The industry extracts and processes stones and earth. It also manufactures products for the building industry. These include cement, lime and plaster as raw materials in their own right and building ceramics and pottery such as bricks, fireclay, earthen-ware, tiles and abrasives.
Medium sized and large works usually discharge their wastewater without treating it. It contains almost exclusively material that can be sedimented, like gravel, sand, limestone or dolomite and is usually collected and treated separately. Precipitation from the roofs and other surfaces with mineral dust or sand is taken to precipitation basins with wastewater from production areas. It is often possible to return the water from here to production. If there is a danger of contamination from carbohydrates, separators should be installed. An example of this is waste from workshops.
There is generally no need for any treatment before the sedimentation of solids. The shape and dimensions of the sedimentation tanks or basins depends on the way the particles settle as does the retention time of wastewater. Tanks are cleaned of sludge periodically, basins usually not.
Addition of flocculating agents to material that takes a long time to settle can accelerate the process. Belt type sludge filters or centrifuges usually drain the resulting sludge until it has water content of no more than 40 % or 50%. The dried sludge can usually be dumped without any problems. Sludges containing insoluble heavy metals from dyes and enamel varnishes should not be dumped. The former usually come from ceramic manufacturers the latter from fiber cement producers. |
