An integral approach to sludge handling in a WWTP operated for EBPR aiming phosphorus recovery: Simulation of alternatives, LCA and LCC analyses

Metal element-based adsorbents for phosphorus capture: Chaperone effect, performance and mechanism

Excessive phosphorus (P) enters the water bodies via wastewater discharges or agricultural runoff, triggering serious environmental problems such as eutrophication. In contrast, P as an irreplaceable key resource, presents notable supply-demand contradictions due to ineffective recovery mechanisms. Hence, constructing a system that simultaneously reduce P contaminants and effective recycling has profound theoretical and practical implications. Metal element-based adsorbents, including metal (hydro) oxides, layered double hydroxides (LDHs) and metal-organic frameworks (MOFs), exhibit a significant chaperone effect stemming from strong orbital hybridization between their intrinsic Lewis acid sites and P (Lewis base). This review aims to parse the structure-effect relationship between metal element-based adsorbents and P, and explores how to optimize the P removal properties. Special emphasis is given to the formation of the metal-P chemical bond, which not only depends on the type of metal in the adsorbent but also closely relates to its surface activity and pore structure. Then, we delve into the intrinsic mechanisms behind these adsorbents' remarkable adsorption capacity and precise targeting. Finally, we offer an insightful discussion of the prospects and challenges of metal element-based adsorbents in terms of precise material control, large-scale production, P-directed adsorption and effective utilization.

Toward Integrating EBPR and the Short-Cut Nitrogen Removal Process in a One-Stage System for Treating High-Strength Wastewater

Enhanced biological phosphorus removal (EBPR) is an economical and sustainable process for phosphorus removal from wastewater. Despite the widespread application of EBPR for low-strength domestic wastewater treatment, limited investigations have been conducted to apply EBPR to the high-strength wastewaters, particularly, the integration of EBPR and the short-cut nitrogen removal process in the one-stage system remains challenging. Herein, we reported a novel proof-of-concept demonstration of integrating EBPR and nitritation (oxidation of ammonium to nitrite) in a one-stage sequencing batch reactor to achieve simultaneous high-strength phosphorus and short-cut nitrogen removal. Excellent EBPR performance of effluent 0.8 ± 1.0 mg P/L and >99% removal efficiency was achieved fed with synthetic high-strength phosphorus wastewater. Long-term sludge acclimation proved that the dominant polyphosphate accumulating organisms (PAOs), Candidatus Accumulibacter, could evolve to a specific subtype that can tolerate the nitrite inhibition as revealed by operational taxonomic unit (OTU)-based oligotyping analysis. The EBPR kinetic and stoichiometric evaluations combined with the amplicon sequencing proved that the Candidatus Competibacter, as the dominant glycogen accumulating organisms (GAOs), could well coexist with PAOs (15.3-24.9% and 14.2-33.1%, respectively) and did not deteriorate the EBPR performance. The nitrification activity assessment, amplicon sequencing, and functional-based gene marker quantification verified that the unexpected nitrite accumulation (10.7-21.0 mg N/L) in the high-strength EBPR system was likely caused by the nitritation process, in which the nitrite-oxidizing bacteria (NOB) were successfully out-selected (<0.1% relative abundance). We hypothesized that the introduction of the anaerobic phase with high VFA concentrations could be the potential selection force for achieving nitritation based on the literature review and our preliminary batch tests. This study sheds light on developing a new feasible technical route for integrating EBPR with short-cut nitrogen removal for efficient high-strength wastewater treatment.

Sidestream characteristics in water resource recovery facilities: A critical review

This review compiles information on sidestream characteristics that result from anaerobic digestion dewatering (conventional and preceded by a thermal hydrolysis process), biological and primary sludge thickening. The objective is to define a range of concentrations for the different characteristics found in literature and to confront them with the optimal operating conditions of sidestream processes for nutrient treatment or recovery. Each characteristic of sidestream (TSS, VSS, COD, N, P, Al³⁺, Ca²⁺, Cl^-, Fe^2+/3+, Mg²⁺, K⁺, Na⁺, SO₄^2-, heavy metals, micro-pollutants and pathogens) is discussed according to the water resource recovery facility configuration, wastewater characteristics and implications for the recovery of nitrogen and phosphorus based on current published knowledge on the processes implemented at full-scale. The thorough analysis of sidestream characteristics shows that anaerobic digestion sidestreams have the highest ammonium content compared to biological and primary sludge sidestreams. Phosphate content in anaerobic digestion sidestreams depends on the type of applied phosphorus treatment but is also highly dependent on precipitation reactions within the digester. Thermal Hydrolysis Process (THP) mainly impacts COD, N and alkalinity content in anaerobic digestion sidestreams. Surprisingly, the concentration of phosphate is not higher compared to conventional anaerobic digestion, thus offering more attractive recovery possibilities upstream of the digester rather than in sidestreams. All sidestream processes investigated in the present study (struvite, partial nitrification/anammox, ammonia stripping, membranes, bioelectrochemical system, electrodialysis, ion exchange system and algae production) suffer from residual TSS in sidestreams. Above a certain threshold, residual COD and ions can also deteriorate the performance of the process or the purity of the final nutrient-based product. This article also provides a list of characteristics to measure to help in the choice of a specific process.

The use of recovered struvite and ammonium nitrate in fertigation in a horticultural rotation: agronomic and microbiological assessment

Phosphorus and nitrogen recovery from wastewater as struvite and ammonium nitrate (AN) may be viable alternative fertilizers to boost circularity in horticulture. A 2-year fertigated crop rotation in soil under greenhouse conditions was evaluated to determine the efficiency of both recovered products as raw materials for a nutrient solution (NS) manufacture. The effects of these treatments versus synthetic fertilizers were compared in terms of crop performance, plant nutrient uptake, soil chemistry and microbiota. This is the first study to implement struvite through fertigation as the sole source of P in soil crops. Results showed that both recovered products can be used as fertilizers in NS, due to the similar response to the control for different parameters and crops (tomato, lettuce, and cauliflower). However, the AN treatment showed lower yield in the first tomato crop, which results may depend on the cultivar ammonium tolerance. Besides, the concentration of heavy metals in fruits/leaves was below the permissible limits. Total and Olsen phosphorus soil analysis revealed no differences among treatments, resulting in a similar performance of P-struvite to commercial phosphate. Bulk soil bacteria structure, richness and relative dominance were increased over time, while archaea only showed lower evenness, both despite the fertilization strategy. Shannon diversity was not significantly affected. A predominance of ammonia-oxidizing bacteria (AOB) versus archaea (AOA) was observed, while nitrite-oxidizing bacteria (NOB), dominated by Nitrospira, increased with fertigation. Our results demonstrate that fertilizer blends for NS containing recovered nutrients are a feasible alternative to synthetic fertilizers.

Enhanced electrochemical precipitation of phosphorus in wastewater by the addition of drifting Corbicula shells

Phosphorus (P) is a finite and essential resource, and its linear movement from mines to waste streams may result in shortages. This has encouraged efforts to recover P from sewage systems for reuse. This study developed a new electrochemical P precipitation system for the subnatant of the sludge flotation thickening process, in which drifting Corbicula shells are added to provide a supply of calcium ions (Ca²⁺) to promote P precipitation. However, adding Corbicula shells to coexisting suspended solids (SS) and coagulant resulted in adsorption of the shells in the neutralized and hydrophobized floc clusters, which limited their electrochemical dissolution. Adding Corbicula shells after SS removal by flotation with electrochemically generated gases resulted in their successful electrochemical dissolution, which enhanced phosphate-P removal. Increasing the amount of Corbicula shells enhanced the phosphate-P removal to a point, after which further addition simply increased Ca²⁺. The consumption of H⁺ generated near the anode for the dissolution of Corbicula shells increased the pH of the bulk solution, which enabled P precipitation not only onto the cathode but also in the bulk solution. Analysis of chemical composition in the generated particles suggests that they can be used as a slow P-release fertilizer and soil conditioner.

Increasing resource circularity in wastewater treatment: Environmental implications of technological upgrades

A paradigm shift is needed in wastewater treatment plants (WWTPs) to progress from traditional pollutant removal to resource recovery. However, whether this transformation produces overall environmental benefits will depend on the efficient and sustainable use of resources by emerging technologies. Given that many of these technologies are still being tested at the pilot scale, there is a lack of environmental assessments quantifying their impacts and benefits. In particular, an integrated approach to energy and nutrient recovery can elucidate the potential configurations for WWTPs. In this study, we conduct a life cycle assessment (LCA) of emergent wastewater treatment technologies aimed at increasing resource circularity in WWTPs. We focus on increasing energy self-sufficiency through biogas upgrades and a more radical circular approach aimed at nutrient recovery. Based on a case-study WWTP, we compare its current configuration with (1) implementing autotrophic nitrogen removal in the mainstream and deriving most of the organic matter for biogas production, which increases the quality and quantity of biogas available for energy production; (2) implementing struvite recovery through enhanced biological phosphorus removal (EBPR) as a radical approach to phosphorus management, offering an alternative to mineral fertilizer; and (3) a combination of both approaches. The results show that incremental changes in biogas production are insufficient for compensating for the environmental investment in infrastructure, although autotrophic nitrogen removal is beneficial for increasing the quality of the effluent. Combined phosphorus and energy recovery reduce the environmental impacts from the avoided use of fertilizers and phosphorus and the nitrogen release into water bodies. An integrated approach to resource management in WWTPs is thus desirable and creates new opportunities toward the implementation of circular strategies with low environmental impact in cities.

Environmental impacts and optimizing strategies of municipal sludge treatment and disposal routes in China based on life cycle analysis

The management and utilization of sludge in a sustainable approach require a systematic analysis of the environmental impacts generated from diverse sludge treatment and disposal processes. This study systematically assessed 12 common sludge treatment and disposal routes based on the existing operating and construction conditions of representative sludge disposal projects in China. We evaluated their environmental impacts using a life cycle assessment following the International Organization for Standardization (ISO 14040 and ISO 14044), and found that the routes of co-incineration, mono-incineration, and anaerobic digestion with or without thermal hydrolysis may be useful in terms of simultaneously controlling environmental pollution and carbon emissions in China. Therein, the route of co-incineration was recommended as the best one because its human toxicity potential (-152.31 kg dichlorobenzene (1,4-DB) eq/ton dry solid (t DS)), freshwater ecotoxicity potential (FEP, -127.40 kg 1,4-DB eq/t DS), terrestrial ecotoxicity potential (TEP, -0.81 kg 1,4-DB eq/t DS), and global warming potential (-27.26 kg CO2 eq/t DS) were all negative (environmental benefits). Furthermore, the toxicity impacts of the mono-incineration route were also negative, but it still needed to further enhance energy recovery to reduce carbon emissions. Despite the routes of anaerobic digestion and thermal hydrolysis in combination with anaerobic digestion had the excellent negative carbon emission attributes (-572.44 kg CO2 eq/t DS, -474.92 kg CO2 eq/t DS), they showed serious FEP and TEP owing to the heavy metals pollution caused by subsequent land use of anaerobic digested sludge. Overall, this study selected the most suitable sludge treatment and disposal routes to simultaneously satisfy the requirements of carbon emission reduction and pollution control in China and proposed optimizing suggestions for future technical improvement and development.

Ionic strength of the liquid phase of different sludge streams in a wastewater treatment plant

In a wastewater treatment plant (WWTP), several sludge streams exist and the composition of their liquid phase varies with time and place. For evaluating the potential for formation of precipitates and equilibria for weak acids/bases, the ionic strength and chemical composition need to be known. This information is often not available in literature, and even neglected in chemical model-based research. Based on a literature review, we proposed three ranges of concentration (low, typical and high) for the major constituents of the liquid phase of the different streams in a WWTP. The study also discusses the reasons for the concentration evolution, and the exceptional cases, to allow readers to consider the right range depending on their situation. The ionic strength of the different streams and the contribution of its constituents were calculated based on the ionic composition. The major contributors to the ionic strength for the wastewater-based streams (influent, effluent and mixed sludge) were Na⁺, Cl^-, Mg²⁺ and Ca²⁺, representing 50-70% of the ionic strength. For digestate, NH₄⁺ and HCO₃^- accounted for 65-75% of the ionic strength. Even though the ionic strength is recognized to impact several important wastewater treatment processes, its utilization in literature is not always adequate, which is discussed in this study.

Life cycle assessment of sewage sludge treatment and disposal based on nutrient and energy recovery: A review

With the acceleration of urbanization, the production of urban sludge is increasing rapidly. To minimize resource input and waste output, it is crucial to execute analyses of environmental impact and assessments of sustainability on different technical strategies involving sludge disposal based on Life Cycle Assessment (LCA), which is a great potential mean of environmental management adopted internationally in the 21st century. This review aims to compare the environmental sustainability of existing sludge management schemes with a purpose of nutrient recovery and energy saving, respectively, and also to include the substitution benefits of alternative sludge products. Simultaneously, LCA research regarding the emerging sludge management technologies and sludge recycling (cement, adsorbent, bricks) is analyzed. Additionally, the key aspects of the LCA process are worth noting in the context of the current limitations reviewed here. It is worth emphasizing that no technical remediation method can reduce all environmental damage simultaneously, and these schemes are typically more applicable to the assumed local conditions. Future LCA research should pay more attention to the toxic effects of different sludge treatment methods, evaluate the technical ways of adding pretreatment technology to the 'front end' of the sludge treatment process, and further explore how to markedly reduce environmental damage in order to maximize energy and nutrient recovery from the LCA perspective.

Acid treatment enhances phosphorus release and recovery from waste activated sludge: Performances and related mechanisms

Waste activated sludge (WAS) has attracted considerable attention as an excellent material for P recovery from sewage. This study took concentrated phosphorus removal sludge as objective, and aimed at providing an effective route to promote the transformation of polyphosphate in sludge pellets to dissolved phosphate. After acid pH adjustment, total dissolved phosphate at pH 3.0 was 37.3-fold higher than that at natural pH. The P distribution results illustrated that acid pH accelerated the degradation of short chain polyphosphate into orthophosphate. Furthermore, cell staining results confirmed that the polyphosphate was sourced from the leakage of intracellular matters. Low field NMR and rheology properties analysis were adopted to illustrate that acid pH treatment further improved WAS dewatering performances. Accompanied with the reduction of heavy metals in WAS pellets, the acid pH treatment was also beneficial for WAS subsequent treatment or final disposal. Lastly, Fe³⁺ addition was proposed as favorable P recovery method, and spherical nanometric materials of FePO₄ crystal was obtained accordingly.

Assessment of sludge management strategies in wastewater treatment systems using a plant-wide approach

The objective of this paper is to use plant-wide modeling to assess the net impacts of varying sludge management strategies. Special emphasis is placed on effluent quality, operational cost and potential resource recovery (energy, nutrients). The study is particularly focused on a centralized bio-solids beneficiation facility (BBF), which enables larger, more capital intensive sludge management strategies. Potential barriers include the ability to process reject streams from multiple donor plants in the host plant. Cape Flats (CF) wastewater treatment works (WWTW) (Cape Town, South Africa) was used as a relevant test case since it is currently assessing to process sludge cake from three nearby facilities (Athlone, Mitchells Plain and Wildevoelvlei). A plant-wide model based on the Benchmark Simulation Model no 2 (BSM2) extended with phosphorus transformations was adapted to the CF design / operational conditions. Flow diagram and model parameters were adjusted to reproduce the influent, effluent and process characteristics. Historical data between January 2014 and December 2019 was used to compare full-scale measurements and predictions. Next, different process intensification / mitigation technologies were evaluated using multiple criteria. Simulation values for COD, TSS, VSS/TSS ratio, TN, TP, NH₄⁺/NH₃, H_xPO4^3-x, NO_x alkalinity and pH fall within the interquartile ranges of measured data. The effects of the 2017 severe drought on influent variations and biological phosphorus removal are successfully reproduced for the entire period with dynamic simulations. Indeed, 80% of all dynamically simulated values are included within the plant measurement uncertainty ranges. Sludge management analysis reveals that flow diagrams with thermal hydrolysis pre-treatment (THP) result in a better energy balance in spite of having higher heat demands. The flow diagram with THP is able to i) increase biodegradability/solubility, ii) handle higher sludge loads, iii) change methanogenic microbial population and iv) generate lower solids volumes to dispose by improving sludge dewaterability. The study also reveals the importance of including struvite precipitation and harvesting (SPH) technology, and the effect that pH in the AD and the use of chemicals (NaOH, MgO) may have on phosphorus recovery. Model-based results indicate that the current aerobic volume in the water line (if properly aerated) would be able to handle the returns from the sludge line and the contribution of a granular partial nitritation/Anammox (PN/ANX) reactor on the overall nitrogen removal would be marginal. However autotrophic N denitrification generates a much lower sludge production and therefore increases AD treatment capacity. The study shows for the very first time in Africa how the use of a (calibrated) plant-wide model could assist water utilities to decide between competing plant layouts when upgrading a WWTW.

The application of life cycle assessment (LCA) to wastewater treatment: A best practice guide and critical review

Life cycle assessment (LCA) has been widely applied in the wastewater industry, but inconsistencies in assumptions and methods have made it difficult for researchers and practitioners to synthesize results from across studies. This paper presents a critical review of published LCAs related to municipal wastewater management with a focus on developing systematic guidance for researchers and practitioners to conduct LCA studies to inform planning, design, and optimization of wastewater management and infrastructure (wastewater treatment plants, WWTPs; collection and reuse systems; related treatment technologies and policies), and to support the development of new technologies to advance treatment objectives and the sustainability of wastewater management. The paper guides the reader step by step through LCA methodology to make informed decisions on i) the definition of the goal and scope, ii) the selection of the functional unit and system boundaries, iii) the selection of variables to include and their sources to obtain inventories, iv) the selection of impact assessment methods, and v) the selection of an effective approach for data interpretation and communication to decision-makers.