General Sewage Technology

Prevention of wastewater by means of a closed production cycle with integrated water-re-use treatment plants in a paper factory

Zülpich Papier GmbH, which has been operating under complete effluent free conditions for 25 years, was forced to conside this technology concept because the concentration of odourous compounds in the process water had largely increased during the last few years. To maintain a closed system, an internal anaerobic/aerobic process water treatment plant was installed. A part of the total process water stream is pretreated in an UASB reactor and after aerobic treatment in an aeration tank followed by sand filtration, it is reused as process water. The efficiency of the in-line plant as well as the main improvements on the characteristics of process water, paper and exhaust was controlled in an extensive monitoring program. Within a few weeks after start-up, the in-line process water treatment plant had already reached the forecast efficiency. The organic load of process water (measured as COD) was reduced by 75 percent. The reduction of odourous low molecular fatty acids totals 95 percent.  

Summary

Zülpich Papier GmbH, which has been operating under complete effluent free conditions for 25 years, was forced to consider this technology concept. The concentration of odourous compounds in the process water had significantly increased during the last few years with negative effects on the paper quality and the exhaust of the paper machines. 

To maintain a closed system, an internal anaerobic/aerobic process water treatment plant was installed. A part of the total process water stream is pretreated in an UASB reactor and after aerobic treatment in an aeration tank followed by sand filtration, it is reused as process water. The efficiency of the in-line plant as well as the main improvements on the characteristics of process water, paper and exhaust was controlled in an extensive monitoring program. 

Within a few weeks after start-up, the in-line process water treatment plant had already reached the forecast efficiency. The organic load of process water (measured as COD) was reduced by 75 percent. The reduction of odourous low molecular fatty acids totaled 95 percent. The reduction rates of these acids in the reduced corrugating papers were from 75 to 90 percent. In a significant way, potential odour problems have been solved in the area surrounding the paper mill. Emissions of odourous compounds were eliminated almost completely.

Within the investigation period from September 1995 to April 1996 the in-line treatment plant was operated without substantial trouble. Negative effects on the paper making process were not observed. Also after the start-up of the new paper machine 6, the in-line treatment plant met all requirements.

„The effluent free paper factory"

Paper factories belong to the big water consumers, therefore the water and sewage management are one of the ecological "Achilles' heels" of the branch. 

With an annual production of nearly 15 million tons of paper and pasteboard in Germany about 340 million cubic meter of treated waste water accumulate. An improvement of this ecologically and economically unsatisfactory situation has been aimed at already for a long time. However, specialists have been argueing just as long regarding the limits, within which a restricting of water circulations is possible for individual types of paper, without negatively affecting the product quality or the production procedures. Since the 70's some endorse the effluent free paper production, while at the same time critical voices increase, which stress technical subsequent problems and difficulties of a closed-loop water circulation.

Is the "effluent free paper factory" a worthwhile and attainable goal at all?  In order to answer this question the Zülpich Papier GmbH, a manufacturer of 175,000 tons corrugated board raw papers and test liners from 100 per cent waste paper per year accomplished the demonstration project "waste water avoidance by closed production cycles with integrated water-re-use treatment plant". The Federal Ministry of Environment supported the project (total investment volume approximately twelve million DM (approx. € 6,1 millions)) with an interest subsidy at a value of DM 1,32 millions (approx. € 675,000) to an interest-favorable environmental loan. In addition to that the EC commission supported the project with a subsidy at a value of DM 732,000 (approx. € 375,000) from its environmental advancement program LIFE.

At first sight Zülpich seemed to be the conceivably worst location for such a demonstration project - the enterprise, which in October 1996 expanded its production capacity to 360.000 tons per year by new machines, had already closed its water circulation since 1970 and therefore kept its paper production effluent free. However, this water circulation without discharge of foreign material increasingly encountered difficulties in recent years. A survey of the circulating water qualities confirmed the expectations regarding a high initial load of the process water: Values between 26,000 and 39,000 mg/l of chemical oxygen demand (COD), 4,500 mg/l volatile acids as well as sulfate and calcium concentrations of 2,000 mg/l left no doubt concerning the causes for the smelling nuisances in the neighbourhood and the unpleasant smell of the produced stationery.

In this situation the enterprise decided to establish a waste water treatment plant, which constantly cleans a partial current of the circulating water. However, this is not discharged into a water afterwards but led back into the closed-loop circulation. For this integrated cleaning the stored process water is pumped into a flotation plant for mechanical pretreatment. Afterwards the water is cooled from 50 °C to 35 °C, in order to be biologically prepurified in an anaerobic operated upflow sludge blanket ("Upflow Anaerobic Sludge Blanket or UASB reactor). The secondary cleaning takes place in an activated sludge tank with surface aeration. In order to decrease the solid content the water is conducted over a sand filter after separation of the sludge in the final clarification basin. The water cleaned in such a way can be distributed to the various consumption places at the paper-making machines.

The fermentation gas produced in the anaerobic reactor is largely released from hydrogen sulfide in a gas scrubber and used for energy production in a fermentation gas burner with attached steam boiler. By the use of the fermentation gas 9.5 tons of brown coal briquettes per day can be saved in the context of the in-plant energy production. 

The integrated cleaning equipment was commissioned for the first time in September 1995 and since then has been working almost problem-free. Only its integration into the water circulation in connection with a use of all possible in-plant measures for waste water avoidance made the effluent free paper manufacture possible on a long-term basis.

Only by a comparison with conventional waste water management methods of appropriate enterprises the obtained environmental reliefs become really obvious: If the circulating water of the Zülpich GmbH was discharged into a water, a waste water quantity of 1.08 million cubic meter per year would arise at an annual production of 360,000 tons and a specific waste water quantity of three cubic meters per ton - which is already a good value at comparable enterprises. Thus the waste water quantity saved by the closed-loop circulation corresponds to about 20,000 inhabitant equivalents. As measured by the COD load the saving even corresponds to approximately 170,000 inhabitant equivalents.

The economic aspects of the procedure are also interesting: After deduction of the brown coal saved by the fermentation gas use (DM 426,000 (approx. € 218,000) per year) the operating costs for the circulating water plant amounted to DM 332,000 (approx. € 165,000) in 1996. Since the electricity costs of the integrated cleaning equipment amount to approximately DM 400,000 (approx. € 205,000) per year, energy costs at a value of DM 26,000 (approx. € 13,000) are saved per year. The specific total costs per cubic meter of circulating water amounted to DM 0.97 (approx. € 0.5) in the last year, which is very favorable compared to the normal disposal costs e.g. in local purification plants. Savings at the effluent charge are not considered.  

With this plant concept a technology is available which is convincing under ecological and economic aspects and is also transferable to other enterprises.  For locations with partially opened water circulations and appropriate discharges substantial environmental reliefs could be achieved by an imitation. Moreover, the procedure in Zülpich proves that waste water management in paper factories is not only a question of subsequent measures. 

Biological cleaning methods and production-integrated environmental protection quite fit, if an intelligent concept stands behind. Thus the question for signification and possibility of closed water circulations in paper production can be clearly answered positively after conclusion of this project.

Project Participants

Implementing Institution

Zülpich Papier GmbH

More Project Informations

Project title:  Abwasservermeidung durch geschlossenen Produktionskreislauf mit integrierter Kreislaufwasserbehandlungsanlage in einer Papierfabrik

Project number:  7041

Reference number:  FKZ: 20441-5/25

Project period:  1994 - 1996

Project region:  Germany (North Rhine-Westphalia)

Project contact:

Frau Fischer

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+49 (340) 2103 3067

+49 (340) 2104 3067

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Source:  Environmental library of the Federal Environment Agency (UBA)