Photo 1: Hygrex Closed-Loop Sludge Drying In industrial waste water treatment plants undesired materials such as heavy metals have to be removed from the waste water by means of physical and chemical methods. Usually a thin sludge with a water content of approx. 95% results from this treatment. By using adequate systems for preliminary desiccation such as filter presses, a filter cake with a chunky consistency and a water content of approx. 60% is attained. With the help of Hygrex sludge drying systems the filter cake can be dried up to a remaining water content of approx. 20% - 5%. Thus the weight of the sludge is reduced by 50%. The overall aim of sludge drying is to reduce the weight of the sludge to be taken to a landfill or to be recycled and thus to gain considerable cost savings. The Hygrex low-temperature drying principle operates on transporting warm and dry air through a defined volume of filter cake. The dry air now takes up the water stored in the filter cake. In the dehumidifying unit it is then cooled down at a heat exchanger to such an extent that the water can condensate. Right after this process another heat exchanger serves to reheat the air again. For this reason the air has an enormous water absorbing capacity. Both the heat exchangers, also called air cooler and air heater, are components of a refrigeration cycle. An advantage of this energy balance is that surplus heat arising to supply the air cooler with refrigerant, is used in the air heater to constantly reheat the air. This air is then led through the container filled with sludge. Now you can see another positive effect of the principle. The Hygrex sludge drying process takes place in a closed air cycle. From the system point of view there are no emissions, so no loss of energy occurs. The drying machines have a simple construction. They are robust and have a long service-life. The experiences of several hundred references has lead to a constant improvement. So nowadays the principle is perfected and field-proven. The system is applicable for standard sludge dryers as well as for customer-tailored solutions.  Problem(s): Cost effective management of hazardous and non-hazardous filter cake sludge/waste Solution(s): Removal of water from sludge/waste using the HYGREX TM dry air generator Description: The HYGREX (TM) dry air generator uses a closed-loop drying process that is particularly efficient in the drying of filter cake sludge, and other wastewater by-products. The filter cake sludge is dropped into an existing hopper or shipping container that is connected to the HYGREX TM unit. Super dry air is then gently forced through the filter cake to begin the drying process. No other handling of the sludge is required, allowing for perfect application with respect to hazardous sludge. No exhaust or air makeup is required. The is a completely closed-loop system. The moisture removed from the filter cake is condensed within the unit. The water is recovered and reusable. Example: If a company produces 360 tons of sludge per year on average with a moisture content of 60% -70%, HYGREX TM can recover 216 tons of water during a year. This water removal will result in a haulage cost reduction of 60% and a sludge volume reduction of 50%. The energy cost to dry 1 ton during a continuous 24-hour period equals $10.80. HYGREX TM dry air generator has the ability to dry large amount of sludge as well, using existing shipping containers or hopper.