If you have access to land that is contaminated with Japanese knotweed, think about growing vegetables there. No need to rid the land of knotweed first, just grow your potatoes and other veg right there in the knotweed patch. If it is a long-established knotweed patch there will be few, if any, other weeds in there. This means that when the knotweed is cleared and the ground raked, you can immediately (and without digging) start to plant your crops. If there are brambles as well, they will be more difficult to deal with. You could have a bonfire to clear a patch and create potassium (potash) at the same time but you will be adding CO2 to the atmosphere. You can chew on the softer stems as you work, even drink water from the stems sometimes (after rain).
As your crops grow, so will the knotweed (from any roots left in the ground) but these are easily controlled just by pulling. Sometimes a length of root will come right out of the ground. Add it all to the compost pile. Comfrey can be grown in order to shade out the new growths of knotweed but it is anyone’s guess which will win the race. Lonicera nitida can be used as a hedge around the plot to contain the knotweed. You will need to help it for the first few seasons by hand pulling the knotweed that grows through it but if your hedge is two metres wide, it should beat the knotweed after a few years. Plant Lonicera nitida by sticking cuttings in the ground in the cool and wet autumn time and it will root easily. If the ground is hard make a hole with a long screwdriver or similar implement and pop the cutting into it. Then just firm it into place with your thumb or a dibber pressed next to the hole. Or you can put the cuttings into water to grow roots and then plant the rooted cuttings in holes dug with a garden trowel.