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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]

The anaerobic ammonium oxidation (anammox) consists on the biological conversion of ammonium (NH 4 + ) into dinitrogen gas under absence of oxygen. Nitrite (NO 2 − ) is a substrate of the anammox reaction, but also an inhibitor at high concentrations. This study investigates the effect of nitrite on the microbial community during the batch enrichment of anammox sludge. Six inoculums collected from different environments were enriched after a conditioning pretreatment and under controlled conditions during 4 months. Concerning the mineral medium used, two different nitrite supply strategies were applied; i.e., (i) initially low concentration at 25 mg NO 2 − –N/L and progressive increase to 150 mg NO 2 − –N/L, and (ii) constant high concentration at 150 mg NO 2 − –N/L. All tested inoculums developed anammox activity but only when the enrichment was started at low nitrite concentration. In such case, the specific ammonium conversion rates finally obtained ranged from 21 ± 1 to 118 ± 1 mg NH 4 + –N/g VS/d (VS, volatile solids). Abundance of the functional gene encoding for the enzyme hydrazine oxidoreductase ( hzo ) was assessed using the real-time quantitative polymerase chain reaction (q-PCR) showing positive correlation with the anammox activity finally reported. In addition, high-throughput DNA sequencing helped to elucidate the underlying microbial community dynamics. The raw inoculum source, the conditioning pretreatment, and the cultivation conditions applied were jointly determinants of the final microbial community structure of the enrichments despite a clear convergence at the end of the experimental period. On the other hand, the cultivation conditions alone determined the selection of anammox species belonging to the genus Candidatus Brocadia . [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is a novel wastewater treatment process. The intrinsic nature of anammox bacteria makes their traditional isolation from a consortium impossible. This study presents a detailed assessment of different pretreatments for percoll density gradient centrifugation (PDGC) to purify anammox bacteria and proposes that the extraction of extracellular polymeric substances (EPS) could significantly increase the purification performance. The results demonstrate that both EPS extraction using cation exchange resin for 2 h and mild ultrasound at an optimal power of 7.2 kJ were suitable pretreatments to increase the purification efficiency in comparison to PDGC performed directly from an original consortium (optimal conditions identified as 8000 rpm, 30 min). Importantly, the implementation of EPS extraction before ultrasound was verified to have the capacity to further increase the purification efficiency up to 95%, which demonstrates the prominent effects of EPS extraction on the PDGC performance. Compared to the previous report, EPS extraction was applied instead of the first centrifugation prior to PDGC to remove large flocs, which correspondingly increased the purified amounts. To clarify the involved mechanism, the bacteria aggregating behaviors before and after EPS extraction over time were visually tracked using a particle size analyzer. The results of this study help to obtain large amounts of anammox bacteria and elucidate the anammox characteristics and communities in both natural and engineered systems. [ABSTRACT FROM AUTHOR]

Quorum sensing (QS) is a microorganism communication system. This study verified the potential existence of the QS system among ANaerobic AMMonium OXidation (anammox) bacteria. The release of three Acyl Homoserine Lactones (AHLs; C 6 -HSL, C 8 -HSL, C 12 -HSL) by anammox culture was confirmed. By conducting series of batch test, the introduction of exogenous C 6 -HSL and C 8 -HSL could significantly increase activity of anammox bacteria, and meanwhile, C 6 -HSL significant increased the growth rate, finally resulting in the increased ammonium nitrogen removal performance of 35% and 20%, respectively, whereas the exogenous C 12 -HSL apparently promoted the growth of heterotrophic bacteria in the community. To further identify how exogenous signal molecular affects anammox culture, analyses of anammox culture supernatant and biomass extraction revealed that these additional signal molecules activated bacteria by inducing the production of endogenous signal molecular by anammox culture. This study might open a new window to overcome the disadvantage of the long-start-up period of anammox reactor restricting the development of current anammox process. [ABSTRACT FROM AUTHOR]

Efficient biological nitrogen removal from high salinity wastewater has been focused recently. The present study comparatively investigated the effects of temperature, salinity and calcium concentration on the performance of anaerobic ammonium oxidation (anammox) processes using anammox granular sludge to treat synthetic wastewater. Four upflow anaerobic sludge blanket reactors were operated in parallel at ambient temperatures evolving from 25 to 9 °C (reactor R 1 ) and thermostatic room temperatures of 35 ± 2 °C (reactors R 2 , R 3 and R 4 ). The results demonstrated that low ambient temperature and high sodium levels impair the nitrogen removal performance of anammox granular sludge. The anaerobic ammonium-oxidizing bacteria gradually adapted to a salt concentration of 15 g L −1 at low ambient temperature, and a nitrogen removal rate of 1.34 ± 0.12 kg N m −3 d −1 was achieved. A nitrogen removal rate of 1.90 ± 0.01 kg N m −3 d −1 in R 4 was achieved at a salt concentration of 15 g L −1 . Moreover, 152 mg L −1 calcium relieved the high salinity inhibition of anaerobic ammonium-oxidizing bacteria. Furthermore, the fractal dimension and permeability of anammox granules were also investigated with settling experiment, which indicated that the anammox granules were porous and permeable. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium-oxidizing (anammox) is a novel wastewater treatment process, which can realize efficient nitrogen removal with low operational cost. The anammox process is usually executed at 35 °C by heating devices. The potential effects of overheating on anammox culture are still remained as an open question. In this study, we share experiences about behavior detection and activity recovery of damaged anammox culture after accidental overheating. When anammox culture suffered 48 °C for 1 h, flocculating and deflocculating occurred, resulting in the suspended culture and the settled. Fluorescence in situ Hybridization, Flow Cytometry and Non-invasive Micro-test Technique showed that the settled culture contained more anammox bacteria than the suspended, leading to its higher death probability as time course, higher bulk liquid H + flux rate and faster activity restoration for nitrogen removal after overheating. The autofluorescence of Candidatus Brocadia fulgida varied during this process and could be considered as a characteristic fingerprint for these anammox bacteria. Experimental results also indicated the shear force produced by 150 rpm stir would contribute to the further damage of the heated bacteria. Reducing shear stress by low stirring rates and static cultivation might potentially be used as effective strategies in the repair of damaged anammox culture. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is a promising technology for autotrophic removal of ammonium and nitrite. In order to expand its industrial application niche, effects of organic matter need more specific investigation. In this study, the effects of C2/C3 fatty acids stress on anaerobic ammonium oxidation (anammox) process were evaluated in batch experiments. BLAST search analysis of 16S rRNA sequences showed that the homology of the highly enriched anammox consortia used here and Candidatus Jettenia asiatica (J. asiatica) reached 99%. Results showed that low acetate (⩽30 mg/L) and propionate (⩽50 mg/L) concentration does not significantly influence ammonium oxidation. Higher acetate/propionate concentrations caused decrease of ammonium removal. A level of acetate no more than 240 mg/L caused the decrease of ammonium consumption rate by 33%, and 29% for propionate with (<400 mg/L). J. asiatica showed higher adaptability to propionate stress than acetate. Real-time quantitative PCR (qPCR) results reveal that anammox bacteria J. asiatica are capable of growing at the present of low-concentration acetate (⩽120 mg/L)/propionate (⩽200 mg/L). The anammox hzo gene concentrations reached to round 0.5 x 108-1.0 x 108 copies/ml after 36 days cultivation with C2/C3 fatty acid. However, there is no superiority for J. asiatica consortia to grow under organotrophic conditions compared to autotrophic ones. [ABSTRACT FROM AUTHOR]