<PAGE>
 
                                                                      Exhibit 24


                               POWER OF ATTORNEY


     KNOW ALL PERSONS BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints William C. Smith and Mark J. Maten, or either of
them, as his or her true and lawful attorneys-in-fact and agents, with full
power of substitution and resubstitution, to do any and all acts, including the
execution of documents, which said attorneys, or either of them, may deem
necessary or advisable to enable Envirogen, Inc. (the "Company") to comply with
the Securities Exchange Act of 1934, as amended, and the rules and regulations
and requirements of the Securities and Exchange Commission, in connection with
the filing under such Act of an annual report of the Company on Form 10-K for
the year ended December 31, 1997, including the power and authority to sign in
the name and on behalf of the undersigned, in any and all capacities in which
the signature of the undersigned would be appropriate, such annual report and
any and all amendments thereto and generally to do and perform all things
necessary to be done in the premises as fully and  effectually in all respects
as the undersigned could do if personally present.

     IN WITNESS WHEREOF, the undersigned has hereto set his or her hand this
25th day of March, 1998.



 
                                         /s/ Robert F. Hendrickson
                                         -------------------------  
                                             Robert F. Hendrickson



                                      52
<PAGE>
 
                                                                      Exhibit 24


                               POWER OF ATTORNEY


     KNOW ALL PERSONS BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints William C. Smith and Mark J. Maten, or either of
them, as his or her true and lawful attorneys-in-fact and agents, with full
power of substitution and resubstitution, to do any and all acts, including the
execution of documents, which said attorneys, or either of them, may deem
necessary or advisable to enable Envirogen, Inc. (the "Company") to comply with
the Securities Exchange Act of 1934, as amended, and the rules and regulations
and requirements of the Securities and Exchange Commission, in connection with
the filing under such Act of an annual report of the Company on Form 10-K for
the year ended December 31, 1997, including the power and authority to sign in
the name and on behalf of the undersigned, in any and all capacities in which
the signature of the undersigned would be appropriate, such annual report and
any and all amendments thereto and generally to do and perform all things
necessary to be done in the premises as fully and effectually in all respects as
the undersigned could do if personally present.

     IN WITNESS WHEREOF, the undersigned has hereto set his or her hand this
25th day of March, 1998.



 
                                         /s/ Robert S. Hillas
                                         --------------------         
                                             Robert S. Hillas


                                      53
<PAGE>
 
                                                                      Exhibit 24


                               POWER OF ATTORNEY


     KNOW ALL PERSONS BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints William C. Smith and Mark J. Maten, or either of
them, as his or her true and lawful attorneys-in-fact and agents, with full
power of substitution and resubstitution, to do any and all acts, including the
execution of documents, which said attorneys, or either of them, may deem
necessary or advisable to enable Envirogen, Inc. (the "Company") to comply with
the Securities Exchange Act of 1934, as amended, and the rules and regulations
and requirements of the Securities and Exchange Commission, in connection with
the filing under such Act of an annual report of the Company on Form 10-K for
the year ended December 31, 1997, including the power and authority to sign in
the name and on behalf of the undersigned, in any and all capacities in which
the signature of the undersigned would be appropriate, such annual report and
any and all amendments thereto and generally to do and perform all things
necessary to be done in the premises as fully and effectually in all respects as
the undersigned could do if personally present.

     IN WITNESS WHEREOF, the undersigned has hereto set his or her hand this
25th day of March, 1998.



 

 
                                         /s/ Robert F. Johnston
                                         ----------------------      
                                             Robert F. Johnston


                                      54
<PAGE>
 
                                                                      Exhibit 24


                               POWER OF ATTORNEY


     KNOW ALL PERSONS BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints William C. Smith and Mark J. Maten, or either of
them, as his or her true and lawful attorneys-in-fact and agents, with full
power of substitution and resubstitution, to do any and all acts, including the
execution of documents, which said attorneys, or either of them, may deem
necessary or advisable to enable Envirogen, Inc. (the "Company") to comply with
the Securities Exchange Act of 1934, as amended, and the rules and regulations
and requirements of the Securities and Exchange Commission, in connection with
the filing under such Act of an annual report of the Company on Form 10-K for
the year ended December 31, 1997, including the power and authority to sign in
the name and on behalf of the undersigned, in any and all capacities in which
the signature of the undersigned would be appropriate, such annual report and
any and all amendments thereto and generally to do and perform all things
necessary to be done in the premises as fully and effectually in all respects as
the undersigned could do if personally present.

     IN WITNESS WHEREOF, the undersigned has hereto set his or her hand this
25th day of March, 1998.



 

 
                                    /s/ Robert C. Miller
                                    --------------------       
                                        Robert C. Miller


                                      55
<PAGE>
 
                                                                      Exhibit 24


                               POWER OF ATTORNEY


     KNOW ALL PERSONS BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints William C. Smith and Mark J. Maten, or either of
them, as his or her true and lawful attorneys-in-fact and agents, with full
power of substitution and resubstitution, to do any and all acts, including the
execution of documents, which said attorneys, or either of them, may deem
necessary or advisable to enable Envirogen, Inc. (the "Company") to comply with
the Securities Exchange Act of 1934, as amended, and the rules and regulations
and requirements of the Securities and Exchange Commission, in connection with
the filing under such Act of an annual report of the Company on Form 10-K for
the year ended December 31, 1997, including the power and authority to sign in
the name and on behalf of the undersigned, in any and all capacities in which
the signature of the undersigned would be appropriate, such annual report and
any and all amendments thereto and generally to do and perform all things
necessary to be done in the premises as fully and effectually in all respects as
the undersigned could do if personally present.

     IN WITNESS WHEREOF, the undersigned has hereto set his or her hand this
25th day of March, 1998.



 


                                         /s/ Peter J. Neff
                                         -----------------       
                                             Peter J. Neff


                                      56