Abstract
The research presented in this work concerns the potential aluminum load of soft-water lake ecosystems as a result of performing chemical reclamation works. On a semitechnical scale, different doses of PAC-type aluminum coagulant (polyaluminum chloride) were tested. The required doses of coagulant (on average, 11 mg Al/L) were determined based on the amount of phosphorus that is bioavailable in the lake ecosystem. The research covered the lake water, near-bottom and interstitial water, and bottom sediments of five lakes with low alkalinity (0.4–2.5 meq/L) and low calcium contents (5–35 mg Ca/L). The experiments were conducted in situ for 2 years using mesocosms with a volume of approximately 20 m3. The effectiveness of the flocculation and sedimentation processes of coagulant flocs was closely related to changes in water pH caused by acidic coagulant application, and the corresponding transformation level ranged from 39.8 to 99.8%. In the waters of these lakes, where the alkalinity did not reach 1 meq/L, the coagulant used in doses adequate for intensive full-scale projects caused high water pollution with dissolved aluminum fractions (from 0.05 ± 0.01 to 4.67 ± 1.32 mg Al/L). In all lakes, the penetration of dissolved aluminum into the interstitial water of the bottom sediment was limited to the first 5-cm layer. After the application of coagulant, the aluminum content in the bottom sediments significantly increased in proportion to the amount of the PAC used (by 12–96% in terms of a 5-cm surface layer of sediment). Within 2 years of the research, solid fractions (flocks) of the coagulant moved to a depth of 5–10 cm below the bottom level. Due to high release rates of aluminum from the applied aluminum treatments, modifications to the treatment protocols are needed in soft-water lakes.
Highlights
The problem of surface water eutrophication is becoming an increasingly serious threat to the conservation of natural resources, the protection of biodiversity, and the economic use of water
The application of aluminum coagulants should be preceded by a detailed analysis of the environmental conditions of the water and bottom sediments
Among the lakes selected for testing, two reservoirs (Zbiornik Zachodni and Kluka Mała, which were the most dystrophic and alkaline of the waters studied at 0.4–0.7 meq/ L) were completely unfit for the safe use of polyaluminum chloride in eutrophication treatments
Summary
The problem of surface water eutrophication is becoming an increasingly serious threat to the conservation of natural resources, the protection of biodiversity, and the economic use of water. The poor ecological status of lakes has led to losses for the tourism industry (Łopata et al 2016a), and it is severe in developing societies. Water quality deterioration causes the unfavorable reconstruction of ichthyofauna caused by the retreat of environmentally valuable and economically desirable species. Mass algal blooms are a real problem in potable water reservoirs and in the case of industrial abstraction. Various protective measures have been taken in different catchments to counteract the effects of eutrophication (Lossow 1998; Jeppesen et al 2007).
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have