BASF wastewater treatment plant

The wastewater treatment plant

Logo - BASF - The Chemical CompanyWater is a crucial resource for the Ludwigshafen site of BASF Aktiengesellschaft. The company needs water in its plants first and foremost for cooling, though water is also used for dissolving, washing and diluting as well as for generating steam. BASF extracts about 1.3 billion cubic meters of water from the Rhine annually.

Most of the water is used for cooling and, following careful checks, can flow back into the Rhine without any further treatment. Internal cooling loops make it possible for the same water to be used over and over again, thereby reducing the quantities extracted from the river. Only about 12 percent of the water is used as process water and as a reaction medium for production. Because this amount is contaminated with various substances and therefore needs to be treated, it is fed into the wastewater treatment plant where it is cleaned up. At BASF, 120 million cubic meters of production wastewater were fed into the wastewater treatment plant in 2001.

BASF’s wastewater treatment plant is one of the biggest of its kind in Europe. It was brought into service in December 1974 and has undergone constant improvement and updating of equipment since then. With regard to its capacity, the treatment plant could purify the wastewater from between six and seven million inhabitants. It treats not only the effluent from the works, but also the municipal wastewater from the towns of Ludwigshafen and Frankenthal and the district of Bobenheim-Roxheim. The total in 2001 was about 144 million cubic meters of sewage.

Where the water goes

The sewage is neutralized with slaked lime whilst it is still in the sewer leading from the works to the wastewater treatment plant. It is then sent, via a pumping station, through a three-kilometer long pressurized sewer to the wastewater treatment plant. There, it runs first into a screening plant where the screens remove all the coarse solids from the water; these are then disposed of separately. Over a period of about 20 minutes the heavy solids then settle out in four sedimentation tanks, the coarse desludgers. What remains at the bottom is then separated out from the sand, which is disposed of separately. The remainder goes to the sludge treatment area as primary sludge.

The wastewater is then treated biologically in five activated sludge tanks. That means the water is set into a swirling motion to provide the microorganisms with oxygen, so the bacteria can convert the organic impurities into endogenous matter, water and carbon dioxide. To keep the odor nuisance to a minimum, these tanks are fitted with Palatal® covers. Biological treatment is complete after 12 - 18 hours and the wastewater is fed into 15 secondary sedimentation tanks. Here it is separated off from the sludge and flows back into the Rhine as clean water. Only the sludge remains behind. It is produced by the solids and bacteria mass which have been separated out from the wastewater. First, this mass goes into the thickening tank. Having become more concentrated here, the sludge is then treated with additives and water removed from it on filter presses. The resulting filter cake is burnt in two fluidized bed incinerators at between 850 and 1000 degrees Celsius. In 2001 the amount was about 400,000 metric tons of filter cake.

The energy released during incineration is used to generate steam in waste-heat boilers. This steam is then used in a turbine to produce electricity and to supply the Pfingstweide area of Ludwigshafen with district heating.
In special cases the wastewater can, in addition, be stored in up to three safety tanks. The wastewater is fed into these if it contains substances which could cause problems in the treatment plant. Only when this water also has undergone special treatment to remove pollutants is it allowed back into the natural water cycle.

Future developments

The quantity of wastewater requiring treatment was cut by 40 percent between 1988 and 2001. Improved water-saving production processes made a major contribution here. The pollutant load was reduced substantially over the same period. As a result, the amounts of sludge to be incinerated are also decreasing. BASF therefore optimized the capacities of the treatment plant. At present, three of the five sludge incinerators, which have been out of use since as long ago as September 1998, are being demolished.

The nitrification trial has been underway in the wastewater treatment plant since September 2001 and is to be maintained for two years. Thus, the scientists will be able to observe how the system responds to seasonal and production-related variations. Nitrification is a process which is designed to reduce the amount of ammonium in the wastewater and thereby prevent over-enrichment of water systems with nutrients. To this end, additional oxygen is blown into the activated sludge tank and the residence time of the sludge increased. Under these conditions, bacteria which break down ammonia grow in the sludge; they are known as nitrifying bacteria. The aim is to reduce the amount of ammoniacal nitrogen in discharges from the treatment plant by at least a further 50 percent over the coming years.

 

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