The sludge / water heat exchanger HE-sw has been specially developed for use with waste water, sludge treatment systems and biogas installations. An effective heat exchange in parallel with high quantities, low differential pressure as well as low risk of blockage is of primary importance when processing sewage sludge. The heat exchanger is of a modular construction with circular sludge pipes and can be modified to suit the actual process parameters. A turbulent sludge circulation is generated by an innovative turning chamber construction. The temperature profile is balanced ensuring an effective heat exchange in a compact construction.