through this invention it is possible to dose a polymer dependent on the amount of organic material present in a dredging sludge , preferably to dose the polymer proportional to the amount of organic material . not only is the polymer now used efficiently , also the overdosing of polymer is prevented . overdosing of polymer will lead to free ( cationic ) polymer being released to the environment with the associated risk of fish kill . according to the present invention it is advantageously possible to measure in any sludge stream ( to be supplied by the dredging operation ) the actual amount of organic material and to use this value to dose the cationic polymer proportional to this . when dredging ( harbor ) sludge the flow of material ( water , sand , clay , organic ) will greatly depend on how the dredging boat is being operated and what the nature of the dredged material would be . the amount and / or type of materials that are being transported to the geotube for dewatering comprise a mixture of water , sand and organic material . for optimal dewatering results , sufficient polymer must be dosed , but the big danger is that a large part of the time the polymer is being underfed ( resulting in a not complete dewatering ) or overfed ( resulting in free polymer being released to the environment ). in particular this last case results in big dangers for the nature e . g . for lakes , rivers and / or seas . the solids in a dredging sludge contain sand ( which will not or only slightly react with the cationic polymer ) and organic material ( which will react with the cationic flocculating agent ). the total flow of sludge is typically stable . fig1 depicts an apparatus 100 according to an exemplary embodiment of the present invention . the total flow of sludge in a pipeline 102 can be measured reliably using an electromagnetic flow meter 105 whereby the flow meter is preferably protected by a rubber lining . the density of the sludge can be measured reliably using a radiometric density meter 103 . the measurement , using preferably an optical immersion sensor 104 , reliably measures the solids level in the sludge . the sand fraction in the sludge is the factor that influences the density of the sludge most considerably . according to the present invention it is advantageously possible that the amount of polymer will react completely with the organic material and clay particles when dosed in proportion . the flow of sludge ( measured , e . g ., in cubic meters per second ( m 3 / s ) or a multiple or fraction thereof ), the density of the sludge ( measured , e . g ., in kilograms per cubic meter ( kg / m 3 ) or a multiple or fraction thereof ) and the solids level in the sludge ( measured , e . g ., by the percentage of the volume of solids compared to the total volume of the sludge or by the percentage of the weight of solids compared to the total weight of the sludge ) are monitored continuously . from the density of the sludge , the amount ( i . e . the percentage ) of sand is being calculated ( second content information ). this percentage is being deducted from the measured amount of total solids in the sludge ( first content information ). the result of this is equal to ( or corresponds at least approximately to ) the fraction of organic material in the sludge . the flow of sludge multiplied by this percentage ( i . e . the fraction of organic material in the sludge ) is equal to the amount of organic material per time . for example , the flow f of sludge , the density d of the sludge and the solids level s in the sludge are measured . the density of water w , organic material o and sand s are well known . the total solids comprise a percentage of organic material and a percentage of sand / clay . therefore there are three equations and three unknown variables : the content of sand in the sludge , the content of organic material in the sludge and the content of water in the sludge , which leads to a solvable problem . preferably the calculations will be made using a programmable logic controller ( plc ), more preferably with a touch screen . according to the present invention , it is advantageously possible to dose the polymer proportional to the calculated value in a dosing unit 101 and prevent under dosing and over dosing of polymer through exact dosing . preferably the apparatus 100 further comprises a polymer dissolving unit 106 . preferably the dosing unit 101 comprises an electromagnetic flow meter that is optionally installed in the polymer injection line . advantageously it is possible to monitor the actual amount of polymer solution that is being dosed to the sludge , knowing the sludge flow , and the solids level . it is then possible to accurately calculate the amount of polymer ( kg ) dosed per mt of dry sludge . the output from the plc is controlling the speed of the polymer solution pump which determines the necessary amount of polymer added . an alternative or an optional embodiment of the present invention is a method for dewatering of sludge , the method comprising the steps of adding an aqueous solution of polymeric flocculating agent to the sludge , wherein a material information related to a material property of a filtrate is determined , wherein the material information is used for controlling the content of the polymeric flocculating agent in the filtrate . therefore it is advantageously possible to avoid leading filtrate with free polymeric agents into the environment . in the following , conducted examples are presented . these examples refer to the second step , wherein the second step comprises measuring a material information related to a material property of the filtrate being determined , wherein the material information is used for controlling the content of the polymeric flocculating agent in the filtrate . the material information comprises in the following examples the ph - value of the filtrate , wherein the ph - value of the filtrate is increased to a predetermined level . the increased ph - value of the filtrate is neutralized after a residence time ( i . e . the ph - value is reduced to a more neutral level such as a level of ph 7 or to ph levels that would be acceptable for the ecosystem where the filtrate is being released to ), wherein during the residence time the filtrate comprises the increased ph - value . in the following examples , the cationic polymer drewfloc 2418 is used . a flocculating agent ( drewfloc 2418 , 10 mol / 22 weight % cationic emulsion polymer based on adame - quat ( methylchloride quaternised dimethylaminoethylacrylate ) and acrylamide ) is used to provide a 0 . 1 % aqueous solution of drewfloc 2418 in desalinated water . then this solution was used to provide a 25 ppm drewfloc 2418 polymer test solution by means of using 975 g of tap - water and 25 g of the 0 . 1 % aqueous solution of drewfloc 2418 . this test solution is provided three times . for a first example , 3 . 2 g naoh ( 20 %) is added to the test solution for obtaining a ph value of 11 . 5 . for a second example , 2 . 0 g naoh ( 20 %) is added to the test solution for obtaining a ph value of 11 . 0 . for a third example , the ph value of the test solution is not changed . after three hours of storage , experiments using a clay suspension have been performed . the solutions of the three examples of test solutions showed a strong flocculation of the clay suspension after three days of further storage , experiments using a particle charge detector produced by the company mütek have been conducted using the three test solutions and it was found that the ionogenity of the solutions has been strongly anionic . the a . m . polymer test solution containing 25 ppm drewfloc 2418 has been used to provide solutions of different ph values using different amounts of naoh ( 20 % solution ) or ca ( oh ) 2 ( 100 g / l ). these solutions having different ph values have been measured using the mütek particle charge detector . the results concerning the ionogenity are presented in the following table : the first column gives the number of the example . in the second column , the obtained ph value is given . the third column specifies the amount of naoh ( 20 % solution ) or ca ( oh ) 2 ( 100 g / l ) added , and the fourth column gives the duration of storage in minutes . the fifth column specifies the ionogenity . examples to test the degradation of cationic activity have been conducted using a filtrate from a geotube installation in herzogenrath , germany . a cross linked polymer , zetag 8848 fs ( basf , ciba ) has been used . the filtrate water contained approximately 20 ppm of this product . this filtrate water has been used for the following examples ( using 1500 g of the filtrate water in the examples ). the results concerning the ionogenity are presented in the following table : the first column gives the number of the example . in the second column , the obtained ph value is given . the third column specifies the amount of naoh ( 20 % solution ) or ca ( oh ) 2 ( 100 g / l ) added ( if applicable ), and the fourth column gives the duration of storage in hours . the fifth column specifies the ionogenity . further experiments have been conducted to find solutions to reduce the time of storage to about 1 minute ( 60 seconds ) and to still eliminated the cationic change measured with the particle charge detector produced by the company mütek . for the examples 17 to 22 , again the flocculating agent ( drewfloc 2418 , 10 mol / 22 weight % cationic emulsion polymer based on adame - quat ( methylchloride quaternised dimethylaminoethylacrylate ) and acrylamide ) is used to provide a 0 . 1 % aqueous solution of drewfloc 2418 in desalinated water . then this solution was used to provide a 25 ppm drewfloc 2418 polymer test solution by means of using 975 g of tap - water and 25 g of the 0 . 1 % aqueous solution of drewfloc 2418 . this test solution is provided for all the examples 17 to 22 . these different polymer test solutions containing 25 ppm drewfloc 2418 have been used to provide solutions of different ph values using different amounts of naoh ( 20 % solution ). these solutions having different ph values have been measured using the mütek particle charge detector . the results concerning the ionogenity are presented in the following table : the first column gives the number of the example . in the second column , the obtained ph value is given . the third column specifies the amount of naoh ( 20 % solution ) added , and the fourth column gives the duration of storage in seconds . the fifth column specifies the ionogenity .