Development of physicochemical methods for restoring eutrophic water bodies
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Ζαμπάρας, Μιλτιάδης
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Abstract
Eutrophication has become the primary water quality issue for most of the freshwater and coastal marine ecosystems in the world. It is one of the most visible examples of human changes to the biosphere, affecting aquatic ecosystems from the Arctic to the Antarctic. More than 40% of water bodies in many regions of the world are considered to have eutrophication problems.
A recent study of over 14,000 lakes <1 ha in size in Great Britain found that 51% are likely to require P-decrease measures to meet the Water Framework Directive to achieve ‘good status’ by the year 2015. Many shallow eutrophic lakes will have difficulties meeting the EU Water Framework Directive (WFD) criteria in 2015 without restoration. Therefore, regional water action plans have been adopted to find possibilities for the lakes to meet the criteria of “moderate”, “high”, or “good” ecological condition.
Restoration has been defined as the return of a disturbed system to some pre-disturbance state that is both self-regulating and integrated into the larger landscape. The chemical restoration methods mainly aim at reducing the P release from the sediment by improving the P binding capacity and thus creating P limitation of the phytoplankton. During the recent decade, scientific research has considered a number of different solid adsorbents to be used in reducing the P levels entering the water bodies.
The main objective of the present PhD thesis was to develop physicochemical methods for restoring degraded and poor quality natural water bodies threatened by eutrophication. In the beginning of our research, a primarily in-depth review of restoration methods, emphasizing remediation methods of internal nutrient release budget as a basic factor to control eutrophication, was of major importance, as this knowledge was lacking from the scientific community. The use of phosphate inactivation agents as a restoration tool, their capacity and application methods, as well as the individual results (in water quality, algal blooms, flora and fauna) in a worldwide range, were also thoroughly examined.
Afterwards, the performance of a modified bentonite Zenith/Fe, a primary unmodified bentonite Zenith-N and a lanthanum modified bentonite PhoslockTM, for phosphate uptake from different types of simulated eutrophic water bodies, were studied in detail. In our effort to improve the precursor material (Zenith/Fe), following the research carried out in the context of PhD Thesis, a novel low-cost composite material was prepared (BephosTM) by embedding Fe, Cu ions and humic acid using in the interlayer space of a natural bentonite. BephosTM was evaluated under various physicochemical conditions prevailing in eutrophic water bodies. Bench-scale batch and column experiments were performed to examine its efficiency as adsorbent for phosphate and ammonium removal from natural waters.
Based on the accumulated knowledge gained from the results of our research, a conceptual model as a process to determine the optimal remediation technique, highlighting the need of an integrated approach to eutrophication management has been conducted. Thus, before the decision to proceed to a restoration method, simultaneous monitoring of external and internal nutrient loads should initially be carried out. In this way we will define the reference conditions of the ecosystem and will choose which method to use in order to have the desired results.
In addition, the research carried out in the PhD Thesis, resulted to understanding the role of P bound in sediments determining on the basis of different P-fractions. In this way, it will be reduced the excessive amounts of P-inactivation agents into the water column and sediment, preventing the disturbance for filter feeders and benthic fauna respectively. Another equally important reason to assess P-fractions in sediments is that these forms are closely influenced by the physicochemical parameters prevailing in eutrophic waters and thereby we can assess when the more appropriate time for a water treatment is. In other words, we can remediate according to the proper timeline certain P-fractions are supposed to emerge, achieving high efficiency in water treatment.
Finally, the use of P-adsorption agents (P-AA) might be an alternative method as the adsorbed phosphorus can be used as fertilizer or enriching soil conditioners. Therefore, it is generated a sustainable cycle taking into account a renewable resource-based P-AA leading to environmental protection and conservation of natural resources. P-AA for removal and recovery of phosphorus from eutrophic water bodies are a promising technique but require further study to be used in agriculture.
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Keywords
Eutrophication, Innovative materials, Lake restoration, Bephos, Modeling, Zeolite