hi,

see since you have completed the bachelors in biotechnology, you should give gate exam from biotechnology paper, you would get much familiarity and would be easier for you to prepare. now the main issue is , environment engineering / environment science and engineering is considered as core branch m.tech course. most of the institute like iit bombay, iit madras allows candidates from only civil, electrical, aerospace etc like b.tech degree holders. so you may not eligible for many of the colleges.

you may check the below link to get list of college name offers m.tech in environment engineering:

https://engineering.careers360.com/colleges/list-of-me-mtech-in-environmental-engineering-colleges-in-india