Casual language should be kept for conversation or other forms of writing. It must be replaced by the correct term, which is often shorter:

avoid	better
nowadays	presently, currently
for instance	for example
despite the fact that	although
goes under the name of	is called
on the contrary	in contrast
firstly	initially
to begin with	initially
be that as it may	however
at last	finally
in as much as	because
by the way	delete
as a matter of fact	delete
'til now (until now)	to date*

*This last example also uses a contraction which cannot be used in scientific writing at all. Other examples include:

avoid	better
it's	it is
weren't	were not
didn't	did not
haven't	have not
can't	cannot