What is the minimum distance requirement between the Production Data Centre Facility and Business Continuity Disaster Recovery Site?

Data Integrity is a way of professional people to prevent Information and An Authorised Things.

Depends upon business requirement, ideally it can be 50 Miles. More far from primary its better.

It is better to be 150 KM and provided that you do risk analysis by considering the geo location and nature issues on the location of your data centers

There have been organizations that preach a 50 mile minimum is an acceptable distance.  There are others that have also concluded that at a minimum there are factors that can minimize the impact to either facility including, separate power grids, water supplies, central offices etc.  Estimates of reasonable distances range from 10 miles in the US, 15 kilometers in Canada and 8 miles in the UK.  However, there is no accurate number of such distance so far.

It depends on the Business Vision and Management. Mission is to get Business keeping running and your customers see significant value in our service provided to them. But Above all, Telecommunications and Data Links play a very dominant role in Business Continuity. Even after disaster recovery, establishing networks by Telecoms will face challenge and that can be a real test for business. Types / Modes of Telecommunication put into business can be Worked out to effectively face Disaster Situations and thus managing business continuity. 

I'm not aware about any recommended distention, I remember that I've read somewhere in the internet that 30km is fear distance but not sure if this was mentioned in ISO or any other best practices.

In my opinion, it is totally depends on your budget. You may have your DRC in a different city or even different country (if you located in European continent, you may have your DRC somewhere in Africa) but this if you have sufficient budget and you may go with cloud services and replications which is the best solution but most expensive. 

Also, you must consider that long distention may save your data from natural disasters such as flood or earthquake, etc... but you need to consider how long you will take to move the team there unless you have different team to operate from the DRC. 

I think is business objective dependent.

It is depends on the buisiness requirement, Idel is production will be in the same site and DR will be in  other location (Anywhere) with proper communication

As Per my knowledge and industry standards backup site should be separate from production site, i would say minumum 1 km to 2 km protecting incase of fire, whereas DR site will be kept 100km away, some countries in EMEA keep a policy of minimum 2 km as standard between production and backups with fiber redundant connectivity. These all depends on what tier data center you built and what you serve for the customers inturn change accordingly.

There is no such standard defined, it depeds on the feasibility and risk assessment.