TWI487671B - Waste water treatment system and method - Google Patents

Description

Wastewater treatment system and wastewater treatment method

The present invention relates to wastewater treatment, and more particularly to the units contained in the wastewater treatment system and the manner in which they are operated.

Factors such as population growth, business activities and climate change have caused global water shortage. In addition to continuously developing water resources and increasing water supply, water recycling is regarded as one of the necessary means for sustainable development of water resources. However, when water is recycled, Affected by the conductivity or salt concentration of the treated water, the water recovery rate cannot be effectively improved, and the concentrate is still highly conductive or contains high concentrations of salt. So far, there is no cost-effective treatment to avoid water body damage. Impact can only be achieved by reducing the water recovery rate. In order to improve the water recovery rate and the impact of concentrated liquid discharge on the environment, technologies such as near-Zero Liquid Discharge (nZLD) or Zero Liquid Discharge (ZLD) have gradually gained attention and research applications. In practical applications, reverse osmosis (RO) (RO reject, ROR), due to the increase in conductivity or salt concentration, its osmotic pressure is high, it is not easy to use the general desalting membrane Concentrate and directly enter the evaporation tank and crystallization tank for reprocessing to achieve near-zero liquid discharge or zero liquid discharge. However, since the water content entering the evaporation tank and the crystallization tank is still high (usually about 3.5% TDS), the operating cost is still high, making near-zero liquid discharge or zero-liquid discharge less acceptable to the industry, and limiting its development and should use.

In summary, there is an urgent need for new wastewater treatment systems for practical application in the industry.

A wastewater treatment system according to an embodiment of the present invention includes: an inlet end; an inverted-electrode dialysis unit connected to the inlet end to receive initial wastewater, and treating the initial wastewater to form a first fresh water and a first concentrated water; a water outlet connected to the inverted electrodialysis unit to discharge the first fresh water; a thin film distillation unit connected to the inverted electrodialysis unit to receive the first concentrated water, and the first concentrated water to form the second fresh water and the first Two concentrated water; and a second water outlet end connected to the thin film distillation unit to discharge the second fresh water.

A wastewater treatment method according to an embodiment of the present invention includes: providing initial wastewater; treating the initial wastewater with an inverted-electrode dialysis unit to form a first fresh water and a first concentrated water; and treating the first concentrated water with a thin film distillation unit, To form a second fresh water and a second concentrated water.

A‧‧‧ anion exchange membrane

C‧‧‧Cation exchange membrane

10‧‧‧ film holder

11‧‧‧ Freshwater room

12‧‧‧Concent water room

14‧‧‧electrode solution

30‧‧‧film

32‧‧‧Steam

100‧‧‧Waste treatment system

101‧‧‧ water inlet

103‧‧‧Inverted electrodialysis unit

105‧‧‧Initial wastewater

107, 117‧‧‧ fresh water

109, 119‧‧ ‧ concentrated water

111, 121‧‧‧ water outlet

113‧‧‧ Thin film distillation unit

123‧‧‧Drying unit

125‧‧‧Return

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of a wastewater treatment system in accordance with one embodiment of the present invention.

Fig. 2 is a schematic view showing an inverted electrodialysis unit employed in an embodiment of the present invention.

Figure 3 is a schematic illustration of a thin film distillation unit employed in an embodiment of the invention.

Figure 1 is a wastewater treatment system 100 of an embodiment, including water inflow The end 101 is connected to the inverted electrodialysis unit 103, and the inverted electrodialysis unit 103 receives the initial wastewater 105. In an embodiment, the initial wastewater 105 may be seawater or industrial wastewater, and the initial wastewater has a calcium ion concentration and a magnesium ion concentration of less than 100 mg/L. If the calcium ion concentration and the magnesium ion concentration of the initial wastewater 105 are too high, fouling is easily caused, and the film life of the inverted-electrode dialysis unit 103 is shortened, and the reversal and regeneration frequency of the inverted-electrode dialysis film are increased. In one embodiment, the softened initial wastewater 105 may be first introduced into the inverted electrodialysis unit 103 after the initial wastewater 105 is softened. The softening method may be an ion exchange method, a fluidized bed crystallization method, or a combination thereof. In one embodiment, the initial wastewater 105 has a conductivity between 5,000 [mu]S/cm and 10,000 [mu]S/cm.

Electrodialysis (ED) treatment technology uses different characteristics of the membrane to separate the ions in the water. The movement of ions in the water is the driving force of the positive and negative direct current. Electrodialysis reversal (EDR) further improves the electrodialysis treatment technology, using DC positive and negative electrodes and internal diversion switching to extend the life of the membrane. Figure 2 is a schematic illustration of an electrodialysis unit. The design of electrodialysis (ED) and inverted electrodialysis (EDR) depends on the processing requirements and the quality of the stock solution. The main components include membrane stacks, cation exchange membrane C, anion exchange membrane A, and membrane holders. The electrode chambers at the two ends of the 10 are respectively provided with an anode and a cathode. The electrode liquid 14 flows into the electrode chamber (as on the cathode side in Fig. 2), and then flows through the outer tube to the electrode chamber on the other side (as on the anode side in Fig. 2). The cation and anion exchange membrane separates the interior of the membrane holder into a fresh water chamber 11 and a concentrated water chamber 12. A through hole (not shown) through which water and liquid flows is formed in the upper edge and the lower edge of the membrane frame of each chamber, and the passage holes form a liquid path when the membrane holder 10 is assembled and overlapped, and the initial wastewater 105 is designed through this. Dilute water 107 and concentrated water The concentrate 109 flows through the fresh water chamber 11 and the concentrated water chamber 12, respectively, without being mixed. By returning (not shown), the treated concentrated water 109 can be again enriched by entering the concentrated water chamber 12. Spacers are provided between the chambers to maintain a certain gap between the liquid chambers to facilitate mixing of the liquid streams. The principle of electrodialysis for desalination is that the cation can only penetrate the cation exchange membrane, and the anion only penetrates the anion exchange membrane. Under the action of the external DC electric field, the anion in the water moves to the anode, the cation moves to the cathode, and finally Fresh water 107 and concentrated water 109 are obtained to achieve desalination and desalination. The above electrodialysis apparatus can be referred to US Patent No. 3,063,924.

The inverted electrodialysis unit 103 can process the initial wastewater 105 to form fresh water 107 and concentrated water 109. The treated fresh water 107 can be discharged via a water outlet end 111 connected to the inverted electrodialysis unit 103. In one embodiment, the discharged fresh water 107 can be used for cooling water at the plant end. In another embodiment, the discharged fresh water 107 can be further purified by reverse osmosis (RO), nanofiltration (NF), or a combination thereof. In one embodiment, the fresh water 107 has a conductivity between 500 μS/cm and 1,000 μS/cm, and the concentrated water 109 has a conductivity between 15,000 μS/cm and 20,000 μS/cm. If the conductivity of fresh water 107 is too high, the standard of discharge or reuse cannot be achieved.

The wastewater treatment system 100 described above also includes a thin film distillation unit 113 coupled to the inverted electrodialysis unit 103 for receiving and treating concentrated water 109 to form fresh water 117 and concentrated water 119. The basic principle of the thin film distillation unit 113 is as shown in Fig. 3, which utilizes a hydrophobic porous organic membrane distillation method, and the conventional thin film 30 includes PP, PTFE, PVDF, or the like. Due to the surface tension, the concentrated water 109 having a higher temperature on the left side of the film 30 cannot enter the pores of the film 30, and only the vapor 32 can pass through the pores of the film 30, and condense on the right side of the film 30 having the flow of the cryogenic liquid to form Fresh water 117. After the treatment by the thin film distillation unit 113, the concentration of the concentrated water 109 on the left side of the film 30 is increased to become concentrated water 119. The thin film distillation unit 113 shown in Fig. 3 is a so-called direct contact type (DCMD). In other embodiments, the thin film distillation unit 113 can be air gap type (AGMD), gas sweep type (SGMD), or vacuum type (VMD).

The treated fresh water 117 can be discharged through the water outlet end 121 connected to the thin film distillation unit 113. In one embodiment, the discharged fresh water 117 can be used for cooling water at the plant end. In another embodiment, the discharged fresh water 117 can be further purified by reverse osmosis (RO), nanofiltration (NF), or a combination thereof. In one embodiment, the fresh water 117 has a conductivity between 500 μS/cm and 2,000 μS/cm, and the concentrated water 119 has a conductivity between 30,000 μS/cm and 80,000 μS/cm. If the conductivity of fresh water 117 is too high, the standard of discharge or reuse cannot be achieved.

In one embodiment, the wastewater treatment system 100 includes a drying unit 123 coupled to the thin film distillation unit 113 to receive and dry the concentrated water 119 to form a solid. The drying unit 123 can be a crystallizer, a centrifuge, or a nebulizer. Since the concentrated water 119 has a high salt content (20%), the drying unit 123 does not need to be a large-volume drying device such as an evaporation can.

In another embodiment of the present invention, the wastewater treatment system 100 includes a return pipe 125 connecting the thin film distillation unit 113 and the water inlet end 101, and the concentrated water 119 is added to the initial wastewater 105 for repurification.

The cost of the inverted electrodialysis unit 103 is low, but has the disadvantage of not being able to handle concentrated water of high conductivity. The thin film distillation unit 113 can handle concentrated water of various conductivity, but directly treating low-conductivity wastewater increases the cost of wastewater treatment. Taking the amount of treated water of 100 tons/day as an example, in the embodiment of the present invention, the combination of the inverted-electrode dialysis unit 103 with the thin film distillation unit 113 and the thin film distillation unit 113 alone has advantages, as in the comparison of the first table:

The above and other objects, features, and advantages of the present invention will become more apparent and understood.

Example

In the following examples, the inverted-electrode dialysis unit is referred to US Pat. No. 3,036,924. Film used in the thin film distillation unit MILLIPORE FLUOROPORE ^TM MEMBRANE FILTERS PTFE 0.45μm, which fresh water (e.g., freshwater Fig. 3 of 117) after the treatment temperature was 30 ℃, while the concentrated water concentrated water before the treatment (e.g., Fig. 3 of 109 The temperature is 70 °C.

Example 1

The initial wastewater of the light power plant was subjected to EDR treatment to form an EDR concentrate (conductivity of about 15,000 μS/cm). The above EDR concentrate was introduced into the thin film distillation unit. After 55 hours of operation, the permeate flux was lowered from about 27 LMH to about 10 LMH, and after the membrane was washed with deionized water, the permeate flux was returned to about 25 LMH. 200 hours of operation Thereafter, the conductivity of the high-temperature concentrated water end rises from about 15,000 μS/cm to 74,300 μS/cm, and the conductivity of the water-generating end is about 1,932 μS/cm.

Comparative example 1

The initial wastewater of the light power plant was subjected to EDR treatment to form an EDR concentrate (conductivity of about 15,000 μS/cm). The concentrate was introduced into the above-described EDR reverse osmosis unit, a reverse osmosis film is a ^{DOW FILMTEC TM Polyamide Thin-Film Composite} Membranes, concentrate flow of 400mL / min, and the operating pressure of 5.1Kg / m ^2. After 13 hours of operation, the permeate flux decreased from about 5.4 LMH to about 0.4 LMH, the conductivity at the concentrated water end increased from about 15,000 μS/cm to 19,600 μS/cm, and the conductivity at the water producing end was about 9,760 μS/cm.

From the comparison between Example 1 and Comparative Example 1, it can be seen that the first EDR and the MD are better than the first EDR and RO. First, after 55 hours of MD treatment, the flux was much greater than the flux after 13 hours of RO treatment. Furthermore, the fresh water conductivity (9,760 μS/cm) at the water producing end of the RO after 13 hours of treatment was much higher than the fresh water conductivity (1,932 μS/cm) at the water producing end after 200 hours of MD treatment.

While the invention has been described above in terms of several preferred embodiments, it is not intended to limit the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

100‧‧‧Waste treatment system

101‧‧‧ water inlet

103‧‧‧Inverted electrodialysis unit

105‧‧‧Initial wastewater

107, 117‧‧‧ fresh water

109, 119‧‧ ‧ concentrated water

111, 121‧‧‧ water outlet

113‧‧‧ Thin film distillation unit

123‧‧‧Drying unit

125‧‧‧Return

Claims (11)

A wastewater treatment system comprising: a water inlet end; an inverted electrodialysis unit connected to the water inlet end to receive an initial wastewater, and treating the initial wastewater to form a first fresh water and a first concentrated water; a first water outlet end connected to the inverted pole electrodialysis unit to discharge the first fresh water; a thin film distillation unit connected to the inverted pole electrodialysis unit to receive the first concentrated water, and processing the first concentrated water Water to form a second fresh water and a second concentrated water; and a second water outlet end connected to the thin film distillation unit to discharge the second fresh water. The wastewater treatment system of claim 1, wherein the initial wastewater has a calcium ion concentration and a magnesium ion concentration of less than 100 mg/L, and the initial wastewater has a conductivity of between 5,000 μS/cm and 10,000 μS/cm. between. The wastewater treatment system of claim 1, wherein the first fresh water has a conductivity between 500 μS/cm and 1,000 μS/cm, and the first concentrated water has a conductivity of 15,000 μS/cm to Between 20,000 μS/cm. The wastewater treatment system of claim 1, wherein the second fresh water has a conductivity between 500 μS/cm and 2,000 μS/cm, and the second concentrated water has a conductivity of 30,000 μS/cm to Between 80,000 μS/cm. The wastewater treatment system of claim 1, further comprising a drying unit coupled to the thin film distillation unit to dry the second concentrated water to form a solid. The wastewater treatment system of claim 1, further comprising a return pipe connecting the thin film distillation unit and the water inlet end to mix the initial wastewater with the second concentrated water. A wastewater treatment method comprising: providing an initial wastewater; treating the initial wastewater with an inverted electrodialysis unit to form a first fresh water and a first concentrated water; and treating the first concentrated water with a thin film distillation unit To form a second fresh water and a second concentrated water. The wastewater treatment method according to claim 7, wherein the first fresh water has a conductivity of between 500 μS/cm and 1,000 μS/cm, and the first concentrated water has a conductivity of 15,000 μS/cm. Between 20,000 μS/cm. The wastewater treatment method according to claim 7, wherein the second fresh water has a conductivity of between 500 μS/cm and 2,000 μS/cm, and the second concentrated water has a conductivity of 30,000 μS/cm. Between 80,000 μS/cm. The wastewater treatment method of claim 7, further comprising treating the second concentrated water with a drying unit to form a solid. The wastewater treatment method of claim 7, further comprising adding the second concentrated water to the initial wastewater.