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• Bipolar membrane ED was used for nutrient recovery from AD dewatering sidestream. • Concentrated acid and base streams containing separated nutrients were produced. • Ammonia was recovered using a produced acid solution by membrane stripping. • Phosphate was recovery as struvite or hydroxyapatite by chemical precipitation. • Nutrient recovery was achieved with minimized chemical and energy inputs. Anaerobic digestion (AD) offers an efficient means for treating sludge generated in wastewater treatment plants (WWTPs), but nutrient-rich AD dewatering sidestream contributes as much as 30 % of the overall nutrient loading of WWTPs. Several electrochemical approaches are being developed as a sidestream treatment strategy to prevent return of nutrients to WWTP headworks and recover them for fertilizer production. One such method is to produce acids and bases, essential chemicals necessary to facilitate nutrient recovery, using bipolar membrane electrodialysis (BMED). In this study we show simultaneous separation of nutrients and production of acid/base streams with an additional consideration for increasing the concentration of ammonium and phosphate in the final product stream by systematically altering compartment flow rates and hence the retention time of each stream. Using a three-compartment BMED system with a synthetic sidestream containing 50 mM NH 3 -N and 2 mM PO 4 -P, we achieved up to 80 % ammonia removal (via a cation exchange membrane) and up to 60 % phosphate removal (via an anion exchange membrane) at a productivity of 34.2 L m−2 h−1. Separated ammonia was recovered (>90 %) in a subsequent membrane contactor (MC) that was fed with acid and base streams produced by the BMED unit. A phosphate recovery > 80 % was achieved by chemical precipitation (CP). In a combined BMED-MC-CP process, the concentrated final product contained 333.9 mM NH 3 -N and 3.1 mM PO 4 -P with an energy consumption of 8.9 kWh kg−1 N recovered. These results illustrate that the BMED-based treatment train is a promising strategy for nutrient recovery from AD dewatering sidestream. [ABSTRACT FROM AUTHOR]

[Display omitted] • UDB and DB at different pyrolysis temperatures played contrasting roles. • DB800-amended group displayed superior nitrogen removal performance. • DB at lower pyrolysis temperature imposed suppression. • Properties of dissolved organic matter released by DB were tracked at molecular level. Biochar has attracted increasingly attention in the biological wastewater treatment owing to its unique environmental behavior. However, the differential effects of undissolved and dissolved fractions of biochar (hereafter named as UDB and DB, respectively) on the anaerobic ammonium oxidation (anammox) process remain unclear. The study evaluated the nitrogen removal performance of anammox system in response to UDB and DB prepared at different pyrolysis temperatures (300 °C, 550 °C and 800 °C). The DB800-amended group displayed superior nitrogen removal performance with the total nitrogen removal efficiency (TNRE) of 92.8 ± 1.4 %. Compared with CK, TNRE was changed by +5.0 % (UDB300), +0.4 % (UDB550) and −22.3 % (UDB800) for UDB-amended groups, and by −16.0 % (DB300), −9.4 % (DB550), and +9.2 % (DB800) for DB-amended groups, respectively. The differences were closely related to the physicochemical properties of UDB and DB. Particularly, dissolved organic matter released by DB were tracked at molecular level, which revealed that CHO occupied the highest proportion of 70.3 % and lignin-like and carboxylic rich alicyclic molecules were dominant in DB800. This study would facilitate the understanding of the differences between the nitrogen removal performance of UDB and DB-amended anammox, thus providing deeper insights for the comprehensive assessment of the impacts of biochar on the anammox process. [ABSTRACT FROM AUTHOR]

Highlights • A tubular PMFC and PBRs were coupled to treat ADE-FW in continuous and batch modes. • Higher algal biomass and nutrient removal rate were obtained in continuous mode. • Nitrogen removal rate in PMFC reached 6.0 mg/(L·d) due to ammonium migration effect. • Anode potentials increased linearly as COD decreased when COD < 3000 mg/L. • Total energy produced in either continuous or batch modes was both 1.8 kWh/m3. Abstract Anaerobically digested effluent from food waste (ADE-FW) needs purification treatment due to its high content of ammonium and organic matter. Here, a system that couples a photosynthetic microbial fuel cell (PMFC) with photobioreactors (PBRs) was developed to recover energy from the ADE-FW. First, the ADE-FW was treated in the PMFC for pollutant removal and power generation. The highest power density obtained from the PMFC was about 3.5 W/m3. Power generation was primarily affected by DO and substrate concentrations, which respectively determined the cathode and anode potentials. About 93% of the ammonium in the anolyte was removed in the continuous mode, owing to the ammonium migration effect. Algal biomass in the PMFC increased from 0.1 mg/L to 0.7 mg/L in the continuous mode, which was 27% higher than that in the batch operating mode (0.55 mg/L). Then the effluents from the cathodic chamber were polished in the PBRs. The nitrogen removal rates in the PBRs under continuous and batch operation were 3.0 mg/(L·d) and 1.8 mg/(L·d), respectively. In terms of energy production, more algal lipid energy was obtained in the continuous mode, but less electricity was obtained in this mode. Consequently, the total energy produced in the coupled systems in the continuous and batch modes were consistently about 1.8 kWh/m3. The high pollutant removal rate and energy recovery efficiency of the coupled system indicated that it would be a practical technology for the industrial-scale applications. [ABSTRACT FROM AUTHOR]

Highlights • Microalgae growth was inhibited at NH 4 +-N concentrations above 100 mg/L. • Microalgae growth in digestate was suppressed by high NH 4 +-N and competing microbes. • Nitrification based pre-treatment was effective in alleviating NH 4 +-N toxicity. • Excellent nitrogen and phosphorus recovery from nitrified digestate by microalgae. • Integrated nitrification and algae cultivation possible using membrane bioreactors. Abstract High ammonium concentration is considered a major challenge in cultivating autotrophic microalgae in anaerobic digestate. In this research, the feasibility of applying nitrification as pretreatment to alleviate ammonium toxicity on microalgae was investigated. Batch experiments conducted in synthetic medium showed that microalgae growth was inhibited at NH 4 +-N > 100 mg/L, but NO 3 −-N was benign at concentrations as high as 350 mg/L. Microalgae growth in 2–50% digestate (v/v) was also affected adversely by invading heterotrophic microorganisms. Digestate pre-treatment using activated sludge mitigated these challenges by converting NH 4 +-N to NO 3 −-N, and reducing organics content in the digestate. Microalgae exhibited excellent growth and nutrients removal in nitrified digestate (5–30% mixed with municipal wastewater) in batch mode. For example, COD, NH 4 +-N, NO 3 −-N and PO 4 3−-P removal in 10% digestate using two-stage bacterial-microalgal process were 87%, 100%, 30% and 77%, respectively. In continuous mode, using a microalgae-based membrane photobioreactor (MPBR) operating downstream to membrane bioreactor (MBR), 91% COD, 97% NH 4 +-N and >99% PO 4 3−-P could be continuously removed from 10% digestate. Although NH 4 +-N removal in the process was mainly through nitrification, total nitrogen removal was >75% at steady state. The effects of lower NH 4 +-N toxicity in the MPBR was also manifested in terms of high microalgae biomass accumulation of about 5 g/L. These results indicate that nitrification can be a promising pretreatment for anaerobic digestate for use in microalgae cultivation. [ABSTRACT FROM AUTHOR]

Under starvation conditions, bacteria could consume intracellular macromolecules, which deteriorates the performance of the bioreactor. However, the fundamental endogenous metabolism of anaerobic ammonium oxidation (anammox) bacteria is poorly understood. Here, we describe the endogenous metabolism of anammox bacteria biomass under short-term anaerobic and anoxic starvation stress (4.5 d and 40 h, respectively) by protein, mRNA and biochemical analyses. The live/dead staining results showed negligible cell death rates. The activity decay rates (decrease in specific activity of active bacteria) were 0.128 d −1 and 0.629 d −1 under anaerobic and anoxic starvation conditions, respectively. The degradation rates of extracellular polymeric substances (EPS) and hydrazine dehydrogenase protein (HDH) were approximately 4- and 5-fold higher under anoxic starvation than under anaerobic starvation tests, suggesting the electron-donor roles for EPS and HDH in denitrification. The greater consumption of intracellular macromolecules during anoxic starvation corresponded with the greater decrease in anammox activities under this condition. Under both starvation conditions, the mRNA decay rates of nirS , hzsA , and hdh mRNA (representing metabolic stability) of anammox bacteria decreased from their normal levels. Such control of specific mRNAs is important for economizing protein synthesis and aids the cells’ recovery after starvation stress. These identified endogenous characteristics of anammox bacteria provide new insights into starvation stress responses at the transcriptional and translational levels, and will assist the optimization of anammox processes in bioreactors, which frequently experience starvation conditions. [ABSTRACT FROM AUTHOR]

Co-occurrence of organic matter (OM) and nitrogen in industrial and domestic wastewaters is a major obstacle in field scale application of anammox process- a novel technology for biological nitrogen removal. This study explored a new symbiosis amongst different consortium i.e., denitrifiers, anammox and anaerobes, which together minimized the inhibition caused due to OM through its concurrent utilization via other metabolic pathways. This symbiosis was achieved by seeding anaerobic granular sludge in existing anammox hybrid reactors at different seed ratios, i.e., 0.2, 0.4, 0.6 and 0.8. COD/TN and seed ratio played a vital role in controlling the overall dynamics of the three different pathways, i.e., denitrification, anammox and anaerobic degradation. The seed ratio of 0.6 was found ideal for synergistic removal of both OM (95.4%) and nitrogen (97.4%). At higher COD/TN ratio, anaerobes were more prevalent and outcompeted anammox bacteria which showed predominance at lower COD/TN ratio. The process performance data were analysed using multi-linear regression (MLR) and non-linear regression models. Biasness of the models were analysed using t -test which dictated MLR model was unbiased and statistically more precise than non-linear regression model. A new mathematical model coceptualised on the mass balance of substrate predicted N 2 and biogas with least error of precision. [ABSTRACT FROM AUTHOR]

The combined anammox (anaerobic ammonium oxidation) and autotrophic desulfurization–denitrification (AADD) process represents a promising innovative technology for biological nitrogen and sulfur removal. In this study, an up-flow anaerobic sludge blanket reactor, which was started with anammox and methanogenic granules, was operated for 245 days to evaluate the co-treatment of wastewater containing nitrogen and sulfur. The reactor demonstrated good performance in terms of nitrogen and sulfide removal and exhibited excellent behavior for removal of NH 4 + -N, NO 2 − -N and S 2− -S exceeding 252, 333 and 330 mg L −1 , respectively. The highest nitrogen removal rate and sulfide removal rate attained were 4.00 kgN m −3 d −1 and 2.39 kgS m −3 d −1 , respectively, which were also the highest reported values for a coupling-system. The influent NH 4 + -N:S 2− -S and NO 2 − -N:S 2− -S ratios set at 1.74 and 2.20–2.27 are suitable for maintaining system stability. The specific activities of anammox and autotrophic desulfurization–denitrification (SAA and SADD), extracellular polymeric substance (EPS), heme c (an important cofactor of some anammox bacterial enzymes) and the diversity of anammox and autotrophic desulfurization–denitrification (ADD) bacteria were investigated during the operation. The SAA and SADD are regarded as key factors for high efficiency. The granules contained many EPS (128.4–204.5 mg g −1 VSS) and minor heme c content (1.17 μmol g −1 VSS). The dominant bacteria belonged to members of Brocadiaceae and Hydrogenophilaceae , a majority of which were anammox bacteria and ADD bacteria, respectively. These observations suggest a new removal process for ammonia, nitrite and sulfide utilizing an uncommon mechanism involving simultaneous anammox and ADD. [ABSTRACT FROM AUTHOR]

A novel bio-zeolite fixed-bed bioreactor combining with physicochemical and biological methods for mitigating ammonia inhibition was developed to improve the anaerobic digestion of ammonium-rich livestock wastes. The fixed-bed bioreactor was constructed by zeolite that was fixed using three different kinds of polymer materials including chlorinated polyethylene (CPE), polymer foaming sponge (PFS) and porous nylon (PN). Using ammonium-rich swine wastes (NH 4 + -N: 7511 mg/l) as substrate, a series of batch anaerobic fermentation experiments were carried out under 35 °C. The bioreactor suspending with CPE fixed zeolite showed the shortest start-up period (2 days) and the highest methane production (about 96 times higher than that of the Control) after 30-days anaerobic digestion. Furthermore, the higher and stable methane concentration and yield during 100-day of semi-continuous anaerobic digestion clearly indicated the long-term practical effectiveness of CPE-fixed zeolite bioreactor. Synergy of ammonia adsorption and microorganism immobilization by CPE fixed zeolite contributed to the enhanced anaerobic digestion efficiency. The developed novel CPE fixed zeolite bioreactor was suggested to be a favorable system for improve the anaerobic digestion of ammonium-rich agricultural wastes. [ABSTRACT FROM AUTHOR]

The performance and hydrodynamic features of a staged up-flow ANAMMOX (anaerobic ammonium oxidation) sludge bed (SUASB) reactor was evaluated. When the reactor was at steady-state conditions, the nitrogen loading rate (NLR) and nitrogen removal rate (NRR) were 5.63 and 4.82 kg N m-3 d-1, respectively. The reactor could withstand a 1.5-fold substrate or hydraulic shock. The modified Stover-Kincannon model was used for the kinetic analysis, and the saturation value (KB) and maximum total substrate utilization rate (Umax) were 14.5 and 14.8 kg N m-3 d-1, respectively. Moreover, the C(t)-Θ curve showed the existence of dead zones in the SUASB at the hydraulic retention times (HRTs) of 3 and 12 h, and the flow pattern performance of the SUASB fell between those of a continuous stirred tank reactor (CSTR) and a plug flow reactor (PFR). [ABSTRACT FROM AUTHOR]

• Oyster shell and lignite modified zeolite (OLMZ) was successfully synthesized. • Intermittent illumination aided OLMZ fixed bioreactor (OLMZ-I) was developed. • Superior CH 4 yield of 372 ± 30 mL/g-DOC removed was achieved in ammonium-rich fermentation. • Mechanism of OLMZ-I process for high-efficient ammonium-rich AD was proposed. • The developed process shows great potential for bioconversion of ammonium-rich waste. A novel oyster shell and lignite modified zeolite (OLMZ) fixed bioreactor incorporated with intermittent light illumination process was developed for alleviating ammonia inhibition to improve efficiency of ammonium-rich anaerobic digestion (AD). The SEM morphology of the newly synthesized OLMZ showed porous structure and rough surface, with increased BET surface area compared to unmodified zeolite (UMZ). After modification with oyster shell and lignite, the metal cations content in OLMZ increased significantly and the ammonia adsorption capability of OLMZ improved by 1.3 folds compared to UMZ. Thus, the results suggested that OLMZ is a better adsorbent than UMZ for ammonia uptake. Furthermore, the pseudo-second-order kinetics and the isotherm results verified the adsorption of ammonia on OLMZ was dominated by ion exchange with high affinity for ammonia uptake. As for the anaerobic digestion, the light illuminated OLMZ fixed bioreactor process (OLMZ-I) resulted in the highest methane yield of 372 ± 30 mL/g-DOC removed , which showed 300% increase compared to the control (124 ± 12 mL/g-DOC removed). In addition, OLMZ-I showed higher ammonia removal capacity and stable pH which indicated that the ammonia inhibition was effectively mitigated. Correspondingly, metal cations supplementation and light stimulation in OLMZ-I showed increased ATP and coenzyme F 420 implying high activation of methanogens leading to improved CH 4 production. The large biomass quantity and SEM observation of microbes immobilized on the fixed OLMZ system aided by light further supported the enhanced performance of the reactor. Furthermore, the conductance of sludge in OLMZ-I bioreactor increased 3 folds compared to the control, reflecting a potential direct interspecies electron transfer (DIET) between the anaerobes was strengthened. The synergetic effects of ammonia removal, microbes immobilization, metal cations supplementation and accelerated electrical communication between methanogenic system combined with light stimulation on methanogen activation facilitated the enhancement of methanogenesis. Therefore, the OLMZ fixed bioreactor coupled with intermittent light stimulation shows great potential in practical application for bioconversion of ammonium-rich livestock waste. [ABSTRACT FROM AUTHOR]