The runoff from a worm bin really should not be used on any plant. It is excess moisture that has perculated through undigested feedstock and therefore could be contaminated. Actually, you want to work toward no leachate at all. I have only added compost when I re-pot my houseplants. An inch on the bo0ttom and (after cutting away extra roots) add a 1/4-1/2 inch around the edge. Making aeratedcompost tea is the best alternative to leachate.
A wormcompost really should not have a rotting smell or leachate coming out of it, either one of these indicate that the system is in overload and needs to be corrected.
Leachate means that the "compost" is saturated with water, the aerobic microbes are dying due to a lack of oxygen and too much water, thus less food for the worm.
Once the "compost" is water saturated and now anaerobic the bad, disease causing microbes take over, ones that attack your plants and even humans.
Aerated Worm tea on the other hand is pure gold, chuck full of defensive, good microbes for you plants.
I would guess that the leachate has a little mineral dissolves in it but the bad fungus/bacteria far out way any good that the minerals bring.
I got my worm bin last year and after holidays and winterstorm excess food, I stuff the wormbins, too much food per lbs of worms and thats when I get leachate.
It stinks and I just flush it down the tiolet.
Could you not simply add more of the feed material for the worms, and instead of moistening it with water, just pour leachate overtop again? If it's draining properly, the action of draining through the vermicompost should pull fresh air behind it as it drains, shouldn't it?
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein
The are other worm systems that do not function off the kitchen scrap under the sink model.
The rain through worm systems produce highly valuable leachate and do not reflect the doom sauce brewing at the bottom of an anaerobic bilge system.
I've done both dry and rain through systems and the only reason I've changed over to a non leachate system is because it's the middle of winter and my system get's diluted. As soon as the weather can hold 60f i'm going to begin watering my flow through system.
Flow through system have no issues with lack of oxygen or excess moisture, if you want to reap beneficial fluids from your system it has to function on a true flow through model or be managed heavily. The worm situations you see on a large scale have to do with ease of harvest hence they feed at the minimal moisture levels, I dump the stuff by the gallon on my plants because it's basically peculative cold tea extract at that point.
I do agree i killed or fungus'ed out every plant I touched with the under the counter scale worm bin models and I don't think it's worth using unless your worm farm is at a biological scale that it has a good immune system. My worm bin is a 250 gallon tote with pipes through the bottom with 3 inch spacing for harvest at the bottom. It's not an income scale setup but it produces enough high quality casting to regenerate our acre at an accelerated rate.