PROMISSORY NOTE

Exhibit 10.48

PROMISSORY NOTE

References in the boxes above are for Lender’s use only and do not limit the applicability of this document to any particular loan or item. Any item above containing ‘ I I - has been omitted due to text length limitations .

PROMISE TO PAY. ADA-ES, INC. 1”Borrower’) promises to pay to COLORADO BUSINESS BANK (‘Lender”), or order, in lawful money of the United States of America, on demand, the principal amount of Four Million & 001100 Dollars ($4,000,000.00) or so much as may be outstanding, together with Interest on the unpaid outstanding principal balance of each advance. Interest shall be calculated from the date of each advance until repayment of each advance.

PAYMENT. Borrower will pay this loan in full immediately upon Lender’s demand. Unless otherwise agreed or required by applicable law, payments will be applied first to any accrued unpaid Interest; then to principal; and then to any unpaid collection costs. Borrower will pay Lender at Lender’s address shown above or at such other place as Lender may designate in writing.

VARIABLE INTEREST RATE. The interest rate on this Note Is subject to change from time to time based on changes In an index which is the WALL STREET JOURNAL PRIME RATE (the ‘Index’). Lender will tell Borrower the current Index rate upon Borrower’s request. The interest rate change will not occur more often than each DAY. Borrower understands that Lender may make loans based on other rates as well. The Index currently is 5.000% per annum. The interest rate to be applied to the unpaid principal balance of this Note will be calculated as described in the ‘INTEREST CALCULATION METHOD” paragraph using a rate equal to the Index, resulting in an initial rate of 5.000% per annum based on a year of 360 days. NOTICE: Under no circumstances will the Interest rate on this Note be more than the maximum rate allowed by applicable law.

INTEREST CALCULATION METHOD. Interest on this Note is computed on a 365/360 basis: that is. by applying the ratio of the Interest rate over a year of 360 days, multiplied by the outstanding principal balance, multiplied by the actual number of days the principal balance 1s outstanding. AR interest payable under this Note Is computed using this method.

INTEREST AFTER DEFAULT. Upon default, including failure to pay upon final maturity, the interest rate on this Note shall be increased by adding a 5.000 percentage point margin (“Default Rate Margin’). The Default Rate Margin shall also apply to each succeeding interest rate change that would have applied had there been no default. However, in no event will the interest rate exceed the maximum Interest rate limitations under applicable law.

LENDER’S RIGHTS. Upon Lender’s demand, Lender may declare the entire unpaid principal balance under this Note and all accrued unpaid interest immediately due, and then Borrower will pay that amount.

ATTORNEYS’ FEES; EXPENSES. Lender may hire or pay someone else to help collect this Note If Borrower does not pay. Borrower will pay Lender the reasonable costs of such collection. This includes, subject to any limits under applicable law, Lender’s attorneys’ fees and Lender’s legal expenses, whether or not there is a lawsuit, including without limitation attorneys’ fees and legal expenses for bankruptcy proceedings (including efforts to modify or vacate any automatic stay or Injunction), and appeals. If not prohibited by applicable law, Borrower also will pay any court costs, in addition to all other sums provided by law.

JURY WAIVER. Lender and Borrower hereby waive the right to any jury trial in any action. proceeding, or counterclaim brought by either Lander or Borrower against the other.

GOVERNING LAW. This Note will be governed by federal law applicable to Lander and, to the extent not preempted by federal law, the laws of the State of Colorado without regard to Its conflicts of law provisions. This Note has been accepted by Lender in the State of Colorado.

DISHONORED ITEM FEE. Borrower will pay a fee to Lender of $25.00 If Borrower makes a payment on Borrower’s loan and the check or preauthorized charge with which Borrower pays is later dishonored.

RIGHT OF SETOFF, To the extant permitted by applicable law, Lender reserves a right of setoff in all Borrower’s accounts with Lender (whether checking, savings, or some other account). This Includes all accounts Borrower holds jointly with someone else and all accounts Borrower may open In the future. However, this does not Include any IRA or Keogh accounts, or any trust accounts for which setoff would be prohibited by law. Borrower authorizes Lender, to the extent permitted by applicable law, to charge OF setoff all sums owing on the indebtedness against any and all such accounts,

LINE OF CREDIT. This Note evidences a straight line of credit. Once the total amount of principal has been advanced, Borrower Is not entitled to further loan advances. Advances under this Note, as well as directions for payment from Borrower’s accounts, may be requested orally or In writing by Borrower or by an authorized person. Lender may, but need not, require that all oral requests be confirmed In writing. Borrower agrees to be liable for all sums either: (A) advanced in accordance with the instructions of an authorized person or (B) credited to any of Borrower’s accounts with Lender. The unpaid principal balance owing on this Note at any time may be evidenced by endorsements on this Note or by Lender’s internal records, including daily computer print-outs.

ADDITIONAL PROVISION. THIS PROMISSORY NOTE IS MADE IN CONJUNCTION WITH LETTER OF CREDIT NO.

1436, OR AS MAY BE

AMENDED, EXTENDED OR RENEWED.

SUCCESSOR INTERESTS. The terms of this Note shall be binding upon Borrower, and upon Borrower’s heirs, personal representatives, successors and assigns, and shall inure to the benefit of Lender and its successors and assigns.

NOTIFY US OF INACCURATE INFORMATION WE REPORT TO CONSUMER REPORTING AGENCIES. Please notify us If we report any Inaccurate information about your account(s) to a consumer reporting agency. Your written notice describing the specific ineccurecy(ies) should be sent to us at the following address: COLORADO BUSINESS BANK ATTN: LOAN OPERATIONS 821 17TH STREET DENVER, CO 80202.

GENERAL PROVISIONS. If any part of this Note cannot be enforced, this fact will not affect the rest of the Note. Lender may delay or forgo enforcing any of its rights or remedies under this Note without losing them. Borrower and any other person who signs, guarantees or endorses this Note, to the extent allowed by law, waive presentment, demand for payment, and notice of dishonor. Upon any change in the terms of this Note, and unless otherwise expressly stated in writing, no party who signs this Note, whether as maker, guarantor, accommodation maker or endorser, shall be released from liability. All such parties agree that Lender may renew or extend (repeatedly and for any length of time) this loan or release any party or guarantor or collateral; or impair, fail to realize upon or perfect Lender’s security Interest in the collateral; and take any other action deemed necessary by Lender without the consent of or notice to anyone. All such parties also agree that Lender may modify this loan without the consent of or notice to anyone other than the party with whom the modification is made. The obligations under this Note are joint and several.

PRIOR TO SIGNING THIS NOTE, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS OF THIS NOTE, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS. BORROWER AGREES TO THE TERMS OF THE NOTE.

BORROWER ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THIS PROMISSORY NOTE.

CHANGE IN TERMS AGREEMENT

Any item above containing “•’ •” has been omitted due to text length limitations.

$4,000,000.00 WITH AN ORIGINAL MATURITY DATE OF PURE DEMAND AND INCLUDING ANY AND ALL SUBSEQUENT EXTENSIONS OR MODIFICATIONS THEREFROM.

DESCRIPTION OF CHANGE IN TERMS. THE MATURITY DATE WILL REMAIN PURE DEMAND. THE PURPOSE OF THIS CHANGE IN TERMS IS TO HEREBY INCREASE THE PRINCIPAL AMOUNT FROM $4,000,000.00 TO $6,600,000.00. ALL OTHER TERMS AND CONDITIONS WILL REMAIN THE SAME.

PROMISE TO PAY. ADA-ES, INC. (“Borrower”) promises to pay to COLORADO BUSINESS BANK (“Lender”), or order. In lawful money of the United States of America, on demand, the principal amount of Six Million Six Hundred Thousand & 00/100 Dollars 1$6,600,000.00) or so much as may be outstanding, together with interest on the unpaid outstanding principal balance of each advance. Interest shall be calculated from the date of each advance until repayment of each advance.

PAYMENT. Borrower will pay this loan in full immediately upon Lender’s demand. Unless otherwise agreed or required by applicable law, payments will be applied first to any accrued unpaid interest; then to principal; and then to any unpaid collection costs. Borrower will pay Lender at Lender’s address shown above or at such other place as Lender may designate in writing.

VARIABLE INTEREST RATE. The interest rate on this loan is subject to change from time to time based on changes in an index which is the WALL STREET JOURNAL PRIME RATE (the “Index”). Lender will tell Borrower the current Index rate upon Borrower’s request. The interest rate change will not occur more often than each DAY. Borrower understands that Lender may make loans based on other rates as well. The Index currently is 5.000% per annum. The interest rate to be applied to the unpaid principal balance of this loan will be calculated as described in the “INTEREST CALCULATION METHOD” paragraph using a rate equal to the Index, resulting in an initial rate of 5.000% per annum based on a year of 360 days. NOTICE: Under no circumstances will the interest rate on this loan be more than the maximum rate allowed by applicable law.

INTEREST CALCULATION METHOD. Interest on this loan is computed on a 365/360 basis; that is, by applying the ratio of the interest rate over a year of 360 days, multiplied by the outstanding principal balance, multiplied by the actual number of days the principal balance is outstanding. All Interest payable under this loan is computed using this method.

INTEREST AFTER DEFAULT. Upon default, including failure to pay upon final maturity, the interest rate on this loan shall be increased by adding a 5.000 percentage point margin (“Default Rate Margin”). The Default Rate Margin shall also apply to each succeeding interest rate change that would have applied had there been no default. However, in no event will the interest rate exceed the maximum interest rate limitations under applicable law.

LENDER’S RIGHTS. Upon Lender’s demand, Lender may declare the entire unpaid principal balance under this Agreement and all accrued unpaid interest immediately due, and then Borrower will pay that amount.

ATTORNEYS’ FEES; EXPENSES. Lender may hire or pay someone else to help collect this Agreement if Borrower does not pay. Borrower will pay Lender the reasonable costs of such collection. This includes, subject to any limits under applicable law, Lender’s attorneys’ fees and Lender’s legal expenses, whether or not there is a lawsuit, including without limitation attorneys’ fees and legal expenses for bankruptcy proceedings (including efforts to modify or vacate any automatic stay or injunction), and appeals. If not prohibited by applicable law, Borrower also will pay any court costs, in addition to all other sums provided by law.

JURY WAIVER. Lender and Borrower hereby waive the right to any jury trial in any action, proceeding, or counterclaim brought by either Lender or Borrower against the other.

GOVERNING LAW. This Agreement will be governed by federal law applicable to Lender and, to the extent not preempted by federal law, the laws of the State of Colorado without regard to its conflicts of law provisions. This Agreement has been accepted by Lender in the State of Colorado.

DISHONORED ITEM FEE. Borrower will pay a fee to Lender of $25.00 if Borrower makes a payment on Borrower’s loan and the check or preauthorized charge with which Borrower pays is later dishonored.

RIGHT OF SETOFF. To the extent permitted by applicable law, Lender reserves a right of setoff in all Borrower’s accounts with Lender (whether checking, savings, or some other account). This includes all accounts Borrower holds jointly with someone else and all accounts Borrower may open in the future. However, this does not include any IRA or Keogh accounts, or any trust accounts for which setoff would be prohibited by law. Borrower authorizes Lender, to the extent permitted by applicable law, to charge or setoff all sums owing on the debt against any and all such accounts.

LINE OF CREDIT. This Agreement evidences a straight line of credit. Once the total amount of principal has been advanced, Borrower is not entitled to further loan advances. Advances under this Agreement, as well as directions for payment from Borrower’s accounts, may be requested orally or in writing by Borrower or by an authorized person. Lender may, but need not, require that all oral requests be confirmed in writing. Borrower agrees to be liable for all sums either: (A) advanced in accordance with the instructions of an authorized person or (B) credited to any of Borrower’s accounts with Lender. The unpaid principal balance owing on this Agreement at any time may be evidenced by endorsements on this Agreement or by Lender’s internal records, including daily computer print-outs.

CONTINUING VALIDITY. Except as expressly changed by this Agreement, the terms of the original obligation or obligations, including all agreements evidenced or securing the obligation(s), remain unchanged and in full force and effect. Consent by Lender to this Agreement does not waive Lender’s right to strict performance of the obligation(s) as changed, nor obligate Lender to make any future change in terms. Nothing in this Agreement will constitute a satisfaction of the obligation(s). It is the intention of Lender to retain as liable parties all makers and endorsers of the original obligationls), including accommodation parties, unless a party is expressly released by Lender in writing. Any maker or endorser, including accommodation makers, will not be released by virtue of this Agreement. If any person who signed the original obligation does not sign this Agreement below, then all persons signing below acknowledge that this Agreement is given conditionally, based on the representation to Lender that the non-signing party consents to the changes and provisions of this Agreement or otherwise will not be released by it. This waiver applies not only to any initial extension, modification or release, but also to all such subsequent actions.

ADDITIONAL PROVISION. THIS CHANGE IN TERMS AGREEMENT IS MADE IN CONJUNCTION WITH LETTER OF CREDIT NO. 1436, OR AS MAY BE AMENDED, EXTENDED OR RENEWED.

SUCCESSORS AND ASSIGNS. Subject to any limitations stated in this Agreement on transfer of Borrower’s interest, this Agreement shall be binding upon and inure to the benefit of the parties, their successors and assigns. If ownership of the Collateral becomes vested in a person other than Borrower, Lender, without notice to Borrower, may deal with Borrower’s successors with reference to this Agreement and the Indebtedness by way of forbearance or extension without releasing Borrower from the obligations of this Agreement or liability under the Indebtedness.

NOTIFY US OF INACCURATE INFORMATION WE REPORT TO CONSUMER REPORTING AGENCIES. Please notify us if we report any inaccurate information about your accountlsi to a consumer reporting agency. Your written notice describing the specific inaccuracy(ies) should be sent to us at the following address: COLORADO BUSINESS BANK ATTN: LOAN OPERATIONS 821 17TH STREET DENVER, CO 80202.

MISCELLANEOUS PROVISIONS. If any part of this Agreement cannot be enforced, this fact will not affect the rest of the Agreement. Lender may delay or forgo enforcing any of its rights or remedies under this Agreement without losing them. Borrower and any other person who signs, guarantees or endorses this Agreement, to the extent allowed by law, waive presentment, demand for payment, and notice of dishonor. Upon any change in the terms of this Agreement, and unless otherwise expressly stated in writing, no party who signs this Agreement, whether as maker, guarantor, accommodation maker or endorser, shall be released from liability. All such parties agree that Lender may renew or extend

parties also agree that Lender may modify this loan without the consent of or notice to anyone other than the party with whom the modification is made. The obligations under this Agreement are joint and several.

PRIOR TO SIGNING THIS AGREEMENT, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS OF THIS AGREEMENT, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS. BORROWER AGREES TO THE TERMS OF THE AGREEMENT.

ASSIGNMENT OF DEPOSIT ACCOUNT

References in the boxes above are for Lender’s use only and do not limit the applicability of this document to any particular loan or Item.

Any item above containing “ • •” h as been o mitted due to text length limitations.

THIS ASSIGNMENT OF DEPOSIT ACCOUNT dated August 15, 2008, Is tried* and executed among ADA ENVIRONMENTAL SOLUTIONS LLC (“Grantor”); ADA-ES, INC. (“Borrower”); and COLORADO BUSINESS BANK (“Lender”).

ASSIGNMENT. For valuable consideration, Grantor assigns and grants to Lender a security Interest in the Collateral, including without limitation the deposit accounts described below, to secure the Indebtedness and agrees that Lender shall have the rights stated in this Agreement with respect to the Collateral, in addition to all other rights which tender may have by law.

COLLATERAL DESCRIPTION. The word ‘Collateral’ means the following described deposit account [‘Account”):

COLORADO BUSINESS BANK MONEY MARKET ACCOUNT NO. 7100701 with Lender with an approximate balance of $4,086,595.49

together with (A) all interest, whether now accrued or hereafter accruing; (B) all additional deposits hereafter made to the Account; (C) any and all proceeds from the Account; and (D) all renewals, replacements and substitutions for any of the foregoing.

In addition, the word “Collateral’ includes all of Grantor’s property (however owned if owned by more that one person or entity), In Lender’s possession (or in the possession of a third party subject to Lander’