Paper Industry

Introduction

It is no secret that the circulating water in a paper machine contains enough nutrients for the growth of all kinds of micro-organisms. Plenty of information exists on the different growth conditions for micro-organisms and the damage to fibres and auxiliary materials, which may be caused by micro-organisms. Micro-organisms are also co-responsible for the sediment formation, unpleasant odours and corrosion.

A Brief Review

In the early 1950s, the paper industry started using fast running paper machines to satisfy the demands of the booming newspaper business. Fibre recovery facilities necessitated the first compression of the water circulation system. Stainless steel and plastic pipes replaced copper and iron pipes. Plastic screens would soon be used instead of the old bronze screens. With the introduction of these innovations the problems caused by biological sludge increased. The innovations changed various parameters in favour of microbial growth.

• Compression of the circulating water
• Extension of the paper machine run-times
• Temperature increase of the circulating water
• Higher pH (more alkaline conditions)
• Storage of additives

In summary, if the system runs with high fresh water demand, low temperature of the circulating water and at a low pH (acidic), mostly aerobic bacteria and mould will grow. In a closed water circulation system at a neutral pH and higher temperature, predominantly anaerobic bacteria and yeast will grow.

BIOCIDE USE

In recent years, most paper mills adapted the maintenance treatment regimens to their paper machine's circulation system. This usually ensures trouble-free paper machine runs. Still, the biocide dosages must be adapted to changing requirements and process management modalities to ensure the sustained efficacy of the biocide treatment.

In the last ten to fifteen years, many paper mills changed their treatment regimens for the circulation systems and added surfactants and emulsifying agents to the biocides. The goal of these new treatment regimens is to lower the toxic load in the circulation system.

In recent years, a series of products for the treatment of circulation systems have become available, which are ecologically less harmful than biocides. These products are all oxidants such as hydantoin, peroxyacetic acid or sodium or ammonium bromide.

We want to use the wealth of currently available information to design the best possible treatment for your system.