Urban Wastewater Research Articles

Environmental and economic assessment of urban wastewater reclamation from ultrafiltration membrane-based tertiary treatment: Effect of seasonal dynamic

This study aimed to assess the environmental and economic performance of an ultrafiltration (UF) tertiary treatment of effluent from an urban wastewater treatment facility. Data from a UF demonstration plant composed of commercially available equipment, including industrial hollow-fiber membranes was used to project a full-scale facility. The results from the demonstration plant recommended different ranges of transmembrane fluxes and sparging air demands under summer and winter conditions to prevent excessive fouling. The energy balance of the full-scale facility would be 0.308 ± 0.112 kWh·m−3 in summer and 0.140 ± 0.040 kWh·m−3 in winter, with blowers' being the main consumers (86–93 %). CAPEX accounted for €0.030 ± 0.002·m−3 in summer and €0.027 ± 0.002·m−3 in winter and membrane acquisition represented 66–69 % of the investment cost. Energy expenditure was the major OPEX cost (66–79 %), with a total operating cost of €0.077 ± 0.023·m−3 and €0.042 ± 0.008·m−3 in summer and winter, respectively. The final average value obtained for the TAC was €0.107 m−3 in summer and €0.068 m−3 in winter. The environmental assessment confirmed optimizing energy consumption and membrane requirements as the main factors influencing environmental sustainability. Specifically, summer and winter emissions of 0.079–0.175 and 0.043–0.079 kgCO2eq·m−3 (Global warming potential); 8.1 · 10−4–1.7 · 10−3 and 4.8 · 10−3–8.1 · 10−3 m3·m−3 (water consumption); 0.019–0.041 and 0.010–0.019 kg oileq·m−3 (fossil fuel scarcity); and 1.4 · 10−4–2.9 · 10−4 and 7.7 · 10−4–1.4 · 10−4 kg Cueq·m−3 (mineral resource scarcity) were calculated, respectively. The obtained permeate quality complied with the most stringent Spanish and EU regulations.

Integrated urban wastewater management through on-site generation and application of ferrous carbonate

Integrated urban water management is an increasingly popular concept that cost-effectively maximizes system-wide performance by holistically considering all aspects of water and wastewater sectors. An innovative technology enabling production of high-quality bioenergy and an iron salt, ferrous carbonate (FeCO3), represents a significant opportunity for integrated urban water management. This study experimentally evaluates the effect of in-sewer FeCO3 dosing on the performance of sewers and the downstream wastewater treatment plants. Two continuous-flow laboratory-scale urban wastewater systems, each consisting of sewer reactors, a sequencing batch wastewater treatment reactor, and an anaerobic digester, were operated in parallel. After establishing comparable performance, one served as the control without any chemical dosing, while the other received a dosing of 10mgFe/L of FeCO3 in its sewer reactors. Compared to the control, the FeCO3-dosed experimental system reduced dissolved sulfide concentrations by 32.2±3.3% (at 0.58±0.05mgS/mgFe, or 1.0molFe/molS) in sewer reactors, decreased phosphate concentrations by 38.3%±3.2% (at 0.37±0.04mgP/mgFe, or 1.5molFe/molP) in sequencing batch reactors, and lowered dissolved sulfide concentrations by 72.0±4.2% (18.9±2.4mgS/L) in the anaerobic sludge digester. Iron accumulated in the sludge and improved sludge settleability by 33.9±5.5% and enhanced dewaterability of anaerobically digested sludge by 15.9±2.0%. The findings indicate multiple benefits from the integrated use of FeCO3, potentially being as a substitute for the currently used iron salts in urban wastewater systems.

Preparation of a novel organic-inorganic composite sludge bioflocculant (SBF) from dewatered sludge as raw material: Characteristics, flocculation mechanism and application for domestic sewage

In this work, a green sludge bioflocculant (SBF) was prepared via chemical hydrolysis of dewatered sludge and applied to flocculation of domestic wastewater. The process parameters for the preparation of the SBF were 1.80 % hydrochloric acid concentration, 60 min extraction time, and 4000 r/min centrifugation speed. SBF is polymeric flocculant composed of organic and inorganic compounds. Flocculation efficiency reached 97.31 ± 0.26 % under optimal flocculation conditions. Charge neutralization promotes the surface adsorption, bridging and net trapping and sweeping of Fe (OH)3, Al (OH)3 and active functional groups OH/NH and C = O in SBF, which together achieve efficient flocculation reactions. SBF had high efficiency and stable flocculation performance for phosphorus in urban domestic wastewater, and the concentration of TP in effluent was lower than 0.30 mg/L. Therefore, SBF prepared from dewatered sludge has efficient flocculation properties and is suitable for removing pollutant phosphorus, which has good application prospects in the field of wastewater treatment.

Polycaprolactone-zinc oxide biocomposite membranes for wastewater treatment by ultrafiltration process: synthesis, characterization and removal of inorganic pollutants

The severe droughts impacting North Africa have intensified the pressure on potable water supplies and agricultural irrigation, highlighting the urgent need for sustainable water management solutions. This study explores the potential of poly(ε-caprolactone)/zinc oxide (PCL/ZnO) biocomposites as ultrafiltration membranes for treating urban wastewater, with the goal of enabling water reuse in agriculture. PCL/ZnO membranes, fabricated using the solvent-casting method, were thoroughly characterized using FTIR, XRD, EDAX, SEM, AFM, DSC, TGA, and water contact angle (WCA) measurements. Key findings revealed that increasing ZnO content (1-4wt%) significantly enhanced membrane thickness, crystallinity, mechanical robustness, and surface roughness, while lowering WCA values to improve hydrophilicity. These enhanced properties are critical for ultrafiltration, as they contribute to higher contaminant rejection and improved water permeability. Performance tests demonstrated ion retention rates of 32% to 61% post-filtration, including for toxic metals, effectively reducing pollutant levels. Notably, the treated water met the Food and Agriculture Organization (FAO) standards for irrigation quality, indicating its suitability for agricultural applications. This work highlights the efficacy of PCL/ZnO membranes in facilitating sustainable wastewater recycling under drought conditions, presenting a promising, adaptable solution for water reclamation in water-scarce regions. The results underscore the potential of these biocomposite membranes to advance sustainable water treatment practices, supporting both environmental resilience and agricultural productivity.

Sustainability Prediction by Evaluating the Emergy of a Co-Treatment System for Municipal Wastewater and Acidic Water Using Intermittent Electrocoagulation

The objective of this research was to evaluate the sustainability of a co-treatment system that combines Municipal Wastewater (MW) and Acid Mine Drainage (AMD) through the technique of intermittent electrocoagulation, applied as an advanced solution to improve contaminant removal efficiency and optimize energy balance. Four scenarios were analyzed: Treatment I (with a 1/7 ratio of urban wastewater to AMD), Treatment II (which includes an artificial wetland), Treatment IIIa (which introduces electrocoagulation to enhance sulfate removal and pH regulation), and Treatment IIIb (which employs a 1/15 ratio of AMD to eutrophic water). The methodology focused on calculating key sustainability indicators such as the Net Yield Ratio (EYR), Emergy Inversion Ratio (EIR), Environmental Loading Ratio (ELR), and Sustainability Index (SI), in order to assess the impact of each technology on the energy efficiency and environmental load of the system. The results showed that, although Treatment IIIa was effective in contaminant removal, the EIR increased to 0.18 and the ELR rose to 0.62, indicating a higher reliance on non-renewable inputs due to increased energy demand. However, Treatment IIIb, which combines electrocoagulation with eutrophic water, significantly improved the sustainability of the system, achieving an SI of 2.31 and an ELR of 1.22, reflecting a reduction in energy efficiency due to intensive use of external resources, but overall greater sustainability compared to the other scenarios. This research concludes that intermittent electrocoagulation, when integrated with synergistic resources like eutrophic water, can enhance contaminant removal efficiency and improve the use of renewable resources, minimizing environmental load and increasing the sustainability of wastewater treatment systems.

Fate of microplastics in urban wastewater treatment plants and their contribution to the receiving river via effluent discharge

Fate of microplastics in urban wastewater treatment plants and their contribution to the receiving river via effluent discharge

Irrigation suitability assessment of urban wastewater for sustainable agriculture: a case study of Musi river, India

In urban areas with dense populations and high water demands, effective management of water resources is crucial for sustainable development. It includes optimizing water usage and recycling wastewater to balance supply and demand. Urban rivers, which now carry sewage year-round due to increased urban water consumption, are increasingly used for irrigation in peri-urban regions. This study aims to assess the suitability of an urban stream for irrigation compared to catchment groundwater, using hydrochemical parameters to evaluate water quality indices. Analysis of major ion distribution from upstream to downstream reveals a significant increase of TDS (r2 = 0.65; p < 0.001) in the surface water and a decrease (r2 = 0.93; p < 0.001) in groundwater samples. The calculated Weighted Arithmetic-Water Quality Index (WA-WQI) indicates that around 85% and 75% of surface water and groundwater samples from the Musi river are classified as very poor to unsuitable for any use, highlighting critical pollution levels. Based on irrigation suitability indices, only 16% of the surface water samples and 60% of the groundwater samples are suitable for irrigation. The nitrate concentration increased from less than 10 mg l−1 in the upstream region to over 100 mg l−1 in the urban stretch. Nitrogen-Phosphate-Potassium (NPK) ratios across the basin are exceptionally higher, representing crops irrigated using the Musi river water might not require fertilizer applications. The adoption of fertilizer application concerning supplied water hydrochemistry, particularly the NPK ratio, might limit the excess usage of fertilizer and benefit farmers. Additionally, this practice may also limits the excess input of nitrate to the groundwater in the Musi river basin.

Fabrication of FeCu/CC Composite for Efficient Removal of Nitrate for Aqueous Solution Via Electrochemical Reduction Process

AbstractThe electrochemical nitrate reduction (ENR) for the conversion of nitrate to nitrogen gas is a significant strategy to remediate the eutrophication in surface water. However, the exploitations and practical applications of suitable electrocatalysts still face great challenges. In this study, FeCu bimetal microparticles were deposited onto surface of carbon cloth (CC) to fabricate the FeCu/CC electrocatalyst for the removal of nitrate. Among obtained catalysts, the sample with Fe/Cu molar ratio of 1 : 15 (Fe1Cu15/CC) exhibits the excellent electroreduction efficiency for nitrate removal (R(NO3−), &gt;90 %) but an ineffective selectivity of N2 formation (S(N2), ~23 %). After the anchor of reduced graphite oxide (rGO) to surface of Fe1Cu15/CC, at the optimized condition without the assistance of chlorine oxidation, R(NO3−) and S(N2) of rGO/Fe1Cu15/CC catalyst reach 94.2 % and 72.8 %. After 5 day endurance test, the values of R(NO3−) and S(N2) are still 82.9 % and 62.8 %, demonstrating the promising durability of this catalyst electrode. Meanwhile, the potential application of rGO/Fe1Cu15/CC was explored for the treatment of simulated wastewater discharged by urban wastewater treatment plant, the concentration of total nitrogen (TN) decreases from 15–1.17 mg/L, and this value is lower than TN threshold limit in Class IV of Chinese surface water quality standard.

Mathematical Modeling and Indirect Carbon Emission Reduction Analysis of Urban Wastewater Treatment Systems Under Different Temperature Conditions

In the context of achieving the two-carbon target, this study utilized a wastewater treatment plant in Shenyang City as a case study to accurately calculate indirect emissions related to energy and chemical consumption within the energy-intensive wastewater treatment industry. Sumo software was employed for precise mathematical modeling. Considering the operational characteristics of wastewater treatment plants in cold regions, this study innovatively divided the annual operation cycle into two periods, namely normal temperature and low temperature, and determined the optimal operational parameters under a low-carbon mode. The results indicate that precise regulation of dissolved oxygen concentration to 0.5–1.5 mg/L (normal temperature period) and 1–2 mg/L (low temperature period) can significantly reduce carbon emissions related to electricity consumption by 13,781.9 t CO2-eq. From the perspective of chemical consumption, adjusting the dosage of polyaluminum chloride (PAC) to 75% and sodium acetate to 70% during the normal temperature period can lead to a reduction in indirect carbon emissions of 1614.4 t CO2-eq compared to the same period last year. During the low-temperature period, by reducing the dosage of polyaluminum chloride to 80% and sodium acetate to 75%, the indirect carbon emissions can be reduced by 1557.3 t CO2-eq compared to the corresponding period last year. After optimization, USD 1.49 million can be saved. This study simulated the operation conditions of cold-region urban wastewater treatment plants at different times to effectively control carbon emissions resulting from energy and chemical consumption in wastewater treatment. This result can provide innovative ideas for energy saving and carbon reduction in cold-region wastewater treatment plants.

Homojunction-Incorporated Oxygen Vacancy Functionalized Spherical TiO2 Nanocrystals for the Electrochemical Detection of Chemical Oxygen Demand.

Chemical oxygen demand (COD) is a critical criterion for the analytical assessment of the degree of organic contaminants in an aqueous system. Typically, toxic and expensive reagents are employed in standardized COD analysis methods, leading to secondary pollution. In this work, we developed a rapid electrochemical method for COD detection based on the oxidation of hydroxyl radicals for organics in water by using oxygen vacancy doped anatase/rutile-TiO2 nanoparticles as electrooxidation catalysts. Homojunction interface generated increasing oxygen vacancies for enhancing electron-transfer rate and accelerating H2O oxidation to substantially improve ·OH yield. Oxygen vacancy further increased the oxygen evolution potential of the material. Initially, glucose was chosen as a standard analyte to evaluate electrochemical responses, and water from urban wastewater treatment plants was assessed as real samples subsequently. Excellent analytical characteristics were achieved with the A/R-TiO2 sensor under the optimal conditions, exhibiting a linear range from 1 to 300 mg L-1 and detection limit of 0.1 mg L-1 COD. The estimated COD values obtained from the samples were highly consistent with those determined using the conventional standard dichromate method. We have presented a fast, cost-effective, and ecologically sustainable method that outperforms the standard COD analysis method and holds great potential for the accurate determination of COD and boasts high detection sensitivity and a broad linear range.

Performance of poplars and willow grown on soil under wastewater irrigation during the first 2 years of establishment.

Recycling wastewaters as irrigation and fertilization of tree species is a market-driven action for purpose-grown timber plantations that promotes the circular economy. A greenhouse experiment was carried out to investigate the performance of poplar clones (Populus alba L. "20/45", P. nigra L. "62/154", and P. euramericana (Dode) Guinier "92/40") and willow (Salix excelsa S.G. Gmel) grown on soils under tap water irrigation (TWI) or wastewater irrigation (WWI) during the first 2 years of establishment. Results showed that at 2 years after planting, poplars and willow exhibited significantly greater performance when grown in WWI versus TWI (P < 0.05). Likewise, phytoremediation of nutrients along with some heavy metals increased in plant organs of WWI-grown plants relative to their TWI counterparts (P < 0.05). After 2 years of growth and under both conditions (TWI and WWI), P. nigra plants showed the greatest growth and biomass; however, leaf area was the largest for P. alba and P. euramericana plants. Also, P. nigra plants had the highest total contents of copper (Cu) and manganese (Mn), P. alba had the most zinc (Zn), and differences for iron (Fe) were negligible across species. In contrast, total contents of nickel (Ni) and chromium (Cr) were higher for S. excelsa, P. nigra, and P. alba plants, while the lowest values were measured in P. euramericana plants. Across all species and soil treatments, the translocation factor (TF) was greater than 1 for Mn, Cu, and Zn, indicating phytoextraction and phytoaccumulation of these elements into leaves and stems, while TF was less than 1 for Fe, lead (Pb), Ni, and Cr, resulting in phytoremediation of these elements as phytostabilization. Differences in tolerance index (TI) values were negligible across species, and TI was greater than 100% after 2 years of growth, indicating that all four species are suitable for phytoremediation applications with urban wastewaters having similar heavy metal concentrations as in the present study. Nevertheless, given the combination of enhanced growth, biomass, and heavy metal accumulation (Mn, Cu, Cr, and Ni), P. nigra plants exhibited the greatest phytoremediation potential of four tested species.

Sustainability Strategies in Municipal Wastewater Treatment

The European Parliament adopted a legislative resolution of 10 April 2024 on the proposal for a directive of the European Parliament and of the Council concerning urban wastewater treatment. The reduction in pollution in discharged treated wastewater in the parameters of BOD5, total nitrogen, and total phosphorus was emphasized. Based on these results, it stated that the impacts on the quality of lakes, rivers, and seas in the EU are visible and tangible. At the same time, it was emphasized that the sector of urban wastewater removal and treatment is responsible for 0.8% of total electricity consumption and about 0.86% of all greenhouse gas emissions in the entire EU. Almost a third of these emissions could be prevented by improving the treatment process, better use of sewage sludge, and increasing energy efficiency, as well as a higher rate of use of renewable resource technologies. It is also necessary to integrate treatment processes into the circular economy. Sludge management and water reuse are suboptimal as too many valuable resources are still being wasted. This article focuses on sustainable municipal wastewater treatment, innovative and new wastewater treatment processes and technologies (combined and hybrid processes, ANAMMOX, etc.) and their use in practice with the aim of increasing environmental and energy efficiency and reducing the carbon footprint. The research is focused on the possibilities of increasing the efficiency of energy processing of sludge, reuse of nitrogen and phosphorus, sludge, and reuse of treated wastewater.

Electrolysis for ammonia removal and hydrogen generation in urban wastewater: Innovative approaches to the water crisis

The global water crisis poses significant challenges, with millions lacking access to clean drinking water and increasing water scarcity affecting urban areas worldwide. This study explores the electrolysis of urban wastewater as a two-fold solution for ammonia (un-ionized NH3, and ionized NH4+) removal and hydrogen gas (H2) production. Traditional treatment methods often fail to remove ammonia efficiently, underscoring the need for innovative approaches. Electrolysis, known for its versatility, energy efficiency, and environmental friendliness, emerges as a promising solution in wastewater treatment applications. This research utilized a dimensionally stable electrode (DSA) comprising a Ru-Ir anode and a stainless-steel cathode to electrochemically oxidize ammonia and produce H2. The study investigates the effects of current density, J (83.33–416.6 A/m2) on the treatability of urban wastewater. Maximum H2 production was achieved at J of 416.6 A/cm2 after 300 min reaction time. Under optimal conditions (333.3 A/m2, 0.5 mm inter-electrode distance, and 300 min of operation), the process achieved removal efficiencies of 98.94 % for ammonia, 78.18 % for total suspended solids (TSS), 50.73 % for chemical oxygen demand (COD), and complete removal (∼100 %) of total coliforms. Gas chromatography (GC) assessed the composition of gases of interest generated during electrolysis. This approach addresses environmental pollution and freshwater scarcity and generates an energy resource, presenting a scalable solution for cities worldwide facing similar challenges.

Innovative Circular Biowaste Valorisation—State of the Art and Guidance for Cities and Regions

The management of the organic fraction of municipal solid waste (OFMSW), also called urban biowaste, and urban wastewater sludge (UWWS) represents a challenge for cities and regions, which want to adopt innovative urban bioeconomy approaches for their treatment and production of high-added-value products beyond the traditional anaerobic digestion (AD) and compost. This adoption is often restricted by the availability and maturity of technologies. The research object of this manuscript, based on the findings of EU Horizon 2020 project HOOP, is the identification of state-of-the-art circular technologies for material valorisation of OFMSW and UWWS, following a novel screening methodology based on the scale of implementation (tested at least at pilot scale). The screening resulted in 25 technologies, which have been compared and discussed under a multidisciplinary assessment approach, showing their enabling factors and challenges, their current or potential commercial status and their compatibility with the traditional technologies for urban biowaste treatment (composting and AD). The bioproducts cover market sectors such as agriculture, chemistry, nutrition, bioplastics, materials or cosmetics. Therefore, the results of this review help project promoters at city/region level to select innovative technologies for the conversion of OFMWS and UWWS into high value products.

Fit-for-Purpose Water in the Baltic Sea Region

Climate change is visible everywhere, including in Baltic Sea Region (BSR). One of the symptoms is water scarcity, occurring relatively locally but persisting over longer and longer periods. The European and Global Drought Observatories (https://drought.emergency.copernicus.eu) present increasing BSR areas where soil moisture is alarmingly low. Water shortages cause technical and organizational problems in water utilities, agriculture, energy, industry, etc. Hence, competition for water between industry, agriculture, and municipal services has emerged. Sustainable water resource management requires solutions that rationalize and optimize the use of available resources with particular care for the environment. One of the methods of remedying local problems is closing local water and nutrient cycles by recovering water from urban wastewater and using rainwater

Biotransformation of microplastics from three-layer face masks by nitrifying-denitrifying consortia

COVID-19 increased microplastics (MP) contamination due to the extensive use of single-use personal protective equipment, particularly three-layer face masks. MP from face masks enter wastewater treatment plants (WWTPs), which were not designed to remove them. We utilized nitrifying-denitrifying microbial consortia and synthetic urban wastewater to evaluate the biotransformation of MP from each layer of three-layer face masks made of polypropylene (PP). The biotransformation carried out by the nitrifying-denitrifying consortia altered the surface of the outer, middle, and inner layers, as a consequence of the chemical modification of the PP-MP structure. Abiotic controls did not show changes on the physicochemical and thermal properties of PP-MP. Biotic tests showed increments in both the carbonyl and hydroxyl indices of the three layers in 42 days. The outer layer showed the greatest degree of biotransformation, which was consistent with morphological changes detected by scanning electron microscopy and in physicochemical properties such as crystallinity, evaporation, and fusion temperature. The nitrifying-denitrifying consortia, which removed 99 % of the total nitrogen from the synthetic urban wastewater, had several genera with proven capacity to biotransform MP such as Cephaloticoccus and Pseudomonas.

Development of decision support methods for efficient maintenance of urban wastewater systems

The sanitation network is a vital urban infrastructure that requires systematic and co-ordinated activities and practices to realize lowest life cycle cost. The sustainable management of this asset is based on the efficient acquisition of diagnostic data from the sanitation network in order to analyze the defects of each section, then to assess their condition to prioritize and consider the effective mode of maintenance of sections deemed failing. In this perspective, knowledge of the sanitation networks is essential for reliable classification of defects and effective maintenance. A numerical model based on weighted criticality is developed to evaluate and prioritize the defects in an urban sanitation network. It is based on the combination of two methods: Fuzzy Analytic Hierarchy Process (F-AHP) and Weighted Product Model (WPM). A case study of a real sanitation network in Bejaia city (Algeria), consisting mainly of non-visitable pipes evaluated from television inspections, is used to illustrate and validate the proposed model. The results show that the weighting of criticality parameters has a considerable influence on the classification of defects in a sanitation network. The weighted criticality results obtained in the present case are significantly better than those obtained using a method based on the notion of classical criticality. This clearly indicates the relevance of the proposed numerical model.

First detection of Hepatitis E virus (Rocahepevirus ratti) in French urban wastewater: Potential implications for human contamination

Hepatitis E virus (HEV) is considered as an emerging zoonotic pathogen circulating in a wide range of animals. In recent decades, the genus Paslahepevirus frequently isolated in pigs were the most involved in human clinical practice. In addition, the genus Rocahepevirus have been isolated in rodents, and transmission to humans is increasingly reported worldwide, although gaps remain regarding the exposure factors. In this study, the presence of HEV was investigated in urban wastewater, swine slaughterhouse wastewater and river waters, in a geographical area where its circulation had previously been reported. In addition to the expected detection of Paslahepevirus in almost all waters samples collected, Rocahepevirus strains were detected with the same frequencies in urban and river waters, at concentrations up to 40-fold higher. No Rocahepeviruses were detected in swine slaughterhouse wastewater. This is the first study demonstrating the presence of Rocahepevirus in French wastewater. Although no evidence of transmission was reported among patients followed for a suspected HEV infection in the same area between April 2019 and October 2023 (i.e. 135/3078 serological tests positive for anti-HEV IgM detection; 46/822 blood samples positive for Paslahepevirus genome detection but none for Rocahepevirus), the circulation of Rocahepevirus in waters in such concentrations raises the question of the possible zoonotic transmission to human. Indeed, the waterborne transmission of HEV is now well documented in industrialized countries, and the exploration of the growing number of human infections in Europe involving Rocahepevirus has not until now made it possible to clarify the transmission routes.

Urban wastewater treatment at ambient conditions using microalgae-bacteria consortia in a membrane high-rate algal pond (MHRAP): The effect of hydraulic retention time and influent strength

The effects of hydraulic retention time (HRT) and influent wastewater strength on microalgae-bacteria performance were studied in two sets of experiments in a 6-day biomass retention time membrane high-rate algal pond (MHRAP) pilot plant to assess its pollutants removal potential. In the first set of experiments, the MHRAP was continuously fed with effluent from primary settling and operated at 6-, 4- and 2-days HRT and in the second set, the MHRAP was operated at 4-, 2-, and 1-day HRT using pre-treatment effluent. Results showed a complex interaction between algae-bacteria consortium, ambient conditions and MHRAP operation. In set 1, the highest total nitrogen (T-N) and total phosphorus (T-P) removal efficiencies were reached with 6-day HRT (23.6±0.6 % and 32±4 %, respectively), partially due to free ammonia nitrogen stripping and phosphorus precipitation, because of abiotic factors, which reduces the activity of nitrite-oxidizing bacteria and led to partial-nitrification. On the other hand, the 4 and 2-day HRT T-N and T-P removal efficiencies were reduced (below 10 % and 5 %, respectively) because the abiotic factors limited the physicochemical processes, and less biomass was taken up. In set 2, a suitable equilibrium between the microalgae and bacterial communities at 2-days HRT achieved high T-N (91±5 %) and T-P (71±8 %) removal efficiencies. Mass balances indicated that the nitrogen was mostly removed by nitrification-denitrification (87 % of T-N) and T-P predominant removal mechanism was precipitation. The COD removal efficiencies were higher than 86 % in both sets, since the particulate COD and colloids were removed by ultrafiltration. The obtained results showed that MHRAP technology would allow reducing COD and nutrient loads in the effluent under certain operating conditions, demonstrating the potential for resource recovery and wastewater treatment of microalgae-bacteria consortia.

Ion exchange columns. A promising technology for nitrogen and phosphorus recovery in the main line of a wastewater treatment plant

Anaerobic membrane bioreactor (AnMBR) technology has great advantages for treating urban wastewaters, but, when irrigation cannot be applied and the effluent is discharged in a sensitive zone, a post-treatment of this effluent is needed for nitrogen and phosphorus removal. Under this scenario, ion exchange processes represent one of the most promising technologies for treating this effluent. Ion exchange technology allows to meet discharge limits and to recover these nutrients in a highly concentrated stream. In this work, the technical feasibility of using a commercial resin for phosphorus recovery and a natural zeolite (clinoptilolite) for nitrogen recovery was evaluated. Purolite FerrIX A33E resin removed phosphate from the AnMBR permeate within 500 Bed Volumes (BVs) with a maximum adsorption capacity (qmax) of 2,1 mg P-PO4/g resin. Regeneration of the resin (2% NaOH 2% NaCl) recovered over 95% of the phosphorous retained, achieving a concentration of 316,7 mg P-PO4/L in the regeneration solution. In the absence of a long-term study, the resin showed a stable adsorption capacity during 16 cycles of saturation-regeneration. Clinoptilolite removed nitrogen within 139 BVs obtaining a qmax of 3,68 mg N-NH4/g zeolite. 97 % of the retained N-NH4 was recovered in the regeneration stage (0,8% NaOH) with an average concentration of 577 mg N-NH4/L. Continuous exposure of the zeolite to alkaline solutions led to reduction of 50% of the adsorption capacity after 17 cycles.