One thought: If you shoot 100.000 pictures (whoever may do that) with a DSRL it may be better than producing 365 gallons of developer waste (just do the math: film tank with 500ml capacity, 36 frames. The ration is far worse with 120). It also depends whether you use Xtol or Pyro. Since no film user I know of reaches such high volumes (and the chemistry used in professional labs which easily reach them is recycled), the whole debate is meaningless. The amount of waste that accumulates through normal amateur use is neglectable if disposed properly.