Treated and highly diluted, but wastewater still impacts diversity and energy fluxes of freshwater food webs

Wastewater treatment plants (WWTPs) have greatly improved water quality globally. However, treated effluents still contain a complex cocktail of pollutants whose environmental effects might go unnoticed, masked by additional stressors in the receiving waters or by spatiotemporal variability. We conducted a BACI (Before-After/Control-Impact) ecosystem manipulation experiment, where we diverted part of the effluent of a large tertiary WWTP into a small, unpolluted stream to assess the effects of a well-treated and highly diluted effluent on riverine diversity and food web dynamics. We sampled basal food resources, benthic invertebrates and fish to search for changes on the structure and energy transfer of the food web with the effluent. Although effluent toxicity was low, it reduced diversity, increased primary production and herbivory, and reduced energy fluxes associated to terrestrial inputs. Altogether, the effluent decreased total energy fluxes in stream food webs, showing that treated wastewater can lead to important ecosystem-level changes, affecting the structure and functioning of stream communities even at high dilution rates. The present study shows that current procedures to treat wastewater can still affect freshwater ecosystems and highlights the need for further efforts to treat polluted waters to conserve aquatic food webs.

Adsorption-desorption of dimethenamid and fenarimol onto three agricultural soils as affected by treated wastewater and fresh sewage sludge-derived dissolved organic carbon

The use of treated wastewaters (TWW) in agriculture is widening in areas suffering drought, such as southern Europe, to preserve freshwater supply for human consumption. The composition of TWW, especially concerning their organic carbon (OC) content, has been demonstrated to influence the processes governing the behavior of non-ionic pesticides in soils. Three OC-poor agricultural soils (SV, RM1 and RM3) from the province of Granada (Spain) were chosen for the assessment of the adsorption and desorption of the herbicide dimethenamid (DIM) and the fungicide fenarimol (FEN). TWW and sewage sludge extracts at different dissolved OC (DOC) concentrations (30, 90 and 300 mg L^-1) were considered to evaluate their effect on pesticide adsorption-desorption. As expected by their properties, DIM and FEN were weakly and moderately adsorbed to the soils, respectively. Soil OC seemed to be the major factor controlling FEN adsorption, whereas the mineral fraction played a key role in DIM adsorption, especially in RM1 with high clay:OC ratio. Although TWW did not significantly modify the adsorption of pesticides, it enhanced DIM desorption from the three soils. Adsorption of FEN to SV and RM3 was directly related to the concentration of DOC, possibly due to co-sorption phenomena. Hysteretic desorption was found in all cases, indicating partially reversible adsorption. While FEN desorption was not altered by the solutions, the use of sludge extracts at the highest DOC concentration (300 mg L^-1) enhanced DIM desorption as occurred with TWW. Interactions with DOC in solution seemed to predominate for this less hydrophobic compound, thus increasing the risk of natural waters contamination if TWW will be used.

Small-scale risk assessment of transmission of parasites from wastewater treatment plant to downstream vegetable farms

AIM

The aim of the present study was to simultaneously investigate parasitic contamination of treated wastewater and downstream vegetable farms that are irrigated with treated sewage, during a year.

BACKGROUND

(Oo) Cysts and eggs of parasites are resistant to most of routine wastewater treatment process. Irrigation of vegetables farms with either treated wastewater or illegally use of raw wastewaters enhances the risk of contamination with enteric pathogens.

METHODS

The treated wastewater samples were taken after chlorination from a wastewater treatment plant located at the south of Tehran. In addition, 60 vegetable samples (5 samples from each farm) were collected from the selected downstream farms that routinely used treated wastewater for irrigation of crops. Parasitological tests were performed using Ziehl-Neelsen, conventional lugol's iodine staining and direct microscopical examination.

RESULTS

Parasites including free living larvae, eggs of Toxoascaris leonina, egg of Toxocara sp. Trichuris sp, Trichostrongylus sp and amoeboid trophozoite were seen in 5/12 (41.7%) of vegetable samples gathered during a year. There was no statistically significant correlation between the season and parasitic contamination of the vegetables (P= 1). Furthermore, parasitic contamination was observed in 7/12 (53.8%) of treated wastewater samples. The correlation between season and parasitic contamination of treated wastewater was evaluated that the results showed a higher contamination of treated wastewater in spring and autumn (P<0.05). Fisher's exact test also showed that there was no significant correlation between parasitic contaminations of vegetable samples and treated wastewater according to seasonal change.

CONCLUSION

The results showed parasites in both treated wastewater plant and downstream crops farms that suggests the public health importance of the quality of water resources that routinely used for irrigation of vegetable farms.