Advanced Chemical Treatment with Flocculation in Pipes

At the beginning of 1988 there were in Finland about ten small chemical wastewater treatment plants that were using flocculation in pipes instead of flocculation basins. This method consists of Me⁺⁺⁺-chemical feeding, mixing, flocculation and sedimentation. Chemicals were fed into the suction openings of the wastewater pump, which is used for rapid mixing and also for pumping wastewater flow to the sedimentation basin. In the sedimentation sludge blanket sedimentation in deep vertical sedimentation basins was used. The sedimentation basin can also be used as sludge storage, if it is made sufficiently large. This method has been found especially suitable for small wastewater treatment plants, because it needs little labour and is cheap to build and to use and it is not affected negatively by fluctuations in the flow. The construction costs of this system in Finland have been about 50 % of those involved in traditional chemical package plants. The limitations of this method are its weakness in removing soluble organic load and its inability to oxygenate or remove nitrogen. However, a biological unit designed to cope with these limitations is under development.