Summary
At the end of April 1990, a recirculation water purification plant was taken into operation to close the in-house water cycle at Kartonfabrik Rieger GmbH & Co. KG. The recirculation water purification plant consists of two series-connected pulp catchers and a flotation unit at the primary treatment stage, and a flotation-filtration pulp catcher at the secondary treatment stage. The clear water generated at primary treatment has a solids content of 240 mg/l, while the super-clear water produced at secondary treatment has a solids content of 10 - 30 mg/l and is deployed instead of fresh water. About 6,5 l wastewater/kg paper is achieved.
In late 1991 a biological high-intensity unit that works according to the HCR (high-performance-compact-reactor) process was taken into operation for final biological treatment of the wastewater resulting from production. The central part of the plant consists of binars jets located in the loop reactors; these jets serve to disperse bacterial floc into fine agglomerates on the basis of the turbulence caused and the shear force. This prevents the development of chlamydobacteriales and thus the formation of bulking sludge. At the same time, the large surface area of the bacterial floc favours the formation of a productive bacteria population and thus enables a high ratio of space loading. Stable operating conditions at the highest possible level of decomposition have been achieved as the result of extensive optimisation measures.
The following values are achieved in the outflow (average 1994 values):
- COD concentration: 878mg/l;
- BOD concentration: 267mg/l;
- Solids content: 74mg/l
These values do not comply with the required standards. In order to meet the required outflow values, a conventional aeration unit has been installed downstream from the HCR plant.
Further information in German:
Introduction of stepped water circuits with a biological heavy-duty sewage plant for cardboard production
The Kartonfabrik Rieger in Trostberg manufactures packaging papers predominantly from waste paper and introduces its waste water directly into the Möglinger Mühlkanal. The paper factory produced relatively high specific waste water quantities (> 35 m³/t) and high specific COD loads (>15 kg COD/t), which substantially exceeded the minimum requirements. It was therefore necessary to restrict the water circulations of the plant and to clean the remaining waste water. The following goals were specified:
- Decreasing the specific waste water volume to approx. 6.6 l/kg cardboard
- Separation of the water circulation into pitch circuits for high-quality, white surface layers and qualitatively less fastidious central and back positions of the cardboard
- Most extensive recuperation of the high-quality cover material in a separate circuit
- Installation of a multi-level precipitation and flocculation in order to win optically highly pure and colourless water
- Improvement of the waste water purification and avoidance of bulking sludge by a compact high-performance biology, which works according to the principle of a loop-type bubble column
- Clear falling below of the limit values of the 19th waste water administrative regulation (1989).
The project had thus two focal points: the separation and restricting of the water circulations and the establishment and optimization of various waste water treatment aggregates. The loop-type bubble column (HCR reactor = high-performance-compact-reactor) applied in the context of this project for the biological cleaning of the waste water of the cardboard mill represented the first installation of this type in the paper industry.
At the end of April 1990 the recirculation water purification plant was taken into operation. The first clarifying stage, a flotation pulp catcher, produces the so-called clear water and works reliably. The subsequent second pulp catcher (the so-called supercell) is to clarify this already preliminarily cleaned waste water so that it can be used instead of fresh water in many application ranges. The second clarifying stage is a complex plant, which unites the cleaning principles flocculation and filtration in closest place in one reactor, in order to save place. Numerous disturbances arose, of which in particular the partial adding of the sand filter was problematic. Although in the meantime the so-called supercell can be operated under optimal operating conditions, the employment of this compact technology for the cleaning of circulating water does not seem to be recommendable because of its susceptibility to interference and thus smaller availability.
Parallel to the installation of the recirculation water purification plant numerous measures for isolating the individual secondary cycles of the paper-making machines were converted in the in-plant material/water system. The specific waste water quantity was decreased to 6.5 l/kg cardboard.
In December 1991 the plant for the biological sewage purification was taken into operation. The operation of the space-saving high-performance purification plant (HCR reactor = High Performance Compact Reactor) of the loop-type bubble column type was for a long time connected with substantial difficulties, which however could be solved in the meantime. Apart from foaming problems the bad setting characteristics of the sludge represented the main difficulty.
On the average the HCR plant reaches a COD reduction of 63 % and a BSB5 degradation of 81 %. The following outflow concentrations were reached:
- COD: 880 mg/l;
- BSB5/day: 270 mg/l;
- Solids: 74 mg/l.
Thus the loads of organic materials introduced into the water were reduced by 3,152 kg COD/day and 2,651 kg BSB5/day (average value January - July 1996).
Despite the accomplished extensive improvement measures the goal values of the project and the required outflow values according to the law on water are not reached. The cardboard mill therefore established a conventional aeration unit downstream from the HCR plant.
Concerning the first application of the HCR reactor in the paper industry the following findings have to be recorded:
Due to its susceptibility to interference, to the insufficient outflow values and the high energy input compared with conventional biological plants this installation type is not recommended for the employment in the paper industry. While for conventional plants approx. 1 KWh/kg BSB5 eliminated are calculated, the HCR reactor needs 3.1 KWh/kg BSB5 eliminated. As technology for the biological pretreatment of relatively concentrated waste water (COD = 2,000 mg/l) the anaerobic technology is a much more suitable engineering technology. The HCR reactor is not - as originally intended - a procedure for the final purification of waste water, but a pretreatment procedure which needs a subsequent clarifying stage.
