Whole effluent assessment of industrial wastewater for determination of bat compliance

Abstract

Background, aim and scope

The applicability of the Whole Effluent Assessment concept for the proof of compliance with the “best available techniques” has been analysed with paper mill wastewater from Germany by considering its persistency (P), potentially bio-accumulative substances (B) and toxicity (T).

Materials and methods

Twenty wastewater samples from 13 paper mills using different types of cellulose fibres as raw materials have been tested in DIN or ISO standardised bioassays: the algae, daphnia, luminescent bacteria, duckweed (Lemna), fish-egg and umu tests with lowest ineffective dilution (LID) as test result. The potentially bio-accumulative substances (PBS) were determined by solid-phase microextraction and referred to the reference compound 2,3-dimethylnaphthalene. Usually, a primary chemical–physical treatment of the wastewater was followed by a single or multi-stage biological treatment. One indirectly discharged wastewater sample was pre-treated biologically in the Zahn–Wellens test before determining its ecotoxicity.

Results

No toxicity or genotoxicity at all was detected in the acute daphnia and fish egg as well as the umu assay. In the luminescent bacteria test, moderate toxicity (up to LID_lb = 6) was observed. Wastewater of four paper mills demonstrated elevated or high algae toxicity (up to LID_A = 128), which was in line with the results of the Lemna test, which mostly was less sensitive than the algae test (up to LID_DW = 8). One indirectly discharged wastewater sample was biodegraded in the Zahn–Wellens test by 96% and was not toxic after this treatment. Low levels of PBS have been detected (median 3.27 mmol L⁻¹). The colouration of the wastewater samples in the visible band did not correlate with algae toxicity and thus is not considered as its primary origin. Further analysis with a partial wastewater stream from thermomechanically produced groundwood pulp (TMP) revealed no algae or luminescent bacteria toxicity after pre-treatment of the sample in the Zahn–Wellens test (chemical oxygen demand elimination 85% in 7 days). Thus, the algae toxicity of the respective paper mill cannot be explained with the TMP partial stream; presumably other raw materials such as biocides might be the source of algae toxicity.

Discussion

Comparative data from wastewater surveillance of authorities confirmed the range of ecotoxicity observed in the study. Wastewater from paper mills generally has no or a moderate ecotoxicity (median LID 1 and 2) while the maximum LID values, especially for the algae and daphnia tests, are considerably elevated (LID_A up to 128, LID_D up to 48).

Conclusions

Wastewater from paper mills generally is low to moderately ecotoxic to aquatic organisms in acute toxicity tests. Some samples show effects in the chronic algae growth inhibition test which cannot be explained exclusively with colouration of the samples. The origin of elevated algae ecotoxicity could not be determined. In the algae test, often flat dose–response relationships and growth promotion at higher dilution factors have been observed, indicating that several effects are overlapping.

Recommendations and perspectives

At least one bioassay should be included in routine wastewater control of paper mills because the paper manufacturing industry is among the most water consuming. Although the algae test was the most sensitive test, it might not be the most appropriate test because of the complex relationship of colouration and inhibition and the smooth dose–effect relationship or even promotion of algae growth often observed. The Lemna test would be a suitable method which also detects inhibitors of photosynthesis and is not disturbed by wastewater colouration.