Your plants aren't going to break down waste into usable nutrients, they're just going to use them, but if there's nothing to grow bacteria on to break down the waste it's just gonna build up and look nasty.
A little confused here. Why would breaking down the waste via bacteria be better than the plants actually consuming the organics? Plants are much more efficient at nutrient and waste removal than bacteria is, which is why more research is being put into constructing wastelands or algae ponds for the use in wastewater treatment in which bacteria removal is currently the conventional method. Certain species like duckweed varieties especially are being researched for their ability to remove heavy metals.