Post-ozonation in a municipal wastewater treatment plant improves water quality in the receiving stream

Abstract

Background: Removal of organic micropollutants from wastewater by post-ozonation has been investigated in a municipal wastewater treatment plant (WWTP) temporarily upgraded with full-scale ozonation, followed by sand filtration, as an additional treatment step of the secondary effluent. Here, the SPEAR (species at risk) indicator was used to analyse macroinvertebrate abundance data that were collected in the receiving stream before, during and after ozonation to investigate whether ozonation improved the water quality.

Results: The SPEAR values indicate a better water quality downstream the WWTP during ozonation. With ozonation the relative abundance of vulnerable macroinvertebrates in the stream receiving the treated wastewater increases from 18 % (CI 15-21 %) to 30 % (CI 28-32 %). This increase of 12 % (CI 8-16 %) indicates improved ecological quality of the stream and shifts classification according to the Water Framework Directive from poor to moderate.

Conclusions: The SPEAR concept, originally developed to indicate pesticide stress, also appears to indicate toxic stress by a mixture of various micropollutants including pharmaceuticals, personal care products and pesticides. The responsiveness of the SPEAR indicator means that those macroinvertebrates that are vulnerable to pesticide pollution are also vulnerable to micropollutants from WWTPs. The change in the macroinvertebrate community downstream the WWTP indicates that toxicity by pollutants decreased by more than one order of magnitude during ozonation. Ozonation followed by sand filtration has favourable impacts on the composition of the macroinvertebrate community and can improve the water quality in the receiving stream.

Keywords: Biodiversity; Good biological status; Micropollutant removal; Stream macroinvertebrates; Trait-based ecological risk assessment; Treatment of wastewater.

Fig. 1

Relative abundance of vulnerable taxa. SPEAR indicates the fraction of vulnerable species in the stream with and without ozonation followed by sand filtration (circles macroinvertebrate surveys, dotted line mean, blue bars 95 % confidence intervals). Ozonation increases the abundance of vulnerable species from 18 to 30 %. This increase of 12 % (CI 8–16 %) indicates improved ecological quality of the stream and shifts classification according to the WFD from poor to moderate [12]

Fig. 2

Location of the WWTP and the sampling sites at the stream Furtbach