When you say 'module', do you really mean 'sub'? If so, you should show how you are calling your sub. This is a way to return a hash-of-arrays from a sub:

use strict;
use warnings;

my %filt = foo();
use Data::Dumper; print Dumper(\%filt);

sub foo {
    # Create a hash-of-arrays
    my %filters = (
        a => [0..2],
        b => [3..5]
    );
    return %filters;
}

__END__

$VAR1 = {
          'a' => [
                   0,
                   1,
                   2
                 ],
          'b' => [
                   3,
                   4,
                   5
                 ]
        };
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You could also return it as a reference to a HoA.