Chapter 38: Biological wastewater treatment as an opportunity for energy and resource recovery of "Sustainable Industrial Water Use: Perspectives, Incentives, and Tools". As raw materials become increasingly scarce, the current linear system of industrial manufacturing - extracting resources, transforming them into products, and discarding the waste - increasingly appears to be inefficient and unsustainable. This approach is now being succeeded by 'the circular economy', a new manufacturing paradigm which closes production cycles by recovering wastes and reusing them as resources. A prime example is the treatment of wastewater, which aside from reuse as a resource of its own (water), is now being treated to recover the chemicals and energy it contains.