Citation: Chamorro, S.; Hernández,
L.; Saéz, K.; Gómez, G.; Vidal, G.
Effects of Black Liquor Shocks on the
Stability of Activated Sludge
Treatment of Kraft Pulp Mill Effluent:
Morphological Alteration in Daphnia
magna and Mutagenicity and
Genotoxicity Response in Salmonella
typhimurium. Sustainability 2022, 14,
3869. https://doi.org/10.3390/
su14073869
Academic Editor: Michalis Diakakis
Received: 17 January 2022
Accepted: 14 March 2022
Published: 25 March 2022
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Article
Effects of Black Liquor Shocks on the Stability of Activated
Sludge Treatment of Kraft Pulp Mill Effluent: Morphological
Alteration in Daphnia magna and Mutagenicity and Genotoxicity
Response in Salmonella typhimurium
Soledad Chamorro
1
, Laura Hernández
1
, Katia Saéz
2
, Gloria Gómez
1
and Gladys Vidal
1,
*
1
Center Europe Latin America (EULA)-Chile, Environmental Engineering & Biotechnology Group (GIBA-UDEC),
Environmental Science Faculty, Universidad de Concepción, Concepcion 4070386, Chile;
schamorr@gmail.com (S.C.); laura.hdez.gonzalez@gmail.com (L.H.); gloriagomezosorio@gmail.com (G.G.)
2
Department of Statistics, Faculty of Mathematics and Physical Sciences, Universidad de Concepción,
Concepcion 4070386, Chile; ksaez@udec.cl
* Correspondence: glvidal@udec.cl
Abstract:
The objective of this study is to evaluate the stability of activated sludge (AS) in the
treatment of kraft pulp mill effluent exposed to black liquor shock, as well as the effect of its exposure
on the morphology of Daphnia magna and DNA damage through mutagenicity and genotoxicity
response in Salmonella typhimurium. To this end, we applied doses of 2-, 4-, 10-, and 30-mL black
liquor/L influent—shock 1 (S1), shock 2 (S2), shock 3 (S3), and shock 4 (S4), respectively—to kraft
pulp mill effluent. The system stability was checked by analyzing heterotrophic biomass activity and
discharge quality, evaluated using Ames test and Daphnia magna. The results show that the chemical
oxygen demand (COD) removal efficiency for normal conditions was 64.84%, falling to 61.68%, and
61.31% for S1 and S2, respectively, and values of 52.11% for S3 and 20.34% for S4. The biomass activity
decreased after each shock was applied, but then recovered. There was no evidence of lethal toxicity
(LC
50
) to Daphnia magna at any of the concentrations. Therefore, it is feasible to apply doses S1 and S2
to an AS system that treats kraft pulp mill effluent.
Keywords:
black liquor toxicity; activated sludge performance; organic matter biodegradation;
heterotrophic biomass activity; effluent toxicity
1. Introduction
The treatment of kraft pulp mill effluent is essential for reducing pollutant load
and complying with environmental legislation and standards. Conventional treatment
technologies such as activated sludge (AS) and moving-bed biofilm reactors (MBBR) are
currently installed in kraft pulp mills to remove organic compounds and acute toxicity from
the kraft mill effluents [
1
,
2
]. The AS aerobic degradation of organic compounds ranges
between 50 and 65% of the chemical oxygen demand (COD) [1,3].
Despite the existence of these technologies, effluent discharges from kraft pulp mills
have been identified as potential contaminants of aquatic environments [
4
]. Their toxic
nature results from the presence of several naturally occurring and xenobiotic compounds,
which are formed and released during various stages of the process [
5
,
6
]. For example,
black liquor is generated in the digestion stage and characterized by inorganic cooking ele-
ments and degraded and dissolved wood substances [
7
,
8
]. The organic component consists
of alkali lignin and the sodium salts of the polysaccharinic acids, phytosterols, resin acids,
and fatty acids, which generate high levels of biological oxygen demand and chemical
oxygen demand [
9
]. In the process, the chemicals used in digestion are regenerated in a
closed cycle, reducing environmental impacts by diverting the black liquor from the pulp
mill effluent treatment system [
2
]. Black liquor spills are accidental and are retained in spill
Sustainability 2022, 14, 3869. https://doi.org/10.3390/su14073869 https://www.mdpi.com/journal/sustainability
