Forbes has an article on vertical farming under lights, claiming that a 2-acre vertical farm can replace a 750 acre outdoor farm and use 95% less water. It doesn’t talk about pollution, but in theory it should be relatively easy to collect and recycle/compost/digest/burn solid waste, and collect and treat wastewater, from a farm like this. I know LED lights are efficient, but you do have to produce enough energy to replace the sunlight that would have fallen on 750 acres of the Earth, plus some extra because the system is not perfectly efficient, and you have to produce fertilizer of some sort. These things will have an ecological footprint. On the other hand, if this is in an urban population center, you potentially have a lot of waste streams you might be able to recover energy and nutrients from. Then you also have 748 acres of land somewhere that you can theoretically reforest or re-wetland. Then you might have a healthy fishery somewhere downstream that is no longer choked by sediment and nutrients from farm waste.