PROCESS AND PLANT FOR TREATING WASTEWATER CONTAINING MICROPOLLUTANTS OF PHARMACEUTICAL ORIGIN
20220411298 · 2022-12-29
Inventors
Cpc classification
Y02W10/10
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
C02F1/001
CHEMISTRY; METALLURGY
C02F2103/343
CHEMISTRY; METALLURGY
International classification
Abstract
A completely biological method for removing a first group of micropollutants of pharmaceutical origin and a second group of micropollutants of pharmaceutical origin from raw wastewater includes: providing a first buffer tank upstream of a bioreactor; providing a moving bed membrane bioreactor (MB-MBR) for developing biomass growth both on a fixed support and in suspension in a form of flocs, and on mobile supports, the bioreactor obtaining an effluent with a COD concentration of organic matter of less than 50 mg l.sup.−1 and a total nitrogen concentration of less than 15 mg l.sup.1; providing a biofiltration tank, separate from the first buffer tank of the bioreactor, that includes one or more biologically activated carbon (BAC) columns containing activated carbon; supplying the first buffer tank upstream of the bioreactor with raw wastewater containing micropollutants of pharmaceutical origin; pretreating the wastewater by passing the wastewater through a fine mesh sieve.
Claims
1.-11. (canceled)
12: A completely biological method for removing a first group of micropollutants of pharmaceutical origin and a second group of micropollutants of pharmaceutical origin from raw wastewater, the method comprising: providing a first buffer tank upstream of a bioreactor; providing a moving bed membrane bioreactor (MB-MBR) for developing biomass growth both on a fixed support and in suspension in a form of flocs, and on mobile supports, the bioreactor being configured to obtain an effluent with a COD concentration of organic matter of less than 50 mg l.sup.−1 and a total nitrogen concentration of less than 15 mg l.sup.1; providing a biofiltration tank, separate from the first buffer tank of the bioreactor, comprising one or more biologically activated carbon (BAC) columns containing activated carbon; supplying the first buffer tank upstream of the bioreactor with raw wastewater comprising micropollutants of pharmaceutical origin; pretreating the wastewater comprising micropollutants of pharmaceutical origin by passing the wastewater comprising micropollutants of pharmaceutical origin through a fine mesh sieve so as to retain particles having a diameter greater than 1 mm to provide sifted wastewater; in a first treatment, introducing the sifted wastewater into the populated bioreactor during a first retention time; introducing a second microbial consortium in the biofiltration tank; in a second treatment, introducing the wastewater treated by the bioreactor into the biofiltration tank to allow residues of micropollutants of pharmaceutical origin to be adsorbed onto the activated carbon; allowing the activated carbon, which has previously adsorbed the residues of micropollutants of pharmaceutical origin, to be colonized by the second microbial consortium in a form of biofilms so as to biodegrade the residues by the second microbial consortium and allowing the activated carbon to bioregenerate, during a second retention time, so as to provide treated wastewater; discharging the treated wastewater into an environment, wherein a total hydraulic retention time comprising a sum of the first retention time and the second retention time is determined so to obtain an average purification efficiency (R) of the micropollutants of pharmaceutical origin of the first group in the treated wastewater greater than 80% and an average purification efficiency of micropollutants of pharmaceutical origin of the second group greater than 40-50%, with reference to the micropollutants' content (C.sub.0) in the raw wastewater, and wherein the method further comprises: providing a second buffer tank inserted between the moving bed membrane bioreactor (MB-MBR) and the biofiltration tank; in normal operation, supplying the second buffer tank with effluent from the first treatment and supplying the second treatment from the second buffer tank; and performing separate backwashing of membranes of the bioreactor and of the biologically activated carbon, without communication through the second buffer tank.
13: The method according to claim 12, wherein the tank of the moving bed membrane bioreactor (MB-MBR) is separated from the biofiltration tank by an ultrafiltration membrane so as to separate the first and second microbial consortia.
14: The method according to claim 12, wherein a hydraulic contact time or EBCT per biologically activated carbon BAC column is greater than 10 minutes with a filtration rate HLR between 2 and 5 mh.sup.−1.
15: The method according to claim 12, wherein the micropollutants of pharmaceutical origin of the first group comprise at least one of amisulpride, carbamazepine, hydrochlorothiazide, or metoprolol.
16: The method according to claim 12, wherein the micropollutants of pharmaceutical origin of the second group comprise at least one of clarithromycin, cyclophosphamide, or diclofenac.
17: The method according to claim 12, wherein the membrane bioreactor is seeded by a first consortium of external microorganisms to colonize the fixed parts and the mobile supports with the microorganisms and to grow a biofilm thereon so as to immobilize the microorganisms.
18: The method according to claim 12, wherein the microorganisms of the second consortium come from an effluent of the bioreactor and/or are at least in part different from microorganisms of the first consortium, following self-selection over time.
19: The method according to claim 12, wherein the biologically activated carbon comprises powdered, granular, or microgranular activated carbon.
20: The method according to claim 12, further comprising: purifying air from the wastewater treatment system so as to eliminate odors using ozone, ultraviolet radiation, or activated carbon.
21: A plant for implementing the method according to claim 12, comprising: the first buffer tank for a stable supply of wastewater containing micropollutants of pharmaceutical origin; a pumping unit; at least one fine mesh sieve configured to retain particles having a diameter greater than 1 mm; the moving bed membrane bioreactor (MB-MBR) configured to develop biomass growth both on the fixed supports and in suspension in the form of flocs, and on the mobile supports; at least one biofiltration tank on biologically activated carbon distinct from the tank of the bioreactor, separated from the tank of the bioreactor by an ultrafiltration membrane and located downstream of the tank of the bioreactor, the at least one biofiltration tank comprising one or more columns with biologically activated carbon (BAC); the second buffer tank inserted between the membrane bioreactor and the biofiltration tank configured to separately backwash membranes of the bioreactor and of the biologically activated carbon; storage and dosing units for chemicals; and an air and odor treatment system.
22: The method according to claim 12, wherein the bioreactor is seeded with a first microbial consortium located and/or developing on fixed parts and in suspension in a form of flocs, and on the mobile supports.
23: The method according to claim 12, wherein the average purification efficiency (R) of the micropollutants of pharmaceutical origin of the first group in the treated wastewater greater than 95%.
24: The method according to claim 14, wherein the hydraulic contact time or EBCT per biologically activated carbon BAC column is between 10 and 20 minutes.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0085] The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:
[0086]
[0087]
[0088]
[0089]
[0090]
[0091]
[0092]
[0093]
[0094]
[0095]
DETAILED DESCRIPTION
[0096] In an embodiment, the present invention provides a solution to the problem of the presence of micropollutants of pharmaceutical origin in wastewater.
[0097] In an embodiment, the present invention keeps the operational costs of purification under control, in particular those related to the electrical consumption of the plants.
[0098] In an embodiment, the present invention provides improvements over the prior art such as 100% biological treatment, the absence of clogging associated with the use of reverse osmosis membranes or even the absence of consumption (losses) of granular activated carbon (GAC) with the possibility of reactivation without expensive recycling.
[0099] In an embodiment, the present invention provides better control and optimizes the industrial use of BAC columns.
[0100] In an embodiment, the present invention uses bacterial supports which do not damage the membranes of the reactors.
[0101] In an embodiment, the present invention provides a purification plant which is compact and which has an acceptable visual appearance.
[0102] A first aspect of the present invention relates to a completely biological method for removing a first group of micropollutants of pharmaceutical origin and a second group of micropollutants of pharmaceutical origin from wastewater, the method comprising the steps of: providing a first buffer tank upstream of the bioreactor; [0103] providing a moving bed membrane bioreactor (MB-MBR) for developing biomass growth both on a fixed support and in suspension in the form of flocs, and on mobile supports, said bioreactor being configured to obtain an effluent with a COD concentration of organic matter of less than 50 mg l.sup.−1 and a total nitrogen concentration of less than 15 mg l.sup.−1; [0104] providing a biofiltration tank, separate from the bioreactor tank, comprising one or more biologically activated carbon (BAC) columns containing activated carbon; [0105] supplying the first buffer tank upstream of the bioreactor with wastewater comprising micropollutants of pharmaceutical origin; [0106] pretreating said wastewater comprising micropollutants of pharmaceutical origin by passing it through a fine mesh sieve, so as to retain particles having a diameter greater than 1 mm; [0107] in a first treatment, introducing the wastewater, once sifted, into the populated bioreactor possibly seeded with a first microbial consortium located and/or developing on the fixed parts and in suspension in the form of flocs, and on the mobile supports, during a first retention time; [0108] introducing or inoculating a second microbial consortium in the biofiltration tank; [0109] in a second treatment, introducing the wastewater treated by the bioreactor into the biofiltration tank and allowing the residues of micropollutants of pharmaceutical origin to be adsorbed onto the activated carbon; [0110] allowing the activated carbon having previously adsorbed the residues of micropollutants of pharmaceutical origin to be colonized by the second microbial consortium in the form of biofilms, allowing said residues to be biodegraded by the second microbial consortium and allowing the activated carbon to bioregenerate, during a second retention time; [0111] discharging treated wastewater into the environment; [0112] the total hydraulic retention time, consisting of the sum of the first retention time and the second retention time, being determined to obtain an average purification efficiency (R) of the micropollutants of pharmaceutical origin of the first group in the treated wastewater greater than 80%, preferably greater than 95%, and an average purification efficiency of micropollutants of pharmaceutical origin of the second group greater than 40-50%, with reference to their content (C.sub.o) in the raw wastewater.
[0113] According to preferred modalities of the invention, the method comprises at least one of the following features, or an appropriate combination thereof: [0114] It comprises the following additional steps: in normal operation, providing a second buffer tank inserted between the moving bed membrane bioreactor (MB-MBR) and the biofiltration tank; supplying the second buffer tank (12) with the effluent from the first treatment and supplying the second treatment from the second buffer tank; [0115] performing separate backwashing of the membranes of the bioreactor (11) and of the biologically activated carbon; [0116] the tank of the hybrid moving bed membrane bioreactor (MB-MBR) is separated from the biofiltration tank by an ultrafiltration membrane, so as to separate the first and second microbial consortia, in particular to develop, without contamination, specialized bacteria on the activated carbon; [0117] the hydraulic contact time or EBCT in a biologically activated carbon (BAC) column is greater than 10 minutes; [0118] the hydraulic contact time is preferably between 10 and 20 minutes, and more preferably greater than 20 minutes, with a filtration rate HLR between 2 and at least 5 mh.sup.−1; [0119] the micropollutants of pharmaceutical origin of the first group considered in the method comprise at least one micropollutant selected from the group consisting of amisulpride, carbamazepine, hydrochlorothiazide and metoprolol; [0120] the micropollutants of pharmaceutical origin of the second group considered in the method comprise at least one micropollutant selected from the group consisting of clarithromycin, cyclophosphamide and diclofenac; [0121] the membrane bioreactor is seeded by a first consortium of external microorganisms, so as to colonize fixed parts and the mobile supports with said microorganisms and to grow a biofilm on these fixed parts and these mobile supports to immobilize said microorganisms; [0122] the microorganisms of the second consortium come from the effluent of the bioreactor and/or are at least in part different from those of the first consortium, following self-selection over time; [0123] biologically activated carbon is used in the form of activated carbon in powder, grains or micrograins; [0124] an additional step of purifying the air coming from the wastewater treatment system is implemented, in particular with a view to eliminating odors; by means of ozone, ultraviolet radiation or activated carbon.
[0125] A second aspect of the invention relates to a plant for implementing the method described above, characterized in that it comprises: [0126] a first buffer tank for a stable supply of wastewater containing micropollutants of pharmaceutical origin; [0127] a pumping unit; [0128] a pretreatment step including at least one fine mesh sieve for the retention of particles having a diameter greater than 1 mm; [0129] a hybrid moving bed membrane bioreactor (MB-MBR) for developing biomass growth both on a fixed support and in suspension in the form of flocs, and on mobile supports; [0130] at least one biofiltration tank on biologically activated carbon distinct from the tank of the bioreactor, separated from the latter by an ultrafiltration membrane and located downstream of the latter, comprising one or more columns with biologically activated carbon (BAC); [0131] a buffer tank inserted between the membrane bioreactor and the biofiltration tank, for the separate backwashing of the membranes of the MB-MBR bioreactor and of the biologically activated carbon; [0132] storage and dosing units for chemicals; [0133] an air and odor treatment system.
[0134] The studies by Nguyen et al. (2012, 2013) showed good performances of MBR purification for hydrophobic contaminants, as well as a certain capacity for degradation of hydrophilic and persistent micropollutants (carbamazepine, diclofenac and fenoprop) on granular activated carbon, justifying the complementarity of the two units. However, they also highlight a problem of degradation of the adsorption capacity over time of the activated carbon for some hydrophilic PPs, which raises questions about the method of activated carbon regeneration.
[0135] The inventors propose to solve this problem by the use of biologically activated carbon, because the regeneration of the activated carbon may be advantageously stimulated by the bacteria that are present.
[0136] When treating micropollutants, the development of new hybrid configurations of MB-MBR/BAC specifically designed to guarantee increased removal of pharmaceutical products (PPs) constitutes both a scientific and an environmental issue.
[0137] The success of this technology is based on (1) perfect control of the biotic (biosorption) or abiotic (volatization, adsorption on a support) transfers of micropollutants within the treatment unit, (2) the development of specific microbial purifying consortia, (3) an increase in the bioavailability of PPs and therefore of their biodegradation, (4) a decrease in membrane clogging and (5) a reduction in the environmental impact and energy costs.
[0138] The scientific approach associated with the project can be summarized as follows: [0139] liquid hospital effluents have an effect on aquatic life; [0140] but the installation of a treatment plant within the hospital center is currently too expensive; [0141] conventional biological treatments are not suitable for removing pharmaceuticals, although biological treatment is the most effective step; [0142] some advanced treatments are adequate (UV, O.sub.3, AC); however, current advanced treatments are energy intensive; [0143] the EU has included several pharmaceutical products in a list of priority substances; this list will be extended; [0144] this project essentially investigates the limits of biological treatment by conceptually splitting the method into two steps allowing the development and optimization of different specialized microbial consortia (flocs, biofilm, BAC).
[0145] The processing line for the MB-MBR/BAC coupling according to a preferred embodiment of the invention and shown schematically in
[0155] The buffer tank 10 ensures a stable supply of the biological treatment method. The fine sieving allows the removal of particles of size greater than 1 mm with a view, in particular, to avoiding sedimentation in the biological tanks (and therefore clogging of pipes, pumps, etc.). The two biological treatment tanks, preferably separated by an ultrafiltration membrane to avoid reciprocal contamination, allow the development of different microbial consortia. The first treatment tank 11 (MB-MBR) uses both suspended and fixed biomass growth methods to increase the biomass concentration and the efficiency of COD and N removal. The biofiltration (or biologically activated carbon) columns 12 are intended for the removal of pharmaceutical products remaining after passing through the MB-MBR tank 11 thanks to the bacteria of the second consortium in biofilms. The drug residues are adsorbed on the activated carbon; then the bacterial colonies develop on the proximal sites. According to the invention, a self-selection of bacteria specialized in the BAC is possible thanks to (1) the reduction of the easily biodegradable COD in the MB-MBR, which deprives the bacteria of nutrients and forces them to colonize the BAC, and (2) an ultrafiltration membrane separating the bacterial consortia of the two tanks.
[0156] According to an alternative embodiment, the two biological treatment tanks are not separated by an ultrafiltration membrane so that, during backwashing of the activated carbon, washing water laden with bacteria from the second consortium (specialized in BAC) may be returned to the MB-MBR to enrich the first bacterial consortium.
[0157] An odor elimination system is advantageously determined or optimized by considering: [0158] environmental and public health problems; [0159] requirements due to a high degree of compactness of the plant.
[0160] Study, Design and Validation of a Biological Treatment System
[0161] Three sampling campaigns were carried out on wastewater discharged by a hospital, in order to optimize, on the one hand, the MB-MBR mixed culture membrane bioreactor system and, on the other hand, to validate the purification mechanism of biologically activated carbon BAC columns.
[0162] Hospital effluents have been characterized. The proportion of micropollutants compared to the COD is quite minimal. The concentration of pharmaceutical residues is of the order of a few micrograms per liter (μg/l) while the COD contains at least several hundred milligrams per liter (mg/l).
[0163] For example,
[0164] Each result corresponds to an analysis of 10 and 17 samples. The boxplots are delimited by the 25th and 75th percentiles, the diamonds correspond to the extreme values, the cross is the mean, while the median is represented by the horizontal line crossing the boxplot.
[0165] The experimental pilot unit was sized to treat the equivalent of discharge corresponding to one hospital bed, i.e. between 300 and 500 liters per day. The operational parameters were optimized to increase the micropollutant removal efficiencies and meet the water quality requirements in terms of macropollutant removal. By way of example, Table 2 shows the quality objectives to be achieved for wastewater treatment plants with capacities between 10 000 and 100 000 PE.
TABLE-US-00002 TABLE 2 Wastewater quality standard (in accordance with Directive 91/271/CEE) Parameters Unit(s) Target values COD mg O.sub.2 l.sup.−1 ≤125 Nt mg N l.sup.−1 ≤15 SS mg l.sup.−1 ≤35
[0166] During the testing period, the micropollutant removal efficiencies were evaluated for various operational conditions (pO2, SRT and HRT), which may stimulate the installation of specific metabolic niches. By acting on these key parameters, special attention was paid to the installation of nitrifying and denitrifying metabolisms in the MB-MBR compartment. Indeed, a biology of this type (called nitrifying or low mass load) is also more efficient in terms of degradation of micropollutants.
[0167] The operating conditions of the MB-MBR unit and the associated macro- and micropollutant removal performance are given below. The efficiencies are expressed as a decimal number and are calculated from the concentration before treatment (C0) and after treatment (C). An efficiency of 1 equals 100% removal and of 0 equals 0% removal.
[0168] The first phase was devoted to the optimization of the nitrification and the second phase to the improvement of the denitrification process.
[0169] Two denitrification mechanisms were investigated: (1) simultaneous nitrification and denitrification (SNDN) and (2) alternation of aerobic and anoxic phases (ANDN). The potential for simultaneous active nitrification and denitrification (SNDN) is based on the presence of a biofilm immobilized on the supports. In a single reactor, the aim is to maintain operating conditions which allow heterotrophic bacteria to denitrify in anoxic areas of the biofilm, while nitrification takes place at the periphery of the biomass in aerobic areas. The theoretical advantage of the SNDN strategy is to save the anoxic volume. The SNDN mechanism may be explained by the limited oxygen transfer within the biofilm (existence of aerobic and anoxic areas).
[0170] The various operating parameters under test of the MB-MBR unit are listed in Table 3.
TABLE-US-00003 TABLE 3 Operational parameters of the pilot unit Parameters Unit(s) Min Mean Max Stand. Dev. MB OPERATIONAL HRT (MB) Hours 8.8 15 28.2 2.5 SRT Day .sup.−1 17 35 50 16 Temperature ° C. 15 19 25 3.1 pH — 7.2 8 8.7 0.4 BIOLOGY [SS].sub.LM kg m.sup.−3 1.3 4.8 13.3 1.9 VSS.sub.LM % 55 74 85 8 [SS].sub.biofilm kg m.sup.−3 0.1 0.5 1 0.3 Bacterial supports % total — 30 — — volume LOADS Cv kg COD 0.2 0.7 2.0 0.3 m.sup.−3 d.sup.−1 Cm kg COD 0.07 0.2 0.3 0.07 kg VSS.sup.−1 d.sup.−1 SNDN O.sub.2 Concentration mg O.sub.2 l.sup.−1 1 1.6 2.4 0.7 ANDN O.sub.2 Concentration mg O.sub.2 l.sup.−1 0.4 0.6 1.0 0.2 Anoxia time min 6.0 9.6 12.0 2.6 Aerobic time min 4.0 5.6 9.0 2.3 Anoxia time % 31 46 57 11 MBR Q surfac. (MBR) 1 m.sup.−2 h.sup.−1 4 9 13 4.2 Production time min — 12 — — Backwashing min — 1 — — time
[0171] Efficiency on Macropollutants
[0172] On average, the quality of the effluents leaving the MB-MBR is very good. The concentrations of COD and suspended solids (SS) are respectively on average between 25 and 3 mg l.sup.−1 (94 and 97% of removal efficiency). Although the nitrification step is not limiting (on average N—NH.sub.4<0.8 mg l.sup.1), the total nitrogen removal efficiencies (TN in the figure) remained low (<50%) when the pilot unit was operating in SNDN configuration. The thickness of the biofilm on the bacterial supports was probably not sufficient to allow an oxygen concentration gradient inducing anoxic conditions. By switching to phase alternation, good performance could be achieved with a total nitrogen concentration at the outlet of the MB-MBR of less than 15 mg l.sup.−1.
[0173] Efficiency on Micropollutants
[0174] The corresponding efficiencies for all the micropollutants are shown in
[0175] The analysis of the purification efficiencies for the indicator molecules is presented with the exception of three molecules (carbamazepine, diclofenac, lidocaine) which could not be assayed using the unique protocol developed by the analysis center.
[0176] Microbiology
[0177] A series of metagenomic analyzes were carried out throughout the project to determine the evolution of bacterial diversity in the biofilm and the mixed liquor. Spot samples of the mixed liquor and biofilm were taken at the end of each key phase of the experimental program.
[0178] The diversity analysis makes it possible to deduce the following information: [0179] 1. The number of species decreases over time in both “biofilm” and “mixed liquor” samples. During the first experimental phase (SNDN), a greater diversity is observed in the bacterial communities of the biofilm and the mixed liquor. The change in aeration strategy (passage from SNDN to ANDN from the “day 177” sample causes the bacterial diversity to drop by approximately 30%. [0180] 2. The structure of bacterial communities evolves towards a limited number of species for both types of biomass. [0181] 3. Bacterial diversity is significantly influenced by the “time” variable, but not by the “biomass type” variable. Indeed, the bacterial diversity between the biofilm and the mixed liquor is close.
[0182] For example, the following bacterial genera are specialized for the colonization of BAC, and are not detected in the MB-MBR compartment: Acidovorax, Alcaligenes, Gemmatimonas, Leuconostoc, Luteimonas, Methylophilus, Methylovorus, Myroides, Ornithinimicrobium, Paludibacter, Phenylobacterium, Polaromonas, Propogenium, Pseudoxanthomonas, Saccharibacter, Staphylococcus, Rhodobium, Saccharibacter, Terrimonas, and Xanthobacter.
[0183] More specifically, the following bacterial genera seem to promote the regeneration of BAC: Acidovorax, Gemmatimonas, Luteimonas, Paludibacter, Phenylobacterium, Propogenium and Terrimonas.
[0184] According to the invention, these bacteria may be advantageously considered as being able to form part of the second microbial consortium in the BAC biofiltration tank.
[0185] Optimal BAC Operating Parameters
[0186] The activated carbon used was in GAC form, for example of the Norit 830W type (Cabot). According to the invention, however, several types of activated carbon may be used, by varying the nature of the carbon, the specific surface developed and the type of pores.
[0187] According to one embodiment, the GAC was conditioned for 2 months with the wastewater effluents coming from the MB-MBR before being placed in an acrylic glass column. Operation was monitored for approximately 5 months. The purpose of conditioning is to reduce the time before the breakthrough point of the filter, i.e. the moment when the adsorption capacity is exhausted and biodegradation is the dominant process.
[0188] The biological purification performance of micropollutants was evaluated according to the following methodology: [0189] 1. Saturation of adsorption sites and verification by measuring the reduction in dissolved organic carbon; [0190] 2. Evaluation of bacterial activity via measurements of oxygen consumption; [0191] 3. Correlation analyzes between bacterial activity and micropollutant removal.
[0192] The shape of the carbon pollution removal curve (Dissolved Organic Carbon or DOC) as a function of the volume treated, expressed in number of bed volume (Bed volume (Nr), BV), is divided into three parts: [0193] a. A type 1 removal phase, [0194] b. A phase in which removal is stopped (“plateau” phase), [0195] c. A type II removal phase.
[0196] The profile of the DOC removal curve shows, in
[0197] The analysis of the cumulative consumption of dissolved oxygen (DO) shown in
[0198] To bring to light a biological activity of degradation of micropollutants, two molecules were monitored: clarithromycin, a moderately biodegradable molecule, and carbamazepine, a hardly biodegradable molecule.
[0199] The shape of the clarithromycin degradation curve follows the same pattern as that of the consumption of DOC (two removal phases separated by a “plateau” phase). This observation suggests that the development of bacterial activity improves the removal of this micropollutant.
[0200] The shape of the cumulative reduction curve of carbamazepine may serve as a (“blank”) control of an activated carbon column without bioactivity. Two reduction regimes are clearly identifiable: junction at 6,000 BV (column C2 and C3) and 13,000 BV (column C1, C4 and C5). All precautions taken, it is reasonable to conclude that the microbial activity contributes significantly to the removal of micropollutants as suggested by the data presented in
[0201] Based on the operational parameters selected for columns C1 to C5, the purification efficiencies of 12 of the 13 molecules indicative of the efficiency of the method are presented in
[0202] Column C2 achieves the best overall performance for a hydraulic contact time (Empty Bed Contact Time or EBCT) of 18.8 min and an HLR of 4.8 mh.sup.−1.
[0203] A few easily biodegradable molecules such as paracetamol, naproxen or ibuprofen show average efficiencies of less than 50%. These low efficiencies are explained by an input concentration close to the LOQ.
[0204] Operational Constraint for the MB-MBR-BAC Coupling
[0205] Note the need to install a buffer tank between the two biological stages (MB-MBR and BAC). This hydraulic buffer is necessary for the backwashing of the membranes of the MBR and that of the carbon of the BAC columns. This structure will be sized on the basis of a hydraulic residence time of 1 to 3 hours depending on the configuration and the number of BAC columns selected.
[0206] Two-Stage Method—Purification Efficiencies
[0207] The purification efficiencies of the method according to the invention were evaluated in terms of removal of macro- and micropollutants on 6 average 24 hrs samples. The purification efficiency R (in percent) is defined as follows:
where C.sub.0 and C are the input (influent) and output (effluent, permeate) concentrations of the respective pollutants, respectively.
[0208] The larger part of the removal of macropollutants takes place in the MB-MBR (BAC efficiency <1% of the overall efficiency for COD and nitrogen). The results are shown in
[0209] Out of the thirteen indicator molecules, twelve show an overall purification efficiency greater than or equal to 80% (
[0210] Candesartan, an anti-hypertensive agent, is characterized by a removal efficiency slightly greater than 40%. Few references are found in the literature on its biological removal. Gurke et al. (2015) analyzed the loads of candesartan entering and leaving a biological wastewater treatment plant. The average removal efficiency of the ten samples analyzed is equal to 0% with a standard deviation of +/−10%. This shows the difficulty of removing this compound by biological treatments. For the rest of the molecules, the effectiveness of the method according to the invention is well confirmed.
[0211] In conclusion, the purification efficiencies, as defined above, were calculated for a pilot unit in stationary conditions, the operating parameters of which were optimized during the experimental phase. The average purification efficiency of several molecules is defined as the arithmetic mean of the respective purification efficiency. Out of the thirteen micropollutants selected as molecules indicating the proper functioning of the process, twelve show an average removal efficiency greater than or equal to 80%. Among these, clarithromycin, erythromycin and diclofenac are on the European watch list. Candesartan, an anti-hypertensive agent that is very difficult to biodegrade, is characterized by an average removal efficiency of 44%.
[0212] The summary of the results shows that the method developed within the framework of the invention is particularly effective for molecules which are difficult to biodegrade (candesartan, cyclophosphamide, diclofenac and metoprolol). The average efficiency of the thirteen molecules is 89% with a standard deviation of 15%.
[0213] A more detailed analysis on 16 molecules shows that two different groups of compounds may be described. The first group includes all the compounds that have been degraded by more than 80% on average (amisulpride, carbamazepine, hydrochlorothiazide and metoprolol) with little variation (dispersion, standard deviation). The second group includes compounds for which the average degradation is around 50% with a fairly high variation (e.g. clarithromycin, cyclophosphamide, diclofenac). This group is the most interesting because apparently some column conditions favor good degradation and others do not. It could be shown that clarithromycin, cyclophosphamide and diclofenac were better degraded with longer EBCTs (e.g. 19 minutes). In addition, higher HLR filtration rates (e.g. 4.8 m/h) make the columns more efficient than lower HLR (e.g. 2.4 m/h).
[0214] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.
[0215] The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.
REFERENCE SYMBOLS
[0216] 1 Wastewater [0217] 2 Treated water (discharge) [0218] 3 Air [0219] 4 Sludge [0220] 10 Pretreatment buffer [0221] 11 MB-MBR [0222] 12 Biofiltration [0223] 13 Air treatment
TABLE-US-00004 Abbreviations list Abbreviation Meaning Unit AC Activated carbon ACP Activated carbon powder AOP Advanced oxidation method BAC Biologically activated carbon (—) BV Bed volume (—) CAS Conventional activated sludge COD Chemical oxygen demand mg O.sub.2 l.sup.−1 DO Dissolved oxygen mg O.sub.2 l.sup.−1 DOC Dissolved Organic Carbon mg C l.sup.−1 EBCT Empty bed contact time min GAC Granulated activated carbon HLR Hydraulic loading rate m h.sup.−1 HRT Hydraulic retention time h LOQ Limit of quantification MB-MBR Moving Bed Membrane Bioreactor (—) Nr Number (—) Nt (or TN) Total nitrogen PE Population equivalent (—) SRT Solids retention time SS Suspended substance mg l.sup.−1 TKN Total Kjeldahl Nitrogen mg N l.sup.−1 VSS Volatile substance in suspension mg l.sup.−1