The stability of drinking water treatment residue with ozone treatment.

The best management of drinking water treatment residue (DWTR) in environmental remediation should be based on comprehensively understanding the effectiveness and risk of DWTR. In this study, the variation in physicochemical properties, metal lability, and adsorption capability of DWTR under oxidizing condition were investigated. The oxidizing condition was set up using ozone treatment, and the laboratory incubation test were performed within 50 d in association with thermogravimetry, Fourier Transform Infrared Spectrometry, specific surface area and porosity analyzer, fractionation, and P adsorption test. The results showed that ozone treatment had limited effect on the properties of organic matter, the lability of Al, Cu, and Fe, the P adsorption capability, and the distributions of the adsorbed P in DWTR, but the treatment increased N2 sorption/desorption, specific surface area, total pore volume of DWTR and led to the transformation of Mn from acid-soluble to reducible fractions. These findings demonstrated that DWTR generally kept stable under oxidizing environment; even oxidizing environment may induce a tendency of increasing the adsorption capability and decreasing the environmental risk of DWTR. Accordingly, the effectiveness and safety of DWTR can be maintained under natural aerobic environment, and DWTR is a reliable adsorbent that could be recycled in environmental remediation.

Bioavailable phosphorus (P) reduction is less than mobile P immobilization in lake sediment for eutrophication control by inactivating agents.

Phosphorus (P) immobilization by inactivating agents in the sediment of eutrophic lakes to reduce immediately available P in lake water is often crucial for mitigating nuisance eutrophication symptoms, such as cyanobacterial blooms. Macrophytes and phytoplankton, however, can directly utilize P from the sediment for growth. Accordingly, a comprehensive analysis of the P bioavailability in lake sediment amended with two promising P-inactivation agents, namely Phoslock® and drinking water treatment residue (DWTR), was investigated in both short- and long-term studies (20 and 180 d). Phosphorus-availability was assessed using six chemical extraction methods and Hydrilla verticillata and Microcystis aeruginosa growth tests. The results showed that Phoslock® and DWTR significantly reduced mobile P (NH4Cl and Na2S2O4/NaHCO3 extractable P) in lake sediment, while P bioavailability that was assessed by different methods showed considerable deviations. Interestingly, appropriate bioavailable P chemical extraction methods were determined based on linear correlation analysis, and further comparison indicated that reduction of bioavailable P by DWTR (<55% for macrophyte available P) and Phoslock® (<17% for cyanobacteria available P) were clearly less than the mobile P immobilization (>75%) at recommended dosages, which was probably caused by the capability of macrophyte and cyanobacteria to utilize various fractions of P (except the residual P) in amended sediment under proper illumination. Therefore, DWTR and Phoslock® can effectively reduce P release from lake sediment, but the potential bioavailable P may pose uncertainties for eutrophication control in lakes that typically have regular sediment re-suspension. Overall, an evaluation of the bioavailable P pool in the lake ecosystem should be essential for successful lake geo-engineering.

Algal bloom sedimentation induces variable control of lake eutrophication by phosphorus inactivating agents.

Lake eutrophication typically occurs with a syndrome of algae breeding and biomass accumulation (e.g., algal blooms). Therefore, the effect of algal bloom sedimentation on eutrophication control by phosphorus (P) inactivating agents was assessed herein. Three commercial products, including aluminum (Al) sulfate, iron (Fe) sulfate, and a lanthanum-modified clay (Phoslock®), as well as one easily available by-product, drinking water treatment residue (DWTR), were selected. The most important finding was that during algae sedimentation, P immobilization from the overlying water by Al, Phoslock®, and DWTR was dominated by a long-term slow phase (>150d), while Fe has limited effectiveness on the immobilization. Further analysis indicated that the algae sedimentation effect was mainly due to the slow release of P from algae, leading to relatively limited P available for the inactivating agents. Then, a more unfavorable effect on the P immobilization capability of inactivating agents was caused by the induced anaerobic conditions, the released organic matter from algae, and the increased sulfide in the overlying water and sediments during sedimentation. Overall, algae sedimentation induced variable control of eutrophication by P inactivating agents. Accordingly, recommendations for future works about algal lake restoration were also proposed.

Variation of physicochemical properties of drinking water treatment residuals and Phoslock(®) induced by fulvic acid adsorption: Implication for lake restoration.

The use of phosphorus (P) inactivating agents to reduce internal P loading from sediment for lake restoration has attracted increasing attention. Reasonably, the physicochemical properties of P inactivating agents may vary with the interference of various environmental factors, leading to the change of control effectiveness and risks. In this study, the effect of fulvic acid (FA) adsorption on the properties of two agents, drinking water treatment residuals (DWTRs) and Phoslock®, was investigated. The results showed that after adsorption, there was little change for the main structures of DWTRs and Phoslock®, but the thermostability of Phoslock®, as well as the particle size and settleability of the two agents decreased. The specific surface area and pore volume of DWTRs also decreased, while those of Phoslock® increased. Further analysis indicated that aluminum and iron in DWTRs were stable during FA adsorption, but a substantial increase of lanthanum release from Phoslock® was observed, in particular at first (P < 0.01). Moreover, the P immobilization capability of DWTRs had little change after FA adsorption, while the capability of Phoslock® after FA adsorption decreased in solutions (P < 0.001) and sediments (P < 0.1); interestingly, from the view of engineering application, the performance of Phoslock® was not substantially affected. Overall, each P inactivating agent had its own particular responses of the physicochemical properties to environment factors, and detailed investigations on the applicability of each agent were essential before practical application.

Aging of aluminum/iron-based drinking water treatment residuals in lake water and their association with phosphorus immobilization capability.

Aluminum and Fe-based drinking water treatment residuals (DWTRs) have shown a high potential for use by geoengineers in internal P loading control in lakes. In this study, aging of Al/Fe-based DWTRs in lake water under different pH and redox conditions associated with their P immobilization capability was investigated based on a 180-day incubation test. The results showed that the DWTRs before and after incubation under different conditions have similar structures, but their specific surface area and pore volume, especially mesopores with radius at 2.1-5.0 nm drastically decreased. The oxalate extractable Al contents changed little although a small amount of Al transformed from oxidizable to residual forms. The oxalate extractable Fe contents also decreased by a small amount, but the transformation from oxidizable to residual forms were remarkable, approximately by 14.6%. However, the DWTRs before and after incubation had similar P immobilization capabilities in solutions and lake sediments. Even the maximum P adsorption capacity estimated by the Langmuir model increased after incubation. Therefore, it was not necessary to give special attention to the impact of Al and Fe aging on the effectiveness of DWTRs for geoengineering in lakes.

Temperature and cyanobacterial bloom biomass influence phosphorous cycling in eutrophic lake sediments.

Cyanobacterial blooms frequently occur in freshwater lakes, subsequently, substantial amounts of decaying cyanobacterial bloom biomass (CBB) settles onto the lake sediments where anaerobic mineralization reactions prevail. Coupled Fe/S cycling processes can influence the mobilization of phosphorus (P) in sediments, with high releases often resulting in eutrophication. To better understand eutrophication in Lake Taihu (PRC), we investigated the effects of CBB and temperature on phosphorus cycling in lake sediments. Results indicated that added CBB not only enhanced sedimentary iron reduction, but also resulted in a change from net sulfur oxidation to sulfate reduction, which jointly resulted in a spike of soluble Fe(II) and the formation of FeS/FeS2. Phosphate release was also enhanced with CBB amendment along with increases in reduced sulfur. Further release of phosphate was associated with increases in incubation temperature. In addition, CBB amendment resulted in a shift in P from the Fe-adsorbed P and the relatively unreactive Residual-P pools to the more reactive Al-adsorbed P, Ca-bound P and organic-P pools. Phosphorus cycling rates increased on addition of CBB and were higher at elevated temperatures, resulting in increased phosphorus release from sediments. These findings suggest that settling of CBB into sediments will likely increase the extent of eutrophication in aquatic environments and these processes will be magnified at higher temperatures.