The Sludge-to-Sludge Heat Exchanger from Walker Process Equipment, A Div. of McNish Corp., is a concentric tube-in-tube design that uses counter-flow circulation of heated thermophilic sludge and raw influent sludge. The arrangement allows cooling of thermophilic sludge and reduces the energy required to heat raw sludge. Sludge tubes’ end castings are removable for cleaning, and end castings include built-in water back-flushing connections. Controls include non-flow-restrictive temperature sensors and glass tube or dial thermometers to measure inlet and outlet temperatures. 630/892-7921; www.walker-process.com.