Under the Securities Exchange Act of 1934
(Amendment No. 4)*

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Name, Address and Telephone Number of Person
Authorized to Receive Notices and Communications)

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. o

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits.  See §240.13d-7 for other parties to whom copies are to be sent.

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

* As a result of the Shareholders’ Agreement described in Item 6 of the initial Schedule 13D and Item 5 of this Amendment No. 4, the Reporting Persons may be deemed to be the beneficial owners of shares of the Issuer’s common stock beneficially owned by Wilon Holdings S.A. and Wayne Hoovestol.  Based on the most recent information filed with the SEC, Wilon Holdings S.A. beneficially owns 2,070,716 shares of the Issuer’s common stock, representing approximately 6.6% of the outstanding common stock of the Issuer, and Wayne Hoovestol beneficially owns 946,592 shares of the Issuer’s common stock, representing approximately 3.0% of the outstanding common stock of the Issuer.  Each Reporting Person expressly disclaims beneficial ownership of the shares beneficially owned by Wilon Holdings S.A. and Wayne Hoovestol.

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* As a result of the Shareholders’ Agreement described in Item 6 of the initial Schedule 13D and Item 5 of this Amendment No. 4, the Reporting Persons may be deemed to be the beneficial owners of shares of the Issuer’s common stock beneficially owned by Wilon Holdings S.A. and Wayne Hoovestol.  Based on the most recent information filed with the SEC, Wilon Holdings S.A. beneficially owns 2,070,716 shares of the Issuer’s common stock, representing approximately 6.6% of the issued and outstanding common stock of the Issuer, and   Wayne Hoovestol beneficially owns 946,592 shares of the Issuer’s common stock, representing approximately 3.0% of the outstanding common stock of the Issuer.  Each Reporting Person expressly disclaims beneficial ownership of the shares beneficially owned by Wilon Holdings S.A. and Wayne Hoovestol.

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* As a result of the Shareholders’ Agreement described in Item 6 of the this Amendment No. 4, the Reporting Persons may be deemed to be the beneficial owners of shares of the Issuer’s common stock beneficially owned by Wilon Holdings S.A. and Wayne Hoovestol.  Based on the most recent information filed with the SEC, Wilon Holdings S.A. beneficially owns 2,070,716 shares of the Issuer’s common stock, representing approximately 6.6% of the issued and outstanding common stock of the Issuer, and Wayne Hoovestol beneficially owns 946,592 shares of the Issuer’s common stock, representing approximately 3.0% of the outstanding common stock of the Issuer.  Each Reporting Person expressly disclaims beneficial ownership of the shares beneficially owned by Wilon Holdings S.A. and Wayne Hoovestol.

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This Amendment No. 4 to Schedule 13D/A (this “Amendment No. 4”) is being filed to amend and supplement (i) the Schedule 13D filed by the Reporting Persons with the Securities and Exchange Commission (“SEC”) on October 27, 2008 (the “initial Schedule 13D”), (ii) Amendment No. 1 to Schedule 13D filed by the Reporting Persons with the SEC on November 4, 2008 (“Amendment No. 1”), (iii) Amendment No. 2 to Schedule 13D filed by the Reporting Persons with the SEC on February 17, 2010 (“Amendment No. 2”) and (iii) Amendment No. 3 to Schedule 13D filed by the Reporting Persons with the SEC on March 19, 2010 (“Amendment No. 3”) (collectively with the foregoing, this “Schedule 13D/A”).  Except as specifically amended by this Amendment No. 4, the initial Schedule 13D, Amendment No. 1, Amendment No. 2 and Amendment No. 3 remain unchanged.  Capitalized terms used and not otherwise defined in this Amendment No. 4 have the meanings given them in the initial Schedule 13D, Amendment No. 1, Amendment No. 2 and Amendment No. 3, as applicable.

This Amendment No. 4 is being filed pursuant to Exchange Act Rule 13d-2(a) to report a transfer of 5,234,000 shares from NTR US Biosystems Holdings Limited to Greenstar North America Holdings, Inc.

Item 2. Identity and Background

This Amendment No. 4 is being filed on behalf of each of the following reporting persons (collectively, the “Reporting Persons”):

NTR plc, a public limited company registered in Ireland (“NTR”), which has its principal office address at Burton Court, Burton Hall Drive, Sandyford, Dublin 18, Ireland. NTR is a leading international developer and operator of renewable energy and sustainable waste management projects.

NTR US Biosystems Holdings Limited, a company organized under the laws of Ireland (“Biosystems”), which has its principal office address at Burton Court, Burton Hall Drive, Sandyford, Dublin 18, Ireland. Biosystems is a holding company and a wholly owned subsidiary of NTR.

Greenstar North America Holdings, Inc., a Delaware corporation (“Greenstar”), which has its principal office address at 3411 Richmond Avenue, Suite 700 Houston TX 77046. Greenstar is a holding company and a wholly owned subsidiary of NTR.

As the ultimate parent of Biosystems and Greenstar, NTR beneficially owns the shares of common stock held of record by Greenstar as described in this Amendment No. 4.

Amendment No. 2 to the Joint Filing Agreement among the Reporting Persons to file this Amendment No. 4 jointly in accordance with Rule 13d-1(k) of the Securities Exchange Act of 1934 is attached as Exhibit (m); the Joint Filing Agreement, as amended by Amendment No. 1, was filed previously as Exhibit (k) and is incorporated herein by reference.  Certain information contained in this Schedule 13D/A relates to share ownership of persons other than the Reporting Persons. The Reporting Persons expressly disclaim any liability for any such information provided in this Schedule 13D/A that does not expressly pertain to a Reporting Person.

During the last five years, none of the Reporting Persons has been (a) convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) nor (b) a party to a civil proceeding of a judicial or administrative body of competent jurisdiction as a result of which it was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws finding any violation with respect to such laws.

Item 3.  Source and Amount of Funds or Other Consideration

Pursuant to an Assignment and Assumption Agreement, effective May 25, 2010, Biosystems transferred and assigned 5,234,000 shares of the Issuer’s common stock (the “Shares”) to its affiliate, Greenstar, and Biosystems received as consideration shares of Greenstar’s common stock.  No cash was exchanged between the parties in connection with the transfer.  Biosystems and Greenstar are each wholly owned subsidiaries of NTR, which remains the indirect beneficial owner of the Shares.   The Shares were originally acquired on October 15, 2008.

SEC 1746 (3-06)

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Item 5.  Interest in Securities of the Issuer

As described in Item 3, Biosystems transferred and assigned the Shares to its affiliate, Greenstar, and received as consideration shares of Greenstar’s common stock.  Biosystems and Greenstar are each wholly owned subsidiaries of NTR, and following the transaction NTR remains the indirect beneficial owner of the Shares.  Following the transfer of shares from Biosystems to Greenstar, the Reporting Persons continue to beneficially own 11,227,653 shares of Issuer’s common stock, or approximately 35.8% of the outstanding common stock of the Issuer.

Additionally, as a result of the Shareholders’ Agreement by and among the Issuer, Bioverda International Holdings Ltd., Biosystems, Wilon Holdings S.A. and Wayne Hoovestol, the Reporting Persons may also be deemed to be the beneficial owners of shares of the Issuer’s common stock beneficially owned by Wilon and Mr. Hoovestol.  Based on the most recent information filed with the SEC, Wilon Holdings S.A. beneficially owns 2,070,716 shares of the Issuer’s common stock, representing approximately 6.6% of the outstanding common stock of the Issuer, and Mr. Hoovestol beneficially owns 946,592 shares of the Issuer’s common stock, representing approximately 3.0% of outstanding common stock of the Issuer. Each Reporting Person expressly disclaims beneficial ownership of the shares beneficially owned by Wilon Holdings S.A. and Mr. Hoovestol.

Item 7.  Material to be Filed as Exhibits

Exhibits (a) — (l) listed below have been previously filed as exhibits (as indicated below) and are incorporated by reference in this Schedule 13D/A by reference thereto.  Exhibits (m) and (n) are filed herewith.

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Signature

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

The original statement shall be signed by each person on whose behalf the statement is filed or his authorized representative. If the statement is signed on behalf of a person by his authorized representative (other than an executive officer or general partner of the filing person), evidence of the representative’s authority to sign on behalf of such person shall be filed with the statement: provided, however, that a power of attorney for this purpose which is already on file with the Commission may be incorporated by reference. The name and any title of each person who signs the statement shall be typed or printed beneath his signature.

ATTENTION:  Intentional misstatements or omissions of fact constitute Federal Criminal Violations (See 18 U.S.C. 1001)

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