Bacterial toxicity assessment of drinking water treatment residue (DWTR) and lake sediment amended with DWTR

A model for predicting reduction in mobile phosphorus of lake sediment by aluminum drinking water treatment residuals

Drinking water treatment residual (DWTR) derived from flocculation and sedimentation of raw water using aluminum coagulants is a valuable environmental remediation byproduct capable of inactivating phosphorus (P). However, no generalizable model exists in the literature to describe reduction of releasable (mobile) P in lake sediment as a result of DWTR addition. The reduction of mobile P (sum of labile P and reductant soluble P) was investigated in over 100 sub-samples using five sediment samples from two lakes and three DWTRs from different water treatment plants. A consistent relationship was determined across a range of mobile P contents (0.23 g/m²/cm to 0.92 g/m²/cm, or 15.8 to 186.1 µg/g DW) and DWTRs. The relationship was best described as a function of the mobile P content of the sediment and the oxalate-extractable aluminum content of the DWTR. An empirical model was developed to predict the immediate reduction in mobile P following the addition of DWTR containing aluminum. This model was validated using two additional lake sediments and one additional DWTR (R² = 0.995). Thus, the immediate inactivation of P in lake sediment following DWTR addition can be predicted with this model, which can be used with internal P loading or other water quality goals to determine an appropriate DWTR dose. Further recommendations were made about dosing DWTRs for lake restoration, allowing practitioners to use DWTR to inactivate P in lake sediment without conducting individual sorption experiments.

Ceramsite made from drinking water treatment residue for water treatment: A critical review in association with typical ceramsite making

The use of ceramsite to construct filtration systems (e.g., biofilters) is a common method for water treatment. To promote such applications, the development of low-cost, high-performance, and environmentally friendly ceramsites has received increasing attention from scientists, and a critical step in the development is the preparation of raw materials. As an inevitable and non-hazardous by-product during potable water production, drinking water treatment residue (DWTR) is typically recycled to make water treatment ceramsite to promote recycling in filtration systems. This study aims to bridge the knowledge gap regarding DWTR in making ceramsites for water treatment. The results suggest that the fabrication methods for DWTR-based ceramsite can be generally classified into sintering and non-sintering procedures. For the sintering method, owing to the heterogeneous properties (especially aluminum, iron, and calcium), DWTR has been applied as various sub-ingredients for raw materials preparations. In contrast, for the non-sintering method, DWTR is commonly applied as the main ingredient, and natural curing, physical crosslinking, and thermal treatment methods have been typically adopted to make ceramsite. However, DWTR-based ceramsites tend to have a high adsorption capability and favorable microbial effects to control different kinds of pollution (e.g., phosphorus, nitrogen, and organic matter). Future work is typically recommended to thoroughly evaluate the performance of DWTR-based ceramsite-constructed filtration systems to control water pollution concerning the making procedures, the potential to control pollution, the stability, and the safety of raw DWTR-based ceramsite, providing systematic information to design more proper planning for beneficial recycling.

A comprehensive review on the coagulant recovery and reuse from drinking water treatment sludge

The main treatment unit in conventional systems for surface water is coagulation-flocculation (CF) process, which consumes huge quantities of coagulant, and produces large volume of sludge. The produced sludge is known as one of the components of water treatment sludge (WTS), which is considered as a global issue and hot topic require careful attention from the plant operators and sludge managers to be managed sustainably with applying an ecofriendly method. Among the suggested technologies, recovery and reuse of coagulants from WTS show the potential to decrease the waste disposal and chemicals usage for drinking water treatment significantly. So, this comprehensive review provides a useful insight into environmental and health problems of WTS, reports the sources, physicochemical properties of sludge, describes different sludge management methods by more focus on coagulant recovery (CR), which significantly point out the different aspects of WTS recovery and reuse, and eventually, economic evaluation of the CR process was also discussed. The results of this review confirm that coagulants can be recovered from WTS by different methods and also will be reused for multiple times in the removal of pollutants from water and wastewater. Moreover, the recovered coagulants can be used as building and construction materials, constructed wetlands substrate and other aims.

A systematic review of the water treatment sludge toxicity to terrestrial and aquatic biota: state of the art and management challenges

Safe drinking water' supply is an essential service and depends directly on the water treatment that produces water treatment sludge (WTS) as a product, whose final destination varies and remains a challenge. The ecotoxicity assessment of the WTS address the ecological implications of the WTS disposal but these information is still scarce in the literature. In this sense, we did a systematic review of the ecotoxicological studies on WTS using databases from six platforms. From the 785 papers recovered; 16 studies were eligible and showed the ecotoxicity assays' applicability to evaluate the WTS. We discussed WTS ecotoxicity considering sample characterization; terrestrial and aquatic toxicity assays; and WTS challenges. WTS proved to be a highly heterogeneous matrix composed mainly of coagulant precipitates, including Al and Fe. Studies lack consensus concerning the most representative/sensitive species for evaluating WTS' toxicity. Crustaceans were the most studied aquatic group, although algae species were more sensitive. Besides, soil ecotoxicity assessed only plant growth, and a single study used the earthworm. Even papers used bioassays to indicate the recycling WTS' feasibility, there is a lack of specific legislation regarding the WTS reuse. Furthermore, are necessary a regulation for WTS management that involves an ecological risk assessment.

Ecological floating bed for decontamination of eutrophic water bodies: Using alum sludge ceramsite

In this study, a combined ecological floating bed (C-EFB) with alum sludge ceramsite (ASC) was designed to improve the water purification effect of traditional ecological floating beds (T-EFBs). During the ASC preparation stage, alum sludge was shaped into a ball, air-dried, and fired under 600 °C. The physical and chemical properties of the ASC meet the requirements of Artificial Ceramsite Filter Materials for Water Treatment (CJ/T229-2008). This study investigated the increased capability of this new-type artificial substrate (ASC) on the removal of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total phosphorus (TP), and total nitrogen (TN) from eutrophic landscape water. Compared with the T-EFB, the C-EFB owns a higher purification efficiency. The highest average efficiency of COD, NH4+-N, TN and TP removals during the four operating stages was 78.2%, 58.1%, 46.7% and 53.2%, respectively, in the C-EFB, which were all higher than those of 53.5%, 32.4%, 27.2% and 25.8%, respectively, for the T-EFB. Among them, the C-EFB showed a higher advantage in the removal of TP. The results showed that the potential benefits of utilizing ASC in seriously eutrophic bodies of water.

Drinking water treatment residual as a ballast to sink Microcystis cyanobacteria and inactivate phosphorus in tropical lake water

The combination of a low dose of coagulant with a ballast that can inactive phosphorus (P) in lake sediment-a technique known as "flock and lock"-is one method for restoration of eutrophic lakes. The effectiveness of a drinking water treatment residual (DWTR) as a ballast in flock and lock was assessed using assays of eutrophic lake water from Thailand dominated by Microcystis aeruginosa cyanobacteria colonies by measuring changes in chlorophyll-a, pH, and zeta potential. P sorption isotherms were developed from long-term batch equilibrium experiments; desorption of nutrients and metals was assessed via leaching experiments; and morphological changes to cellular structure were assessed using scanning electron microscopy. Results showed that combining DWTR with a low dose of aluminum sulfate (0.6-4.0 mg Al/L) effectively sank 74-96% of Microcystis, with DWTR dose (50-400 mg/L), initial chlorophyll-a concentration (92-976 µg/L), pH (7.4-9.3), and alkalinity (99-108 ppm CaCO₃) identified as factors significantly associated with sinking efficacy. P sorption capacity of the DWTR (7.12 mg/g) was significantly higher than a local soil (0.33 mg/g), enabling the DWTR to inactivate P in lake sediment. Desorption of Al, Fe, Ca and N from the DWTR was estimated to contribute to a marginal increase in concentrations of those compounds in the water column of a small shallow lake (1.2, 0.66, 53.4, and 0.07 µg/L, respectively) following a simulated application. Therefore, pre-treated DWTRs may be a viable alternative ballast in the flock and lock approach to lake restoration, supplementing or replacing modified local soils or lanthanum modified clays.

The feasibility of recycling drinking water treatment residue as suspended substrate for the removal of excess P and N from natural water

Eutrophication of natural water commonly involves the pollution of both P and N. Here, we developed a new application of drinking water treatment residuals (DWTRs) for suspensions that permits the simultaneous removal of excess P and N from natural water and demonstrates that DWTRs recycling can provide a means for eutrophication control. Based on 364-day continuous flow tests, the suspension application of DWTRs effectively adsorbed P from overlying water under various conditions, decreasing total P concentrations from 0.0739 ± 0.0462 to 0.0111 ± 0.0079-0.0149 ± 0.0106 mg L^-1, which achieved a class Ⅱ level of the China surface water quality standards during the tests. The total N concentrations were also reduced from 1.46 ± 0.63-1.52 ± 0.63 to 0.435 ± 0.185-0.495 ± 0.198 mg L^-1, which achieved a class Ⅲ level during the stable stage of the tests. N removal was closely related to doses of DWTRs and aeration intensities. Effective N removal was mediated by the enriched microbial communities in the suspended DWTRs with simple, stable, and resilient networks, including many taxa associated with the N cycle (e.g., Rhodoplanes, Brevibacillus, and Pseudomonas). Further analysis indicated that both effective P adsorption and functional microbial community construction were closely related to Fe and Al in DWTRs. Suspension application prevented the burial effect of solids sinking from overlying water, which aided the ability of DWTRs to control pollution, and is potentially applicable to other materials for natural water remediation.

Modification of the Microtox® Basic Solid Phase Test: A new application for the ecotoxicological studies on poorly soluble antihypertensive drugs

Increasing consumption of angiotensin II receptor blockers (ARBs: valsartan, losartan potassium, telmisartan) is inevitably associated with their appearance in the environment and impact on aquatic and terrestrial organisms. Since the pharmaceuticals do not occur as pure substances in the environment, but as complex mixtures with other active pharmaceutical ingredients (APIs) and excipients used in pharmaceutical formulations, we compared the ecotoxicity of ARBs in various forms: as pure APIs, in pharmaceutical formulations and in mixtures with hydrochlorothiazide (HCT). Because the studied APIs are poorly water-soluble, the Microtox® Basic Solid Phase Test, utilizing bacteria Aliivibrio fischeri, has been modified by using a neutral matrix. Thus, this test, which is correlated with other tests for higher aquatic organisms, may be applied for the ecotoxicological evaluation of poorly soluble APIs. This is the first study reflecting the real situation in the environment, where non-target species are exposed to the pharmaceuticals, which can be dissolved/suspended in the liquid medium or adsorbed on the solid matrix. The results obtained indicate that the excipients are not inert substances and their presence in the environment may cause an increased risk to non-target organisms. Moreover, antagonistic effects were observed for two-component drug-drug (ARBs-HCT) mixtures.

The Physiological and Biochemical Responses of Daphnia magna to Dewatered Drinking Water Treatment Residue

There have been widespread attempts to recycle drinking water treatment residue (DWTR) after dewatering for environmental remediation, which is beneficial for both the environment and the economy. The directly discharged DWTR without dewatering to natural water bodies, however, was reported to show signs of chronic toxicity to Daphnia magna (D. magna), a typical zooplankton in the aquatic environment. This study comprehensively assessed the effect of dewatered DWTR on the physiological and biochemical characteristics of D. magna based on acute and chronic toxicity tests. The results showed that the survival, growth, reproduction, body morphology of offspring, and the antioxidant enzymes of D. magna were not affected by the dewatered DWTR. These physiological and biochemical indexes also had no undesirable changes for the DWTR-amended sediments (with ratios of 0–50%) incubated for 10 and 180 d; the growth and reproduction were even promoted when D. magna was exposed to 5000 mg-sediment L⁻¹, which may be due to the extra nutrients supplied by the amended sediments for the animals. The results demonstrated that by contrast with the directly discharged DWTR without dewatering, the dewatered DWTR could be safe to D. magna. Further analysis suggested that heavy metals (Pb, Ni, Cu, Cr, and Zn) with relatively low concentrations and high stability could be the main reasons leading to the high safety of the dewatered DWTR. Overall, dewatered DWTR can be considered a non-hazardous material for zooplankton.

Valorization of alum sludge via a pyrolysis platform using CO2 as reactive gas medium

In an effort to seek a new technical platform for disposal of drinking water treatment sludge (DWTS: alum sludge), pyrolysis of DWTS was mainly investigated in this study. To establish a more sustainable thermolytic platform for DWTS, this study particularly employed CO₂ as reactive gas medium. Thus, this study laid great emphasis on elucidating the mechanistic roles of CO₂ during the thermolysis of DWTS. A series of the TGA tests of DWTS in CO₂ in reference to N₂ revealed no occurrence of the heterogeneous reaction between CO₂ and the sample surface of DWTS. As such, at the temperature regime before initiating the Boudouard reaction (i.e., ≥700 °C), the mass decay patterns of DWTS in N₂ and CO₂ were nearly identical. However, the gaseous effluents from lab-scale pyrolysis of DWTS in CO₂ in reference to N₂ were different. In sum, the homogeneous reactions between CO₂ and volatile matters (VMs) evolved from the thermolysis of DWTS led to the enhanced generation of CO. Also, CO₂ suppressed dehydrogenation of VMs. Such the genuine mechanistic roles of CO₂ in the thermolysis of DWTS subsequently led to the compositional modifications of the chemical species in pyrolytic oil. Furthermore, the biochar composite was obtained as byproduct of pyrolysis of DWTS. Considering that the high content of Al₂O₃ and Fe-species in the biochar composite imparts a strong affinity for As(V), the practical use of the biochar composite as a sorptive material for arsenic (V) was evaluated at the fundamental levels. This work reported that adsorption of As(V) onto the biochar composite followed the pseudo-second order model and the Freundlich isotherm model.

Enhancing wastewater remediation by drinking water treatment residual-augmented floating treatment wetlands

In this study, the involvement of aluminum-based drinking water treatment residual (DWTR) as substrate in floating treatment wetland (FTW) to enhance its treatment performance was firstly proposed and trialed. A laboratory scale DWTR-FTW fed with synthetic wastewater containing COD, nitrogen (N), phosphorus (P) and mineral salts was operated in three stages of unplanted (1-30 days), planted (31-60 days) and aerated (61-135 days) modes. The results showed that the average removal rates of COD, total nitrogen (TN), total phosphorus (TP) in stage 3 were 88%, 85%, and 90.2%, respectively, indicating the outstanding purification performance of DWTR-FTW in comparison of traditional FTWs. The embedded DWTR enriches the biomass and robustly adsorbs P, while aeration supplies sufficient dissolved oxygen for the microorganism. The results revealed that 7.022 g P was accumulated in DWTR, which is 400 times higher than that in sediment and plants during the experimental period, reflecting that DWTR adsorption is the major P removal pathway in DWTR-FTW. Overall, DWTR-FTW could significantly remove pollutants, especially P, and provide an alternative pathway to enhance purification performance of FTW.

Volumetric modeling of two sludge piles from water treatment plants in a Brazilian reservoir

Water treatment plants are designed to continuously produce drinkable water, meeting defined criteria of potability. However, besides potable water, these plants produce sludges that are disposed of in the environment. The present work aimed to evaluate the sludges generated in two water treatment plants and disposed of in the margin of the Juturnaíba dam. Since alum has been used as a flocculating agent in these two plants, the concentrations of aluminum were measured in the sludges and in surface sediments. The generated piles are extremely soft to walk on and difficult to measure, so indirect modeling procedures had to be applied. The calculated mass of the sludge piles at each plant are similar and respectively 60,370 and 61,479 tons. The aluminum content of the residues, calculated according to its dosage, was 33.2 and 32.6 g kg^-1 in the piles from the two plants. The amount of alum dosed to the water corresponds almost to the excess of aluminum in the sludge, compared to the sediments. It was concluded that regardless of the fact that residues are disposed of in very restricted areas, they are directly in contact with the water and may constitute a threat for the environment and humans' health.