Waste Water Treatment

Biological waste water treatment using pre-formed PVC packings

Aerobic treatment processes are used for the removal from waste water of organic carbonaceous material and nitrification.
The most common system for the growth of the treatment organism on a supporting surface is the so-called "Trickling filter", comprising a bed of highly permeable material to which the micro-organisms are attached and through which the water for treatment percolates from the top, where it is distributed by spray branches, to the base. The filtration material on which the micro-organisms grow can be of rock or a packing of preformed PVC sheets in modules. The synthetic fill pack is normally employed for trickling filters with high flowrate and high biological load.
Underneath the packing the bottom-drain receives the treated water plus those biological solids which break away from the supporting surface. It also serves as a porous structure through which air can circulate, often by natural convection. The recovered liquid passes into a sedimentation tank where the solids separate from the treated water.

Whilst all the biological sludge is passed from this tank to a suitable treatment unit, a part of the existing treated liquid is recycled to dilute the entering water and to humidify the biological slime layer.
The organic material in the water to be treated is broken-down by the micro-organisms present on the surface of the fill. The organic matter present in the water is absorbed on to the biological layer, in the outer part of which the decomposition is performed by aerobic organisms. During the growth of the micro-organisms, the thickness of the biological layer increases and the oxygen diffusing through it is consumed before it reaches the bottom of this layer which becomes an anaerobic zone. The absorbed organic material is metabolised before reaching the organisms at the support surface: they pass into a phase of endogenous growth and are no longer able to adher to the fill. The water then removes them from the support surface and the growth of a new layer is initiated. This phenomenon depends upon the organic and the hydraulic loading, usually controlled to maintain a uniform biological slime layer.

Products for Waste Water Treatment

ONDA synthetic fill media consist of a series of high quality PVC shaped sheets: they are assembled with the shape inverted every two sheets and glued to form standard modules with dimensions of 2400 x 600 x 600 mm. ensures excellent water distribution, allowing maximum use of the contact surfaces, increasing efficiency.

For high flow percolation filters, the shape (or ripple) is 27 mm with a specific surface greater than 100 m2 / m3. The shape favors the growth of the biological silt and the maintenance time. The embossing of the surface, intended as a structural reinforcement of the filling, also contributes to the development of the silt. Thanks to the lower tendency of these blocks to block (97% vacuum index) compared to traditional fillings (50-60% vacuum index), our product has found use in high-flow, high-load percolation filters.

With 27 mm corrugation (Onda 27) the available sheet thicknesses are 500 - 600 and 700 μm. Where there is the need to reinforce the block, the insertion of additional flat sheets is foreseen. It is also possible to supply the blocks shaped to measure to facilitate the positioning inside the percolator. Certain applications, such as upgrading rock-based percolation filters, may employ our synthetic fill to achieve a higher surface to volume ratio.

For low load applications (mini-systems) and for nitrification applications where the biological layer is much finer, the Onda 9 - Onda 13 and Onda 20, Onda S21 series filling can be used or the Corefill 20 filling characterized by its structure shaped that allows an extension of the contact surface and consequently increase the available surface per volume of the biofilter. Compared to other filling models, the modular bodies allow the use of a simpler and more economical support system. Compared to traditional crushed stone fillings, the lightness of the Onda packs allows the design of percolating beds of considerable height.