A process for the production of waste paper fibres and grass fibre containing paper is published. In a pulper, waste paper material and grass material and process water are inserted. A mass of waste paper fibre supplied by the pulp and of grass fibre supplied by the pulp material shall be applied to at least one carrier sieve to form a paper trail, separated from any part of the process water. In any case, part of the process water is returned for re-insertion into the powder. The process water is originally obtained from fresh water,which has a pH value in the range of 7,0 to 8,5. In any case, process water is given a reduction in the formation of process-damaging microorganisms probiotic bacteria, but not biocides. The pH value of the process water is monitored and, if the pH value decreases below a threshold, a basic medium is added in increased dosage to achieve a set of the pH value of the process water to a target value and to keep the pH value to the target value. The threshold value of the pH value shall be at least 0,2, in particular at least 0,3 higher than the target value.
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