WO2012082967A2

WO2012082967A2 - Integrated biological treatment and membrane filtration for nutrient removal and advanced reuse

Info

Publication number: WO2012082967A2
Application number: PCT/US2011/065014
Authority: WO
Inventors: Philip Sorrentino; Paul M. Gallagher
Original assignee: Siemens Industry, Inc.
Priority date: 2010-12-17
Filing date: 2011-12-15
Publication date: 2012-06-21
Also published as: WO2012082967A3

Abstract

The present disclosure relates to systems and methods of wastewater treatment and, in particular, to systems and methods of treating wastewater utilizing biological treatments and a post-treatment or polishing stage. The systems and methods may provide for a reduction or elimination of fouling of membranes in the post-treatment or polishing stage

Description

INTEGRATED BIOLOGICAL TREATMENT AND MEMBRANE FILTRATION FOR NUTRIENT REMOVAL AND ADVANCED REUSE

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to systems and processes of wastewater treatment and, in particular, to systems and methods of treating wastewater utilizing biological treatments and downstream filtration systems for water reuse.

SUMMARY OF THE INVENTION

One or more aspects of the present disclosure involve embodiments directed to a method of treating wastewater. The method may comprise treating a wastewater feed in a biological treatment system to provide a biologically treated effluent. The biologically treated effluent is filtered in a filtration system comprising at least one of a microfiltration unit and an ultrafiltration unit to provide a filtered treated effluent. The at least one of the microfiltration unit and the ultrafiltration unit may comprise a membrane having a normalized fouling rate of less than about 2.5 m^"2.

Treating the wastewater feed may comprise nitrifying the wastewater feed. The filtration system may comprise a cleaning-in-place interval of greater than about two months. In certain aspects, the filtration system may comprise a cleaning-in-place interval of greater than about six months.

The method may further comprise denitrifying the second biologically treated effluent prior to filtering. The method may also further comprise reducing a

concentration of total phosphorous in the filtered treated effluent. Reducing the concentration of total phosphorous in the filtered treated effluent may comprise adding coagulant. The coagulant may be added to at least one of the wastewater feed and the biologically treated effluent. The method may further comprise chlorinating the biologically treated effluent. The biologically treated effluent may comprise an ammonia concentration of less than about 5 ppm. The filtration system may further comprise a reverse osmosis unit. The filtered treated effluent may comprise a total suspended solids concentration of less than about 15 ppm.

One or more further aspects of the disclosure are directed to a method of reducing fouling in a filtration system of a wastewater treatment system. The method may comprise treating a wastewater feed in a biological treatment system to provide a nitrified effluent. The nitrified effluent may be filtered in a filtration system comprising at least one of a microfiltration unit and an ultrafiltration unit to provide a filtered treated effluent. The filtration system may have a normalized fouling rate of less than about 2.5 m-².

A cleaning-in-place step may be performed on the filtration system at an interval of greater than about two months. In certain aspects, the interval may be greater than about six months.

The method may further comprise denitrifying the nitrified effluent prior to filtering. The method may also further comprise reducing a concentration of total phosphorous in the filtered treated effluent. Reducing the concentration of total phosphorous in the filtered treated effluent may comprise adding coagulant. The coagulant may be added to at least one of the wastewater feedand the nitrified effluent. The method may further comprise chlorinating the first biologically treated effluent. The nitrified effluent may comprise an ammonia concentration of less than about 5 ppm. The filtration system may further comprise a reverse osmosis unit. The filtered treated effluent may comprise a total suspended solids concentration of less than about 15 ppm.

One or more further aspects of the present disclosure are directed to a method of treating wastewater. The method may comprise treating a wastewater feed in a biological treatment system to provide a biologically treated effluent. The biologically treated effluent may be filtered in a filtration system to provide a filtered treated effluent. The filtration system may have a normalized fouling rate of less than about 2.5 m^"2. The biologically treated effluent may be treated with a nitrifying bacteria.

The method may further comprise anoxically treating the biologically treated effluent prior to filtering.

The method may also further comprise reducing a concentration of total phosphorous in the filtered treated effluent. Reducing the concentration of total phosphorous in the filtered treated effluent may comprise adding coagulant. The coagulant may be added to at least one of the wastewater feed and the biologically treated effluent. The nitrified effluent may comprise an ammonia concentration of less than about 5 ppm. The filtration system may comprise a reverse osmosis unit and at least one of a microfiltration unit and an ultrafiltration unit. The filtered treated effluent may comprise a total suspended solids concentration of less than about 15 ppm.

One or more further aspects of the present disclosure are directed to a method of facilitating a reduction in fouling in a filtration system of a wastewater treatment system is provided. The wastewater treatment system may comprise a biological treatment process and the filtration system. The method may comprise nitrifying a wastewater in the biological treatment process to provide a nitrified effluent. The method may further comprise filtering the nitrified effluent to provide a filtered effluent comprising a total suspended solids concentration of less than about 15 ppm.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are not intended to be drawn to scale. For purposes of clarity, not every component may be labeled in the drawings, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. In the drawings: FIG. 1 is a flow diagram illustrating a representative treatment system pertinent to one or more aspects of the disclosure;

FIG. 2 is a flow diagram illustrating a representative treatment system pertinent to one or more aspects of the disclosure;

FIG. 3 is a graph of flux, temperature, transmembrane pressure (TMP), turbidity, and permeability based on a treatment system pertinent to one or more aspects of the disclosure;

FIG. 4 is a graph of resistance and flux versus time based on a treatment system pertinent to one or more aspects of the disclosure;

FIG. 5 is a graph of resistance versus time based on a treatment system pertinent to one or more aspects of the disclosure;

FIG. 6 is a graph of flux, temperature, transmembrane pressure, turbidity, and permeability versus time based on a treatment system pertinent to one or more aspects of the disclosure;

FIG. 7 is a graph of flux, temperature, transmembrane pressure, turbidity, and permeability versus time based on a treatment system pertinent to one or more aspects of the disclosure;

FIG. 8 is a graph of total phosphorous and coagulant versus time based on a treatment system pertinent to one or more aspects of the disclosure;

FIG. 9 is a bar graph of normalized fouling rate for treatment systems pertinent to one or more aspects of the disclosure; and

FIG. 10 is a bar graph of normalized fouling rate for a treatment system pertinent to one or more aspects of the disclosure. DETAILED DESCRIPTION

It is recognized that water is a valuable resource, and it is in demand in many areas due to drought, population growth, and continuous generation of waste. To reduce the demand and scarcity of water in particular areas, it may be advantageous to provide systems in which effluent water from a wastewater treatment system is further processed in a post-treatment or polishing unit or system to provide a treated water effluent that may be reused for specific applications. For example, the treated water effluent may be reused, recycled or reclaimed as reuse water that may be used for agricultural and landscape irrigation, wetlands, and wildlife habitats. The treated water effluent may also be used in industrial processes, such as industrial cooling processes or as boiler feed water, toilet flushing, replenishing ground water basins, or indirect potable reuse, such as groundwater recharge of a potable aquifer.

In a typical wastewater treatment process that comprises a downstream post- treatment or polishing system or step to provide water for reuse, wastewater may be fed to one or more of a pretreatment system and a secondary treatment process that may comprise a biological process. The effluent of the secondary treatment process may then be fed into a post-treatment or polishing step to provide the water for reuse. In certain embodiments, in which a filtration system may be used as the post-treatment or polishing step, the effluent from the secondary treatment process may be chlorinated. The chlorination may be accomplished by adding a source of chlorine to the effluent from the secondary treatment process. For example, sodium hypochlorite may be added to the effluent from the secondary treatment process to chlorinate the water. The chlorination of the water may reduce the concentration of ammonia (NH₃) in the water by producing chloramines. The chloramines may provide a disinfection effect on the effluent being processed, and may also aid in reducing the rate of fouling of membranes that may be used in the post-treatment or polishing step.

In certain instances it has been found that chlorination of the water does not provide adequate disinfection or does not reduce the rate of fouling of membranes that may be used in the post-treatment or polishing step. This ineffectiveness of chlorinating the water may lead to higher operating costs due to inefficiencies in the process, including significant fluctuations in membrane permeability and transmembrane pressure due to clogging of the membranes of the post-treatment or polishing step. The clogging may be due to accumulation of biofilm on the membrane surfaces. This may lead to increased periods of inoperation of the water treatment system in order to clean the membranes more frequently, thereby adding to the operation costs.

The systems and methods of the present disclosure may address the significant fluctuations in membrane permeability and transmembrane pressure due to clogging of the membranes. The systems and methods of the invention may provide cost advantages relative to other wastewater treatment systems through use of nitrification in the biological treatment process, or adding a nitrification step prior to the post-treatment or polishing step. The nitrification may reduce the concentration of ammonia in the effluent from the secondary treatment process. The nitrification step may also reduce the amount of extracellular polymeric substances that are in the effluent from the secondary treatment process, and that may contribute to the formation of biofilms on the membranes of the post-treatment or polishing step. In addition to or in the alternative, chemicals such as coagulants may be added to reduce or eliminate clogging of the membranes of the post- treatment or polishing step. Chlorination may also still be used in conjunction with nitrification to reduce or prevent clogging or fouling of the membranes.

The wastewater treatment systems and methods of the present invention may reduce or eliminate inefficiencies that may occur within the post-treatment or polishing step of the system and may also overcome some of the difficulties in achieving a consistent treated effluent reuse product that complies with established regulations or guidelines. This may be done by removing inefficiencies associated with removal, elimination, or reduction in membrane fouling or clogging materials within the system that may cause fluctuations in transmembrane pressure and fouling rate of the membranes in the post-treatment or polishing step. The systems and methods of the present invention also may reduce costs due to less need for periodic shut-down of the process for cleaning or defouling of the membranes.

The present disclosure may also provide for sustainability of the post-treatment step or polishing step, without having to shut down the system for extended periods of time. For example, in some instances, the operation of the post-treatment or polishing step may be sustained for at least four weeks. In other instances, the operation of the post-treatment or polishing step may be sustained for at least two months. In yet other instances, the operation of the post-treatment or polishing step may be sustained for at least six months, or longer. The present disclosure may also reduce variations in the flow of the treated effluent reuse water, and delivery of this water to a point of use. The overall efficiency and effectiveness of the system is improved to provide a consistent product water to be used in a variety of reuse applications.

Certain embodiments of the disclosure are directed to systems and methods of treating wastewater and wastewater effluent to reduce the potential for fouling of post- treatment or polishing step membranes, and to render water suitable for particular desired applications. One or more aspects of the disclosure relate to wastewater treatment systems and methods of operation and facilitating thereof. The disclosure is not limited in its application to the details of construction and the arrangement of components, systems, or subsystems set forth herein, and is capable of being practiced or of being carried out in various ways. Typically, the waste to be treated, such as wastewater, a wastewater feed, or a wastewater stream, contains waste matter which, in some cases, may comprise solids and soluble and insoluble organic and inorganic material. Prior to discharge to the environment, such streams may require treatment to decontaminate or at least partially render the wastewater streams benign or at least satisfactory for discharge under established regulatory requirements or guidelines. For example, the water may be treated to reduce its nitrogen content or concentration, or phosphorus content or concentration or other characteristic such as biological oxygen demand (BOD) content to within acceptable limits. BOD involves the measurement of the dissolved oxygen used by microorganisms in the oxidation of organic matter. BOD₅, for example is the amount of dissolved oxygen used by microorganisms in the oxidation of organic matter in five days. Some aspects of the disclosure may involve biologically treating wastewater by promoting bacterial digestion of biodegradable material, conversion of an undesirable species, such as a nutrient, to a more desirable species of at least a portion of at least one species in the wastewater. Other aspects of the disclosure may involve separation systems and method for treating wastewater or wastewater effluent by separating or filtering the water or wastewater effluent to allow it to be reused for particular desired applications. Other aspects of the disclosure may involve improving one or more properties of the water or wastewater effluent that is introduced to the separation system to reduce or prevent fouling of one or membranes of the separation system.

As used herein, the terms "water," "wastewater," "wastewater stream,"

"wastewater feed" and "influent wastewater" refer to water to be treated such as streams or bodies of water from residential, commercial, municipal, industrial, and agricultural sources, as well as mixtures thereof, that typically contain at least one undesirable species, or pollutant, comprised of biodegradable, inorganic or organic, materials which may be decomposed or converted by biological processes into environmentally benign or at least less objectionable compounds. The water to be treated may also contain biological solids, inert materials, organic compounds, including recalcitrant or a class of compounds that are difficult to biodegrade relative to other organic compounds as well as constituents from ancillary treatment operations such as, but not limited to nitrosamines and endocrine disrupters.

As used herein, the term "anoxic" refers to an environment in which oxygen is either not present or is at a level such that the biological demand of the system cannot be met by the oxygen level. Typically, anoxic conditions suggest the lack of presence of dissolved oxygen concentration. Anoxic zones or reactors may utilize endogenous respiration or commercially available carbon sources, such as ethanol, which can be added to an anoxic zone or reactor at a predetermined amount or rate, and can be adjusted throughout a treatment process. At least one embodiment of the present disclosure includes at least one biological reactor, bioreactor, or reactor in a biological treatment system. As used herein, a single "biological reactor," "bioreactor," or "reactor" may include one or more treatment zones or vessels. According to one embodiment, a first biological reactor may comprise a first biological population. As used herein, the phrase "biological population" defines a mixture of different microorganisms. It is understood that the ratio of each of the different microorganisms to one another may differ according to conditions and residence time within the bioreactors. The biological reactor may, but need not, be aerated depending on the desired conditions. Operating conditions of the bioreactor may be changed to alter growing conditions of the biological population. That is to say, operating conditions in a biological reactor may alternate between anoxic and aerobic conditions.

At least one embodiment of the present disclosure includes a biological reactor that may comprise a bioreactor having one or more treatment zones. As used herein, the phrase "treatment zone" is used to denote an individual treatment region. Individual treatment regions may be housed in a single vessel with one or more compartments. Alternatively, individual treatment regions may be housed in separate vessels, wherein a different treatment is carried out in separate vessels. The treatment zone, i.e. the vessel, tank, or compartment, may be sized and shaped according to a desired application and volume of wastewater to be treated to provide a desired hydraulic retention time.

Accordingly, a biological treatment system may comprise a biological reactor having one or more vessels or compartments. For example, a biological reactor may contain two or more treatment zones wherein the treatment zone proximate an inlet of the biological reactor may contain more oxygen than the treatment zone proximate an outlet of the biological reactor.

One or more of the treatment zones may be operated as a batch flow mode, a sequencing batch reactor, or as a continuous flow batch reactor having a continuous wastewater inflow. The treatment zone or zones may be operated under anoxic, aerobic, or anaerobic conditions as desired for a particular purpose. The microorganisms used in the individual treatment zones may be any microorganism or combination of

microorganisms suitable to thrive in anoxic, aerobic, anaerobic conditions, and combinations thereof. Representative aerobic genera, include the bacteria Acinetobacter, Pseudomonas, Zoogloea, Achromobacter, Flavobacterium, Norcardia, Bdellovibrio, Mycobacterium, Shpaerotilus , Baggiatoa, Thiothrix, Lecicothrix, and Geotrichum, the nitrifying bacteria Nitrosomonas, and Nitrobacter, and the protozoa Ciliata, Vorticella, Opercularia, and Epistylis. Representative anoxic genera include the denitrifying bacteria Achromobacter, Aerobacter, Alcaligenes, Bacillus, Brevibacterium, Flavobacterium, Lactobacillus, Micrococcus, Proteus, Pserudomonas, and Spirillum. Anaerobic organisms typically present include Clostridium spp., Peptococcus anaerobus,

Bifidobacterium spp., Desulfovibrio spp., Corynebacterium spp., Lactobacillus,

Actinomyces, Staphylococcus and Escherichia coli. In certain embodiments, the dissolved oxygen content in the aerobic reactor is sufficient to support the biological oxygen demand. In certain examples, the dissolved oxygen content may be in a range between about 0.5 mg/L and about 2.0 mg/L

A "treated" portion, such as a "treated effluent" is typically water having less undesirable species, pollutants, or nutrients relative to a starting wastewater after one or more treatment stages, such as one or more biological or separation operations. A

"treated filtered effluent," "treated reuse water," "effluent reuse water," or a "treated effluent reuse product water" is typically treated water that has been further treated in one or more post-treatment or polishing steps.

One or more of the systems disclosed herein may comprise one or more biologically-based or non-biologically-based unit operations. The systems and techniques of the disclosure may be effected as, or at least as a portion, of

decontamination or treatment systems that typically include one or more of pre-treatment, primary treatment, secondary treatment, and post-treatment or polishing operations, systems, or steps. Further, the treatment facilities that may employ one or more aspects of the disclosure may include at least one of the pre-treatment, primary treatment, secondary treatment, and post-treatment or polishing operations.

Pretreatment systems and operations may remove grit, sand, and gravel. Primary treatment operations or systems may involve at least partial equalization, neutralization, and/or removal of large insoluble material of the water to be treated such as, but not limited to fats, oils, and grease. The pretreatment and primary treatment operations may be combined to remove such materials as well as settleable solids and floating bodies, and insoluble objects such as rags and sticks. Primary clarifiers may be utilized to separate solids.

Secondary treatment unit operations or systems may involve biological treatment such as those that typically employ a biomass with bacteria or a consortium of microorganisms to at least partially hydrolyze or convert biodegradable material such as, but not limited to sugar, fat, organic molecules, and compounds that create an oxygen demand in the water. Some advantageous aspects of the disclosure may utilize biological processes and systems to remove or convert at least a portion of the organic material in the water to be treated or wastewater. The secondary treatment unit operations or systems may include processes that involve at least one of biological nitrification, denitrification, and phosphorus removal.

Post-treatment or polishing operations or systems may include biological treatments, chemical treatments, and separation systems, such as filtration systems. The post-treatment operations may include processes that involve at least one of biological nitrification, denitrification, and phosphorus removal. Chemical treatments that may be used may include chemical oxidation and chemical precipitation. Chemical treatments may include the addition of sodium hypochlorite, sulfuric acid, anti-scalant additives, and hydrogen peroxide. Separation systems may include dissolved inorganic solids removal by filtration systems that may include at least one of filter screens, cartridge filters, ion exchange, microfiltration, ultrafiltration, reverse osmosis, membrane bioreactors, or electrodialysis. Further treatment processes may involve disinfection, decontamination or inactivation of at least a portion of any residual microorganisms by chemical or physical means. For example, disinfection may be effected by exposure to any one or more of oxidizing agents or to actinic radiation. Commercially available filtration systems that may be utilized in some embodiments of the disclosure include those employing the MEMCOR® L20V ultrafiltration membrane module, the MEMCOR® S10V

ultrafiltration membrane module, and the MEMCOR® S10T microfiltration module from Siemens Industry, Inc. Other separators that may be used include filter presses and centrifuges.

In the treatment of wastewater, removal of nutrients from the wastewater prior to reuse or disposal is typically desirable. Nutrients, such as nitrogen and phosphorus, are taken up by microorganisms and used in their biological processes. Because both nitrogen and phosphorus may impact receiving water quality, the discharge of one or both of these constituents may have to be controlled.

Additionally, components in the wastewater undergoing treatment may contribute, at least in part, to clogging or fouling of downstream separation systems. For example, components of a wastewater effluent from a biological treatment process positioned upstream of a filtration system may contribute to clogging or fouling of one or more of the membrane units in the separation or filtration system. This may reduce the overall effectiveness of the wastewater treatment system, thereby adding to the costs associated with more frequent cleaning of the filtration system and out of operation time of the treatment system.

Biological nitrogen removal to nitrogen gas is typically a two-step process. In the first step, ammonia is oxidized to nitrate (nitrification) and various process configurations are then employed to provide the nitrate as an electron acceptor for biological respiration so that it may be reduced to molecular nitrogen (denitrification) under anoxic conditions. Nitrifying bacteria, such as Nitrosomonas and Nitrobacter may oxidize ammonia sequentially to nitrite and then to nitrate, respectfully. Addtionally, oxidation of ammonia may occur by way of Nitrosococcus, Nitrospira, Nitrosocyctis, and Nitrosoglea, and the oxidation of nitrite by way of Nitrocystis. Typically, nitrification in wastewater treatment processes is typically attributed primarily to Nitrosomonas and Nitrobacter.

The removal of nitrogen in the form of nitrate by conversion to nitrogen gas may be accomplished biologically under anoxic conditions in a denitrification process.

Several bacteria may be used to accomplish this conversion including Achromobacter, Aerobacter, Alcaligenes, Bacillus, Brevibacterium, Flavobacterium, Lactobacillus, Micrococcus, Proteus, Pseudomonas, and Spirillum. Nitrate is converted to nitrite which is then converted to nitric oxide, nitrous oxide and nitrogen gas, which are all gaseous products which may be released to the atmosphere.

Biological phosphorus removal may be accomplished through phosphorus uptake by microorganisms. Biological phosphorus removal is a two step process. Phosphorus is first released from microorganisms such as phosphorus accumulating organisms (POAs), that are capable of storing BOD. This typically occurs in an anoxic or aerated anoxic environment in which the BOD needs to be stored by the microorganisms because there is no oxygen available to metabolize it. The energy required for storage is generated by breaking a polyphosphate bond, which releases phosphate from the microorganisms. As the PAOs move progressively through the treatment system into zones with higher levels of oxygen, they are able to metabolize the stored BOD. As they gain energy from this BOD, they reclaim the available phosphate in the wastewater, accumulating it for later use. PAOs accustomed to living within a continuous cycle of anoxic to aerobic environments, develop the capability to store more phosphorus than they need, termed luxury phosphorus uptake. The removal of phosphorus may be accomplished by removing a portion of the microorganisms that have taken up the excess phosphorus.

Phosphorous may also be removed by chemical precipitation with, for example, coagulants. Chemicals that may be used may include metal salts and lime. Typically, metal salts such as ferric chloride and aluminum sulfate (alum) may be used, but others, such as ferrous sulfate and ferrous chloride may also be used. Polymers may also be used in conjunction with iron salts and alum. The precipitation of phosphorous from wastewater may occur in a number of different locations within a wastewater treatment process, such as in the wastewater feed, in the biological treatment process, in the effluent from the biological treatment process, or in the filtration process.

In certain embodiments of the invention, methods for treating wastewater and methods of reducing fouling in a filtration system of a wastewater treatment system are provided. A wastewater feed may be treated in a biological treatment system to provide a biologically treated effluent. The biologically treated effluent may comprise

concentrations of various components. The biological treatment system may allow for nitrification, for example, with nitrifying bacteria, to convert the ammonia to nitrites and nitrates. This may reduce a concentration of ammonia in the biologically treated effluent. The biologically treated effluent or nitrified effluent may comprise an ammonia concentration of less than about 5 ppm. In certain embodiments, the biologically treated effluent may comprise an ammonia concentration of less than about 1.5 ppm. This biologically treated effluent may then be filtered in a post-treatment or polishing unit or system that may provide a filtered treated effluent. The filtered treated effluent may comprise a total suspended solids concentration of less than about 15 ppm. The post- treatment or polishing unit or system may comprise a filtration system comprising at least one of a microfiltration unit and an ultrafiltration unit. In certain embodiments, the post- treatment or polishing unit may comprise a reverse osmosis and other unit operations that may filter, sanitize, disinfect, decarbonate, or otherwise treat an effluent. The at least one of the microfiltration unit and the ultrafiltration unit may comprise a membrane having a normalized fouling rate of less than about 2.5 m^"2.

The biologically treated effluent may be chlorinated prior to introducing the effluent into the post-treatment system. The biologically treated effluent may be denitrified by providing an anoxic environment prior to introducing it to the post- treatment or polishing unit or system. In certain embodiments, the biological treatment may comprise nitrification, and the biologically treated effluent is not chlorinated prior to introducing the effluent into the post-treatment system. This may allow for a filtration system comprising a membrane having a normalized fouling rate of less than about 2.5 m^"

2

Based at least in part on the conditions of the treatment system, the membranes of the post-treatment or polishing unit or system may require cleaning due to clogging or fouling of the membranes. Typically, it is desired to lengthen the period time that the post-treatment or polishing unit or system may require cleaning, because this may contribute to inefficient operation of the treatment system, and may result in down-time in which the treatment system may not be in operation. Thus, typically, the longer the interval between cleanings, or the "cleaning-in-place interval," the more efficient treatment system achieved. In certain embodiments, it may be desirable to have a post- treatment or polishing unit or system comprising a filtration system that has a cleaning- in-place interval of at least two weeks. In other embodiments, it may be desirable to have a post-treatment or polishing unit or system comprising a filtration system that has a cleaning-in-place interval of at least four weeks. In other embodiments, it may be desirable to have a post-treatment or polishing unit or system comprising a filtration system that has a cleaning-in-place interval of at least two months. In still other embodiments, it may be desirable to have a post-treatment or polishing unit or system comprising a filtration system that has a cleaning-in-place interval of at least six months.

In some embodiments of the disclosure, it may be beneficial to reduce the concentration of total phosphorous in the filtered treated effluent. This may be accomplished by adding a coagulant to the treatment system, such as to the wastewater feed, the first biologically treated effluent, and the second biologically treated effluent.

In order to understand the benefits that may be attributed to addition of nitrification in the wastewater treatment system, a normalized fouling rate may be calculated based on data obtained from testing sites. This normalized fouling rate takes into account fluctuations in conditions between operational runs and between testing sites. For example, the normalized fouling rate may take into account the flux, of the wastewater or wastewater effluent, its viscosity, and temperature. Resistance of the membrane may first be calculated by normalizing the measured transmembrane pressure (TMP) of the membrane. The resistance may be calculated as follows:

R (Resistance) = TMP / (Flux * Viscosity)

The normalized fouling rate, which has units of 1/m² or m^"2 may be calculated as follows: Normalized Fouling Rate = Δ R / Δ V Where,

Δ V = Volume of Filtrate Between Cleanings or Cleanings-in Place (CIPs) (m³/m²) Δ R = R₂ - Ri (m^"1)

Where,

R₂ is the temperature normalized resistance at the end of a run (m^"1); and

Ri is the temperature normalized resistance at the end of a run (m^"1).

To obtain efficient operation of a treatment system and reduce operating costs it is desired to reduce or eliminate fouling of any membranes used in the system.

Accordingly, it is desired to obtain a normalized fouling rate that approaches zero. In order to maintain operation of a treatment system with minimal or no cleaning of the membranes required, it would be beneficial to have a normalized fouling rate of less than about 5 m^"2. In certain embodiments, it may be desirable to have a lower normalized fouling rate of less than about 2.5 m^"2. In certain other embodiments it may be desired to have a lower normalized fouling rate of less than about 2 m^"2. It may also be desired to have a normalized fouling rate of less than about 0.1 m^"2 to further optimize the efficiency of the treatment system.

In still further embodiments of the disclosure, a method of facilitating a reduction in fouling in a filtration system of a wastewater treatment system is provided. The wastewater treatment system may comprise a biological treatment process and the filtration. The method may comprise nitrification in the biological treatment process. The method may further comprise filtering the nitrified effluent to provide a filtered effluent comprising a total dissolved solids concentration of less than about 15 ppm.

FIG. 1 exemplarily illustrates an embodiment in accordance with some aspects of the disclosure. The treatment system 10 may be fluidly connected or connectable to a source 110 of wastewater. The wastewater can comprise an undesirable constituent, such as a nutrient. In accordance with any one of the aforementioned aspects of the disclosure, treatment system 10 may comprise one or more treatment unit operations, which may include one or more biological treatment processes and one or more separation processes.

Source 110 of wastewater can be a water collection system from any one or more of a municipality, a residential community, and an industrial or a commercial facility, and an upstream pre-treatment system, or combinations thereof. For example, source 110 may be wastewater from a sewer system.

Treatment system 10 may comprise a biological treatment system 114 that promotes biological treatment of wastewater feed 112. Biological treatment system 114 can comprise or is configured to contain a biomass of microorganisms that can metabolize nutrients in the wastewater or convert components of the wastewater to usable or more desirable constituents. Biological treatment system 114 may contain more than one zone or more than one treatment reactor within the system. Biological treatment system 114 may include aeration to help maintain aerobic and anoxic zones within biological treatment system 114.

Biological treatment system 114 may receive wastewater feed 112 from source of wastewater 110 and can produce first biologically treated effluent 116 which may be introduced into post-treatment or polishing step 118. Post-treatment or polishing step 118 can produce filtered treated effluent 120 that may be used in water reuse applications 122 as discussed above.

In certain embodiments, source of chlorine 124 may be fluidly connected to treatment system 10. As shown in FIG. 1, source of chlorine 124 may be fluidly connected, for example, to first biologically treated effluent to provide chloramines in the effluent that may act to disinfect and prevent clogging of any downstream membranes.

FIG. 2 exemplarily illustrates another embodiment in accordance with some aspects of the disclosure. The treatment system 20 may be fluidly connected or connectable to a source 210 of wastewater. The wastewater can comprise an undesirable constituent, such as a nutrient. In accordance with any one of the aforementioned aspects of the disclosure, treatment system 20 may comprise one or more treatment unit operations, which may include one or more biological treatment processes and one or more separation processes.

Source 210 of wastewater can be a water collection system from any one or more of a municipality, a residential community, and an industrial or a commercial facility, and an upstream pre-treatment system, or combinations thereof. For example, source 210 may be wastewater from a sewer system.

Treatment system 20 may comprise a biological treatment system 214 that promotes biological treatment of wastewater feed 212. Biological treatment system 214 can comprise or is configured to contain a biomass of microorganisms that can metabolize nutrients in the wastewater or convert components of the wastewater to usable or more desirable constituents. Biological treatment system 214 may contain more than one zone or more than one treatment reactor within the system. Biological treatment system 214 may include aeration to help maintain aerobic and anoxic zones within biological treatment system 214.

Biological treatment system 214 may receive wastewater feed 212 from source of wastewater 210 and can produce biologically treated effluent 216. The biological treatment may enable nitrification within biological treatment system 214, or a separate nitrification reactor 226 may be located downstream of biological treatment system 214, which can comprise or is configured to contain a biomass of microorganisms that can metabolize ammonia to nitrites and nitrates. Nitrification reactor 226 can provide biologically treated effluent or nitrified effluent 228. Biologically treated effluent or nitrified effluent 216 or 228 can be introduced into post-treatment or polishing step 218. Post-treatment or polishing step 218 can produce filtered treated effluent 220 that may be used in water reuse applications 222 as discussed above.

In certain embodiments, source of chlorine 224 may be fluidly connected to treatment system 20. As shown in FIG. 2, source of chlorine 224 may be fluidly connected, for example, to biologically treated effluent or nitrified effluent 228 to provide chloramines in the effluent that may act to disinfect and prevent clogging of any downstream membranes of post-treatment or polishing step 218. One or more coagulants may also be added to treatment system 20, for example, to one or more of wastewater feed 212, biologically treated effluent 216, second biologically treated effluent or nitrified effluent 228, and post-treatment or polishing step 218.

In certain examples, filtered treated effluent 220 may be monitored for particular characteristics, such as nitrogen content, phosphorus content, ammonia, ammonium (NH₄ ⁺)), dissolved solids content, chemical oxygen demand, biological demand, or other characteristics. If the level of any one characteristic is not within a desired range or at a desired level, adjustments can be made to the treatment system. For example, if the ammonia content of filtered treated product differs from a desired level, an adjustment may be made to the conditions of one or more of the biological treatment system, nitrification reactor, and the post-treatment or polishing step of the system.

Existing wastewater treatment facilities may be modified or retrofitted to incorporate one or more various aspects of the systems and techniques disclosed herein, such as nitrification. In addition to nitrification, a denitrification stage may also be added and may contribute to a reduction in ammonia and a reduction in fouling of any membranes in the post-treatment or polishing step.

The function and advantage of these and other embodiments of the systems and techniques disclosed herein will be more fully understood from the examples below. The following example are intended to illustrate the benefits of the disclosed treatment approach, but do not exemplify the full scope thereof.

Example 1

A treatment system such as that disclosed in the present disclosure was operated and included a biological treatment and chlorination of the biologically treated effluent. The biological treatment system included a pure oxygen activated sludge plant with a short sludge retention time and a hydraulic retention time of less than five days, and tertiary media filtration. The post-treatment step included testing of a submerged ultrafiltration module, Memcor® ultrafiltration membrane module S10V, comprising polyvinylidene fluoride (PVDF) and having a nominal pore size of 0.04 microns, and a dead-end pressure ultrafiltration membrane module, Memcor® ultrafiltration membrane module L20V, comprising PVDF and having a nominal pore size of 0.04 microns. A nitrification stage was not employed, and no coagulant was added to the system. Effluent quality from the biological treatment, which comprised no nitrification, included a total suspended solids concentration of less than 5 ppm, a BOD₅ of less than 5 ppm, and an ammonia concentration of 20 ppm. The residual chloramine concentration was 2 ppm.

As shown in FIG. 3, over an approximately 18 day period, permeability of the membrane decreased from approximately 10 gfd/psi@20°C to about 1 gfd/psi@20°C (about 6 cm/kPa-day to about 0.6 cm/kPa-day), while transmembrane pressure increased from about 8 psi to about 50 psi (about 55 kPa to about 345 kPa). Temperature, and turbidity remained constant, while the flux began to decrease in the last three days. This demonstrates that in certain circumstances, chlorination of the effluent of the biological treatment system may not be sufficient to prevent clogging of the downstream

membranes of the filtration system.

Example 2

Another treatment system such as that disclosed in the present disclosure was operated and included a biological treatment system and chlorination of the biologically treated effluent. The biological treatment system included a pure oxygen activated sludge plant with a low sludge retention time and a low hydraulic retention time, and a trickling filter. The post-treatment step included testing of a submerged microfiltration module, Memcor® microfiltration module S10T, comprising polypropylene and having a nominal pore size of 0.2 microns, and a submerged ultrafiltration module, Memcor® ultrafiltration membrane module S10V, comprising PVDF and having a nominal pore size of 0.04 microns. This treatment system was operated for approximately three years. For approximately two years, the effluent from the biological treatment system was chlorinated, without any nitrification in the biological treatment system. After approximately two years, nitrification was added, as shown in FIG. 4. No coagulant was added to the system at any time. Initially, the ammonia concentration of the effluent from the biological treatment was about 25-30 ppm. The average BOD₅ of the effluent of the biological treatment was 28 ppm, and the residual chloramine concentration was about 3- 5 ppm.

As shown in FIG. 4, over approximately the first two years, the resistance of the membranes increased from approximately 3 x 10¹² m^_1 to about 9 x 10¹² m^"1. These large fluctuations over short periods of time resulted in frequent periodic shut-downs in order to clean or replace the membranes. A period of time after nitrification was added, the resistance range of the membranes changed from about 4 x 10¹² m^"1 to about 5 x 10¹² m^"1, and these changes occurred over longer periods of time. Therefore, after adding nitrification to the biological treatment, fewer shut-downs were required, leading to more efficient operation of the treatment system, and lower operating costs. Example 3

Another treatment system such as that disclosed in the present disclosure was operated and included a biological treatment system having a sludge retention time of about two days and a short hydraulic retention time. The post-treatment step included testing of a submerged ultrafiltration module, Memcor® ultrafiltration membrane module S10V, comprising polyvinylidene fluoride (PVDF) and having a nominal pore size of 0.04 microns. The effluent from the biological treatment system was chlorinated, with no nitrification taking place in the biological treatment. A coagulant of 1 ppm FeCl₃, with a 60 second detention time for mixing, reacting, and flocculation between the coagulation dosing point and the filtration system, was added to the system. The effluent of the biological treatment had a turbidity of 7 nephelometric turbidity units (NTU), a BOD₅ of 28 ppm, and an ammonia concentration of 25-30 ppm. The residual chloramine concentration was 2 ppm.

As shown in FIG. 5, Run 1 and Run 2 were operated were operated without the addition of a coagulant, while Run 3, Run 4, and Run 5 were operated with addition of FeCl₃ coagulant. The resistance of the membrane in Run 1 (without coagulant) increased sharply in the last 10 days. The resistance of the membrane in Run 2 (without coagulant) increased sharply over the course of its operation. In contrast, the resistance of membrane in Run 4 (with coagulant) remained relatively constant through its operation. Run 5, which is a continuation of Run 4, but at a higher flow of 23 gallons per square foot per day (gfd) (about 94 cm/day). At the higher flow, some increased resistance was observed, but the system was able to correct itself and maintained a lower resistance for several days. Similarly, Run 3 (with coagulant), is a continuation of Run 2 (without coagulant) and demonstrates that addition of coagulant may correct some of the fouling and reduce the membrane resistance over the course of 2-3 days. By adding coagulant, the resistance of the membrane was positively effected and allowed for increased flux and increased interval between cleaning of the membranes. Example 4

Another treatment system such as that disclosed in the present disclosure was operated and included a biological treatment system having a sludge retention time of 12 days. The post-treatment step included testing of a dead-end pressure ultrafiltration membrane module, Memcor® ultrafiltration membrane module L20V, comprising PVDF and having a nominal pore size of 0.04 microns. Nitrification was enabled in the biological treatment system. In the effluent of the biological treatment system, the total suspended solids concentration was in a range of about 3-5 ppm, and the BOD₅ was less than 5 ppm. The average turbidity was about 3 NTU, and the ammonia concentration was less than 1 ppm.

A coagulant of 50 ppm alum was added to the secondary clarifiers in the biological treatment. The effluent from the biological treatment was chlorinated, but no residual chlorine was detected in the effluent from the post-treatment.

As shown in FIG. 6, the treatment system was tested over an approximately 5 week period. The permeability of the membrane remained constant at approximately 6 gfd/psi@20°C (3.6 cm/kPa-day), while the transmembrane pressure remained constant at approximately 10 psi (about 69 kPa). The only divergence from the constant values occurred between 3 weeks and 4 weeks, and may be attributed to the increased flux rate observed just before and during this period of time. Temperature and turbidity remained constant. The constant transmembrane pressure and membrane permeability shows that this system may be operated for at least 5 weeks or more, without the need for shut-down or cleaning of the membranes. This example demonstrates the excellent performance that may be achieved by including nitrification and chemical coagulation in the treatment system.

Example 5

Another treatment system such as that disclosed in the present disclosure was operated and included a biological treatment system comprising an oxidation ditch process. The sludge retention time was approximately 30 days. In the effluent of the biological treatment, the total suspended solids concentration, before coagulation was less than 11 ppm. The BOD₅ was less than approximately 6 ppm. The phosphate (P0₄) concentration was less than 1.5 ppm, and the ammonia concentration was less than 1.4 ppm.

The treatment system also included media filtration after the biological treatment and before post-treatment with a dead-end pressure ultrafiltration membrane module, Memcor® ultrafiltration membrane module L20V, comprising PVDF and having a nominal pore size of 0.04 microns. Nitrification was employed in the biological treatment system, and coagulant was added to the system. Forty ppm of polyaluminum chloride (Kemira® PAX-XL 19) was added to a clarifier upstream of the post-treatment step, and 30-40 ppm of the same coagulant was added to the membrane. The effluent from the biological treatment was not chlorinated.

As shown in FIG. 7, the treatment system was tested over an approximately 4 week period. Overall, the membrane performance was acceptable. The transmembrane pressure gradually increased over the 4 week period, while the permeability of the membrane gradually decreased, but it appears that these values tapered off in the last 10 days of operation. Temperature, turbidity, and flux remained constant. The lack of sharp increases in transmembrane pressure and sharp decreases in membrane permeability shows that this system may be operated for at least 4 weeks or more, without the need for shut-down or cleaning of the membranes. This example demonstrates the excellent performance that may be achieved through use of chemical coagulation in the treatment system.

As shown in FIG. 8, during about a 3 ½ week testing operation, the total phosphorous level was reduced significantly between the feed to the biological treatment system, and the effluent of the post-treatment process. With the exception of when the total phosphorous level in the feed was greater than about 0.65 mg/liter, the total phosphorous level in the effluent was maintained a levels well below 0.1 mg/liter.

Accordingly, this example demonstrates that nitrification in combination with coagulant addition, without chlorination of the effluent of the biological treatment process is effective in significantly reducing the levels of phosphorous in wastewater being treated.

Example 6

The normalized fouling rate of the membranes used in Examples 1-5 was calculated. As shown in FIG. 9, the normalized fouling rate for Example 1, which included chlorination, but no nitrification, and no coagulation was the highest at 11.9 m^"2. For Example 3, which included chlorination and coagulation, but no nitrification, the normalized fouling rate was the second highest at 8.0 m^"2. For the portion of Example 2, which included chlorination, but no nitrification and no coagulation, the normalized fouling rate was the third highest at 6.9 m^"2. For Examples 2, 4 and 5, which included nitrification, the normalized fouling rates were significantly lower at 1.7 m^"2, 0.1 m^"2 and 2.1 m^"2, respectively. This comparison of normalized fouling rates for processes that included nitrification versus those that do not demonstrate the significant impact that including nitrification in the treatment system can have on the overall efficiency of the treatment system. The low normalized fouling rates for the processes that included nitrification indicates that less cleaning of the membranes will be required over the operation of the treatment system, which will lower operating costs, and reduce or eliminate shut-down periods.

Example 7

The normalized fouling rate of the membrane used in the treatment system of Example 3 was calculated for the testing runs in which coagulant was added to the system, and in which coagulant was not added to the system. As shown in FIG. 10, when coagulant was added to the system, the normalized fouling rate was 0.5 m^"2. When no coagulant was added to the system, the normalized fouling rate was 8.0 m^"2. This demonstrates the significant effect that addition of a coagulant to the system may have on the treatment process, and the fouling of the membranes. Through use of a coagulant, less cleaning of the membranes will be required over the operation of the treatment system, which will lower operating costs, and reduce or eliminate shut-down periods.

While exemplary embodiments of the disclosure have been disclosed many modifications, additions, and deletions may be made therein without departing from the scope of the disclosure and its equivalents, as set forth in the following claims.

Those skilled in the art would readily appreciate that the various parameters and configurations described herein are meant to be exemplary and that actual parameters and configurations will depend upon the specific application for which the system and methods of the present disclosure are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. For example, those skilled in the art may recognize that the system, and components thereof, according to the present disclosure may further comprise a network of systems or be a component of a water purification or treatment system. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the disclosed wastewater treatment system and methods may be practiced otherwise than as specifically described. The present system and methods are directed to each individual feature or method described herein. In addition, any combination of two or more such features, apparatus or methods, if such features, apparatus or methods are not mutually inconsistent, is included within the scope of the present disclosure.

Further, it is to be appreciated various alterations, modifications, and

improvements will readily occur to those skilled in the art. Such alterations,

modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the disclosure. For example, an existing facility may be modified to utilize or incorporate any one or more aspects of the disclosure. Thus, in some cases, the apparatus and methods may involve connecting or configuring an existing facility to comprise a particular aspect of this disclosure. Accordingly, the foregoing description and drawings are by way of example only.

Further, the depictions in the drawings do not limit the disclosures to the particularly illustrated representations.

As used herein, the terms "comprising," "including," "carrying," "having," "containing," and "involving," whether in the written description or the claims and the like, are open-ended terms, i.e., to mean "including but not limited to." Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases "consisting of and "consisting essentially of," are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as "first," "second," and the like in the claims to modify a claim element and in the written description does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Claims

What is claimed is:

1. A method of treating wastewater comprising:

treating a wastewater feed in a biological treatment system to provide a biologically treated effluent;

filtering the biologically treated effluent in a filtration system comprising at least one of a microfiltration unit and an ultrafiltration unit to provide a filtered treated effluent, the at least one of the microfiltration unit and the ultrafiltration unit comprising a membrane having a normalized fouling rate of less than about 2.5 m^"2.

2. The method of claim 1, wherein treating the wastewater feed comprises nitrifying the wastewater feed.

3. The method of claim 1, wherein the filtration system comprises a cleaning-in- place interval of greater than about two months.

4. The method of claim 3, wherein the filtration system comprises a cleaning-in- place interval of greater than about six months.

5. The method of claim 1, further comprising denitrifying the biologically treated effluent prior to filtering.

6. The method of claim 1, further comprising reducing a concentration of total phosphorous in the filtered treated effluent.

7. The method of claim 6, wherein reducing the concentration of total phosphorous in the filtered treated effluent comprises adding a coagulant.

8. The method of claim 7, wherein reducing the concentration of total phosphorous in the filtered treated effluent comprises adding coagulant to at least one of the wastewater feed and the biologically treated effluent.

9. The method of claim 1, further comprising chlorinating the biologically treated effluent.

10. The method of claim 1, wherein the biologically treated effluent comprises an ammonia concentration of less than about 5 ppm.

11. The method of claim 1 , wherein the filtration system further comprises a reverse osmosis unit.

12. The method of claim 1, wherein the filtered treated effluent comprises a total suspended solids concentration of less than about 15 ppm.

13. A method of reducing fouling in a filtration system of a wastewater treatment system comprising:

treating a wastewater feed in a biological treatment system to provide a nitrified effluent;

filtering the nitrified effluent in a filtration system comprising at least one of a microfiltration unit and an ultrafiltration unit to provide a filtered treated effluent, the filtration system having a normalized fouling rate of less than about 2.5 m^"2.

14. The method of claim 13, wherein a cleaning-in-place step is performed on the filtration system at an interval of greater than about two months.

15. The method of claim 14, wherein a cleaning-in-place step is performed on the filtration system at an interval of greater than about six months.

16. The method of claim 13, further comprising denitrifying the nitrified effluent prior to filtering.

17. The method of claim 13, further comprising reducing a concentration of total phosphorous in the filtered treated effluent.

18. The method of claim 17, wherein reducing the concentration of total phosphorous in the filtered treated effluent comprises adding a coagulant.

19. The method of claim 18, wherein reducing the concentration of total phosphorous in the filtered treated effluent comprises adding coagulant to at least one of the wastewater feed and the nitrified effluent.

20. The method of claim 13, wherein the nitrified effluent comprises an ammonia concentration of less than about 5 ppm.

21. The method of claim 13, wherein the filtration system further comprises a reverse osmosis unit.

22. The method of claim 13, wherein the filtered treated effluent comprises a total suspended solids concentration of less than about 15 ppm.

23. A method of treating wastewater comprising:

treating a wastewater feed in a biological treatment system to provide a biologically treated effluent ; and

filtering the biologically treated effluent in a filtration system to provide a filtered treated effluent, the filtration system having a normalized fouling rate of less than about 2.5 m^"2.

24. The method of claim 23, wherein treating the wastewater feed comprises treating the wastewater feed with a nitrifying bacteria.

25. The method of claim 24, further comprising anoxically treating the biologically treated effluent with a denitrifying bacteria prior to filtering.

26. The method of claim 23, wherein a cleaning-in-place step is performed on the filtration system at an interval of greater than about two months.

27. The method of claim 26, wherein a cleaning-in-place step is performed on the filtration system at an interval of greater than about six months.

28. The method of claim 23, further comprising reducing a concentration of total phosphorous in the filtered treated effluent.

29. The method of claim 28, wherein reducing the concentration of total phosphorous in the filtered treated effluent comprises adding a coagulant.

30. The method of claim 29, wherein reducing the concentration of total phosphorous in the filtered treated effluent comprises adding coagulant to at least one of the wastewater feed and the biologically treated effluent

31. The method of claim 23, wherein the biologically treated effluent comprises an ammonia concentration of less than about 5 ppm.

32. The method of claim 23, wherein the filtration system comprises a reverse osmosis unit and at least one of a microfiltration unit and an ultrafiltration unit.

33. The method of claim 23, wherein the filtered treated effluent comprises a total dissolved solids concentration of less than about 15 ppm.

34. A method of facilitating a reduction in fouling in a filtration system of a wastewater treatment system, the wastewater treatment system comprising a biological treatment process and the filtration system, the method comprising:

nitrifying a wastewater in the biological treatment process to provide a nitrified effluent.

35. The method of claim 34, further comprising filtering the nitrified effluent to provide a filtered treated effluent comprising a total suspended solids concentration of less than about 15 ppm.