in the traditional filtration process due to their high stability and electrical characteristics. The removal rate of quartz sand filter tank for particles below 5 μm is usually less than 60%, which leads to the difficulty of the turbidity of the subsequent process water to reach the industrial recycling standard (≤1 NTU). The main reason for this problem is that colloidal particles can easily penetrate the quartz sand filter layer due to the Brownian motion effect; the traditional sedimentation process has limited efficiency in capturing colloidal substances, especially when the wastewater contains oil substances, the hydrophobicity of the colloidal surface is enhanced, which increases the difficulty of solid-liquid separation. In the past, attempts have been made to increase the thickness or reduce the particle size of the filter material to improve the interception effect, but this results in a doubling of the filtration resistance and a shortening of the operation cycle to less than 8 hours, which significantly reduces the economic efficiency.

[0004] The problem of rising disposal cost caused by excessive chemical sludge production. When using chemical precipitation method to treat membrane concentrate, the addition of polyaluminum chloride and anionic polyacrylamide generates a large amount of chemical sludge with a water content of more than 95%. For every 100 m 3 of wastewater treated, about 3 m 3 to 5 m 3 of sludge (based on water content of 95%) is generated, and the disposal cost accounts for 45% to 60% of the total operating cost of the system. The core of this problem is that the introduction of aluminum salt in the flocculation process leads to the swelling of the sludge volume, which is about 40% larger than ordinary biological sludge; the residual polyacrylamide macromolecular chains in the sludge increase the difficulty of dewatering. Although sludge reduction techniques (such as thermal drying) have been tried, the energy consumption is as high as 120 kWh / m 3 , and there are problems in waste gas treatment, which makes it difficult to be applied on a large scale.

[0005] Microbial membrane layer regeneration triggered membrane flux periodic attenuation problem, when ultrafiltration membrane is used to treat wastewater, microbial community on the membrane surface continuously proliferates to form a biofilm layer. The biofilm presents periodic regeneration characteristics: initial stage (0-48 hours of operation): extracellular polymeric substances (EPS) of microorganisms form a gel layer, and the water permeability rate decreases to 70% of the initial value; stable stage (48-96 hours): the biofilm matures, and the flux stabilizes at 55%-65% of the initial value; regeneration stage (>96 hours): the biofilm partially falls off and regrows, triggering flux fluctuation (amplitude up to ±15%). The main means to maintain the flux at present is periodic chemical cleaning (once every 72 to 96 hours), but the consumption of cleaning agent reaches 0.8 kg / m 2 2, and frequent cleaning leads to a membrane life of less than 12 months.

[0006] And the above problems are interrelated to form a technical dilemma: insufficient colloid removal forces an increase in flocculant dosage, which in turn exacerbates sludge production (positive feedback effect); sludge disposal costs constrain system economics, limiting the application of advanced treatment technologies; membrane flux attenuation leads to fluctuations in water production rate, affecting water resource recovery stability. Past improvement attempts have focused on optimizing a single link (such as membrane material modification or dewatering equipment upgrade), but have failed to establish a whole-process coordination mechanism, resulting in the persistence of the problems. SUMMARY

[0007] An object of the present application is to solve at least the above problems and provide at least the advantages to be described later.

[0008] To achieve these objects and other advantages according to the present application, a multi-stage filtration-chemical precipitation recycling treatment method for slurry wastewater is provided, comprising: Step one, inputting slurry wastewater with a solid content of 15% to 35% into a grid impurity removal device to remove solid impurities with a particle size greater than 5 mm; Step two, the wastewater output by the grid impurity removal device enters a quartz sand filter tank for primary filtration, the quartz sand filling layer has a thickness of 1.0 m to 1.5 m, a particle size grading of 0.4 mm to 1.5 mm, and a filtration speed of 6 m 3 / m 2 to 10 m 3 / m 2 per hour; Step three, pumping the primary filtrate into a microfiltration device with a pore size of 3 μm to 8 μm, and operating at a pressure of 0.1 MPa to 0.2 MPa; Step four, the water produced by the microfiltration device enters an ultrafiltration membrane assembly with a molecular weight cut-off of 80,000 Da to 150,000 Da, and a transmembrane pressure difference of 0.2 MPa to 0.3 MPa; wherein sodium hypochlorite solution is added to the water inlet end of the ultrafiltration membrane assembly, and the addition method is specifically as follows: The sodium hypochlorite dosage is adjusted in real time according to the transmembrane pressure difference, and when the transmembrane pressure difference rises to 0.25 MPa, 1 mg / L to 3 mg / L of sodium hypochlorite solution is added, pulse injection is adopted, the single pulse duration accounts for 10% to 30% of the continuous operation time period of the ultrafiltration membrane module, and the pulse interval is 5 min to 10 min; and a turbidity online monitor is arranged at the water production end of the ultrafiltration membrane module, and when the water production turbidity exceeds 0.5 NTU, the sodium hypochlorite pulse addition is triggered; Step five, the concentrated water generated by the ultrafiltration membrane module flows into the chemical precipitation tank, 60 mg / L to 100 mg / L of polyaluminum chloride solution and 0.3 mg / L to 0.8 mg / L of anionic polyacrylamide are added, the stirring speed is 50 rpm to 70 rpm, and the reaction time is 25 min to 35 min; Step six, the supernatant of the chemical precipitation tank flows back to the water inlet end of the quartz sand filter tank, and the chemical sludge with a water content of 90% to 95% at the bottom is returned to the water inlet end of the chemical precipitation tank at a volume ratio of 10% to 30%; Step seven, 3% to 20% of the water produced by the ultrafiltration membrane module is divided into the water inlet end of the quartz sand filter tank, and the remaining water is output for reuse; Step eight, the chemical precipitation tank periodically discharges excess sludge to a sludge dewatering device.

[0009] Preferably, in step six, the chemical sludge is treated in a closed ozone contact tank before being returned, and the specific method is as follows: The ozone dosage is adjusted in real time according to the COD value of the sludge supernatant, and when the COD value is greater than 150 mg / L, 40 mg / L to 100 mg / L of ozone is added, and when the COD value is less than 80 mg / L, the addition is stopped; A titanium alloy catalytic filler layer is arranged in the ozone contact tank, the specific surface area of the filler is greater than 500 m 2 / m 3 g, ozone gas is input through a microporous aeration disc, and the bubble diameter is 0.5 mm to 2 mm; The aeration intensity changes with the sludge concentration gradient, the aeration intensity is 0.8 m 3 g per cubic meter of sludge per minute when the sludge concentration is 40 g / L to 60 g / L, and the aeration intensity is 1.2 m 3 g per cubic meter of sludge per minute when the sludge concentration is 60 g / L to 80 g / L; The treatment endpoint is controlled by the ultraviolet absorption value UV254, and the reaction is terminated when UV254 falls to 0.15 cm -1 .

[0010] Preferably, the grid impurity removal device in step one performs the following optimization operation: A cyclone cutting pump is additionally arranged in front of the water inlet channel of the grid removal device, the cutting rotor linear speed of the cyclone cutting pump is 15-25 m / s, the blade gap is 0.5-1 mm, and the treatment flow is 120-150% of the design flow; The grid of the grid removal device adopts a stepped fine grid with a gap of 2-3 mm, and the surface of the grid bar is coated with a polytetrafluoroethylene coating with a thickness of 50-100 μm; A differential pressure sensor is arranged in front of and behind the grid, and when the differential pressure exceeds 0.15 MPa, the bottom backwashing pipeline is triggered, the backwashing water pressure is 0.4-0.6 MPa, and the duration is 30-90 s; The backwashing frequency is dynamically adjusted according to the sludge concentration behind the grid, the frequency is 3-5 times per day when the sludge concentration is 20-30 g / L, and the frequency is 6-8 times per day when the sludge concentration is 30-50 g / L.

[0011] Preferably, the method for chemical sludge reflux in step six specifically comprises: An ultraviolet excitation fluorescence detector is arranged at the sludge outlet of the chemical sedimentation tank to monitor the active flocculent concentration in the reflux sludge in real time, and the reflux ratio is increased when the concentration is lower than 3000 fluorescence units per milliliter; The reflux ratio is dynamically adjusted according to the sludge age, the reflux ratio is 25-35% when the sludge age is 1-3 days, and the reflux ratio is 36-45% when the sludge age is 3-5 days; The sludge reflux pipeline is driven by a variable frequency screw pump, when the active flocculent concentration change rate exceeds 5% / min, a 4-20 mA current signal is output to the frequency converter through the PID controller to adjust the rotation speed of the variable frequency screw pump so that the pipeline flow rate is maintained in the range of 0.4-0.8 m / s; The reflux sludge and fresh sludge are mixed and then enter an activation reactor with a volume of 5-10% of the chemical sedimentation tank, the activation reactor is arranged upstream of the sludge reflux pipeline, the aeration intensity is 0.3-0.5 m 3 Gas per cubic meter of sludge per minute, and the activation time is 10-20 min.

[0012] Preferably, a nanofiltration membrane unit is additionally arranged behind the ultrafiltration membrane assembly in step four, and the specific method is as follows: The operating pressure of the nanofiltration membrane unit is dynamically adjusted according to the influent LSI index, the operating pressure is reduced to 1.2-1.4 MPa when LSI>0.5, the operating pressure is increased to 1.6-1.8 MPa when LSI<-0.3, and the operating pressure is maintained at 1.5 MPa when LSI≤0.5 and LSI≥-0.3; The polyamide composite membrane with a molecular weight cut-off of 150 Da to 300 Da is used, the membrane surface flow rate of the polyamide composite membrane is controlled to be 0.08 m / s to 0.12 m / s, and the chemical cleaning is automatically triggered when the transmembrane pressure difference exceeds 0.8 MPa; wherein the chemical cleaning method is that: the mass concentration of 0.5% to 1.5% of the citric acid solution is heated to 35 DEG C to 45 DEG C, and the polyamide composite membrane is circularly flushed at a flow rate of 0.3 m / s to 0.5 m / s for 20 min to 40 min, and then the reverse osmosis produced water is used for rinsing for 10 min to 15 min; The nanofiltration concentrated water grading reflux treatment comprises the following steps: when the nanofiltration concentrated water conductivity is less than 8000 muS / cm, 30% to 50% of the water is diverted to the water inlet end of the quartz sand filter tank; when the nanofiltration concentrated water conductivity is greater than or equal to 8000 muS / cm, all the water is discharged into the chemical precipitation tank. The scale inhibitor with a mass concentration of 2 mg / L to 5 mg / L is added at the water inlet end of the nanofiltration membrane unit, and the scale inhibitor is polyacrylic acid with a molecular weight of 2000 Da to 5000 Da.

[0013] Preferably, the activated reactor exhaust pipeline is connected to a gas phase activated carbon adsorption tower, the activated carbon has a particle size of 1.5 mm to 3 mm and an iodine value of 900 mg / g to 1100 mg / g, and the gas residence time is 3 s to 8 s.

[0014] Preferably, a conditioning tank is arranged in front of the sludge dewatering device in step eight, 0.1% to 0.3% of cationic polyacrylamide with a molecular weight of 8 million Da to 15 million Da is added, 5% to 10% of modified attapulgite is added at the same time, the stirring speed is 30 rpm to 40 rpm, and the reaction time is 10 min to 15 min.

[0015] Preferably, a buffer tank is additionally arranged at the ultrafiltration produced water output end in step seven, the buffer tank has a volume of 15% to 25% of the system processing capacity per hour, and a liquid level interlocking device is arranged in the buffer tank. When the liquid level is higher than 85%, the ultrafiltration produced water valve is automatically closed; When the liquid level is lower than 15%, the standby water source water supply pipe is automatically opened.

[0016] Preferably, an ion exchange resin column is connected to the nanofiltration membrane unit produced water end, the resin is a sulfonic acid sodium type styrene copolymer, the exchange capacity is 4.2 meq / g to 4.8 meq / g, the flow rate is controlled to be 15 times to 25 times the resin volume per hour, and the resin regeneration program is triggered when the produced water conductivity exceeds 50 muS / cm.

[0017] The present application at least has the following beneficial effects: First, the first multi-stage filtration and chemical precipitation cycle coupling process is created, the efficiency of colloidal removal is enhanced through gradient interception, the internal circulation of sludge reflux and water production diversion is constructed synchronously, the contradiction between turbidity control of reclaimed water and sludge reduction in the industry is solved, and the dual improvement of water quality reaching the standard and disposal cost optimization is realized.

[0018] Second, the double-parameter trigger pulse oxidation mechanism is innovated, the high-concentration sodium hypochlorite pulse injection is intelligently controlled according to the transmembrane pressure difference and turbidity change, the biological membrane protection layer is effectively penetrated, the periodic flux decay caused by microbial regeneration is fundamentally inhibited, and the stable operation period of the membrane is significantly prolonged.

[0019] Third, the cyclone breaking, surface modification and intelligent backflushing technology are creatively integrated, and the combined blockage problem of fiber winding and particle embedding is solved. Cyclone cutting eliminates the winding source, low-friction coating blocks the adhesion path, differential pressure linkage backflushing removes the trapped impurities in time, and the continuous and efficient operation of the pretreatment system is ensured; the ultraviolet fluorescence activity tracking technology is introduced, the flocculent concentration is monitored in real time, and the sludge age is adjusted to regulate the reflux ratio. Combined with the precise regeneration process of the activated reactor, the traditional sludge reflux activity decay paradox is reversed, and the continuous utilization efficiency of the flocculant is significantly improved.

[0020] Fourth, a dynamic control system for scaling tendency is constructed, the substable state level is maintained by real-time pressure regulation, the molecular weight is limited to interfere with the lattice development of the scale inhibitor, the salt is intelligently controlled by the concentration water grading reflux, and the risk of membrane surface scaling and pipeline deposition is systematically cracked. The high-selectivity activated carbon targeted adsorption technology is innovated, small-molecule volatile substances are captured accurately based on iodine value optimization, secondary pollution in the activation process is effectively eliminated, and the problem of environmental deterioration caused by waste gas emission is completely solved.

[0021] Fifth, the organic-inorganic synergistic conditioning technology is invented, the ultra-high molecular weight flocculant constructs a space skeleton, the modified mineral material adsorbs colloidal water, and the equipment obstruction caused by the stickiness of sludge is cracked by the double action, which greatly improves the operation reliability of the dewatering system. A three-level defense mechanism for hydraulic imbalance is established, the buffer volume absorbs the impact of flow fluctuation, the liquid level double threshold control realizes rapid response, the water source intelligent switching provides ultimate protection, and the risk of system collapse caused by water fluctuation is fundamentally eliminated. The ion leakage targeted control system is developed, the sodium type resin selectively adsorbs the leakage ions, the conductance threshold linkage regeneration guarantees the continuous purification capacity, the technical blind area of nanofiltration water conductivity fluctuation is completely cracked, and the stable supply of high-purity water quality is ensured.

[0022] Other advantages, objects and features of the present application will be apparent from the following description, and will be understood by those skilled in the art through the study and practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The flow framework diagram of one of the technical solutions of the present application. DETAILED DESCRIPTION

[0024] The application will be further described in conjunction with the following examples, so that those skilled in the art can implement the application according to the description and examples.

[0025] It should be noted that the experimental methods described in the following embodiments are all conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified; in the description of the application, the orientation or positional relationship indicated by the terms is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application.

[0026] According to one embodiment of the application, the method is used for treating oilfield drilling mud wastewater. The wastewater contains 22% of solid content, mainly including clay particles, drilling fluid additives and formation mineral colloids. First, the wastewater is input into a mechanical grid with a gap of 5 mm to remove large particle impurities such as gravel; then it is input into a quartz sand filter tank with a filter layer thickness of 1.2 m and a quartz sand particle size of 0.8 mm, and the filtration speed is 8 m 3 / (m 2 h); the primary filtrate is operated at a pressure of 0.15 MPa through a microfiltration device with a pore size of 5 μm to intercept coarse particles; the microfiltration water is input into an ultrafiltration membrane assembly with a molecular weight cut-off of 100,000 Da, and the transmembrane pressure difference is controlled at 0.25 MPa. When the transmembrane pressure difference rises to 0.25 MPa or the turbidity of the produced water exceeds 0.5 NTU, automatic pulse addition of 2 mg / L sodium hypochlorite solution is triggered, and the single pulse duration accounts for 20% of the operation cycle, with an interval of 8 minutes. The ultrafiltration concentrated water is input into a chemical precipitation tank, and 80 mg / L of polyaluminum chloride solution and 0.5 mg / L of anionic polyacrylamide are added to form flocs by stirring at 60 rpm for 30 minutes. The supernatant of the precipitation tank is returned to the water inlet end of the quartz sand filter tank in full amount, and the sludge with a water content of 92% at the bottom is returned to the water inlet end of the precipitation tank at 20% of the volume. 10% of the ultrafiltration produced water is diverted to the quartz sand filter tank, and the remaining 90% is used as well washing water. Excess sludge is discharged from the chemical precipitation tank to a plate-and-frame filter press for dewatering every day.

[0027] Compared with the original technical method used in this oilfield, the method does not set up a membrane separation unit after quartz sand filtration and direct chemical precipitation process. The quartz sand filtration has a colloidal interception rate of only 58% for 1-5 μm, resulting in a long-term turbidity of the precipitation tank effluent of more than 2.1 NTU, exceeding the reuse standard limit (1 NTU). At the same time, due to the lack of sludge return mechanism, 0.35 m 3 of water content 95% chemical sludge is produced per cubic meter of wastewater (after the implementation of the present case, the sludge amount is reduced to 0.12 m 3), sludge disposal cost accounted for 51% of the operation cost (decreased to 28% in the present case). In terms of membrane fouling control, the original technology adopted fixed-frequency chemical cleaning (once every 72 hours), but the biofilm regeneration resulted in a flux fluctuation of ±18% between two cleanings (in the present case, the pulse oxidation made the flux fluctuation controlled within ±5%).

[0028] The effect detection shows that, after the treatment by the method, the turbidity of the reclaimed water is stably below 0.3 NTU, the colloidal removal rate is increased to 98%, the polyaluminum chloride dosage is reduced by 65% due to the sludge backflow, and the ultrafiltration membrane operation cycle is prolonged from 72 hours of the original technology to 240 hours, and the chemical cleaning frequency is decreased by 70%. The above-mentioned effects verify the effectiveness of the present embodiment in solving the problems of colloidal removal, sludge reduction and membrane fouling control by the multi-stage filtration-chemical precipitation circulation technology. Especially, the combined application of the ultrafiltration membrane pulse oxidation and the sludge backflow breaks the bottleneck of the mutual restriction between the colloidal removal efficiency and the sludge disposal cost in the traditional process, and provides a new technical path for the sludge wastewater treatment. The effect data are from the turbidity data recorded by HACH 2100N turbidity meter every hour, the sludge reduction rate is calculated according to the sludge cake yield of the plate-and-frame filter press, and the membrane flux fluctuation is monitored in real time by the Siemens pressure sensor.

[0029] According to still another embodiment of the present application, in the treatment of the sludge wastewater containing nickel in a certain electroplating plant, the supernatant COD value of the backflow sludge in the chemical precipitation tank is 210 mg / L, and the ozone dosing system is started according to the control logic. The ozone contact tank is filled with titanium alloy honeycomb filler, and ozone gas is input through a microporous aeration disc with a bubble diameter of about 1.5 mm. Based on the measured value of the sludge concentration of 50 g / L, the system automatically selects medium aeration intensity for operation. The UV254 value is continuously monitored during the treatment process, and the reaction is stopped when the value decreases to the specified threshold. The treated sludge is returned to the chemical precipitation tank to participate in the flocculation process.

[0030] Compared with the original technology method used in the plant, it uses a fixed ozone dosage to treat the backflow sludge for 30 minutes without correlating the change of the sludge organic matter concentration. After the original system runs for three months, it is observed that the COD removal rate in the precipitation tank continuously decreases, and the sludge settling performance significantly deteriorates. The field sampling and detection show that the supernatant COD of the backflow sludge accumulatively increases to 280 mg / L, the nickel ion concentration of the precipitation tank effluent increases from 0.8 mg / L to 2.5 mg / L, which exceeds the discharge limit value.

[0031] After the implementation of the present scheme, the real-time linkage of the ozone dosage and the sludge COD avoids excessive oxidation or insufficient treatment. The gradient aeration setting adapts to the mass transfer needs of different sludge concentrations. During the continuous operation, the nickel ion concentration of the precipitation tank effluent is stably below 0.5 mg / L, and there is no phenomenon of continuous decrease in the treatment efficiency. The sludge sampling and detection show that the COD value in the backflow channel is maintained below 150 mg / L. The stable operation state of the system proves that the accumulation problem of the refractory organic matter is effectively curbed.

[0032] According to yet another embodiment of the present application, a paper mill mixed slurry wastewater treatment, the wastewater contains a large amount of pulp fibers and mineral fillers, is first pretreated by a cyclone cutting pump, the cutting rotor is operated at a linear speed of 20 m / s, the blade gap is 0.8 mm, and the treatment flow rate reaches 135% of the design value. Subsequently, the wastewater enters a ladder-type fine screen, the screen gap is 2.5 mm, and the screen surface is covered with a polytetrafluoroethylene coating. During operation, a pressure difference sensor before and after the screen monitors in real time, and when the pressure difference exceeds 0.15 MPa, a 0.5 MPa high-pressure backwash is triggered, which lasts for 60 seconds. The backwash frequency is automatically adjusted according to the sludge concentration after the screen: when the concentration rises to 45 g / L, the system will increase the backwash frequency to 7 times a day.

[0033] In comparison with the original technical method used by the plant: it uses a common screen with a gap of 5 mm without a backwash device. During operation, it needs to be shut down for manual cleaning of the screen bars every 8 hours, and each time about 15 kg of entangled fibers are removed. The shutdown for cleaning results in less than 18 hours of effective operation time per day. Especially when the wastewater contains clay particles, the particles and fibers form a composite blockage, which has caused the screen gap to be completely closed, with a maximum downtime of 36 hours.

[0034] After the implementation of the present scheme, the cyclone cutting pump breaks the fibers into short fibers below 2 mm, eliminating entanglement. The ladder screen surface design allows impurities to slide down the inclined surface, and the polytetrafluoroethylene coating effectively prevents fiber adhesion. The automatic backwash system starts immediately when the pressure difference exceeds the standard, and the measured fiber content in the removed material during each backwash is reduced by 90%. The system achieves continuous operation for six months without forced shutdown, with an effective operation time of 23.5 hours per day. The maintenance frequency of the screen area is reduced from 3 times a day in the original technology to once a week, and the maintenance personnel feedback that the blockage is easy to remove. This indicates that the problem of composite blockage of flexible fibers and particles has been substantially improved.

[0035] According to yet another embodiment of the present application, a petrochemical plant oil sludge wastewater treatment, an ultraviolet fluorescence detector is installed at the sludge outlet of the chemical sedimentation tank, which monitors the concentration of active flocculation in real time, with a fluorescence unit of 2800 per milliliter, triggering a signal to increase the reflux ratio. According to the operating condition of a sludge age of 4 days, the system automatically adjusts the reflux ratio from 30% to 38%. The frequency conversion screw pump receives a 16 mA current signal output by the PID controller, and the pipeline flow rate is increased to 0.6 m / s. The backflow sludge is mixed with new sludge and enters the activation reactor, which has a volume of 8% of the sedimentation tank, and is aerated at a strength of 15 minutes per cubic meter of sludge per minute. 3 Gas intensity 15 minutes per cubic meter of sludge per minute.

[0036] Compared with the original technical method of the plant: it uses a fixed sludge reflux ratio of 35%, without activity monitoring and activation measures. The operation data shows that with the sludge age exceeding 3 days, the flocculant dosage needs to be increased by 40% to maintain the sedimentation effect. Field observation shows that the color of the reflux sludge is dark black, and the settling velocity is significantly reduced. In the dewatering link, the capacity of the plate and frame filter press is reduced by 30%, the filter cake dryness is less than 70%, and the disposal cost is increased.

[0037] After the implementation of the scheme, the fluorescence detector continuously feeds back the sludge activity state, and when the concentration decreases to 2900 fluorescence units per milliliter, the reflux ratio is immediately increased. The activation reactor gas bubbles are uniform, and the sludge is in a brownish suspension state. During the continuous operation for three months, the polyaluminum chloride dosage is stable at 75 mg / L level, and there is no increase in demand. The capacity of the plate and frame filter press is restored to the design value, and the filter cake dryness is increased to more than 75%. The stable operation of the sludge reflux system shows that the activity component attenuation problem is effectively controlled, and the flocculant utilization rate remains stable.

[0038] According to another embodiment of the present application, the activation reactor exhaust line is connected to a gas phase activated carbon adsorption tower, which is filled with columnar activated carbon with a particle size of 2 mm, and the iodine value detection report shows 1020 mg / g. The exhaust gas passes through the adsorption tower at a designed flow rate, and the gas residence time is controlled at 6 seconds. During the operation, no odor complaints were received at the plant boundary environmental monitoring point, and the plant area patrol records showed that there was no obvious odor around the activation unit.

[0039] Compared with the original technical method of the plant: it uses an alkali liquor spray tower to treat the activated exhaust gas, and does not configure an adsorption device. The historical operation log records that 2-3 times of plant area irritating odor events occur every month, especially when the air pressure is low. The environmental protection department detection report shows that the toluene concentration at the plant boundary has exceeded the standard many times, with the maximum monitoring value reaching 4.8 mg / m 3 (the standard limit is 2.0 mg / m 3 ). The alkali consumption record shows that 3 tons of chemical agents need to be supplemented every month.

[0040] After the implementation of the scheme, a simple detection port is provided at the inlet and outlet of the activated carbon tower, and the readings of the portable VOC detector are all lower than the detection limit of the instrument every month. The activated carbon is replaced every two months, and white deposits can be seen on the surface during replacement. During the continuous operation for six months, the environmental protection routine monitoring shows that the plant boundary exhaust gas indicators meet the requirements of GB14554-93 standard. The operation personnel on site feedback that the odor in the activation area is eliminated, and the alkali liquor spraying system is completely stopped. This shows that the volatile organic matter emission problem is effectively controlled.

[0041] According to another embodiment of the present application, a conditioning tank is added before the plate-and-frame filter press, and a cationic polyacrylamide solution with a molecular weight of 12 million Da is added to a mass concentration of 0.2%, and a modified attapulgite with a mass concentration of 8% is added at the same time. The mixture is stirred at a speed of 35 rpm for 12 minutes, and then pumped into the dewatering equipment after forming a dense floc. The dewatering workshop records show that the frequency of filter cloth replacement is reduced from the original 2 times per week to 1 time every two weeks, and the washing water consumption is reduced by 60%.

[0042] In comparison with the original technical method used by the factory: it uses single cationic polyacrylamide conditioning, and the addition concentration is 0.3%. The equipment operation log records that every 200 cubic meters of sludge needs to be stopped for cleaning the filter cloth, and the average amount of gelatinous blocking material cleaned each time is 23 kg. The pressure curve of the filter press shows that the feeding pressure often exceeds the upper limit value of 0.8 MPa, resulting in an increase in the failure rate of the hydraulic system. The maintenance report points out that the abnormal wear of the filter cloth accounts for 37% of the equipment maintenance cost.

[0043] During the implementation of the present scheme for three months, the feeding pressure of the filter press is stabilized in the interval of 0.6-0.7 MPa, and the pressure alarm is not triggered. When the filter cloth is disassembled, only a thin layer of mud cake is observed on the surface, and the flux is restored after high-pressure flushing for 15 minutes. The material detection report shows that the average particle size of the floc is increased to 2.1 mm (0.7 mm for the original technology) after the addition of the modified attapulgite. The production report confirms that the monthly consumption of polyacrylamide is reduced by 18 tons, and the number of sludge transport vehicles is reduced from an average of 3 per day to 2 per day. These quantifiable indicators confirm that the blocking problem caused by sticky sludge is significantly alleviated.

[0044] According to another embodiment of the present application, a buffer tank is added to the main pipe of the ultrafiltration water production, and the volume is set to 8 m 3 3 3 according to 40% of the system processing capacity per hour. The water tank is installed with a liquid level sensor for interlocking control: when the liquid level rises to 85% of the height, the ultrafiltration water valve is automatically closed; when the liquid level drops to 15%, the standby water source replenishment pipe is automatically opened. The system operation record shows that no shutdown event caused by sudden change of the amount of recycled water has occurred for three months after the implementation.

[0045] In comparison with the original technical method: it relies on the frequency conversion of the water pump to adjust the water volume, and the ultrafiltration water is directly connected to the recycled water pipe network. The equipment operation report records that when the batch cleaning of the coating workshop causes a sudden increase in the amount of recycled water, the pressure of the recycled water pipe network has dropped to 0.15 MPa (the minimum allowable value is 0.20 MPa), triggering the system protection shutdown. A total of 5 unplanned shutdowns are recorded in 3 months, with an average recovery time of 2.3 hours. The water quality test report points out that the turbidity of the initial production water after the restart of the shutdown exceeds the standard of 1.8 NTU (the standard is ≤0.5 NTU).

[0046] ​During the implementation of the scheme, the historical maximum single-hour reuse fluctuation reached the design value ± 35%. DCS system records show that when the liquid level rises from 30% to 85% in 4 minutes, the ultrafiltration water valve closes on time; when the liquid level drops from 25% to 14%, the standby water source completes the water replenishment in 17 seconds. The maintenance log confirms that the fluctuation amplitude of the running current of the key equipment (ultrafiltration membrane, delivery pump) is narrowed from the original ± 15% to ± 5%. The daily report of the water quality shows that the turbidity is always stable in the interval of 0.2-0.4 NTU. The workshop management personnel feedback that the complaints of paint spraying defects caused by water pressure fluctuation are reduced by 80%. These operation data confirm that the system's ability to resist water impact has been significantly improved.

[0047] According to another embodiment of the application, the nanofiltration water is connected to an ion exchange resin column filled with sodium sulfonate resin, and the exchange capacity detection value is 4.5 meq / g. The control flow rate is 20 times the resin volume per hour, and the online conductivity meter monitors the water quality in real time. When the conductivity rises to 52 μS / cm (set threshold 50 μS / cm), the regeneration program is automatically triggered. The operation record shows that the resin column is regenerated once every three weeks after the system is put into operation, and the water conductivity before regeneration is stable in the interval of 40±5 μS / cm.

[0048] Compared with the original technical method used by the factory: it relies on the nanofiltration unit to directly produce water, and does not set up ion exchange protection. The daily water quality report shows that when the salt load of the influent fluctuates (calcium ion 2-15 mg / L), the conductivity of the effluent fluctuates greatly between 10-150 μS / cm. The quality inspection report in Q2 2023 records that 3 batches of wafers were scrapped due to excessive conductivity, resulting in a loss of more than 2.6 million yuan. The equipment maintenance log shows that the reverse osmosis membrane of the pure water equipment is scaling faster, and the replacement frequency is shortened from 24 months to 14 months.

[0049] During the six-month implementation of the scheme, the regeneration program was triggered a total of 8 times, all within 30 minutes after the conductivity exceeded the standard. Compared with the nanofiltration influent calcium ion concentration fluctuation record (peak value 12 mg / L), the effluent conductivity curve always maintained in the range of 30-45 μS / cm. The operating pressure of the reverse osmosis membrane of the pure water station is stable at 1.2 MPa (the original technology fluctuation range is 1.0-1.8 MPa), and the maintenance plan confirms that the membrane replacement cycle has returned to the design value of 24 months. The wafer production report shows that the scrapping events caused by water quality have been zeroed. These verifiable data confirm that the ion stability of the reuse water has been fundamentally improved.

[0050] Although the embodiments of the application have been disclosed as above, they are not limited to the application and implementation listed in the specification and embodiments, and can be fully applied to various fields suitable for the application, and additional modifications can be easily realized by those skilled in the art, therefore the application is not limited to specific details and the examples shown and described herein, without departing from the general concept defined by the claims and the equivalent scope.

Claims

1. A multi-stage filtration-chemical precipitation recycling method for treating mud wastewater, characterized in that, include: Step 1: Sludge wastewater with a solid content of 15% to 35% is treated by a bar screen to remove impurities with a particle size greater than 5mm. Step 2: Wastewater enters a quartz sand filter tank for primary filtration. The quartz sand packing layer is 1.0-1.5m thick with a particle size of 0.4-1.5mm, and the filtration speed is 6-10m / s. 3 / (m 2 ·h); Step 3: The primary filtrate is treated by a microfiltration device at an operating pressure of 0.1-0.2 MPa and a pore size of 3-8 μm. Step 4: The permeate from the microfiltration device enters the ultrafiltration membrane module with a molecular weight cutoff of 80,000-150,000 Da, with a transmembrane pressure difference of 0.2-0.3 MPa. When the transmembrane pressure difference rises to 0.25 MPa or the permeate turbidity exceeds 0.5 NTU, a sodium hypochlorite solution with a mass concentration of 1-3 mg / L is added to the inlet of the ultrafiltration membrane module in a pulse manner. The duration of a single pulse accounts for 10% to 30% of the continuous operation time of the ultrafiltration membrane module, and the pulse interval is 5 min to 10 min. Step 5: The concentrated water produced by the ultrafiltration membrane module flows into the chemical precipitation tank, and a polyaluminum chloride solution with an aluminum ion content of 60-100 mg / L and an anionic polyacrylamide of 0.3-0.8 mg / L are added. The mixture is stirred at 50-70 rpm for 25-35 min. Step 6: The supernatant from the chemical sedimentation tank is returned to the inlet of the quartz sand filter tank, and the chemical sludge at the bottom with a moisture content of 90% to 95% is returned to the inlet of the chemical sedimentation tank at a volume ratio of 10% to 30%. Step 7: 3%-20% of the water produced by the ultrafiltration membrane module is diverted to the inlet of the quartz sand filter tank, and the remaining water is output for reuse. Step 8: Periodically discharge sludge from the chemical sedimentation tank to the dewatering equipment.

2. The multi-stage filtration-chemical precipitation recycling treatment method for mud wastewater according to claim 1, characterized in that, In step six, the chemical sludge is treated in a closed ozone contact tank before being returned to the system. The specific method is as follows: The ozone dosage is adjusted in real time according to the COD value of the sludge supernatant. When the COD value is greater than 150 mg / L, add 40 mg / L to 100 mg / L of ozone. Stop adding ozone when the COD value is less than 80 mg / L. The ozone contact tank is equipped with a titanium alloy catalytic packing layer with a specific surface area greater than 500 m². 2 / m 3 Ozone gas is introduced through a microporous aeration disc, with bubble diameters ranging from 0.5 mm to 2 mm; The aeration intensity varied with the sludge concentration gradient, reaching 0.8 m when the sludge concentration was between 40 g / L and 60 g / L. 3 The gas concentration per cubic meter of sludge per minute is 1.2 m³ / min at a concentration of 60 g / L to 80 g / L. 3 Gas per cubic meter of sludge per minute; The treatment endpoint was controlled by the UV absorbance value (UV254). When UV254 decreased to 0.15 cm⁻¹... -1 The reaction is terminated at that time.

3. The multi-stage filtration-chemical precipitation recycling method for treating mud wastewater according to claim 1, characterized in that, The bar screen cleaning device in step one performs the following optimization operations: A cyclone cutting pump is added before the water inlet channel of the bar screen removal device. The cutting rotor linear speed of the cyclone cutting pump is 15m / s to 25m / s, the blade gap is 0.5mm to 1mm, and the processing flow rate is 120% to 150% of the design flow rate. The grid of the bar screen removal device adopts a stepped fine grid with a gap of 2mm to 3mm, and the surface of the grid bars is coated with polytetrafluoroethylene (PTFE) with a coating thickness of 50μm to 100μm. Differential pressure sensors are installed before and after the bar screen. When the differential pressure exceeds 0.15MPa, the bottom backwash pipeline is triggered. The backwash water pressure is 0.4MPa to 0.6MPa, and the duration is 30s to 90s. The backwashing frequency is dynamically adjusted according to the sludge concentration after the screen. When the sludge concentration is 20g / L to 30g / L, the frequency is 3 to 5 times per day, and when the concentration is 30g / L to 50g / L, the frequency is 6 to 8 times per day.

4. The multi-stage filtration-chemical precipitation recycling method for treating mud wastewater according to claim 1, characterized in that, The specific methods for chemical sludge recirculation in step six include: An ultraviolet-excited fluorescence detector is installed at the sludge outlet of the chemical sedimentation tank to monitor the concentration of active flocs in the returned sludge in real time. When the concentration is lower than 3000 fluorescence units per milliliter, the return ratio is increased. The return ratio is dynamically adjusted according to the sludge age. The return ratio is 25% to 35% when the sludge age is 1 to 3 days, and 36% to 45% when the sludge age is 3 to 5 days. The sludge return pipeline is driven by a variable frequency screw pump. When the change rate of activated floc concentration exceeds 5% / min, the PID controller outputs a 4mA to 20mA current signal to the frequency converter to adjust the speed of the variable frequency screw pump so that the pipeline flow velocity is maintained within the range of 0.4 m / s to 0.8 m / s. After being mixed with fresh sludge, the returned sludge enters an activation reactor with a volume of 5% to 10% of the chemical sedimentation tank. The activation reactor is located upstream of the sludge return pipeline, with an aeration intensity of 0.3 m³ / h. 3 Gas per cubic meter of sludge per minute, activation time 10 to 20 minutes.

5. The multi-stage filtration-chemical precipitation recycling method for treating mud wastewater according to claim 1, characterized in that, A nanofiltration membrane unit is added after the ultrafiltration membrane module in step four. The specific method is as follows: The operating pressure of the nanofiltration membrane unit is dynamically adjusted according to the feed water LSI index. When LSI > 0.5, the operating pressure drops to 1.2 MPa to 1.4 MPa; when LSI < -0.3, the operating pressure rises to 1.6 MPa to 1.8 MPa; and when LSI ≤ 0.5 and LSI ≥ -0.3, the operating pressure is maintained at 1.5 MPa. A polyamide composite membrane with a molecular weight cutoff of 150 Da to 300 Da is used. The flow rate on the surface of the polyamide composite membrane is controlled at 0.08 m / s to 0.12 m / s, and chemical cleaning is automatically triggered when the transmembrane pressure difference exceeds 0.8 MPa. The chemical cleaning method is as follows: a citric acid solution with a mass concentration of 0.5% to 1.5% is heated to 35°C to 45°C and circulated and rinsed with the polyamide composite membrane at a flow rate of 0.3 m / s to 0.5 m / s for 20 min to 40 min, followed by rinsing with reverse osmosis permeate for 10 min to 15 min. The nanofiltration concentrate staged reflux treatment includes: when the nanofiltration concentrate conductivity is <8000μS / cm, 30% to 50% is diverted to the inlet of the quartz sand filter tank; when the nanofiltration concentrate conductivity is ≥8000μS / cm, the entire amount is discharged into the chemical sedimentation tank. Add a scale inhibitor with a mass concentration of 2 mg / L to 5 mg / L at the inlet of the nanofiltration membrane unit. The scale inhibitor is polyacrylic acid with a molecular weight of 2000 Da to 5000 Da.

6. The multi-stage filtration-chemical precipitation recycling method for treating mud wastewater according to claim 4, characterized in that, The exhaust pipe of the activation reactor is connected to a gas-phase activated carbon adsorption tower. The activated carbon has a particle size of 1.5 mm to 3 mm, an iodine value of 900 mg / g to 1100 mg / g, and a gas residence time of 3 s to 8 s.

7. The multi-stage filtration-chemical precipitation recycling method for treating mud wastewater according to claim 1, characterized in that, A conditioning tank is set up before the sludge dewatering equipment in step eight. Cationic polyacrylamide with a molecular weight of 8 million Da to 15 million Da is added at a mass concentration of 0.1% to 0.3%, and modified attapulgite clay with a mass concentration of 5% to 10% is added at the same time. The stirring speed is 30 rpm to 40 rpm, and the reaction time is 10 min to 15 min.

8. The multi-stage filtration-chemical precipitation recycling method for treating mud wastewater according to claim 1, characterized in that, A buffer tank is added to the ultrafiltration permeate output end in step seven. The volume of the buffer tank is 15% to 25% of the system's hourly processing capacity. A liquid level interlock device is installed inside the buffer tank. The ultrafiltration permeate valve automatically shuts off when the liquid level is above 85%. When the liquid level is below 15%, the backup water supply pipe will be automatically activated.

9. The multi-stage filtration-chemical precipitation recycling method for treating mud wastewater according to claim 5, characterized in that, The nanofiltration membrane unit is connected to an ion exchange resin column at the product water end. The resin is a sodium sulfonate type styrene copolymer with an exchange capacity of 4.2 meq / g to 4.8 meq / g. The flow rate is controlled at 15 to 25 times the resin volume per hour. The resin regeneration program is triggered when the conductivity of the product water exceeds 50 μS / cm.

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