More than 2000 years separate the invention of handmade paper in China and today’s highly modern machines in a paper mill, hundreds of yards long, producing high-quality paper by the ton at speeds of close to 2000 metres per minute – up to one thousand tons per day. The basic idea of paper production has remained almost unchanged, however, and water is a constant topic, whether as a necessary medium in preparing the fibres, or as a hazard for the quality of the paper.
Paper is alive. It is continually absorbing or giving off moisture due to the ambient climate. Paper that is too damp or whose moisture content increases during storage is less easy to print and paint, has a greater tendency to form blisters and is less dimension-stable. Especially for the heavily technical applications of the special paper of the Cham Paper Group an excellent dimension stability is absolutely essential.
Through the glass doors of two Memmert constant climate chambers, visitors to the Cham Group trade fair stand were able to observe how different paper behaves under humidity – and how this environmentally-friendly trade show innovation, which does without the standard coating with polyethylene, comes out of the chamber as the clear winner.
Up to 20 cubic metres of fresh water are used in industrial countries per ton of paper manufactured, according to a study by Voith Paper Environmental Solutions from 2007, and considerably more than this in developing countries. At the end of production, almost the same amount of waste water flows back into the sewerage and water system. Even if this waste water is biodegradable, precious oxygen is removed from the water, burdening the habitat of fish and other water creatures. Machine and plant manufacturers are working flat out on eco-friendly and resource-saving procedures to drastically reduce the amount of waste water – target amounts here are 1 to 2 litres per kilogram of paper manufactured according to Voith Paper – and to keep the amounts still needed as pollutant-free as possible.
One of many key indicators for assessing wastewater quality is the so-called BSB 5, the “biochemical oxygen demand“, in accordance with DIN EN 1899-1, which is used within five days by bacteria and other microorganisms to break down organic substances at a temperature of 20 °C. The water sample is mixed with oxygen-saturated water containing bacteria, and then its oxygen content is determined. After five days in the incubator, the oxygen content is again measured and the result – that is, the oxygen consumption – is specified as BSB 5 in mg O2/l.
Microorganisms such as yeast, fungus and bacteria can make life really difficult for a paper mill, because the production process with fluid media, heat and organic raw materials is an ideal culture medium. In the worst case, biofilms are deposited in the equipment, corrosion occurs, raw materials can go off, the equipment may not function properly or there is a drop in product quality. Starting with the fibre materials and ending with the finished products, the spreading of microorganisms is constantly monitored in the laboratory, among other things, via the surface colony count in accordance with DIN EN 54378, as well as the total colony count in accordance with 54379.
