An element of a mixing apparatus having no moving parts. The element includes a hollow cylindrical body provided on an inner surface thereof with projecting plates for disturbing a flow of fluids within the hollow cylindrical body. The hollow cylindrical body is provided on one end thereof with a plurality of projections disposed at regular angular intervals. The hollow cylindrical body is provided on the other end thereof with a plurality of indents disposed at the same regular angular intervals as the projections. Each of the projections of one element is engageable with each of the indents of another element.

A tower packing element for randomly dumped beds includes a straight leg portion attached at one end to an arcuate portion. The length of the straight leg portion is substantially equal to the length of a cord that extends between the ends of the arcuate portion. The arcuate portion and the straight leg portion have at least one slot therein. A tongue depends from each slot and points away from the packing element.

A multi-stage anaerobic treatment device, using a pipe as a column filter, mixes sewage to create a homogeneous environment throughout the reactor while simultaneously preventing clogging of the filter. The column filter contains inclined rectangular through-holes bored systematically through the wall of the straight pipe of the column filter. Projecting baffle plates to the inside of the pipe from the respective long side of the through-holes on the same level result in counter-flow as well as cross-flow being generated not only in the column filters but also between the column filters and outside the column filters, resulting in an efficient anaerobic treatment system.

A high-performance rectifying device promotes the diffusion of energy, temperature and concentration in a fluid stream with a small pressure loss. The device is a lattice type rectifying device provided within a fluid flow passageway for equalizing the flow velocity distribution of the same fluid. Lattice elements each consist of two triangular plates disposed so as to form two opposed surfaces of a pyramid having its apex on the downstream side of the fluid flow and two other triangular plates forming two opposed surfaces of another pyramid having its apex jointed with the first-mentioned apex and having its bottom surface positioned on the downstream side of the fluid flow. The latter two opposed surfaces have their orientations deviated by 90 degrees from the two opposed surfaces on the upstream side. The lattice elements are arrayed in juxtaposition in directions perpendicular to the fluid flow with the orientation of adjacent lattice elements deviated by 90 degrees from each other and are connected in such a manner that the bottom surfaces of the above-mentioned pyramids may form a lattice. Furthermore the ratio of the length, in a direction parallel to the flow, of the lattice element to the breadth, in the direction perpendicular to the flow, of the lattice element should be kept in a range of 1.5-2.0. The lattice element may also be formed of a rectangular plate twisted by 90 degrees in the direction along the direction of the fluid flow.

The invention refers to a carrier element to be used as a carrier for a microbial film in a biological water or waste water purification process in which the carrier elements are kept moving in the water. The surface of the carrier element is partly protected against collision with the surfaces of the other carrier elements. The carrier element has flow passages therethrough and is moreover designed to allow good flow of water therethrough also after a microbial film having been established on the surfaces. The carrier element has a length, width and/or height which exceeds 1.5 cm, and the protected area is larger than 100 m.sup.2 /m.sup.3 of the volume of the carrier element. The cross-sectional area of the passage opening in the boundary surface towards the surroundings of the element comprises at least 35% of the boundary surface towards the surroundings of a homogenous body having the same dimensions. The invention also relates to the use of such carrier elements for the treatment of waste water from the wood-processing industry, the waste water containing at least 100 mg/l suspended matter as measured on a GF/A-filter, as well as a reactor for biological water or waste water purification, comprising a reactor tank (20) which contains carrier elements (25) according to the invention and wherein a grid (26) covering the bottom of the tank is provided over aerators (21) at said bottom.