Assessing Domestic Wastewater Effluent with a Battery of Bioassays after Treatment with a Specific Consortium of Microalgae and Different Flocculation Methods

Abstract

Wastewater stabilization ponds (WSP) are a common method to treat wastewater before release. The purpose of the current study was to find the most inexpensive coagulation and flocculation reagents to use during harvesting of WSP algae from effluent so that water without algae can be generated for irrigation purposes. In the study, the toxicity of effluent from the algae-based WSP system after treatment with alum and chitosan was investigated. The chemical composition of the resultant supernatants was tested in conjunction with a battery of bioassays (Daphnia magna, Allium cepa, Lactuca sativa and Triticum aestivum). The bioindicator organisms were exposed to varying concentrations of the supernatant resulting from harvesting the algae biomass with chitosan (0.368 g/L chitosan) and aluminium sulphate (9.96 g/L powder). Alum was lethal to D. magna, while chitosan did not seem to affect the Daphnia test specimens. Undiluted chitosan supernatant and 100% alum resulted in minimal inhibition of the rate of T. aestivum seed germination, while both resulted in significant inhibition of the L. sativa seed germination rates. Similarly, minimal effects were found for the root growth in T. aestivum, with significant root growth inhibition observed in L. sativa and A. cepa. In A. cepa, clear differences were observed in the inhibition of root growth when the two reagents were compared. The alum and chitosan supernatants had a total carbon, iron and sulphate concentration of 327.78 mg/L, 0.12 mg/L and 68.44 mg/L and 182.04 mg/L, 0.16 mg/L and 166.80 mg/L, respectively. Based on the test specimens' response, chitosan as flocculation method was less toxic when compared with alum coagulation, even though both algae harvesting methods changed the chemical composition of the algae-treated water.

Water Quality Assessment Using Daphnia: A Brief Review

“…From the comparative analysis presented in Table 1, it was possible to detect that most of the explained articles used the Daphnia magna species for toxicological bioassays. This data is linked to the fact that D. magna is widely used as a bioindicator for the analysis of water quality since it has a short doubling time and high sensitivity [11]. However, Daphnia similis also has a significant level of importance when referred to ecotoxicological assessments, for being broadly distributed in the world, as in Europe, North America, and South America [6,12].…”

“…Daphnia magna [1,6,11,13,14] Metal Exposure [1] Exposure to metal lead(Pb) and the fungicide mancozeb [6] Exposure to supernatants resulting from alum coagulation and chitosan flocculation of algae biomass from wastewater effluent [11] Exposure to TiO2 - [13] Exposure to TI [14] Mortality [1,11,13,14] Immobilization [6,11] Reproduction [6,13] Daphnia similis [6,12] Exposure to metal lead(Pb) and the fungicide mancozeb [6] Exposure to effects of a neurotoxic strain of cyanobacterium Raphidiopsis raciborskii [12] Immobilization [6] Antennae movements, thoracic limbs, post-abdominal claw and heartrate [12] Daphnia pulex [14] Exposure to TI [14] Mortality [14] Immobilization [14] It was also identified that among the compounds analyzed in the studies, Daphnia species are more sensitive to metals. For example, the study that addresses the exposure of Daphnia to lead (Pb), showed that Daphnia magna tends to decrease in size compared to Daphnia similis [6].…”

Cultivation of Daphnia similis Species in Standard Conditions

“…They are small (0.5 to 5.0 nm), easier to handle, and favorable for cultivation in laboratory environments. The difference is their life cycle, in which D. magna has a longer life cycle than D. similis and is more sensitive [7][8][9]. However, in Brazil, the species most used for testing is D. similis since it is recommended for ecotoxicological evaluation in tropical and subtropical climatic countries [3].…”

A Comparative Study of Improvement of Phycoremediation Using a Consortium of Microalgae in Municipal Wastewater Treatment Pond Systems as an Alternative Solution to Africa’s Sanitation Challenges

“…The above-mentioned pond treatment syste treats 0.5 mL day −1 of domestic effluent and is categorized as a micro-WWTP system (F ure 1). Five semi-transparent photobioreactor tanks with a capacity of 5000 L each, diameter of 1800 mm, and height of 2040 mm, were installed at the Motetema wastewater pond system (Figure 2A), and three at the Brandwag wastewater pond system (Figure 2B), also with a capacity of 5000 L each [12,22].…”

“…Five semi-transparent photobioreactor tanks with a capacity of 5000 L each, diameter of 1800 mm, and height of 2040 mm, were installed at the Motetema wastewater pond system (Figure 2A), and three at the Brandwag wastewater pond system (Figure 2B), also with a capacity of 5000 L each [12,22]. The microalgae strains, Chlorella vulgaris (Beijerinck, ATCC: 30821) and Chlorella protothecoides (Kruger, ATCC: 30411), were acquired from American Type Culture Collection (ATCC) and cultured as described by the ATCC protocol and used as starting culture.…”