debris in my urine

Today I noticed a little change in my urine. The colour is normal, but it's accompanied by dark brown debris/dust-like matter that settles at the bottom of the toilet. It doesn't hurt when I pee, but I do feel a slight burning sensation. But it's so slight, it's hardly noticeable.

What does this mean? Should I be worried? And what should I do to stop this from happening?

A day or so beforehand, I cut short The Master Cleanse because I was too weak to continue. I wasn't doing it right and I eliminated only once. Tweet