Abstract
The study aimed to assess the usefulness of mineral aggregates in orthophosphate (OP) removal from hypolimnetic water withdrawn from eutrophic lakes. Two low-cost and easily available reactive materials were tested: lightweight expanded clay aggregate (LECA) and crushed limestone (LS). Their performance regarding OP removal and the effect on the pH, Ca2+, Mg2+, N-NO3 and N-NH4 concentrations of treated water were investigated in a column experiment with four-filter beds made of LECA and amended with LS (additions of 0, 25, 50 and 75% of the bed volume). The highest OP removal (>50%) was achieved in LECA beds with high (75% by volume) amendments of LS. Neither LECA nor LS distinctly affected the pH (maximum pH increase, from 7.1 or 7.2 to 7.6, occurred in the case of the LECA bed). In real-life conditions, it is not feasible to install a full-scale bed made of these mineral aggregates on the outflow from a lake due to the large required size of such a bed. At the operation time set for 30 d, the size of a bed would need to reach between 6113.2 and 12,226.4 m3. The proposed bed should be just one of the elements of an integrated treatment system. Constructions consisting of sorption beds ought to be coupled with adequately designed zones of aquatic vegetation. Three conceptional solutions were proposed for in situ treatment of the withdrawn water, differing in arrangement and construction of the potential sorption bed. Application of such solutions should be regarded as a substantial improvement of Olszewski’s method, as it can mitigate the pollution of downstream ecosystems.
Highlights
Many lake restoration methods have been developed and implemented [1,2], including the technical engineering methods and the ecological engineering solutions [3,4], often referred to as “methods supporting the proper restoration of waterbodies”
A combined bed made of lightweight expanded clay aggregate (LECA) and LS at a volumetric ratio of 1:3 is recommended as a treatment method for the purification of hypolimnetic water
Our study revealed that the treatment of hypolimnetic water on sorption beds made of LECA and LS can be a useful method of OP removal
Summary
Many lake restoration methods have been developed and implemented [1,2], including the technical engineering methods and the ecological engineering solutions [3,4], often referred to as “methods supporting the proper restoration of waterbodies”. The simplest and the least expensive method of lake restoration is to withdraw water from the lake’s hypolimnion directly through a pipeline and discharge it into a downstream water body, usually a small river or a creek. The principle of the method is that deoxygenated and nutrient-rich water is removed from the lake together with organic residues settling from the trophogenic zone. Such a technology was developed by Prof
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