Tertiary Wastewater Treatment Research Articles

Tertiary Wastewater Treatment Technologies: A Review of Technical, Economic, and Life Cycle Aspects

The activated sludge process is the most widespread sewage treatment method. It typically consists of a pretreatment step, followed by a primary settling tank, an aerobic degradation process, and, finally, a secondary settling tank. The secondary effluent is then usually chlorinated and discharged to a water body. Tertiary treatment aims at improving the characteristics of the secondary effluent to facilitate its reuse. In this work, through a literature review of the most prominent tertiary treatment methods, a benchmarking of their technical efficiency, economic feasibility, and environmental impact was carried out. The photo-Fenton method proved to be the most technically efficient process, significantly reducing the microbial load and pharmaceutical content (by 4.9 log and 84%, respectively) of the secondary effluent. Chlorination and UV irradiation exhibited the lowest treatment costs (0.004 EUR/m−3) and the lowest global warming potential (0.04 and 0.09 kg CO2eq. m−3, respectively). After all the data were aggregated, a decision-making tool was constructed in the form of a ternary diagram, which indicates the most appropriate tertiary treatment method according to the weight-per-process aspect (technical, economic, and environmental) selected by the user, with chlorination, UV irradiation, ozonation, microalgae cultivation, and constructed wetlands prevailing in the final results.

Kinetic modelling of yeast growth and pollutant removal in secondary effluent

In recent years, there has been significant interest in yeast-based wastewater treatment due to its high pollutant removal rate and ability to perform in non-sterile environments. In this work, a kinetic model was developed to predict yeast growth and substrate consumption during wastewater treatment. To determine the biological constants for use in the kinetic models, a unique approach is presented. Candida utilis was cultivated in synthetic wastewater, using eight different ratios of carbon, nitrogen and phosphorus to determine its growth rate, and the removal rates of carbon, nitrogen, and phosphorus. The concentrations of C, N and P were chosen within the range of secondary effluent wastewater. In all experiments, carbon was found to be the limiting substrate, and 100 % TOC removal was achieved in all cases. Candida utilis reduced the COD concentration by up to 99 % in <24 h. In the model, both yeast growth and substrate consumption were satisfactorily described by Monod kinetics. The apparent half-saturation coefficients for carbon, nitrogen, and phosphorus, determined via the optimization of the model, were found to the function of initial substrate concentration. The maximum specific growth rate found was 0.59 h−1. This model was used on different initial concentrations of substrates, and predicted data with an R2 above 80 %. Both model and experimental results suggest that Candida utilis can be used in the tertiary treatment of wastewater. The simple approach described here can be applied to find biological coefficients for other microorganisms.

Fe3+/Mn2+ (Oxy)Hydroxide Nanoparticles Loaded onto Muscovite/Zeolite Composites (Powder, Pellets and Monoliths): Phosphate Carriers from Urban Wastewater to Soil.

The development of an efficient adsorbent is required in tertiary wastewater treatment stages to reduce the phosphate-phosphorous content within regulatory levels (1 mg L-1 total phosphorous). In this study, a natural muscovite was used for the preparation of muscovite/zeolite composites and the incorporation of Fe3+/Mn2+ (oxy)hydroxide nanoparticles for the recovery of phosphate from synthetic wastewater. The raw muscovite MC and the obtained muscovite/sodalite composite LMC were used in the powder form for the phosphate adsorption in batch mode. A muscovite/analcime composite was obtained in the pellets PLMCT3 and monolith SLMCT2 forms for the evaluation in fixed-bed mode for continuous operation. The effect of pH, equilibrium and kinetic parameters on phosphate adsorption and its further reuse in sorption-desorption cycles were determined. The characterization of the adsorbents determined the Fe3+ and Mn2+ incorporation into the muscovite/zeolite composite's structure followed the occupancy of the extra-framework octahedral and in the framework tetrahedral sites, precipitation and inner sphere complexation. The adsorbents used in this study (MC, LMC, PLMCT3 and SLMCT2) were effective for the phosphate recovery without pH adjustment requirements for real treated wastewater. Physical (e.g., electrostatic attraction) and chemical (complexation reactions) adsorption occurred between the protonated Fe3+/Mn2+ (oxy)hydroxy groups and phosphate anions. Higher ratios of adsorption capacities were obtained by powder materials (MC and LMC) than the pellets and monoliths forms (PLMCT3 and SLMCT2). The equilibrium adsorption of phosphate was reached within 30 min for powder forms (MC and LMC) and 150 min for pellets and monoliths forms (PLMCT3 and SLMCT2); because the phosphate adsorption was governed by the diffusion through the internal pores. The adsorbents used in this study can be applied for phosphate recovery from wastewater treatment plants in batch or fixed-bed mode with limited reusability. However, they have the edge of environmentally friendly final disposal being promissory materials for soil amendment applications.

The environmental assessment of tertiary treatment technologies for wastewater reuse by considering LCA uncertainty

Tertiary treatment methods can result in severe environmental impacts that should be taken into consideration when deciding about the best system for wastewater reuse applications beside technical and economic issues. Life cycle assessment (LCA) commonly is used for evaluating the environmental impacts of these methods. Given the importance of uncertainty analysis, it is still an uncommon practice in LCA researches in recent years, especially those focused on tertiary wastewater treatment technologies (TWWTTs). Therefore, the main purpose of this study is to investigate the parameter and input data uncertainty in LCA of TWWTTs. Considering huge amount of data collected for LCA from different sources with various precision, there is high uncertainty in obtained LCA results that could affect the ranking of different methods based on their environmental impacts. The Monte-Carlo based method is used for uncertainty analysis of LCA and it is investigated how it can affect the final ranking of tertiary treatment methods based on their environmental impacts. In present study, LCA is used to study the environmental impacts of 22 tertiary treatment systems used for further treatment of effluent of South of Tehran wastewater treatment plant (WWTP) located at the south of Tehran, Iran. The treated wastewater of this WWTP is planned to be used for different purposes including landscape irrigation and groundwater recharge as well as industrial and non-potable household (toilet flushing) usages. Among the 22 tertiary treatment systems, the best system for each application was chosen, based on the LCA results and the uncertainty of LCA.

Freshwater microbial metagenomes sampled across different water body characteristics, space and time in Israel

Freshwater bodies are critical components of terrestrial ecosystems. The microbial communities of freshwater ecosystems are intimately linked water quality. These microbes interact with, utilize and recycle inorganic elements and organic matter. Here, we present three metagenomic sequence datasets (total of 182.9 Gbp) from different freshwater environments in Israel. The first dataset is from diverse freshwater bodies intended for different usages – a nature reserve, irrigation and aquaculture facilities, a tertiary wastewater treatment plant and a desert rainfall reservoir. The second represents a two-year time-series, collected during 2013–2014 at roughly monthly intervals, from a water reservoir connected to an aquaculture facility. The third is from several time-points during the winter and spring of 2015 in Lake Kinneret, including a bloom of the cyanobacterium Microcystis sp. These datasets are accompanied by physical, chemical, and biological measurements at each sampling point. We expect that these metagenomes will facilitate a wide range of comparative studies that seek to illuminate new aspects of freshwater microbial ecosystems and inform future water quality management approaches.

Disinfection and particle removal by a nature-based Daphnia filtration system for wastewater treatment

Nature-based solutions (NBS) to treat wastewater are ecological treatments that work to mitigate the impact of conventional systems in wastewater treatment processes. In this study, the efficiency of an innovative wastewater tertiary treatment based on Daphnia filtration in removing suspended solids and E. coli is evaluated in combination with either vermifiltration or conventional secondary treatments. Daphnia filtration NBS was found to increase particle removal and E. coli inactivation over a wide range of water temperatures, solar radiation intensities, and hydraulic residence times. Moreover, two models to predict the quality of the treated wastewater, one that describes the removal of particles and another for E. coli inactivation, are developed and presented here. Both models depend on water temperature, the exposure to solar radiation and the hydraulic residence time in the reactor. The results using these models align with the experimental results in all cases. Hydraulic residence times above 24 h allowed suspended particle concentrations to be reduced by >75 % with water temperatures in the range of 10 °C to 27 °C and for E. coli to be inactivated by 1–3 log units in water temperature ranging from 8 °C to 27 °C. The developed models can also be used to provide information regarding the operating conditions (i.e. hydraulic residence times) required to obtain the desired regenerated water quality in accordance with reuse purposes and the regulations of different countries.

Life Cycle Assessment of UV-C based treatment systems for the removal of compounds of emerging concern from urban wastewater

In the last decades particular attention is being paid to the efficient and effective removal of compounds of emerging concern (CECs) present in wastewater before their eventual reuse or disposal. Several technologies have been developed for the degradation of CECs in aqueous matrix, in this regard advanced oxidation processes (AOPs) represent a nascent technological solution developed on a laboratory scale with applications on a prototype scale. The experimental evidences have shown that AOPs processes can oxidize numerous organic compounds in a much faster and more efficient way than that of the most common disinfection processes. The most common AOPs processes are those that involve the use of H2O2/UV, O3/UV, H2O2/O3, H2O2/O3/UV, Fenton and photo-Fenton. The aim of this work is to illustrate the results of a comparative LCA study of a laboratory scale UV-C photoreactor for the tertiary treatment of urban wastewater of three treatment systems (UV-C, UV-C + H2O2 e UV-C + TiO2). In particular, the specific objective is to evaluate, from an environmental point of view, an innovative advanced oxidation system based on nanostructures TiO2 immobilized on a stainless steel mesh. Compared to the UV-C photolysis reference system, the addition of hydrogen peroxide reduces the total environmental impact of the system by almost 75 %, while the use of the stainless-steel mesh coated by the nanostructures titanium dioxide reduces the UV-C environmental impact by 30 %. These results are due to the lower energy consumption of these last treatments compared to photolysis alone. The main impacts of the three systems are related to the electric power consumption of the centrifugal pump (63–64 %) and of the UV-C lamp (32–33 %). The LCA applied to these systems has shown that TiO2 assisted photocatalysis is not yet advantageous from an environmental point of view and that, therefore, the efficiency of the system needs to be improved.

Tertiary urban wastewater treatment with microalgae natural consortia in novel pilot photobioreactors

The aim of this work was to evaluate the efficiency of the new GreenDune photobioreactors for tertiary wastewater treatment, treated wastewater reuse and biomass application, using naturally occurring microalgae consortia. The study was conducted on a pilot installation in a wastewater treatment plant in Portugal and different operational conditions were tested. The system was capable to remove up to 95% of NH4+, the main pollutant in wastewater after secondary treatment using hydraulic retention times as low as 24 h. The application of a non-conservative scenario allowed the reuse of treated wastewater for seed production, and irrigation of naturally restricted use areas. The produced biomass was rich in proteins and carbohydrates with potential for biofuel production such as biogas or use as biofertilizers, closing the energy and nutrients cycle. Finally, the life cycle assessment of both the GreenDune and existing nitrification/denitrification systems were compared revealing that the operation of the GreenDune are more environmentally favourable than the existing system.

A natural microalgae consortium for the biological nutrient removal in a upflow photobioreactor as tertiary wastewater treatment

A natural microalgae consortium from a eutrophic lagoon was used and evaluated for the tertiary treatment in a upflow photobioreactor. The photobioreactor was continuously fed with the effluent of a UASB high-rate reactor. The photobioreactor average concentration of the inflow pre-treated wastewater in terms of chemical oxygen demand (COD), nitrogen (N), and phosphorus (P) was 125 mg/L, 49 mg/L, and 8 mg/L, respectively. The operation variables of the photobioreactor include a hydraulic retention time (HRT) of 1 day and 2 days of solids retention time (SRT). The photoperiod in the photobioreactor was 24 h at a light illuminance of 5000 lx. The highest nutrient uptake rates in the photobioreactor were 14 mg TN/L·d and 2 mg TP/L·d. Environmental conditions in the photobioreactor favour the cyanobacteria dominance over the microalgae taxonomic groups. In addition, the outcomes established CO2:N ratios of 9:1 to ensure the N removal in wastewater microalgae treatment systems.

Microbial communities and processes in biofilters for post-treatment of ozonated wastewater treatment plant effluent

Ozonation is an established solution for organic micropollutant (OMP) abatement in tertiary wastewater treatment. Biofiltration is the most common process for the biological post-treatment step, which is generally required to remove undesired oxidation products from the reaction of ozone with water matrix compounds. This study comparatively investigates the effect of filter media on the removal of organic contaminants and on biofilm properties for biologically activated carbon (BAC) and anthracite biofilters. Biofilms were analysed in two pilot-scale filters that have been operated for >50,000 bed volumes as post-treatment for ozonated wastewater treatment plant effluent. In parallel, the removal performance of bulk organics and OMP, including differentiation of adsorption and biotransformation through sodium azide inhibition, were carried out in bench-scale filter columns filled with material from the pilot filters. The use of BAC instead of anthracite resulted in an improved removal of organic bulk parameters, dissolved oxygen, and OMP. The OMP removal observed in the BAC filter but not in the anthracite filter was based on adsorption for most of the investigated compounds. For valsartan, however, biotransformation was found to be the dominant pathway, indicating that conditions for biotransformation of certain OMP are better on BAC than on anthracite. Adenosine triphosphate analyses in the media-attached biofilms of the pilot filters showed that biomass concentrations in the BAC filter were significantly higher than in the anthracite filter. The microbial communities (16S rRNA gene sequencing) appeared to be similar with respect to the types of organisms occurring on both filter materials. Alpha diversity also exhibited little variation between filter media. Beta diversity analysis, however, revealed that filter media and bed depth substantially influenced the biofilm composition. In practice, the impact of filter media on biofilm properties and biotransformation processes should be considered for the design of biofilters.

Adaptable Process Design as a Key for Sustainability Upgrades in Wastewater Treatment: Comparative Study on the Removal of Micropollutants by Advanced Oxidation and Granular Activated Carbon Processing at a German Municipal Wastewater Treatment Plant

Micropollutants have been increasingly detected at low concentrations in surface waters and may have harmful effects on humans, organisms, and the environment. As wastewater treatment plants are one of the main sources of micropollutants, conventional wastewater treatment methods and plants (mainly one to three cleaning stages) must be improved through an advanced (fourth) treatment stage. The optimal fourth treatment stage should be determined based not only on removal efficiencies but also on a holistic sustainability assessment that further considers the process’s adaptability, economic, environmental, and social parameters. The ability of a tertiary wastewater treatment plant to remove organic pollutants was investigated over four months using two different advanced treatment methods: (1) an advanced oxidation process (AOP) (using UV + H2O2) and (2) granular activated carbon (GAC). The resulting average micropollutant removal efficiencies were 76.4 ± 6.2% for AOP and 90.0 ± 4.6% for GAC. As the GAC became saturated, it showed a decreasing performance from 97.6% in week one to 80.7% in week 13, after 2184 bed volumes were processed. For the AOP, adjusting the UV and H2O2 doses results in higher removal efficiencies. With 40 ppm H2O2 and 10 kJ/m2 UV, a removal of 97.1% was achieved. Furthermore, the flexibility and adaptability of the AOP process to adjust to real-time water quality, along with a lower resource consumption and waste disposal, make it a more promising technology when comparing the sustainability aspects of the two methods.

Energy-efficient removal of trace antibiotics from low-conductivity water using a Ti4O7 reactive electrochemical ceramic membrane: Matrix effects and implications for byproduct formation

The inevitably high energy consumption of traditional electrochemical processes to treat low-conductivity water has limited their wider application. Herein, we present an energy-efficient alternative, i.e., a Ti4O7 reactive electrochemical ceramic membrane (Ti4O7-REM) system with a superior mass transfer ability. For the removal of 10−200 μM norfloxacin (NOR) from low-conductivity (178−832 μS cm−1) water, the Ti4O7-REM system increased the kinetics rate constant by 4.3−34.0 times, thus decreasing the energy cost by 80.5−97.3% compared with a flow-by system. The rapid NOR removal was related to the enhanced direct electron transfer process in the Ti4O7-REM system, which allowed for higher resistance to HCO3− scavenging and a favorable reaction between NOR and the active sites. Meanwhile, this mechanism likely contributed to the less formation of inorganic chlorinated product, ClO3−, in the presence of Cl−. Although organic chlorinated byproducts were not detected during NOR degradation in the Ti4O7-REM system, Cl– influenced the speciation of the intermediates. A single-pass Ti4O7-REM system demonstrated 94−97% removal of trace antibiotics from real water samples in 30 s. The additional energy consumption (<0.02 kWh m−3) using a Ti4O7-REM system only contributed to 5.0−6.4% of the total in a typical tertiary wastewater treatment plant. Based on the above results, we can conclude that the convection-enhanced REM technique is viable for the purification of low-conductivity natural waters.

A multidimensional study of wastewater treatment

Water usage generates wastewater, which must be collected and treated properly before being returned into the hydrological cycle for reasons of sustainable development and water supply.The content and volume of waste water generated are determined by a range of elements, as most of them are the waste of households, industries and so on. It also dictates the necessary treatment methods. Waste water treatment facilities function at a crucial stage in the water cycle, assisting nature in protecting water from contamination. Treatment methods can be categorized into four segments: preliminary, primary, secondary and tertiary wastewater treatment. Screening and grit removal are ordinary parts of preliminary wastewater treatment. Basically, it prepares wastewater for further treatment. Although the primary purpose of wastewater treatment is to separate easily-removable suspended particles and BOD, wastewater components that occur as dissolved solids or settleable wastewater solids may also be eliminated here using a septic tank, the Imhoff tank. The conversion of organic materials to more oxidised or reduced forms occurs in treatment plants of secondary wastewater treatments and sometimes in tertiary treatment also. Disinfection and suspended particles removal are the most common techniques used to modify conventional wastewater treatment plant effluents for crop application. Advanced wastewater treatment, also known as tertiary treatment, is used in treatment technologies when a higher quality of water is desired but secondary treatment procedures cannot provide. Advanced or tertiary water treatment includes the removal of nitrogen, phosphorus, several organics and metals. Finally, the treated waters can be used for multiple purposes. Rainfall waters being less polluted, can be easily treated and fewer treatment methods will require here. However, to make them more efficient, several improvements are needed for commonly used systems like trickling filters, oxidising ponds, rotating bio contractors (RBCs), septic tanks, etc.

Removal of Nitrogen and Phosphorus from Wastewater Using Layered Filter Media

After biological wastewater treatment, ammonium nitrogen (NH4-N), nitrate nitrogen (NO3-N), and phosphate phosphorus (PO4-P) remain in the effluent, which is discharged into natural water bodies. For further removal of these wastewater compounds, three selected materials were used as filter media: quartz sand used in drinking water treatment plants, Purolite A502PS resin, and natural zeolite. After placing all selected materials in the first filtration column (height of each layer-30 cm), the concentration of NH4-N in the wastewater was reduced by 5 times (from 8.22 to 1.5 mg/L), the concentration of NO3-N by 6 times (from 2.46 to 0.44 mg/L), and the concentration of PO4-P by 3 times (from 1.56 to 0.45 mg/L). The second column was without a Purolite A502PS layer, so the concentration of NO3-N in the filtrate from the second column was not reduced. The filtration columns were operated for about 2 months, and the filtration was stopped due to clogging with suspended solids (TSS) with an average concentration of 53.2 mg/L. The preliminary removal of TSS from wastewater before filtration through sorbents is recommended. The tested materials effectively treat wastewater of nitrogen (average efficiency 80–83%) or phosphorus (average efficiency 65–67%) and do not pollute the wastewater with environmentally hazardous substances, so they can be used in the development of tertiary wastewater treatment filters.

Sustainability assessment of wastewater reuse in a Portuguese military airbase

The current water-scarcity crisis that is being felt in Europe, namely in the southern region, has leveraged the development and implementation of national and regional water management plans. These policies aim to promote efficient wastewater reuse in industrial and urban sectors. Thus, stakeholders are now seeking strategies to enhance the sustainability of their wastewater treatment processes. The present work details the evaluation of the wastewater treatment methods used at an Air Force Base located in Portugal. In addition, this study also intended to determine how wastewater reuse can be implemented and add value to the environmental protection mission of the military airbase. Hence, an assessment of wastewater treatment practices was carried out, considering primary and secondary treatments. The chemical, physical, and biological indicators of samples collected over two consecutive years were analyzed to determine trends and fluctuations. The results revealed that the overall effectiveness of nutrient removal is low due to the oversized nature of the treatment plant, the age of the facility, and the composition of the wastewater. The effluent produced meets standards for non-potable reuse and could be used on base for aircraft maintenance and the cleaning of facilities. Nonetheless, the effectiveness of the plant could be improved by implementing a more advanced tertiary wastewater treatment to decrease the concentration of undesired compounds (e.g., total nitrogen), enabling the reuse of water in a broader range of activities.

Establishing log reduction values for wastewater treatment processes from ambient influent and effluent pathogen monitoring data

In developing wastewater treatment regulations and guidelines for potable reuse, the reduction of pathogens is of critical importance. In draft regulations, the state of California has proposed overall treatment process log reduction values (LRVs) of 20, 14, and 15 respectively for viruses, Giardia cysts, and Cryptosporidium oocysts, for direct potable reuse. In meeting the log reduction requirements, agencies have sought to obtain credit for LRVs achieved consistently through secondary biological and tertiary wastewater treatment, in addition to the LRVs achieved through advanced water treatment. The purpose of this paper is to illustrate how to determine pathogen LRVs, using ambient wastewater treatment pathogen monitoring data and the rank-paired covariant method of analysis.

Characterization, Transformation, and Bioavailability of Dissolved Organic Nitrogen in Biofilters Treating Domestic Onsite Wastewater

This study investigated the transformation, bioavailability, and seasonal changes of dissolved organic nitrogen (DON) in nitrogen removing biofilters (NRBs) treating domestic onsite wastewater. The results demonstrated that NRBs were able to remove 92.6–94.3% DON from septic tank effluent with low effluent DON concentrations (0–5.8 mg N L–1), comparable to the levels detected in the tertiary municipal wastewater treatment plant. Both hydrophilic and hydrophobic DON were efficiently removed by the sand filters, while additional hydrophilic DON (0.8–1.8 mg N L–1) was produced in the lignocellulose/sand layer due to soluble microbial product formation. Seasonal change (i.e., temperature variation) did not impact the effluent DON composition or its removal efficiency by NRBs, while higher concentrations of hydrophilic DON (1.7–2.5 mg N L–1) were detected in the final effluent during the summer months (16.4–22.9 °C). DON in the NRB effluent had a higher potential to stimulate algal growth than other nitrogen forms (NH4+ and NOx–), confirmed by higher chlorophyll-a concentrations observed in the bioassay tests. The results suggest the DON levels in the final effluent of an onsite wastewater treatment system shall also be considered in onsite wastewater quality management and the effluent discharge regulations.

Wastewater treatment using bamboos in constructed wetlands: experiences and future perspectives.

Wastewater treatment using constructed wetlands (CWs) based on natural wetlands constitute a viable alternative with excellent cost and benefit, presenting themselves as efficient technologies in the secondary and tertiary treatment of wastewaters with low implementation, operation, and maintenance costs. The present study aims to evaluate the use of bamboo species, as an alternative to macrophytes, frequently used in CWs, through bibliometric analysis, besides to a review based on case studies. The maps generated by the VOSviewer software and by the analyses of the Web of Science and Scopus databases allowed for a review of typical concepts of CWs, in addition to revealing potential benefits of using bamboos in CWs, such as their hyperaccumulation capacity and bioproduct generation. Other promising aspects were identified, for example the use of bamboo charcoal as a substrate used in subsurface wetlands and the application of ornamental bamboo species for landscape improvements, among other observations. The efficiencies found in six case studies showed values between 89-99.7%, 47.6-99.7%, 58.3-99.9%, and 85.5-99.8% for BOD5, COD, total nitrogen (TN), and total phosphorus (TP), respectively. Despite the promising results, the lack of studies using bamboos in CWs for the treatment of wastewaters limits an assertive statement about the use of this technology, requiring further research, focusing on the morphological functions of bamboos in this treatment with landscape integration and resources recovery.

Biogas Production from Microalgal Biomass Produced in the Tertiary Treatment of Urban Wastewater: Assessment of Seasonal Variations

The valorization of microalgal biomass produced during wastewater treatment has the potential to mitigate treatment costs. As contaminated biomass (e.g., with pharmaceuticals, toxic metals, etc.) is often generated, biogas production is considered an effective valorization option. The biomass was obtained from a pilot facility of photobioreactors for tertiary wastewater treatment. The pilots were run for one year with naturally formed microalgal consortia. The biogas was generated in 70 mL crimp-top vials at 35 °C, quantified with a manometer and the methane yield measured by gas chromatography. A maximum biogas production of 311 mL/g volatile solids (VS) with a methane yield of 252 mL/g VS was obtained with the spring samples. These rather low values were not improved using previous thermo-acidic hydrolysis, suggesting that the low intrinsic biodegradable organic matter content of the consortia might be the cause for low yield. Considering the total volume of wastewater treated by this plant and the average amount of methane produced in this study, the substitution of the current tertiary treatment with the one here proposed would reduce the energy consumption of the plant by 20% and create an energy surplus of 2.8%. The implementation of this system would therefore contribute towards meeting the ambitious decarbonization targets established by the EU.

LTA and FAU-X Iron-Enriched Zeolites: Use for Phosphate Removal from Aqueous Medium.

Hydrothermally synthesized Linde type A (LTA) and faujasite X (FAU-X) zeolites are low-cost and environmentally benign inorganic carriers for environmental applications. In this study, (oxy)hydroxides were incorporated onto LTA and FAU-X zeolites to promote the phosphate adsorption. The performance of LTA-Fe and FAU-X-Fe was evaluated through batch adsorption assays. A complete evaluation was performed to recover phosphate from synthetic wastewater. The effect of pH, concentration, equilibrium, and kinetic parameters on phosphate adsorption and its further reuse in sorption–desorption cycles were evaluated. LTA-Fe and FAU-X-Fe are effective for adsorption of phosphate at neutral (e.g., pH 7.0 ± 0.2) and in a broad range of phosphate concentrations. Higher ratios of adsorption capacities were obtained by synthetic zeolites enriched with iron in comparison to their parent forms. The phosphate adsorption occurred through hydrogen bonding and complexation reactions between protonated iron hydroxyl groups and phosphate anions. The phosphate monolayer adsorption was followed by diffusion through the internal pores and 80% of the equilibrium adsorption was reached within 50 min. The LTA-Fe and FAU-X-Fe can be used for phosphate recovery from wastewater treatment plants. The use of LTA-Fe and FAU-X-Fe in a tertiary wastewater treatment stage could allow to reduce the phosphate–phosphorous content, reaching the regulatory levels (equal 1 mg L−1 total phosphorous). The phosphate adsorption using LTA-Fe and FAU-X-Fe does not require pH adjustment, and it is endothermic. The reusability of both iron zeolites is limited, and they can be finally disposed for soil amendment applications.