In a large soup pot, heat olive oil over medium heat. Add the chopped celery root and sauté for 10 minutes or until it starts to brown. Rinse beans thoroughly and add to pot of sautéed celery root. Add the water and 1 tsp of sea salt to the mixture, and bring to a boil. Reduce heat and simmer for 30 minutes.
At 30 minutes, blend soup with an immersion stick blender until smooth and creamy. Add the juice of one lemon, sea salt and pepper to taste, and continue blending. Top with chopped scallions.