"This video shows how adding precipitants and flocculants enhances conventional primary treatment. In contrast to primary treatment without chemicals, more organic pollution load is transferred into the sludge resulting in a clear supernatant. This technology is suitable for wastewater treatment plants which are only designed for mechanical treatment. can be applied for mechanical wastewater treatment without any requirements regarding the nitrogen elimination. On the other hand, it can help to improve the energy efficiency of a biological wastewater treatment plant by providing more organic substrate for digestion thus leading to a higher gas production." This is part of the Open Educational Resources Initiative by the Faculty of Civil Engineering of the RWTH Aachen University.