EXHIBIT 10.22

                                CONVERTIBLE NOTE


San Mateo, California
April 30, 1997                                                     $399,201.60

         FOR VALUE RECEIVED, EMCON, a California corporation (hereinafter called
the  "Borrower"),  hereby  promises  to  pay  to  Charles  H.  Gearhart,  or his
respective  registered assigns (the "Holder") or order, the sum of Three Hundred
Ninety-Nine  Thousand Two Hundred One Dollars and Sixty Cents ($399,201.60) (the
"Principal"),  on May 1,  2002,  and to pay  interest  on the  unpaid  principal
balance  hereof at the rate of eight percent (8%) per annum from the date hereof
until the same becomes due and payable.  Interest shall commence accruing on the
date hereof and shall be payable  quarterly on each July 31, October 31, January
31 and April 30 beginning on July 31, 1997, with all interest  remaining  unpaid
at maturity due at such time.  All payments of principal  and interest  shall be
made in lawful money of the United States of America. All payments shall be made
at the  address  of the  Holder,  as set forth in  Section  6.4 hereof or as the
Holder shall hereafter give to the Borrower by written notice made in accordance
with the provisions of this Note.

         The following terms shall apply to this Note:

                                    ARTICLE I

                         PROHIBITION AGAINST PREPAYMENT

         1.1      Borrower shall have no right to prepay this Note at any time.

                                   ARTICLE II

                        CONVERSION INTO BORROWER'S STOCK

     Holder shall have the right to convert the  Principal  into shares of EMCON
Common  Stock  pursuant  to the terms of this  Article  II. In such  event,  any
accrued but unpaid interest shall be immediately due and payable.

     2.1 Conversion Price. The number of shares of EMCON Common Stock into which
the Principal shall be converted  shall be the amount of the Principal,  divided
by the EMCON Conversion Price. The EMCON Conversion Price shall initially be Six
Dollars and Fifty Cents  ($6.50),  and shall be adjusted as set forth in Section
2.2. hereof.

     2.2 Adjustment to EMCON Conversion  Price. The EMCON Conversion Price shall
be adjusted as set forth in this Section 2.2.

                  (a) Subdivisions. In case Borrower shall at any time subdivide
the  outstanding  shares of EMCON Common Stock,  the EMCON  Conversion  Price in




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effect immediately prior to such subdivision shall be proportionately decreased,
and in case the  Company  shall at any time  combine the  outstanding  shares of
EMCON Common Stock, the EMCON Conversion  Price in effect  immediately  prior to
such combination shall be proportionately  increased,  effective at the close of
business on the date of such subdivision or combination, as the case may be.

                  (b) Stock Dividends.  In case Borrower shall at any time pay a
dividend with respect to EMCON Common Stock payable in EMCON Common Stock,  then
the EMCON  Conversion Price in effect  immediately  prior to the record date for
distribution  of such  dividend  shall be adjusted to that price  determined  by
multiplying  the  EMCON  Conversion  Price in effect  immediately  prior to such
record date by a fraction  (i) the  numerator of which shall be the total number
of shares of EMCON Common Stock  outstanding  immediately prior to such dividend
and (ii) the  denominator  of which shall be the total number of shares of EMCON
Common Stock outstanding immediately after such dividend.

                  (c)    Reclassification    or   Merger.   In   case   of   any
reclassification,  change or conversion of the EMCON Common Stock (other than as
a result of a subdivision or combination described above and other than upon any
Acceleration Event, as defined below), Borrower shall have the right to receive,
upon  exchange of this Note  (which may occur at the option of the Holder  only)
the kind and amount of shares of stock,  other  securities,  money and  property
receivable upon such  reclassification,  change or conversion by a holder of the
number of shares of EMCON  Common  Stock  into  which  this Note  could  then be
exchanged.  The provisions of this  subparagraph  (c) shall  similarly  apply to
successive reclassifications, changes, and conversions.

         2.3  Authorized  Shares.  EMCON  convenants  that during the period the
conversion  right set forth in this Article exists,  EMCON will reserve from the
authorized  and unissued  EMCON  Common  Stock a sufficient  number of shares to
provide for the issuance of EMCON Common Stock upon the full  conversion  of the
Principal.  EMCON  represents  that upon issuance,  such shares will be duly and
validly issued, fully paid and non-assessable.

         2.4 Method of  Exchange.  Except as  otherwise  agreed by EMCON and the
Holder,  the Principal  balance of the Note may be converted in whole or in part
(provided at least $250,000 in Principal is converted) in up to two installments
by (i)  submitting  to EMCON a  conversion  notice  setting  forth the amount of
Principal to be converted and (ii)  surrendering  the Note held by the Holder at
the principle  office of EMCON. In the event of a partial  conversion EMCON will
thereafter  reissue a new Note for the  remaining  unpaid  Principal  balance or
terms otherwise identical to those set forth herein.

         2.5  Restrictions  Concerning  the Shares.  The shares of EMCON  Common
Stock to be held by the Holder pursuant to the exercise of the conversion rights
set forth herein may not be sold or  transferred  unless  either (i) such shares
first shall have been  registered  under the  Securities Act of 1933 (the "Act")
and  applicable  state  securities  laws or (ii) EMCON shall have been furnished
with an opinion of legal  counsel to the effect  that such sale or  transfer  is
exempt from the  registration  requirements of the Act and all applicable  state
securities laws. Each certificate for shares of EMCON Common Stock to be held by
the Holder that have not been so registered and that have not been sold pursuant
to an  exemption  that  permits  removal  of the  legend,  shall  bear a  legend
substantially in the following form, as appropriate:


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         THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
         UNDER THE SECURITIES ACT OF 1933, AS AMENDED.  THE SECURITIES HAVE BEEN
         ACQUIRED FOR INVESTMENT AND MAY NOT BE SOLD, TRANSFERRED OR ASSIGNED IN
         THE ABSENCE OF AN EFFECTIVE  REGISTRATION  STATEMENT FOR THE SECURITIES
         UNDER THE SECURITIES ACT OF 1933, AS AMENDED,  OR AN OPINION OF COUNSEL
         THAT REGISTRATION IS NOT REQUIRED UNDER SAID ACT.

Upon the request of the Holder, EMCON shall remove the foregoing legend from the
certificate representing the EMCON Common Stock held by the Holder upon exercise
of the conversion  rights or issue to Holder a new certificate  therefor free of
any transfer legend, if, with such request, EMCON shall have received either (i)
an opinion of counsel  to the effect  that any such  legend may be removed  from
such  certificate,  or  (ii)  if the  present  paragraph  (k) of  Rule  144 or a
substantially  similar successor rule remains in force and effect,  satisfactory
representations from the Holder that Holder is not then, and has not been during
the proceeding three (3) months,  an affiliate of EMCON, and that a period of at
least two (2) years has elapsed since the later of the date the securities  were
acquired (as determined under Rule 144) from EMCON or an affiliate of EMCON.

         2.6      EMCON Registration.

                  (a)  If,  EMCON  shall   determine  to  register  any  of  its
securities  either for its own  account or the  account of a security  holder or
holders,  other than a registration  relating to employee  benefit  plans,  or a
registration relating solely to a Rule 145 transaction, or a registration on any
registration form that does not permit secondary sales, EMCON will:

                    (i) promptly give the Holder written notice thereof;

                    (ii) use its best  efforts to  include in such  registration
(and any related qualification under blue sky laws or other compliance),  except
as set forth in Section 2.6 (b) below, and in any underwriting involved therein,
all the shares of EMCON Common Stock  issued upon  conversion  of this Note (the
"Holder's Shares") specified in a written request or requests made by the Holder
and  received by EMCON  within  twenty  (20) days after the written  notice from
EMCON  described  in clause  (i) above is mailed  or  delivered  by EMCON.  Such
written request may specify all or a part of the Holder's Shares;

                    (iii)  furnish  such  number  of   prospectuses   and  other
documents  incident  thereto,  including  any  amendment of or supplement to the
prospectus, as the Holder from time to time may reasonably request;

                    (iv) cause all such EMCON Common Stock  registered  pursuant
hereunder to be listed on each securities  exchange on which similar  securities
issued by EMCON are then listed.

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                  (b) If the  registration  of which EMCON gives notice is for a
registered public offering involving an underwriting,  EMCON shall so advise the
Holder as a part of the written notice given pursuant to Section  2.6(a)(i).  In
such event,  the right of Holder to  registration  pursuant to this  Section 2.6
shall be conditioned upon Holder's  participation  in such  underwriting and the
inclusion  of the Holder's  Shares in the  underwriting  to the extent  provided
herein.  The  Holder  shall  (together  with  EMCON  and the  other  holders  of
securities of EMCON with registration rights to participate therein distributing
their securities through such underwriting) enter into an underwriting agreement
in customary form with the  representative  of the  underwriter or  underwriters
selected by EMCON.

                  (c)  Notwithstanding  any other provision of this Section 2.6,
if  the  representative  of the  underwriters  advises  EMCON  in  writing  that
marketing   factors  require  a  limitation  on  the  number  of  shares  to  be
underwritten,  the  representative  may  (subject tot he  limitations  set forth
below)  exclude all Holder's  Shares  from,  or limit the number of the Holder's
Shares to be included  in, the  registration  and  underwriting.  EMCON shall so
advise the Holder and all other holders of EMCON securities (the "Other Shares")
requesting  registration and the number of Holder's Shares and Other Shares that
may be  included  shall  be  allocated  amount  the  Holder  and  other  selling
stockholders  requesting inclusion of shares pro rata on the basis of the number
of Holder's Shares and Other Shares that are requested to be registered.

                  (d) EMCON's  obligations  pursuant  to this  Section 2.6 shall
expire at such time as Holder may sell all Holder's Shares during any successive
two quarter period pursuant to Rule 144 under the Act.

                  (e)  All  Registration   Expenses  (as  hereinafter   defined)
incurred  in  connection  with any  registration,  qualification  or  compliance
pursuant  to this  Section  2.6  hereof  shall be borne by  EMCON.  All  Selling
Expenses (as hereinafter  defined) relating to securities so registered shall be
borne by the Holder. For purposes hereof,  Registration  Expenses shall mean all
expenses  incurred  in  effecting  any  registration   pursuant  to  this  Note,
including, without limitation, all registration, qualification, and filing fees,
printing  expenses,  escrow fees, fees and  disbursements  of counsel for EMCON,
blue sky fees and  expenses,  and  expenses  of any  regular or  special  audits
incident to or required by any such registration,  but shall not include Selling
Expenses  and fees and  disbursements  of counsel for Holder.  Selling  Expenses
shall mean all underwriting  discounts and selling commissions applicable to the
sale of the  Holder's  Shares and fees and  disbursements  of counsel for Holder
(other  than the fees and  disbursements  of counsel  included  in  Registration
Expenses).

                                   ARTICLE III

                                     OFFSET

         3.1 Offset. The Holder acknowledges that this Note is being made by the
Borrower  pursuant to that certain Stock Purchase  Agreement,  dated as of April
30,  1997,  by and among the  Borrower,  Organic  Waste  Technologies,  Inc.,  a
Delaware  corporation  and the  holders  of the  outstanding  capital  stock  of
National  Earth  Products,  Inc. (the "Stock  Purchase  Agreement").  The Holder
further acknowledges that he or she is bound by the Stock Purchase Agreement and
that the  Principal  due  hereunder  may be reduced by any  amounts due from the
Holder to Borrower pursuant thereto.

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                                   ARTICLE IV

                                  ACCELERATION

         4.1 Notwithstanding  anything to the contrary herein, in the event that
any of the events set forth in Section 4.1 (each, an "Acceleration Event") shall
occur at any time after the date hereof,  then, subject to the qualification set
forth below,  the Principal and all interest thereon shall, at the option of the
Holder, be immediately due and payable.

                  (a) upon a  consolidation  or merger of EMCON with or into any
other corporation or corporations (other than a wholly-owned subsidiary of EMCON
and other than a merger in which  EMCON is the  surviving  corporation),  or the
sale, transfer or other disposition of all or substantially all of the assets of
EMCON;

                  (b) upon a change in ownership of Fifty  Percent (50%) or more
of the stock of Borrower  to a single  buyer or an  affiliated  group of buyers,
resulting in a change in the majority of the Board of Directors of Borrower from
the  Board of  Directors  as it  existed  immediately  prior to such  change  in
ownership;

                  (c) upon the  liquidation,  dissolution  or  winding up of the
Borrower or the  consolidation  or merger of the Borrower  with and into another
corporation  (other  than a  merger  in  which  the  Borrower  is the  surviving
corporation);

         provided, however, that upon any Acceleration Event, no amount shall be
due and payable  hereunder in the event that the Holder has exchanged  this Note
for Common Stock of EMCON, pursuant to the Note Agreement.

                                    ARTICLE V

                                EVENTS OF DEFAULT

         If any of the following events of default (each, an "Event of Default")
shall occur:

          5.1.  Failure to Pay Principal or Interest.  The Borrower fails to pay
the Principal or interest when due;

         5.2 Receiver or Trustee.  The Borrower shall make an assignment for the
benefit of creditors,  or apply for or consent to the  appointment of a receiver
or trustee for it or for a substantial part of its property or business, or such
a receiver or trustee shall otherwise be appointed;

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          5.3 Bankruptcy. Bankruptcy, insolvency,  reorganization or liquidation
proceedings or other  proceedings for relief under any bankruptcy law or any law
for relief of debtors shall be instituted by or against the Borrower,

         then upon the  occurrence and during the  continuation  of any Event of
Default,  then, at the option of the Holder,  the Principal and all interest due
thereon shall be  immediately  due and payable,  and the Borrower shall have all
other remedies available at law or equity.

                                   ARTICLE VI

                                  MISCELLANEOUS

         6.1 Late  Charge.  The  Borrower  shall pay to the Holder a late charge
equal to 1.5% per month, but not to exceed the maximum rate allowable by law, on
any amount due hereunder that is not received by the Holder within 10 days after
the date on which such amount is due. Borrower agrees that it would be extremely
difficult or impractical  to determine the Holder's  actual damages in the event
of such late payment,  that the amount specified above is a reasonable  estimate
of such damages and that such amount  shall  constitute  liquidated  damages for
such late payment.  The foregoing provision shall not be construed to extend the
due date for any amount required to be paid hereunder.  The Holder shall have no
obligation to accept any late payment not accompanied by such late charge.

         6.2  Collection  Costs and Expenses.  The Borrower shall pay all costs,
fees and expenses (including court costs and reasonable attorneys fees) incurred
by the Holder in collecting or attempting to collect any amount that becomes due
hereunder or in seeking legal advice with respect to such collection or an Event
of Default.

         6.3 Failure or Indulgence Note Waiver.  No failure or delay on the part
of the Holder 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 privileges.

         6.4 Notices. All notices,  consents,  waivers, and other communications
under this  Agreement  must be in  writing  and will be deemed to have been duly
given when (a) delivered by hand (with  written  confirmation  of receipt),  (b)
sent by telecopier (with written confirmation of receipt),  provided that a copy
is mailed  within three (3) business  days by registered  mail,  return  receipt
requested,  (c)  when  received  by  the  addressee,  if  sent  by a  nationally
recognized  overnight  delivery  service (receipt  requested),  or (d) three (3)
business days after being sent by registered or certified  mail,  return receipt
requested,  in each case to the appropriate addresses and telecopier numbers set
forth below (or to such other  addresses and  telecopier  numbers as a party may
designate by notice to the other parties):

         Holder:  Charles H. Gearhart
                           1054 Hunters Path
                           Lancaster,  PA  17601

         Borrower:         EMCON
                           400 South El Camino Real, Suite 1200
                           San Mateo, California  94402
                           Attn:  Chief Financial Officer
                           Facsimile: 415/375-0763



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         6.5 Amendment Provision.  The term "Note" and all reference thereto, as
used  throughout  this  instrument,  shall mean this  instrument  as  originally
executed,  or  if  later  amended  or  supplemented,   then  as  so  amended  or
supplemented.

          6.6 Governing Law. This Note shall be governed by the internal laws of
the State of California, without regard to the principles of conflict of laws.

         6.7  Confession  of  Judgment.  THE  FOLLOWING  PARAGRAPH  SETS FORTH A
WARRANT OF ATTORNEY TO CONFESS JUDGMENT  AGAINST THE BORROWER.  IN GRANTING THIS
WARRANT OF  ATTORNEY TO CONFESS  JUDGMENT  AGAINST THE  BORROWER,  THE  BORROWER
HEREBY KNOWINGLY,  INTENTIONALLY AND VOLUNTARILY, AND, ON THE ADVICE OF SEPARATE
COUNSEL OR THE BORROWER,  UNCONDITIONALLY WAIVES ANY AND ALL RIGHTS THE BORROWER
HAS OR MAY HAVE TO  PRIOR  NOTICE  AND AN  OPPORTUNITY  FOR  HEARING  UNDER  THE
RESPECTIVE  CONSTITUTIONS  AND LAWS OF THE UNITED STATES AND THE COMMONWEALTH OF
PENNSYLVANIA.

                  As further security for payment hereunder and upon an event of
default, Borrower authorizes and empowers any attorney of any court of record of
Pennsylvania  or  elsewhere  to appear for and CONFESS  JUDGMENT  against it and
immediately  execute  on  such  judgment,   without  notice  of  such  immediate
execution,  for the then  unpaid  principal  amount and  interest  of this Note,
together with late charges,  costs of suit and reasonable  attorneys' fees, with
or without  declaration  or stay of execution,  and with release of errors,  for
which this Note or a copy hereof shall serve as a sufficient warrant. This power
to CONFESS  JUDGMENT  against Borrower shall not be exhausted by any exercise of
the power  and shall  continue  from  time to time and at all times  until  full
payment of all amounts due under this Note.

         IN WITNESS  WHEREOF,  Borrower has caused this Note to be signed in its
name by its duly authorized officer as of the 30th day of April, 1997.

                     EMCON

                     By:  /S/
                          --------------------------------
                     Name: R. Michael Momboisse
                           --------------------------------
                     Title: CFO & VP Legal
                            ------------------------------




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                                CONVERTIBLE NOTE


San Mateo, California
April 30, 1997                                                 $400,798.40

         FOR VALUE RECEIVED, EMCON, a California corporation (hereinafter called
the  "Borrower"),  hereby  promises to pay to Dennis M. Grimm, or his respective
registered  assigns (the  "Holder") or order,  the sum of Four Hundred  Thousand
Seven  Hundred  Ninety  Eight  Dollars  and  Forty  Cents   ($400,798.40)   (the
"Principal"),  on May 1,  2000,  and to pay  interest  on the  unpaid  principal
balance  hereof at the rate of eight percent (8%) per annum from the date hereof
until the same becomes due and payable.  Interest shall commence accruing on the
date hereof and shall be payable  quarterly on each July 31, October 31, January
31 and April 30 beginning on July 31, 1997, with all interest  remaining  unpaid
at maturity due at such time.  All payments of principal  and interest  shall be
made in lawful money of the United States of America. All payments shall be made
at the  address  of the  Holder,  as set forth in  Section  6.4 hereof or as the
Holder shall hereafter give to the Borrower by written notice made in accordance
with the provisions of this Note.

         The following terms shall apply to this Note:

                                    ARTICLE I

                         PROHIBITION AGAINST PREPAYMENT

         1.1      Borrower shall have no right to prepay this Note at any time.

                                   ARTICLE II

                        CONVERSION INTO BORROWER'S STOCK

         Holder  shall have the right to convert  the  Principal  into shares of
EMCON Common Stock pursuant to the terms of this Article II. In such event,  any
accrued but unpaid interest shall be immediately due and payable.

         2.1 Conversion  Price.  The number of shares of EMCON Common Stock into
which the  Principal  shall be converted  shall be the amount of the  Principal,
divided  by the  EMCON  Conversion  Price.  The  EMCON  Conversion  Price  shall
initially be Six Dollars and Fifty Cents  ($6.50),  and shall be adjusted as set
forth in Section 2.2.
hereof.

          2.2 Adjustment to EMCON  Conversion  Price. The EMCON Conversion Price
shall be adjusted as set forth in this Section 2.2.

                  (a) Subdivisions. In case Borrower shall at any time subdivide
the  outstanding  shares of EMCON Common Stock,  the EMCON  Conversion  Price in
effect immediately prior to such subdivision shall be proportionately decreased,
and in case the  Company  shall at any time  combine the  outstanding  shares of
EMCON Common Stock, the EMCON Conversion  Price in effect  immediately  prior to
such combination shall be proportionately  increased,  effective at the close of
business on the date of such subdivision or combination, as the case may be.

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                  (b) Stock Dividends.  In case Borrower shall at any time pay a
dividend with respect to EMCON Common Stock payable in EMCON Common Stock,  then
the EMCON  Conversion Price in effect  immediately  prior to the record date for
distribution  of such  dividend  shall be adjusted to that price  determined  by
multiplying  the  EMCON  Conversion  Price in effect  immediately  prior to such
record date by a fraction  (i) the  numerator of which shall be the total number
of shares of EMCON Common Stock  outstanding  immediately prior to such dividend
and (ii) the  denominator  of which shall be the total number of shares of EMCON
Common Stock outstanding immediately after such dividend.

                  (c)    Reclassification    or   Merger.   In   case   of   any
reclassification,  change or conversion of the EMCON Common Stock (other than as
a result of a subdivision or combination described above and other than upon any
Acceleration Event, as defined below), Borrower shall have the right to receive,
upon  exchange of this Note  (which may occur at the option of the Holder  only)
the kind and amount of shares of stock,  other  securities,  money and  property
receivable upon such  reclassification,  change or conversion by a holder of the
number of shares of EMCON  Common  Stock  into  which  this Note  could  then be
exchanged.  The provisions of this  subparagraph  (c) shall  similarly  apply to
successive reclassifications, changes, and conversions.

         2.3  Authorized  Shares.  EMCON  convenants  that during the period the
conversion  right set forth in this Article exists,  EMCON will reserve from the
authorized  and unissued  EMCON  Common  Stock a sufficient  number of shares to
provide for the issuance of EMCON Common Stock upon the full  conversion  of the
Principal.  EMCON  represents  that upon issuance,  such shares will be duly and
validly issued, fully paid and non-assessable.

         2.4 Method of  Exchange.  Except as  otherwise  agreed by EMCON and the
Holder,  the Principal  balance of the Note may be converted in whole or in part
(provided at least $250,000 in Principal is converted) in up to two installments
by (i)  submitting  to EMCON a  conversion  notice  setting  forth the amount of
Principal to be converted and (ii)  surrendering  the Note held by the Holder at
the principle  office of EMCON. In the event of a partial  conversion EMCON will
thereafter  reissue a new Note for the  remaining  unpaid  Principal  balance or
terms otherwise identical to those set forth herein.

         2.5  Restrictions  Concerning  the Shares.  The shares of EMCON  Common
Stock to be held by the Holder pursuant to the exercise of the conversion rights
set forth herein may not be sold or  transferred  unless  either (i) such shares
first shall have been  registered  under the  Securities Act of 1933 (the "Act")
and  applicable  state  securities  laws or (ii) EMCON shall have been furnished
with an opinion of legal  counsel to the effect  that such sale or  transfer  is
exempt from the  registration  requirements of the Act and all applicable  state
securities laws. Each certificate for shares of EMCON Common Stock to be held by
the Holder that have not been so registered and that have not been sold pursuant
to an  exemption  that  permits  removal  of the  legend,  shall  bear a  legend
substantially in the following form, as appropriate:


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         THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
         UNDER THE SECURITIES ACT OF 1933, AS AMENDED.  THE SECURITIES HAVE BEEN
         ACQUIRED FOR INVESTMENT AND MAY NOT BE SOLD, TRANSFERRED OR ASSIGNED IN
         THE ABSENCE OF AN EFFECTIVE  REGISTRATION  STATEMENT FOR THE SECURITIES
         UNDER THE SECURITIES ACT OF 1933, AS AMENDED,  OR AN OPINION OF COUNSEL
         THAT REGISTRATION IS NOT REQUIRED UNDER SAID ACT.

Upon the request of the Holder, EMCON shall remove the foregoing legend from the
certificate representing the EMCON Common Stock held by the Holder upon exercise
of the conversion  rights or issue to Holder a new certificate  therefor free of
any transfer legend, if, with such request, EMCON shall have received either (i)
an opinion of counsel  to the effect  that any such  legend may be removed  from
such  certificate,  or  (ii)  if the  present  paragraph  (k) of  Rule  144 or a
substantially  similar successor rule remains in force and effect,  satisfactory
representations from the Holder that Holder is not then, and has not been during
the proceeding three (3) months,  an affiliate of EMCON, and that a period of at
least two (2) years has elapsed since the later of the date the securities  were
acquired (as determined under Rule 144) from EMCON or an affiliate of EMCON.

         2.6      EMCON Registration.

                  (a)  If,  EMCON  shall   determine  to  register  any  of  its
securities  either for its own  account or the  account of a security  holder or
holders,  other than a registration  relating to employee  benefit  plans,  or a
registration relating solely to a Rule 145 transaction, or a registration on any
registration form that does not permit secondary sales, EMCON will:

                    (i) promptly give the Holder written notice thereof;

                    (ii) use its best  efforts to  include in such  registration
(and any related qualification under blue sky laws or other compliance),  except
as set forth in Section 2.6 (b) below, and in any underwriting involved therein,
all the shares of EMCON Common Stock  issued upon  conversion  of this Note (the
"Holder's Shares") specified in a written request or requests made by the Holder
and  received by EMCON  within  twenty  (20) days after the written  notice from
EMCON  described  in clause  (i) above is mailed  or  delivered  by EMCON.  Such
written request may specify all or a part of the Holder's Shares;

                    (iii)  furnish  such  number  of   prospectuses   and  other
documents  incident  thereto,  including  any  amendment of or supplement to the
prospectus, as the Holder from time to time may reasonably request;

                    (iv) cause all such EMCON Common Stock  registered  pursuant
hereunder to be listed on each securities  exchange on which similar  securities
issued by EMCON are then listed.


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         (b) If the registration of which EMCON gives notice is for a registered
public offering involving an underwriting, EMCON shall so advise the Holder as a
part of the written notice given pursuant to Section  2.6(a)(i).  In such event,
the  right of Holder  to  registration  pursuant  to this  Section  2.6 shall be
conditioned upon Holder's  participation in such  underwriting and the inclusion
of the Holder's Shares in the  underwriting to the extent provided  herein.  The
Holder shall  (together  with EMCON and the other holders of securities of EMCON
with registration  rights to participate  therein  distributing their securities
through such  underwriting)  enter into an  underwriting  agreement in customary
form with the  representative  of the  underwriter or  underwriters  selected by
EMCON.

         (c)  Notwithstanding  any other  provision  of this Section 2.6, if the
representative  of the  underwriters  advises  EMCON in writing  that  marketing
factors  require a limitation  on the number of shares to be  underwritten,  the
representative  may (subject  tot he  limitations  set forth below)  exclude all
Holder's  Shares from, or limit the number of the Holder's Shares to be included
in, the registration and underwriting.  EMCON shall so advise the Holder and all
other holders of EMCON securities (the "Other Shares")  requesting  registration
and the number of Holder's Shares and Other Shares that may be included shall be
allocated amount the Holder and other selling stockholders  requesting inclusion
of shares  pro rata on the  basis of the  number of  Holder's  Shares  and Other
Shares that are requested to be registered.

         (d) EMCON's  obligations  pursuant to this  Section 2.6 shall expire at
such time as Holder  may sell all  Holder's  Shares  during any  successive  two
quarter period pursuant to Rule 144 under the Act.

         (e) All  Registration  Expenses (as  hereinafter  defined)  incurred in
connection with any registration,  qualification or compliance  pursuant to this
Section 2.6 hereof shall be borne by EMCON. All Selling Expenses (as hereinafter
defined) relating to securities so registered shall be borne by the Holder.  For
purposes  hereof,  Registration  Expenses  shall mean all  expenses  incurred in
effecting any registration pursuant to this Note, including, without limitation,
all registration,  qualification,  and filing fees,  printing  expenses,  escrow
fees, fees and  disbursements of counsel for EMCON,  blue sky fees and expenses,
and  expenses  of any regular or special  audits  incident to or required by any
such  registration,  but  shall  not  include  Selling  Expenses  and  fees  and
disbursements   of  counsel  for  Holder.   Selling   Expenses  shall  mean  all
underwriting  discounts  and selling  commissions  applicable to the sale of the
Holder's Shares and fees and disbursements of counsel for Holder (other than the
fees and disbursements of counsel included in Registration Expenses).
                                   
                                  ARTICLE III

                                     OFFSET

         3.1 Offset. The Holder acknowledges that this Note is being made by the
Borrower  pursuant to that certain Stock Purchase  Agreement,  dated as of April
30,  1997,  by and among the  Borrower,  Organic  Waste  Technologies,  Inc.,  a
Delaware  corporation  and the  holders  of the  outstanding  capital  stock  of
National  Earth  Products,  Inc. (the "Stock  Purchase  Agreement").  The Holder
further acknowledges that he or she is bound by the Stock Purchase Agreement and
that the  Principal  due  hereunder  may be reduced by any  amounts due from the
Holder to Borrower pursuant thereto.

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                                   ARTICLE IV

                                  ACCELERATION

         4.1 Notwithstanding  anything to the contrary herein, in the event that
any of the events set forth in Section 4.1 (each, an "Acceleration Event") shall
occur at any time after the date hereof,  then, subject to the qualification set
forth below,  the Principal and all interest thereon shall, at the option of the
Holder, be immediately due and payable.

                  (a) upon a  consolidation  or merger of EMCON with or into any
other corporation or corporations (other than a wholly-owned subsidiary of EMCON
and other than a merger in which  EMCON is the  surviving  corporation),  or the
sale, transfer or other disposition of all or substantially all of the assets of
EMCON;

                  (b) upon a change in ownership of Fifty  Percent (50%) or more
of the stock of Borrower  to a single  buyer or an  affiliated  group of buyers,
resulting in a change in the majority of the Board of Directors of Borrower from
the  Board of  Directors  as it  existed  immediately  prior to such  change  in
ownership;

                  (c) upon the  liquidation,  dissolution  or  winding up of the
Borrower or the  consolidation  or merger of the Borrower  with and into another
corporation  (other  than a  merger  in  which  the  Borrower  is the  surviving
corporation);

         provided, however, that upon any Acceleration Event, no amount shall be
due and payable  hereunder in the event that the Holder has exchanged  this Note
for Common Stock of EMCON, pursuant to the Note Agreement.

                                    ARTICLE V

                                EVENTS OF DEFAULT

         If any of the following events of default (each, an "Event of Default")
shall occur:

          5.1.  Failure to Pay Principal or Interest.  The Borrower fails to pay
the Principal or interest when due;

         5.2 Receiver or Trustee.  The Borrower shall make an assignment for the
benefit of creditors,  or apply for or consent to the  appointment of a receiver
or trustee for it or for a substantial part of its property or business, or such
a receiver or trustee shall otherwise be appointed;



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<PAGE>

          5.3 Bankruptcy. Bankruptcy, insolvency,  reorganization or liquidation
proceedings or other  proceedings for relief under any bankruptcy law or any law
for relief of debtors shall be instituted by or against the Borrower,  then upon
the occurrence and during the continuation of any Event of Default, then, at the
option of the Holder,  the  Principal  and all  interest  due  thereon  shall be
immediately  due and  payable,  and the Borrower  shall have all other  remedies
available at law or equity.

                                   ARTICLE VI

                                  MISCELLANEOUS

         6.1 Late  Charge.  The  Borrower  shall pay to the Holder a late charge
equal to 1.5% per month, but not to exceed the maximum rate allowable by law, on
any amount due hereunder that is not received by the Holder within 10 days after
the date on which such amount is due. Borrower agrees that it would be extremely
difficult or impractical  to determine the Holder's  actual damages in the event
of such late payment,  that the amount specified above is a reasonable  estimate
of such damages and that such amount  shall  constitute  liquidated  damages for
such late payment.  The foregoing provision shall not be construed to extend the
due date for any amount required to be paid hereunder.  The Holder shall have no
obligation to accept any late payment not accompanied by such late charge.

         6.2  Collection  Costs and Expenses.  The Borrower shall pay all costs,
fees and expenses (including court costs and reasonable attorneys fees) incurred
by the Holder in collecting or attempting to collect any amount that becomes due
hereunder or in seeking legal advice with respect to such collection or an Event
of Default.

         6.3 Failure or Indulgence Note Waiver.  No failure or delay on the part
of the Holder 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 privileges.

         6.4 Notices. All notices,  consents,  waivers, and other communications
under this  Agreement  must be in  writing  and will be deemed to have been duly
given when (a) delivered by hand (with  written  confirmation  of receipt),  (b)
sent by telecopier (with written confirmation of receipt),  provided that a copy
is mailed  within three (3) business  days by registered  mail,  return  receipt
requested,  (c)  when  received  by  the  addressee,  if  sent  by a  nationally
recognized  overnight  delivery  service (receipt  requested),  or (d) three (3)
business days after being sent by registered or certified  mail,  return receipt
requested,  in each case to the appropriate addresses and telecopier numbers set
forth below (or to such other  addresses and  telecopier  numbers as a party may
designate by notice to the other parties):


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<PAGE>



         Holder:  Dennis M. Grimm
                           1035 Eshelman Mill Road
                           Lancaster,  PA  17602

         Borrower:         EMCON
                           400 South El Camino Real, Suite 1200
                           San Mateo, California  94402
                           Attn:  Chief Financial Officer
                           Facsimile: 415/375-0763

          6.5 Amendment Provision. The term "Note" and all reference thereto, as
used  throughout  this  instrument,  shall mean this  instrument  as  originally
executed,  or  if  later  amended  or  supplemented,   then  as  so  amended  or
supplemented.

          6.6 Governing Law. This Note shall be governed by the internal laws of
the State of California, without regard to the principles of conflict of laws.

          6.7  Confession  of Judgment.  THE  FOLLOWING  PARAGRAPH  SETS FORTH A
WARRANT OF ATTORNEY TO CONFESS JUDGMENT  AGAINST THE BORROWER.  IN GRANTING THIS
WARRANT OF  ATTORNEY TO CONFESS  JUDGMENT  AGAINST THE  BORROWER,  THE  BORROWER
HEREBY KNOWINGLY,  INTENTIONALLY AND VOLUNTARILY, AND, ON THE ADVICE OF SEPARATE
COUNSEL OR THE BORROWER,  UNCONDITIONALLY WAIVES ANY AND ALL RIGHTS THE BORROWER
HAS OR MAY HAVE TO  PRIOR  NOTICE  AND AN  OPPORTUNITY  FOR  HEARING  UNDER  THE
RESPECTIVE  CONSTITUTIONS  AND LAWS OF THE UNITED STATES AND THE COMMONWEALTH OF
PENNSYLVANIA.

                  As further security for payment hereunder and upon an event of
default, Borrower authorizes and empowers any attorney of any court of record of
Pennsylvania  or  elsewhere  to appear for and CONFESS  JUDGMENT  against it and
immediately  execute  on  such  judgment,   without  notice  of  such  immediate
execution,  for the then  unpaid  principal  amount and  interest  of this Note,
together with late charges,  costs of suit and reasonable  attorneys' fees, with
or without  declaration  or stay of execution,  and with release of errors,  for
which this Note or a copy hereof shall serve as a sufficient warrant. This power
to CONFESS  JUDGMENT  against Borrower shall not be exhausted by any exercise of
the power  and shall  continue  from  time to time and at all times  until  full
payment of all amounts due under this Note.

         IN WITNESS  WHEREOF,  Borrower has caused this Note to be signed in its
name by its duly authorized officer as of the 30th day of April, 1997.

                     EMCON

                     By:  /S/
                          --------------------------------
                     Name:   R. Michael Momboisse
                            ------------------------------
                     Title: CFO & VP Legal
                            ------------------------------

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