Microalgal-bacterial consortia for the treatment of livestock wastewater: Removal of pollutants, interaction mechanisms, influencing factors, and prospects for application

The livestock sector is responsible for a significant amount of wastewater globally. The microalgal-bacterial consortium (MBC) treatment has gained increasing attention as it is able to eliminate pollutants to yield value-added microalgal products. This review offers a critical discussion of the source of pollutants from livestock wastewater and the environmental impact of these pollutants. It also discusses the interactions between microalgae and bacteria in treatment systems and natural habitats in detail. The effects on MBC on the removal of various pollutants (conventional and emerging) are highlighted, focusing specifically on analysis of the removal mechanisms. Notably, the various influencing factors are classified into internal, external, and operating factors, and the mutual feedback relationships between them and the target (removal efficiency and biomass) have been thoroughly analysed. Finally, a wastewater recycling treatment model based on MBC is proposed for the construction of a green livestock farm, and the application value of various microalgal products has been analysed. The overall aim was to indicate that the use of MBC can provide cost-effective and eco-friendly approaches for the treatment of livestock wastewater, thereby advancing the path toward a promising microalgal-bacterial-based technology.

Environmental health hazards of untreated livestock wastewater: potential risks and future perspectives

Due to technological and economic limitations, waste products such as sewage and manure generated in livestock farming lack comprehensive scientific and centralized treatment. This leads to the exposure of various contaminants in livestock wastewater, posing potential risks to both the ecological environment and human health. This review evaluates the environmental and physical health risks posed by common pollutants in livestock wastewater and outlines future treatment methods to mitigate these risks. Residual wastes in livestock wastewater, including pathogenic bacteria and parasites surviving after epidemics or diseases on various farms, along with antibiotics, organic wastes, and heavy metals from farming activities, contribute to environmental damage and pose risks to human health. As the livestock industry's development increasingly impacts society's future negatively, addressing the issue of residual wastes in livestock wastewater discharge becomes imperative. Ongoing advancements in wastewater treatment systems are consistently updating and refining practices to effectively minimize waste exposure at the discharge source, mitigating risks to environmental ecology and human health. This review not only summarizes the "potential risks of livestock wastewater" but also explores "the prospects for the development of wastewater treatment technologies" based on current reports. It offers valuable insights to support the long-term and healthy development of the livestock industry and contribute to the sustainable development of the ecological environment.

Strategies for livestock wastewater treatment and optimised nutrient recovery using microalgal-based technologies

Global sustainable development faces several challenges in addressing the needs of a growing population. Regarding food industries, the heightening pressure to meet these needs has resulted in increased waste generation. Thus, recognising these wastes as valuable resources is crucial to integrating sustainable models into current production systems. For instance, the current 24 billion tons of nutrient-rich livestock wastewater (LW) generated yearly could be recovered and valorised via biological uptake through microalgal biomass. Microalgae-based livestock wastewater treatment (MbLWT) has emerged as an effective technology for nutrient recovery, specifically targeting carbon, nitrogen, and phosphorus. However, the viability and efficacy of these systems rely on the characteristics of LW, including organic matter and ammonium concentration, content of suspended solids, and microbial load. Thus, this systematic literature review aims to provide guidance towards implementing an integral MbLWT system for nutrient control and recovery, discussing several pre-treatments used in literature to overcome the challenges regarding LW as a suitable media for microalgae cultivation.

Simultaneous decontamination of phosphorus and bisphenol A from livestock wastewater with boehmite-modified carbon composite

In this work, a novel boehmite-modified carbon adsorbent (BMCC) derived from moldy corn was used for simultaneous removal of P and bisphenol A (BPA) from livestock wastewater. The results showed that BMCC had a high specific surface area (308.82 m2/g) with boehmite nanoparticles anchored on its surface. BMCC showed high P and BPA decontamination capabilities (40.98 mg/g for P and 54.65 mg/g for BPA by Langmuir model). The adsorbed amount of P declined as pH increased from 4 to 10, while the adsorbed amount of BPA remained steady until pH increased to 10. After 6 cycles of BMCC use, the P and BPA adsorption efficiencies reduced by 21.75 % and 19.41 %, respectively. The adsorption of P was dominated by electrostatic attraction and complexation, while the adsorption of BPA was controlled by hydrogen bonding, electrostatic interaction, and π-π association. In conclusion, BMCC is an effective treatment for decontaminating P- and BPA-contaminated livestock wastewater.

Effects of zinc ion concentrations on the performance of SBR treating livestock wastewater and analysis of microbial community

Zinc ion (Zn2+) is a frequently occurring heavy metal in livestock wastewater. The effects of Zn2+ on the physicochemical properties and the microbial distribution of activated sludge are essential to controlling nitrogen removal performance. Nevertheless, there are raw studies on the effects of Zn2+ on nitrogen removal. This study investigated the effect of Zn2+ on the treatment performance of livestock wastewater in a sequencing batch reactor (SBR). The results indicated the low Zn2+ concentrations could improve nitrogen removal performance. However, as the Zn2+ concentration increased, the total nitrogen (TN) removal performance of the reactor gradually deteriorated. When the Zn2+ concentration was 90.00 mg/L, the TN removal efficiency was the lowest, only 2.40%. The contents of the Extracellular polymeric substance (EPS) presented a trend of first increasing and then decreasing with the increase of Zn2+ concentration, and the main reason was the decrease of protein-like and tryptophan-like. The 16SrRNA analysis indicated that Zn2+ within a specific concentration could increase the operational taxonomic units (OTUs) number, microbial richness, and diversity of microorganisms in the SBR. However, with Zn2+ concentration exceeding 10.00 mg/L, the relative abundance of denitrification functional bacteria (Dechloromonas, Nitrospira, and Thauera) decreased.

Experimental study of microwave-catalytic oxidative degradation of COD in livestock farming effluent by copper-loaded activated carbon

The problem of massive discharge of livestock wastewater is becoming more and more severe, causing irreversible damage to the ecological environment, and how to treat livestock wastewater efficiently and rapidly deserves to be studied in depth. In this work, CuO/granular activated carbon (GAC) loaded catalysts were prepared and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption/desorption techniques, and X-ray energy spectroscopy (EDS). The results showed that CuO was successfully attached to the GAC surface with good adsorption performance. The effects of catalyst dosage, H2O2 dosage, initial pH, microwave power and microwave irradiation time in different reaction systems on the degradation efficiency of chemical oxygen demand (COD) in wastewater were investigated, and the orthogonal experiments were used to explore the importance ranking of these factors. The highest degradation rate of COD was found to be enhanced by 12.1% in the reaction system of CuO/GAC, and the initial pH had the greatest effect on the COD removal rate. The combined MW/catalyst/H2O2 method used in this work provided a rapid and effective degradation of COD in wastewater, which can be helpful for reference in other microwave catalytic oxidation studies.

Role of a typical swine liquid manure treatment plant in reducing elements of antibiotic resistance

Biological treatment of swine liquid manure may be a favorable environment for the enrichment of bacteria carrying antibiotic resistance genes (ARGs), raising the alert about this public health problem. The present work sought to investigate the performance of a swine wastewater treatment plant (SWWTP), composed of a covered lagoon biodigester (CLB) followed by three facultative ponds, in the removal of usual pollutants, antibiotics, ARGs (blaTEM, ermB, qnrB, sul1, and tetA), and intI1. The SWWTP promoted a 70% of organic matter removal, mainly by the digester unit. The facultative ponds stood out in the solids' retention carried from the anaerobic stage and contributed to ammonia volatilization. The detected antibiotic in the raw wastewater was norfloxacin (< 0.79 to 60.55 μg L-1), and the SWWTP seems to equalize peaks of norfloxacin variation probably due to sludge adsorption. CLB reduced the absolute abundance of ARGs by up to 2.5 log, while the facultative stage does not seem to improve the quality of the final effluent in terms of resistance elements. Considering the relative abundances, the reduction rates of total and ARG-carrying bacteria appear to be similar. Finally, correlation tests also revealed that organic matter and solids control in liquid manure treatment systems could help reduce the spread of ARGs after the waste final disposal.

Optimization of pig manure-derived biochar for ammonium and phosphate simultaneous recovery from livestock wastewater

Livestock wastewater has led to serious eco-environmental issues. To effectively treat livestock wastewater and realize the resource utilization of livestock solid waste, manure waste has been widely used to prepare biochar for the recovery of nitrogen and phosphorus. However, fresh biochar has a poor ability to adsorb phosphate due to its negative charge. To overcome the defect, the proportion of biochar samples prepared at 400 °C and 700 °C was optimized under a mass ratio of 2:3 to obtain mixed biochar PM 4-7, achieving the purpose of enhanced ammonium and phosphate recovery in livestock wastewater simultaneously without any modification. The effects of pyrolysis temperature, dosage, and pH were studied, different adsorption models were used to explore the adsorption mechanism, and the effect of biochar loaded with nutrient elements on seed was verified through a seed germination experiment. It was revealed that the maximum removal rates of phosphate and ammonium were 33.88 % and 41.50 %, respectively, endorsing that mixed biochar PM 4-7 can recover nutrients from livestock wastewater, and could be used as a slow-release fertilizer to promote seed germination and growth. This method provides a new potential way for the efficient resource utilization of pig manure and the recovery of nutrients from breeding wastewater.

The synergistic effect of chemical oxidation and microbial activity on improving volatile fatty acids (VFAs) production during the animal wastewater anaerobic digestion process treated with persulfate/biochar

Improving volatile fatty acid (VFA) production, rather than producing methane from the anaerobic digestion (AD) of waste, has become a new strategy of resource utilization. In regard to animal wastewater, the effectiveness of persulfate/biochar (potassium peroxodisulfate, PDS/BC) on the hydrolysis and acidogenesis stages and the reaction mechanisms are still unclear. In this study, the AD process on cow wastewater was controlled at the hydrolysis and acidification stages by setting the hydraulic retention time (HRT) at 25 days. The results showed that the contents of total solids (TS) and volatile solids (VS) were further reduced by PDS/BC treatment with 0.15 gPDS/gTS of PDS added. The VFAs production increased by 12.4 % from day 0 to 25 compared to the blank set. Based on our molecular analysis, the rate of increase for the dissolved organic matter with low molecular weight (0-10 kDa) was 699.5 mg/(L·d) in the first 10 days. The change rate increased nearly 2.1 times, leading to higher VFAs yield. Moreover, the activities of fermentative bacteria were enhanced and Anaerocella was determined to be the specific and critical genus. However, excessive PDS (0.3 gPDS/gTS) prolonged the acidification period and caused the inactivation of fermentative bacteria. Structural equation modeling demonstrated that PDS can directly affect VFAs yield and also had an indirect effect by influencing the decomposition of particulate matter and microbial activities. Therefore, the enhancement of VFAs production using the PDS/BC method could be due to synergistic chemical and microbial effects. Findings from this study can provide a practical strategy to enhance the VFAs production of AD technology for livestock wastewater and help reveal the reaction mechanism of PDS/BC treatment.

Non-antibiotics matter: Evidence from a one-year investigation of livestock wastewater from six farms in East China

Livestock wastewater is an important source of pharmaceuticals in aquatic environments; however, most related studies only focused on antibiotics. This study investigated 18 pharmaceutical active compounds (PhACs), including 12 antibiotics and 6 non-antibiotics, in livestock wastewater during a one-year survey of six livestock farms in East China. The results showed that four non-antibiotic PhACs-caffeine, N,N-diethyl-m-toluamide, gemfibrozil, and diclofenac-exhibited high detection frequencies (80% to 97%), high concentrations (median 0.43 to 3.79 μg/L), poor removal efficiencies (3% to 53%), and high environmental risks. A ranking system was developed to prioritize PhACs based on their occurrence, removal, and environmental risks in livestock wastewater; diclofenac, N,N-diethyl-m-toluamide, sulfamethazine, sulfadiazine, and gemfibrozil, were identified as the top five priority PhACs that should be considered first. Finally, a preliminary source apportionment protocol using four priority PhACs was proposed to trace the emission originating from treated and untreated livestock wastewater and to indicate the major contributor (cattle or swine farms) in the region. To the best of our knowledge, this is the first long-term investigation on the pollution characteristics of non-antibiotics in livestock wastewater in China, and our findings highlight the importance of considering non-antibiotics and the prioritized PhACs for the pollution control of PhACs in livestock wastewater.

Effects of hydroxylamine on treatment of anaerobic digestate of pig manure in partial nitrification-anaerobic ammonium oxidation

Partial nitrification-anaerobic ammonium oxidation (PN-anammox) was started up within 40 days by bioaugmentation and aeration control, and its performance in the treatment of anaerobic digestate of pig manure (ADPM) was evaluated. Inhibitors in ADPM decreased the nitrogen removal rate (NRR) by 0.24 g N/L/d. The effect and mechanism of hydroxylamine (NH₂OH) alleviation of PN-anammox inhibition during ADPM treatment were investigated. As an intermediate product of anammox and ammonia-oxidizing bacteria, NH₂OH strengthened energy metabolism, improved the activity and abundance of functional bacteria, and eliminated miscellaneous bacteria, increasing the average NRR by 31%. However, the average nitrous oxide emission was increased by 10.1% via hydroxylamine oxidation. The results showed that synergy and competition among nitrogen-transforming microorganisms were crucial for NRR and that NH₂OH played an essential role in maintaining efficient operation. This study lays a foundation for restoring PN-anammox for treating livestock wastewater.

Dynamics of antibiotic resistance genes and microbial community in shortcut nitrification-denitrification process under antibiotic stresses

In this study, the performance of shortcut nitrification-denitrification (SCND) at different TC and SD stress conditions (0 μg/L, 1-97 days; 100 μg/L, 98-138 days; 500 μg/L, 139-175 days) was investigated. Higher level antibiotic stress (500 μg/L) led to the serious deterioration of nitrogen removal, and denitrification was more sensitive to antibiotic stress than nitrification. The dynamics of antibiotic resistance genes (ARGs) and microbial community were revealed by quantitative real-time PCR and 16S rDNA high-throughput sequencing, respectively. Tet-genes (tetA, tetQ, tetW), sul-genes (sulI, sulII), and mobile genetic element (intI1) in activated sludge increased by 1.2 ~ 2.5 logs with long-term exposure of antibiotic stress, and sulI, tetA, tetQ, and tetW were significantly positively correlated with intI1. Long-term antibiotics stress caused the decrease of most denitrifiers, and five genera were identified as the potential host of ARGs. The key impact factors of SCND drove the dynamics of ARGs and microbial community. Except for sulII gene, DO and FA were significantly positively correlated with ARGs, while FNA, NAR, and NO₂^--N showed opposite effects to ARGs. Overall, maintaining relative lower DO, higher FNA, NAR, and NO₂^--N conditions are not only benefit to the stable operation of SCND, but may also conducive to the control of ARG dissemination. This study provides theoretical basis on the control of ARGs in the SCND process.

The reduction and fate of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in microbial fuel cell (MFC) during treatment of livestock wastewater

The fate and removal efficiency of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in livestock wastewater by microbial fuel cell (MFC) was evaluated by High-throughput quantitative PCR. The results showed that 137 ARGs and 9 MGEs were detected in untreated livestock wastewater. The ARG number of macrolide-lincosamide-streptogramin group B (MLSB), tetracycline and sulfonamide were relatively higher. Throughout the treatment process, the number and abundance of ARGs and MGEs significantly decreased. The relative abundance of tetracycline, sulfonamide and chloramphenicol resistance genes showed the most obvious decreasing trend, and the relative abundance of MGEs decreased by 75% (from 0.012 copies/16S rRNA copies to 0.003 copies/16S rRNA copies). However, the absolute abundance of beta-lactamase resistance genes slightly increased. The operation process of MFC produces selective pressure on microorganisms, and Actinobacteria were predominant and had the ability to decompose antibiotics. The COD removal rate and TN removal rate of livestock wastewater were 67.81% and 62.09%, and the maximum power density and coulomb efficiency (CE) reached 11.49% and 38.40% respectively. This study demonstrated that although the removal of COD and TN by MFC was limited, MFC was quite effective in reducing the risk of antibiotic toxicity and horizontal gene transfer.

Microalgae-based livestock wastewater treatment (MbWT) as a circular bioeconomy approach: Enhancement of biomass productivity, pollutant removal and high-value compound production

The intensive livestock activities that are carried out worldwide to feed the growing human population have led to significant environmental problems, such as soil degradation, surface and groundwater pollution. Livestock wastewater (LW) contains high loads of organic matter, nitrogen (N) and phosphorus (P). These compounds can promote cultural eutrophication of water bodies and pose environmental and human hazards. Therefore, humanity faces an enormous challenge to adequately treat LW and avoid the overexploitation of natural resources. This can be accomplished through circular bioeconomy approaches, which aim to achieve sustainable production using biological resources, such as LW, as feedstock. Circular bioeconomy uses innovative processes to produce biomaterials and bioenergy, while lowering the consumption of virgin resources. Microalgae-based wastewater treatment (MbWT) has recently received special attention due to its low energy demand, the robust capacity of microalgae to grow under different environmental conditions and the possibility to recover and transform wastewater nutrients into highly valuable bioactive compounds. Some of the high-value products that may be obtained through MbWT are biomass and pigments for human food and animal feed, nutraceuticals, biofuels, polyunsaturated fatty acids, carotenoids, phycobiliproteins and fertilizers. This article reviews recent advances in MbWT of LW (including swine, cattle and poultry wastewater). Additionally, the most significant factors affecting nutrient removal and biomass productivity in MbWT are addressed, including: (1) microbiological aspects, such as the microalgae strain used for MbWT and the interactions between microbial populations; (2) physical parameters, such as temperature, light intensity and photoperiods; and (3) chemical parameters, such as the C/N ratio, pH and the presence of inhibitory compounds. Finally, different strategies to enhance nutrient removal and biomass productivity, such as acclimation, UV mutagenesis and multiple microalgae culture stages (including monocultures and multicultures) are discussed.

Effects of organic carbon and sulfide on the anammox reaction in the anoxic column in the SRDAPN process for treating high-strength wastewater

Low energy consumption treatment of high-strength wastewater is crucial in controlling groundwater pollution and eutrophication in closed waterbodies. In this study, the sulfate reduction, denitrification/anammox, and partial nitrification (SRDAPN) process, which is an effective organic carbon and nitrogen removal process with low energy consumption for low strength wastewater, was applied to treat livestock wastewater with high COD and sulfate concentration, and microbial reaction and community were examined using an anaerobic-anoxic biological filter reactor that simulates circulation from an aerobic reactor. At a total organic carbon loading rate of 2.7-5.8 kgC/m³·day, sulfate reduction and methane production occurred simultaneously in the anaerobic column of the reactor. Specifically, sulfate reduction resulted in organic matter removal rates of 38 and 26% at ambient temperature and 25 °C, respectively. Furthermore, both heterotrophic and autotrophic denitrification occurred in the anoxic column, and when the organic loading rate in the anoxic reactor was below 0.2 kgC/m³·day, 33%-37% of ammonium and 33%-34% of nitrite were removed by the anammox reaction. Heterotrophic denitrification bacteria (Thauera, Comamonas, and Denitratisoma) and sulfur denitrification bacteria (Sulfurimonas denitrificans) grew in the lower and middle parts of the anoxic column, whereas anammox bacteria (2.5% of Candidatus Brocadia at ambient temperature and 9.4% of Candidatus Kuenenia at 25 °C) grew in the upper part of the anoxic column. These results indicate that the SRDAPN process based on sulfur cycle and anammox is useful for treatment of high strength wastewater with low energy consumption.

Application of magnetic biochar/quaternary phosphonium salt to combat the antibiotic resistome in livestock wastewater

The overuse and misuse of antibiotics in animal breeding for disease treatment and growth enhancement have been major drivers of the occurrence, diffusion, and accumulation of antibiotic resistance genes (ARGs) in wastewater. Strategies to combat ARG dissemination are pressingly needed for human and ecological safety. To achieve this goal, a biochar-based polymer, magnetic biochar/quaternary phosphonium salt (MBQ), was applied in livestock wastewater and displayed a high performance in bacterial deactivation and ARG decrease. Efficient antibacterial effects were achieved by both MBQ and quaternary phosphonium salt; however, the abundance and fold change of ARGs in the MBQ treatment indicated a more powerful ARG dissemination control than quaternary phosphonium salt. The application of MBQ evidently reduced the microbial diversity and may primarily be responsible for altering the ARG profiles in wastewater. Network, redundancy, and variation partitioning analyses were further employed to reveal that the microbial community and the presence of mobile genetic elements were two critical factors shaping the pattern of the antibiotic resistome in livestock wastewater. Considered together, these findings extend the application field of biochar and have important implications for reducing ARG dissemination risks in livestock wastewater.

Removal of tetracycline from livestock wastewater by positive single pulse current electrocoagulation: Mechanism, toxicity assessment and cost evaluation

The widespread use of veterinary antibiotics has led to the significant problem of contamination of livestock wastewater with significant amount of antibiotics. Electrocoagulation (EC) has become a prominent research topic because of the technique's ability to remove antibiotics from livestock wastewater. However, an urgent solution is needed to reduce the high operating costs associated with the process. Therefore, in this study, we developed a positive single pulse current (PSPC)-EC system to remove tetracycline (TC) from synthetic and actual livestock wastewater. Influential factors were investigated, and the optimal PSPC-EC operating parameters were identified as follows: duty ratio = 60%, pH = 4, electrode spacing = 1 cm, current intensity = 0.2 A, and conductivity = 2 mS cm^-1. The mechanism of PSPC-EC was characterised using techniques including scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TC decomposition pathway was proposed based on the generation of its intermediate products. A toxicity estimation software tool (TEST) model was used to evaluate the toxicity of TC and its main degradation products, and most of its intermediates were found to be less toxic than TC. The contribution ratios of floc adsorption and electrochemical oxidation for removing TC were 74.17% and 21.48%, respectively. The highest TC removal rate reached 95% with an operating cost of 0.011 USD/m³. Finally, under the optimum conditions identified, actual livestock wastewater was treated by PSPC-EC. Compared with conventional EC and coagulation treatment techniques that consume electricity and produce pollution, the results indicate that the PSPC-EC technique with changing current operation mode is a more cost-effective and attractive option for removing TC from livestock wastewater.

The anode is more beneficial to the advanced treatment of wastewater containing antibiotics by three-dimensional electro-biofilm reactor: Degradation, mechanism and optimization

The three-dimensional electrode biological aerated filter (3DE-BAF) has the potential to overcome inherent limitations of conventional electrochemical and biofilm methods. Electrochemical means could enhance the performance and sustainability of biofilm technologies and stimulate the spread of new applications in (waste) water treatment. This paper describes the construction and performance of 3DE-BAF in the treatment of simulated wastewater represented by tetracycline (TC). This is followed by a discussion of electrode performance, the electron transport mechanism and the electrode's effect on the biological community of 3D-EBAF. Given the gap between experimental studies and practical applications, the enlarged anode 3DE-BAF named 3DEAE-BAF reactor was applied with good results to duck farm wastewater. This study could provide guidance as to developing new methods to construct a highly stable 3DE-BAF. The paper concludes that improved 3DE-BAF technology is promising for advanced treatment of livestock wastewater containing antibiotics.

The role of nitrification inhibitors on the removal of antibiotics in livestock wastewater by aerobic biodegradation

An optimized aerobic-based treatment method that effectively removes antibiotics and retains ammonia is urgently needed for the field-return-based management of livestock wastewater. Allylthiourea (ATU, used for BOD determination), and 2-chloro-6-trichloromethylpyridine (TCMP) and 3,4-dimethylpyrazole phosphate (DMPP) (commonly used as nitrogen fertilizer synergists) were separately added to sequencing batch reactors (SBRs), in order to investigate their effect on nitrification inhibition and pollutant removal for livestock wastewater treatment. The laboratory test shows that the daily addition of 43.8 mg/L ATU or 17.5 mg/L TCMP to SBRs effectively inhibited nitrification. Nitrification inhibition by DMPP seemed fluctuated and insufficient even various dosing strategies were attempted. The removal efficiency of antibiotics was reduced from 95% to 85% with the addition of ATU, while not significantly influenced by TCMP and DMPP. The COD removal efficiency was reduced by only 6%-10% with the addition of three inhibitors. The pilot study shows that nitrification inhibition efficiency reached 89% with the daily addition of 11.5 mg/L TCMP. The total removal efficiency of antibiotics remained over 93%. The laboratory and pilot studies consistently demonstrate that TCMP played a satisfactory nitrification inhibition role and had a negligible effect on antibiotic removal. The current work provides a novel insight for the proper field-return-based management of livestock wastewater, which achieves the dual goals of reducing the risk of antibiotic exposure and preserving its nutrient value as fertilizers.

Overcoming organic matter limitation enables high nutrient recovery from sewage sludge reject water in a self-powered microbial nutrient recovery cell

In order to meet the global demand of fertilizers for food production, there is an urgent need to recover macronutrients (such as NH₄⁺, PO₄^3-, Ca²⁺, K⁺, and Mg²⁺) from non-conventional sources (e.g., waste streams). Sludge reject water - a by-product produced during the dewatering of anaerobically-stabilized sewage sludge - is considered an ideal feedstock for bioelectrochemical nutrient recovery due to its high nutrient content. However, its low readily available organic matter and alkalinity usually limit electric current generation, resulting in low nutrient recovery. Here, we designed and operated self-powered microbial nutrient recovery cells (MNRCs) to test whether or not the addition of high-strength livestock wastewater could improve the macronutrients recovery from sludge reject water into a liquid concentrate. MNRCs fed with sludge reject water exhibited a low current density generation of 0.98 ± 0.31 A/m³ with approximately 24 ± 2% reduction in chemical oxygen demand (COD) concentration. The NH₄⁺ removal was only 37.1 ± 11% with an up-concentration factor of ~0.43 ± 0.15. Macronutrients recovery and up-concentration were optimized by mixing sludge reject water with livestock wastewater, which its content varied from 10 to 30%. Consequently, the current output and NH₄⁺ up-concentration factor were remarkably increased, peaking at 14.10 ± 1.14 A/m³ and 2.19 ± 0.51, respectively, for MNRCs fed with sludge reject water:livestock wastewater = 70%:30% (v:v). Detailed analysis of the liquid concentrate revealed that it could be efficiently used as a liquid fertilizer to replace chemical fertilizers with comparable agricultural productivity at a lower cost. These results suggest that the MNRC can promote self-powered, chemical-free macronutrients recovery from sludge reject water (and other low-strength wastewater, too) by controlling the availability of organic matter in waste streams.

The relationship between the molecular composition of dissolved organic matter and bioavailability of digestate during anaerobic digestion process: Characteristics, transformation and the key molecular interval

In this study, swine wastewater (SW) and cow wastewater (CW) were used for anaerobic digestion (AD). We found the bioavailability of dissolved organic matter (DOM) was affected by the molecular weight ranges and molecular composition during the AD process. The organic substance in the small molecular range (0-5 kDa) accumulated due to a larger molecular fraction (>10 kDa) degradation, which enhanced the bioavailability of the DOM. Moreover, based on the excitation emission matrix-parallel factor (EEM-PARAFAC) analysis, the protein-like component in 0-5 kDa molecular size and humic-like component over 5 kDa are significantly positively correlated with DOM bioavailability. This study indicated that increasing the hydrolysis of larger organic matter and humification degree of molecular weights>5 kDa are critical solutions to improving the bioavailability of DOM. These conclusions can help explain the molecular mechanisms of DOM transformation and the AD process of livestock wastewater.

Economic feasibility of phosphorus recovery through struvite from liquid anaerobic digestate of animal waste

Although the struvite crystallization process has proven to be an effective process for the recovery of nutrients from wastewater, this process has not been widely used due to the excessive use of chemicals. In this study, the optimal production conditions, yield, and economic feasibility of struvite using the anaerobic digestion of livestock wastewater were investigated. In addition, the economic feasibility of adding zeolite to improve the productivity of struvite and additionally remove nitrogen was evaluated. The result of the experiment on the struvite yield change according to the molar ratios at pH 9.0 showed that the struvite yield ratio was 99.0% of the stoichiometric yield at the Mg²⁺ :NH₄⁺ :PO₄^3- molar ratios of 1.2:1.0:1.1. As a magnesium source, MgCl₂, concentrated seawater in the seawater desalination process, and MgO were compared, and when MgO was used, struvite productivity and economic efficiency were the best. Also, while the addition of zeolite greatly increased the struvite production and zeolite was also sold as a soil conditioner, the struvite sales benefit was estimated to be 103% of the operating cost.

Gas-diffusion-electrode based direct electro-stripping system for gaseous ammonia recovery from livestock wastewater

Livestock wastewater (LW) typically contains a substantial amount of NH₄⁺ that can potentially be recovered and used in fertilizers or chemicals. In an attempt to recover NH₄⁺ from LW, a novel electrochemical approach using a gas diffusion electrode (GDE) was developed and its efficacy was demonstrated in this study. The GDE-based electrochemical device, when operated at an air-flow rate of 20 mL/min, was free of back-diffusion flux, which is a fatal drawback of any membrane-based NH₄⁺ separation approach. Continuous operation resulted in a nitrogen flux of 890 g N/m²d with synthetic LW and 770 g N/m²d with real LW at a current density of 10 mA/cm². The electrochemical energy input was 7.42 kWh/kg N with synthetic LW and 9.44 kWh/kg N with real LW. Compared with the traditional stripping method, the GDE-based electrochemical system has a certain potential to be competitive, in terms of energy consumption. For instance, a rough-cost estimate based only on operating costs regarding chemical usage, air blowing, and water pumping revealed that the system consumed 13.44 kWh/kg N, whereas the conventional stripper required 27.6 kWh/kg N. This analysis showed that an electrochemical approach such as our GDE-based method can recover NH₃, (particularly in gaseous form) from LW. In addition, with the future development of a smart operation method, as proposed and demonstrated in this study, the cost-effective implementation of a GDE-based method is feasible.

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.

Organoarsenic feed additives in biological wastewater treatment processes: Removal, biotransformation, and associated impacts

Aromatic organoarsenicals are widely used in animal feeding operations and cause arsenic contamination on livestock wastewater and manure, thereby raising the risk of surface water pollution. Biological wastewater treatment processes are often used for livestock wastewater treatment. Organoarsenic removal and biotransformation under aerobic and anaerobic conditions, and the associated impacts have received extensive attention due to the potential threat to water security. The removal efficiency and biotransformation of organoarsenicals in biological treatment processes are reviewed. The underlying mechanisms are discussed in terms of functional microorganisms and genes. The impacts associated with organoarsenicals and their degradation products on microbial activity and performance of bioreactors are also documented. Based on the current research advancement, knowledge gaps and potential research in this field are discussed. Overall, this work delivers a comprehensive understanding on organoarsenic behaviors in biological wastewater treatment processes, and provides valuable information on the control of arsenic contamination from the degradation of organoarsenicals in biological wastewater treatment processes.

Influence of hydraulic loading rate on antibiotics removal and antibiotic resistance expression in soil layer of constructed wetlands

Behavior of veterinary antibiotics, the corresponding resistant genes in soil layer of constructed wetlands (red soil), and their response to different hydraulic loading rates (HLR) (2, 5, and 10 cm/d) were investigated. Results indicated that the soil layer had perfect performance for oxytetracycline and ciprofloxacin, yet sulfamethazine removal was unsatisfactory. Detection rates of oxytetracycline, ciprofloxacin and sulfamethazine in the effluent of simulation systems of soil layer were 8.33-36.36%, 8.33-47.83% and 100%, respectively. The model analysis of adsorption and hydrolysis indicated that physical adsorption, which was controlled by exchange reaction process based on diffusion, was the primary adsorption mechanism of target antibiotics in red soil, and the hydrolysis half-life values of antibiotics in the water of soil layer were shorter than them in wastewater. The removal response of oxytetracycline and ciprofloxacin to change of HLR was insignificant, yet the respective effluent concentrations of sulfamethazine at HLR of 2-10 cm/d were 41.90, 61.35 and 73.54 μg/L during treating synthetic livestock wastewater, which revealed significant positive correlation (P < 0.05). The relative abundances of each target resistance genes in soil showed significant increase after treating wastewater (10^-5-10^-6 to 10^-4-10^-1), and the total level of those at different HLRs (2, 5, and 10 cm/d) were 3.02 × 10^-2, 7.54 × 10^-2 and 8.65 × 10^-1, respectively. In summary, HLR could affect the removal efficiency of partial antibiotic in soil layer of constructed wetlands, and the expression of antibiotic resistance in the soil gradually increased with increase in the HLR.

Identification of indicator PPCPs in landfill leachates and livestock wastewaters using multi-residue analysis of 70 PPCPs: Analytical method development and application in Yangtze River Delta, China

The source apportionment of pharmaceuticals and personal care products (PPCPs) in the water environment based on indicators (i-PPCPs) requires a comprehensive characterization of various emission sources using reliable analytical methods for a wide spectrum of PPCPs. In this study, a robust and sensitive method based on solid phase extraction (SPE) and ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) for analyzing 70 PPCPs belonging to 17 therapeutic classes in landfill leachates and livestock wastewaters was developed. The SPE cartridges, sample pH, elution solvents and chelating agent additions were optimized, and acceptable recoveries (60- 130% for 67 target compounds), low method quantification limits (landfill leachate: 3- 1309 ng/L; livestock wastewater: 3- 686 ng/L) and high precisions (repeatability: 0- 20% for over 99% injections; reproducibility: 0- 20% for over 90% injections) were obtained. Using the optimized analytical method to characterize PPCPs in the typical landfill leachate and livestock wastewater in Yangtze River Delta, China, we found anthelmintics, which were first reported in landfill leachates globally, exhibited the highest concentration (albendazole, maximum concentration of 61.6 μg/L), and therefore proposed albendazole as one of the promising i-PPCP candidates in landfill leachates. In livestock wastewaters, antibiotics lincomycin was the most abundant PPCP (maximum concentration: 735 μg/L) and identified as an i-PPCP candidate for livestock-originated contamination. In addition, 15 non-antibiotic PPCPs were first investigated in the livestock wastewater in China and some non-steroidal anti-inflammatory drugs, acetaminophen, diclofenac and naproxen, were detected at similar concentration level (1.16- 91.1 μg/L) to antibiotics, highlighting the necessity to include representative non-antibiotic PPCPs in the studies of emerging contaminants in livestock wastewaters. The developed method provides a tool to comprehensively investigate PPCPs in high-strength wastewater, and the preliminary findings in the characterization of typical landfill leachates and livestock wastewaters are helpful to select i-PPCPs for the source apportionment of PPCPs in Yangtze River Delta, China.

Evaluation of wetland substrates for veterinary antibiotics pollution control in lab-scale systems

The behaviors of typical veterinary antibiotics (oxytetracycline, ciprofloxacin and sulfamethazine) and 75 types of corresponding antibiotic resistant genes (ARGs) in four substrate systems (zeolite, gravel, red brick, and oyster shell) were investigated in this study. The results indicated that during treating synthetic livestock wastewater with individual antibiotic influent concentration of 100 μg/L, the effluent contained oxytetracycline and ciprofloxacin concentrations of 0.7-1.5 μg/L and 1.0-1.9 μg/L, respectively, in the zeolite and red brick systems, which were significantly lower than those of the other substrate systems (4.6-14.5 μg/L). Statistical correlation analyses indicated that the difference regarding oxytetracycline and ciprofloxacin removal among the four substrates was determined by their adsorption capacity which was controlled by the chemisorption mechanism. The average removal efficiency of sulfamethazine in the gravel system (48%) was higher than that of the other substrate systems (34-45%), and biodegradation may alter the sulfamethazine performance because of its co-metabolism process. Although tetG, floR, sul1, and qacEΔ1 were the dominant ARGs in all substrate systems (8.74 × 10^-2-6.34 × 10^-1), there was difference in the total ARG enrichment levels among the four substrates. Oyster shell exhibited the lowest total relative abundance (1.56 × 10⁰) compared to that of the other substrates (1.82 × 10⁰-2.27 × 10⁰), and the ARG total relative abundance exhibited significant negative and positive correlations with the substrate pH and system bacterial diversity (P < 0.05), respectively. In summary, this study indicated that due to the difference of adsorption capacity and residual abundant nutrient in wastewater, the wetland substrate selection can affect the removal efficiency of veterinary antibiotics, and antibiotics may not be the determining factor of ARG enrichment in the substrate system.

Microbial fuel cell driven mineral rich wastewater treatment process for circular economy by creating virtuous cycles

The aim of this work is to study for concurrent harvesting bioelectricity and struvite mineral from mineral rich wastewater containing with nitrogen (N) and phosphorous (P) contents using MFCs and a chemical precipitation system. Whole reaction was constructed to sequentially run hybrid reactor (consisting of MFCs and struvite precipitation), gravitational sedimentation, nitrogen purging and MFCs. The MFCs generated around 6.439 ± 0.481 mA and 2.084 ± 0.310 mW as I_max and P_max, respectively under 2g/l of COD. More than 70% of C source, and around 95% of P and N sources have been removed. Struvite mineral was precipitated in the hybrid reactor after the injection of Mg²⁺ and collected in sedimentation tank. Economic feasibility and beneficial concerns were carefully investigated, and it is proposed for applications in the "decentralised treatment process" of agriculture and livestock wastewater in order to realise circular and strong economy in agriculture by creating virtuous cycles.

Sulfonamide degradation and metabolite characterization in submerged membrane photobioreactors for livestock excreta treatment

Residual veterinary antibiotics have been detected in livestock wastewater treatment plants. Despite the long retention time, antibiotic treatment efficiency has shown clear limitations. In this study, we evaluated submerged membrane photobioreactors (SMPBR) during sulfonamide antibiotic-containing livestock wastewater treatment under mixotrophic and photoautotrophic conditions. The results showed that microalgal sulfur degradation and consumption under mixotrophic conditions accelerated the biomass concentration increase to 2800 mg VSS/L compared to the 1800 mg VSS/L measured under photoautotrophic conditions. Although microalgal metabolites, such as soluble microbial products and extracellular polymeric substances, might cause membrane fouling in the SMPBR, we proved that microalgae could remove sulfonamide and release degradation-associated sulfur, along with nitrogen and phosphorus. Moreover, this study confirms the statistical correlation between metabolites and sulfonamides. In summary, the results of this study provide promising insights into antibiotic-containing livestock wastewater treatment.

Effect of sludge recirculation on removal of antibiotics in two-stage membrane bioreactor (MBR) treating livestock wastewater

Two-stage MBR consisting of anaerobic and aerobic reactors was operated at total hydraulic retention time (HRT) of 48 h for the treatment of livestock wastewater containing antibiotics, i.e. amoxicillin (AMX), tiamulin (TIA), and chlortetracycline (CTC), under the (1st) absence and (2nd) presence of sludge recirculation between the reactors. During the operation with sludge recirculation, the removals of organic and nitrogen were enhanced. Meanwhile, the removals of TIA and CTC were found to decrease by 9% and 20% in the aerobic reactor but increased by 5% to 7% in the anaerobic reactor due to the relocation of biomass from the aerobic to the anaerobic reactor. A high degree of AMX biodegradation under both anaerobic and aerobic conditions and partial biodegradation of TIA and CTC under aerobic conditions were confirmed in batch experiments. Moreover, the effect of sludge recirculation on biomass and pollutant removal efficiencies in the 2-stage MBR was revealed using microbial community analyses. Membrane filtration also helped to retain the adsorbed antibiotics associated with small colloidal particles in the system.

Sustainable livestock wastewater treatment via phytoremediation: Current status and future perspectives

Phytoremediation, the application of vegetation and microorganisms for recovery of nutrients and decontamination of the environment, has emerged as a low-cost, eco-friendly, and sustainable approach compared to traditional biological and physico-chemical processes. Livestock wastewater is one of the most severe pollution sources to the environment and water resources. When properly handled, livestock wastewater could be an important alternative water resource in water-scarce regions. This review discussed the characteristics and hazards of different types of livestock wastewater and available methods for the treatment. Meanwhile, the current status of investigations on phytoremediation of livestock wastewater via different hydrophyte systems such as microalgae, duckweed, water hyacinth, constructed wetlands, and other hydrophytes is reviewed, and the utilization of hydrophytes after management is also discussed. Furthermore, advantages and limitations on livestock wastewater management via phytotechnologies are emphasized. At last, future research needs are also proposed.

A new approach to removing and recovering phosphorus from livestock wastewater using dolomite

Recovering phosphorus from livestock wastewater could partly mitigate the global phosphorus resource crisis. Crystallization is a promising method for removing phosphorus from wastewater, but the costs of calcium- and magnesium-containing reagents are increasing. Cheap, available, efficient materials are required to replace conventional calcium and magnesium reagents. Here, we describe a new approach to removing and recovering phosphorus from livestock wastewater of a large pig farm, containing a high phosphorus concentration. The effects of the pH, stirring speed, stirring time, and extract dose (containing calcium and magnesium) on phosphorus removal from livestock wastewater were investigated. The product was characterized by X-ray diffractometry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Under optimized conditions (pH 9.0, stirring speed 200 r/m, stirring time 600 s, Ca 207.62 mg/L, Mg 122.86 mg/L), 92% of the phosphorus was removed from livestock wastewater. The product was mainly the hydroxyapatite (Ca₅(PO₄)₃OH) precursor amorphous calcium phosphate but also contained 1.65% (by mass) magnesium ammonium phosphate (MgNH₄PO₄·6H₂O) crystals. The cost of dolomite to treat 1 m³ of high-phosphorus wastewater was 0.20 yuan (45.9%, 25.9%, and 75.9% lower than for pure MgCl₂, MgSO₄, and CaCl₂, respectively) in 2019. Using dolomite to provide calcium and magnesium effectively decreases the crystallization process cost and should encourage the use of crystallization to remove phosphorus from wastewater.

Selective removal of color substances by carbon-based adsorbents in livestock wastewater effluents

Livestock wastewater effluent generated after the anaerobic treatment process contains the considerable amount of color-causing organic matter. In this study, a quantitative comparison of three carbon-based adsorbents included granular activated carbon (GAC), expanded graphite (EG), and multi-walled carbon nanotubes (MWNTs) was carried out for the potential application to the removal of color substances, and their mechanism was proposed. Although GAC showed the highest specific dissolved organic carbon (DOC) adsorption capacity, the color removal efficiency was the smallest among three adsorbents. The selective color removal ratios of EG and MWNTs reached 22.7 ± 0.1 PtCo/mg-DOC-removed and 21.2 ± 0.1 PtCo/mg-DOC-removed, respectively, while that of GAC was only 12.3 ± 0.1 PtCo/mg-DOC-removed. The selective adsorption of color substances by graphene-based carbon materials was due to the aromatic π-π interaction between organic matter and the hexagonal carbon lattice of graphene. The analysis of molecular weight distribution also confirmed that the exposed surface area and macro-pores were responsible for the adsorption of high molecular weight color substances. The chemical regeneration of three adsorbents was examined using 1% NaOCl solution and MWNTs showed almost complete recovery of the initial color removal capacity. In conclusion, MWNTs were the most suitable carbon nanomaterial for the selective color removal from livestock wastewater effluent.

Selective oxidation of tetracyclines by peroxymonosulfate in livestock wastewater: Kinetics and non-radical mechanism

Tetracyclines (TCs) discharged from livestock wastewater have received worldwide concerns owing to their potential threats to the ecosystem and human health. Advanced oxidation processes always exhibit low efficiency to remove TCs in livestock wastewater due to the radical scavenging by water matrices. Herein, we report selective elimination of TCs by peroxymonosulfate (PMS) in livestock wastewater. A kinetic model was developed to describe the rapid degradation of TCs by PMS in the real livestock wastewater. The radical scavenging study and electron paramagnetic resonance (EPR) technique excluded the contribution of radical species (e.g., SO₄^-) in the PMS-promoted oxidation of TCs. Theoretical calculations revealed the electrophilic attacks of PMS most likely located on the B-ring of TCs. Transformation product analysis further elucidated that hydroxylation dominated in the PMS-promoted oxidation of TCs, and N-demethylation also significantly contributed to chlorotetracycline (CTC) oxidation by PMS. These results demonstrate a promising strategy to eliminate TCs in livestock wastewater, because PMS shows specific reactivity towards TCs, and thus suffers less interference from the complicated water matrices.

Mixture of different Pseudomonas aeruginosa SD-1 strains in the efficient bioaugmentation for synthetic livestock wastewater treatment

Strains selection for inoculation is the key to the successful construction of a bioaugmentation system, a promising strategy for specific pollutant removal. Pseudomonas aeruginosa SD-1 wild-type (WT) strain exhibited high capacity for biofilm formation but low efficiency for nitrate (NO₃^-) removal. Meanwhile, quorum sensing deficient strain ΔlasR showed excellent efficiency for NO₃^- removal but poor capability for colonization in activated sludge. The opposite effect of biofilm formation and NO₃^- removal exist in WT or ΔlasR, which limits the construction of bioaugmentation system of strain SD-1 and its application. To solve this issue, a mixture of WT and ΔlasR (v/v = 1:1) was used to construct a bioaugmentation system. Compared with the inoculation of WT or ΔlasR alone, the mixed inoculation not only was beneficial for activated sludge development but also for pollutant removal. The indicators for activated sludge including the abundance of P. aeruginosa, the sludge volume index and the average particle size in mixed inoculated reactors were close to those of reactors with single and repeated inoculation of WT. The effluent of chemical oxygen demand (COD) and NO₃^--N were stable at 3.9-22.6 mg L^-1 and 0-5.53 mg L^-1 after d 3, respectively. This study presents a detailed case on the ecological tradeoff of colonization and pollutant removal of inoculated strains during bioaugmentation. The results provide information on the appropriate conditions for application of P. aeruginosa SD-1 for livestock wastewater treatment and further enrich our ecological understanding of bioaugmentation.

Reducing water use by alternate-furrow irrigation with livestock wastewater reduces antibiotic resistance gene abundance in the rhizosphere but not in the non-rhizosphere

Livestock wastewater is rich in nutrients but may contain antibiotics and antibiotic resistance genes (ARGs). Their discharge to watercourses or soil may result in proliferation of ARGs. Irrigation with wastewater appears to be the most feasible option of disposing of it. One efficient irrigation technology used in arid regions is alternate-furrow irrigation (AFI) by alternately drying part of the plant roots for a prolonged period to physiologically reduce transpiration without compromising yield. However, the extent to which AFI with wastewater influences the concentration of antibiotics and spread of ARGs in soil is poorly understood. The purpose of this paper is to investigate how AFI using swine wastewater alters antibiotic kinetics and ARGs abundance under different irrigation rates, using pepper as the model plant. We examined three AFI treatments using 50%, 65% and 80% of the amount of water employed in sufficient conventional furrow irrigation. Each treatment had a groundwater irrigation control. The results showed that antibiotic concentrations and relative ARGs abundance in the top 20 cm of soil did not increase with the irrigation amount, although they were higher than those in the groundwater-irrigated soils. The relative ARGs abundance in the soil was modulated by irrigation amount and reducing the irrigation amount in AFI reduced ARGs dispersion only in rhizosphere. When the soil moisture was close to field capacity, ARGs were more abundant in rhizosphere than in non-rhizosphere, possibly because the rhizosphere is rich in microbes and increasing antibiotic concentrations due to an increase in irrigation rate favors antibiotic-resistant microbiome in competing for substrates. These, however, were not mirrored in the relative ARGs abundance in the roots. These results have important implications as it revealed that reducing the input of antibiotics and ARGs into soil with AFI does not necessarily reduce ARGs proliferation.

Antibiotic resistance genes and intI1 prevalence in a swine wastewater treatment plant and correlation with metal resistance, bacterial community and wastewater parameters

The livestock wastewater treatment plant represents an important reservoir of antibiotic resistance determinants in the environment. The study explored the prevalence of five antibiotic resistance genes (ARGs, including sulI, tetA, qnrD, mphB and mcr-1) and class 1 integron (intI1) in a typical livestock wastewater treatment plant, and analyzed their integrated association with two metal resistance genes (copA and czcA), two pathogens genes (Staphylococcus and Campylobacter), bacterial community and wastewater properties. Results indicated that all investigated genes were detected in the plant. The treatment plant could not completely remove ARGs abundances, with up to 2.2 × 10⁴~3.7 × 10⁸ copies/L of them remaining in the effluent. Mcr-1 was further enriched by 27-fold in the subsequent pond. The correlation analysis showed that mphB significantly correlateed with tetA and intI. Mcr-1 strongly correlated with copA. MphB and intI significantly correlated with czcA. The correlations implied a potential co-selection risk of bacterial resistant to antibiotics and metals. Redundancy analyses indicated that qnrD and mcr-1 strongly correlated with 13 and 14 bacterial genera, respectively. Most ARGs positively correlated to wastewater nutrients, indicating that an efficient reduction of wastewater nutrients would contribute to the antibiotic resistance control. The study will provide useful implications on fates and reductions of ARGs in livestock facilities and receiving environments.

Nitrogen recovery from wastewater using gas-permeable membranes: Impact of inorganic carbon content and natural organic matter

Gas-permeable membranes coupled with low-rate aeration is useful to recover ammonia (NH₄⁺) from livestock effluents. In this study, the role of inorganic carbon (bicarbonate, HCO₃^-) to enhance the N recovery process was evaluated using synthetic effluents with various NH₄⁺ to HCO₃^- molar ratios of 0.5, 1.0, 1.5 and 2.0. The study also evaluated the effect of increased organic matter on the NH₄⁺ recovery using humic acids (3000-6000 mg L^-1), and the N recovery from high-strength swine manure. The release of hydroxide from the HCO₃^- with aeration increased the wastewater pH and promoted gaseous ammonia formation and membrane uptake. At the same time, the recovery of gaseous ammonia (NH₃) through the membrane acidified the wastewater. Therefore, an abundant inorganic carbon supply in balance with the NH₄⁺ is needed for a successful operation of the technology. NH₄⁺ removal efficiencies >96% were obtained with NH₄⁺ to HCO₃^- ratios ≤1. However, higher molar ratios inhibited the N recovery process resulting in lower efficiencies (<65%). Fortunately, most swine manures contain ample supply of endogenous inorganic carbon and the process can be used to more economically recover the ammonia using the natural inorganic carbon instead of expensive alkali chemicals. In 4 days, the recovered NH₄⁺ from swine manure contained 48,000 mg L^-1. Finally, it was found the process was not inhibited by the increasing levels of organic matter in the wastewater evaluated.

Recovery of ammonia and phosphate minerals from swine wastewater using gas-permeable membranes

Gas-permeable membrane technology is useful to recover ammonia (NH₃) from liquid manures. In this study, phosphorus (P) recovery via MgCl₂ precipitation was enhanced by combining it with NH₃ recovery through gas-permeable membranes. Anaerobically digested swine wastewater containing approximately 2300 mg NH₄⁺-N L^-1 and 450 mg P L^-1 was treated using submerged membranes plus low-rate aeration to recover the NH₃ from within the liquid and MgCl₂ to precipitate the P. The experiments included a first configuration where N and P were recovered sequentially and a second configuration with simultaneous recovery. The low-rate aeration reduced the natural carbonate, increased pH and accelerated NH₃ uptake by the gas-permeable membrane system, which in turn benefited P recovery. Phosphorus removal efficiency was >90% and P recovery efficiency was about 100%. With higher NH₃ capture, the recovered P contained higher P₂O₅ content (37-46%, >98% available), similar to the composition of the biomineral newberyite (MgHPO₄·3H₂O).

Multi-stage hybrid subsurface flow constructed wetlands for treating piggery and dairy wastewater in cold climate

This study followed three field-scale hybrid subsurface flow constructed wetland (CW) systems constructed in Hokkaido, northern Japan: piggery O (2009), dairy G (2011), and dairy S (2006). Treatment performance was monitored from the outset of operation for each CW. The ranges of overall purification efficiency for these systems were 70-86%, 40-85%, 71-90%, 91-96%, 94-98%, 84-97%, and 70-97% for total N (TN), NH₄-N, total P, chemical oxygen demand (COD), biochemical oxygen demand, suspended solid, and total Coliform, respectively. The hybrid system's removal rates were highest when influent loads were high. COD removal rates were 46.4 ± 49.2, 94.1 ± 36.6, and 25.1 ± 15.5 g COD m^-2 d^-1 in piggery O, dairy G, and dairy S, with average influent loads of 50.5 ± 51.5, 98.9 ± 37.1, and 26.9 ± 16.0 g COD m^-2 d^-1, respectively. The systems had overall COD removal efficiencies of around 90%. TN removal efficiencies were 62 ± 19%, 82 ± 9%, and 82 ± 15% in piggery O, dairy G, and dairy S, respectively. NH₄-N removal efficiency was adversely affected by the COD/TN ratio. Results from this study prove that these treatment systems have sustained and positive pollutant removal efficiencies, which were achieved even under extremely cold climate conditions and many years after initial construction.

Algae mediated treatment and bioenergy generation process for handling liquid and solid waste from dairy cattle farm

In the present work four algae were tested for their biomass production potential in neat livestock wastewater. Chroococcus sp.1 was found to be the best for biomass production under controlled (2.13 g L(-1)) and outdoor conditions (4.44 g L(-1)) with >80% of nutrients removal. The produced biomass was then digested with cattle dung as cosubstrate. Interestingly, up to 291.83 ± 3.904 mL CH4 g(-1) VS fed was produced during codigestion studies (C/N ≈ 13.0/1). In contrast to this, only 202.49 ± 11.19 and 141.70 ± 2.57 mL CH4 g(-1) VS fed was recorded with algae (C/N ≈ 9.26/1) and cattle dung (C/N ≈ 31.56/1) alone, respectively. The estimated renewable power generation potential of the investigated coupled process was around 333.79-576.57 kW h d(-1) for a dairy farm with 100 adult cattle. However, further scale-up and testing is needed to make this process a reality.