[Composition and ways of reusing activated carbon sludge from surface water treatment plants].

By using activated carbon (PAC) or by other water treatment procedures remarkable amounts of sludges are produced that have normally to be discharged as wastes outside the plant site. The research objective of this study is to get basic information about the quality of PAC sludges to characterise these materials in order to decide between depositing or re-use/recycling. On four water works with artificial ground water recharge and PAC treatment plants to eliminate pesticides from surface waters detailed analyses and experiments were carried out. The determination of carbon, nitrogen, other nutrient elements, heavy-metals and organic pollutants reveal greatly differing amounts within the water works and during the year. The treatment techniques had an important influence on the chemical composition of the sludges. Mixing of PAC sludges with other sludges strongly reduced the amount of carbon. Heavy metals were present only in small quantities. Sludge from one plant, however, contained elevated concentrations of arsenic. PAC sludges from plants treating river water had considerably high amounts of adsorbable organohalogen. Leaching experiments performed with the sludges demonstrated that only small quantities of pollutants are extractable. For most sludges a deposition on domestic refuse dumps is possible. An alternative way is to discharge the liquid sludges into municipal sewage treatment plants. Addition to the biological treatment tank significantly reduced the concentration of AOX in the sewage effluent. Laboratory experiments and field studies on heavily polluted dump leachates showed a remarkable remaining adsorption capacity of the PAC. As a consequence, PAC sludges have to be considered not exclusively as wastes, but rather as valuable materials for purification processes treating waste waters with high loads of organic, especially organohalogen, substances.