Research and application of in-situ control technology for sediment rehabilitation in eutrophic water bodies

The effect of microenvironment in the sediment on phosphorus immobilization under capping with ACPM and Phoslock®

Currently, in situ capping is a typical popular geoengineering method for eutrophication control. It is crucial to better understand the effect of microenvironment change due to capping, such as amended calcium peroxide material (ACPM) and Phoslock®, on phosphorus (P) adsorption and immobilization under the addition of external P. The microenvironment in sediment was presented by the concentration of O₂, NH₄⁺, and Fe²⁺ and microbial activity. The P removal and immobilization were also analyzed. The results show that the stronger oxidation in the microenvironment under the capping with ACPM was due to the higher reduction of NH₄⁺ and Fe²⁺ and the higher increase of microbial activity, compared to Phoslock®. Although, under the capping of ACPM, less amount of external P was removed and there was a faster release of sedimentary P, compared to Phoslock®, ACPM improved the transformation of P from mobile P fractions to inert P fractions. In addition, sedimentary P under the capping of ACPM presents less release than that under the capping of Phoslock® during the anaerobic incubation. However, the settlement of suspended solids decreased the function of capping. All these results indicated that the mechanism of P removal and immobilization was different under the capping of ACPM and Phoslock®.

Floating treatment wetlands as biological buoyant filters for wastewater reclamation

Floating treatment wetlands (FTWs) are an innovative product of ecological engineering that can play a promising role in wastewater treatment. It provides low-cost, eco-friendly, and sustainable solutions for the treatment of wastewater, particularly in regions with economic constraints. Generally, FTWs comprise rooted plants that grow on the surface of water with their roots extending down into the pelagic zone rather than being embedded into the sediments. This drooping structure helps develop (1) a hydraulic flow between the root network and the bottom of the treatment system and (2) a large biologically active surface area for the physical entrapment (filtration) of contaminants, as well as their biochemical transformation and degradation. Furthermore, the rooted network allows proliferation of microorganisms that form biofilms and enhance pollutant degradation while promoting plant growth. The augmentation of bacteria in FTWs has been proven to be the most effective approach for reclamation of wastewater. This article discusses the operational parameters of FTWs for maximal remediation of wastewater and highlights the importance of plant-bacteria partnerships in a typical FTW system for enhanced cleanup of wastewater. We propose that this technology is preferable over other methods that require high energy, costs, and area to install or operate machinery.

Recruitment of cyanobacteria by reverse transcription quantitative real-time PCR based on expression of Microcystis gene

In this study, a SYBR Green quantitative real-time PCR method was established and applied. Relative expression of the synthetic genes from Microcystis gas vesicles (gvpC), algal toxin genes (mcyA), and polysaccharides (espL) from water and sediments of Meiliang Bay and from the center of Lake Taihu were tested from January to June, 2017. Indoor Microcystis aeruginosa was used as the control group. The kit for total RNA extraction in Microcystis was optimized. Results showed that the optimized kit extracted high-concentrations and high-quality total RNA from Microcystis. The extraction purity and concentration were significantly higher than those extracted by the original kit. The transcription level of gvpC increased gradually until a peak was reached in March. However, expression of gvpC decreased continuously at the proliferating and floating stages of Cyanobacterial biomass. The maximum level of expression of gvpC in April in comparison to expression of mcyA in March occurred first. We found that the SYBR Green qRT-PCR method, which is characterized by high specificity, repeatability, is rapid, and can be used for quantitative detection of expression of gvpC, mcyA, and espL. The recruitment of cyanobacteria is the process in which cyanobacteria in the sediment began to regain their activity, started to grow and migrated to the water column.

Eutrophication management in surface waters using lanthanum modified bentonite: A review

This paper reviews the scientific knowledge on the use of a lanthanum modified bentonite (LMB) to manage eutrophication in surface water. The LMB has been applied in around 200 environments worldwide and it has undergone extensive testing at laboratory, mesocosm, and whole lake scales. The available data underline a high efficiency for phosphorus binding. This efficiency can be limited by the presence of humic substances and competing oxyanions. Lanthanum concentrations detected during a LMB application are generally below acute toxicological threshold of different organisms, except in low alkalinity waters. To date there are no indications for long-term negative effects on LMB treated ecosystems, but issues related to La accumulation, increase of suspended solids and drastic resources depletion still need to be explored, in particular for sediment dwelling organisms. Application of LMB in saline waters need a careful risk evaluation due to potential lanthanum release.

Restoration of eutrophic freshwater by managing internal nutrient loads. A review

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 biosphere's alteration due to human activities affecting aquatic ecosystems from the Arctic to the Antarctic. As eutrophication becomes frequent and many eutrophic ecosystems have difficulties meeting the EU Water Framework Directive (WFD) criteria the removal of phosphate and/or ammonium gains great importance, in water treatment. The objective of this paper is to review the restoration methods of eutrophic ecosystems, emphasizing remediation methods of internal nutrient release budget as a major factor to control eutrophication. 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 areas that have been implemented were also examined. Moreover, a conceptual model was conducted as a process to determine remediation technique, highlighting the need of an integrated approach to eutrophication management. The chemical lake restoration methods are not a panacea and their implementation should consist a targeted management approach as a part of an integrated management plan. The longevity of the treatment effectiveness using P-inactivation agents is reduced if not given the necessary importance in managing the external nutrient loads. The successful implementation of internal P management measures requires a site-specific study of a range of factors affecting viability of the method used, in connection with an assessment of the potential adverse effects on humans, livestock, biotic and abiotic factors.

Phosphorous control in a eutrophied reservoir

Water in lakes and reservoirs accumulate phosphorous (P) from both internal and external loads. The external P load (EPL) coming from the watershed is considered to be the main cause of eutrophication of water bodies, and control strategies therefore focus on its reduction. However, algae blooms and anoxic conditions often continue even after EPL have been controlled, being the internal P load (IPL) originating from the sediment the main sources of P. To assess the efficiency of the adsorbent Phoslock (a modified bentonite) in controlling P concentrations in water and immobilize releasable P in sediments, mesocosm trials were carried out in a eutrophied reservoir and a model was described and applied that determines the amount of adsorbent and the application frequency necessary to control P concentrations in a eutrophied reservoir. The mesocosm trials confirm that Phoslock reduced P concentrations to or below the limits that define water in mesotrophic state, in approximately 2 weeks. The modeling results suggest that periodic reapplications of the adsorbent are required, unless EPL is reduced by 36 %, which allows the P concentrations in the water column to be constant. Such reduction in EPL would allow future applications of the adsorbent to be required only for control of IPL. The developed model allows planning remediation actions by determining quantities and frequencies for application of adsorbents for P control in eutrophied lakes and reservoirs.