The new plate and frame module M39 from DSS is introduced. The main advantage is a reduction of pressure difference over the module compared to previous modules. This enables adjustment of the permeate flux according to needs. Sterile and sanitary design is discussed and the DSS UF-spiral constructed for heal sterilisation is introduced.. The advantages and disadvantages of batch and continuous ultrafiltration plants are discussed. A new diafiltration concept -counter current diafiltration - is introduced and discussed together with the possibility of using purified permeate as diafiltration water. Ultrafiltration is only one part of a total factory. An important factor in obtaining the best economic and environmental process is determining the optimum overall process layout. The new diafiltration concept offers advantages by reducing environmental problems and investment requirements.