diff --git a/cps/db.py b/cps/db.py
index 520d724b..491e95b3 100644
--- a/cps/db.py
+++ b/cps/db.py
@@ -426,18 +426,19 @@ class CalibreDB():
     # instances alive once they reach the end of their respective scopes
     instances = WeakSet()
 
-    def __init__(self):
+    def __init__(self, expire_on_commit=False):
         """ Initialize a new CalibreDB session
         """
         self.session = None
         if self._init:
-            self.initSession()
+            self.initSession(expire_on_commit)
 
         self.instances.add(self)
 
 
-    def initSession(self):
+    def initSession(self, expire_on_commit):
         self.session = self.session_factory()
+        self.session.expire_on_commit = expire_on_commit
         self.update_title_sort(self.config)
 
     @classmethod
diff --git a/cps/tasks/convert.py b/cps/tasks/convert.py
index 659c6e9c..f9d6dd2a 100644
--- a/cps/tasks/convert.py
+++ b/cps/tasks/convert.py
@@ -9,7 +9,7 @@ from shutil import copyfile
 from sqlalchemy.exc import SQLAlchemyError
 
 from cps.services.worker import CalibreTask
-from cps import calibre_db, db
+from cps import db
 from cps import logger, config
 from cps.subproc_wrapper import process_open
 from flask_babel import gettext as _
@@ -33,8 +33,10 @@ class TaskConvert(CalibreTask):
     def run(self, worker_thread):
         self.worker_thread = worker_thread
         if config.config_use_google_drive:
-            cur_book = calibre_db.get_book(self.bookid)
-            data = calibre_db.get_book_format(self.bookid, self.settings['old_book_format'])
+            worker_db = db.CalibreDB()
+            cur_book = worker_db.get_book(self.bookid)
+            data = worker_db.get_book_format(self.bookid, self.settings['old_book_format'])
+            worker_db.session.close()
             df = gdriveutils.getFileFromEbooksFolder(cur_book.path,
                                                      data.name + "." + self.settings['old_book_format'].lower())
             if df:
@@ -71,7 +73,7 @@ class TaskConvert(CalibreTask):
 
     def _convert_ebook_format(self):
         error_message = None
-        local_session = db.CalibreDB().session
+        local_db = db.CalibreDB()
         file_path = self.file_path
         book_id = self.bookid
         format_old_ext = u'.' + self.settings['old_book_format'].lower()
@@ -82,10 +84,11 @@ class TaskConvert(CalibreTask):
         # this will allow send to kindle workflow to continue to work
         if os.path.isfile(file_path + format_new_ext):
             log.info("Book id %d already converted to %s", book_id, format_new_ext)
-            cur_book = calibre_db.get_book(book_id)
+            cur_book = local_db.session.get_book(book_id)
             self.results['path'] = file_path
             self.results['title'] = cur_book.title
             self._handleSuccess()
+            local_db.session.close()
             return os.path.basename(file_path + format_new_ext)
         else:
             log.info("Book id %d - target format of %s does not exist. Moving forward with convert.",
@@ -105,18 +108,19 @@ class TaskConvert(CalibreTask):
             check, error_message = self._convert_calibre(file_path, format_old_ext, format_new_ext)
 
         if check == 0:
-            cur_book = calibre_db.get_book(book_id)
+            cur_book = local_db.get_book(book_id)
             if os.path.isfile(file_path + format_new_ext):
                 # self.db_queue.join()
                 new_format = db.Data(name=cur_book.data[0].name,
                                          book_format=self.settings['new_book_format'].upper(),
                                          book=book_id, uncompressed_size=os.path.getsize(file_path + format_new_ext))
                 try:
-                    local_session.merge(new_format)
-                    local_session.commit()
+                    local_db.session.merge(new_format)
+                    local_db.session.commit()
                 except SQLAlchemyError as e:
-                    local_session.rollback()
+                    local_db.rollback()
                     log.error("Database error: %s", e)
+                    local_db.session.close()
                     return
                 self.results['path'] = cur_book.path
                 self.results['title'] = cur_book.title
@@ -125,6 +129,7 @@ class TaskConvert(CalibreTask):
                 return os.path.basename(file_path + format_new_ext)
             else:
                 error_message = _('%(format)s format not found on disk', format=format_new_ext.upper())
+        local_db.session.close()
         log.info("ebook converter failed with error while converting book")
         if not error_message:
             error_message = _('Ebook converter failed with unknown error')