Besides power washer what can be used to clean black from concrete

Try Wet and Forget

An electric sander.

scrub brush w/ long handle

Here's an article with a bunch of natural ingredients to try:

http://homeguides.sfgate.com/natural-homemade-cleaners-concrete-patios-79379.html

Here's another article that might interest you since black spots might be mold:

https://www.concretenetwork.com/fix-concrete-cleaning/clean-mold-on-concrete.html

What is it from? If it's tarry, I would use a petroleum based cleaner to remove it. I've also found wonderful success on tough marks with Goof-off.

Vinegar, dawn dish soap, a stiff bristle long handled push broom and a hose!

Use some SuperClean, It's usually called the purple stuff. You can purchase at any auto parts store or Walmart has it to. Just spray it on let it sit for a few minutes then rinse it off.

Bleach. Don't put bleach into the power washer, but, rather, pour or spray onto the concrete. Let sit a few minutes, then use a power washer (or sprayer) Wear protective glasses and a mask. We did this and it worked great.

MOVED TO FLORIDA seems all sidewalks\driveways like that tried bleach with purple stuff does a lil whitening not much