Water demand is constantly rising to meet the needs of expanding industrial production, food and energy consumption. For many decades water resources have been withdrawn, wasted and polluted at elevated rates. In order to ensure an environmentally sustainable future, water use practices need to be changed. A more responsible individual approach to water saving and conservation is crucial, but at a global scale it is not enough. As usual, the solution is offered by the technologies of water treatment that allow its reuse in various fields: from industrial applications to drinking water supplies.
The evolution of microfiltration
In the last 30 years the evolution of water filtration, especially in the tertiary treatment section of the WWTP, received a remarkable impulse from agriculture, industrial activities, urban services and facilities. In these fields the main requirements are removal of suspended solids and hygienic quality. The interest in the prospects of water recycling and reuse, fueled research and development and brought on some important technological shifts.
At the beginning the filtration processes were carried out by “depth filtration” systems that were later replaced by “surface filtration” applications. Substantially the change consisted in passing from sand filter plants, that needed large spaces for installation, elevated amounts of back washing water and electrical power, to the filtration performed by micro-screening, which is comparable to mechanical microfiltration using very thin elements.
From drums to disks
At first, following the decision to put aside sand filtration technology, the microfiltration systems were composed of differently structured parts, mostly of rotating drums with horizontal axle immersed into the water to be filtered. Most of these machines, apart from few exceptions, were characterized by internal feeding. The microfiltration units were installed before the disinfection tanks or directly inside them, as secondary clarifiers had limited height.
In the course of the years the drum systems changed into disk systems with an intermittent operating, that allowed to increase the filtration surface while maintaining the same overall dimensions. The working principle has remained, as the machines are constructed using rotating disks with horizontal axle that maintain the “orthogonal” filtration towards the filtering media.
The new approach
The demand for water reuse on the global scale and, in particular, in the geographical areas with low water resources, have led to the development of a new approach to tertiary treatment. Today the microfiltration systems are designed to last for long periods of time, even more than twenty years, and the emphasis is on high quality and economical maintenance.