added filtering step to preprocess script
added filtering step to preprocess script

iimog/meta-barcoding-dual-indexing,iimog/meta-barcoding-dual-indexing,molbiodiv/meta-barcoding-dual-indexing,iimog/meta-barcoding-dual-indexing,molbiodiv/meta-barcoding-dual-indexing,molbiodiv/meta-barcoding-dual-indexing