Vacuum ammonia stripping from liquid digestate: Effects of pH, alkalinity, temperature, negative pressure and process optimization

High ammonia-nitrogen digestate has become a key bottleneck limiting the anaerobic digestion of organic solid waste. Vacuum ammonia stripping can simultaneously remove and recover ammonia nitrogen, which has attracted a lot of attention in recent years. To investigate the parameter effects on the efficiency and mass transfer, five combination conditions (53 °C 15 kPa, 60 °C 20 kPa, 65 °C 25 kPa, 72 °C 35 kPa, and 81 °C 50 kPa) were conducted for ammonia stripping of sludge digestate. The results showed that 80% of ammonia nitrogen was stripped in 45 min for all experimental groups, but the ammonia transfer coefficient varied under different conditions, which increased with the rising of boiling point temperature, and reached the maximum value (39.0 mm/hr) at 81 °C 50 kPa. The ammonia nitrogen removal efficiency was more than 80% for 30 min vacuum stripping after adjusting the initial pH to above 9.5, and adjustment of the initial alkalinity also affects the pH value of liquid digestate. It was found that pH and alkalinity are the key factors influencing the ammonia nitrogen dissociation and removal efficiency, while temperature and vacuum mainly affect the ammonia nitrogen mass transfer and removal velocity. In terms of the mechanism of vacuum ammonia stripping, it underwent alkalinity destruction, pH enhancement, ammonia nitrogen dissociation, and free ammonia removal. In this study, two-stage experiments of alkalinity destruction and ammonia removal were also carried out, which showed that the two-stage configuration was beneficial for ammonia removal. It provides a theoretical basis and practical technology for the vacuum ammonia stripping from liquid digestate of organic solid waste.

Selective electrodialysis for nutrient recovery and pharmaceutical removal from liquid digestate: Pilot-scale investigation and potential fertilizer production

The present research employs a pilot-scale selective electrodialysis system to treat liquid digestate, fractionating nutrient ions and exploring fertilizer creation via ammonia stripping and phosphorus precipitation, while studying pharmaceutical transport behavior and examining membrane fouling. The influence of diverse potentials was studied in simulated and real digestate, with 30 V application proven more efficient overall. Applying consecutive runs resulted in products that were 7.9, 7.4, 1.7, 5.3, and 6 times more concentrated compared to the feed solution for NH4+, K+, PO43-, Ca2+, and Mg2+, respectively. Pharmaceuticals analysis showed that ciprofloxacin was completely retained in the liquid digestate, while ibuprofen was detected in the anionic product. Diclofenac was initially present in the digestate but was undetectable in the final products, suggesting it adhered to the membrane. Membranes showed inorganic and organic fouling. The monovalent cation exchange membrane had severe salt scaling, showing calcium and magnesium deposits, and fewer functional groups.

Ultrahigh-purity ammonia recovery from synthetic coke wastewater via membrane contactor: Overcoming phenolic interference and assessing cost efficiency

Ammonia recovery from industrial wastewater using membrane contactor processes is emerging as a promising method owing to the diverse applications of ammonia. This study uniquely addressed ammonia recovery from coke plant wastewater, which is challenging due to the presence of numerous toxic and volatile phenolic compounds. Experiments were conducted using a synthetic coke plant effluent to assess the effects of various pH levels and temperatures on ammonia recovery. Specifically, the aim was to achieve high-purity ammonia recovery while minimizing the permeation of phenolic compounds. The results demonstrate that ammonia recovery in the membrane contactor processes is highly efficient, even in the presence of phenolic compounds. During temperature variations at 25 °C and 40 °C, the recovery of ammonia increased from 42.36% to 52.97% at pH 11. Additionally, increasing the pH of a feed solution from 7 to 12 significantly increased the ammonia content to 58.3%. At this pH, the recovered ammonia was of exceptional purity (>99%), with phenol, p-Cresol, and 2,4-xylenol present at negligible concentrations (0.001%, 0.002%, and 0.004%, respectively). This was attributed to the ionization of phenolic compounds at higher pH levels, which prevents their permeation through the hydrophobic membrane. The estimated cost analysis revealed that the membrane contactor process at pH 12 was approximately 1.41 times more cost-effective than conventional air-stripping processes over eight years of operating period (pH-12 membrane contactor: $19.79; pH-12 air stripping: $23.75). This study provides a detailed analysis of the optimal conditions for selective ammonia recovery from complex wastewater, highlighting both effective treatment and sustainable resource recovery and offering a superior alternative to traditional methods.

Ammonia Detection by Electronic Noses for a Safer Work Environment

Providing employees with proper work conditions should be one of the main concerns of any employer. Even so, in many cases, work shifts chronically expose the workers to a wide range of potentially harmful compounds, such as ammonia. Ammonia has been present in the composition of products commonly used in a wide range of industries, namely production in lines, and also laboratories, schools, hospitals, and others. Chronic exposure to ammonia can yield several diseases, such as irritation and pruritus, as well as inflammation of ocular, cutaneous, and respiratory tissues. In more extreme cases, exposure to ammonia is also related to dyspnea, progressive cyanosis, and pulmonary edema. As such, the use of ammonia needs to be properly regulated and monitored to ensure safer work environments. The Occupational Safety and Health Administration and the European Agency for Safety and Health at Work have already commissioned regulations on the acceptable limits of exposure to ammonia. Nevertheless, the monitoring of ammonia gas is still not normalized because appropriate sensors can be difficult to find as commercially available products. To help promote promising methods of developing ammonia sensors, this work will compile and compare the results published so far.

Literature review on the potential of urban waste for the fertilization of urban agriculture: A closer look at the metropolitan area of Barcelona

Urban agriculture (UA) activities are increasing in popularity and importance due to greater food demands and reductions in agricultural land, also advocating for greater local food supply and security as well as the social and community cohesion perspective. This activity also has the potential to enhance the circularity of urban flows, repurposing nutrients from waste sources, increasing their self-sufficiency, reducing nutrient loss into the environment, and avoiding environmental cost of nutrient extraction and synthetization. The present work is aimed at defining recovery technologies outlined in the literature to obtain relevant nutrients such as N and P from waste sources in urban areas. Through literature research tools, the waste sources were defined, differentiating two main groups: (1) food, organic, biowaste and (2) wastewater. Up to 7 recovery strategies were identified for food, organic, and biowaste sources, while 11 strategies were defined for wastewater, mainly focusing on the recovery of N and P, which are applicable in UA in different forms. The potential of the recovered nutrients to cover existing and prospective UA sites was further assessed for the metropolitan area of Barcelona. Nutrient recovery from current composting and anaerobic digestion of urban sourced organic matter obtained each year in the area as well as the composting of wastewater sludge, struvite precipitation and ion exchange in wastewater effluent generated yearly in existing WWTPs were assessed. The results show that the requirements for the current and prospective UA in the area can be met 2.7 to 380.2 times for P and 1.7 to 117.5 times for N depending on the recovery strategy. While the present results are promising, current perceptions, legislation and the implementation and production costs compared to existing markets do not facilitate the application of nutrient recovery strategies, although a change is expected in the near future.

An update on sustainabilities and challenges on the removal of ammonia from aqueous solutions: A state-of-the-art review

An insightful attempt has been made in this review and the primary objective was to meticulously provide an update on the sustainabilities, advances and challenges pertaining the removal of ammonia from water and wastewater. Specifically, ammonia is a versatile compound that prevails in various spheres of the environment, and if not properly managed, this chemical species could pose severe ecological pressure and toxicity to different receiving environments and its biota. The notorious footprints of ammonia could be traced to anoxic conditions, an infestation of aquatic ecosystems, hyperactivity, convulsion, and methaemoglobin, popularly known as the "blue baby syndrome". In this review, latest updates regarding the sustainabilities, advancements and challenges for the removal of ammonia from aqueous solutions, i.e., river and waste waters, are briefly elucidated in light of future perspectives. Viable routes and ideal hotspots, i.e., wastewater and drinking water, for ammonia removal under the cost-effective options have been unpacked. Key mechanisms for the removal of ammonia were grossly bioremediation, oxidation, adsorption, filtration, precipitation, and ion exchange. Finally, this review denoted biological nutrient removal, struvite precipitation, and breakpoint chlorination as the most effective and promising technologies for the removal of ammonia from aquatic environments, although at the expense of energy and operational cost. Lastly, the future perspective, avenues of exploitation, and technical facets that deserve in-depth exploration are duly underscored.

A Prussian-blue analogue (PBA) ion-chromatography-based technique for selective separation of Rb+ (as RbCl) from brines

A new general method is presented for separating pure RbCl(s) from solutions rich in Na+ and K+. The method relies on Rb+ adsorption via ion exchange performed by self-synthesized PES coated Zn-Hexa-Cyanoferrate material. The procedure starts by passing the wastewater through an ion exchange column, which is thereafter regenerated with 1 M NH4Cl. If the Rb+ absorbed on the column does not reach a minimal predetermined value (e.g., 8%, eq-based), the ammonia is removed by sublimation and the remaining salts are passed again through a Na+-preadsorbed column. Once the adsorbed Rb+ is substantial (>8%), a chromatography-based separation between Rb+ and Na+/K+ is performed, using a 2nd column, fully pre-adsorbed with NH4+. First, 0.05M NH4+-solution is used to extract Na+ and K+ out of the first column, along with a small Rb+ mass, which is thereafter partly re-adsorbed on the second column, while Na+/K+ ions are not. Once the exiting eluent solution is devoid of the competing ions, 1M NH4+-solution is used to extract all the remaining Rb+ into the regeneration solution, which is thereafter subjected to water evaporation followed by NH3/HCl sublimation to result in pure RbCl(s) product. We used theoretical simulations corroborated by empirical results to present proof of concept for the suggested approach. A detailed cost analysis (Capex and Opex) reveals that the RbCl(s) production cost does not exceed ∼25% of the current salt price.

Approaches to mitigation of hydrogen sulfide during anaerobic digestion process - A review

Anaerobic digestion (AD) is the primary technology for energy production from wet biomass under a limited oxygen supply. Various wastes rich in organic content have been renowned for enhancing the process of biogas production. However, several other intermediate unwanted products such as hydrogen sulfide, ammonia, carbon dioxide, siloxanes and halogens have been generated during the process, which tends to lower the quality and quantity of the harvested biogas. The removal of hydrogen sulfide from wastewater, a potential substrate for anaerobic digestion, using various technologies is covered in this study. It is recommended that microaeration would increase the higher removal efficiency of hydrogen sulfide based on a number of benefits for the specific method. The process is primarily accomplished by dosing smaller amounts of oxygen in the digester, which increases the system's oxidizing capacity by rendering the sulfate reducing bacteria responsible for converting sulfate ions to hydrogen sulfide inactive. This paper reviews physicochemical and biological methods that have been in place to eliminate the effects of hydrogen sulfide from wastewater treated anaerobically and future direction to remove hydrogen sulfide from biogas produced.

Machine-learning-aided application of high-gravity technology to enhance ammonia recovery of fresh waste leachate

Stripping is widely applied for the removal of ammonia from fresh waste leachate. However, the development of air stripping technology is restricted by the requirements for large-scale equipment and long operation periods. This paper describes a high-gravity technology that improves ammonia stripping from actual fresh waste leachate and a machine learning approach that predicts the stripping performance under different operational parameters. The high-gravity field is implemented in a co-current-flow rotating packed bed in multi-stage cycle series mode. The eXtreme Gradient Boosting algorithm is applied to the experimental data to predict the liquid volumetric mass transfer coefficient (K_La) and removal efficiency (η) for various rotation speeds, numbers of stripping stages, gas flow rates, and liquid flow rates. Ammonia stripping under a high-gravity field achieves η = 82.73% and K_La = 5.551 × 10^-4 s^-1 at a pH value of 10 and ambient temperature. The results suggest that the eXtreme Gradient Boosting model provides good accuracy and predictive performance, with R² values of 0.9923 and 0.9783 for K_La and η, respectively. The machine learning models developed in this study are combined with experimental results to provide more comprehensive information on rotating packed bed operations and more accurate predictions of K_La and η. The information mining behind the model is an important reference for the rational design of high-gravity-field-coupled ammonia stripping projects.

Calcium cyanamide reduces methane and other trace gases during long-term storage of dairy cattle and fattening pig slurry

Calcium cyanamide (CaCN₂) has been used in agriculture for more than a century as a nitrogen fertilizer with nitrification inhibiting and pest-controlling characteristics. However, in this study, a completely new application area was investigated, as CaCN₂ was used as a slurry additive to evaluate its effect on the emission of ammonia and greenhouse gases (GHG) consisting of methane, carbon dioxide, and nitrous oxide. Efficiently reducing these emissions is a key challenge facing the agriculture sector, as stored slurry is a major contributor to global GHG and ammonia emissions. Therefore, dairy cattle and fattening pig slurry was treated with either 300 mg kg^-1 or 500 mg kg^-1 cyanamide formulated in a low-nitrate CaCN₂ product (Eminex®). The slurry was stripped with nitrogen gas to remove dissolved gases and then stored for 26 weeks, during which gas volume and concentration were measured. Suppression of methane production by CaCN₂ began within 45 min after application and persisted until the storage end in all variants, except in the fattening pig slurry treated with 300 mg kg^-1, in which the effect faded after 12 weeks, indicating that the effect is reversible. Furthermore, total GHG emissions decreased by 99% for dairy cattle treated with 300 and 500 mg kg^-1 and by 81% and 99% for fattening pig, respectively. The underlying mechanism is related to CaCN₂-induced inhibition of microbial degradation of volatile fatty acids (VFA) and its conversion to methane during methanogenesis. This increases the VFA concentration in the slurry, lowering its pH and thereby reducing ammonia emissions.

Potential use of algae for the bioremediation of different types of wastewater and contaminants: Production of bioproducts and biofuel for green circular economy

Remediation by algae is a very effective strategy for avoiding the use of costly, environmentally harmful chemicals in wastewater treatment. Recently, industries based on biomass, especially the bioenergy sector, are getting increasing attention due to their environmental acceptability. However, their practical application is still limited due to the growing cost of raw materials such as algal biomass, harvesting and processing limitations. Potential use of algal biomass includes nutrients recovery, heavy metals removal, COD, BOD, coliforms, and other disease-causing pathogens reduction and production of bioenergy and valuable products. However, the production of algal biomass using the variable composition of different wastewater streams as a source of growing medium and the application of treated water for subsequent use in agriculture for irrigation has remained a challenging task. The present review highlights and discusses the potential role of algae in removing beneficial nutrients from different wastewater streams with complex chemical compositions as a biorefinery concept and subsequent use of produced algal biomass for bioenergy and bioactive compounds. Moreover, challenges in producing algal biomass using various wastewater streams and ways to alleviate the stress caused by the toxic and high concentrations of nutrients in the wastewater stream have been discussed in detail. The technology will be economically feasible and publicly accepted by reducing the cost of algal biomass production and reducing the loaded or attached concentration of micropollutants and pathogenic microorganisms. Algal strain improvement, consortium development, biofilm formation, building an advanced cultivation reactor system, biorefinery concept development, and life-cycle assessment are all possible options for attaining a sustainable solution for sustainable biofuel production. Furthermore, producing valuable compounds, including pharmaceutical, nutraceutical and pigment contents generated from algal biomass during biofuel production, could also help reduce the cost of wastewater management by microalgae.

Ammonia recovery from anaerobic digestate: State of the art, challenges and prospects

Nitrogen-containing wastewater and organic wastes are inevitably produced during human activities. To reduce nitrogen pollution, much energy has been used to convert ammonia nitrogen into nitrogen gas through biological nitrogen removal method. However, it needs to consume high energy again during industrial nitrogen fixation, which give rise to massive greenhouse gas (GHG) emissions. Therefore, ammonia recovery from organic wastes has attracted much attention in recent years. In this review, the advantages and disadvantages of ammonia stripping, membrane separation and struvite precipitation are discussed firstly. The ammonia stripping mechanisms, influencing factors, mass transfer process, and the latest innovative ammonia stripping techniques from the anaerobic digestate of organic wastes are critically reviewed. Additionally, a comprehensive economic analysis of different ammonia removal or recovery processes is carried out. The challenges and prospects of ammonia recovery are suggested. Ammonia recovery is of great significance for promoting nitrogen cycle, energy saving and GHG emission reduction.

Ecotoxicological assessment of estuarine surface waters receiving treated and untreated sanitary wastewater

Pollution from sewage discharge is one of the most critical environmental problems worldwide, e.g., in Brazil, where basic sanitation is still scarce. As pollution can affect biomes, especially estuaries where intensive ecological and human activities occur, has caused widespread concern. This work aimed to study the water quality of the Jundiaí/Potengi Estuary (JPE) in an area close to the discharge of treated and untreated wastewater for 18 months. Physicochemical and microbiological parameters were measured and integrated using the Water Quality Index of the Canadian Council of Ministers of the Environment. Ecotoxicological tests were performed with Brazilian endemic organisms to assess the impact of water pollution on biota. A generalized linear regression model was applied to understand the effects of water quality on ecotoxicological responses. Concentrations of metals, dissolved oxygen, total ammonia nitrogen, nitrate, and thermotolerant coliforms did not comply with Brazilian environmental regulations. A significant increase in the mortality rate of Mysidopsis juniae and Nitocra sp. and a significant decrease in the reproductive rate of Nitocra sp. indicated the most affected areas related to the discharge of treated and untreated wastewater. Only 10% of the samples from sites without direct wastewater impact showed a toxic response in at least one organism. Both water quality and sampling sites were statistical predictors of ecotoxicological response, describing not only the pollutant load but also the type of effluent. This study demonstrated the degradation of the environmental quality of the JPE, particularly due to the discharge of sanitary wastewater, and highlights the importance of protection and remediation measures to preserve this protected area.

A review of advances in valorization and post-treatment of anaerobic digestion liquid fraction effluent

Traditionally, digestate is considered a waste, which is used as fertiliser in the agriculture industry. Recent studies focus on increasing the profitability of digestate by extracting reusable nutrients to promote biogas plants cost-effectiveness, sustainable management and circular economy. This review focuses on the post-treatment and valorization of liquor which is produced by solid-liquid fractioning of digestate. Nutrient recovery and removal from liquor are possible through mechanical, physicochemical and biological procedures. The processes discussed involve complex procedures that differ in economic value, feasibility, legislative restrictions and performance. The parameters that should be considered to employ these techniques are influenced by liquor characteristics, topography, climate conditions and available resources. These are key parameters to keep in mind during designing and manufacturing a biogas plant. In the following chapters, a discussion on available liquor treatment methods takes place. The present study examines the critical aspects of the available liquor treatment methods.

Recovery of nitrogen and phosphorus from livestock slurry with treatment technologies: A meta-analysis

The livestock industry has developed rapidly in recent decades, but the improper treatment of livestock manure, especially slurry, causes environmental pollution. Treatment technologies are considered to be effective in alleviating nitrogen (N) and phosphorus (P) losses from livestock slurry. Here, we used published research data to conduct a meta-analysis of the recovery efficiencies of N and P of five mainstream treatment technologies, including ammonia stripping, air scrubbing, membrane filtration, microalgae cultivation and struvite crystallization. Additionally, the agronomic effects of the recovered products of these treatment technologies were evaluated. The results showed that all technologies exhibited clear recovery effects on N and P. The N recovery efficiencies ranged from 57% to 86%, and those of P ranged from 64% to 87%. Struvite crystallization was the most efficient treatment technology for both N and P recovery; moreover, the ammonia stripping and microalgae cultivation technologies were less efficient. The pH levels and temperatures are the main factors that influence ammonia stripping, struvite crystallization and microalgae cultivation, while membrane filtration and air scrubbing are mainly affected by the membrane types and properties. When the equal amount of N or P input to fields, the recovered products (ammonium sulfate and struvite crystals) may achieve a similar crop yield, relative to commercial N or P fertilizers. Our findings can provide deep suggestions and parameters for designing proper treatment technologies to reduce nutrient discharge from livestock slurry in regions with high livestock density and also for identifying the research gaps that should be paid more attention in the future.

Bioaugmentation with a propionate-degrading methanogenic culture to improve methane production from chicken manure

Volatile fatty acid (VFA) accumulation caused by high ammonia concentrations is often encountered during the anaerobic digestion (AD) of ammonia-rich substrates. In this study, propionate-degrading methanogenic cultures were introduced to augment the semi-continuous AD of chicken manure under high ammonia levels. Introduction of a methanogenic culture enhanced the methane yield in the bioaugmented digester by 17-26% when the organic loading rate (OLR) was 2-4 g L^-1d^-1 compared to that in the control. When the OLR was further increased from 4.0 L^-1d^-1 to 5.0 g L^-1d^-1, and bioaugmentation ceased, methane yield improved by 15-18% under a high total ammonia nitrogen level of 5.0-8.4 g NH₄⁺-N/L. Moreover, bioaugmentation reconstructed the methanogenic community in the digester, promoting the dominance of hydrogenotrophic Methanobacterium and slightly increasing the abundance of aceticlastic Methanothrix and the syntrophic propionate-oxidizing bacteria Syntrophobacter, which were the key contributors to the improved AD under high ammonia concentrations.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Nutrients Recovery from Dairy Wastewater by Struvite Precipitation Combined with Ammonium Sorption on Clinoptilolite

Struvite precipitation from Wastewater involves an excess of ammonium to create a supersaturated initial solution. The remaining fraction can be a threat to the environment. This work combined struvite precipitation and ammonium sorption using natural zeolite to decrease the ammonium level in the effluent. Two approaches of estimation of feed sample doses were used. One consisted of gradient experiments for ammonium precipitation to the asymptotic level and was combined with clinoptilolite to lower the ammonium level in the effluent. This approach used doses of 0.05:1.51:0.61:1 of Ca:Mg:NH₄⁺:PO₄³⁻ mole ratios, respectively. In contrast, three level design with narrowed NH₄⁺:PO₄³⁻ range reached 0.25:1.51:0.8:1 for Ca:Mg:NH₄⁺:PO₄³⁻ mole ratios. The addition of zeolite decreased effluent ammonium concentration. In both ways, the P and N recoveries were higher than 94% and 72%, respectively. The complexity of the precipitation mixture decreased the ammonium sorption capacity (Q_e) of clinoptilolite from Q_e of 0.52 to 0.10 meq∙g⁻¹ in single and complex solutions, respectively. Thermodynamically, the addition of 1.5 % of clinoptilolite changed the struvite precipitation spontaneity from ∆G of −5.87 to −5.42 kJ·mol⁻¹ and from 9.66 to 9.56 kJ·mol⁻¹ for gradient and three level experimental procedures, respectively. Thus, clinoptilolite demonstrated a positive effect on the struvite precipitation process and its environmental impact.

Resource recovery from industrial effluents through the cultivation of microalgae: A review

Industrial effluents such as pharmaceutical residues, pesticides, dyes, and metal processes holds abundant value-added products (VAPs), where its recovery has become essential. The purpose of such recovery is for sustainable treatment, which is an approach that considers the economic, social, and environmental aspects. Microalgae with its potential in the recovery process from effluents, can reduce energy usage of waste management strategies and regenerate nutrients such as carbon, phosphorus, and nitrogen. Microalgae cultures offer the use of inorganic materials by microalgae for their growth and the help of bacteria to produce biomass, thus, resulting in the absence of secondary emissions due to its ability to eliminate volatile organic compounds. Moreover, recovered bioactive compounds are transformed into bioethanol, bio-fertilizers, biopolymer, health supplements and animal feed. Therefore, it is significant to focus on an economical and efficient utilization of microalgae in recovering nutrients that can be further used in various commercial applications.

External electric field promotes ammonia stripping from wastewater

The gas stripping process is widely used for the removal and recovery of ammonia from wastewater. The ammonia removal in the stripping process depends on the pH, temperature, and air supply, and in general, 10.5, 60 °C, 5 L/min or more are recommended as near-optimal. However, alkaline chemicals and energy can seriously burden the stripping process operation, depending on the wastewater characteristics. Herein, external electric field-coupled ammonia stripping, which improves ammonia removal from aqueous solutions, was investigated. The ammonia removal in the conventional stripping was between 17.7 % and 90.6 %, depending on how close to the near-optimal conditions. The electric field increased the removal efficiency from 51.1 % to 94.3 %, as the strength and frequency increased to 15 V/cm and 50 MHz. The electric field promotion of ammonia stripping correlated closely with the increase in ammonia molecular diffusion. The electric field has been shown to improve the diffusion of ammonia molecules without dielectric heating by increasing the kinetic energy. The electric field improved the ammonia removal more as the pH, temperature, and air supply conditions were far from optimal. The electric field reduces the alkaline chemicals and the electric energy for heating and air supply, and the energy consumption to form the electric field is only a few watts. The electric field-coupled process offers a new gas stripping platform that can economically improve ammonia removal from wastewater.

Technologies to recover nitrogen from livestock manure - A review

Today, the livestock industry is considered to be one of the biggest emitters of ammonia in the world. The nitrogen present in livestock manure has been linked to the contamination of water bodies. Livestock manures contain a significant quantity of recoverable nitrogen. Recovering nitrogen from livestock manure can minimize negative environmental consequences. This also presents an opportunity to generate some revenue by converting the captured nitrogen to marketable nitrogenous fertilizers. Substantial research efforts have been made toward recovering nitrogen from raw as well as digested livestock manures over the last decade. Many novel technologies as well as ones that have already been implemented to recover nitrogen from municipal wastewaters have been studied for their use in the livestock sector. This paper reviews the common manure nitrogen-recovery technologies reported in the literature, summarizes their efficiencies, discusses their pros and cons, and identifies the areas for future research. Owing to their higher ammonia recovery efficiencies, relatively fewer drawbacks, lower costs, and ability to produce ammonium fertilizers, air stripping by direct aeration, thermal vacuum stripping, and gas-permeable membrane stripping appear to be the most viable choices for livestock farmers. Further studies should focus on the economic feasibility, long-term performance on the manure of varying strengths, and the quality of recovered nitrogenous products.

Anaerobic digestion of organic waste: Recovery of value-added and inhibitory compounds from liquid fraction of digestate

Anaerobic digestion, as an eco-friendly waste treatment technology, is facing the problem of low stability and low product value. Harvesting value-added products beyond methane and removing the inhibitory compounds will unleash new vitality of anaerobic digestion, which need to be achieved by selective separation of certain compounds. Various methods are reviewed in this study for separating valuable products (volatile fatty acids, medium-chain carboxylic acids, lactic acid) and inhibitory substance (ammonia) from the liquid fraction of digestate, including their performance, applicability, corresponding limitations and roadmaps for improvement. In-situ extraction that allows simultaneous production and extraction is seen as promising approach which carries good potential to overcome the barriers for continuous production. The prospects and challenges of the future development are further analyzed based on in-situ extraction and economics.

State-of-the-art management technologies of dissolved methane in anaerobically-treated low-strength wastewaters: A review

The recent advancement in low temperature anaerobic processes shows a great promise for realizing low-energy-cost, sustainable mainstream wastewater treatment. However, the considerable loss of the dissolved methane from anaerobically-treated low-strength wastewater significantly compromises the energy potential of the anaerobic processes and poses an environmental risk. In this review, the promises and challenges of existing and emerging technologies for dissolved methane management are examined: its removal, recovery, and on-site reuse. It begins by describing the working principles of gas-stripping and biological oxidation for methane removal, membrane contactors and vacuum degassers for methane recovery, and on-site biological conversion of dissolved methane into electricity or value-added biochemicals as direct energy sources or energy-compensating substances. A comparative assessment of these technologies in the three categories is presented based on methane treating efficiency, energy-production potential, applicability, and scalability. Finally, current research needs and future perspectives are highlighted to advance the future development of an economically and technically sustainable methane-management technology.

Cost-effective and sensitive anthocyanin-based paper sensors for rapid ammonia detection in aqueous solutions

In this work, we developed a cost-effective and environmentally friendly anthocyanin-based paper sensor with high sensitivity and optical visibility for the rapid detection of ammonia in aqueous solutions. The detection principle is based on a color change upon ammonia exposure to an anthocyanin-containing paper, which can be recorded simply via a smartphone. The paper sensors were fabricated by extracting anthocyanin from different sources (i.e., red cabbage, blueberry, and blackberry) and immersing pre-cut paper in anthocyanin extracts. Anthocyanin was extracted from different sources into water and aqueous ethanolic solution (80%) using solid-liquid extraction (SLE) and sonication assisted extraction (SAE) methods. The sensor sensitivity and optical visibility were improved by selecting a suitable combination of anthocyanin source, extraction technique, and solvent and controlling the ammonia release from the samples via alkalinization using a suitable base. Sensors fabricated with anthocyanin extracted from red cabbage (Red-C) into water using the SLE method and samples alkalinized with NaOH showed higher sensor sensitivity and better optical visibility. The Red-C anthocyanin sensors also exhibited a visible color change from dark to light blue for ammonia samples with concentrations as low as 2 mg NH₃-N/L. Moreover, the spike recovery results of the sensors (101.9-109.4%) were in good agreement with those of the standard spectrophotometry method (105.4-112.2%), which suggest that these biosensors are a promising analytical tool as a replacement for time-consuming and environmentally unfriendly standard spectrophotometry methods for the on-site screening of ammonia.

Significant removal of ammonia nitrogen in low concentration from aqueous solution at low pH by advanced air stripping

In recent years, the excess discharge of ammonia nitrogen from wastewater into surface water has been regulated by more stringent standard. The air stripping method is successfully used to treatment of high-concentration ammonia nitrogen; however, alkali will be added to keep pH more than 10, which is costly and not environment-friendly operation. In this study, an advanced air stripping (AAS) based on foam separation of removing ammonia nitrogen in low concentration from aqueous solution at low pH was proposed. The effect of conditions such as air flow rate, temperature, SDS dosage, coexisting ionic strength, pH, and initial ammonia nitrogen concentration on the removal efficiency was studied. The advanced air stripping exhibited favorable removal efficiency for NH₄⁺-N in low concentration from aqueous solution (20 mg·L^-1) with a broad range of low pH 3.0-9.0. Besides, for strongly alkaline (pH=11.0) solution, the advanced air stripping can alleviate the decrease of pH to some extent and keep ammonia nitrogen stripping out continuously based on equilibrium shift between NH₄⁺ and NH₃. A microcalorimeter was applied to demonstrate the interaction between the negatively charged hydrophilic groups of SDS and NH₄⁺ ions, helping to understand the mechanisms more clearly. The simple operation and the satisfactory removal efficiency could imply that the advanced air stripping is a promising technology for minimizing low-concentration NH₄⁺-N.

Microbial nitrogen removal in synthetic aquaculture wastewater by fixed-bed baffled reactors packed with different biofilm carrier materials

Fixed-bed baffled reactors packed with carbon fiber (CFBR), polyurethane, or non-woven fabrics were developed to support microbial nitrification-denitrification reactions for nitrogen removal from synthetic aquaculture wastewater. The CFBR showed the best performance, with a short hydraulic retention time and low C/N ratio. Microbial communities in the reactor's biofilms and deposited sludge were analyzed using high-throughput sequencing and quantitative polymerase chain reactions. The biofilms efficiently enriched the nitrifying and denitrifying bacteria in the CFBR. Moreover, bacteria capable of denitrification under aerobic conditions were detected in the aerobic chamber biofilm, showing positive correlations with the main nitrifiers and denitrifiers, which provides potential synergistic interactions for simultaneous nitrification-denitrification in the aerobic chamber. A network analysis revealed that the CFBR had more complex cooperative interactions than others. This study provides insights into the influence of different carrier materials on biofilm formation, proving that the CFBR has potential applications in aquaculture wastewater treatment.

Electrochemical ammonia accumulation and recovery from ammonia-rich livestock wastewater

High levels of ammonia inhibit microbial activities and lead to process instability of traditional wastewater treatment. Nitrogen recovery via ammonia stripping is the best developed method, but this approach requires large amounts of alkaline chemicals and substantial energy for stripping. In this study, we designed a simple electrochemical system that allows the facile accumulation of a neutral species of ammonia (NH₃), resulting in much lower overall stripping costs. In batch operation treatment of synthetic livestock wastewater (LW), the energy efficiency for total ammonia nitrogen (TAN) migration was found to be the best at a current density of 93.8 mA cm^-2. Fed-batch operation, using synthetic or real LW, resulted in very high degrees of TAN accumulation (10,158 mg-N L^-1 for synthetic and 17,704 mg-N L^-1 for real LW) in catholyte after 400 min. It was found that TAN migration was responsible for 0.221 and 0.492 of total charge migration for synthetic and real LW, respectively. The nitrogen flux across a cation exchange membrane was 5975 g-N m^-2 d^-1 with an energy input of 28.2 kWh (kg-N)^-1 when using real LW. All this supported the conclusion that an electrochemical approach such as this makes it possible to achieve highly desirable ammonia recovery from wastewater in a sustainable manner.

Enhanced ammonia sensing performance based on MXene-Ti3C2Tx multilayer nanoflakes functionalized by tungsten trioxide nanoparticles

Low-power consumption and high sensitivity are highly desirable for a vast range of NH₃ sensing applications. As a new type of two-dimension (2D) material, Ti₃C₂T_x is extensively studied for room temperature NH₃ sensors recently. However, the Ti₃C₂T_x MXene based gas sensors suffer mainly from low sensitivity. Herein, we report a sensitive Ti₃C₂T_x/WO₃ composite resistive sensor for NH₃ detection. The Ti₃C₂T_x/WO₃ composite consisting of WO₃ nanoparticles anchored on Ti₃C₂T_x nanoflakes were synthesized successfully with a facile ultra-sonication technique. The composite sensor with optimized components exhibits a high sensitivity of 22.3% for 1 ppm NH₃ at room temperature, which is 15.4 times higher than the pure Ti₃C₂T_x sensor. Furthermore, the composite sensor has excellent reproducibility, good long-term stability, and high selectivity to NH₃. The relative humidity influence on NH₃ gas sensing properties of the sensors was systematically studied. This research provides an efficient route for the preparation of novel MXene-based sensitive materials for high-performance NH₃ sensors.

Chemico-nanotreatment methods for the removal of persistent organic pollutants and xenobiotics in water - A review

While the technologies available today can generate high-quality water from wastewater, the majority of the wastewater treatment plants are not intended to eliminate emerging xenobiotic pollutants, pharmaceutical and personal care items. Most endocrine disrupting compounds (EDCs) and personal care products (PPCPs) are more arctic than most regulated pollutants, and several of them have acid or critical functional groups. Together with the trace occurrence, EDCs and PPCPs create specific challenges for removal and subsequent improvements of wastewater treatment plants. Various technologies have been investigated extensively because they are highly persistent which leads to bioaccumulation. Researchers are increasingly addressing the human health hazards of xenobiotics and their removal. The emphasis of this review was on the promising methods available, especially nanotechnology, for the treatment of xenobiotic compounds that are accidentally released into the setting. In terms of xenobiotic elimination, nanotechnology provides better treatment than chemical treatments and their degradation mechanisms are addressed.

Horticulture and Orchards as New Markets for Manure Valorisation with Less Environmental Impacts

Animal manure management is a real challenge to minimize environmental impacts and ensure that this valuable material is efficiently used in a circular economy context. One of the main limitations for larger use of animal manure as fertilizer is the availability of land to receive it in an area close to the farm. Indeed, animal manure is traditionally used for cereals and animal feed growth, but the soil area occupied with these crops might not be enough to receive all the manure produced and/or part of this soil might have nutrient contents, namely phosphorous, that do not permit further application of manure. Hence, extra land used for other agricultural activities might be an option. The main objective of the present review was to analyse the constraints and solutions to increase the use of manure in horticulture and orchards. Emphasis was given to the legal framework for manure utilization in the EU that might stimulate or restrain such a solution. The main characteristics of manure that might limit or stimulate manure reuse were also described, and the potential of some treatments to valorise manure was analysed. Several examples of alternative uses of manure in horticulture and orchards were examined, and the society and farmers’ acceptance of the proposed solution was addressed.

Simultaneous Stripping of Ammonia from Leachate: Experimental Insights and Key Microbial Players

Air stripping is commonly used to remove the ammonia in multistage treatment systems for municipal landfill leachate (LFL). This paper proposes a novel approach combining the process of stripping with biological removal of ammonia, based on simultaneous nitrification and denitrification (SND) in a single hybrid sequencing batch reactor (HSBR). To avoid the accumulation of free ammonia (N-FAN), the shallow aeration system was used for the treatment of raw LFL with N-TAN level of 1520 mg/L and pH 9.24. The mean N-FAN removal efficiency of 69% with the reaction rate of 55 mg L−1 h−1 and mean ammonium (N-NH4+) removal efficiency of 84% with the reaction rate of 44 mg L−1 h−1 were achieved within a month in such an HSBR (R1). The comparative HSBR (R2), with conventional aeration system maintaining the same concentration of dissolved oxygen (DO ≤ 1 mg/L), was removing only trace amounts of N-FAN and 48% of N-NH4+. The quantitative analysis of 16S rRNA genes indicated that the number of total bacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Beta- and Gammaproteobacteria increased during the operation of both HSBRs, but was always higher in R1. Moreover, the bacterial community shift was observed since the beginning of the experiment; the relative abundance of Firmicutes, and Beta- and Gammaproteobacteria increased by 5.01, 3.25 and 9.67% respectively, whilst the abundance of Bacteroidetes and Actinobacteria decreased by 15.59 and 0.95%. All of the surveyed bacteria groups, except Gammaproteobacteria, correlated significantly negatively (p < 0.001) with the concentrations of N-NH4+ in the outflows from R1. The results allow us to suppose that simultaneous stripping and SND in a single reactor could be a promising, cost-effective and easy-to-operate solution for LFL treatment.

Ammonia recovery from food waste digestate using solar heat-assisted stripping-absorption

The highest costs of stripping-absorption processes for ammonia recovery are related to energy (for heating and air supply) and chemical addition (for pH adjustment). In this paper, a simplified system that used no chemicals, and a renewable source of energy for heating, was tested to recover nitrogen as ammonium sulfate from food waste digestate. pH adjustment was achieved by CO₂ stripping, and vacuum tube solar collectors were used to provide heating. The effect of different temperatures (25 °C and 45 °C) and gas to liquid ratios (1700 and 2600) on ammonia removal and recovery were assessed. Ammonia removal efficiencies higher than 91% were achieved for all evaluated experimental conditions. The solar heater showed adequate capacity to increase the temperature of the liquid digestate by 21 °C and maintain the temperature at 45 °C throughout the experiment. Tests carried out at 45 °C achieved the highest ammonia removal efficiency (98%) at the lowest evaluated G/L ratio (1700). Better absorption efficiencies could potentially have been achieved if lower inlet airflow rates and packing material had been used in the absorption column.

Effects of Ammonia Stripping and Other Physico-Chemical Pretreatments on Anaerobic Digestion of Swine Wastewater

In order to overcome anaerobic digestion (AD) inhibition due to the large nitrogen content of swine wastewater (SW), air stripping (AS) and other chemical and physical pretreatments were applied on raw SW before AD. The efficiency of these pretreatments on both ammonia removal—recovering ammonia salts to be used as fertilizers in agriculture—and the increase of methane production were assessed in batch tests. Since the pH, temperature, and air flow rate heavily influence AS efficiency and the composition of treated SW, these parameters were set individually or in combination. In more detail, the pH was increased from the natural value of SW to 8 or 10, temperature was increased from the room value to 40 °C, and the air flow rate was increased from zero to 5 Lair LSW−1 min−1. AS was generally more efficient at removing ammonia (up to 97%) from raw (non-treated) SW compared to the other treatments. However, the tested pretreatments were not as efficient as expected in increasing the biogas production, because the methane yields of all pretreated substrates were lower (by about 10–50%) to compared raw SW. The inhibitory effect on AD could have been due to the lack of nutrients and organic matter in the substrate (due to the excessive removal of the pretreatments), the concentration of toxic compounds (such as metal ions or furfural due to water evaporation), and an excess of alkali ions (used to increase the pH in AS). Overall, AS can be considered a sustainable process for the recovery of ammonium sulphate and the removal of other polluting compounds (e.g., organic matter) from SW. Conversely, the use of AS and other chemical and/or thermal processes tested in this study as pretreatments of SW before AD is not advised because these processes appear to reduce methane yields.

Environmental and Economic Sustainability of Swine Wastewater Treatments Using Ammonia Stripping and Anaerobic Digestion: A Short Review

One of the most promising systems to treat swine wastewater is air stripping. This system simultaneously recovers nitrogen salts, to be used as fertiliser, and reduces the organic pollutant load in the effluents of swine breeding farms. Several reviews have discussed the air stripping as a treatment for many types of industrial wastewater or nitrogen-rich digestate (the liquid effluent derived from the anaerobic digestion plants) for the stripping/recovery of nutrients. However, reviews about the use of air stripping as treatment for raw or anaerobically digested swine wastewater are not available in literature. To fill this gap, this study: (i) Summarises the experiences of air stripping for recovery of ammonium salts from both raw and digested swine wastewater; and (ii) compares air stripping efficiency under different operational conditions. Moreover, combined systems including air stripping (such as struvite crystallisation, chemical precipitation, microwave radiation) have been compared. These comparisons have shown that air stripping of raw and digested swine wastewater fits well the concept of bio-refinery, because this system allows the sustainable management of the piggery effluent by extracting value-added compounds, by-products, and/or energy from wastewater. On the other hand, air stripping of raw and digested swine wastewater has not been extensively studied and more investigations should be carried out.

Pilot-scale demonstration of nitrogen recovery in the form of ammonium phosphate (AP) from anaerobic digestate

Nitrogen in anaerobic digestate was recovered as ammonium phosphates (APs), a valuable fertilizer, in a pilot-scale system consisting of ammonia stripper, absorber and crystallizer. The dissolved ammonium concentration in the anaerobic digestate was stripped and then absorbed into the phosphoric acid (42.5 wt%) with 95% absorbing efficiency. As the NH₃ stripping continued, both the N/P ratio and pH, key operating parameters in the absorber are optimized N/P = 0.6 and pH = 1.7. The residual AP solution after crystallization was reused to enhance the crystallization efficiency up to 88%. The overall recovery efficiency of APs was estimated at 72% of the input nitrogen mass. Analyses of SEM and XRD revealed that the recovered AP crystals were mainly composed of mono-ammonium phosphate (MAP). This pilot-scale study demonstrated that nitrogen load in anaerobic digestates could be effectively recovered as a valuable fertilizer source of AP crystals.

Building an operational framework for selective nitrogen recovery via electrochemical stripping

Recovering nitrogen from wastewater can simultaneously fulfill the roles of traditional removal technologies such as nitrification-denitrification and fertilizer production processes such as Haber-Bosch. We have recently demonstrated a proof-of-concept for selective recovery of the fertilizer ammonium sulfate via electrochemical stripping, a combination of electrodialysis and membrane stripping. In this study, we furthered electrochemical stripping from concept to informed practice by investigating the effects of influent concentration (30, 300, and 3000 mg N/L), catholyte temperature (15, 23, and 35 °C), and gas permeable membrane choice on electrochemical nitrogen removal and recovery. We also proposed and validated a nitrogen mass transport model for the experimental results, providing mechanistic rationale behind observed effects of varying operating parameters. While changing operating parameters did affect performance, electrochemical stripping exhibited robust performance over a range of realistic ambient temperatures, three gas permeable membranes, and three orders of magnitude of influent concentrations. Practically, these results demonstrate that electrochemical stripping is viable across a range of waste streams and resilient to fluctuations in temperature and nitrogen concentration; they also establish operational trade-offs between residence time and energy consumption. As a result of this work, electrochemical stripping continues to mature from concept to practice and provides lessons for developing other resource recovery technologies.

Kinetics of carbon and nitrogen assimilation by heterotrophic microorganisms during wastewater treatment

The present study highlights microbial assimilation of carbon (glucose) and nitrogen (NH₃-N) from wastewater using heterotrophic bioconversion process. Experiments were conducted to study the role of heterotrophic microbes towards removal of carbon and nitrogen at varying initial concentrations of carbon (COD, 533 to 1600 mg/l) and nitrogen (NH₃-N, 73 to 249 mg/l) keeping the initial biomass of microorganisms constant. Removal of COD and ammonia from wastewater represented a first-order rate reaction, upon analysis of kinetics, indicating that the rate of reaction is dependent on the initial concentration of nutrients available. Rate equations were developed using the Monod model, and the maximum specific consumption rate (k₄) and half saturation constant (K_s) values for NH₃-N and COD were found to be 2.59 mg/l/h and 64.13 mg/l/h and 38.46 mg/l and 2162.69 mg/l, respectively. Assimilation of NH₃-N followed the Freundlich isotherm model. The mass transfer coefficient for COD and NH₃-N were found to be 0.13 h^-1 and 0.81 h^-1 respectively. The NH₃-N is converted to N₂O during nitrification, and observed values of N₂O coincided with the empirically predicted values indicating the activity of heterotrophic nitrifiers. The regeneration/doubling time of heterotrophic microbial biomass varied from 26 to 121 h. Statistical techniques, viz. analysis of variance, multi-linear regression analysis and principal component analysis, validated the results.

Effect of Pressure on the Removal of NH3 from Hydrolyzed and Pre-Fermented Slaughterhouse Waste for Better Biomethanization

Slaughterhouse waste (SW) is potentially a good source of biomethane; however, its excessive ammonia content quickly causes inhibition of microbial processes. Our aim was therefore to remove ammonia from SW before putting it into a biogas reactor. Experimental 120 L pressure container was constructed to observe NH3 removal from diluted slaughterhouse waste at constant air flow of 144 NL/min, temperature 130 °C, and at different pressures: 300 kPa, 600 kPa, and 900 kPa. SW was first allowed to hydrolyze for 14 days at 38 °C. The SW was diluted with water (DSW) to 8.4% dry matter (DM) and forcibly aerated for 334 min. From the DSW, 0.7%, 3.8%, and 9% of initial total N were removed at 300 kPa, 600 kPa, and 900 kPa, respectively. However, the C/N ratio changed only slightly, from the initial 4.38 to 3.17, which is not a promising result for biomethanization. Further research on the presented system with the addition of bases might be promising to remove more ammonia.