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• In-situ forming nano Fe 3 O 4 @CaFe-LDH in Fe(II)-catalytic wastewater treatment. • Achieving zero Fe sludge and reusing all Fe resources into Fe 3 O 4 @CaFe-LDH. • Advancing organics removal via in-situ forming Fe 3 O 4 @CaFe-LDH. • Fe 3 O 4 modified by oxidation products benefited CaFe-LDH formation. • The proposed strategy was suitable for many organic wastewaters' treatment. Due to its high efficiency, Fe(II)-based catalytic oxidation has been one of the most popular types of technology for treating growing organic pollutants. A lot of chemical Fe sludge along with various refractory pollutants was concomitantly produced, which may cause secondary environmental problems without proper disposal. We here innovatively proposed an effective method of achieving zero Fe sludge, reusing Fe resources (Fe recovery = 100%) and advancing organics removal (final TOC removal > 70%) simultaneously, based on the in situ formation of magnetic Ca-Fe layered double hydroxide (Fe 3 O 4 @CaFe-LDH) nano-material. Cations (Ca2+ and Fe3+) concentration (≥ 30 mmol/L) and their molar ratio (Ca:Fe ≥ 1.75) were crucial to the success of the method. Extrinsic nano Fe 3 O 4 was designed to be involved in the Fe(II)-catalytic wastewater treatment process, and was modified by oxidation intermediates/products (especially those with COO− structure), which promoted the co-precipitation of Ca2+ (originated from Ca(OH) 2 added after oxidation process) and by-produced Fe3+ cations on its surface to in situ generate core-shell Fe 3 O 4 @CaFe-LDH. The oxidation products were further removed during Fe 3 O 4 @CaFe-LDH material formation via intercalation and adsorption. This method was applicable to many kinds of organic wastewater, such as bisphenol A, methyl orange, humics, and biogas slurry. The prepared magnetic and hierarchical CaFe-LDH nanocomposite material showed comparable application performance to the recently reported CaFe-LDHs. This work provides a new strategy for efficiently enhancing the efficiency and economy of Fe(II)-catalyzed oxidative wastewater treatment by producing high value-added LDHs materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract The comparative process performance and efficiency of reactors treating swine wastewater for biogas production at 35 °C were evaluated for three biomass-retaining reactors with different configurations and operational conditions: an anaerobic sequencing batch reactor (ASBR), an upflow anaerobic sludge bed-filter (UBF) and an upflow solid reactor (USR). The maximum volumetric methane production rates of the ASBR, UBF and USR were 1.679, 1.669 and 1.234 L L−1 d−1, respectively, at the OLR of 8 g TS L−1 d−1. Compared with the USR, the ASBR and UBF achieved better performance, which was attributed to more efficient biomass retention indicated by a higher solids residence time-to-hydraulic residence time ratio. The worst performance of the USR was caused by serious washout of sludge. The microorganism distribution profile along with depth showed that methanogenic genera of Methanosaeta and Methanospirillum accounted for 81.37–90.83% and 77.67–88.50% of all archaeal clones in the ASBR and UBF, respectively, and presented non-obvious spatial heterogeneity, while the abundances of methanogenic genera decreased from 93.61 to 4.64% with depth in the USR, instead of an increase in the populations of acid resistant bacteria. Highlights • Three biomass-retaining reactors of the ASBR, the UBF and the USR were compared. • The SRT/HRT ratio was proposed to evaluate the performance of reactor. • The ASBR and the UBF showed better performance than the USR. • Microorganism distribution profile with the reactor' depth was described. • Distinct community structures were formed in the USR due to acidification. [ABSTRACT FROM AUTHOR]

Three sequencing batch reactors (SBRs) were used to investigate the influence of pulse frequencies on the partial nitrification (PN) process in this study. At a total aeration time of 6 min each hour, the aerated frequencies of R1, R2 and R3 were 6, 3 and 2 time h −1 . During the steady period (117-143d), the nitrite accumulation rates (NARs) were 90.80%, 90.71% and 90.23% in R1, R2 and R3, respectively, indicating a steady nitritation was acquired. Activity measurements of the sludge samples taken at day 138 showed the activity of nitrite oxidating bacteria (NOB) was 0, indicating NOBs were successfully suppressed. The ratio of NO 2 − -N to NH 4 + -N in the effluent of R3 was 1.35, which most closely matched the influent of Anammox process. However, the energy efficiency evaluation showed that R1 had the highest actual oxygen transfer efficiency (AOTE) and dynamical efficiency (DE). [ABSTRACT FROM AUTHOR]

Digested swine wastewater effluent was treated in sequencing batch reactors at different hydraulic retention times (HRTs), and the acidification process and its effects on pollutant removal were investigated. At influent chemical oxygen demand (COD) andconcentrations of 540 mg/L and 400 mg/L, respectively, all reactors experienced acidification due to nitrification, and the lowest pH values reached approximately 6. The COD removals were −22.1%, −14.3% and 3.23%, andremovals were 70.1%, 77.0% and 80.7% in reactors with HRTs of 1.25, 2.5, and 5 days, respectively. Practically, no TP was removed. At HRTs of 7.5, 10 and 12.5 days, COD removal reached 4.34%, 5.46% and 8.88%, respectively, andremoval reached 81.1%, 82.3% and 83.0%, respectively. Although longer HRT increased the removal of, it decreased theremoval rate. Acidification significantly restricted the performance of reactors. Low pH not only inhibited the growth and metabolism of microorganisms, but also influenced the availability and toxicity of substrates and products of nitrifying bacteria. Acidification was also responsible for leakage of phosphate from microbial cells and the dissolution of precipitated phosphorus. [ABSTRACT FROM PUBLISHER]

China has a long history of utilizing biogas technology for the treatment of waste and the production of energy. This paper reviews the development and technology of the three types of biogas digesters used in China: household-scale digesters, biogas septic tanks, and biogas plants for the treatment of municipal, industrial, and agricultural waste. The structure of household-scale digesters is simple and practical; the basic type is the fixed-dome digester, also called the hydraulic digester. The biogas septic tank for sewage treatment is a combination of the traditional digester, an anaerobic filter, and a facultative filter. Biogas plants apply several different processes depending on the type of waste treated. The treatment of municipal waste biogas is conducted using the completely stirred tank rector (CSTR). The upflow anaerobic sludge blanket (UASB) is the most common technology used in the anaerobic treatment of industrial wastewater, followed by the CSTR and the anaerobic contact (AC) process. The treatment of agricultural waste mainly employs traditional hydraulic digesters, while newer biogas plants use advanced anaerobic processes such as CSTR and UASB as well as upflow solids reactors (USR) and upflow blanket filter (UBF) reactors. Biogas plants for agricultural waste are classified as small, medium, large and super large based on the scale of biogas production and digester volume. Although small-scale biogas plants are the most common, large-scale biogas plants produce the largest biogas output. With the changes associated with socio-economic development, the growth of household-scale digesters will slow down in the future. As central sewage treatment networks become more widespread, biogas septic tanks will be confined to villages and small towns. The development of biogas plants holds the most growth potential for the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of air mixing on high-solids anaerobic digestion of cow manure was studied. • Optimal air mixing intensity of 37.5 mL/(L·min) enhanced CH 4 production by 13 %. • Air mixing improved the hydrolysis of macromolecular substrate and carbon recovery. • Air mixing enriched SOB, SAOB and aceticlastic methanogen. • Predicted hydrolase demonstrated high abundance under air mixing condition. This study aimed to further investigate the effect of air mixing on the performance of a high-solids anaerobic digestion system and reveal its underlying mechanisms via analyses of carbon conversion, microbial communities and key functional genes. When the air mixing intensity was 12.5, 37.5 and 62.5 mL/(L‧min), compared with the anaerobic digestion without air mixing, the methane yield was increased by 6 %, 13 % and 6 %, respectively. The improved performance was partly attributed to the increased hydrolysis rate of macromolecular substances by 5 %–16 % and carbon recovery in the form of methane by 6 %–7% compared with the controls. Functional flora (Magnetospirillum , Synergistaceae) and hydrolytic metabolism-related enzymes (cellulose, α-amylase) demonstrated higher abundance under air mixing condition, thus promoting the degradation of organic matter and methane production. This work provides some new insights into the use of air mixing to improve anaerobic digestion of high-solids waste. [ABSTRACT FROM AUTHOR]

A study was conducted using a laboratory-scale anaerobic sequencing batch digester to investigate the quantitative influence of organic loading rates (OLRs) on the methane production rate during digestion of swine wastewater at temperatures between 15 °C and 35 °C. The volumetric production rate of methane (R p ) at different OLRs and temperatures was obtained. The maximum volumetric methane production rates (R pmax ) were 0.136, 0.796, 1.294, 1.527 and 1.952 L CH4 L −1 d −1 at corresponding organic loading rates of 1.2, 3.6, 5.6, 5.6 and 7.2 g volatile solids L −1 d −1 , respectively, which occurred at 15, 20, 25, 30 and 35 °C, respectively. A new model was developed to describe the quantitative relationship between R p and OLR. In addition to the maximum volumetric methane production rate (R pmax ) and the half-saturation constant (K LR ) commonly used in previous models such as the modified Stover–Kincannon model and Deng model, the new model introduced a new index (K D ) that denoted the speed of volumetric methane production rate approaching the maximum as a function of temperature. The new model more satisfactorily described the influence of OLR on the rate of methane production than other models as confirmed by higher determination coefficients (R 2 ) (0.9717–0.9900) and lower bias between the experimental and predicted data in terms of the root mean square error and the Akaike Information Criterion. Data from other published research also validated the applicability and generality of the new kinetic model to different types of wastewater. [ABSTRACT FROM AUTHOR]

Laboratory-scale experiments were performed on the dry digestion of solid swine manure in a semi-continuous mode using 4.5 L down plug-flow anaerobic reactors with an organic loading rate of 3.46 kg volatile solids (VS) m −3 d −1 to evaluate the effects of temperature (15, 25 and 35 °C). At 15 °C, biogas production was the poorest due to organic overload and acidification, with a methane yield of 0.036 L CH 4 g −1 VS added and a volumetric methane production rate of 0.125 L CH 4 L −1 d −1 . The methane yield and volumetric methane production rate at 25 °C (0.226 L CH 4 g −1 VS added and 0.783 L CH 4 L −1 d −1 , respectively) were 6.24 times higher than those at 15 °C. However, the methane yield (0.237 L CH 4 g −1 VS added) and the volumetric methane production rate (0.821 L CH 4 L −1 d −1 ) at 35 °C were only 4.86% higher than those at 25 °C, which indicated similar results were obtained at 25 °C and 35 °C. The lower biogas production at 35 °C in dry digestion compared with that in wet digestion could be attributed to ammonia inhibition. For a single pig farm, digestion of solid manure is accomplished in small-scale domestic or small-farm bioreactors, for which operating temperatures of 35 °C are sometimes difficult to achieve. Considering biogas production, ammonia inhibition and net energy recovery, an optimum temperature for dry digestion of solid swine manure is 25 °C. [ABSTRACT FROM AUTHOR]

There are two problems associated with treatment of swine wastewater, low efficiency of anaerobic digestion during winter and poor performance for aerobic treatment of digested effluent. A strategy employing unbalanced distributions of the pollutant mass and wastewater volumes in anaerobic and aerobic units was proposed. To accomplish this, swine wastewater was separated into high content liquid (HCL) and low content liquid (LCL). Three separation ratios of HCL to LCL (v/v), 1:9 (S1), 2:8 (S2), and 3:7 (S3), were evaluated. Anaerobically digestion of the HCL accounted for only 10%, 20% and 30% of the total volume of raw wastewater, but produced 63.38%, 73.79% and 76.61% of the total methane output for S1, S2 and S3, respectively. The mixed liquid of digested effluents of HCL and LCL were treated aerobically using sequencing batch reactors. S2 generated the best performance, with removal efficiencies of 96.98% for COD, 98.95% for NH 3 –N, 91.69% for TN and 74.71% for TP. The results obtained for S1 were not as good as those for S2, but were better than those for S3. Based on methane output from the anaerobic unit and pollutants removal in the aerobic unit, S2 was the most suitable system for the treatment of swine wastewater. Additionally, the anaerobic digestion efficiency of S2 was 282% higher than that of previous techniques employing balanced distribution. Taken together, these findings indicate that unbalanced distribution could improve the efficiency of the anaerobic unit remarkably, while ensuring good performance of the aerobic unit. [ABSTRACT FROM AUTHOR]

In this study, the performance and mechanism of nitrogen removal were investigated in a zero-valent iron-mediated nitrogen removal system operated in co-substrate mode with sodium acetate as the organic carbon source. The results showed that the additional organic matter had the capacity to promote NH 4 +-N and total inorganic nitrogen (TIN) removal with efficiencies of 91.09% and 84.10%, and increases of 60.06% and 75.32% compared with the control group, respectively. The organic matter also stimulated the production of extracellular polymer substances that reduced the passivation and toxicity of iron to microorganisms. The ammonia oxidation activity was 2.5 times higher than that in the control group, and the anammonia oxidation activity and denitrification activity were substantially higher than in the control group with TIN removal efficiencies of 1.02 and 1.19 mgN/(gVSS·d), respectively. In addition, the organic matter increased the enrichment of the heterotrophic denitrification bacterium Diaphorobacter and facultative iron salt-based bacterium Dechloromonas. [Display omitted] • Nitrogen removal can be promoted in a zero-valent iron-mediated biological system operated in co-substrate mode with sodium acetate. • Sodium acetate can increase the enrichment of eterotrophic denitrification bacterium and facultative iron salt-based bacterium. • Sodium acetate can reduce the passivation and toxicity of iron to microorganisms. [ABSTRACT FROM AUTHOR]

Swine wastewater was separated into a solid fraction and a liquid fraction in a biogas plant using a separator with hydraulic wedge-shaped sieve. The liquid fraction (separated slurry) was further separated into concentrated slurry and dilute liquid by gravity sedimentation in the laboratory. Components and methane production of the solid fraction accounted for about 15% of those of the raw wastewater. The majority of the organic matter and phosphorus (more than 60%) were distributed in the concentrated slurry. The concentrated slurry represented 15% of the volume of initial wastewater but produced more than 70% of the total methane production. The condensation of the pollutants and nutrients in the concentrated slurry can facilitate land application of digestate. The dilute liquid with less organic matter and nutrients can be treated easily using less expensive and easier treatment options. [ABSTRACT FROM AUTHOR]

The effects of temperature on biogas production and the heating strategy for anaerobic digestion of swine wastewater were investigated. Through a kinetic model, the maximum volumetric rate of biogas production ( R pmax ) for digestion at 15, 20, 25, 30, and 35 °C were found to be 0.282, 1.189, 1.464, 1.789, and 2.049 L L −1 d −1 , respectively. The temperature–activity coefficient of R pmax was 1.332 at 15–20 °C, 1.043 at 20–25 °C, 1.041 at 25–30 °C, and 1.028 at 30–35 °C. Anaerobic digestion appeared to be more sensitive to temperature variation within 15–20 °C than to variation within 20–35 °C. In terms of energy input–output ratio and total annual cost, the optimal heating strategy is an increase in the fermentation temperature from 15 to 20 °C. [ABSTRACT FROM AUTHOR]

Highlights: [•] Influence of swine slurry concentration on separation effects was investigated. [•] Separation efficiency is a more logical index to evaluate separation effects. [•] After separation, the efficiency of biogas generation was improved markedly. [Copyright &y& Elsevier]

Abstract: This paper aims to demonstrate the benefits of using gravitational sedimentation to separate raw swine slurry into two substances: one thick and highly-concentrated, the other a low-concentration liquid. The volume of the concentrated liquid, accounting for 18.3% of the raw slurry, contained about 61.0% of the chemical oxygen demand or biochemical oxygen demand and could produce about 60% of the total biogas production potential. The digestion temperature could be raised by approximately 22 °C by heating the concentrated liquid with the excess heat of biogas generation but only by about 6.43 °C by heating the raw slurry. The size of digester with the new process could be reduced by two-thirds that of the digester with the conventional process. After separation, the digestate of the concentrated liquid, with nearly three times total nutrient content as that of raw slurry, can readily be used as fertilizer and the low content liquid can easily meet discharge standards after aerobic treatment. [Copyright &y& Elsevier]

Abstract: The feasibility of a new flowchart describing simultaneous hydrogen sulfide removal from biogas and nitrogen removal from wastewater was investigated. It took 30days for the reactor inoculated with aerobic sludge to attain a removal rate of 60% for H2S and NO x –N simultaneously. It took 34 and 48days to attain the same removal rate for the reactor without inoculated sludge and the reactor inoculated with anaerobic sludge respectively. The reactor without inoculated sludge still operated successfully, despite requiring a slightly longer startup time. The packing material was capable of enhancing the removal efficiency of reactors. Based on the concentration of NO x –N and H2S in the effluent, the loading rate and the ability of the system to resist shock loading, the performance of the reactor filled with hollow plastic balls was greater than that of the reactor filled with elastic packing and the reactor filled with Pall rings. [Copyright &y& Elsevier]

Abstract: The performance of sequencing batch reactor (SBR) during post-treatment of digested effluent of swine wastewater was investigated. While operating SBR to treat the digested effluent directly, the performance was very poor with COD removal rate about 10%, and removal rate nearly 50%, with a scarce removal of total phosphorus. The performance apparently improved after adding raw swine wastewater or alkali to digested effluent. Although similar results for removal were achieved adopting both measures, the addition of raw wastewater proved superior in removing total nitrogen and total phosphorus. The addition of raw wastewater obtained effluent COD around 300mg/L which was lower than that after alkali addition i.e. around 550mg/L. Judged from the investment, oxygen demand, sludge yield, biogas production and running cost, the traditional combined anaerobic-SBR process is unfeasible to treat swine wastewater, while the combined anaerobic-SBR process with addition of raw swine wastewater can be a suitable biotechnology. [Copyright &y& Elsevier]

The performance of an Anaerobic-Adding Raw Wastewater-Intermittent Aeration (ANARWIA) process was investigated in a full-scale plant. After 1 year''s operation, a successful treatment for swine wastewater had been developed, without adding alkali or external organic matter. The anaerobic unit can maintain chemical oxygen demand (COD) removal efficiencies of approximately 85% during most times of the year, while removing 5% of NH4 +-N. The anaerobic unit recovered 5000–7000m3 d−1 of biogas in summer and 2500–3500m3 d−1 in winter. In aerobic units, more than 85% of COD could be removed, with a COD concentration of around 300mgl−1 in the effluent. More than 98% of NH4 +-N could be removed with an NH4 +-N effluent concentration of about 10mgl−1. The results confirmed that the addition of raw wastewater to the digested effluent was the key for stable operation of the aerobic unit. It can be concluded that treatment plants using the ANARWIA process can reach similar treatment effects to those plants using the sequence batch reactor (SBR) to directly treat raw wastewater. However, the hydraulic retention time (HRT), the constructing investment for the reactors, the power consumption and the running costs of the ANARWIA process are remarkably lower than those using the direct SBR process. [Copyright &y& Elsevier]

• Operating condition of air mixing for anaerobic digestion was investigated. • The maximum air mixing time was determined. • A full-scale digester was selected to investigate the feasibility of air mixing. • The air mixing was applied in full-scale plant successfully. An air mixing system for anaerobic digestion has been proved to be beneficial for methane production. The aim of the present study was to further investigate the appropriate conditions for air mixing. The effective methane production time (EMPT) was defined to determine the air mixing time in the article. The results indicated that the appropriate aeration intensity was 66.7 mL air per volume of reactor per min and mixing time was 1.5 min. When air mixing time exceeded 3 min on each occasion, total CH 4 production was less than that achieved under the no mixing condition due to a decrease in the EMPT. In addition, the possibility of air mixing was evaluated in an anaerobic full-scale plant comprising a continuous stirred tank reactor. One year of operating data validated the feasibility of air mixing during the anaerobic digestion of swine wastewater. [ABSTRACT FROM AUTHOR]

• A new mixing method for anaerobic digestion was proposed. • Methane production from air mixing was higher than from biogas mixing. • Mixing and the microaerobic environment affected CH 4 production differently. • Air mixing facilitated hydrolysis and VFA generation and consumption. This study proposed a new mixing method for anaerobic digestion treating animal wastewater using air as gas source of agitation (named "air mixing") and demonstrated its feasibility by comparing with other mixing modes. The results indicated that the methane production for air mixing was increased by 6.4%, 11.9% and 19.6% compared with biogas mixing, mechanical mixing and no mixing. Air mixing improved the mass transfer and the homogeneous mixing time was shortened from 10 min of mechanical mixing to 1.5 min at the same power input. A transient microaerobic environment was created by air mixing, which increased the hydrolysis efficiency by 1.7–11.4% compared with biogas mixing and facilitated VFAs generation and consumption, as well as promoted the syntrophic relationship between facultative bacteria and hydrogenotrophic methanogens. The relative contribution of the improvement of mass transfer and the reaction of microaerobic environment to methane production was 62.9% and 37.1%, respectively. [ABSTRACT FROM AUTHOR]

The performance of an autotrophic nitrogen removal process to treat digested piggery wastewater (DPW) was investigated by gradually shortening the HRT and enhancing the DPW concentration during 390 days of operation. The results showed that the total nitrogen removal rate and efficiency reached 3.9 kg-N m −3 day −1 and 73%, which were significantly higher than the levels reported previously. A high relative abundance of Nitrosomonas (4.2%) and functional microbes (12.15%) resulted in a high aerobic ammonium oxidizing activity (1.25 ± 0.1 g-N g VSS −1 d −1 ), and a good settling ability (SVI, 78.42 mL g −1 SS) resulted in a high sludge concentration (VSS, 11.01 g L −1 ), which laid a solid foundation for the excellent performance. High-throughput pyrosequencing indicated that, compared with synthetic wastewater, the DPW decreased the relative abundances of every functional group of nitrogen removal microbes, and increased relative abundances of anaerobes (15.7%), sulfur-oxidizing bacteria (9.4%) and methanogens (40.8%). [ABSTRACT FROM AUTHOR]

This research investigated the startup of the partial nitritation (PN) process in a sand filter at ambient room temperature (5.5–27 °C) to produce an effluent suitable for the subsequent anaerobic ammonium oxidation (anammox) process. A naturally ventilated sand filter was used to treat anaerobically digested effluent of swine wastewater. Startup strategy of gradual step increases in the influent ammonium nitrogen concentration and pH successfully achieved the PN process. The principal cause for nitrite accumulation was high free ammonia concentration (up to about 20 mg L −1 ). An effluent with a nitrite-to-ammonium ratio of 1.02 was obtained, with the optimal influent ammonium nitrogen concentration of 600.0 mg L −1 and pH of 8.09. Overall, the PN process can be maintained in a sand filter without forced aeration, and coupling with the subsequent anammox process to achieve completely unpowered autotrophic nitrogen removal. [ABSTRACT FROM AUTHOR]

Researchers have long been captivated by the remarkable swimming abilities of fish, inspiring the development of robotic counterparts that mimic their undulatory movements in pursuit of achieving comparable efficiency and maneuverability. While a flexible body has the potential to enhance the performance of robotic fish, it is crucial to note that excessive flexibility does not necessarily correlate with improved functionality. Consequently, this paper introduces an innovative design for a robotic fish equipped with a fully flexible tail capable of dynamically adjusting its stiffness in response to varying working conditions. The fishtail incorporates a compressible bionic spine, constructed from silicone. This design enables the robotic fish to modify its body stiffness promptly by either compressing or releasing the elastic spine. This paper delves into the theoretical derivation of the flexible spine's stiffness and proposes a calculation method for the stiffness of a periodically heterogeneous flexible beam. To further elucidate the system, a dynamic model of the flexible fish is established using the pseudo-rigid body model and the Lagrangian method. Subsequently, simulations and experiments are conducted to assess the impact of variable stiffness on swimming velocities and COTs(Cost of Transport) across different frequencies. The vibration of the passive joint and the phase difference between the two joints are analyzed incorporately to elucidate the influence of stiffness and frequency on swimming performance. This comprehensive approach aims to provide valuable insights into the interplay of these factors in optimizing the efficiency and maneuverability of robotic fish. • Variable Stiffness Design: Present a novel robotic fish with a fully flexible tail, dynamically adjusting its stiffness for diverse working conditions. • Compressible Bionic Spine: The tail incorporates a compressible bionic spine, enabling modification of stiffness by compressing or releasing it. • Theoretical Derivation of the Stiffness of flexible beam: Introduces a calculation method for the stiffness of a periodically heterogeneous flexible beam. • Comprehensive Analysis: Evaluate the impact of variable stiffness on swimming velocities and Cost of Transport (COT) across different frequencies. [ABSTRACT FROM AUTHOR]

[Display omitted] • AnMBR was used to treat real municipal wastewater. • CO 2 % was reduced to balance with the alkalinity in carbonate equilibrium system. • Successful pH control was accomplished by in-situ CO 2 removal. • Biogas upgradation, pH control and reduction of GHG were realized in the AnMBR. This study addressed a less-reported issue: the insufficient alkalinity encountered when anaerobic membrane bioreactors (AnMBRs) are used to treat municipal wastewater (MWW). In the present study, a 20-L AnMBR was initiated at an MWW treatment plant. During the initial startup, a continuous decrease in pH was observed. Through the analyses of the balance between HCO 3 –/CO 2 in the biogas and alkalinity in the reactor, the cause of pH instability was determined to be that the alkalinity could not balance the acidity induced by the continuous dissolution of CO 2 from biogas in the liquid phase. Therefore, this study employed the in-situ removal of CO 2 from biogas using soda lime to reduce the CO 2 partial pressure, thereby achieving stable control of the pH in the reactor. This study provides valuable experience and technical support for anaerobic processes for treating low-alkalinity MWW in the future applications. [ABSTRACT FROM AUTHOR]

Severe inhibition by volatile fatty acids (VFAs) frequently occurs during the dry anaerobic digestion of kitchen waste at high organic load rate (OLR), leading to decreased biogas production and even the collapse of the anaerobic digestion system. In this study, VFAs accumulation was significantly reduced by adding powder-activated carbon (PAC) or alkaline additives (AA), thus restoring the collapsed system to a stable operating state. With the addition of PAC or AA, the maximal OLR reached 11.14 g VS/(L·d), which was 30 % higher than observed without any additives (control group), while the VFAs concentration was maintained below 3000 mg/L. At this OLR, the volumetric biogas production rate stabilized at 5.1 L/(L·d) in the presence of PAC and AA, while that of the control group gradually decreased to zero. The VFAs concentration with PAC addition was 86 % lower than that of the control group, possibly because PAC might stimulate the formation of direct interspecies electron transfer between syntrophic bacteria and methanogens (Methanosarcina), thereby promoting VFAs degradation. The addition of AA, which resulted in a 95 % decrease in ammonia-nitrogen concentration, can provide a good growth environment for the microorganisms involved in acidogenesis and hydrogenotrophic methanogenesis. [Display omitted] [ABSTRACT FROM AUTHOR]

Biochar production using swine manure (SM) from large-scale piggeries is increasingly needed. However, little is known about the economic feasibility for SM biochar production. Herein, SM biochar production was simulated via Aspen Plus, and techno-economic model was applied to calculate the net present value (NPV), internal rate of return (IRR), and discounted payback period (DPP) for SM biochar production with a processing capacity of 8000 tons SM per year. Results suggest that this project is susceptible to biochar selling price and operation cost. When the biochar price is > 116 USD/ton, the NPV is positive. When the biochar selling price is increased from 154 to 193 USD/ton, the IRR is increased from 11 % to 41 %. The DPP analyses show that the investment payback period for this project is 4.6 years. Moreover, compared to conventional SM treatment routes, valorization of SM into biochar in large-scale piggery in China has a shorter investment period. Finally, this study suggests that swine manure biochar production in large-scale piggeries in China is profitable, deserving investment. [Display omitted] • Swine manure biochar production in large-scale piggeries in China is assessed. • The biochar price and operating costs have significant impacts on the project. • At a biochar price of 116 USD/ton, the net present value is zero. • At a biochar price of 154 USD/ton, the internal return rate is 11 %. • The payback period is 4.6 years, with profitability in the fifth year. [ABSTRACT FROM AUTHOR]

The widespread use of antibiotics has led to a severe pollution issue with antibiotic resistance genes (ARGs), which poses a significant threat to both ecological environments and human health. In this study, we developed an iron-based nanocopper bimetallic material (Fe-nCu) for the efficient removal of ARGs. Our results indicate that nCu can attach to the surface of iron, forming aggregated copper nanoclusters resembling wheat ears. The composition of Fe-nCu particles consists of 75.90 % iron and 20.95 % copper. Fe-nCu demonstrates a unique capability in eliminating ARGs, achieving removal efficiencies of 3.75 and 4.36 logs for intracellular and extracellular ARGs, respectively. Furthermore, Fe-nCu remains stable in complex water environments and is unaffected by organic substances in the water. This material induces oxidative stress in cells within a short period, leading to an imbalance in intracellular redox levels and resulting in cell membrane damage. nCu causes severe membrane damage to E. coli , penetrating the cell due to its size advantage, which leads to the encapsulation and internalization of E. coli by the copper nanoparticles. Once inside, the nCu particles cleave DNA and disrupt the function of ARGs. This study not only provides a cost-effective material for the removal of ARGs but also offers an in-depth understanding of the action mechanism of Fe-nCu, presenting a novel pathway for inhibiting the propagation of ARGs. [Display omitted] • Iron-based nanocopper efficiently removes ARGs. • 3.75 logs of iARGs and 4.36 logs of eARGs removal were achieved within 30 min • Iron-based nanocopper induces oxidative stress and cell membrane damage in ARB. • Nanocopper can be internalized inside ARB. • Iron-based nanocopper causes DNA breaks and disrupts ARGs functioning. [ABSTRACT FROM AUTHOR]

A large amount of greenhouse gas nitrous oxide (N 2 O) will be produced during the biological nitrogen removal process for organic wastewater of low C/N ratio. One of the effective methods to solve this problem is to incorporate inexpensive carbon source. In this study, raw wastewater (RW) from pig farm, that was not anaerobically digested, was utilized as exogenous carbon in both A/O and SBR aerobic reactor to treat liquid digestate with high ammonia nitrogen and low C/N ratio. The results showed that N 2 O emission in SBR was higher than that of A/O process under the same nitrogen load. The N 2 O conversion in the biological nitrogen removal process was investigated by the strategy of integrating stable isotope method and metagenomics. The δO18-N 2 O, δN15-N 2 O, and SP values of the SBR were closer to the denitrification values of Ammonia-Oxidizing Bacteria (AOB) than those of A/O. The abundance of AOB in the SBR reactor was higher than that in the A/O reactor, while the abundance of denitrifying bacteria was lower. The amoA/B/C gene abundance in the SBR was greater than that in the A/O, and the NOS gene abundance was the opposite. The results indicated that both AOB denitrification and bacterial denitrification led to the increase of N 2 O emissions of the SBR. [Display omitted] • RW as source of exogenous carbon source improved nitrogen removal while reducing N 2 O emissions. • Insufficient carbon source would result in more N 2 O emission. • A/O had more N 2 O emission reduction potential than SBR. • The denitrification of ammonia oxidizing bacteria (AOB) resulted in more N 2 O emission from the SBR. [ABSTRACT FROM AUTHOR]

To date, the anaerobic digestion (AD) of chicken manure has been difficult because of the inhibition caused by high ammonia nitrogen levels. In this study, granular activated carbon (GAC), zeolite, and medical stone (MS) were added to improve dry AD of chicken manure. The semi-continuous processes amended with GAC were stable throughout the experiment despite the presence of extremely high NH 4 +-N (∼11 500 mg L−1) and NH 3 –N (∼2350 mg L−1) levels. By adding GAC, the methane yield increased from 0.115 L g−1 VS in phase I to 0.128 L g−1 VS in phase III. The methane yield of zeolite group, MS group and control group decreased from ∼0.041 to 0.098 L g−1 VS in phase I to ∼0.005–0.012 L g−1 VS in phase III. The addition of zeolite improved dry AD during the early stage, but there was no improvement when MS was added. Different hydrolysis efficiency of macromolecular compounds and GAC adsorption of ammonium contributed to the improved biogas production, but the key reason for the improvement was promotion of the syntrophic acetate oxidation-hydrogenotrophic methanogenesis pathway. In contrast to previous studies, the GAC was not lost along with the digestate discharge because the activated carbon was packed in nylon bags with holes. [Display omitted] [ABSTRACT FROM AUTHOR]

l The enrichment of AOB under K+ stress ensured the efficient ammonia oxidation. l High K+ stress inhibited NOB activity and deteriorates the NO 2 −-N oxidation. l High K+ stress accelerates sludge settlement and enriches biomass in SBR. l The K+ concentration do not exceed 5.23 g/L to ensure efficiency of SBR. The recycling reverse osmosis (RO) membrane concentrate of some high-ammonia nitrogen (NH 4 +-N) organic wastewater to the biological unit could cause potassium ion (K+) accumulation, thereby affecting the removal of NH 4 +-N by activated sludge. Thus, the effects of high K+ stress on activated sludge nitrification performance was studied. The results showed that the high K+ stress promoted the floc sludge to produce more extracellular polymers (EPS), which accelerated the sludge sedimentation and enriched the biomass in sequential batch reactors (SBRs). The ammonia oxidation process and nitrite (NO 2 --N) oxidation process were further analyzed in the nitrification process. High K+ stress enriched ammonia oxidizing bacteria (AOB), which ensured the efficient ammonia oxidation process in SBRs, and ensured the removal rate of NH 4 +-N was maintained above 93%. However, high K+ stress (15g/L KCl) inhibited the activity of NO 2 −-N oxidizing bacteria (NOB) and reduced the abundance of NOB, thus leading to the accumulation of NO 2 −-N, and finally worsened the nitrification performance of activated sludge. In short, the performance of activated sludge will not be inhibited when the K+ in the wastewater does not exceed 5.23 g/L. The results could provide a reference for the optimization of the biological performance in treating high-NH 4 +-N organic wastewater with activated sludge coupled RO membrane treatment process. [Display omitted] [ABSTRACT FROM AUTHOR]

Biogas industry in China is developing rapidly. This is particularly the case for livestock farm biogas plants, which are built to treat manure and wastewater. Managing the liquid digestate (LD) generated by anaerobic digestion of livestock wastes is becoming a bottleneck, restricting the sustainable development of the biogas industry in China. The separation of livestock breeding and arable farming, caused by rapid intensive animal husbandry development, is the main reason for the LD problem. Researchers, government representatives, and biogas plant operators in China have invested significant research efforts to maximize biogas‐linked agro‐ecosystem balance, which is considered as an important solution to the LD problem. This article reviewed these studies and proposed several solutions from the following four aspects: breeding mode, waste treatment mode, LD transportation mode, and LD utilization mode. One proposal is to reduce the scale of newly built livestock farms and disperse them in farmland, by promoting the "company + agent" livestock breeding mode. In this approach, farm scale would be based on the size of available farmland, and would allow for the use of LD in the near farmland. The second approach involves the intense separation of the livestock slurry and further transportation of the LD produced by the thick slurry. The third one is to expand the possible distances for transferring LD, using a pipe network or vehicle supervised by a professional third party. Finally, the development of high value‐added products and bringing them to market is the ultimate solution for the future. [ABSTRACT FROM AUTHOR]

The effect of granular activated carbon (GAC) on batch dry anaerobic digestion of swine manure was studied under different temperatures and ammonia concentrations. At 20 °C, 35 °C and 55 °C, the digester was inhibited when the initial total ammonia nitrogen (TAN) concentration reached 2500, 3500 and 3500 mg/L, respectively. The degradation of protein at 20 °C decreased as ammonia concentration increased, but the process was little effected by ammonia at 35 °C and 55 °C. Results showed that when the initial TAN increased from 500 to 3500 mg/L, the TAN produced at 20 °C decreased by 526 mg/L, but it only decreased by 20 and 145 mg/L at 35 °C and 55 °C, respectively. Adding GAC improved the methane production rate by 8.4%–45.6%. Under adverse condition (20 °C and TAN = 3500 mg/L), GAC has the most positive effect on methane production. In which the maximum methane potential and maximum methane production rate increased by 38.8%, 34.1% respectively, the lag time shortened by 23.1%. The dominant bacteria at 20 °C and 35 °C were Tricibacter, Terrisporobacter and Clostridium_sensu_stricto_1 , and Methanosaeta was the dominant archaea. At 55 °C, the dominant bacteria were Hydrogenispora and Ruminiclostridium_1, and the dominant archaea were Methanosaeta , Methanosarcina and Methanoculleus. • GAC effect on dry AD under dual stress of ammonia and temperature was studied. • The CH 4 production at 20 °C was most vulnerable to ammonia concentration. • GAC enhanced the CH 4 production rate at any of the involved treatment. [ABSTRACT FROM AUTHOR]

Most anaerobically digested wastewaters have high concentrations of suspended solids, while little is known about whether they adversely affect the performance of the autotrophic nitrogen removal process. In this work, using air-lift internal circulation reactor we studied the effect of suspended solids on the autotrophic nitrogen removal process by adding 600–900 mg/L suspended solids from digested swine wastewater to the influent (R–SS). The results showed that during the formation of autotrophic nitrogen removal granular sludge, suspended solids containing Ca, Mg, Cu P, and Pb can enter the granular sludge, occupy the ecological niche of anammox bacteria, lead to loose internal structure, and damage the internal anoxic environment. It then reduces the settling performance in the R–SS, causes heavy wash-out of granular sludge from the R–SS reactor (2.5 times more than the control, R–CK), and finally reduces the maximum nitrogen removal rate of the autotrophic nitrogen removal process from 5.16 kg N/m3/d to 4.31 kg N/m3/d. Meanwhile, the metagenomic analysis showed that suspended solids reduce the relative abundance of reads from key nitrogen genes of anammox bacteria yet increases reads from both nitrite-oxidizing and denitrifying bacteria, especially nir and nor genes. Further analysis of 16 highly abundant genomes assembled via metagenomics showed that suspended solids decrease the relative abundance of Kuenenia _seed103, an anammox bacterium, from 13.36% (R–CK) to 11.03% (R–SS). Since suspended solids can act as a carbon source for denitrifiers to compete with nitrite or nitric oxide with anammox bacteria, the denitrifier community has progressed from a simple denitrifier consisting of only one or two denitrification steps (nar or nos) that acts as an ammonia and nitrite sink to a complete one that directly reduces nitrite to nitrogen gas. This study will lay a good foundation for its application in wastewater treatment. [Display omitted] • Suspended solids in swine digested wastewater leads to a decrease in the nitrogen removal rate. • Suspended solids increase sludge losses more than 2.5 times. • Suspended solids with lots of heavy metals changes the granulation process of anammox sludge. • Metagenome showed that suspended solids reduce the abundance of anammox bacteria and key genes. • Suspended solids change the role of denitrifiers from substrate sink of anammox to competitor. [ABSTRACT FROM AUTHOR]

• An aeration sedimentation integrated microaerobic reactor were developed. • When the HRT was 4.45 h, ASIMR achieved the highest NRR, 3.15 kg·(m3 d)-1. • When the HRT less than 4.45 h, the performance of ASIMR was deteriorated. • The deterioration was due to the loss of nitrified sludge and iron deficiency. • ASIMR is suitable for scaling up of PN/A process to treat digested effluent. The existing microaerobic reactors for PN/A process have the drawbacks of complex structure and hard to scale-up in full scale application. Aiming at these problems, we have designed new aeration sedimentation integrated microaerobic reactor (ASIMR). The feasibility of ASIMR for PN/A processes and the optimal HRT were explored by gradually reducing the hydraulic retention time (HRT). When the HRT was 4.45 h and the NLR was 3.98 kg·(m3·d)-1, ASIMR achieved the highest nitrogen removal performance, with the ammonia nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (NRE) of 90.5 % and 79.2 %, respectively, and the total nitrogen removal rate (NRR) could reach 3.15 kg·(m3·d)-1. When HRT decreased to 3.60 h with the NLR of 4.76 kg·(m3·d)-1, the performance deterioration was observed, with ARE and NRE decreasing to 35.9 % and 12.4 %, and NRR decreasing to 0.59 kg·(m3·d)-1. The main reasons for the decrease in nitrogen removal performance were overhigh hydraulic load in the sedimentation zone which led to the loss of nitrifying sludge. The loss of nitrifying sludge in turn reduced the efficiency of ammonia nitrogen removal resulting in the accumulation of free ammonia (FA) which inhibited the activity of nitrogen removal functional bacteria. Although reactor performance deteriorated at too low HRT, when the HRT was much than 4.45 h, ASIMR could achieve a good performance for nitrogen removal owe to the combined action of reactor design, enriched nitrified and anammox sludge as inoculum, and dissolved oxygen control. Except good nitrogen removal performance, ASIMR has another advantage, such as simple structure, low cost for manufacture, and more suitable for engineering scale-up in full scale application. [ABSTRACT FROM AUTHOR]

[Display omitted] • N transformation wasn't affected by K+ or Na_K combined stress at 2.86% salinity. • Na+ stress decreased NH 4 +-N removal and caused the serious NO 2 –-N accumulation. • Na+ stress significantly enhanced the expression of narH gene at 2.86% salinity. • Na+ stress resulted in the high abundance of denitrifiers especially Ottowia. High salinity has attracted much attention because of its serious effects on functional microorganisms during wastewater treatment. Most of the research on salt stress has investigated the impacts on individual nitrification or denitrification by controlling the total salinity of wastewater. However, the effects and mechanisms of the ion composition on simultaneous nitrification and denitrification (SND) are poorly understood under salt stress. Na+ and K+ are important components of salt stress because of their high contents and difficult removal characteristics from wastewater. This study systematically investigated the individual and combined effects of Na+ and K+ on SND using continuous tests with the increasing salinity. Compared with the control, K+ and combined stresses had no effects on nitrogen transformation and removal within 2.86% salinity. However, Na+ stress decreased ammonia nitrogen (NH 4 +-N) removal and caused the serious nitrite nitrogen (NO 2 –-N) accumulation at 2.36% and 2.86% salinities. Moreover, Na+ stress significantly enhanced narH expression and the relative abundance of denitrifying bacteria, especially Ottowia at 2.86% salinity. Na+ stress results in an out-of-synch problem between NO 2 –-N production and consumption by destroying the balance of the bacterial community. This study indicates that Na+ concentration and accumulation should be considered in the SND for nitrogen removal. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Bacteria from LD SBR effluent and Chlorella can form stable MBC. • The established stable MBC facilitates the continuous nutrient removal. • The established stable MBC promotes the biomass and lipids accumulation. • The established stable MBC facilitates the formation of bioflocculation. Abstract In this study, a microalgal-bacterial consortium (MBC) was established in liquid digestate (LD) by optimizing sequencing batch reactor (SBR) operating parameters and microalgae inoculation to address the abovementioned challenges. The bacteria from LD SBR-Activated Sludge System effluent under the optimum conditions of 25 °C, 7.0 g/L MLSS, 5 mg/L DO concentration, and 6 h hydraulic retention time with 0.5 mg/L DW Chlorella sp. BWY-1 could form stable MBCs outdoors in an airlift photoreactor. The stable MBC facilitates the continuous removal of nitrogen and phosphorus, promotes the accumulation of biomass and lipids, and contributes to the improvement of the sedimentation. The results from this study provided a new technique for the purification and utilization of LD, more importantly decreasing the environmental threat caused by improperly processed LD. [ABSTRACT FROM AUTHOR]

With high percentage of washing water, swine wastewater is characterized by large volume and low concentration of total solids. Thus, in treating swine wastewater, it is relatively difficult to heat digesters, resulting in low methane production at low ambient temperatures (ATs). To increase methane production from swine wastewater, this study proposed a novel “two-step heating (TSH)” mode with the same energy consumption as a one-step process for anaerobic digestion. Compared with the traditionally heated digesters (one-step heating), the digestion temperature in TSH digesters increased by 3.50–10.50 °C under the assumption of no heat dissipation and by 3.30–9.25 °C in the actual experiments. Although methane production of the TSH digesters improved by 15% in our experiments, the improvement was far less than theoretically estimated. This was mainly caused by short hydraulic retention time and sludge washout in the digesters. Moreover, the acetoclastic methanogenesis, accomplished by genus Methanosaeta , was the major methanogenesis pathway at low temperatures in both the TSH and conventional heating modes. However, the relative abundance of syntrophic bacteria and hydrogenotrophic methanogens in TSH mode were both higher than in the digesters operation in conventional heating mode when the atmospheric temperature was below 10 °C. [ABSTRACT FROM AUTHOR]

This study presents a novel strategy for remedying acidification and improving the removal efficiency of pollutants from digested effluent by using Zero-Valent Iron (iron scraps) in a sequencing batch reactor. Through this strategy, the pH increased from 5.7 (mixed liquid in the reactor without added ZVI) to 7.8 (reactors with added ZVI) because of Fe 0 oxidation and NO 3 − reduction. The removal efficiencies of COD increased from 11.5% to 77.5% because of oxidation of ferric ion and OH produced in chemical reactions of ZVI with oxygen and because of flocculation of iron ions. The removal efficiencies of total nitrogen rose from 1.83% to 93.3% probably because of autotrophic denitrification using electron donors produced by the corrosion of iron, as well as the favorable conditions for anammox due to iron ions. Total phosphorus increased from −25.8% to 77.1% because of the increase in pH and the precipitation with iron ions. [ABSTRACT FROM AUTHOR]

Nitrification is an acidifying process that requires the addition of external alkalinity because of the alkaliphilic nature of the most ammonia-oxidizing bacteria. In this study, aerobic activated sludge was used as inoculum in an internal loop air-lift reactor, which resulted in successful enrichment of acid-tolerant nitrifying (ACIN) sludge at pH 6.0 by sequential addition of tea orchard soil suspension. The results showed that ACIN sludge had a remarkable acid tolerant capability with a volumetric ammonia conversion rate of 1.13 kg N m −3 day −1 . ACIN sludge showed a higher maximum specific ammonia conversion rate (0.29 g N g −1 VSS day −1 ) than neutrophilic nitrifying sludge (0.14 g N g −1 VSS day −1 ) at pH 6.0 and had good resistance against pH fluctuations, with a maximum specific ammonia conversion rate (0.584 g N g −1 VSS day −1 ) at pH 7.5. Microbial community analysis indicated that the higher abundance of acid tolerant Nitrosospira and ammonia-oxidizing archaea laid a solid foundation for the remarkable acid-tolerant capability of ACIN sludge. [ABSTRACT FROM AUTHOR]

Partial nitritation (PN) is the controllable bottleneck of the combined PN-anaerobic ammonium oxidation process, because it has a low nitrogen conversion rate. In this study, a “co-culture and screening” technology was developed to start up PN, and a dual dissolved oxygen-hydraulic retention time (DO-HRT) control strategy was developed to regulate the NH 4 + -N/NO 2 − -N ratio. The results showed that PN could be successfully started up and it had a high nitrogen loading rate and ammonium conversion rate (9.42 kg-N m −3 day −1 and 4.74 kg-N m −3 day −1 ), respectively. A response surface methodology (RSM) with a central composite design (CCD) was used to optimize the parameters of DO and HRT. When DO and HRT satisfied the relationships 0.66–0.5 × DO ≤ HRT ≤ 0.79–0.53 × DO and 0.5 mg L −1 ≤ DO ≤ 0.75 mg L −1 , the performance of PN was excellent with an NH 4 + -N/NO 2 − -N ratio ranging from 1:1.04 to 1:1.47, an ammonium conversion efficiency of 53.6–62.1% and a nitrite accumulation efficiency greater than 90%. The excellent performance of PN process was attributed to the high specific activity of sludge (3.69 g-N g −1 VSS day −1 ), the predominance of ammonia-oxidizing bacteria, Nitrosomonas , and the inhibition of nitrite-oxidizing bacteria, Nitrospira . [ABSTRACT FROM AUTHOR]

Four reactors were initiated to study the effect of inoculum and sulfide type on the simultaneous hydrogen sulfide removal from biogas and nitrogen removal from swine slurry (Ssu-Nir) process. Anaerobic sludge, aerobic sludge, and water were used as inocula, and NaS and biogas were used as a sulfide substrate, respectively. Additionally, 454 pyrosequencing of the 16S rRNA gene was used to explore the bacterial diversity. The results showed that sulfur-oxidizing bacteria ( Thiobacillus, 42.2-84.4 %) were dominant in Ssu-Nir process and led to the excellent performance. Aerobic sludge was more suitable for inoculation of the Ssu-Nir process because it is better for rapidly enriching dominant sulfur-oxidizing bacteria ( Thiobacillus, 54.4 %), denitrifying sulfur-oxidizing bacteria (40.0 %) and denitrifiers (23.9 %). Lower S removal efficiency (72.6 %) and NO removal efficiency (<90 %) of the Ssu-Nir process were obtained using biogas as a sulfide substrate than when NaS was used. For the Ssu-Nir process with biogas as the sulfide substrate, limiting HS absorption caused a high relative abundance of sulfur-oxidizing bacteria, Thiobacillus (84.8 %) and Thiobacillus sayanicus (39.6 %), which in turn led to low relative abundance of denitrifiers (1.6 %) and denitrifying sulfur-oxidizing bacteria (24.4 %), low NO removal efficiency, and eventually poor performance. [ABSTRACT FROM AUTHOR]

In this study, two experiments were conducted to evaluate the impact of substrate concentrations on methane potential and degradation kinetics of substrate. The biochemical methane potential (BMP) tests in Experiment I were performed at a constant inoculum to substrate ratio (ISR), whereas, different ISRs were applied in Experiment II. Results obtained from Experiment I revealed that methane potential of substrate increased at a saturating trend with higher substrate concentrations, and could differ by up to 30% between the lowest and highest investigated concentrations. The results of Experiment II verified the results of Experiment I, and further showed that this trend also occurs when the substrate concentration is regulated with ISRs. In contrast, substrate concentration had no significant impact on the degradation kinetics. It was concluded that dilutions should be avoided when the substrate concentration is lower than 10 g VS/L in order to avoid underestimations of methane potential from BMP test. [ABSTRACT FROM AUTHOR]

Tobacco is widely planted across the world especially in China, which means that a large amount of tobacco waste needs to be treated. This study investigated the biogas fermentation of tobacco stalks co-digested with different biomass feedstocks and the inactivation of Tobacco mosaic virus (TMV), Cucumber mosaic virus (CMV) by anaerobic digestion. Results showed that the maximum methane yield of tobacco stalks at 35 °C was 0.163 m 3 CH 4 ⋅kg VS −1 , which was from the co-digestion of tobacco stalks, wheat stalks and pig manure. The largest VS removal rate of tobacco stalks was 59.10%. Proven by indicator paper stripe, half-leaf lesion and RT-PCR, CMV could be inactivated by mesophilic and thermophilic anaerobic digestion, whereas TMV could be only inactivated by thermophilic anaerobic digestion over 20 days. These results suggested that using tobacco stalks as feedstock for anaerobic digestion and applying the digested residue and slurry to Solanaceae crop land are feasible. [ABSTRACT FROM AUTHOR]

Sequencing batch reactor (SBR) and anoxic/oxic process (A/O) are the predominant process for the treatment of digested effluent of swine wastewater. However, which is optimal process for their treatment? The question remains unclear. In this study, lab-scale SBR and A/O anoxic/oxic process were employed to treat digested effluent with addition of different proportion (v/v 10%–40%) of raw swine wastewater in order to make clear performance difference of the pollutant removal. The results showed that the NH 4 +-N and TN removal efficiencies of the A/O were more than 5.5 and 6.0 percentage points higher than that of the SBR respectively when the proportion of added raw wastewater was 20% (low COD/N ratios), due to the limitations caused by the low BOD 5 concentration and the higher dissolved oxygen concentration during the anoxic phase. While, the NH 4 +-N and TN removal efficiencies of the SBR were more than 3.3 and 14.3 percentage points higher than that of the A/O respectively when the added raw wastewater proportion was 40% (high COD/N ratios), owing to limitation by the lower mixed liquor recycling ratio in the A/O. The sludge activity tests and microbial community analysis showed that the SBR displayed higher ammonia-oxidizing and anammox activity, whereas the A/O revealed higher denitrifying activity. These results uncovered that there are differences when A/O and SBR were employed to treat digested effluent and provide good insights for process selection when treating different C/N ratios wastewater. [Display omitted] • A/O and SBR display opposite performance in treating digested effluent. • The A/O could be suitable for treatment of wastewater with a low C/N ratio. • The SBR could be appropriate to treat wastewater with a high C/N ratio. • The differences were due to BOD 5 in anoxic phase and feeding strategy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Energy self-sufficiency in CAO systems were studied using Monte Carlo simulation. • The MPC-CAO system outperformed C-CAO and PRB-CAO systems. • Organic matter content and ambient temperature influenced net energy production. • CAO system integrated with matters capture exhibited 80% energy self-sufficiency. • Balancing energy input and output is the key of realizing energy self-sufficiency. A combined anaerobic–aerobic (CAO) system is a feasible animal wastewater treatment approach, and one of the prerequisites for its sustainable application is to realise energy self-sufficiency. Here, we built an energy balance model to calculate the probability of achieving energy self-sufficiency in three CAO systems with multiple uncertainties through Monte Carlo simulation. Upon comparison with the conventional combined anaerobic–aerobic (C-CAO) system and partial raw wastewater bypassed combined anaerobic–aerobic (PRB-CAO) system, the matters pre-captured combined anaerobic–aerobic (MPC-CAO) system displayed the highest probability (45.5%) and stability (with 10.9% coefficient of variation) in achieving energy self-sufficiency with the uniformly distributed input parameters. The uncontrollable factor of ambient temperature mainly contributed to the CAO system's net energy production among all input parameters. However, operating with the optimal control parameters of anaerobic digestion temperature (approximately 20 °C for C-CAO and PRB-CAO systems, 25–35 °C for MPC-CAO system) and organic loading rate (OLR) (50% of simulated maximum OLR) reduced the ambient temperature effect, thereby increasing the probability of energy self-sufficiency. And increasing the organic capture efficiency further reduced the effect of ambient temperature on net energy production of the MPC-CAO system. In addition, the probability of achieving energy self-sufficiency in the MPC-CAO system was more than 80%, with 30–50% of nitrogen captured simultaneously with organic matter and the direct use of anaerobic digestate (e.g., as fertilizer). These findings indicate that capturing more matter and increasing the capture efficiency is highly conducive for achieving energy self-sufficiency in CAO systems. Meanwhile, Monte Carlo simulation efficiently locates the key factors determining the CAO system's energy production performance from the different levels of uncertainty of multi-parameters, which is demonstrated as a time saving method for further system evaluation, design and upgrade. However, additional factors such as capital investment, social and environmental impacts should also be further considered for increasing the robustness of energy balance simulation model and providing a comprehensive assessment of CAO system for animal wastewater treatment. [ABSTRACT FROM AUTHOR]

The effects of granular activated carbon (GAC) and organic load rate (OLR) on semi-continuous dry anaerobic digestion of swine manure were investigated. A kinetic model of anaerobic digestion provided a good description of the quantitative effect of OLR on the methane production rate, with a maximum methane production rate of 1.46 and 1.60 LCH 4 /L/d without and with addition of GAC, respectively; this rate reached approximately 80% of the reported maximum methane production rate for the wet anaerobic digestion of swine manure, thus suggesting favorable application prospects of dry anaerobic digestion of swine manure. With an increase in OLR from 1.0 to 5.0 g TS/L/d, the ammonia nitrogen concentration increased from 3433 to 4094 mg/L; after the OLR reached 7.0 g TS/L/d, the ammonia nitrogen concentration decreased, to 3654 mg/L at 7.0 g TS/L/d and 2324 mg/L at 9.0 g TS/L/d, and ammonia inhibition was alleviated. The improvement in the biogas production efficiency with the addition of GAC was apparent at the start-up stage and under high OLR (≥7.0 g TS/L/d). • Kinetic analysis was carried out for dry anaerobic digestion of swine manure. • High OLR (≥7.0 g TS/L/d) alleviated ammonia inhibition. • GAC enhanced the CH 4 production at the start-up stage and the high OLR conditions. [ABSTRACT FROM AUTHOR]

• We first proposed a direct mRNA multiplexed detection strategy using xMAP array. • It enables single-nucleotide and high sensitivity (5–50000 amol) detection. • A LNA-modified universal probe was designed with 78% coverage for all amo A genes. • We have successfully detected amo A mRNA semi-quantitatively in sludge samples. • Our results are consistent with batch activity test, RT-PCR and metatranscriptome. Nitrogenous pollutants are the main causes of water eutrophication, which greatly interfere with the balance of the aquatic ecosystem. The biological nitrogen removal using bacteria is the leading technology to control nitrogenous pollutants. The α-subunit (amo A) of ammonia monooxygenase (AMO) of aerobic ammonia-oxidizing bacteria (AOB) is an ammonia-depleting biomarker in nitrogen removal processes. Currently, RT-PCR and metatranscriptome are the general methods for analyzing amo A gene expression, however they can introduce amplification bias and are time consuming. Herein we report a new direct mRNA multiplexed detection strategy based on xMAP array, for analyzing gene expression without reverse transcription and amplification steps. After analyzing all amo A sequences in database, we design a universal probe for AOB with coverage of 79.8% whose high coverage is further confirmed by metatranscriptome. Moreover, we classify AOB into 10 clusters, and then design the specific probes of each cluster. This technique enables single-nucleotide, wide linear dynamic range (5–50,000 amol) and high sensitivity (5 amol with detection volume of 1 µL) detection with using locked-nucleic-acid probes. Particularly, the sensitivity is by far among the highest level for multiplex mRNA detection without amplification. We found that mRNA fragmentation is not necessary in our direct detection, simplifying our strategy. We have successfully detected amo A mRNA semi-quantitatively and determined the predominant cluster in sludge from wastewater treatment plants, which was consistent with RT-PCR and metatranscriptome results. Meanwhile, the ammonia-oxidizing activities of sludge verified the amo A mRNA detection results. In conclusion, we have developed a mRNA direct, simple, specific and sensitive multiplexed detection strategy, which shows great potential for application in gene expression analysis, environmental microbial detection and activity diagnosis of wastewater treatment plants. [ABSTRACT FROM AUTHOR]

• mFe/nCu presented an excellent removal capacity against ARGs. • Nanoscale copper in mFe/ncu system contributed to the ARG removal. • mFe/nCu could kill bacteria and destroy ARG structure and function. • ARG removal by mFe/nCu was permanent and irreversible. In this study, a distinct type of nanoscale copper, produced by iron-copper replacement (mFe/nCu), was used to reduce ARGs from post-treated swine wastewater. The effects of several key parameters (i. e., theoretical Cu mass loadings, mFe/nCu dosage, air flow rate, initial pH and temperature) were investigated in details. The contribution of nanoscale copper in mFe/nCu system towards ARGs removal was determined. Furthermore, the removal mechanism of ARGs by mFe/nCu was examined by SEM, TEM and living/dead cell staining. Results indicate that the mFe/nCu process can promptly remove the absolute abundances of ARGs (˃2.4 logs) from post-treated swine wastewater. The outstanding performance of this approach could be attributed to the use of nanoscale copper itself rather than the oxidation by Fenton-like reaction of mFe/nCu bimetallic system. Moreover, the mFe/nCu process exhibited an excellent activity in regards bacterial killing and destruction of ARGs structure and function which, ultimately, could serve as a plausible mechanism of ARGs removal. Reactivation experiments showed that ARGs removal by mFe/nCu was permanent and irreversible. Altogether, our findings suggest that mFe/nCu treatment can be a promising advanced method for ARGs removal from post-treated swine wastewater. [ABSTRACT FROM AUTHOR]