Nitrogen recovery from wastewater and human urine with hydrophobic gas separation membrane: experiments and modelling

Feasibility of ammonium sulfate recovery from wastewater sludges: Hydrothermal liquefaction pathway vs. anaerobic digestion pathway

This study evaluated two pathways to recover the nitrogen-content of wastewater sludges as ammonium sulfate (AmS) for use as fertilizer. The first pathway entails sludge stabilization by hydrothermal liquefaction (HTL) followed by recovery of AmS from the resulting aqueous product by gas permeable membrane (GPM) separation. The second one entails stabilization of the sludges by anaerobic digestion (AD) followed by recovery of AmS from the resulting centrate by GPM separation. A bench-scale GPM reactor is shown to be capable of recovering >90% of N in the feed. Recoveries of NH3-N in the HTL-pathway ranged 96-100% in 5.5-7.5 h at mass removal rates of 0.2-0.3 g N/day, yielding 3.3-6.0 g AmS/L of feed. Recoveries of 98% were noted in the AD-pathway in 4 h at mass removal rates of 0.06-0.97 g N/day and a yield of 1.7-2.1 g AmS/L of feed. Inductively coupled plasma optical emission spectrometer analysis confirmed that both pathways yielded AmS meeting the US EPA and European region guidelines for land application. The GPM reactor enabled higher nitrogen-recoveries in the HTL-pathway than those reported for current practice of AD followed by ammonia stripping, ion exchange, reverse osmosis, and/or struvite precipitation (96-100% vs. 50-90%). A process model for the GPM reactor is validated using performance data on three different feedstocks.

Synergetic effect on fouling alleviating of membrane distillation in urine resource recovery by thermally activated peroxydisulfate pretreatment

Given that the spontaneous precipitation of minerals caused by urea hydrolysis and abundant organic compounds, membrane fouling became a major obstacle for urine recovery by membrane distillation (MD). Herein, this study developed a combined system (TAP-MD) by integrating thermally activated peroxydisulfate (TAP) and MD process to inhibit membrane fouling and improve separation efficiency. Based on the TAP-MD system, the separation performance was improved significantly, improving nutrient recovery efficiency and quality of reclaimed water. More than 80% of water could be recovered from urine, and about 94.13% of total ammonia nitrogen (TAN), 99.02% of total nitrogen (TN), 100% of total phosphate (TP), and 100% of K+ were rejected. The mechanism for alleviating urine-induced fouling was systematically and intensively studied. With TAP pretreatment, the TAN concentration of pretreated urine was kept at a low level steadily and the pH was at neutral or weakly acidic. Hence, inorganic scaling represented by carbonate and phosphate precipitates were significantly inhibited by creating unfavorable solvent environment for crystallization with TAP pretreatment. Additionally, aromatic proteins were found as the main organic foulants. According to the secondary structure of protein, the proteins were degraded by the cleavage of peptide bonds by TAP pretreatment. Meanwhile, the hydrophilicity of protein increased, which reduced the hydrophobic interaction of protein and membrane surface and thus alleviated protein-induced membrane fouling. This study revealed the inorganic and organic foulants in urine that caused membrane fouling and demonstrated the mechanism of membrane fouling alleviation by TAP-MD system. The experimental results will be instrumental in better understanding the mechanisms of membrane fouling induced by urine and optimize MD process for resource recovery from urine.

Nitrogen recovery from sludge centrate by membrane contactor: Influence of operating parameters and cleaning conditions

In urban wastewater treatment, the sludge generated is treated by anaerobic digestion, to be subsequently dehydrated by centrifuges. Currently, the liquid fraction obtained in this dehydration process is recirculated at the head of the treatment plant. However, its high nitrogen and phosphorus content makes it an effluent with high added value. The recovery of these nutrients could be an excellent alternative for the production of fertilizers or other industrial applications. In this study, the use of a liquid-liquid phase membrane contactor is presented as a favorable solution for the recovery of ammoniacal nitrogen from sludge centrated. The polypropylene hollow fiber membrane was evaluated considering its ammonia removal and recovery capacity. For this, different parameters were evaluated: the influence of the type and concentration of the acid solution, the wastewater pH, the flow rates of feeding and the acid stripping solution, and the contact time. Results showed that with a contact time of 65 min, ammonia removal and recovery percentages of the order of 90% were achieved. The flow rates of the stripping and feed solutions together with the acid concentration did not have a significant influence on the removal but on the recovery. Concerning used acid, sulphuric and phosphoric acid solutions achieved better results than nitric acid solution. The most critical parameter was the pH, obtaining the highest removal and recovery of ammonium at the highest pH. Finally, a stable cleaning protocol was obtained, between preventive and moderate cleanings to avoid severe cleanings, keeping the membrane at its maximum capacity.

Nutrient recovery from yellow water to soil-crop systems

The potentials of the nutrient recovered (NRM), via a facile green and sustainable approach from human urine, as a fertilizer in soil-crop system was studied. Nutrient was recovered using a highly decentralized modular reactor, with packed bed of granular gastropod shell. The cultivations of Zea mays (maize) and Solanum lycopersicum (tomato) were the cases studied. The total nutrient composition, the P-speciation, and the safety-risk assessment of the NRM were determined. Using NPK as the standard fertilizer, and a non-fertilized soil as the control, the fertilizing potential of the NRM was evaluated. The influence of the different fertilizer application regimes on the wet and dry biomass nutrient composition, after-harvest soil nutrient composition, and pH values was studied. The NRM contained 106 mg/g of TN and 374.6 mg/g of TP, and the P species identified were Ca₂-P (31.66%), Ca₈-P (14.99%), and Ca₁₀-P (53.32%). The growth rate of the NRM crops were lower than that of the NPK crops until the 17th day, when the NRM crops grew faster than that of the NPK and control (p < 0.05). The NRM is beneficial to acidic soils and also acts as a slow nutrient releasing fertilizer.

Life Cycle, PESTLE and Multi-Criteria Decision Analysis of Membrane Contactor-Based Nitrogen Recovery Process

Nitrogen is one of the most critical nutrients in the biosphere, and it is an essential nutrient for plant growth. Nitrogen exists in the atmosphere vastly as a gaseous form, but only reactive nitrogen is usable for plants. It is a valuable resource and worth recovering in the wastewater sector. The aim of this work was to prepare a comprehensive environmental analysis of a novel membrane contactor-based process, which is capable of highly efficient nitrogen removal from wastewater. Life cycle assessment (LCA), PESTLE and multi-criteria decision analysis (MCDA) were applied to evaluate the process. The EF 3.0 method, preferred by the European Commission, IMPACT World+, ReCiPe 2016 and IPCC 2021 GWP100 methods were used with six different energy resources-electricity high voltage, solar, nuclear, heat and power and wind energy. The functional unit of 1 m³ of water product was considered as output and "gate-to-gate" analysis was examined. The results of our study show that renewable energy resources cause a significantly lower environmental load than traditional energy resources. TOPSIS score was used to evaluate the alternatives in the case of MCDA. For the EU region, the most advantageous option was found to be wind energy onshore with a score of 0.76, and the following, nuclear, was 0.70.

Comparison of the Ammonia Trapping Performance of Different Gas-Permeable Tubular Membrane System Configurations

The technology of gas-permeable tubular membranes (GPMs) is promising in reducing ammonia emissions from livestock manure, capturing NH₃ in an acidic solution, and obtaining final products suitable for valorization as fertilizers, in line with the principles of the circular economy. This study aimed to evaluate the performance of several e-PTFE membrane systems with different configurations for the recovery of NH₃ released from pig slurry. Ten different configurations were tested: only a submerged membrane, only a suspended membrane in the same chamber, only a suspended membrane in an annex chamber, a submerged membrane + a suspended membrane in the same chamber, and a submerged membrane + a suspended membrane in an annex chamber, considering in each case the scenarios without and with agitation and aeration of the slurry. In all tests, sulfuric acid (1N H₂SO₄) was used as the NH₃ capture solution, which circulated at a flow rate of 2.1 L·h^-1. The results showed that NH₃-N removal rates ranged from 36-39% (for systems with a single submerged or suspended membrane without agitation or aeration of the slurry) to 70-72% for submerged + suspended GPM systems with agitation and aeration. In turn, NH₃-N recovery rates were found to be between 44-54% (for systems with a single membrane suspended in an annex compartment) and 88-91% (for systems based on a single submerged membrane). However, when choosing a system for farm deployment, it is essential to consider not only the capture and recovery performance of the system, but also the investment and operating costs (ranging from 9.8 to 21.2 €/kg N recovered depending on the selected configuration). The overall assessment suggests that the simplest systems, based on a single membrane, may be the most recommendable.

Ammonia recovery from acidogenic fermentation effluents using a gas-permeable membrane contactor

A gas-permeable membrane (GPM) contactor was used to recover ammoniacal nitrogen from a synthetic and a biowaste fermentation broth under different pH (from 6 to 11) and temperatures (35 and 55 °C). Ammonia mass transfer constant (K_m) increased as pH and temperature increased. For synthetic broth, pH 10 provided the best results, when considering the K_m (9.2·10^-7 m·s^-1) and the reagents consumption (1.0 mol NaOH·mol^-1 TAN and 0.6 mol H₂SO₄·mol^-1 TAN). Biowaste fermentation generated a broth with a high concentration of ammoniacal nitrogen (4.9 g N·L^-1) and volatile fatty acids (VFA) (41.1 g COD·L^-1). Experiments using the biowaste broth showed a lower K_m (5.0·10^-7 m·s^-1 at pH 10) than the synthetic broth, related to the solution matrix and other species interference. VFAs were not detected in the trapping solution. Overall, these results show that GPM is a suitable technology to efficiently separate ammoniacal nitrogen and VFA from fermentation broths.

Bioelectricity generation from human urine and simultaneous nutrient recovery: Role of Microbial Fuel Cells

Urine is a 'valuable waste' that can be exploited to generate bioelectricity and recover key nutrients for producing NPK-rich biofertilizers. In recent times, improved and innovative waste management technologies have emerged to manage the rapidly increasing environmental pollution and to accomplish the goal of sustainable development. Microbial fuel cells (MFCs) have attracted the attention of environmentalists worldwide to treat human urine and produce power through bioelectrochemical reactions in presence of electroactive bacteria growing on the anode. The bacteria break down the complex organic matter present in urine into simpler compounds and release the electrons which flow through an external circuit generating current at the cathode. Many other useful products are harvested at the end of the process. So, in this review, an attempt has been made to synthesize the information on MFCs fuelled with urine to generate bioelectricity and recover value-added resources (nutrients), and their modifications to enhance productivity. Moreover, configuration and mode of system operation, and factors enhancing the performance of MFCs have been also presented.

Modelling and Optimisation of Multi-Stage Flash Distillation and Reverse Osmosis for Desalination of Saline Process Wastewater Sources

Nowadays, there is increasing interest in advanced simulation methods for desalination. The two most common desalination methods are multi-stage flash distillation (MSF) and reverse osmosis (RO). Numerous research works have been published on these separations, however their simulation appears to be difficult due to their complexity, therefore continuous improvement is required. The RO, in particular, is difficult to model, because the liquids to be separated also depend specifically on the membrane material. The aim of this study is to model steady-state desalination opportunities of saline process wastewater in flowsheet environment. Commercial flowsheet simulator programs were investigated: ChemCAD for thermal desalination and WAVE program for membrane separation. The calculation of the developed MSF model was verified based on industrial data. It can be stated that both simulators are capable of reducing saline content from 4.5 V/V% to 0.05 V/V%. The simulation results are in accordance with the expectations: MSF has higher yield, but reverse osmosis is simpler process with lower energy demand. The main additional value of the research lies in the comparison of desalination modelling in widely commercially available computer programs. Furthermore, complex functions are established between the optimized operating parameters of multi-stage flash distillation allowing to review trends in flash steps for complete desalination plants.

Removal and recovery of nutrients from municipal sewage: Algal vs. conventional approaches

This paper presents a pilot scale study of an algal-based sewage treatment and resource recovery (STaRR) system capable of treating municipal sewage and recovering its nitrogen- and phosphorous-content as fertilizer. Core components of the STaRR system include i) mixotrophic cultivation of algal biomass in settled sewage; ii) hydrothermal liquefaction (HTL) of the resulting algal biomass, and iii) processing of the products of HTL to recover energy in the form of biocrude and nutrients in the form of struvite. Performance of a pilot-scale STaRR system in recovering nitrogen (N) and phosphorus (P) from settled sewage as struvite is documented and compared with that of existing and emerging technologies. Nutrient removal per unit energy input in the STaRR system is estimated as 257.1 g N/kWh and 36.6 g P/kWh while that in eight full-scale sewage treatment plants (STPs) averaged 74.3 g N/kWh and 135.1 g P/kWh. Energy required to treat primary effluent in the STaRR system (531.5 kWh/MG) is estimated to be lower than the average in the 8 STPs (1,037.9 ± 503.3 kWh/MG). While existing technologies had been originally designed for removal of nutrients rather than any recovery, a review of the literature revealed 12 emerging technologies for nutrient recovery. Nutrient recovery performance of the STaRR system (5.9% N and 71.6% P) is shown to be superior to that of those 12 emerging technologies. Recoveries recorded in the STaRR system translate to a yield of 2.4 kg struvite per 100 m³ of primary effluent. Results of this study imply that the STaRR system deserves due consideration as a greener and sustainable pathway for nutrient removal and recovery from sewage.

Plant-wide modelling in wastewater treatment: showcasing experiences using the Biological Nutrient Removal Model

Plant-wide modelling can be considered an appropriate approach to represent the current complexity in water resource recovery facilities, reproducing all known phenomena in the different process units. Nonetheless, novel processes and new treatment schemes are still being developed and need to be fully incorporated in these models. This work presents a short chronological overview of some of the most relevant plant-wide models for wastewater treatment, as well as the authors' experience in plant-wide modelling using the general model BNRM (Biological Nutrient Removal Model), illustrating the key role of general models (also known as supermodels) in the field of wastewater treatment, both for engineering and research.

Microwave-assisted synthesis of coal fly ash-based zeolites for removal of ammonium from urine

Zeolites synthesized from biomass waste materials offer a great opportunity in the sustainable utilization of the waste.