Patent Publication Number: US-2021163328-A1

Title: System and method for attached growth biological treatment and activated carbon treatment of a wastewater stream

Description:
FIELD 
     This invention relates to treatment processes and systems, and in particular to processes and systems for activated carbon and attached growth biological treatment of contaminants in a wastewater stream. 
     BACKGROUND 
     Waste streams are commonly treated by a wide variety of solutions in order to remove organics, solids, and any other undesirable contaminants therefrom. For one, biological treatment of wastewater is widely practiced, wherein the wastewater is treated with waste activated sludge within a treatment tank (bioreactor). Oftentimes, waste streams comprise a mixture of contaminants, e.g., chemical oxygen demand (COD)—some of which are at least slowly biodegradable and treatable with biological material and others referred to as recalcitrant (non-biodegradable) COD which do not readily biodegrade and are instead typically treated with an activated carbon material. The activated carbon is typically in the form of a granulated activated carbon (GAC) or a finer powdered activated carbon (PAC). 
     Conventional wisdom in the art is that activated carbon should not be added directly to a bioreactor designed for attached growth treatment. By its nature, attached growth biological treatment relies upon the build up of a film of biological material on a surface of a media which then contacts the wastewater stream to digest the biodegradable contaminants. The conventional thought is that, given its abrasiveness at high concentrations (e.g., &gt;0.5:1 carbon to biological material ratio), the addition of activated carbon to an attached growth bioreactor would quickly result in the erosion of the biofilm and then degradation of the underlying media, thus limiting its efficiency and effectiveness in treating a wastewater stream. For this reason, a wastewater stream comprising both biodegradable and adsorbable contaminants is generally first delivered to a bioreactor comprising the biological material to reduce biodegradable contaminants followed by treatment in a separate tank containing powdered activated carbon (PAC) or a column containing granular activated carbon (GAC) for removal of the remaining biodegradable contaminants and adsorbable contaminants. This arrangement results in a relatively large footprint, as well as high material and operational costs. In addition, conventional wisdom was to separate the biological material from the activated carbon since it was believed that the activated carbon and the biological material would coalesce when present together. In turn, it was believed this coalescence would result in a loss of oxygen to the biological material, and thus loss of performance. 
     SUMMARY 
     In accordance with an aspect, the present inventors have surprisingly found that a wastewater comprising both biodegradable and adsorbable contaminants therein may be successfully treated to below standard allowable limits with an activated carbon and attached growth biological treatment system and process. Surprisingly, the inventors have found that a biological growth was able to be maintained on the attached growth media notwithstanding the presence of the activated carbon in the bioreactor. In fact, the inventors found that the activated carbon is actually capable of being maintained on the attached growth media along with a desirable build up of the biological media on the attached growth media. The systems and processes described herein thus eliminate the need for separate activated carbon and attached growth bioreactor components, thereby providing significant footprint, material, and operational savings. Further, the systems and processes allow for less biological solids generation and reduced wasting needs. 
     In accordance with an aspect of the present invention, there is provided a process for treating a wastewater stream comprising an amount of biodegradable and adsorbable contaminants therein. The process comprises delivering the wastewater stream to an attached growth reactor comprising an amount of activated carbon and an attached growth support media having active biological material thereon; and contacting the wastewater with attached growth support media and the powdered activated carbon under conditions to reduce an amount of the biodegradable and adsorbable contaminants in the wastewater. 
     In accordance with another aspect of the present invention, there is provided a system for treating a wastewater stream comprising an amount of biodegradable and adsorbable contaminants therein, the system comprising a source of the wastewater and an attached growth reactor in fluid communication with the source, the attached growth reactor comprising an amount of activated carbon and an attached growth support media having active biological material thereon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a schematic illustration of a system in accordance with an aspect of the present invention. 
         FIG. 2  comprises a schematic illustration of another system in accordance with an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings,  FIG. 1  illustrates a first embodiment of a treatment system  10  in accordance with an aspect of the present invention. The system  10  comprises a source  12  of a wastewater stream  14  in fluid communication with an attached growth reactor  16  via a fluid line  18 . As used herein, by “fluid communication,” it is meant that a fluid may flow from one component to another component. The wastewater stream  14  may comprise any fluid comprising an amount of biodegradable and adsorbable contaminants to be treated by the systems and processes described herein. The biodegradable and adsorbable contaminants comprise any undesirable compounds which are capable of being digested by biological material. In addition, the wastewater stream  14  comprises any contaminants capable of being adsorbed by activated carbon. Thus, by “adsorbable contaminants,” it is meant a chemical species, compound, or the like, which is capable of being adsorbed by an activated carbon material. 
     In an embodiment, the biodegradable and adsorbable contaminants an amount of biodegradable chemical oxygen demand (COD) therein and also an amount of recalcitrant COD therein. By “biodegradable,” it is meant that the stream  14  comprises a COD concentration therein which is capable of being reduced by an amount of biological material. As used herein, the term “recalcitrant” defines a class of compounds which may be slower to biodegrade relative to the biodegradable COD or otherwise not biodegradable. Examples of recalcitrant organics include synthetic and natural organic chemicals. Other recalcitrant organics include polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxin, and polychlorinated dibenzofurans. Endocrine disrupting compounds are also a class of recalcitrant organics which can affect hormone systems in organisms, and are found in the environment. 
     The attached growth reactor  16  comprises a suitable housing of a material, size, and shape suitable for its intended operation. When the wastewater stream  12  is delivered or otherwise provided within the attached growth reactor  16 , the attached growth reactor  16  comprises an attached growth support media comprising an amount of biological material thereon and an amount of activated carbon. Generally, the biological material on the attached growth support media will work to reduce an amount of the biodegradable material in the wastewater stream  24  while the activated carbon will adsorb otherwise difficult to biodegrade or non-biodegradable material. 
     The wastewater stream  14  may be contacted with the activated carbon and the biological material for a time suitable to provide a desired reduction of biodegradable and adsorbable contaminants in the wastewater stream  14 . In certain embodiments, the activated carbon may be introduced directly into the attached growth reactor  16 . In other embodiments, the activated carbon may be introduced into the fluid line  18  extending between the source  12  of the wastewater stream  14  and the attached growth reactor  16  as is shown by arrow  20  in  FIG. 1 . In this way, an amount of the activated carbon is combined with the wastewater stream  12  upstream from the attached growth reactor  16 , and a feed comprising the activated carbon and wastewater stream  12  may be delivered to the attached growth reactor  16 . 
     The attached growth support media in the reactor  16  may comprise any suitable media suitable for retaining and growing an amount of microorganisms thereon. In addition, the attached growth support media may be provided in any suitable form and be of any suitable inert material, such as a synthetic polymeric material. For example, the attached growth support media may comprise attached growth support media comprises a member selected from the group consisting of high-density polyethylene (HDPE), polypropylene, polyethylene, and combinations thereof. In a particular embodiment, the attached growth support media comprise a high-density polyethylene (HDPE) material. 
     It is appreciated that the biological material is contacted with the attached growth support media under conditions and for a duration effective to generate a film of biological material on a surface of the media. The attached growth support media and the contact of the stream  12  therewith may be provided in any suitable configuration. In an embodiment, the attached growth reactor is configured as a submerged attached growth reactor (SAGR), a moving media attached growth reactor (MMAGR), a stationary media attached growth reactor (SMAGR), a moving bed biofilm reactor (MBBR), or a submerged fixed bed biofilm reactor (SFBBR) as are known in the art. 
     The biological material (or population) may include any suitable population of microorganisms effective to reduce an amount of biodegradable compounds in the wastewater stream  12 . In addition, the microorganisms may comprise any bacteria or combination of bacteria suitable to thrive in anoxic and/or aerobic conditions. Representative microorganisms for use herein may be from one or more of the following bacteria families:  Acetobacteraceae, Acidobacteriaceae, Aeromonadaceae, Alcaligenaceae, Alteromonadaceae, Anaerolineaceae, Aurantimonadaceae, Bacillaceae, Bacteroidaceae, Beijerinckiaceae, Bradyrhizobiaceae, Brevibacteriaceae, Brucellaceae, Burkholderiaceae, Burkholderiales, Cam pylobacteraceae, Caulobacteraceae, Chitinophagaceae, Chromatiaceae, Chromobacteriaceae, Chroococcales, Clostridiaceae, Clostridiales, Clostridiales  Family XI.  Incertae Sedis, Clostridiales  Family XIII.  Incertae Sedis, Comamonadaceae, Cryomorphaceae, Cytophagaceae, Desulfobacteraceae, Desulfobulbaceae, Desulfomicrobiaceae, Ectothiorhodospiraceae, Enterobacteriaceae, Erysipelotrichaceae, Erythrobacteraceae, Flavobacteriaceae, Gamma proteobacteria, Hydrogenophilaceae, Hyphomicrobiaceae, Legionellaceae, Methylobacteriaceae, Methylococcaceae, Methylocystaceae, Methylophilaceae, Microbacteriaceae, Micrococcineae, Moraxellaceae, Mycobacteriaceae, Nitrosomonadaceae, Nostocaceae, Oxalobacteraceae, Peptostreptococcaceae, Phycisphaeraceae, Phyllobacteriaceae, Planctomycetaceae, Porphyromonadaceae, Pseudoalteromonadaceae, Pseudomonadaceae, Rhizobiaceae, Rhizobiales, Rhodobacteraceae, Rhodobiaceae, Rhodocyclaceae, Rhodospirillaceae, Rhodospirillales, Rickettsiales, Rikenellaceae, Ruminococcaceae, Saprospiraceae, Shewanellaceae, Sinobacteraceae, Sphingobacteriaceae, Sphingomonadaceae, Staphylococcaceae, Synergistaceae, Thioalkalispiraceae, Verrucomicrobiaceae, Vibrionaceae, Xanthobacteraceae , and  Xanthomonadaceae.    
     Generally, the activated carbon may comprise any suitable carbon material suitable for the adsorption of desired contaminants, namely recalcitrant organics, from the wastewater stream  12 . In an embodiment, the activated carbon comprises a granulated activated carbon material or a powdered activated carbon as are known in the art. In a particular embodiment, the activated carbon comprises a powdered activated carbon material. The activated carbon and the biological material may be provided in a suitable ratio relative to one another for the targeted contaminants. In a particular embodiment, the ratio of activated carbon to biological material is from 0.5:1 to 25:1 by weight. 
     In certain embodiments and as shown in  FIG. 2 , an effluent from the attached growth reactor  16  may be delivered to a liquid/solid separator  22  to separate the effluent into a liquid portion and a solids portion, wherein the solids portion comprises an amount of spent carbon and biological material. In an embodiment, the liquid/solid separator  22  comprises a membrane unit comprising a plurality of membranes therein. The membrane unit may comprise one or more porous or semipermeable membranes  14  (also referred to as “membrane(s)” or “membrane” for ease of reference). In an embodiment, the membrane comprises a microfiltration membrane or an ultrafiltration membrane as is known in the art. In addition, the membrane may have any configuration suitable for its intended application, such as a sheet or hollow fibers. Further, the membrane has a suitable porosity and/or permeability for its intended application. Still further, the membrane may have any suitable shape and cross sectional area such as, for example, a square, rectangular, or cylindrical shape. In one embodiment, the membrane has a rectangular shape. 
     Within the membrane unit, the one or more membranes may be positioned, e.g., vertically, in a treatment zone of the membrane unit in such a way as to be completely submerged by material within the unit therein during operation. In certain embodiments, the membrane unit may include a blower or the like for supplying a gas to scour the membrane(s) and prevent solids build up on a surface of the membrane(s) therein. Each blower may produce fine bubbles, coarse bubbles, a jet stream of gas, a jet of gas and fluid, and combinations thereof. Typically also, a pump (not shown) may be provided to generate a suitable suction force to draw fluid through each membrane of the membrane unit to generate a retentate and a filtrate. In certain embodiments, the membrane unit may also comprise an amount of powdered activated carbon therein for further polishing/treating the filtrate to reduce any remaining contaminants therein. In other embodiments, the liquid/solid separator  22  may comprises one or more clarifiers, dissolved gas flotation units, or any other device or system for carrying out the separation. 
     Regardless of the structure or process used, the liquid/solid separator  22  provides a liquid portion (with a reduced amount of biodegradable and adsorbable contaminants relative to the waste stream) and a solids portion which comprises an amount of spent carbon and biological solids. From the liquid/solid separator, the liquid portion may be directed to storage, transport, discharge, reinjection, irrigation, reuse, or the like. In an embodiment, the liquid portion comprises a COD concentration below a predetermined level prior to discharge. In certain embodiments, the predetermined level is 30 mg/L ora greater amount (160, 150, 125, 100, 75, 60, 50, or 40 mg/L). In certain embodiments, the solids portion comprises spent carbon (wherein at least a portion of the spent carbon comprises activated carbon comprising adsorbed material thereon) and biological material. The solids portion is in fluid communication with a carbon regeneration unit  24  as shown in  FIG. 2  for delivery of the solids portion thereto. At the carbon regeneration unit  24 , the solids portion undergoes oxidation of any oxidizable materials therein and regeneration of the spent carbon material therein. In this way, waste is avoided and the activated carbon/biological material may be recycled for treatment of further incoming wastewater. 
     In an embodiment, the regeneration unit  24  comprises a wet air regeneration (WAR) unit  26  having an input in fluid connection with an output of the liquid/solid separator  22 . The WAR unit  26  may comprise one or more dedicated reactor vessels in which oxidation and/or regeneration of the spent activated carbon portion takes place. The regeneration process therein typically involves treatment of the incoming feed with an oxidant, generally molecular oxygen from an oxygen-containing gas, at elevated temperatures and pressures. In an embodiment, the regeneration of the spent carbon is done at a pressure from about 20 atm to about 240 atm and at a temperature from about 150° C. to about 373° C. with the addition of oxygen to the feed stream or the WAR unit  26 . In an embodiment, sufficient oxygen is provided to the unit to provide an offgas having an oxygen concentration of at least 3 vol. %, and in a particular embodiment from 5-15 vol. % oxygen. In a particular embodiment, the wet air regeneration is carried out at a temperature of about 200° C. or less, and in a particular embodiment from about 150° C. to about 200° C. for a duration of at least about 1 hour, and in a particular embodiment from about 3 to 8 hours. 
     The wet air regeneration of carbon destroys the volatile portion of the biological solids and oxidizes and/or changes the organic substances adsorbed on the activated carbon to restore its adsorptive capacity, and results in a regenerated slurry. The regenerated slurry (shown as  28 ) from the wet air regeneration process consists primarily of reactivated carbon particles and oxidized biological solids. In certain embodiments, the regenerated slurry  28  comprises inorganic ash particles removed from the wastewater by the carbon and formed during the regeneration process. The ash may be further separated from the regenerated slurry by known separation methods such as those reported in U.S. Pat. Nos. 4,778,598 and 4,749,492, both of which are incorporated herein by reference in their entireties for all purposes. In any case, the regenerated slurry  28  may be directed to back to the attached growth reactor  16  or to the fluid line  18  between the wastewater source  12  and the attached growth reactor  16  via line  30  to provide the necessary activated carbon for subsequent treatment of stream  12 . In certain embodiments, fresh activated carbon or biological material may be introduced to the line  18  or attached growth reactor  16  in lieu of or in addition to the regenerated material. 
     The function and advantages of these and other embodiments of the present invention will be more fully understood from the following examples. These examples are intended to be illustrative in nature and are not considered to be limiting the scope of the invention. 
     EXAMPLE 
     Below is data generated during bench-scale studies performed on refinery de-oiled wastewater using conventional activated sludge (CAS) and the PACT® AG process with two plastic carrier media types. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 CAS vs PACT AG Pre &amp; Post PAC addition 
               
            
           
           
               
               
               
               
            
               
                   
                 CAS 
                 Media 1 
                 Media 2 
               
               
                   
                 (Effluent DOC, 
                 (Effluent DOC, 
                 (Effluent DOC, 
               
               
                   
                 mg/L) 
                 mg/L) 
                 mg/L) 
               
               
                   
                   
               
            
           
           
               
            
               
                 PRE PAC 
               
            
           
           
               
               
               
               
            
               
                 Mar. 1, 2018 
                 73.80 
                 75.00 
                 80.30 
               
               
                 Mar. 6, 2018 
                 71.50 
                 78.10 
                 79.90 
               
               
                 Mar. 8, 2018 
                 72.4 
                 77.8 
                 80 
               
               
                 Mar. 13, 2018 
                 76.2 
                 79.4 
                 80.6 
               
               
                 Mar. 15, 2018 
                 74.6 
                 81.1 
                 81.5 
               
               
                 Mar. 20, 2018 
                 73.9 
                 80.3 
                 79.5 
               
               
                 Mar. 22, 2018 
                 74.3 
                 79.4 
                 80.5 
               
               
                 Mar. 27, 2018 
                 76.8 
                 81 
                 77.4 
               
               
                 Mar. 30, 2018 
                 73.2 
                 79.4 
                 76.3 
               
               
                 Apr. 3, 2018 
                 76.5 
                 78.8 
                 78.3 
               
            
           
           
               
            
               
                 POST PAC 
               
            
           
           
               
               
               
               
            
               
                 Apr. 5, 2018 
                 77.7 
                 69.2 
                 65.7 
               
               
                 Apr. 10, 2018 
                 74.8 
                 69.0 
                 71.5 
               
               
                 Apr. 12, 2018 
                 67.1 
                 64.6 
                 69.3 
               
               
                 Apr. 17, 2018 
                 70.1 
                 60.6 
                 59.2 
               
               
                 Apr. 19, 2018 
                 74.5 
                 58.9 
                 58.6 
               
               
                 Apr. 24, 2018 
                 73.4 
                 38.5 
                 40.4 
               
               
                 Apr. 26, 2018 
                 70.5 
                 39.5 
                 43.5 
               
               
                   
               
            
           
         
       
     
     Bench-scale testing was performed using a total of six bioreactors resulting in three controls and three test units. One sequencing batch reactor (SBR) representing conventional activated sludge (CAS) treatment as the control, one SBR representing a conventional PACT® treatment system to gauge PAC efficiency and four continuous flow reactors (CFRs) with equivalent amounts (m 2  of media surface are per m 3  of treated wastewater to yield equal surface area loading rates (SALR) of biofilm carrier media as the attached growth control as well as the two test reactors. The six reactors were allowed to acclimate and stabilize prior to PAC addition. Post acclimation, a PAC plus water slurry equivalent to a “typical” carbon dose was added four times daily directly to the PAC bioreactors. 
     Treatment performance was monitored by performing laboratory analytical testing on reactor effluent samples. Critical performance indicators were chemical oxygen demand (COD), soluble total organic carbon (sTOC), biochemical oxygen demand (BOD 5 ), ammonium (NH 4 ) and phosphate (PO 4 ). Key process variables, namely dissolved organic carbon (DOC), pH, and temperature were also monitored and recorded. 
     Post-PAC addition, the DOC (Table 1) was used as the metric to gauge treatment performance. The post PAC results for the attached growth (AG) reactors were used to demonstrate the increase in treatment performance when compared to the CAS reactor, as well as the performance against the PACT® control. Treated effluent sTOC results indicated that attached growth treatment of the de-oiled refinery wastewater was enhanced when compared to CAS and comparable to the conventional PACT® system effluent. These results indicate that the attached growth biofilm in the presence of PAC is capable of metabolizing organic contaminants the same as that typically seen in a suspended growth treatment system. This will allow the attached growth biofilm to realize the symbiotic benefits of a PAC plus biomass system. 
     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.