CN110342690B

CN110342690B - Method for treating and utilizing high-sulfate radical leachate nanofiltration concentrated solution

Info

Publication number: CN110342690B
Application number: CN201910754284.6A
Authority: CN
Inventors: 许玉东; 林振琳; 谢锦灯; 伍玉全
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2019-08-15
Filing date: 2019-08-15
Publication date: 2021-09-24
Anticipated expiration: 2039-08-15
Also published as: CN110342690A

Abstract

The invention discloses a high-efficiency treatment and utilization method of high sulfate radical leachate nanofiltration concentrate, which mainly adopts a two-stage ultrafiltration system to separate and concentrate humic acid in the nanofiltration concentrate, realizes the standard reaching of process tail water through a nanofiltration system, and adopts additional calcium chloride to carry out gypsum precipitation to efficiently remove high-concentration SO in nanofiltration trapped fluid containing scale inhibitor and secondary ultrafiltration permeated fluid formed in the process₄ ^2‑And Ca²⁺Regulating and controlling SO remained in supernatant after solid-liquid separation₄ ^2‑<10000mg/L, so as to achieve the purpose of full treatment of leachate nanofiltration concentrated solution and humic acid extraction. The method is efficient, simple, economical, wide in adaptability and stable in operation, and can realize good recycling of resources.

Description

Method for treating and utilizing high-sulfate radical leachate nanofiltration concentrated solution

Technical Field

The invention belongs to the technical field of landfill leachate treatment, and particularly relates to a high-efficiency treatment and utilization method of a high sulfate radical leachate nanofiltration concentrated solution.

Background

MBR + NF technology has become the mainstream typical technology of landfill leachate treatment, but it can inevitably produce nanofiltration concentrate which accounts for 10-20% of the volume of the stock solution, and at present, methods such as recharging, advanced oxidation, evaporation and incineration are mainly used for harmless treatment of the concentrate, but the technologies respectively have the defects of infeasibility, unreliability, poor economic benefit and the like, and are actually difficult to operate stably for a long time. Because nanofiltration concentrated solution is rich in humic acid and other components are mainly harmless inorganic salt, a method for separating and recovering humic acid and simultaneously realizing harmless treatment based on a compact ultrafiltration and nanofiltration combined process is gradually paid attention to and developed, and patents such as ' extraction method of humic acid ' (ZL 201110272483.7), ' advanced treatment process and special equipment for landfill leachate ' (ZL 201210289032.9) and ' high-concentration SO-containing gas concentration₄ ^2-The invention relates to a process for separating and recovering humic acid in landfill leachate nanofiltration concentrated solution (ZL 201410633759.3), and the invention relates to a method for extracting humic acid in high-concentration divalent salt ion leachate MBR + NF concentrated solution (application No. 201410689333. X) and a method for extracting humic acid in low-concentration divalent salt ion leachate MBR + NF concentrated solution (application No. 201710843650.6).

Generally, nanofiltration intercepts divalent ions at a high level (more than 90 percent) and dense ultrafiltration intercepts divalent ions at different levels, SO that the concentration of the divalent ions in feed liquid formed in the process of extracting humic acid from the existing nanofiltration concentrated solution is higher and higher, such as SO₄ ^2-The concentration can reach more than 25000mg/L, and the membrane flux is greatly reduced. Studies have shown that the order in which the main divalent ions in nanofiltration concentrates have an adverse effect on flux is in turn SO₄ ^2->Ca²⁺>Mg²⁺. In order to reduce the concentration of divalent ions, the patent "Ca in high concentration interferent wastewater²⁺And SO₄ ^2-The precipitation method of (application No. 201710809154.9) shows the removal of Ca from gypsum crystals²⁺And SO₄ ^2-But mainly aims at SO in the ultrafiltration permeate without containing commercial scale inhibitor₄ ^2-And Ca²⁺The gypsum precipitate is removed. In fact, the nanofiltration concentrate extracts the SO from the nanofiltration retentate formed during the humic acid extraction process₄ ^2-The concentration of divalent ions is usually higher than that of the secondary ultrafiltration permeate, and the amount of water is more, so that the divalent ions contained in the secondary ultrafiltration permeate are more necessary to be removed. However, the nanofiltration trapped fluid contains a special scale inhibitor for calcium sulfate precipitation, so that the patent' Ca in high-concentration interferent wastewater²⁺And SO₄ ^2-The precipitation method of (application No. 201710809154.9) does not specifically refer to the SO contained therein₄ ^2-And Ca²⁺And (5) removing. In the prior art, Ca in the nanofiltration trapped fluid containing the scale inhibitor can be removed by a lime-sodium carbonate method²⁺And Mg²⁺Or patent "high concentration Ca in leachate nanofiltration concentrate²⁺、Mg²⁺The removal and reuse method (ZL 201510822143.5) comprises addingMethod for reducing Ca by adding trisodium phosphate and adjusting pH²⁺And Mg²⁺The methods have the defects of large medicine consumption, large sludge amount and high operation cost, and more importantly, SO is not considered₄ ^2-The removal measures of (1) make it difficult to avoid high SO concentrations in the feed liquid₄ ^2-Strong concentration polarization effect on a nanofiltration and compact ultrafiltration membrane system and the phenomenon that the flux of the membrane is deteriorated. While the patent "contains high concentration of SO₄ ^2-The technique for separating and recovering humic acid in landfill leachate nanofiltration concentrated solution (ZL 201410633759.3) adopts BaCl₂Removal of SO₄ ^2-Ion and precipitate BaSO₄Elution is carried out, albeit with SO₄ ^2-The removal effect is good, but the process is complex, the cost is high, the labor safety risk is high, and the engineering applicability is poor. In addition, a substantial portion of the SO in the nanofiltration concentrate₄ ^2-Higher concentration, some of which can even reach more than 6500mg/L, and Ca²⁺Is much higher than the stoichiometric ratio 1:1, SO in the nanofiltration trapped fluid and the secondary ultrafiltration permeating fluid formed in the technological process of extracting humic acid₄ ^2-And Ca²⁺The concentration also deviates far from the gypsum reaction stoichiometry. Therefore, the Ca in the concentrated solution is simply utilized²⁺Removal of SO₄ ^2-The effect is poor, the membrane flux can not be effectively improved, the energy consumption is reduced, and calcium chloride is required to be added to supplement Ca²⁺In an amount to remove SO in large quantities₄ ^2-. However, the excessive calcium chloride not only increases the medicine consumption and the cost, but also increases the Cl in the concentrated solution^-Concentration, nanofiltration system in the combined process can be due to Cl^-The partial interception causes the osmotic pressure to be increased and the power consumption to be increased, namely, the unsuitable calcium chloride adding amount causes high medicine consumption, large sludge amount and Cl introduction^-Many adverse effects. Therefore, further research and development of a method for treating and utilizing the nanofiltration concentrated solution of the high sulfate radical leachate, which has the advantages of more efficient technology, more economic efficiency, more reasonable applicability and stable and simple operation, is needed.

Disclosure of Invention

The invention aims to provide high sulfate radical percolationA high-efficiency treating and utilizing method for the concentrated liquid nanofiltration liquid features that two-stage ultrafiltering and nanofiltering system is used to extract humic acid and obtain tail water reaching standard, and the SO in the feed liquid is regulated by gypsum precipitation₄ ^2-And Ca²⁺At lower concentration levels. The method is efficient, simple, economical, wide in adaptability and stable in operation, and can realize good recycling of resources.

In order to achieve the purpose, the invention adopts the following technical scheme:

a high-efficiency treatment and utilization method of high sulfate radical leachate nanofiltration concentrate comprises the following steps:

1) pumping the landfill leachate nanofiltration concentrated solution into a primary ultrafiltration system, and performing membrane separation to obtain primary ultrafiltration trapped fluid and primary ultrafiltration permeate; pumping the primary ultrafiltration trapped fluid into a secondary ultrafiltration system, performing membrane separation to obtain secondary ultrafiltration trapped fluid and secondary ultrafiltration permeated fluid, and using the secondary ultrafiltration trapped fluid as a raw material of the humic acid-containing water-soluble fertilizer; pumping the primary ultrafiltration permeate into a nanofiltration system to obtain nanofiltration permeate and nanofiltration retentate, wherein the nanofiltration permeate can meet the limit of the industrial discharge standard through detection of various indexes and can be directly discharged;

2) the secondary ultrafiltration permeating liquid and the nanofiltration trapped liquid obtained in the step 1) flow into a gypsum precipitation system according to SO in the feed liquid₄ ^2-、Ca²⁺According to the concentration of (Ca) in the reaction²⁺With SO₄ ^2-Is 1: 1) of residual SO₄ ^2-<Adding calcium chloride in an amount of 10000mg/L, mechanically stirring and mixing, adjusting the pH of the feed liquid to 1.5-2.7, maintaining the water temperature at 25-40 ℃, and reacting for 3-5 h; carrying out solid-liquid separation on the reacted mud-water mixed solution to obtain supernatant and precipitate; filtering the supernatant, and refluxing to a primary ultrafiltration system for concentration and separation; and (4) mixing the precipitate into a percolate treatment system, and dehydrating and disposing the precipitate and the residual sludge together.

The invention has the following remarkable advantages:

(1) high efficiency. Containing a low concentration of (<100 mg/L) SO in nanofiltration retentate of commercial scale inhibitor₄ ^2-Plasma concentration is generally higher in the second stage than in the second stageThe ultrafiltration permeate is high and the water amount is generally larger, while in the patent 'method for extracting humic acid from high-concentration divalent salt ion leachate MBR + NF membrane retentate' (application No. 201410689333. X), the NF retentate needs to be treated by Fenton, and the supernatant is mixed with leachate MBR + NF process effluent and then discharged after reaching the standard, so that the defects of complex operation and maintenance, high cost, large sludge amount and the like exist; in the patent of 'advanced treatment process and special equipment for landfill leachate' (ZL 201210289032.9), nanofiltration trapped fluid is directly or softened by gypsum-sodium carbonate and then returned to a leachate treatment system, and the existence of the nanofiltration trapped fluid counteracts the treatment capacity and SO of the leachate treatment system₄ ^2-The adverse effect is still in existence, the medicine consumption of softening treatment is high, the sludge amount is large, and the like; in the patent "high concentration of interferent in waste water Ca²⁺And SO₄ ^2-The precipitation method of (application No. 201710809154.9) is mainly directed to removing a high concentration of (A)>1000 Mg/L) fulvic acid and Mg²⁺Ca in wastewater of inhibitor (not commercial scale inhibitor)²⁺And SO₄ ^2-And there are no specific solution steps (such as calcium chloride addition) that are clearly not in line with the stoichiometric ratio of the gypsum precipitation reaction. In the method, the whole process system contains high-concentration SO₄ ^2-And Ca²⁺The nanofiltration trapped fluid (containing low-concentration commercial scale inhibitor) and the secondary ultrafiltration permeating fluid (containing only high-concentration fulvic acid and Mg)²⁺Inhibitor) is subjected to gypsum precipitation treatment, SO that concentration polarization of a membrane system is mainly caused in the process₄ ^2-And Ca²⁺Can be removed sufficiently and sufficiently, SO that each membrane system can achieve high-multiple concentration, the volume proportion of tail water discharged after the nanofiltration concentrated solution is treated can reach the standard is high, the humic acid concentration in the obtained humic acid-containing water-soluble fertilizer raw material is also high, and the contained SO is₄ ^2-And Ca²⁺The concentration is proper, thereby comprehensively showing the high efficiency of the method.

(2) The adaptability is wide, and the system operation is stable. No matter SO in the concentrated solution₄ ^2-And Ca²⁺If the concentration meets the stoichiometric ratio of gypsum precipitation reaction, the method can effectively remove SO₄ ^2-. When the method is in accordance with the requirements, calcium chloride is not required to be added, and the two components in the concentrated solution are directly reacted to achieve the aim of removing the calcium chloride simultaneously. But is common to SO₄ ^2-High concentration, reasonable SO residue after reaction₄ ^2-Concentration of (<10000 mg/L) to effectively remove SO₄ ^2-The added calcium chloride is not wasted so as to reduce the medicament cost and the sludge amount, and simultaneously, the Ca remained in the supernatant after the solid-liquid separation²⁺At a lower concentration level. Therefore, the method is suitable for full-scale treatment and humic acid resource recovery of nanofiltration concentrated solution with various water quality characteristics, and greatly reduces SO₄ ^2-And Ca²⁺The feed liquid is very beneficial to the operation of the membrane system, and the stability is enhanced.

(3) The method has complete process, can comprehensively achieve full treatment of nanofiltration concentrated solution and recycling of humic acid resources, and is simple and economic.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

The process flow of the present invention is further described below with reference to FIG. 1.

The whole process comprises a primary ultrafiltration system, a secondary ultrafiltration system, a nanofiltration system and a gypsum precipitation system for the reaction of sulfate radicals and calcium ions. The specific process is as follows: (1) will contain high concentration of SO₄ ^2-Pumping the leachate nanofiltration concentrated solution of divalent ions into a primary ultrafiltration system for separation and concentration to form primary ultrafiltration trapped fluid and primary ultrafiltration permeate; (2) pumping the obtained primary ultrafiltration trapped fluid into a secondary ultrafiltration system for separation and concentration to form secondary ultrafiltration trapped fluid and secondary ultrafiltration permeate; humic acid concentration in secondary ultrafiltration trapped fluid>30g/L, can be used as a raw material of a humic acid-containing water-soluble fertilizer; (3) pumping the primary ultrafiltration permeating liquid obtained in the step (1) into a nanofiltration system for separation and concentration to form nanofiltration trapped liquid and permeating liquid; the nanofiltration permeating liquid can reach the standard and be discharged; (4) the obtained SO₄ ^2-Nanofiltration retentate with high divalent ion content and secondary ultrafiltration permeateDischarging the liquid into a gypsum precipitation system according to SO in the liquid₄ ^2-And Ca²⁺According to the concentration of residual SO after the reaction of gypsum (stoichiometric ratio 1: 1)₄ ^2-<Calculating the required calcium chloride adding amount according to the amount of 10000mg/L, then adding the calcium chloride according to the calculated adding amount, mechanically stirring and mixing for 10-15 min, then adjusting the pH value of the feed liquid to 1.5-2.7, maintaining the water temperature to 25-40 ℃, and reacting for 3-5 h; after the reaction, solid-liquid separation is carried out, and the supernatant fluid contains SO after being filtered₄ ^2-<10000mg/L, and refluxing the solution to a first-stage ultrafiltration system for re-separation and concentration; the gypsum precipitate can be mixed into a percolate treatment system to be dewatered and treated together with the residual sludge.

Example 1

The present invention will be further described with reference to the efficient treatment and utilization of nanofiltration concentrate in leachate treatment engineering of a household refuse incineration power plant.

The scale of the percolate treatment project of the household garbage incineration power plant is 500 tons/day, and a combined process flow of UASB + secondary A/O + UF (MBR) + NF + RO is adopted. The treatment project produces about 100 tons of nanofiltration concentrated solution per day, and the water quality is as follows: pH of 6.5 to 7.8, COD of 2000-3000mg/L, conductivity of 22 to 24mS/cm, SO₄ ^2-Between 2500 and 5000mg/L of Ca²⁺And Mg²⁺The concentration ranges of the compounds are 100-400 mg/L and 500-1000 mg/L respectively. The nanofiltration concentrated solution is lifted by a collection pool through a pump, enters a primary ultrafiltration water inlet barrel, is pumped into a primary ultrafiltration system for 7-9 times separation and concentration after the pH is adjusted to 6.0-6.5, the obtained primary ultrafiltration trapped fluid is firstly collected in an intermediate material barrel, and then enters a secondary ultrafiltration system for 6-9 times separation and concentration, the concentration of humic acid in the obtained secondary ultrafiltration trapped fluid reaches 34g/L, the index requirements on humic acid in national agricultural standard 'humic acid-containing water soluble fertilizer' (NY 1106-2010) are met, and the nanofiltration concentrated solution can be used as a raw material of the humic acid-containing water soluble fertilizer. The obtained primary ultrafiltration permeating liquid is collected in an intermediate charging basket at first, and is pumped into a nanofiltration system for 3-5 times of separation and concentration, and the formed nanofiltration permeating liquid meets the requirements of the pollution control standard of domestic garbage landfill (GB 16889-2008) and can be directly discharged. Nanofiltration trapped fluid generated by nanofiltration system and secondary ultrafiltration systemSO in the resultant second ultrafiltration permeate₄ ^2-The concentration respectively reaches 25000mg/L and over 20000mg/L (Ca)²⁺Concentration respectively lower than 800mg/L and 600 mg/L), and flows into a gypsum precipitation system for sulfate radical and calcium ion reaction according to SO after reaction₄ ^2-Residual concentration less than 10000mg/L and stoichiometric ratio 1:1 calculation of Ca required²⁺The total concentration is subtracted by the Ca existing in the feed liquid²⁺Content of Ca to be increased²⁺And further calculating the required dosage of calcium chloride. And (3) adding calcium chloride in the reaction zone, stirring for 15min, maintaining the water temperature at 25-40 ℃, adjusting the pH of the feed liquid to 1.8-2.5, and reacting for 3-5 h. After the reaction, the mud-water mixed liquid enters a precipitation zone for solid-liquid separation, and the supernatant is filtered to obtain SO₄ ^2-<10000mg/L（Ca²⁺<900 mg/L), and the mixture flows back to the primary ultrafiltration water inlet tank to be mixed with the NF concentrated solution (mixed solution) to be used as primary ultrafiltration feed solution; the precipitate may be incorporated into excess sludge produced by the leachate treatment system for dewatering and disposal.

The method can realize the long-term stable operation of the process system, keep higher membrane flux and achieve good economical efficiency of engineering construction and operation.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims

1. A high-efficiency treatment and utilization method of a high sulfate radical leachate nanofiltration concentrated solution is characterized by comprising the following steps:

1) pumping the landfill leachate nanofiltration concentrated solution into a primary ultrafiltration system, and performing membrane separation to obtain primary ultrafiltration trapped fluid and primary ultrafiltration permeate; pumping the primary ultrafiltration trapped fluid into a secondary ultrafiltration system, performing membrane separation to obtain secondary ultrafiltration trapped fluid and secondary ultrafiltration permeated fluid, and using the secondary ultrafiltration trapped fluid as a raw material of the humic acid-containing water-soluble fertilizer; pumping the primary ultrafiltration permeate liquid into a nanofiltration system to obtain nanofiltration permeate liquid and nanofiltration trapped liquid, wherein the nanofiltration permeate liquid is discharged after reaching standards;

2) subjecting the product obtained in step 1)The secondary ultrafiltration permeating liquid and the nanofiltration trapped liquid flow into a gypsum precipitation system, the pH of the feed liquid is adjusted, and the pH is adjusted according to SO in the feed liquid₄ ^2-、Ca²⁺Adding calcium chloride into the mixture, and mechanically stirring the mixture for reaction; carrying out solid-liquid separation on the reacted mud-water mixed solution to obtain supernatant and precipitate; filtering the supernatant, and refluxing into a primary ultrafiltration system for cyclic concentration and separation; the precipitate is mixed into a leachate treatment system and is dehydrated and disposed together with the residual sludge;

the adding amount of the calcium chloride in the step 2) is determined by the residual SO after the reaction₄ ^2-<Conversion is carried out at 10000 mg/L;

the reaction temperature in the step 2) is 25-40 ℃, the pH of the feed liquid is 1.5-2.7, and the reaction time is 3-5 h.