Method for treating highly concentrated resin-desorption liquid generated from wastewater deep purification

This invention relates to a method for treating resin-desorption liquid, specifically to a method for treating highly concentrated resin-desorption liquid generated from the wastewater deep purification that adopts anion exchange resin.

China's fine chemical industry has experienced soaring development and contributed enormously to its national economy since it adopted reform and opening-up policy. However, the wastewater discharged by this industry is complicatedly constituted, highly concentrated and toxic, deep in color and hard to be biodegradated. It has caused severe pollution to the ecosystem and the environment as a whole. Therefore, it is urgent to find appropriate methods for treating this kind of wastewater.

Biotechnology is the most economical way in wastewater treatment, however, it may leave residual metabolites of microorganisms and their decomposition products, toxic substances that cannot be degradated by microorganisms and various inorganics in the wastewater, which requires a deep treatment procedure to ensure that the discharged wastewater reaches the state environmental standards. Resin adsorption is one of the most widely used technologies in the wastewater deep treatment field. This method has such advantages as high adsorption capacity, desirable mechanical properties and capability of recycled use. However, when adopting resin adsorption to treat biochemical effluent, there would be a large amount of desorption liquid, which is complicatedly constituted, highly concentrated and toxic, deep in color and hard to be biodegradated. These properties make treatment of desorption liquid a great challenge widely recognized in the environmental protection field, and restrict the application of resin in various industries as well. Therefore, it is very urgent to find out a cheaper and more efficient method for treating the desorption liquid.

Currently, the most common methods for treating the desorption liquid include enhanced coagulation, catalytic oxidation, catalytic reduction and membrane filtration. The coagulation method presents great efficiency in removing hydrophobic large molecules, but its performance in removing polar organic small molecules is limited. This means the desorption liquid treated with this method cannot directly meet the discharge standards. In addition, this method also results in large consumption of coagulating agent and a large amount of sludge. The catalytic oxidation method is essentially a kind of advanced oxidation process. It presents many advantages such as complete degradation, no secondary pollution, low energy and raw material consumption; however, the Fenton oxidation method requires precise control of pH value while the ozone oxidation requires large construction investment and high operation expenses. Insofar as the membrane filtration method is concerned, the membrane adopted therein presents such defects as high cost in manufacturing and being easy to be contaminated. Therefore, separate exploitation of above-mentioned methods can hardly realize economical and efficient treatment of desorption liquid; a combined method that integrates two or more methods is of great necessity.

1. The Technical Problems to be Solved

Due to the wide use of resin adsorption technology, a large amount of resin-desorption liquid generated therein requires to be properly treated, however, the various methods in the prior arts are unable to achieve highly effective treatment of the desorption liquid. The present invention provides a new method that integrates coagulation and advanced oxidation for treating and recovering highly concentrated resin-desorption liquid generated from magnetic anion exchange resin treatment of biochemical effluent; it can remove most of TOC and UV 254 in the nanofiltration retentate, increase the ratio of BOD 5 /COD cr and guarantee the stability of the biochemical effluent; the difficult technical problem caused by highly concentrated resin-desorption liquid is therefore successfully solved.

2. Technical Solutions

a method for treating highly concentrated resin-desorption liquid generated from wastewater deep purification, comprising the following steps:

1) channeling the highly concentrated desorption liquid generated from anion exchange resin treatment of the biochemical effluent through a nanofiltration membrane for separation; keeping the operation pressure at 1.0-2.5 MPa and the liquid is separated into nanofiltration permeate containing small-molecule substances and nanofiltration retentate containing mainly big-molecule organics; the volume of the nanofiltration retentate is about 1/7 of that of the highly concentrated desorption liquid, and the nanofiltration permeate can be reused as the desorption agent after oxidation; 2) adding a coagulating agent to the nanofiltration retentate to generate coagulation-precipitation; the coagulating agent is FeCl 3 .6H 2 O, FeSO 4 .7H 2 O, Al 2 (SO 4 ) 3 .18H 2 O or polyaluminum chloride (PAC); the mass percentage of the coagulating agent is 1%-5%, and the pH value of the solution obtained after coagulation-precipitation is 2-5; the removal percentage of total organic carbon (TOC) reaches 35%-55%; 3) subjecting the supernatant obtained after the coagulation-precipitation in step 2) to Fenton oxidation or ozone oxidation; the mass percentage of added FeSO 4 .7H 2 O is 0.1%-2% and the mass percentage of added 30% (by weight) H 2 O 2 solution is 1%-4%; the concentration of ozone pumped therein is 3 mg/L-10 mg/L; after 1-5 hours of reaction, the removal percentage of TOC is 60%-80%; 4) adding NaOH or Ca(OH) 2 solution to the oxidation liquid obtained in step 3) and adjusting its pH value to 8.5-10.5; after further coagulation-precipitation, the ratio of BOD 5 /COD cr increases to 0.4 or even higher; 5) channeling the liquid obtained in step 4) to a simulated biochemical system of activated sludge for further treatment.

In step 5, the concentration of inflow COD is 200-400 mg/L; adding in the liquid obtained in step 4) (namely, after the coagulation process caused by the alkali solution) and keeping its volume 1%-5% of that of the inflow; after 12-18 hours of treatment, the removal percentage of outflow COD is 40%-65%. Even so, the activated sludge can still function well in further treating this treated water; it can be channeled back to the biochemical system of biochemical effluent treatment for further biodegradation. Thus, the recycled treatment of the highly concentrated desorption liquid is realized.

The coagulating agent used in step 2) is FeCl 3 .6H 2 O, FeSO 4 .7H 2 O, Al 2 (SO 4 ) 3 .18H 2 O or polyaluminum chloride (PAC). The mass percentage of the coagulating agent in the solution is 1%-5%. The pH value of the solution after coagulation-precipitation is 2-5.

In step c), the mass percentage of FeSO 4 .7H 2 O in the solution is 0.1%-2%. The mass percentage of 30% (by weight) H 2 O 2 solution in the Fenton reagent is 1%-4%. The concentration of the ozone is 3 mg/L-10 mg/L.

The alkali solution used in step 4) is NaOH or Ca(OH) 2 solution.

3. Beneficial Effects

This invention discloses a method for treating highly concentrated resin-desorption liquid generated from wastewater deep purification; it adopts a nanofiltration membrane to separate the resin-desorption liquid into two parts: nanofiltration permeate and nanofiltration retentate; the nanofiltration permeate can be reused as the desorption agent after oxidation, while the nanofiltration retentate is pretreated by combined processes including coagulation, oxidation and re-coagulation; after the pretreatment, most of TOC, UV 254 in the nanofiltration retentate is removed and the ratio of BOD 5 /COD cr increases to 0.4 or even higher; the pretreated liquid is then further treated by activated sludge. After the treatment processes mentioned above, the nanofiltration retentate can be channeled back to the biochemical system of biochemical effluent treatment so that better treatment effect can be achieved. The present method can be widely used in the treatment of highly concentrated desorption liquid generated from anion exchange resin treatment of biochemical effluent.

This invention is more specifically described in the following embodiments

The anion exchange resin is adopted for deep treatment of effluent generated from the biochemical treatment of dyeing wastewater, which results in a large amount of resin-desorption liquid. Channeling the resin-desorption liquid through a nanofiltration membrane and the nanofiltration retentate (TOC=3000 mg/L, pH=9.0-10.5) is therefore obtained; adding in 1% (by weight) of FeCl 3 .6H 2 O solution for coagulation-precipitation, and the supernatant so obtained is subject to Fenton oxidation wherein 0.1% (by weight) of FeSO 4 .7H 2 O and 1% (by weight) of 30% H 2 O 2 solution are added to the supernatant; after 3 hours of Fenton reaction, adding Ca(OH) 2 emulsion to the oxidation liquid to generate another around of coagulation-precipitation and to adjust pH value at 8.5; after 0.5 hour of precipitation, the removal percentage of TOC in the treated liquid is 60%. After the Ca(OH) 2 coagulation process mentioned above, channeling the treated liquid to an activated sludge system for further treatment. The concentration of inflow COD is 200 mg/L and the volume of treated liquid is 1% of that of biochemical effluent; after 12 hours of treatment, the removal percentage of outflow COD is 40%. The repeated experiments have proven that the treated liquid can be channeled back to the biochemical system of biochemical effluent treatment for further biodegradation so that the recycled treatment of the highly concentrated desorption liquid can be obtained.

Channeling the resin-desorption liquid through a nanofiltration membrane and the nanofiltration retentate (TOC=3500 mg/L, pH=9.0-10.5) is therefore obtained; adding in 5% (by weight) of Al 2 (SO4) 3 .18H 2 O solution for coagulation-precipitation, and the supernatant so obtained is subject to Fenton oxidation wherein 0.5% (by weight) of FeSO 4 .7H 2 O and 1% (by weight) of 30% H 2 O 2 solution are added to the supernatant; after 3 hours of Fenton reaction, adding NaOH solution to the oxidation liquid to adjust pH value at 9.5; after 0.5 hour of precipitation, the removal percentage of TOC in the treated liquid is 80%. After the NaOH coagulation process mentioned above, channeling the treated liquid to an activated sludge system for further treatment. The concentration of inflow COD is 200 mg/L and the volume of treated liquid is 1% of that of biochemical effluent; after 12 hours of treatment, the removal percentage of outflow COD is 40%. The repeated experiments have proven that the treated liquid can be channeled back to the biochemical system of biochemical effluent treatment for further biodegradation so that the recycled treatment of the highly concentrated desorption liquid can be obtained.

Channeling the resin-desorption liquid through a nanofiltration membrane and the nanofiltration retentate (TOC=3000 mg/L, pH=9.5-10) is therefore obtained; adding in 1% (by weight) of FeSO 4 .7H 2 O solution for coagulation-precipitation, and the supernatant so obtained is subject to ozone oxidation wherein the concentration of ozone is 3 mg/L; after 3 hours of ozone reaction, adding Ca(OH) 2 emulsion to the oxidation liquid to generate another around of coagulation-precipitation and to adjust pH value at 10.5; after 0.5 hour of precipitation, the removal percentage of TOC in the treated liquid is 65% and the ratio of BOD 5 /COD cr increases to 0.41. After the Ca(OH) 2 coagulation process mentioned above, channeling the treated liquid to an activated sludge system for further treatment. The concentration of inflow COD is 400 mg/L and the volume of treated liquid is 5% of that of biochemical effluent; after 18 hours of treatment, the removal percentage of outflow COD is 65%. The repeated experiments have proven that the treated liquid can be channeled back to the biochemical system of biochemical effluent treatment for further biodegradation so that the recycled treatment of the highly concentrated desorption liquid can be obtained.

Channeling the resin-desorption liquid through a nanofiltration membrane and the nanofiltration retentate (TOC=3500 mg/L, pH=9.5-10) is therefore obtained; adding in 2% (by weight) of PAC solution for coagulation-precipitation, and the supernatant so obtained is subject to ozone oxidation process wherein the concentration of ozone is 10 mg/L; after 5 hours of ozone reaction, adding NaOH solution to the oxidation liquid to generate another around of coagulation-precipitation and to adjust pH value at 9.0; after 0.5 hour of precipitation, the removal percentage of TOC in the treated liquid is 70% and the ratio of BOD 5 /COD cr increases to 0.45. After the NaOH coagulation process mentioned above, channeling the treated liquid to an activated sludge system for further treatment. The concentration of inflow COD is 400 mg/L and the volume of treated liquid is 5% of that of biochemical effluent; after 18 hours of treatment, the removal percentage of outflow COD is 65%. The repeated experiments have proven that the treated liquid can be channeled back to the biochemical system of biochemical effluent treatment for further biodegradation so that the recycled treatment of the highly concentrated desorption liquid can be obtained.