TREATMENT OF WASTEWATER EFFLUENT FROM PULP AND PAPER MANUFACURING

Abstract

A system and method for treatment of wastewater produced in pulp and papermaking processes, for TSS removal and COD decreasing to a de-colored, near neutral pH, liquid effluent, is disclosed. The system and method utilizes a series of tanks which can hold the wastewater and mix the wastewater or bring it in contact with various agents and membranes with an in-line continuous process.

Claims

1. A system for treatment for pulp and paper recycling wastewater treatment comprising: a first stage that receives wastewater leaving a papermaking process so that an effluent enters a rapid mixing tank for rapid mixing for coagulation, wherein coagulants are added to the effluent for coagulation of the effluent ; a second stage that receives the effluent from the first stage so that the effluent enters a slow mixing tank for flocculation of the effluent; a third stage that receives the effluent from the second stage so that the effluent enters a membrane tank having at least one membrane for filtration of the effluent; a fourth stage that receives the effluent from the their stage so that the effluent enters an oxidation tank for oxidation of the effluent, wherein the oxidation tank includes an oxidizer and a catalyst for at least partial removal of organic compounds and colors; and a fifth stage that receives the effluent from the fourth stage so that the effluent enters a purification tank for purification of the effluent.

2. The system of claim 1, wherein the hydraulic retention time is approximately 60 seconds in the rapid mixing tank and approximately 30 minutes in the slow mixing tank.

3. The system of claim 1, wherein the effluent is stirred approximately at 200 RPM in the rapid mixing tank and approximately at 25-30 RPM in the slow mixing tank.

4. The system of claim 1, wherein the third stage membrane includes a micro-membrane and an ultra-membrane.

5. The system of claim 4, wherein micro-membrane further comprises a steel-solophone-polyester membrane and the ultra-membrane further comprises a colophone membrane.

6. The system of claim 1, wherein the second stage does not include adding of coagulants.

7. The system of claim 1, wherein the coagulants do not include at least one of ferric chloride, sodium aluminate, aluminum sulfate and aluminum chloride.

8. The system of claim 1, wherein the coagulants do not include any of ferric chloride, sodium aluminate, aluminum sulfate and aluminum chloride.

9. The system of claim 1, wherein the membrane tank includes a hydraulic cylinder pipe.

10. The system of claim 9, wherein the hydraulic cylinder pipe performs backwashing of the membranes.

11. A method of treatment of pulp and paper recycling wastewater, the method comprising steps of; coagulating an effluent, by adding coagulants to the effluent in a rapid mixing tank; subsequent to the step of coagulating, flocculating the effluent, in a slow mixing tank; subsequent to the step of flocculating, filtering the effluent, by passing the effluent through a membrane tank having a micro-membrane and an ultra-membrane; subsequent to the step of filtering, oxidizing the effluent, by passing the effluent through an oxidation tank containing a catalyst and adding an oxidizing agent; and subsequent to the step of oxidizing, purifying the effluent, by passing the effluent through a purification tank.

12. The method of claim 11, wherein the coagulants do not include at least one of ferric chloride, sodium aluminate, aluminum sulfate and aluminum chloride.

13. The method of claim 11, wherein the hydraulic retention time is approximately 60 seconds in the rapid mixing tank and approximately 30 minutes in the slow mixing tank.

14. The method of claim 11, wherein the effluent is stirred approximately at 200 RPM in the rapid mixing tank and approximately at 25-30 RPM in the slow mixing tank.

15. The method of claim 11, wherein the membrane tank includes a micro-membrane and an ultra-membrane, wherein the micro-membrane further comprises a steel-colophone-polyester membrane and the ultra-membrane further comprises a colophone membrane.

16. The method of claim 11, wherein the membrane tank includes a hydraulic cylinder pipe.

17. The method of claim 16, wherein the hydraulic cylinder pipe performs backwashing of the membranes.

18. The method of claim 11, wherein flocculation is performed without adding a flocculating aid and without adding a coagulating aid.

19. The method of claim 11, wherein the effluent from the purification tank is recycled to the pulp and paper making process and reused.

20. The method of claim 11, wherein the coagulants do not include any of ferric chloride, sodium aluminate, aluminum sulfate and aluminum chloride.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features of the subject technology are set forth in the appended claims. However, for purpose of explanation, several implementations of the subject technology are set forth in the following figure.

[0018] FIG. 1 illustrates a schematic diagram of the treatment of paper recycling wastewater plant, according to a preferred implementation of the instant application.

DETAILED DESCRIPTION

[0019] In the following detailed description, various examples are presented to provide a thorough understanding of inventive concepts, and various aspects thereof that are set forth by this disclosure. However, upon reading the present disclosure, it may become apparent to persons of skill that various inventive concepts and aspects thereof may be practiced without one or more details shown in the examples. In other instances, well known procedures, operations and materials have been described at a relatively high-level, without detail, to avoid unnecessarily obscuring description of inventive concepts and aspects thereof.

[0020] FIG. 1 depicts the treatment of paper recycling wastewater treatment plant according to a preferred implementation of the present application. The system and process for treatment of pulp and paper effluent 100 consists of five consecutive stages which occurs in five consecutive tanks: In the first stage 110, the effluent leaving the papermaking process enters a rapid mixing tank for rapid mixing for coagulation. Coagulants are added to facilitate the coagulation process. In the second stage 112, effullent leaving the first stage 110 enters a slow mixing tank for flocculation wherein, in some implementations, no additional flocculation aid is added. The second stage 112 provides extended time for the coagulation process to proceed. In the third stage 114, effluent leaving the second stage 112 enters a membrane tank which includes a membrane for wastewater filtration. In the fourth stage 116 effluent from the third stage 114 then enters an oxidation tank for organic material removal in the fourth stage 118. In the fifth stage 118, effluent leaving the fourth stage 116 enters a purification tank for final purification.

[0021] The first stage 110 will now be described. The first stage includes a rapid mixing tank. Rapid or Flash mixing is the process by which a coagulant agent is rapidly and uniformly dispersed through the mass of water. This process usually occurs in a small basin immediately preceding or at the head of the coagulation basin. Generally, the detention period is 30 to 60 seconds and the head loss is 20 to 60 cms of water. Here colloids are destabilized and the nucleus for the floc is formed. Slow mixing brings the contacts between the finely divided destabilized matter formed during rapid mixing. The flocculation process can be broadly classified into two types, perikinetic and orthokinetic. Perikinetic flocculation refers to flocculation (contact or collisions of colloidal particles) due to Brownian motion of colloidal particles. The random motion of colloidal particles results from their rapid and random bombardment by the molecules of the fluid. Orthokinetic flocculation refers to contacts or collisions of colloidal particles resulting from bulk fluid motion, such as stirring. In systems of stirring, the velocity of the fluid varies both spatially (from point to point) and temporally (from time to time). The spatial changes in velocity are identified by a velocity gradient, G. G is estimated as G=(P/hV).sup.1/2, where P=Power, V=channel volume, and h=absolute viscosity. The mechanisms of flocculation are divided into two groups. 1Gravitational flocculation: Baffle type mixing basins are examples of gravitational flocculation. Water flows by gravity and baffles are provided in the basins which induce the required velocity gradients for achieving floc formation. And 2Mechanical flocculation: Mechanical flocculators consists of revolving paddles with horizontal or vertical shafts or paddles suspended from horizontal oscillating beams, moving up and down. Present application uses both methods to enhance the flocculation process.

[0022] The first stage 110 utilizes a stainless steel rapid nixing tank which is 125 cm in height and 80 cm in diameter. The hydraulic retention time (HRT) is approximately 60 seconds for 150 cubic meter of wastewater per day. The effluent leaves the rapid mixing tank through a 10 cm in diameter polyethylene tube, which is shut on and off manually.

[0023] Salts of Al(III) and Fe(III) are commonly used as coagulant agents in water and wastewater treatment. When a salt of Al(III) and Fe(III) is added to water, it dissociates to yield trivalent ions, which hydrate to form aqua-metal complexes Al(H.sub.2O).sub.6.sup.3+ and Fe(H.sub.2O).sub.6.sup.3+. These complexes then pass through a series of hydrolytic reactions in which H.sub.2O molecules in the hydration shell are replaced by OH.sup. ions to form a variety of soluble species such as Al(OH).sup.2+ and Al(OH).sup.2+. These products are quite effective as coagulants as they adsorb very strongly onto the surface of most negative colloids.

[0024] Al(III) and Fe(III) accomplish destabilization by two mechanisms: (1) Adsorption and charge neutralization and (2) Enmeshment in a sweep floc.

[0025] In an aspect, the coagulation agents can include ferric chloride, sodium aluminate, aluminum sulfate and aluminum chloride. In other aspects, any one or more or all of these coagulation agents may be eliminated.

[0026] Interrelations between pH, coagulant dosage, and colloid concentration determine mechanism responsible for coagulation. Charge on hydrolysis products and precipitation of metal hydroxides are both controlled by pH. The hydrolysis products possess a positive charge at pH values below iso-electric point of the metal hydroxide. Negatively charged species which predominate above iso-electric point, are ineffective for the destabilization of negatively charged colloids. Precipitation of amorphous metal hydroxide is necessary for sweep-floc coagulation.

[0027] The solubility of Al(OH).sub.3(s) and Fe(OH).sub.3(s) is minimal at a particular pH and increases as the pH increases or decreases from that value. Thus, pH must be controlled to establish optimum conditions for coagulation. Alum and Ferric Chloride reacts with natural alkalinity in water as follows:

Al.sub.2(SO.sub.4).sub.3.14H.sub.2O+6 HCO.sup.3.fwdarw.2 Al(OH).sub.3(s)+6CO.sub.2+14 H.sub.2O+3 SO.sub.4.sup.2(1)

FeCl.sub.3+3 HCO.sup.3.fwdarw.Fe(OH).sub.3(S)+3 CO.sub.2+3 Cl.sup.(2)

[0028] The coagulants are stored in a 1000-liter storage tank and being injected to the mixing tank via an injection pump. The rapid mixing tank includes a variable-speed propeller 100 cm in length. In a preferred application, the rotation speed is set to 200 RPM. A 4 kW electromotor provides the power for mixing the materials inside the rapid mixing tank. The rapid mixing process is facilitated by 3 baffles installed vertically on the interior wall of the mixing tank. The 120*40 cm.sup.2 baffles are designed to make turbulence which improves the mixing process. A manual 10 cm in diameter safety valve is installed at the bottom of the tank for emergency draining.

[0029] Flocculation is stimulation by mechanical means to agglomerate destabilized particles into compact, fast settleable particles (or flocs). Flocculation or slow mixing results from velocity differences or gradients in the coagulated wastewater, which causes the fine moving, destabilized particles to come into contact and become large, readily settleable flocs. An initial rapid mixing step is provided for the dispersal of the coagulant or other chemicals into the water prior to slow mixing

[0030] The second stage 112 will not be described. The second stage includes a slow mixing tank. Slow mixing is done in this stage, during which flocculation, ie., the growth of the floc takes place.

[0031] The second stage 112, includes a 300 cm-long 130 cm-high stainless steel tank. The effluent exiting from the first stage 110 remains slowly-stirred in the second stage 112 for approximately 30 min. The effluent is stirred by 4 propellers 120 at 25-30 RPM. Afterwards, the effluent leaves the tank through a 7.5 cm polyethylene tube. A floater which floats inside the second stage tank 112. controls the wastewater level.

[0032] In some implementations the rapid mixing tank 110 and the slow mixing tank 112 can be implemented as one tank having two impeller speeds. In such implementations the first and second stages can be performed in order in a common tank.

[0033] The third stage 114 will now be described. The third stage includes a membrane tank. There are two types of membrane filtration technology for water and wastewater treatment, namely ultrafiltration (UF) and microfiltration (MF). UF has pores of 0.01-0.02 m, while ME for water treatment has pores of 0.04-1 m. In wastewater applications, coarser MF pore sizes of 0.2 and 0.4 m can be used, but the finer MF membranes for water treatment duties are also suitable. MF removes common particles found in water including bacteria and other microbial organisms, while UF removes viruses in addition, thereby providing a physical disinfection barrier.

[0034] The third stage 114 for treatment of pulp and paper effluent includes a hydraulically-driven membrane system for wastewater filtration. The membranes are a polyester-steel-polysolophon micro-membrane (MF) followed by a polysolophon ultra-membrane (UF). A hydraulic cylinder pipe installed inside the membrane tank drives the effluent through the membranes. The hydraulic cylinder pipe also provides backwashing of the membranes which is furthermore results in minimizing the fouling the membranes. The hydraulic cylinder pipe may also enable the membranes to work continuously as opposed to the most commercial systems. The speed of the hydraulic cylinder pipe is controlled by 2 control valves through 2 high pressure (250 bar) tubes. The effluent and influent flow rates and their ratio is measured by a sensor. There are 2 collectors to collect effluent from the membranes which may be used for further backwashing via a 10 bar back air. The variable time is 6 seconds and the tube is 2 cm in diameter. The membrane system may be controlled by a PLC system.

[0035] The fourth stage 116 will now be described. The fourth stage includes an oxidation tank. In the fourth stage, a catalytic oxidation process is capable of converting organic contaminants ultimately to carbon dioxide and water, and can also remove oxidizable inorganic components such as cyanides and ammonia. While the process usually uses air as the oxidant, which is mixed with the effluent and passed over a catalyst at elevated temperatures and pressures, the present application uses hydrogen peroxide (H.sub.2O.sub.2) as the oxidizer and zinc oxide (ZnO) as the catalyst. The zinc oxide catalyst is installed on the interior wall of the advanced oxidation tank. Hydrogen peroxide is injected to the tank at 12-20 mg/l rate.

[0036] The fifth stage 118 will now be described. The fifth stage includes a purification tank. The effluent from the fourth stage 116 enters the fifth stage 118 for final purification. It should be noted that, the final sludge from any or all stages may be recycled and reused for the pulp and paper making process.

[0037] An air compresser 122 is provided in some implementations to provide pressure to move the effulent between tanks, back pressure for backwashing of the membrane, and/or to provide air for oxidation in the fourth stage.

[0038] Except as stated immediately above, nothing that has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is or is not recited in the claims.

[0039] It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms comprises, comprising, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by a or an does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0040] The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various implementations. This is for purposes of streamlining the disclosure, and is not to be interpreted as reflecting an intention that the claimed implementations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed implementation. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.