Abstract
Two controlled experiments were operated to evaluate the impact of pH on the treatment efficiency of azo dyes within artificial textile wastewater using ponds as a polishing step. The objectives were to assess the (1) inflow water quality; (2) the presence of Lemna minor and the algae Oedogonium spp. on the dye removal and the outflow water quality; and (3) suitability of applying artificial textile wastewater and the impact of this wastewater and the dye on plants. Findings indicate that the shallow ponds planted with L. minor and/or algae treated the dye Basic Red 46 (BR46) significantly (p < 0.05) higher than the control ponds without any significant (p > 0.05) impact of pH. The potential of L. minor and algae for removal of BR46 was 31% and 25%, respectively. The removal of BR46 was around 89% for ponds planted with L. minor and algae, 58% for algae ponds and 33% for control ponds. Wetlands with L. minor are successful and economic in the complete degradation of BR46 at concentrations of 10 mg L−1 for any pH value between 6 and 9. The removal of ammonium-nitrogen (NH4-N), nitrate-nitrogen (NO3-N) and ortho-phosphate-phosphorus (PO4-P) was higher in planted than in unplanted ponds. The mean outflow values of chemical oxygen demand, NH4-N, NO3-N, suspended solids and total dissolved solids were within the limits for safe discharge. The artificial wastewater constituents after dilution (1 part of artificial wastewater to 24 parts of raw water) were suitable to use within the treatment system containing L. minor.
Highlights
BackgroundThis section provides an overview of previous related work and puts this research study into a broader context
The commercial synthetic dyes used in this study were Acid Blue 113 (AB113), Reactive Blue 198 (RB198), Basic Red 46 (BR46) and Direct Orange 46 (DO46), which were applied without any purification
In terms of N O3-N concentrations, all average outflow concentrations were lower compared to the inflow ones (Supplementary materials 6 and 4, respectively), the control ponds showed outflow concentrations higher than the planted ponds. These findings indicated that L. minor and algae used nitrate as a source for nutrients resulting in a significant (p < 0.05) potential for NO3-N reduction by both L. minor and algae, in addition to the denitrification mechanism
Summary
BackgroundThis section provides an overview of previous related work and puts this research study into a broader context. The growth of the textile industry worldwide has led to increase in discharge of contaminated water to the environment (Saratale et al 2011), especially in developing countries, which discharge textile effluents directly to the receiving watercourses (Chandanshive et al 2016). Shallow ponds with free-floating plants are recommended as ecosystems, because they require low costs for construction and maintenance, especially when the land value is low, and are effective and sustainable (Yaseen and Scholz 2016). These artificial ponds have proven to be efficient to treat diverse wastewaters. This parameter required more attention concerning the purification using pond technology, especially the effect of the inflow pH concerning the long-term system operations
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