This book has shown that wastewater treatment by trickling filter technology in cold and warm climate can be the more economical, sustainable and green solutions as it consumes low energy where the energy prices increase worldwide. Using the trickling filter or combing it with different technologies is possible to make it very flexible applicable and more modern solutions for industrial and municipal wastewater treatment to different treatment levels to meet different local and international standards for treated water reuse or for different water discharged goals.