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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]

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]

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]

Fulvic acid (FA), a humics, was employed as a model representing bio-refractory soluble organic matter to investigate the performance of co-utilized FeSO 4 and Ca(ClO) 2 in advanced wastewater treatment. The removal efficiency of FA was greatly enhanced upon the synergistic effect of Fe2+ and ClO−, varying from 22% to 89% when the loading of ClO− varied from 1.6 to 80 mM at Fe2+/ClO−=0.5, TOC 0 = 130 mg/L, and neutral pH. The results of Electron paramagnetic resonance (EPR) demonstrated the generation of hydroxyl radicals (•OH) in Fe2+/ClO− system, indicating that this treatment involved an advanced oxidation process. The contributions of both oxidation and coagulation showed that FA was removed incrementally by oxidation with the increase of reagent dosage. According to TOC, molecular weight distribution, UV–Vis, and FTIR results, on the one hand, FA was degraded and its aromaticity was reduced due to the breakage of the chemical bonds (such as amide and C−C bond) and the opening of aromatic rings by oxidative species (such as •OH and ClO−), which was benefit for coagulation; on the other hand, the degraded organics were further mineralized. The remained FA mainly contained alkyl substituted and/or C O conjugated aromatic ring structures as well as ether/ester structures. [Display omitted] • Oxidation and coagulation were mutually promoted in Fe2+/ClO system. • Generation of hydroxyl radicals greatly advanced the function of oxidation. • The mechanism of fulvic acid transformation in the Fe2+/ClO system was revealed. • Mild conditions met the operating requirement of easy efficient treatment. [ABSTRACT FROM AUTHOR]

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 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]

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]

[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]

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]

[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]