The effect of anaerobiosis on measurement of sulfite pulp mill effluent concentration in estuarine water by U.V. spectrophotometry

Conclusions

Our results demonstrate two possible sources of error in the field determination of lignins and lignosulfonates. They are caused by:

• 1. Possible microbial degradation of PME, particularly under anaerobic conditions.

• 2. Interference by the bisulfide ion under anaerobic conditions.

One practical application of these observations is that lignins and lignosulfonates as measured by U.V. spectrophotometry cannot be used as a conservative indication of PME in receiving waters, particularly where part of the system is anaerobic. This conclusion probably applies also to other non-specific techniques. Lignins and lignosulfonates have been used as natural tracers in preference to fluorescent dyes (see, for example, WILANDER et al. 1974) because dyes are expensive, they do not change physical conditions of the system and, because they have been previously regarded as conservative, allow ample time for observations of dispersion. AUNINS and TUPREINE (1974) also report coagulation of lignosulfonic complexes on addition to seawater, the degree of this effect depending on salinity, temperature, and degree of turbulent mixing.

Interference from the bisulfide ion can be removed by purging with air or nitrogen. If it is necessary to store water samples before analysis, they must be sterilized effectively, such as by membrane filtration. Field samples filtered through. 22μ or 45μ membrane filters and held in covered test tubes maintained their U.V. absorbance values unchanged for at least 3 months.