Seems like someone runs aspell program from one of the php scripts. You can disable aspell from being run from php scripts by using disable_functions directive in php.ini, but your customers may need it, not sure, try to find out who is using it.
GNU Aspell is a Free and Open Source spell checker designed to eventually replace Ispell. It can either be used as a library or as an independent spell checker. Its main feature is that it does a much better job of coming up with possible suggestions than just about any other spell checker out there for the English language, including Ispell and Microsoft Word. It also has many other technical enhancements over Ispell such as using shared memory for dictionaries and intelligently handling personal dictionaries when more than one Aspell process is open at once.
as phpdeveloper mentions, probably from one of your php scripts.
mostly likely your webmail program or file editor.
with not knowing the web mail program you are using (which would be my best guess is running the program) the best I can tell you and take a look at the configuration files. I know with horde you can just comment it out in one of the conf files.
I have an account using all the resources with aspell.
I terminated the account but sometimes the process is running again.
I can see the pids running in wht:
sh -c /usr/bin/aspell -a -d american -H < /tmp/spellNVnpd9