Smell around waste/septic tank

I posted in February that our kingspan waster water treatment tank (septic tank) was causing problems.

I had to replace the pump and the blower, and everything seems to be working as is.

But...there is still a smell lingering around the tank. Depending on which way the wind is blowing, it can be prominent.

So, everything is working and cannot see any leaks anywhere so the last thing I can think of is the lid on the tank needa repaired/sealed.

The two latches on it are damaged so its been held down with 2 blocks, one at either end.

Cannot think of anything else!