Is it possible to grant trigger permissions on only one schema MySQL
This is going to depend greatly on what version of mysql you are on. If you are on 5.1 or higher (specifically later than 5.1.6)
https://stackoverflow.com/questions/19815837/in-mysql-what-privileges-are-required-for-executing-a-trigger

MySQL takes the DEFINER user into account when checking trigger privileges as follows:
At CREATE TRIGGER time, the user who issues the statement must have the TRIGGER privilege. (SUPER prior to MySQL 5.1.6.)
At trigger activation time, privileges are checked against the DEFINER user. This user must have these privileges:
The TRIGGER privilege. (SUPER prior to MySQL 5.1.6.)
The SELECT privilege for the subject table if references to table columns occur using OLD.col_name or NEW.col_name in the trigger body.
The UPDATE privilege for the subject table if table columns are targets of SET NEW.col_name = value assignments in the trigger body.
Whatever other privileges normally are required for the statements executed by the trigger.