Persulfate oxidation for alternative sludge treatment and nutrient recovery: An assessment of technical and economic feasibility

Feasibility of sludge deep dewaterability improvement for incineration disposal by combined conditioning of freeze-thaw and sawdust

Sludge incineration is the main strategy for sludge reduction in China. The combined conditioning of lime and chemical agents has been proven to achieve sludge dewatering by disrupting the extracellular polymeric substances (EPS) of sludge and reducing its compressibility. However, when incineration is the intended disposal purpose, this method poses challenges such as incomplete combustion, equipment corrosion, secondary pollution, and decreased calorific value of sludge cake. In contrast, freeze-thaw conditioning, coupled with sawdust as a high-calorific-value bio-waste, emerges as an efficient and clean alternative. The research investigates the synergistic effects of freeze-thaw and sawdust co-conditioning on various sludge properties, including dewaterability, compressibility, consolidation, permeability, microscopicity, and calorific value. The study reveals that the combined conditioning significantly reduces water content and compressibility while increasing void ratio, consolidation, permeability, and enhancing the calorific value of the sludge cake. Specifically, sludge cake conditioned with 60% dried solids (DS) sawdust and freeze-thaw achieved a water content (Wc) of 49.07% and a calorific value of 1422.3 kcal/kg, meeting standards for self-sustained incineration. With heat recovery, the combined conditioning generates an economic revenue of 25.1 $/t DS after deducting costs, thereby reducing the overall cost of sludge reduction treatment. This research offers a clean and practical solution for sludge incineration and reduction, demonstrating great economic value and application potential.

Bibliometric analysis of Advanced Oxidation Processes studies with a focus on Life Cycle Assessment and Costs

Advanced oxidation processes (AOPs) are wastewater treatment technologies that stand out for their ability to degrade Contaminants of Emerging Concern (CECs). The literature has extensively investigated these removal processes for different aqueous matrices. Once technically mature, some of these systems have become accredited to be applied on a large scale, and therefore, their systemic performances in the environmental and cost spheres have also become essential requirements. This study proposed corroborating this trend, analyzing the available literature on the subject to verify how experts in the AOP area investigated this integration during 2015-2023. For this purpose, a sample of publications was treated by applying the Systematic Review (SR) methodology. This resulted in an extract of 83 studies that adopted life-cycle logic to estimate environmental impacts and process costs or evaluated them as complementary to the technical dimension of each treatment technology. This analysis found that both dimensions can be used for selecting or sizing AOPs at the design scale. However, the appropriate choice of the impact categories for the environmental assessment and establishing a methodology for cost analysis can make the approach still more effective. In addition, a staggering number of processes would broaden the reality and applicability of the estimates, and adopting multicriteria analysis methodologies could address essential aspects of decision-making processes during the design of the arrangements. By meeting the original purposes, the study broadened the requirements for designing AOPs and disseminating their use in mitigating the discharge of CECs.

Effects of vermicompost leachate on nitrogen, phosphorus, and microbiome in a food waste bioponic system

Food waste is rich in nutrients, such as nitrogen and phosphorus, and can be integrated with bioponics, a closed-loop agricultural system that combines hydroponics with biological nutrient recovery. Vermicompost leachate (VCL) supplementation has been shown to improve the co-composting of organic waste (i.e., compost quality) and the biodegradation of organic compounds. Thus, VCL has high potential for enhancing nutrient availability in bioponics from food waste. However, the understanding of nitrogen and phosphorus availability in food waste-based bioponics is limited, both with and without VCL. In this study, food waste derived from cafeteria vegetable waste was used as the substrate (500 g dry wt./system) in bioponics to grow lettuce (Lactuca sativa L.) for two consecutive cycles (35 days/cycle) without substrate replacement. VCL was applied weekly (1-5% v/v) and compared to the control without VCL. The results showed that the food waste in bioponics provided nitrogen and phosphorus for plant growth (15.5-65.8 g/lettuce head). Organic-degrading and nutrient-transforming bacteria (Hydrogenispora, Clostridium_sensu_stricto_1, Ruminiclostridium_1, Cellvibrio, Thauera, Hydrogenophaga, and Bacillus) were predominantly found in plant roots and residual food waste. VCL addition significantly increased nitrate, phosphate, and chemical oxygen demand levels in bioponics, owing to the nutrients in VCL and the enhancement of keystone microorganisms responsible for organic degradation and nutrient cycling (e.g., Ellin6067, Actinomyces, and Pirellula). These findings suggest that nitrogen, phosphorus, and organic carbon concentrations in an ecosystem of nutrient-transforming and organic-degrading microbes are key in managing nutrient recovery from food waste in bioponics.

Advanced thermal hydrolysis for biopolymer production from waste activated sludge: Kinetics and fingerprints

Waste activated sludge (WAS) is the main residue of wastewater treatment plants, which can be considered an environmental problem of prime concern due to its increasing generation. In this study, a non-energetic approach was evaluated in order to use WAS as a renewable resource of high value-added products. For this reason, WAS was treated by thermal hydrolysis, H₂O₂ oxidation and advanced thermal hydrolysis (ATH) promoted by H₂O₂. The influence of temperature, H₂O₂ concentration and dosing strategy on biomolecule production (proteins and carbohydrates), size distribution (fingerprints) and various physico-chemical parameters (VSS, total and soluble COD, soluble TOC, pH and colour) was studied. The results revealed a synergistic effect between TH and H₂O₂ oxidation, which led to a significant increase in the production of both proteins and carbohydrates. In this sense, the concentration of proteins and carbohydrates obtained during TH at 85 °C for120 min was found to be 1376 ± 9 mg/L (121 mg/gVSS_o) and 208 ± 4 mg/L (18 mg/gVSS_o), respectively. However, in the presence of 4.5 mM H₂O₂/gVSS_o under the same process conditions, the concentrations of proteins and carbohydrates exhibited a significant increase of 1.9-fold and 3.1-fold, respectively. Besides, the addition of H₂O₂ promoted the transformation of hydrophobic compounds, such as proteins and or lipids, into hydrophilic compounds, which presented low and medium sizes. An increase in temperature improved the solubilization rate and the yield of biomolecules significantly. Besides, the analysis of the kinetics related to the dosing strategy of H₂O₂ suggested the existence of two fractions during WAS solubilization, one of them being easily oxidizable, whereas the other one was more refractory to oxidation. Thus, the value of k_H2O2 for the first addition of 1 mM H₂O₂/g VSS_o was 0.020 L^0.4 mgH₂O₂^-0.4 min^-1, while it was 4.3 and 8 times lower for the second and third additions, respectively.

Enhanced technology for sewage sludge advanced dewatering from an engineering practice perspective: A review

The increasing production of sludge poses significant environmental risks. Sludge disposal and transport are costly because of the high water content (WC). Reducing the WC of sludge is the most efficient strategy to decrease treatment costs. However, the sludge contains a large amount of hydrophilic organic matter, causing poor dewaterability. Therefore, research on preconditioning and mechanical dewatering has great significance for advanced sludge dewatering. In this study, the features of sludge, the advantages and disadvantages of preconditioning methods, and the action mechanisms (including physical, chemical, and biological preconditioning) are thoroughly described. In addition, the dewatering principle and engineering applications of mechanical dewatering techniques are introduced in this manuscript, especially the application of vacuum preloading as an in-situ dewatering technology in sludge. Finally, cost analysis of different conditioning and mechanical dewatering methods is conducted to explore their application feasibility. This manuscript provides new insights for engineering applications of preconditioning methods and mechanical dewatering technology.

Activation of Peroxydisulfate by Bimetallic Nano Zero-Valent Iron for Waste-Activated Sludge Disintegration

Waste-activated sludge (WAS) disintegration using peroxydisulfate (PDS) has attracted scientific attention over the past few years. Despite several advantages offered by a sulfate radical-advanced oxidation process, there are still too many downsides of this treatment that limit its facile large-scale application. This study investigated whether modifying nano zero-valent iron (nZVI) with a second metal such as Ag and Cu enhanced the disruption of WAS. The disintegration efficiency was assessed using standard techniques, i.e., soluble chemical oxygen demand, Fourier-transform infrared spectroscopy and a scanning electron microscope. The bimetallics were shown to have an improved disintegration efficiency of > 2.5-fold compared with the untreated sample. Furthermore, nZVI/Ag was found to be more efficient than nZVI/Cu for PDS activation, which was validated by the higher ratio (3 and 2.5 for nZVI/Ag and nZVI/Cu, respectively) between the soluble extracellular polymeric substances and the bound extracellular polymeric substances (S-EPS/B-EPS). Similar conclusions were derived from a SEM analysis. The improved disintegration efficiency could be related to the enhanced electron transfer from nZVI to PDS or the intrinsic properties of silver, which was found to be one of the best activators for PDS under homogeneous conditions. We believe that this study deepens the understanding of PDS heterogeneous activation processes.

Bioremediation of micropollutants using living and non-living algae - Current perspectives and challenges

The emergence and continual accumulation of industrial micropollutants such as dyes, heavy metals, organic matters, and pharmaceutical active compounds (PhACs) in the ecosystem pose an alarming hazard to human health and the general wellbeing of global flora and fauna. To offer eco-friendly solutions, living and non-living algae have lately been identified and broadly practiced as promising agents in the bioremediation of micropollutants. The approach is promoted by recent findings seeing better removal performance, higher efficiency, surface area, and binding affinity of algae in various remediation events compared to bacteria and fungi. To give a proper and significant insight into this technology, this paper comprehensively reviews its current applications, removal mechanisms, comparative efficacies, as well as future outlooks and recommendations. In conducting the review, the secondary data of micropollutants removal have been gathered from numerous sources, from which their removal performances are analyzed and presented in terms of strengths, weaknesses, opportunities, and threats (SWOT), to specifically examine their suitability for selected micropollutants remediation. Based on kinetic, isotherm, thermodynamic, and SWOT analysis, non-living algae are generally more suitable for dyes and heavy metals removal, meanwhile living algae are appropriate for removal of organic matters and PhACs. Moreover, parametric effects on micropollutants removal are evaluated, highlighting that pH is critical for biodegradation activity. For selective pollutants, living and non-living algae show recommendable prospects as agents for the efficient cleaning of industrial wastewaters while awaiting further supporting discoveries in encouraging technology assurance and extensive applications.

A Multi-Criteria Decision-Making Approach to Evaluate Different UVC/H2O2 Systems in Wastewater Treatment

High azoxystrobin (AZO), difenoconazole (DFZ), and imidacloprid (IMD) pesticide removal rates in sixteen bench-scale experiments concerning tomato washing water treatment were obtained through a UVC/H2O2 advanced oxidative process. Experimental conditions ([H2O2]0) and irradiance (EUVC) were optimized for higher degradation rates (pseudo-first-order reaction). To consider both economic aspects and environmental impacts when defining the treatment technology, as well as technological requirements, this study applied a multi-criteria decision-making method (MCDM) to assess and differentiate similar UVC/H2O2 process configurations. This allowed for the identification of the cheapest experimental arrangement with the lowest associated environmental impacts, coupled to the highest degradation rate (kIMD). After consulting experts to determine the importance of the applied criteria and measuring alternative performances, experiment E7 ([H2O2]0 = 43.5 mg L−1; EUVC = 15.0 W m−2; kIMD = 0.236 s−1) was determined as meeting the three criteria in a balanced manner. Although E7′s technological performance regarding degradation rate did not achieve the best individual result, it presented the lowest impacts and costs among the analyzed series, although alternatives are sensitive to decision-maker priorities. This study considered different factors of a process displaying potential industrial applications still in the design stage to achieve a more efficient and balanced solution.

Efficient degradation of minocycline by natural bornite-activated hydrogen peroxide and persulfate: kinetics and mechanisms

Natural bornite (NBo), a sulfide mineral of copper and iron, is one of the main mineral raw materials for copper extraction. In this study, NBo-activated hydrogen peroxide (H₂O₂) and persulfate processes (PS) for the degradation of minocycline (MNC) in aqueous solution were systemically investigated and compared. The MNC removal rates with the NBo/PS and NBo/H₂O₂ processes were 86.40% and 87.50%, respectively. The mineralization rate of NBo/PS (33.96%) was higher than that of NBo/H₂O₂ (29.94%) after reaction for 180 min. The effects of oxidant and activator dosage, pH, common inorganic anions (i.e., Cl^-, NO₃^-, and HCO₃^-), and water composition on MNC degradation were systematically evaluated. In addition, the degradation of MNC in natural water matrix and toxicity evaluation was also studied to better evaluate the feasibility of practical application of those two processes. The results of free radical quenching experiments and electron paramagnetic resonance spectroscopy (EPR) showed that HO· was the main activated species in the NBo/H₂O₂ system, while SO₄^·- and HO· were the main activated species in the NBo/PS system. The degradation of MNC in the NBo/PS system was achieved through electron transfer, while the degradation of MNC in the NBo/H₂O₂ system was mainly achieved through free radical addition. The degradation pathway mainly included deamidation reactions, C-C bond breakage and hydroxylation. Reusability of NBo showed that NBo was considerably stable in activating PS and H₂O₂ for degradation of MNC, which was cost-effective activator. This work provides a new perspective on the degradation mechanism of pollutants by Fe-Cu bimetallic sulfide activation of PS and H₂O₂.