ENVIROCELL

Home | Consultancy | Training | Publications | CD-roms | Site map | Contact

CONSULTANCY ACTIVITIES

WATER MANAGEMENT

There are three essential ingredients in papermaking - fibre, energy and water. Although the greatest by volume, water is also the cheapest raw material and this can engender a relaxed attitude to its overall handling. However, the actual cost of bought-in water is a small fraction of total water-related costs, which are mainly associated with losses of raw materials in the mill wastewater. Water consumption is also important as an indicator of environmental-soundness in view of its potential contribution to clean, sustainable operation. These aspects are summarised in the diagram below.

Consultancy can be provided in the following four broad areas:

Water supply and treatment

Although this is not a problem area for most mills, new technologies and chemicals have been developed for removal of particulate contaminants and for disinfection. Incoming water quality also has some bearing on wet end chemistry and thereby on retention effects and wastewater losses.

Waste minimisation

The loss of materials in the raw wastewater reflects a number of facets of machine operation - wet end retentions, dissolution/fragmentation from broke, spillages, degree of water closure, cleaning, etc. Raw material selection and wet end chemistry play important roles in optimising paper quality and machine runnability whilst at the same time minimising losses.

Wastewater treatment

Wastewaters may be treated for several reasons:
- in order to provide purified water for further in-mill use,
- to comply with standards for external discharge or
- to reduce charges imposed on direct and indirect discharges.

Such systems are usually located on the mixed mill wastewater, but may be better applied to treat individual streams. Treatment plant must be considered as an integral part of the overall mill system and not simply as an end-of-pipe fix. In order to be environmentally-sound as well as meeting the above objectives, the recovery of useful materials (eg energy) should be maximised and the inputs of other resources (eg chemicals) should be minimised. Whilst there are a finite number of process types suitable for mill wastewater treatment, the number of configurations and commercial variants within each type is endless. Selection of the "best" option needs careful appraisal of not only its cost performance, but also of its size, flexibility, adaptability, runnability and ease of maintenance. Proven treatment options are now beginning to extend well beyond the traditional combination of primary clarification and secondary bio-treatment to include membrane processes, evaporation and chemical oxidation techniques.

Closing up water systems

The main motivators for closing up are to reduce reliance on an external resource (albeit a renewable one) and to reduce wastewater emissions. The number of ways to accomplish this are myriad with the optimum combination of techniques being totally dependent on individual mill circumstances. Whilst technically feasible, complete closure of a mill's water system may not be the best environmental or economic option. Zero effluent discharge (ZED) is not synonymous with zero emissions or zero impact. Wastewater treatment is an important issue within, not separate from, closing up programmes. Mill targets for fresh water consumption need to be set progressively over a timescale of years rather than months and should anticipate other changes that are inevitably taking place within the mill operation over that time. The effect on process chemistry and biology is an important factor within closing up programmes that is likely to dictate the best approach to and extent of closure at most mills. Closing up needs to be carefully integrated with other clean operating techniques in order to provide the best environmental and most economic solution. In turn, water needs to be managed within an overall environmental management system that addresses all the other issues relevant to the mill's impacts on the total paper cycle.