Not sure how to answer the second question about the best country, but I'd say - the one that allows you to get a globally recognised degree in that field, as well as where the courses lead to recognised professional qualifications such as CEng (Chartered Engineer) in the UK and PE (Professional Engineer) in the US.
Thank You for the prompt response given ! . Is maths essential in all universities to pursue an environmental engineering degree ?
Any engineering degree will have maths as a requirement, however at the same time majority of the Universities in the UK also offer what's called a "Foundation year" where they teach you maths and physics so that you're fully prepared to study the engineering degree of your choice.