can be manufactured in countercurrent furnaces allowing the heat to reach high temperatures using low cost, low temperature burning fuel. historically this was developed by the japanese in certain types of the anagama kiln. the kiln is built in stages, where fresh air coming to the fuel is passed downwards while the smoke and heat is pushed up and out. the heat does not leave the kiln, but is transferred back to the incoming air, and thus slowly builds up to 3000 °c and more. cement counter-current rotary kiln cement may be created using a countercurrent kiln where the heat is passed in the cement and the exhaust combined, while the incoming air draft is passed along the two, absorbing the heat and retaining it inside the furnace, finally reaching high temperatures. gasification: the process of creating methane and carbon monoxide from organic or fossil matter, can be done using a counter-current fixed bed ("up draft") gasifier which is built in a similar way to the anagama kiln, and must therefore withstand more harsh conditions, but reaches better efficiency. in nuclear power plants, water leaving the plant must not contain even trace particles of uranium. counter current decantation (ccd) is used in some facilities to extract water, totally clear of uranium. exchange current decantation depicted in centrifugal extractors as 1st stage zippe-type centrifuges use countercurrent multiplication between rising and falling convection currents to reduce the number of stages needed in a cascade. some centrifugal extractors use counter current exchange mechanisms for extracting high rates of the desired material. some protein skimmers (devices used to clean saltwater pools and fish ponds of organic matter) use counter current technologies. countercurrent processes have also been used to study the behavior of small animals and isolate individuals with altered behaviors due to genetic mutations.