Evaluating Microbial and Chemical Hazards in Commercial Struvite Recovered from Wastewater

Technological solutions to landfill management: Towards recovery of biomethane and carbon neutrality

Inadequate landfill management poses risks to the environment and human health, necessitating action. Poorly designed and operated landfills release harmful gases, contaminate water, and deplete resources. Aligning landfill management with the Sustainable Development Goals (SDGs) reveals its crucial role in achieving various targets. Urgent transformation of landfill practices is necessary to address challenges like climate change, carbon neutrality, food security, and resource recovery. The scientific community recognizes landfill management's impact on climate change, evidenced by in over 191 published articles (1998-2023). This article presents emerging solutions for sustainable landfill management, including physico-chemical, oxidation, and biological treatments. Each technology is evaluated for practical applications. The article emphasizes landfill management's global significance in pursuing carbon neutrality, prioritizing resource recovery over end-of-pipe treatments. It is important to note that minimizing water, chemical, and energy inputs in nutrient recovery is crucial for achieving carbon neutrality by 2050. Water reuse, energy recovery, and material selection during manufacturing are vital. The potential of water technologies for recovering macro-nutrients from landfill leachate is explored, considering feasibility factors. Integrated waste management approaches, such as recycling and composting, reduce waste and minimize environmental impact. It is conclusively evident that the water technologies not only facilitate the purification of leachate but also enable the recovery of valuable substances such as ammonium, heavy metals, nutrients, and salts. This recovery process holds economic benefits, while the conversion of CH4 and hydrogen into bioenergy and power generation through microbial fuel cells further enhances its potential. Future research should focus on sustainable and cost-effective treatment technologies for landfill leachate. Improving landfill management can mitigate the adverse environmental and health effects of inadequate waste disposal.

Use of Capsid Integrity-qPCR for Detecting Viral Capsid Integrity in Wastewater

Quantifying viruses in wastewater via RT-qPCR provides total genomic data but does not indicate the virus capsid integrity or the potential risk for human infection. Assessing virus capsid integrity in sewage is important for wastewater-based surveillance, since discharged effluent may pose a public health hazard. While integrity assays using cell cultures can provide this information, they require specialised laboratories and expertise. One solution to overcome this limitation is the use of photo-reactive monoazide dyes (e.g., propidium monoazide [PMAxx]) in a capsid integrity-RT-qPCR assay (ci-RT-qPCR). In this study, we tested the efficiency of PMAxx dye at 50 μM and 100 μM concentrations on live and heat-inactivated model viruses commonly detected in wastewater, including adenovirus (AdV), hepatitis A (HAV), influenza A virus (IAV), and norovirus GI (NoV GI). The 100 μM PMAxx dye concentration effectively differentiated live from heat-inactivated viruses for all targets in buffer solution. This method was then applied to wastewater samples (n = 19) for the detection of encapsulated AdV, enterovirus (EV), HAV, IAV, influenza B virus (IBV), NoV GI, NoV GII, and SARS-CoV-2. Samples were negative for AdV, HAV, IAV, and IBV but positive for EV, NoV GI, NoV GII, and SARS-CoV-2. In the PMAxx-treated samples, EV, NoV GI, and NoV GII showed -0.52-1.15, 0.9-1.51, and 0.31-1.69 log reductions in capsid integrity, indicating a high degree of potentially infectious virus in wastewater. In contrast, SARS-CoV-2 was only detected using RT-qPCR but not after PMAxx treatment, indicating the absence of encapsulated and potentially infectious virus. In conclusion, this study demonstrates the utility of PMAxx dyes to evaluate capsid integrity across a diverse range of viruses commonly monitored in wastewater.

Role of suspended solids on the co-precipitation of pathogenic indicators and antibiotic resistance genes with struvite from digested swine wastewater

Struvite recovered from wastewater contains high concentration of fecal indicator bacteria (FIB), porcine adenoviruses (PAdV) and antibiotic resistance genes (ARGs), becoming potential resources of these microbial hazards. Understanding the precipitation behavior of pathogenic indicators and ARGs with suspended solids (SS) will provide the possible strategy for the control of co-precipitation. In this study, SS was divided into high-density SS (separated by centrifugation) and low-density SS (further separated by filtration), and the role of SS on the co-precipitation of FIB, PAdV and ARGs was investigated. The distribution analysis showed that 35.5-73.0% FIB, 79.6% PAdV and 64.5-94.8% ARGs existed in high-density SS, while the corresponding values were 26.9-64.4%, 11.7% and 3.5-24.3% in low-density SS. During struvite generation, 82.7-96.9% FIB, 75.5% PAdV and 56.3-86.5% ARGs were co-precipitated into struvite. High-density SS contributed 20.7-68.5% FIB, 63.9% PAdV and 38.7-87.2% ARGs co-precipitation, and the corresponding contribution of low-density SS was 31.4-79.2%, 3.9% and 6.2-54.7%. Moreover, the precipitated SS in struvite obviously decreased inactivation efficiency of FIB and ARGs in drying process. These results provide a potential way to control the co-precipitation and inactivation of FIB, PAdV and ARGs in struvite through removing high-density SS prior to struvite recovery.

Virus-pathogen interactions improve water quality along the Middle Route of the South-to-North Water Diversion Canal

Bacterial pathogens and viruses are the leading causes of global waterborne diseases. Here, we discovered an interesting natural paradigm of water "self-purification" through virus-pathogen interactions over a 1432 km continuum along the Middle Route of the South-to-North Water Diversion Canal (MR-SNWDC) in China, the largest water transfer project in the world. Due to the extremely low total phosphorus (TP) content (ND-0.02 mg/L) in the MR-SNWDC, the whole canal has experienced long-lasting phosphorus (P) limitation since its operation in 2015. Based on 4443 metagenome-assembled genomes (MAGs) and 40,261 nonredundant viral operational taxonomic units (vOTUs) derived from our recent monitoring campaign, we found that residential viruses experiencing extreme P constraints had to adopt special adaptive strategies by harboring smaller genomes to minimize nucleotide replication, DNA repair, and posttranslational modification costs. With the decreasing P supply downstream, bacterial pathogens showed repressed environmental fitness and growth potential, and a weakened capacity to maintain P acquisition, membrane formation, and ribonucleotide biosynthesis. Consequently, the unique viral predation effects under P limitation, characterized by enhanced viral lytic infections and an increased abundance of ribonucleotide reductase (RNR) genes linked to viral nuclear DNA replication cycles, led to unexpectedly lower health risks from waterborne bacterial pathogens in the downstream water-receiving areas. These findings highlighted the great potential of water self-purification associated with virus-pathogen dynamics for water-quality improvement and sustainable water resource management.

Competitive adsorption of heavy metals between Ca-P and Mg-P products from wastewater during struvite crystallization

Wastewater usually contains high concentration of calcium (Ca), posing a competitive reaction with magnesium (Mg) on phosphorus (P) recovery during the struvite crystallization. The differences in the adsorption of heavy metals by Ca-P and Mg-P (struvite) generated are still unclear. Herein, we analyzed the residues of four kinds of common heavy metals (Cu, Zn, Cd, Pb) in Ca-P and Mg-P (struvite) under varying conditions (solution pH, N/P ratio, Mg/Ca ratio) in the swine wastewater and explored their possible competitive adsorption mechanisms. The experiments using synthetic wastewater and real wastewater have similar experimental patterns. However, under the same conditions, the metal (Pb) content of struvite recovered from the synthetic wastewater (16.58 mg/g) was higher than that of the real wastewater (11.02 mg/g), as predicted by the Box-Behnken Design of Response Surface Methodology (BBD-RSM). The results demonstrated that Cu was the least abundant in the precipitates compared to Zn, Cd, and Pb of almost all experimental groups with an N/P ratio greater than or equal to 10. The fact might be mainly attributed to the its stronger binding capacity of Cu ion with NH₃ and other ligands. Compared with struvite, the Ca-P product had a higher adsorption capacity for heavy metals and a lower P recovery rate. In addition, the higher solution pH and N/P ratio were favorable to obtain qualified struvite with lower heavy metal content. It can be applied to reduce the incorporation of heavy metals by modulating pH and N/P ratio through RSM, which is suitable for different Mg/Ca ratios. It is anticipated that the results obtained would offer support for the safe utility of struvite from wastewater containing Ca and heavy metals.

Co-precipitation of heavy metals with struvite from digested swine wastewater: Role of suspended solids

Struvite production can recover ammonia and phosphorous from digested wastewater as fertilizer. During struvite generation, most of the heavy metals was co-precipitated with ammonia and phosphorous into struvite. Understanding the precipitation behavior of heavy metals with suspended solids (SS) might provide the possible strategy for the control of co-precipitation. In this study, the distribution of heavy metals in SS and their role on the co-precipitation during struvite recovery from digested swine wastewater were investigated. The results showed that the concentration of heavy metal (including Mn, Zn, Cu, Ni, Cr, Pb and As) ranged from 0.05 to 17.05 mg/L in the digested swine wastewater. The distribution analysis showed that SS with particles > 50 μm harbored most of individual heavy metal (41.3-55.6%), followed by particles 0.45-50 μm (20.9-43.3%), and SS-removed filtrate (5.2-32.9%). During struvite generation, 56.9-80.3% of individual heavy metal was co-precipitated into struvite. The contributions of SS with particles > 50 μm, 0.45-50 μm, and SS-removed filtrate on the individual heavy metal co-precipitation were 40.9-64.3%, 25.3-48.3% and 1.9-22.9%, respectively. These finding provides potential way for controlling the co-precipitation of heavy metals in struvite.

Closing the Nutrient Loop-The New Approaches to Recovering Biomass Minerals during the Biorefinery Processes

The recovery of plant mineral nutrients from the bio-based value chains is essential for a sustainable, circular bioeconomy, wherein resources are (re)used sustainably. The widest used approach is to recover plant nutrients on the last stage of biomass utilization processes-e.g., from ash, wastewater, or anaerobic digestate. The best approach is to recover mineral nutrients from the initial stages of biomass biorefinery, especially during biomass pre-treatments. Our paper aims to evaluate the nutrient recovery solutions from a trans-sectorial perspective, including biomass processing and the agricultural use of recovered nutrients. Several solutions integrated with the biomass pre-treatment stage, such as leaching/bioleaching, recovery from pre-treatment neoteric solvents, ionic liquids (ILs), and deep eutectic solvents (DESs) or integrated with hydrothermal treatments are discussed. Reducing mineral contents on silicon, phosphorus, and nitrogen biomass before the core biorefinery processes improves processability and yield and reduces corrosion and fouling effects. The recovered minerals are used as bio-based fertilizers or as silica-based plant biostimulants, with economic and environmental benefits.

Recovery of phosphorus from wastewater: A review based on current phosphorous removal technologies

Phosphorus (P) as an essential nutrient for life sustains the productivity of food systems; yet misdirected P often accumulates in wastewater and triggers water eutrophication if not properly treated. Although technologies have been developed to remove P, little attention has been paid to the recovery of P from wastewater. This work provides a comprehensive review of the state-of-the-art P removal technologies in the science of wastewater treatment. Our analyses focus on the mechanisms, removal efficiencies, and recovery potential of four typical water and wastewater treatment processes including precipitation, biological treatment, membrane separation, and adsorption. The design principles, feasibility, operation parameters, and pros & cons of these technologies are analyzed and compared. Perspectives and future research of P removal and recovery are also proposed in the context of paradigm shift to sustainable water treatment technology.

Quantitative characterization and effective inactivation of biological hazards in struvite recovered from digested poultry slurry

Struvite formed from digested poultry slurries can serve as an alternative to chemical fertilizers; however, the biological safety of such products is questionable. Therefore, quantification and inactivation of foodborne pathogens existing in struvite are important. Herein, the dynamics of foodborne pathogens' (Streptococcus faecalis, S. typhimurium, Clostridium perfringens, and Escherichia coli) living status, whether culturable and viable but non-culturable (VBNC) in struvite, were quantified for the first time. Meanwhile, inactivation technologies, namely high-humidity hot air impingement blanching (HHAIB), cold plasma, and hot air treatment, were evaluated and compared for their potential to inactivate/kill foodborne pathogens in struvite. An increase in precipitation pH from 9.0 to 11.0 decreased the culturable count of pathogens in the struvite from 75 to 86% to 7-20%, while the VBNC pathogen counts increased from 16 to 24% to 35-55%. Among the tested inactivation technologies, the HHAIB treatment at 130 °C for 120 s killed approximately 68-79% of foodborne pathogens in struvite precipitated at pH 9.0. VBNC pathogens increased from 16 to 24% to 57-68% after HHAIB treatment at 130 °C for 120 s. Struvite treatment with different inactivation technologies did not change its crystalline structure; however, it reduced functional group abundance. Therefore, further research on inactivation technologies is required to achieve better pathogen reduction efficiency in struvite to make it a biologically safe fertilizer for crop production.

Decoupling of wastewater eco-environmental damage and China's economic development

Wastewater pollution has been considered as a prominent bottleneck restricting global sustainable development. China is one of the largest discharges and eco-environmental damages of wastewater in the world. Through analyzing wastewater discharge data using emergy method in China from 2011 to 2017, the wastewater eco-environmental damage of 31 provinces is calculated with GDP and area to reveal the fundamental origins of inflection point of wastewater discharge in China. Studies results show that, (i) Chinese "12th Five-Year Plan" (2011-2015) is a watershed in wastewater discharge, and the eco-environment damages caused by China's wastewater accounted for more than 1/4 of GDP; (ii) China has the great potential to reduce eco-environment damages of 1.73 trillion $/year; (iii) In 2016 and 2017, wastewater eco-environmental damage has decreased by about 50% compared with that in 2015, and the effect of government policies was remarkable. We conclude that decoupling of China's economic development form eco-environmental damages of wastewater is began to appear, the strict formulation and implementation of China's environmental policies and the green upgrading of industrial structure are main driving forces, and it is little correlation with economic slowdown. This study offers the detailed list of China wastewater pollution and reveals the relationship between wastewater eco-environmental damages and economic development, and shows the experience and achievements of the Chinese government in the treatment of wastewater pollution, which provides a useful reference for the treatment of wastewater pollution in the world.

Effects of micro-aeration on microbial niches and antimicrobial resistances in blackwater anaerobic digesters

Anaerobic digestion (AD) of source-diverted blackwater (toilet flush) at ambient room temperature presents challenges for fast hydrolysis of particulate matters. This study investigated the effect of different micro-aeration dosages for blackwater AD. Sequencing batch reactors were operated at ambient room temperature (22 ± 1°C) with micro-aeration (0, 5, 10, 50, and 150 mg O₂ g^-1 COD_feed per cycle) and gradually reduced hydraulic retention times from 5 d to 2 d. The methanogenesis efficiencies were greater at low oxygen dosages (i.e., 0, 5, 10) while the volatile fatty acids (VFAs) accumulated more at high oxygen dosages (i.e., 50, 150). Microbial communities were significantly different under different oxygen dosages (p<0.05), with segregation of microbial ecological niches in low and high oxygen dosage communities. The low-oxygen-dosage niche (0, 5, and 10 mg g^-1 COD_feed) was inhabited by fermenting and syntrophic bacteria (e.g., Cytophaga, Syntrophomonas) and methanogens (e.g., Methanobacterium, Methanolinea, Methanosaeta). The high-oxygen-dosage niche (50 and 150 mg g^-1 COD_feed) had significantly (p<0.05) more facultative anaerobic bacteria (Ignavibacteriales and Cloacamonales), and aerobic bacteria (Rhodocyclales). Moreover, blackwater can be a source of antimicrobial resistance genes (ARGs), which are affected by different oxygen dosages. The ARG variation correlated with the microbial community composition (p<0.05). Low-oxygen-dosage communities contained a higher prevalence of mobile gene elements (intI1 and korB) and tetM, ermB, sul1, sul2, and blaCTX-M than the high-oxygen-dosage communities, indicating that oxygen dosage influenced the prevalence of populations carrying ARGs. These findings suggest that application of micro-aeration to AD can be used to control ARG profiles.

Capsid integrity quantitative PCR to determine virus infectivity in environmental and food applications - A systematic review

Capsid integrity quantitative PCR (qPCR), a molecular detection method for infectious viruses combining azo dye pretreatment with qPCR, has been widely used in recent years; however, variations in pretreatment conditions for various virus types can limit the efficacy of specific protocols. By identifying and critically synthesizing forty-one recent peer-reviewed studies employing capsid integrity qPCR for viruses in the last decade (2009-2019) in the fields of food safety and environmental virology, we aimed to establish recommendations for the detection of infectious viruses. Intercalating dyes are effective measures of viability in PCR assays provided the viral capsid is damaged; viruses that have been inactivated by other causes, such as loss of attachment or genomic damage, are less well detected using this approach. Although optimizing specific protocols for each virus is recommended, we identify a framework for general assay conditions. These include concentrations of ethidium monoazide, propidium monoazide or its derivates between 10 and 200 μM; incubation on ice or at room temperature (20 - 25 °C) for 5-120 min; and dye activation using LED or high light (500-800 Watts) exposure for periods ranging from 5 to 20 min. These simple steps can benefit the investigation of infectious virus transmission in routine (water) monitoring settings and during viral outbreaks such as the current COVID-19 pandemic or endemic diseases like dengue fever.

Capsid integrity quantitative PCR to determine virus infectivity in environmental and food applications - A systematic review

Capsid integrity quantitative PCR (qPCR), a molecular detection method for infectious viruses combining azo dye pretreatment with qPCR, has been widely used in recent years; however, variations in pretreatment conditions for various virus types can limit the efficacy of specific protocols. By identifying and critically synthesizing forty-one recent peer-reviewed studies employing capsid integrity qPCR for viruses in the last decade (2009-2019) in the fields of food safety and environmental virology, we aimed to establish recommendations for the detection of infectious viruses. Intercalating dyes are effective measures of viability in PCR assays provided the viral capsid is damaged; viruses that have been inactivated by other causes, such as loss of attachment or genomic damage, are less well detected using this approach. Although optimizing specific protocols for each virus is recommended, we identify a framework for general assay conditions. These include concentrations of ethidium monoazide, propidium monoazide or its derivates between 10 and 200 μM; incubation on ice or at room temperature (20 - 25 °C) for 5-120 min; and dye activation using LED or high light (500-800 Watts) exposure for periods ranging from 5 to 20 min. These simple steps can benefit the investigation of infectious virus transmission in routine (water) monitoring settings and during viral outbreaks such as the current COVID-19 pandemic or endemic diseases like dengue fever.

Phosphorus recovery from source-diverted blackwater through struvite precipitation

Phosphorus recovery from wastewater through struvite precipitation is becoming a promising strategy to both mitigate eutrophication risk due to excess phosphorus discharge into water bodies and alleviate the global phosphorus crisis by producing value-added fertilizer. However, the composition and quality of wastewater differ among regions and home to home. Source-diverted blackwater, especially concentrated blackwater collected from vacuum toilet systems, typically has a moderate phosphate-phosphorus (PO₄-P) content, high ammonia-nitrogen (NH₄-N) content, strong buffering capacity as a result of high alkalinity, and a high pH close to 9. Thus, concentrated blackwater is a good source for phosphorus recovery through struvite precipitation. In this study, we examined the feasibility of recovering phosphorus from concentrated blackwater through struvite precipitation by conducting batch experiments. The characterization of the struvite produced from concentrated blackwater was performed via X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) techniques. The metal contents of the struvite product were analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and its purity was determined. A phosphorus removal efficiency exceeding 90% was achieved as a result of both an appropriate supersaturation ratio of struvite (>4.0) and a high initial pH. The high quality of the produced struvite was demonstrated by a purity of 94.9%, the Mg/P/N mass ratio of 10:12:4.7 based on the EDS analysis, and low heavy-metals contents. This feasibility study provides evidence for the efficacy of phosphorus recovery from concentrated blackwater through struvite precipitation in decentralized wastewater management systems.

Struvite crystallization induced the discrepant transports of antibiotics and antibiotic resistance genes in phosphorus recovery from swine wastewater

Struvite (MgNH₄PO₃·6H₂O) crystallization is one of important methods of phosphorus recovery from wastewater. As to livestock wastewater, the high-strength occurrence of antibiotics and antibiotic resistance genes might induce struvite recovery to spread antibiotic resistance to the environment. However, limited information has been reported on the simultaneous transport of antibiotics and ARGs in struvite recovery. In the present study, tetracyclines (TCs) and tetracyclines antibiotic resistance genes (ARGs) were selected as the targeted pollutants, and their discrepant residues in struvite recovery from swine wastewater were investigated. TCs and ARGs were obviously detected, with their contents of 4.88-79.5 mg/kg and 6.99 × 10⁷-2.14 × 10¹¹ copies/g, notably higher than those of TCs 0.550-1.94 mg/kg and ARGs 3.98 × 10⁴-5.66 × 10⁷ copies/g obtained from synthetic wastewater. The correlational relationship revealed that predominant factors affecting TCs and ARGs transports were different. Results from network analyses indicated that among the total edges, the negative correlations between TCs and ARGs predominately occupied 18.0%. The redundancy analysis revealed that mineral components in the recovered products, including struvite, K-struvite and amorphous calcium phosphate, coupling with organic contents, displayed insignificant roles on TCs residues, where heavy metals exerted positive and remarkable functions to boost TCs migration. Unexpectedly, mineral components and heavy metals did not displayed significant promotion on ARGs transport as a whole.

Ultrasonic assisted fabrication of silver tungstate encrusted polypyrrole nanocomposite for effective photocatalytic and electrocatalytic applications

Ultrasonication is an emerging and evergreen technique for the efficient synthesis of the catalytically active heterostructured materials. In-situ one-pot ultrasonic-assisted synthesis method was demonstrated in this work for the fabrication of silver tungstate encrusted polypyrrole nanocomposite using semi-automatic ultrasonic probe maintained at 34°C/50 kHz ultrasonic frequency and at 150 W ultrasonic power. This material retains enhanced optical, electrical, morphological properties, photocatalytic behavior in photodegradation of congo red dye, tetracycline drug and its electrochemical sensing potential for the effective determination of a broad spectrum of antibacterial drug, nitrofurazone. Optical properties were investigated using UltraViolet-Visible diffuse reflectance spectral (UV-VIS DRS) data along with Tauc's bandgap energy calculations. The morphological properties were examined using FESEM and TEM micrographs. All the PXRD and XPS details prove the effective distribution of PPy on the surface of Ag₂WO₄ rods with the help of powerful ultrasonic assistance. PPy acted as a support for nucleation and growth of Ag₂WO₄ and an inhibitor of phase transformations. Ag₂WO₄/PPy exhibits great photocatalytic behavior while comparing with pure PPy and Ag₂WO₄ in the degradation of carcinogenic dye congo red and antibiotic drug tetracycline. In addition to that, Ag₂WO₄/PPy modified GCE exposed a widespread linear range from 0.1 to 107 µM along with a very low detection limit of 12 nM and huge sensitivity of 1.74 µA µM^-1cm^-2 in the electrochemical determination of nitrofurazone.

An African perspective on the prevalence, fate and effects of carbapenem resistance genes in hospital effluents and wastewater treatment plant (WWTP) final effluents: A critical review

This article provides an overview of the antibiotic era and discovery of earliest antibiotics until the present day state of affairs, coupled with the emergence of carbapenem-resistant bacteria. The ways of response to challenges of antibiotic resistance (AR) such as the development of novel strategies in the search of new antibiotics, designing more effective preventive measures as well as the ecology of AR have been discussed. The applications of plant extract and chemical compounds like nanomaterials which are based on recent developments in the field of antimicrobials, antimicrobial resistance (AMR), and chemotherapy were briefly discussed. The agencies responsible for environmental protection have a role to play in dealing with the climate crisis which poses an existential threat to the planet, and contributes to ecological support towards pathogenic microorganisms. The environment serves as a reservoir and also a vehicle for transmission of antimicrobial resistance genes hence, as dominant inhabitants we have to gain a competitive advantage in the battle against AMR.