Abstract:
A novel, economical, efficient and versatile lagoon aeration system is provided which can be used with existing or new wastewater (sewage) lagoons to increase the lagoons treatment efficiency and capacity, and to allow for a continuous, year round discharge of treated wastewater to environment. The system can be operated in warm and cold climates for treatment of municipal and industrial wastewaters of varying strength and flow rates in a secondary activated sludge treatment process or in a tertiary activated sludge treatment process, or an extended aeration treatment process. The system employs patented (Patent No: U.S. Pat. No. 6,969,052 B2) Air Aspirator-Mixer (AAM) which provides highly efficient wastewater aeration outside the lagoon which facilitates an easy and economical operation and maintenance of the system throughout the year.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a process and apparatus for aeration of municipal and industrial wastewaters in lagoons (stabilization ponds) to accomplish the wastewater treatment to secondary or tertiary treatment standards. 
       BACKGROUND OF THE INVENTION 
       [0002]    Wastewater lagoons or stabilization ponds provide the simplest and the oldest wastewater treatment for municipal and industrial wastewaters which support bacteriological activity and decomposition, and reduction of organic matter. 
         [0003]    Wastewater lagoons are primarily used for wastewater treatment by small municipalities and industries, where adequate land is available. 
         [0004]    Wastewater lagoons are typically known as conventional lagoons and aerated lagoons. 
         [0005]    In the conventional lagoons, aeration of the wastewater is not used and in the aerated lagoons the wastewater is aerated inside the lagoons, for a period of several days to several weeks, depending on the climatic conditions and strength of the wastewater. Air is introduced into the wastewater by air blowers through pipes and air diffusers which are located at the bottom of the lagoons, in a grid pattern, in order to cover the lagoons evenly and adequately. The air diffusers produce air bubbles which vary in size from fine to coarse and which rise from the bottom to the top of the wastewater under static conditions. 
         [0006]    The purpose of the aeration is to introduce oxygen into the wastewater which contain aerobic bacteria and which need oxygen for living, reproduction and degradation of organic matter contained in the wastewater. 
         [0007]    Another method of the wastewater aeration is by surface mechanical mixers located on the surface of the wastewater or by submerged mechanical mixers c/w air aspirators located in the lower part of the wastewater. Both types of the air-wastewater mixers introduce air into the wastewater under dynamic conditions and produce air bubbles of varying size, quantity and range of dispersion, and efficiency of transfer of oxygen into the wastewater. 
         [0008]    Both conventional and aerated lagoons have several essential drawbacks. 
         [0009]    The conventional lagoons require a large area, impermeable soil or synthetic plastic or asphalt or concrete liners and are costly to construct. Lagoons which are not watertight may cause serious environmental problems of contamination of soil and ground and surface waters, and become a health hazard. The conventional aerated lagoons are not efficient, require a large area as compared to mechanical/biological wastewater treatment plants, have a high electric power demand and are not suitable for installation in cold climates. Also the equipment located inside the lagoons is difficult and costly to maintain. 
         [0010]    The invention is based on aeration of wastewater outside lagoons by means of a wastewater pump and an efficient air aspirator-mixer which renders an economical aeration system and which facilitates maintenance of the aeration equipment, and which lends itself to a flexible design of the aeration process to operate as an activated sludge process in a secondary treatment system or as an activated sludge process in a tertiary treatment system or as an extended aeration treatment process. 
         [0011]    The invention provides an efficient and economical wastewater treatment process which can operate in warm and cold climates, and which can be used with existing or new lagoons having a single or multi-cell design including anaerobic, primary and secondary cells. 
         [0012]    The invention is well suited to treatment of municipal and industrial wastewaters with varying strength and flow rates. 
         [0013]    New wastewater treatment facility can be provided with a small lagoon having retention time of several days to several weeks in order to store settled suspended solids and to provide daily flow balancing of incoming wastewater, and to provide adequate clarification of treated wastewater for a continuous discharge of the treated wastewater to the environment throughout the year, without a seasonal storage. 
         [0014]    The wastewater treatment system, according to the invention, requires a small building to house the aeration equipment and small tanks for installations in cold climates. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    The aeration system of the present invention is a process and apparatus for aeration of wastewater in lagoons or stabilization ponds for municipal and industrial wastewater treatment. 
         [0016]    The treatment system can operate as an activated sludge process in a secondary or a tertiary wastewater treatment system and it comprises a lagoon and an aeration system located outside the lagoon as shown on  FIGS. 1 ,  1 A,  2  &amp;  2 A. 
         [0017]    The lagoon consists of at least one primary settling and one clarification (secondary settling) cell or a primary settling, a clarification (secondary settling) and an activated sludge return cell; although, an additional storage cell of treated wastewater can be provided in existing and new lagoons. 
         [0018]    The treatment system can operate as an extended aeration treatment process which comprises a lagoon and an aeration system located outside the lagoon as shown on  FIGS. 3 &amp; 3A . 
         [0019]    The lagoon consists of a single cell, although a multiple cell lagoon can be used as well. 
         [0020]    The aeration system as shown in  FIGS. 1 ,  1 A,  2 ,  2 A,  3  &amp;  3 A comprises primarily an aeration pump, an air aspirator-mixer, and associated piping and control system. Alternatively, an aeration tank and an activated sludge return tank, and an anoxic tank can be used as options depending on the level of treatment required. 
         [0021]    The primary settling cell as shown in  FIGS. 1 ,  1 A,  2  &amp;  2 A allows for settling and decomposition of primary suspended solids (primary sludge) and for equalization of the raw wastewater flow rates throughout a day or several days. 
         [0022]    The primary settling cell retention capacity can range from several days to several weeks of an average day wastewater flow volume. The settled primary suspended solids (primary sludge) undergo an anaerobic decomposition in the primary settling cell. 
         [0023]    The clarification (secondary settling) cell as shown in  FIGS. 1 ,  1 A,  2  &amp;  2 A allows for settling and decomposition of secondary suspended solids (secondary sludge) which are predominantly the bio-mass developed in the biological treatment processes which take place in the treatment system. The decomposition of the secondary suspended solids (secondary sludge) in the clarification (secondary settling) cell is primarily anaerobic. 
         [0024]    The clarification cell retention capacity can be from several days to several weeks of an average day flow volume of the wastewater. 
         [0025]    The sludge return cell as shown in  FIGS. 1 &amp; 1A  allows for settling of a portion of the secondary suspended solids (activated sludge) and for return of the activated sludge and the aerated wastewater to the aeration system which is located outside the lagoon. 
         [0026]    The sludge return cell may be partitioned from the clarification cell with a low height partition wall made of concrete, wood, plastic, earth or other material. 
         [0027]    The sludge return cell holding capacity can be from one to several hours or longer, of the average daily raw wastewater flow rate, although, one to two hours may be adequate to retain a portion of the settled secondary solids (activated sludge) for recirculation to the aeration system, at a flow rate of between ten to hundred percent or larger of the incoming raw wastewater flow rate. 
         [0028]    The aeration pump can be a single pump or a multiple pump system, although a minimum of two pumps are preferred, one duty and one stand-by, for a reliable system. 
         [0029]    The pump is usually a centrifugal wastewater pump with a capacity of several times the average daily flow rate for a peak day wastewater flow volume, for an adequate activated sludge and aerated wastewater recirculation to the aeration system. 
         [0030]    The air aspirator-mixer is preferably the J.K. patented air aspirator-mixer, although other air aspirator-mixers can be used. The air aspirator-mixer aspires and mixes air and the wastewater to introduce a sufficient oxygen level into the wastewater for an aerobic biological wastewater treatment process. 
         [0031]    The aeration tank as shown in  FIGS. 1 ,  1 A,  3  &amp;  3 A is provided for an additional aeration of the wastewater, in addition to the aeration of the wastewater provided in the air aspirator-mixer, for a period of one to several hours for an adequate aeration of the wastewater; although, the aeration tank can be eliminated in some systems, depending on the treatment system efficiency and the level of treatment required. The aeration tank is preferred in cold climates. 
         [0032]    The aeration tank as shown in  FIGS. 2 &amp; 2A  can also be supplemented with a clarification/settling tank for a partial settling of the secondary suspended solids (activated sludge) for recirculation of the activated sludge to the aeration pump and the aeration tank. The activated sludge return tank is an option to the activated sludge return cell described above and as shown in  FIGS. 1 &amp; 1A . 
         [0033]    The activated sludge return tank retention capacity may be adequate in the range of one to two hours of the aeration system flow rate. 
         [0034]    The anoxic tank as shown in  FIGS. 1 &amp; 2  is provided for a tertiary wastewater treatment and it preferably consists of two compartments; raw wastewater and activated sludge mixing compartment and return aerated wastewater and the raw wastewater and activated sludge mixture mixing compartment. 
         [0035]    The flow rates and the retention capacities of the system components may vary depending on the wastewater quality, the treatment level required and local climatic conditions. 
         [0036]    The aeration system may include a recirculation of a portion of the aerated wastewater and activated sludge to the anoxic tank, to promote phosphorous removal and denitrification as shown in  FIGS. 1 &amp; 2 . 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0037]    Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: 
           [0038]      FIG. 1  is a schematic of a plan of a lagoon and an aeration system according to the first embodiment of the present invention showing a lagoon with a primary settling cell, a clarification cell, a sludge return cell and a storage cell which is optional, and an aeration system with two aeration pumps and two air aspirator-mixers, and an aeration tank, and an anoxic tank. This treatment system is provided for a tertiary treatment process. 
           [0039]      FIG. 1A  is a schematic of a plan of a system similar to that shown in  FIG. 1  but without the anoxic tank and with the aeration tank which is optional. This system is provided for a secondary treatment process. 
           [0040]      FIG. 2  is a schematic of a plan of a lagoon with an aeration system according to the second embodiment of the present invention showing a lagoon with a primary settling cell and a clarification cell and a storage cell which is optional, and an aeration system with two aeration pumps and two air aspirator-mixers, an aeration tank, a sludge return tank, and an anoxic tank. This treatment system is provided for a tertiary treatment process. 
           [0041]      FIG. 2A  is a schematic of a plan of a system similar to that shown in  FIG. 2  but without the anoxic tank. This system is provided for a secondary treatment process. 
           [0042]      FIG. 3  is a schematic of a plan of a lagoon with an aeration system according to the third embodiment of the present invention showing a single cell lagoon and an aeration system with two aeration pumps and two air aspirator-mixers and an aeration tank, which is optional. This treatment system is provided for an extended aeration treatment process. 
           [0043]      FIG. 3A  shows a version of the system shown on  FIG. 3  with a reversed wastewater flow direction from the lagoon to the aeration system and from the aeration system to the lagoon. This treatment system is provided for an extended aeration treatment process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0044]    A first embodiment of the invention is shown on  FIG. 1 . The treatment system primarily comprises a raw wastewater inlet pipe, generally indicated by the reference numeral  1 , a primary settling cell  4 , a clarification (secondary settling) cell  7 , a sludge return cell  9 , an anoxic tank  23 , and an aeration system  14  which comprises aeration pumps  15 , air aspirator-mixers  16  and an aeration tank  18 . The treatment system may also include a new or an existing treated wastewater storage cell  24 . 
         [0045]    The raw wastewater inlet pipe  1  may be provided with a flow meter  2 , and a single or multiple inlet  3  into the primary settling cell  4 . 
         [0046]    On the opposite side of the inlet  3 , an outlet pipe  5  is located in the primary settling cell  4 , preferably throughout the entire adjacent side of the cell  4  and with adequate perforation or multiple inlet nozzles to promote a “plug” like flow, indicated by an arrow  6 , through the cell  4 . 
         [0047]    The settled raw wastewater flows from the primary settling cell  4  to the aeration system  14 , through the outlet pipe  5 , a control valve  21 , to the anoxic tank  23 , the aeration pumps  15 , the air aspirator-mixers  16 , the aeration tank  18  and into the sludge return cell  9 . 
         [0048]    A portion of the aerated wastewater is returned from the aeration tank  18  to the anoxic tank  23  through a return pipe  20  and a control valve  19 . 
         [0049]    The balance of the aerated wastewater is discharged into the sludge return cell  9 , through an inlet pipe  12 , and it undergoes a partial clarification by settling some suspended solids (activated sludge) in the cell  9 . The suspended solids (activated sludge) settled in the cell  9  are returned into the aeration system  14  through an outlet pipe  11  and a control valve  22 , and the anoxic tank  23 , to the aeration pumps  15 , the air aspirator-mixers  16  and the aeration tank  18 , where the returned activated sludge is mixed and aerated with the settled raw wastewater which flows from the primary settling cell  4 . The aerated mixture of the returned activated sludge and the settled raw wastewater is partially discharged back into the sludge return cell  9  and the anoxic tank  23 . 
         [0050]    The partially settled, aerated and treated wastewater flows from the sludge return cell  9  into the clarification cell  7  where it undergoes a final clarification before it is discharged into the storage cell  24  or directly to an environment, through an outlet pipe  8 , which is preferably perforated or has multiple inlet nozzles along the entire adjacent wall of the clarification cell  7  to promote a “plug” like flow, indicated by an arrow  13 , through the cell  9  and the cell  7 . 
         [0051]    The wastewater treatment as described above is provided primarily by the aeration system  14  and the anoxic tank  23 , and additionally in cells  4 ,  7  and  9  and it functions as a tertiary, activated sludge process for removal of suspended solids (SS) and biochemical oxygen demand (BOD) and nutrients; phosphorous and nitrogen. 
         [0052]    Alternatively, as shown in  FIG. 1A , the aerated settled raw wastewater and the returned sludge from the sludge return cell  9  can flow directly to the aeration pumps  15 , air aspirator-mixers  16  and back to the sludge return cell  9  to accomplish a secondary treatment process for removal of suspended solids (SS) and biochemical oxygen demand (BOD). 
         [0053]    The aeration tank  18  is preferred in cold climates, although, it may be eliminated in warm climates and the treatment process will be completed in the sludge return cell  9  which will function as an aeration and sludge return cell. 
         [0054]    The automatic control valves  21  and  22  allow for optimization of the settled raw wastewater and the return sludge flow rates through the aeration system, proportioning of the ratio of the return sludge to the wastewater flow rates and operation of the wastewater treatment system within a specified wastewater levels in the primary settling cell  4  in order to use the primary settling cell  4  as a daily flow balancing cell. 
         [0055]    The automatic control valve  19  allows for a control of the aerated wastewater recirculation from the aeration tank  18  to the anoxic tank  23 . 
         [0056]    A second embodiment of the invention is shown on  FIG. 2 . 
         [0057]    For the various embodiments disclosed here, the same reference numerals are used for the same or substantially similar features. Hence, the raw wastewater inlet pipe  1 , the primary settling cell  4 , the control valve  21 , and the anoxic tank  23  are in essence the same as those shown and described in  FIG. 1 . The clarification (secondary settling) cell  7  and the aeration system  14  are similar to those shown and described in  FIG. 1 . 
         [0058]    The treatment system, according to this embodiment, primarily comprises the raw wastewater inlet pipe  1 , the primary settling cell  4 , the clarification (secondary settling) cell  7 , the anoxic tank  23  and the aeration system  14 . 
         [0059]    The treatment system may also include a new or existing treated wastewater primary storage cell  24 . 
         [0060]    The aeration system  14 , comprises the aeration pumps  15 , the air aspirator-mixers  16 , the aeration tank  18 , a sludge return tank  26 , the recirculation by-pass pipe  20 , the control valve  19  and the sludge return valve  22 . 
         [0061]    The aeration tank  18  is provided for a continuing aeration of the wastewater in addition to the aeration which takes place in the air aspirator-mixers  16 . 
         [0062]    The sludge return tank  26  allows for a partial clarification of the aerated wastewater, settling of some sludge to the bottom of the return tank  26  and return of the settled sludge to the anoxic tank  23  and mixing of the sludge with the settled raw wastewater from the primary settling cell  4  in the anoxic tank  23 . 
         [0063]    The overflow from the sludge return tank  26  which is a partially clarified (settled) aerated wastewater flows partially to the clarification cell  7  and to the anoxic tank  23  where it mixes with the settled raw wastewater from the primary settling tank  4  and the return sludge from the sludge return tank  26 . 
         [0064]    The return sludge and the raw and aerated wastewater mixture flows from the anoxic tank  23  to the aeration pumps  15  and the air aspirator-mixers  16  and back to the aeration tank  18  to complete the aeration process. 
         [0065]    The partially clarified treated wastewater undergoes further clarification in the clarification cell  7  before it flows to the outlet pipe  8  and into the storage cell  24  or directly to the environment for the final disposal. The control valves  19 ,  21  and  22  purpose and function are the same as those shown in  FIG. 1 . 
         [0066]    The wastewater treatment system as described above is a tertiary treatment process for removal of Biochemical Oxygen Demand (BOD), Suspended Solids (SS), and the nutrients: Phosphorous and Nitrogen. 
         [0067]    Alternatively, as shown in  FIG. 2A , the anoxic tank  23  and the aerated wastewater recirculation pipe  20 , and the control valve  19  can be eliminated and the treatment process will function as a secondary activated sludge process for removal of Biochemical Oxygen Demand (BOD) and Suspended Solids (SS). 
         [0068]    A third embodiment of the invention is shown on  FIG. 3  and  FIG. 3A . 
         [0069]    For the various embodiments disclosed here, the same reference numerals are used for the same or substantially similar features. Hence, the raw wastewater inlet pipe  1  is in essence the same as that shown in  FIG. 1  and  FIG. 2  and the aeration system  14  is similar to that shown on  FIG. 1  and  FIG. 2 . Also, the wastewater inlet and outlet pipes  5  &amp;  12  located in the lagoon are similar to those shown on  FIG. 1  &amp;  FIG. 2 . 
         [0070]    The treatment system, according to this embodiment, primarily consists of the raw wastewater inlet pipe  1 , a settling and aeration cell  27 , and the aeration system  14 . 
         [0071]    The treatment system is provided for an extended aeration treatment process. 
         [0072]    The treatment system may also include a storage cell  28 . 
         [0073]    The settling and aeration cell  27  is provided for settling of the primary suspended solids and the bio-mass suspended solids (bacteria) produced during the treatment process and for aeration and recirculation of the wastewater to the aeration system  14 . 
         [0074]    The settling and aeration cell  27  is provided with the raw wastewater inlet  3 , an aerated wastewater return pipe  12  and an aerated wastewater outlet pipe  5  which returns the wastewater to the aeration system  14 . The wastewater flows in a direction  6  that is from the inlet  3  to an outlet  29  or  25 . 
         [0075]    The aerated wastewater return pipe  12  and the aerated wastewater outlet pipe  5  are preferably perforated pipes, extended throughout the settling and aeration cell  27 , and spaced such to provide preferably between one and two hours or longer wastewater retention time between the pipes. The pipes perforation or inlet/outlet nozzles are spaced evenly and frequently throughout the pipes&#39; length to provide a “plug” like wastewater flow pattern between the pipes. The pipes are preferably located closer to the centre of the lagoon in order to allow for adequate settling of the primary suspended solids contained in the raw wastewater before the wastewater is drawn through the wastewater outlet pipe  5  into the aeration system  14  and to allow for adequate settling of the bio-mass suspended solids before the treated wastewater is discharged through an outlet  29  or  25 . 
         [0076]    The arrangement of the aerated wastewater return pipe  5  and the aerated wastewater outlet pipe  12  can be reversed as shown on  FIG. 3  and  FIG. 3A . 
         [0077]    The aeration system  14  consists of the aeration pumps  15 , air aspirator-mixers  16 , associated inlet and discharge piping and an optional aeration tank  18 . The aeration tank  18  is preferred in cold climates where the wastewater freezing is expected. 
         [0078]    The wastewater flow rate through the aeration system  14  is usually several times the raw wastewater inlet design flow rate and it depends on the raw wastewater quality and the treated wastewater effluent quality required. 
         [0079]    The settling and aeration cell  27  capacity is usually from several days to several weeks of the raw wastewater peak day flow volume.