Exhibit
      4.1

     

    THIS
      NOTE AND THE SHARES OF COMMON STOCK ISSUABLE UPON CONVERSION OF THIS NOTE HAVE
      NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE
      SECURITIES LAWS. NEITHER THIS NOTE NOR SUCH SHARES OF COMMON STOCK MAY BE SOLD,
      OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE
      REGISTRATION STATEMENT UNDER SUCH SECURITIES ACT AND ANY APPLICABLE STATE
      SECURITIES LAW OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE ISSUING
      CORPORATION THAT SUCH REGISTRATION IS NOT REQUIRED.

    


    
      	
              Principal
                Amount: $500,000.00

            	
              Issue
                Date: August 12, 2008

            


    

    


    7.5%
      CONVERTIBLE PROMISSORY NOTE DUE DECEMBER 31, 2008

     

    FOR
      VALUE
      RECEIVED, ThermoEnergy Corporation, a Delaware corporation (the “Borrower”),
      hereby promise to pay to the order of Robert S. Trump (the “Holder”), the sum of
      Five Hundred Thousand Dollars ($500,000.00) on December 31, 2008 (the “Maturity
      Date”). 

     

    Interest
      on the outstanding principal balance shall be paid at the rate of seven and
      one-half percent (7.5%) per annum, payable on the Maturity Date. Interest shall
      be computed on the basis of a 365-day year, using the number of days actually
      elapsed.

     

    At
      the
      election of the Borrower by written notice to the Holder (a “Deferral Notice”)
      and payment to the Holder of a deferral fee in an amount equal to ten percent
      (10%) of the principal amount then outstanding (the “Deferral Fee”) no later
      than five business days after the Maturity Date, the Maturity Date may be
      extended to March 31, 2009. At the election of the Borrower, the Deferral Fee
      may be paid by adding such amount of to the principal amount of this
      Note.

     

    The
      Holder shall have the right at any time and from time to time until the
      principal and interest on this Note shall have been paid in full, to convert
      the
      principal and any interest and Deferral Fee due under this Note into shares
      of
      the Borrower’s Common Stock, par value $0.001 per share (the “Common Stock”). If
      the Holder exercises his right of conversion, the Holder shall give the Borrower
      a Notice of Conversion in the form annexed to this Note, setting forth the
      amount of principal, interest and Deferral Fee which the Holder is converting
      into Common Stock (the “Conversion Amount”) at the Conversion Price in effect on
      the date of such notice. The date of such notice is referred to as the
“Conversion Date.” Upon delivery to the Borrower of a completed Notice of
      Conversion, the Borrower shall deliver, within five (5) business days after
      the
      Conversion Date (such fifth day being the “Delivery Date”), irrevocable
      instructions to the transfer agent for the Common Stock to issue and deliver
      to
      the Holder a certificate for that number of shares of Common Stock into which
      the Conversion Amount is being converted. Except to the extent that the entire
      unpaid principal balance of this Note is being presented for conversion, the
      Holder shall not be required to present this Note in order to effect conversion,
      and the Holder shall maintain a ledger setting forth each conversion of
      principal and interest on this Note and such ledger shall, absent manifest
      error, be deemed to be binding and conclusive on the Borrower.

     

    This
      Note
      may be prepaid, in whole or in part, at any time without premium or penalty
      upon
      ten (10) days’ prior written notice to the Holder. Partial prepayments shall be
      applied (i) first to any unpaid Deferral Fee, (ii) then to accrued and unpaid
      interest, and (iii) the balance to principal.

     

    If
      the
      Maturity Date of this Note is extended to March 31, 2009 as provided above
      and
      if this Note is not repaid in full on such Maturity Date, then the entire
      principal amount of this Note, together with all interest accrued hereon and
      the
      Deferral Fee, shall automatically and without any action on the part of the
      Borrower or the Holder convert into shares of Common Stock at the Conversion
      Price in effect on the Maturity Date. On the Maturity Date, the Holder shall
      surrender this Note for cancellation and, against such surrender, the Borrower
      shall deliver irrevocable instructions to the transfer agent for the Common
      Stock to issue and deliver to the Holder a certificate for that number of shares
      of Common Stock into which this Note has been automatically
      converted.

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    

     

    1.1. Conversion
      Price.
      The
      Conversion Price shall be $0.75 per share of Common Stock; provided,
      however, that
      the
      Conversion Price is subject to adjustment as set forth in Section 1.2 of this
      Note. The number of shares of Common Stock to be issued upon each conversion
      of
      this Note shall be determined by dividing the Conversion Amount by the
      Conversion Price in effect on the Conversion Date.

     

    1.2. Adjustment
      to the Conversion Price.
      The
      Conversion Price and number and kind of shares or other securities to be issued
      upon conversion shall be subject to adjustment from time to time upon the
      happening of certain events while this conversion right remains outstanding,
      as
      follows:

     

    1.2.1. Stock
      Dividends, Subdivisions and Combinations.
      If the
      Borrower shall at any time:

     

    (a) declare
      or pay to the holders of its Common Stock a dividend payable in, or other
      distribution of, shares of Common Stock or in securities convertible into shares
      of Common Stock (“Convertible Securities”); or

     

    (b) subdivide
      its outstanding shares of Common Stock into a larger number of shares of Common
      Stock; or

     

    (c) combine
      its outstanding shares of Common Stock into a smaller number of shares of Common
      Stock;

     

    then
      (i)
      the number of shares of Common Stock into which this Note is convertible
      immediately after the occurrence of any such event shall be adjusted to equal
      the number of shares of Common Stock which a record holder of the same number
      of
      shares of Common Stock into which this Note is convertible immediately prior
      to
      the occurrence of such event would own or be entitled to receive after the
      occurrence of such event, and (ii) the then-current Conversion Price shall
      be
      adjusted to equal (A) the then-current Conversion Price multiplied by the number
      of shares of Common Stock into which this Note is convertible immediately prior
      to the adjustment divided by (B) the number of shares into which this Note
      is
      convertible immediately after such adjustment.

     

    1.2.2. Certain
      Other Distributions.
      If at
      any time the Borrowers shall declare or pay to the holders of its Common Stock
      any dividend or other distribution of:

     

    (a) cash;

     

    (b) any
      evidences of its indebtedness, any shares of its stock or any other securities
      or property of any nature whatsoever (other than cash, Convertible Securities
      or
      additional shares of Common Stock); or

     

    (c) any
      warrants or other rights to subscribe for or purchase any evidences of its
      indebtedness, any shares of its stock or any other securities or property of
      any
      nature whatsoever (other than cash, Convertible Securities or additional shares
      of Common Stock);

     

    
      
        
        

      

      
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    then,
      upon conversion of this Note, the Holder shall be entitled to receive such
      dividend or distribution as if the Holder had converted the Conversion Amount
      prior to the date of such dividend or distribution. A reclassification of the
      Common Stock (other than a change in par value, or from par value to no par
      value or from no par value to par value) into shares of Common Stock and shares
      of any other class of stock shall be deemed a distribution by the Company to
      the
      holders of its Common Stock of such shares of such other class of stock within
      the meaning of this Section 1.2.1 and, if the outstanding shares of Common
      Stock
      shall be changed into a larger or smaller number of shares of Common Stock
      as a
      part of such reclassification, such change shall be deemed a subdivision or
      combination, as the case may be, of the outstanding shares of Common Stock
      within the meaning of Section 1.2.1.

     

    1.2.3 Reorganization,
      Reclassification, Merger, Consolidation or Disposition of Assets.
      In case
      the Borrower shall reorganize its capital, reclassify its capital stock,
      consolidate or merge with or into another Person (where the Borrower is not
      the
      survivor or where there is a change in or distribution with respect to the
      Common Stock), or sell, convey, transfer or otherwise dispose of all or
      substantially all its property, assets or business to another Person, or
      effectuate a transaction or series of related transactions in which more than
      50% of the voting power of the Borrower is disposed of (each, a “Fundamental
      Corporate Change”) and, pursuant to the terms of such Fundamental Corporate
      Change, shares of common stock of the successor or acquiring corporation, or
      any
      cash, shares of stock or other securities or property of any nature whatsoever
      (including warrants or other subscription or purchase rights) in addition to
      or
      in lieu of common stock of the successor or acquiring corporation (“Other
      Property”), are to be received by or distributed to the holders of Common Stock,
      then the Holder shall have the right thereafter to receive, upon conversion
      of
      this Note, such number of shares of common stock of the successor or acquiring
      corporation or of the Borrower, if it is the surviving corporation, and Other
      Property as is receivable upon or as a result of such
      Fundamental Corporate Change by a holder of the number of shares of Common
      Stock
      into which this Note is convertible immediately prior to such Fundamental
      Corporate Change. In case of any such Fundamental Corporate Change, the
      successor or acquiring corporation (if other than the Borrower) shall expressly
      assume the due and punctual observance and performance of each and every
      covenant and condition of this Note to be performed and observed by the Borrower
      and all the obligations and liabilities hereunder, subject to such modifications
      as may be deemed appropriate (as determined by resolution of the Board of
      Directors of the Borrower) in order to provide for adjustments of shares of
      Common Stock into which this Note is convertible which shall be as nearly
      equivalent as practicable to the adjustments provided for in this Section 1.2.
      For purposes of this Section 1.2.3, “common stock of the successor or acquiring
      corporation” shall include stock of such corporation of any class which is not
      preferred as to dividends or assets over any other class of stock of such
      corporation and which is not subject to redemption and shall also include any
      evidences of indebtedness, shares of stock or other securities which are
      convertible into or exchangeable for any such stock, either immediately or
      upon
      a specified date or upon the happening of a specified event, and any warrants
      or
      other rights to subscribe for or purchase any such stock. The foregoing
      provisions of this Section 1.2 shall similarly apply to any successive
      Fundamental Corporate Change of the successor corporation.

     

    
      
        
        

      

      
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          3
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    1.2.4 Other
      Action Affecting Common Stock.
      In case
      at any time or from time to time the Borrower shall take any action in respect
      of the Common Stock, other than any action described in this Section 1.2, which
      would have a materially adverse effect upon the rights of the Holder, the number
      of shares of Common Stock into which this Note is convertible and/or the
      Conversion Price shall be adjusted in such manner as may be equitable in the
      circumstances, as determined in good faith by the Board of Directors of the
      Borrower.

     

    1.2.5
      Certain
      Limitations.
      Notwithstanding anything herein to the contrary, the Borrower agrees not to
      enter into any transaction which, by reason of any adjustment hereunder, would
      cause the Conversion Price to be less than the par value per share of Common
      Stock.

     

    1.3. Notice
      of Adjustment.
      Whenever the Conversion Price is adjusted pursuant to Section 1.2 of this Note,
      the Borrower shall promptly mail to the Holder a notice setting forth the
      Conversion Price after such adjustment and setting forth a statement of the
      facts requiring such adjustment.

     

    1.4. Mechanics
      of Conversion.

     

    1.4.1. Delivery
      of Certificate Upon Conversion.
      Except
      as otherwise set forth herein, not later than the Delivery Date, the Borrower
      shall deliver to the Holder (a) a certificate or certificates representing
      the
      number of shares of Common Stock being acquired upon the conversion of the
      Note
      (which certificate or certificates shall bear a legend indicating that such
      shares have been issued in reliance on an exemption from the registration
      requirements of the Securities Act of 1933 (the “Securities Act” and may not be
      sold, transferred or otherwise disposed of except pursuant to an effective
      registration statement under the Securities Act or in reliance on an exemption
      to the registration requirements of the Securities Act), and (b) a bank check
      in
      the amount of accrued and unpaid interest on the portion of the Note being
      converted unless the Holder converts such interest into Common Stock. If in
      the
      case of any Notice of Conversion such certificate or certificates are not
      delivered to or as directed by the applicable Holder by the Delivery Date,
      the
      Holder shall be entitled to elect by written notice to the Borrower at any
      time
      on or before its receipt of such certificate or certificates thereafter, to
      rescind such conversion, in which event the conversion shall be deemed void
      ab
      initio.

     

    1.4.2. Obligation
      Absolute.
      The
      Borrower’s obligations to issue and deliver the Common Stock upon conversion of
      this Note in accordance with the terms hereof are absolute and unconditional,
      irrespective of any action or inaction by the Holder to enforce the same, any
      waiver or consent with respect to any provision hereof, the recovery of any
      judgment against any Person or any action to enforce the same, or any setoff,
      counterclaim, recoupment, limitation or termination, or any breach or alleged
      breach by the Holder or any other Person of any obligation to the Borrower
      or
      any violation or alleged violation of law by the Holder or any other Person,
      and
      irrespective of any other circumstance which might otherwise limit such
      obligation of the Borrower to the Holder in connection with the issuance of
      such
      shares. In the event the Holder shall elect to convert any or all of this Note,
      The Borrower may not refuse conversion based on any claim that such Holder
      or
      any one associated or affiliated with the Holder of has been engaged in any
      violation of law, agreement or for any other reason unless an injunction from
      a
      court, on notice, restraining and or enjoining conversion of all or part of
      this
      Note shall have been sought and obtained. In the absence of an injunction
      precluding the same, the Borrower shall issue the Common Stock or, if
      applicable, cash, upon a properly noticed conversion.

     

    1.4.3. 
      Fractional Shares.
      Upon a
      conversion hereunder, the Borrower shall not be required to issue stock
      certificates representing fractions of shares of the Common Stock. All
      fractional shares shall be carried forward and any fractional shares which
      remain after a Holder converts all of this Note shall be rounded up to the
      next
      whole number of shares.

     

    
      
        
        

      

      
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    1.4.4. Transfer
      Taxes.
      The
      issuance of certificates for shares of the Common Stock on conversion of this
      Note shall be made without charge to the Holder thereof for any documentary
      stamp or similar taxes that may be payable in respect of the issue or delivery
      of such certificate, provided that the Borrower shall not be required to pay
      any
      tax that may be payable in respect of any transfer involved in the issuance
      and
      delivery of any such certificate upon conversion in a name other than that
      of
      the Holder of this Note and the Borrower shall not be required to issue or
      deliver such certificates unless or until the person or persons requesting
      the
      issuance thereof shall have paid to the Borrower the amount of such tax or
      shall
      have established to the satisfaction of the Borrower that such tax has been
      paid.

     

    Section
      2. Events
      of Default.

     

    2.1. The
      entire unpaid principal amount of this Note, together with interest thereon
      shall, on written notice from the Holder, forthwith become and be due and
      payable if any one or more Events of Default shall have occurred (for any reason
      whatsoever and whether such happening shall be voluntary or involuntary or
      be
      affected or come about by operation of law pursuant to or in compliance with
      any
      judgment, decree or order of any court or any order, rule or regulation of
      any
      administrative or governmental body) and be continuing.

     

    2.2. The
      occurrence of any one or more of the following events or conditions shall
      constitute an “Event
      of Default”
under
      this Agreement:

     

    2.2.1. Borrower’s
      failure to make any payment of principal or interest or any other sums within
      fifteen (15) days of the date when due on this Note, unless the Borrower timely
      gives a Deferral Notice and pays the required Deferral Fee with respect to
      such
      payment; or

     

    2.2.2. Any
      representation or warranty or other statement made or furnished to the Holder
      by
      or on behalf of the Borrower in any document or instrument furnished in
      connection with this Note proves to have been false or misleading in any
      material respect when made or furnished; or

     

    2.2.3. Breach
      of
      or failure in the due observance or performance in any material respect of
      any
      covenant, condition or agreement on the part of the Borrower to be observed
      or
      performed pursuant to this Note and the failure to cure (if curable) any such
      breach or failure within fifteen (15) days after receipt of written notice
      thereof from the Holder; or

     

    2.2.4. If
      the
      Borrower shall (a) apply for or consent to the appointment of a receiver,
      trustee or liquidator of all or a substantial part of any of its assets; (b)
      be
      unable, or admit in writing its inability, to pay its debts as they mature;
      (c)
      file or permit the filing of any petition, case arrangement, reorganization,
      or
      the like under any insolvency or bankruptcy law, or the adjudication of it
      as a
      bankrupt, or the making of an assignment for the benefit of creditors or the
      consenting to any form or arrangement for the satisfaction, settlement or delay
      of debt or the appointment of a receiver for all or any part of its properties;
      or (d) any action shall be taken by the Borrower for the purpose of effecting
      any of the foregoing; or

     

    2.2.5. An
      order,
      judgment or decree shall be entered, or a case shall be commenced, against
      the
      Borrower, without its application, approval or consent by any court of competent
      jurisdiction, approving a petition or permitting the commencement of a case
      seeking reorganization or liquidation of the Borrower or appointing a receiver,
      trustee or liquidator of the Borrower, or of all or a substantial part of the
      assets of the Borrower, and the Borrower, by any act, indicate its approval
      thereof, consent thereto, or acquiescence therein, or such order, judgment,
      decree or case shall continue unstayed and in effect for any period of 90
      consecutive days or an order for relief in connection therewith shall be
      entered; or

     

    
      
        
        

      

      
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          5
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    2.2.6. If
      the
      Borrower shall dissolve or liquidate, or be dissolved or liquidated, or cease
      to
      legally exist, or merge or consolidate, or be merged or consolidated, with
      or
      into any other corporation.

     

    Section
      3. Miscellaneous

     

    3.1. Usury
      Saving Provision.
      All
      payment obligations arising under this Note are subject to the express condition
      that at no time shall the Borrower be obligated or required to pay interest
      at a
      rate which could subject the Holder to either civil or criminal liability as
      a
      result of being in excess of the maximum rate which the Borrower is permitted
      by
      law to contract or agree to pay. If by the terms of this Note, the Borrower
      is
      at any time required or obligated to pay interest at a rate in excess of such
      maximum rate, the applicable rate of interest shall be deemed to be immediately
      reduced to such maximum rate, and interest thus payable shall be computed at
      such maximum rate, and the portion of all prior interest payments in excess
      of
      such maximum rate shall be applied and shall be deemed to have been payments
      in
      reduction of principal.

     

    3.2. Failure
      or Indulgence Not Waiver.
      No
      failure or delay on the part of the Holder hereof in the exercise of any power,
      right or privilege hereunder shall operate as a waiver thereof, nor shall any
      single or partial exercise of any such power, right or privilege preclude other
      or further exercise thereof or of any other right, power or privilege. All
      rights and remedies existing hereunder are cumulative to, and not exclusive
      of,
      any rights or remedies otherwise available.

     

    3.3. Governing
      Law.
      This
      Agreement and the rights of the parties shall be construed and enforced in
      accordance with the laws of the State of New
      York
      applicable to agreements executed and to be performed wholly within such state
      and without regard to
      principles of conflicts of law.
      Each
      party irrevocably (a) consents to the jurisdiction of the federal and state
      courts situated
      in
      Pulaski County, Arkansas in
      any
      action that may be brought pursuant to this Agreement, and (b)
      submits to and accepts, with respect to its properties and assets, generally
      and
      unconditionally, the in personam jurisdiction of the aforesaid courts, waiving
      any defense that such court is not a convenient forum. In any such litigation
      to
      the extent permitted by applicable law, each party waives personal service
      of
      any summons, complaint or other process, and agrees that the service thereof
      may
      be made either (i) in the manner for giving of notices provided in Section
      3.5
      of this Note (other than by telecopier) or (ii) in any other manner permitted
      by
      law. 

     

    3.4. Waiver
      of Right to Trial by Jury.
      BORROWER
      HEREBY KNOWINGLY, VOLUNTARILY AND INTENTIONALLY WAIVES THE RIGHT TO A TRIAL
      BY
      JURY IN RESPECT OF ANY CLAIM BASED HEREON, ARISING OUT OF, UNDER OR IN
      CONNECTION WITH THIS NOTE AND WAIVE ANY RIGHT TO BRING A COUNTERCLAIM AGAINST
      THE HOLDER IN ANY ACTION TO ENFORCE THIS NOTE. THIS WAIVER CONSTITUTES A
      MATERIAL INDUCEMENT FOR HOLDER TO ACCEPT THIS NOTE.

     

    3.5. Notice.
      All
      notices, requests or other communications required or permitted to be given
      under this Agreement to any party shall be in writing and shall be deemed to
      have been sufficiently given when delivered by personal service or sent by
      registered mail, overnight
      courier services with provided evidence of delivery or attempted
      delivery,
      or
      facsimile, to the Borrower at 124 West Capitol Avenue, Suite 880, Little Rock,
      Arkansas 72201 (fax: 501-375-5249) or to the Holder at its principal place
      of
      business. Either party may, be like notice, change the address or telecopy
      number or the person to whom notice is to be given.
      Notice
      shall be deemed given when received or when attempted delivery is made (based
      on
      evidence of attempted delivery by the United States Postal Service or an
      overnight courier or a messenger service), provided that notice by telecopier
      shall be deemed given when receipt is acknowledged by the
      recipient.

     

    
      
        
        

      

      
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    3.6. Amendment.
      This
      Note may be amended or supplemented only by the written agreement of the Holder
      and the Borrower.

     

    3.7. Assignability.
      This
      Note shall be binding upon the Borrower and its successors and assigns, and
      shall inure to the benefit of the Holder and its successors and assigns. The
      Borrower may not assign any of its obligations under this Note without the
      consent of the Holder.

     

    3.8. Cost
      of Collection.
      If
      default is made in the payment of this Note, the Borrower shall pay the Holder
      hereof reasonable costs of collection, including reasonable attorneys’ fees,
      regardless of whether the Holder commenced litigation in order to enforce its
      rights under this Note.

     

    3.9. Stockholder
      Status.
      The
      Holder shall not have rights as a stockholder of the Borrower with respect
      to
      unconverted portions of this Note. However, from and after the Conversion Date,
      the Holder will have all the rights of a shareholder of the Borrower with
      respect to the shares of Common Stock to be received by Holder after delivery
      by
      the Holder of a Conversion Notice to the Borrower regardless of whether physical
      certificates shall have been delivered.

     

    IN
      WITNESS WHEREOF, the
      parties have caused this Agreement to be executed and delivered by its duly
      authorized Executive Vice President and Chief Financial Officer as of the date
      and year first above written.

     

    
      	
              ThermoEnergy
                Corporation

            
	 	 
	
              By:

            	
              /s/
                Andrew T. Melton

            
	 	
              Andrew
                T. Melton

            
	 	
              Executive
                Vice President and
                CFO

            


    

    


    
      
        
        

      

      
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    NOTICE
      OF CONVERSION

    


    (To
      be
      executed by the Holder in order to convert the Note)

    


    The
      undersigned hereby elects to convert $_________ of the principal and $_________
      of the interest due on the Note issued by ThermoEnergy Corporation on August
      12,
      2008 into shares of Common Stock of ThermoEnergy Corporation according to the
      conditions set forth in such Note, as of the date written below.

    


    Date
      of
      Conversion:__________________________________

    


    Conversion
      Price:____________________________________

    


    Number
      of
      Shares To Be Delivered:_______________________________

    


    Signature:________________________________________

    


    Print
      Name and
      Title:_____________________________________________________________________________

    


    Address:_______________________________________________________________________________________

    


    _______________________________________________________________________________________