Similarities: They both remove nitrogenous wastes; they both maintain blood water and blood salt concentrations
Differences: In the kidney, pressure filtration occurs, in dialysis diffusion occurs; the tubule is teh selectively permeable membrane in the kidney, the dialysis tubing is the the selectively permeable membrane in diaslysis; in the kidney both filtration and reabsorbtion occur, in dialysis on filtration occurs; the kidney works continually and is very efficient, while dialysis is intermittent.
The role of the dialysate solution is to maintain glucose, amino acid, water, mineral and vitamin concentration in the blood. Because there is no reabsorption, if it were not for the dialysate solution, these substances would diffuse out of the blood, however, by maintaining the same concentration in the solution as there is in the blood there is no gradient for diffusions (osmosis for water)