Hi,
Here is how you how you can do it,
Let us assume that the 4 column of numbers are in Column A:D,
In Cell A2, Below is the formula you can write in conditional formatting
=SMALL($A2:$D2,COUNTIF($A2:$D2,"0")+1)=A2
Once done, You can use format painter and roll the rule to all the cells.
Hope this helps,
Regards,
Harish Gupta