System for recycling wastewater from reverse osmosis filtering processes and method for treating wastewater

Abstract

A system and a method for reusing waste water from a Reverse Osmosis (RO) filtering process are described, said system including: a Reverse Osmosis (RO) filtration system, from which a flow of highly alkaline waste water results; two tanks intended to receive waste water and able to alternately determine the physical and chemical properties of waste water through sensors or, and perform homogenization, chlorination and chemical treatments of said waste water; an output line which comprises a pump and connects the tanks to a reservoir; and said reservoir being able to blend the water treated by the tanks with treated chlorinated drinking water, depending on the physical and chemical properties of these volumes of water; the chlorination and chemical treatment includes addition of a hypochlorite compound, which reaction releases chlorine in the waste water and causes evaporation of at least O.sub.2 and H.sub.2 gases, reducing the alkaline pH of said waste water.

Claims

1. A method of treatment of waste water originating from reverse osmosis (RO) filtration treatment comprising the steps of: receiving waste water from RO in a pre-treatment tank, wherein the waste water is discarded when a pH of the waste water is greater than 13; adding a hypochlorite compound to the waste water in the pre-treatment tank; homogenizing the waste water in the pre-treatment tank; and measuring the pH of the waste water in the pre-treatment tank, wherein: when the measured pH of the waste water is not within a pre-established pH limit, returning the waste water to the step of addition of a hypochlorite compound; and when the measured pH of said waste water is within the pre-established pH limit, sending the waste water to a blending reservoir and mix a quantity of up to 45% in volume of the waste water with a quantity of at least 55% in volume of a treated chlorinated drinking water, and wherein the pre-established pH limit is 8.2 to 9.5.

2. The method according to claim 1, wherein the step of adding a hypochlorite compound comprises adding a hypochlorite salt.

3. The method according to claim 1, wherein the step of adding a hypochlorite compound comprises adding sodium hypochlorite.

4. The method according to claim 1, wherein the step of homogenizing the waste water comprises recirculating the waste water in the pre-treatment tank.

5. The method according to claim 1, wherein the step of homogenizing the waste water comprises stirring the waste water in the pre-treatment tank.

6. The method according to claim 1, wherein the measuring step comprises employing a pH sensor to directly measure the pH.

7. The method according to claim 1, wherein the measuring step comprises employing an electrical conductivity sensor to measure a quantity of electrical conductivity proportional to the pH of the waste water.

8. The method according to claim 7, wherein in the measuring the pH of the waste water step, the pre-established pH limit corresponds to an electrical conductivity of 500 micro-Siemens.

9. The method according to claim 7, wherein the measuring step comprises employing a temperature sensor to thermally adjust the electrical conductivity of the waste water.

10. The method according to claim 1, wherein the measuring step comprises employing a temperature sensor to thermally adjust the pH value of the waste water.

11. The method according to claim 1, wherein in the measuring the pH of the waste water step, the pre-established pH limit is 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be better understood from the detailed description of a preferential and non-limiting embodiment of the invention, which is based on the attached figures and is illustrative and not limitative, wherein:

(2) FIG. 1 is a schematic drawing of a plant for implementing the system of the present invention; and

(3) FIG. 2 is a flow diagram relating to the method of the invention.

PREFERRED EMBODIMENT OF THE INVENTION

(4) In accordance with FIG. 1, (1) indicates generally a plant for treatment of waste water (2) from a Reverse Osmosis (RO) treatment system (not shown).

(5) Numerals (10, 11) indicate two tanks for receiving waste water (2) coming from the RO system, said tanks (10, 11) being chained and each one comprising: one water recirculation system, via line (18) comprising a centrifugal pump (17) for homogenization and chlorination by addition of hypochlorite solution (16), and comprising a pH sensor (S1) and/or an electrical conductivity sensor (S2) and/or a temperature sensor (S3). Alternatively, instead of using a recirculation system (18, 17), each of the tanks (10, 11) is equipped with a stirring system (not shown), such as a mechanical stirrer or a similar device, as well as a respective doser for sodium hypochlorite (16).

(6) Furthermore, said tanks (10, 11) are opened to the atmosphere, in order to allow evaporation of volatiles, as will be described below.

(7) At the bottom of each of the tanks (10, 11) an output port for the stored volume is provided, intermediated by respective valves (12, 13) which, when opened, allow the flow of water contained in one of the tanks (10, 11), via line (14) and pump (15), to the reservoir (20). In addition, both tanks (10, 11) further comprise a drain (not shown) intended for disposal of waste water when it do not reach the minimum standards of treatment, as will be explained later.

(8) Finally, the reservoir (20) is a reservoir having a capacity greater than at least twice the capacity of any of the tanks (10, 11). In addition, the reservoir (20) comprises mixing means intended to promote homogenization of the waters contained therein, as will be explained later. Among such mixing means, mechanical stirrers, branches equipped with pumps and connecting the top to the bottom of the tank, or any other appropriate means, can be selected.

(9) Furthermore, at the top (21) of said reservoir (20) there is also provision for a first input port to receive the flow from the tanks (10, 11), via line (14), and also a second input port to receive a flow of treated chlorinated drinking water (23). In addition, the bottom (22) of the reservoir (20) also has an output port (24) through which the treated water is removed, according to the method of the present invention.

(10) In operation, the system of the invention provides that the flow of waste water (2), originating from a Reverse Osmosis (RO) filtering system, is continuously deposited in a first tank (10), until a certain operating volume of water is reached. At that moment, the flow of waste water (2) is diverted to the second tank (11), which begins to be filled while the treatment is carried out in the volume of water contained in the first tank (10). This chained tanks mechanism allows the treatment of the invention to be carried out in one tank, while the other tank is gradually filled, and vice versa.

(11) Usually, said waste water received has a pH of about 13 and several dissolved elements, such as S, Mg, Cl, F and others.

(12) Thus, in said first tank (10) the pH of waste water (2) is measured, either directly by a pH sensor (S1), or indirectly by an electrical conductivity sensor (S2). Preferably, the pH or electrical conductivity measurements are thermo-adjusted from the waste water (2) temperature indication, measured by the temperature sensor (S3), in order to increase the accuracy of the measured pH value of the waste water contained in the tank (10).

(13) Once determined the pH of the waste water (2), the quantity of hypochlorite compound needed to promote pH reduction of the water to a value between 8.2 and 9.5, and preferably approximately 9, is calculated. In particular, and in the event that the waste water (2) has a pH value greater than about 13, or an electrical conductivity value greater than 500 micro-Siemens, such waste water is discarded through the respective drain. In these particular conditions, it is decided to discard it since the quantity of sodium hypochlorite would be too much high, which would compromise the economic benefits of the present process.

(14) This controlled and selective addition of a hypochlorite compound, preferably a hypochlorite salt and more preferably sodium hypochlorite (NaClO), as discovered by the inventors, leads to several chemical reactions, which have the purpose of neutralizing the pH of waste water, since the ionic species (OH.sup.−) react with the hypochlorite anion and form H.sub.2 and O.sub.2, which simply evaporate, since the tanks (10, 11), as mentioned, are open to the atmosphere.

(15) In addition to the evaporation of these chemical species, there is also the evaporation of some other species, such as H.sub.2S. As a whole, as the inventors discovered, their evaporation leads to a reduction in the pH of the water under treatment, which, as mentioned, reaches a pH value usually between 8.2 and 9.5. In addition, some minerals still remain in solution, such as chlorine and fluorine.

(16) As is evident to any technician skilled in the art, for a perfect dissolution of NaClO in water within a predetermined period of time, it is preferable to promote a forced mixing action, for example using mechanical stirrers, recirculators (18, 17) and the like.

(17) Thus, and once a pH value (S1) of the solution is detected within the desired parameters, or even an electrical conductivity value (S2) is detected within the desired parameters, the tank is emptied via line (14) by action of the centrifugal pump (15) and its content is sent to the blending reservoir (20).

(18) Within said reservoir, a calculated quantity of treated chlorinated drinking water (24) is added to the volume of solution received from the tank (10), such treated chlorinated drinking water being supplied by the concessionaire of water supply. According to legal standards, such treated water has a pH between 6.5 and 7, that is, slightly acidic. Thus, adding an quantity corresponding to at least 55% in volume of treated water in relation to the total volume contained in the reservoir (20), and carrying out homogenization (by mechanical agitation, recirculation, or the like), chlorinated reuse water is obtained, within the parameters that allow it to be classified as drinking water. In this way, such recycled drinking water can be sent back to the RO filtering system, in order to be used later as PW or WFI, or else consumed.

(19) FIG. 2 illustrates schematically, as a flow diagram, the steps of the method of the invention. In particular, the method starts (S100) and receives (S101) in a tank (10, 11) the volume of waste water that is discarded from a RO filtration system, microfiltration, or similar fine filtration systems.

(20) Then occurs addition (S102) of hypochlorite compound, preferably sodium hypochlorite, in order to reduce the pH of the water by evaporation of H.sub.2 and O.sub.2 gases resulting from reactions between the hypochlorite and the chemical species in solution in the waste water. Then begins homogenization (S103) of the waste water by recirculation or, alternatively, using agitators. During recirculation, the sensors (S1/S2; S3) evaluate the pH (S104) of the waste water as a function of its temperature, until a pH of up to about 9 is reached. As mentioned, the pH can be directly calculated using the pH sensor (S1), or indirectly calculated through the electrical conductivity sensor (S2). It should be noted that the steps of addition of NaClO (S102), homogenization (S103) and pH measurement (S104) are more efficient when performed continuously, that is, with the waste water being recirculated, wherein NaClO is continuously added until the sensors (S1/S2; S3) determine substantially continuously a pH of approximately 9.

(21) Thus, once a pH of about 9 (usually between 8.2 and 9.5) is determined, according to step (S104), and with pH readings approximately constant in time, it results that the waste water is satisfactorily pre-treated and mainly homogenized, so it can be sent (S105) via line (14) and pump (15) to the reservoir (20), in order to be blended with treated chlorinated drinking water (23) provided by the concessionaire of water supply. In said reservoir (20) occurs blending (S106) of the volume of pre-treated water coming from the tank (10, 11) with treated chlorinated drinking water, in a minimum ratio of 45%:55% in volume (pre-treated water:treated chlorinated drinking water). Thus, and in this step, the slightly alkaline content of the pre-treated water is reduced with an appropriate volume of treated chlorinated drinking water supplied by the concessionaire of water supply, according to steps S101 to S104, in order to result in a volume of water with neutral pH, or slightly acidic, and within the parameters that define drinking water for human consumption.

(22) Thus, after blending (S107) the treated water according to the present method is ready to be used as drinking water, according to common uses.

(23) Test Plant—Specifications

(24) The data, indices, parameters and specific equipment reported in the description below are all linked to a test plant, particularly a pharmaceutical plant, used to validate preliminary laboratory tests, adjust operational parameters to an industrial scale, and mainly certify the procedures adopted according to agencies of control such as ANVISA (Agência Nacional de Vigância Sanitária—National Health Surveillance Agency), responsible for approval of all drugs and respective production processes, in Brazil, among others. The inventors also report that the test plant was recently approved by all governmental control and certification agencies.

(25) Below are the processing steps for reusing waste water from reverse osmosis.

(26) (1) Step of Pre-Treatment and Chlorination of Reverse Osmosis Waste Water

(27) The reverse osmosis waste water from the PW generation equipment installed in the industry where the system was implemented has a waste water flow of up to 45% of the flow that feeds the equipment. Such water has a high concentration of saline ions, resulting in a basic and normally high pH value (a pH value up to 13) and a high electrical conductivity.

(28) This waste water is directed to a storage system comprising two 10,000 litres reservoirs, two pumps for recirculation and flow of water, interconnecting pipes for all these components with automatically activated shut-off valves via control software, an automatic water chlorination unit having controlled and proportional addition of sodium hypochlorite solution (using a control routine), and sensor instruments installed in the pipes and tanks to determine on-line readings of temperature, pH, electrical conductivity, pressure and chlorination index of water. The system has two conductivity meters installed, the first one at the “waste water inlet in the system”, which provides values for disposal of water that will not be reused, and the second one in the common water recirculation line to determine the final conductivity value of the chlorinated waste water.

(29) Through reading of a conductivity meter and use of automatic valves installed in the pipeline, the osmosis waste water having an electrical conductivity above of a certain parameter (500 micro-Siemens, start and end of the osmosis cycle in the equipment) is promptly discarded directly to the drain and sewer line of the plant, such water not being usable for the process of the invention.

(30) With data obtained in real time from the instruments sensors, the developed control routine determines the required recirculation time and the exact quantity of chlorine addition to the waste water, so that such water has actual “chlorination values” contained within the standards determined by law. The electrical conductivity values of the chlorinated waste water to be reused are available in real time and must always be within established standards.

(31) In the reservoirs, the pH value of waste water (initially having pH values up to 13.0) decreases to about 9.0, because the addition and recirculation of Sodium Hypochlorite Solution (NaClO) in the reservoirs cause spontaneous chemical reactions, with formation of gas molecules of oxygen (O.sub.2), hydrogen (H.sub.2) and hydrogen sulfide (H.sub.2S), among others, that simply migrate into the atmosphere since the tanks are opened and have atmospheric vents; the overall result of all these chemical reactions is the reduction of water pH values up to 9.0 and the availability of chlorine ions in solution (chlorinated water), which allows such water from the reservoirs to be blended with treated water from the concessionaire of water supply in the next step.

(32) From then on, the waste water is ready to be added and blended in the main chlorinated drinking water reservoir of the plant.

(33) There are two 10,000 litres reservoirs, thus while one reservoir is receiving waste water, the other is in process of chlorination and water transfer in the next step (2), and vice versa.

(34) (2) Step of Blending of Chlorinated Waste Water

(35) Such water has a slightly higher chlorination rate and electrical conductivity, both within legal standards.

(36) The waste water is directed to the main storage reservoir of the plant, which has a capacity of 620,000 litres and is divided in two spaces (compartments) by the sending pump of the pre-treatment station.

(37) The piping to the reservoir comprises automatic activation shut-off valves via control routine, and a totalizing flow meter also controlled by control routine.

(38) Automatic activation shut-off valves and a totalizing flow meter (controlled via control routine) were installed in the treated chlorinated drinking water piping of SABESP (SAneamento Básico do Estado de São Paulo—Concessionaire responsible for water supply and sewage collection in São Paulo State) which feeds the main reservoir of the plant.

(39) The main reservoir of the industrial plant is bipartite and has two compartments. A 372,000 litres upper compartment is used for blending chlorinated waste water (within a proportion between 40% to 45%) with treated chlorinated drinking water from SABESP, with such blending being then transferred by gravity to a 248,000 litres lower compartment, which feeds the plant with treated chlorinated drinking water. These two reservoirs are interconnected during the operation of the plant.

(40) The transfer of chlorinated waste water to the upper reservoir is triggered by control routine, and the quantity of chlorinated waste water to be blended in the system is exactly quantified by the transfer pipe flow meter.

(41) Once the quantity of chlorinated waste water is obtained and recorded via control routine, the routine calculates the quantity of SABESP treated chlorinated drinking water to be added, so that the resulting blended water continues within its standards of electrical conductivity, pH and chlorination.

(42) Next, an automatic transfer of the quantity of SABESP water necessary for a correct blending is carried out through an automatic control routine.

(43) After the transfer of SABESP treated chlorinated drinking water to the upper part of the reservoir, a recirculation is carried out to unify the contained water therein, and the conductivity of this blended water is obtained in real time through the conductivity meter sensor installed in the recirculation line.

(44) Once such electrical conductivity value obtained is “approved” by the automatic control routine (within the legal standards), the routine releases transfer of this water to the lower reservoir, from which it will be used for consumption in any sector of the plant where necessary.

(45) The system is able to reuse all the water generated in the reverse osmosis waste, provided that the water electrical conductivity is below the disposal value described in step (1) above.

(46) Therefore, the process is completed and the reuse cycle of waste water in chained batches of 10,000 litres each is closed, such process being a semi-continuous chained process.

(47) Due to the blending of quantities of chlorinated waste water having conductivity normally higher than the conductivity of water from the concessionaire of water supply, the average electrical conductivity of water in the plant reservoir will present a slight increase which, over the months of operation, will reach the higher value determined by the legal standards. The elapsed time cannot be precisely determined, as it depends on many variables, such as parameters and quality of water supplied by concessionaire SABESP and the volume of use of chlorinated drinking water from the plant.

(48) When this electrical conductivity value is reached, the operation of the plant will discard all the water in the reservoir, without renewal, and proceed to fill the reservoir entirely with treated chlorinated drinking water, making it possible to start again the process of tenuous increase in electrical conductivity from “zero”, and so on.