Introduction: We have known for some time that lime precipitation causes an increase in operating problems for recycled paper processors with the usual circulation constrictions and pH control. Those affected directly are biological processing stages for cleaning process water. Little known in the past was the factthatCaCO_3-precipitation and its consequence are meanwhile responsible for a considerable share of the operating expenses for biological process water cleaning and that they cause obstacles for the reusing of the biowater. As a result of frequent lengthy and cost-intensive cleaning shutdowns in the anaerobic and aerobic cleaning stages, AEROCYCLE Ltd. -Deutschland- was commissioned to conduct operational trials on process water softening by one of the major European recycled paper processors in March of 2003. The examinations represent a continuation of the research project on ,,Enthaertung und Wiederverwendung biologisch aufbereiteter Prozesswasser aus der Papierfabrikation " (Softening and reutilisation of biologically treated process water from paper manufacturing) elsewhere in Europe. Objective of the study The objective of the study was to record the calcium-based damages, their follow-up costs (actual status) and to develop a concept to solve the calcium problem. To check the concept of the prepared solution, complex trials were used to simulate the operation of all the processing steps involved. The core of the trial setup is the AZE process, which was developed and patented by AEROCYCLE Ltd. In addition to proving the technical feasibility, a balance sheet for the developed process control will also be prepared to show the expected potential savings. Conclusion: Simulating industrial-scale process has shown that the Ca level in the influent to the biological cleaning stages can be lowered considerably through water softening and recirculation. The corrosion-promoting chloride load and the conductivity are both decreased by 30%. Softening the process water with the AZE process effectively reduces the CaCO_3-precipitation and drastically reduces the operating costs while increasing the efficiency. Improved biological metabolism increases the anaerobic COD elimination; in this case by more than 10%. The bio-gas yield is appropriately increased. It was possible to lower the COD-effluent values from the aerobic process by 60 mg/l using the introduced process, in order to keep to the municipal discharge values. We will be reporting shortly on the Client's experiences with the industrial scale system for partial flow water softening based on the AZE process.
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