Exhibit 10.6

FOURTH AMENDMENT TO CREDIT AGREEMENT

FOURTH AMENDMENT TO CREDIT AGREEMENT dated as of September 15, 2008 (this
“Fourth Amendment”), among CALGON CARBON CORPORATION, a corporation organized
under the laws of the State of Delaware (the “Company”), CALGON CARBON
INVESTMENTS INC., a corporation organized under the laws of the State of
Delaware (“Calgon Investments”), CHEMVIRON CARBON LIMITED, a private company
limited by shares organized under the laws of England and Wales with company
number 02208285 (“Chemviron”), WATERLINK (UK) HOLDINGS LIMITED, a private
company limited by shares organized under the laws of England and Wales with
company number 03181974 (“Waterlink”), SUTCLIFFE SPEAKMAN LIMITED, a private
company limited by shares organized under the laws of England and Wales with
company number 029081113 (“Sutcliffe”), LAKELAND PROCESSING LIMITED, a private
company limited by shares organized under the laws of England and Wales with
company number 02926645 (“Lakeland”), CHARCOAL CLOTH (INTERNATIONAL) LIMITED, a
private company limited by shares organized under the laws of England and Wales
with company number 02743909 (“Charcoal International”), BSC COLUMBUS, LLC, a
limited liability company organized under the laws of the State of Delaware
(“BSC”), and CCC COLUMBUS LLC, a limited liability company organized under the
laws of the State of Delaware (“Columbus”), the Lenders party hereto, J.P.
MORGAN EUROPE LIMITED, as the European Administrative Agent, JPMORGAN CHASE
BANK, N.A., as the US Administrative Agent, and J.P. MORGAN SECURITIES, INC., as
Sole Bookrunner and Sole Lead Arranger.
 
WHEREAS, the Loan Parties are party to a Credit Agreement dated as of August 18,
2006, as amended (the “Existing Credit Agreement”), with the Lenders party
thereto (the “Lenders”) and the Administrative Agents party thereto (as further
amended and modified by this Fourth Amendment and as the same may be further
amended, modified, supplemented or restated from time to time, the “Credit
Agreement”); and
 
WHEREAS, the Loan Parties, the Administrative Agents and the Lenders have agreed
to amend Section 5.10(a) of the Credit Agreement as more fully set forth below.
 
NOW, THEREFORE, in consideration of the foregoing and the agreements contained
herein, the parties hereby agree as follows:
 
1. Capitalized Terms.
 
Capitalized terms used herein which are defined in the Credit Agreement have the
same meanings herein as therein, except to the extent that such meanings are
amended hereby.
 
2. Amendment to Credit Agreement.
 
Subject to the terms and conditions set forth herein and in reliance on the
representations set forth in Section 3 hereof, the Loan Parties, the Lenders and
the Administrative Agents agree that Section 5.10(a) of the Credit Agreement be,
and it hereby is, amended, by deleting Section 5.10(a) of the Credit Agreement
and replacing it with the following new Section 5.10(a):
 
“(a) Each Loan Party will, and will cause each Subsidiary to, (i) maintain with
financially sound and reputable carriers having a financial strength rating of
at least A- by A.M. Best Company (a) insurance in such amounts (with no greater
risk retention) and against such risks (including loss or damage by fire and
loss in transit; theft, burglary, pilferage, larceny, embezzlement, and other
criminal activities; business interruption; and general liability) and such
other hazards, as is customarily maintained by companies of established repute
engaged in the same or similar businesses operating in the same or similar
locations and (b) all insurance required pursuant to the Collateral Documents;
(ii) maintain such other insurance as may be required by law; and (iii) upon
request by an Administrative Agent, which request need not be made in writing,
furnish the Administrative Agents with certificates evidencing the insurance
required by this paragraph. In the event of Loan Parties’ failure to obtain or
maintain the insurance required by this paragraph, the Administrative Agents
shall have the right to obtain the required coverage and bill the applicable
Borrowers for the premium payments therefor.”

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3. No Default; Representations and Warranties, etc.
 
Each of the Loan Parties represents and warrants to the Lenders and the
Administrative Agents that as of the date hereof and after giving effect to the
amendments set forth herein (a) the representations of the Loan Parties
contained in Article III of the Credit Agreement are true and correct in all
material respects as of the date hereof as if made on such date (except to
extent that such representations and warranties expressly relate to an earlier
date, in which case they shall be true and correct in all material respects as
of such date); (b) the Loan Parties are in compliance in all material respects
with all of the terms and provisions set forth in the Credit Agreement and the
other Loan Documents to be observed or performed by them thereunder; (c) no
Default shall have occurred and be continuing; and (d) the execution, delivery
and performance by the Loan Parties of this Fourth Amendment (i) have been duly
authorized by all necessary corporate and, if required, shareholder action on
the part of the Loan Parties, (ii) will not violate any applicable material law
or regulation or the organizational documents of any Loan Party, (iii) will not
violate or result in a default under any material indenture, agreement or other
instrument binding on any Loan Party or any of its assets and (iv) do not
require any consent, waiver or approval of or by any Person (other than the
Administrative Agents and the Lenders) which has not been obtained.
 
4. Effective Date.
 
Upon receipt by the Administrative Agents from each party hereto of either (i) a
counterpart of this Fourth Amendment signed on behalf of such party or (ii)
written evidence reasonably satisfactory to the Administrative Agents (which may
include telecopy transmission of a signed signature page to this Fourth
Amendment) that such party has signed a counterpart of this Fourth Amendment,
the amendments set forth in this Fourth Amendment shall be deemed to be
effective as of the date of this Fourth Amendment.
 
5. Confirmation of Guarantee and Collateral Documents.
 
Each Loan Guarantor hereby confirms that all Obligations of the Borrowers under
the Credit Agreement are and shall continue to be entitled to the benefits of
the guarantee set forth in Article X of the Credit Agreement, and each Loan
Party hereby confirms that the Obligations under the Credit Agreement, and in
respect of its guarantee under Article X of the Credit Agreement (in the case of
the Loan Guarantors), are and shall continue to be entitled to the benefits of
the collateral security provided by the Collateral Documents. Each Affiliate or
Subsidiary of any Loan Party that is a party to any Other Collateral Documents
hereby confirms that the Obligations under the Credit Agreement are and shall
continue to be entitled to the benefits of the collateral security provided by
the Other Collateral Documents.

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6. Miscellaneous.
 
(a) The Loan Parties, the Lenders and the Administrative Agents hereby ratify
and confirm the terms and provisions of the Credit Agreement and the other Loan
Documents and agree that, except to the extent specifically amended hereby, the
Credit Agreement, the other Loan Documents and all related documents shall
remain in full force and effect. Nothing contained herein shall constitute an
amendment or waiver of any provision of the Loan Documents, except such
amendments as are expressly set forth herein.
 
(b) The Loan Parties jointly and severally agree to pay all reasonable
out-of-pocket costs and expenses incurred by JPMorgan Chase Bank, N.A. and its
respective Affiliates (including the reasonable fees, charges and disbursements
of counsel for the Agent), in connection with the preparation of this Fourth
Amendment.
 
(c) This Fourth Amendment may be executed in any number of counterparts
(including by way of facsimile transmission), each of which, when executed and
delivered, shall be an original, but all counterparts shall together constitute
one instrument.
 
(d) This Fourth Amendment shall be governed by the laws of the State of New York
and shall be binding upon and inure to the benefit of the parties hereto and
their respective successors and assigns.
 
[Signature Pages Follow]

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IN WITNESS WHEREOF, the parties hereto have caused this Fourth Amendment to be
duly executed by their respective authorized officers as of the day and year
first above written.
 
BORROWERS:
 
CALGON CARBON CORPORATION
   
By:
/s/ Leroy M. Ball
 
Name: Leroy M. Ball
 
Title: Director
   
CALGON CARBON INVESTMENTS, INC.
   
By:
/s/ Leroy M. Ball
 
Name: Leroy M. Ball
 
Title: Director
   
BSC COLUMBUS, LLC
   
By:
/s/ Leroy M. Ball
 
Name: Leroy M. Ball
 
Title: Director
   
CCC COLUMBUS, LLC
   
By:
/s/ Leroy M. Ball
 
Name: Leroy M. Ball
 
Title: Director

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EXECUTED AND DELIVERED as a Deed by
CHEMVIRON CARBON LIMITED acting by:
   
Director:
/s/ C.H.S.(Kees)Majoor
   
Director/secretary:  C.H.S. (Kees) Majoor
   
EXECUTED AND DELIVERED as a Deed by
WATERLINK (UK) HOLDINGS LIMITED acting by:
   
Director:
/s/ C.H.S.(Kees)Majoor
   
Director/secretary:  C.H.S. (Kees) Majoor
 
EXECUTED AND DELIVERED as a Deed by
SUTCLIFFE SPEAKMAN LIMITED acting by:
   
Director:
/s/ C.H.S.(Kees)Majoor
   
Director/secretary:  C.H.S. (Kees) Majoor
 
EXECUTED AND DELIVERED as a Deed by
LAKELAND PROCESSING LIMITED acting by:
   
Director:
/s/ C.H.S.(Kees)Majoor
   
Director/secretary: C.H.S. (Kees) Majoor
 
EXECUTED AND DELIVERED as a Deed by
CHARCOAL CLOTH (INTERNATIONAL)
 
LIMITED acting by:
   
Director:
/s/ C.H.S.(Kees)Majoor
   
Director/secretary:  C.H.S. (Kees) Majoor

 
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ADMINISTRATIVE AGENTS AND LENDERS:
 
JPMORGAN CHASE BANK, N.A., as
US Administrative Agent and as a Lender
   
By:
/s/ Donna DiForio
 
Name:  Donna DiForio
 
Title:    Vice President
   
J.P. MORGAN EUROPE LIMITED, as
European Administrative Agent
 
By:
/s/ Tim Jacob
 
Name:   Tim Jacob
 
Title: Senior Vice President
   
CITIZENS BANK OF PENNSYLVANIA,
as a Lender
   
By:
/s/ Paul Rebholz
 
Name:  Paul Rebholz
 
Title:    Vice President

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