diff --git a/etk/knowledge_graph/graph.py b/etk/knowledge_graph/graph.py
index 69abff1b..ec387593 100644
--- a/etk/knowledge_graph/graph.py
+++ b/etk/knowledge_graph/graph.py
@@ -47,7 +47,9 @@ def serialize(self, format='ttl', namespace_manager=None, **kwargs):
             b_string = self._g.serialize(format=format, contexts=namespace_manager, **kwargs)
         else:
             b_string = self._g.serialize(format=format, **kwargs)
-        return b_string.decode('UTF-8')
+        if isinstance(b_string, bytes):
+            b_string.decode('UTF-8')
+        return b_string
 
     @lru_cache()
     def _resolve_uri(self, uri: URI) -> rdflib.URIRef:
diff --git a/etk/knowledge_graph/node.py b/etk/knowledge_graph/node.py
index 22f5b98a..cd56328f 100644
--- a/etk/knowledge_graph/node.py
+++ b/etk/knowledge_graph/node.py
@@ -3,7 +3,7 @@
 from datetime import date, datetime
 from xml.dom.minidom import Document, DocumentFragment
 from etk.etk_exceptions import InvalidGraphNodeValueError, UnknownLiteralType
-
+import re
 
 class Node(object):
     def __init__(self, value):
@@ -118,6 +118,13 @@ def __getattr__(self, item):
 
 
 class LiteralType(URI, metaclass=__Type):
+
+    valid_time_pattern = re.compile(r"[\-]?(\d{4})-((0[1-9])|(1[0-2]))-(0[1-9]|[12][0-9]|3[01])T(0[0-9]|1[0-9]|2[0-3]):(0[0-9]|1[0-9]|2[0-9]|3[0-9]|4[0-9]|5[0-9]):(0[0-9]|1[0-9]|2[0-9]|3[0-9]|4[0-9]|5[0-9])")
+    valid_month_pattern = re.compile(r"[\-]?(\d{4})-((0[1-9])|(1[0-2]))-(00)T00:00:00")
+    valid_year_decade_millennium_pattern = re.compile(r"[\-]?(\d{4})-(00)-(00)T00:00:00")
+    valid_hundred_thousand_years_pattern = re.compile(r"[\-]?(\d{6,7})-(0[0|1])-(0[0|1])T00:00:00")
+    valid_million_billion_years = re.compile(r"[\-]?(\d{8}\d+)-(0[0|1])-(0[0|1])T00:00:00")
+
     def __init__(self, s, common_check=True):
         self.common_check = common_check
         self._type = None
@@ -172,6 +179,7 @@ def is_value_valid(self, s):
 
     @staticmethod
     def _is_valid_date_time(s):
+
         if isinstance(s, datetime):
             return True
 
@@ -193,7 +201,12 @@ def _is_valid_date_time(s):
         except:
             pass
 
-        return False
+        validity_list = [LiteralType.valid_time_pattern.match(s), 
+        LiteralType.valid_month_pattern.match(s),
+        LiteralType.valid_year_decade_millennium_pattern.match(s),
+        LiteralType.valid_hundred_thousand_years_pattern.match(s), 
+        LiteralType.valid_million_billion_years.match(s)]
+        return any(validity_list)
 
     xsd = 'http://www.w3.org/2001/XMLSchema#'
     rdf = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#'
diff --git a/etk/wikidata/value.py b/etk/wikidata/value.py
index 255b284e..35181e1d 100644
--- a/etk/wikidata/value.py
+++ b/etk/wikidata/value.py
@@ -77,7 +77,12 @@ def __build_full_value(self):
         self.full_value.add_property(URI('wikibase:timePrecision'), self._precision)
         self.full_value.add_property(URI('wikibase:timeTimezone'), self._time_zone)
         self.full_value.add_property(URI('wikibase:timeCalendarModel'), self._calendar.value)
-        self.full_value.add_property(URI('wikibase:timeValue'), self.value)
+        self.full_value.add_property(URI('wikibase:timeValue'), self.value) 
+        # TODO fix import bug
+        # if not self.value.startswith("+"):
+        #     self.full_value.add_property(URI('wikibase:timeValue'), self.value) 
+        # else:
+        #     self.full_value.add_property(URI('wikibase:timeValue'), self.value[1:]) 
 
     def _v_name(self):
         time = self.value.value.replace(':', '').replace(' ', '-')
diff --git a/setup.py b/setup.py
index 477ad889..0253b2c3 100644
--- a/setup.py
+++ b/setup.py
@@ -12,7 +12,7 @@
 
 setuptools.setup(
     name="etk",
-    version="2.2.4",
+    version="2.2.5",
     author="Amandeep Singh",
     author_email="amandeep.s.saggu@gmail.com",
     description="extraction toolkit",