Enhanced nitrogen removal and microbial analysis in partially saturated constructed wetland for treating anaerobically digested swine wastewater

Anaerobically digested swine wastewater was treated by a novel constructed wetland. Tidal operation was better for total nitrogen removal than intermittent flow. Mechanism of nitrogen removal by biozeolite-based constructed wetland was discussed. Simultaneous nitrification and denitrification were determined in zeolite layer. Nitrogen removal of wastewater containing high-strength ammonium by the constructed wetlands (CWs) has been paid much attention. In this study, the ability of a partially saturated CW to treat anaerobically-digested decentralized swine wastewater under varying operating parameters from summer to winter was investigated. The partially saturated CW achieved better NH₄⁺-N and TN removal by tidal flow than intermittent flow. With surface loading rates of 0.108, 0.027, and 0.029 kg/(m²·d) for COD, NH₄⁺-N, and TN, the partially saturated CW by tidal operation achieved corresponding removal efficiencies of 85.94%, 61.20%, and 57.41%, respectively, even at 10°C. When the rapid-adsorption of NH₄⁺-N and the bioregeneration of zeolites reached dynamically stable, the simultaneous nitrification and denitrification in the aerobic zeolite layer was observed and accounted for 58.82% of the total denitrification of CW. The results of Illumina high-throughput sequencing also indicated that nitrifiers (Nitrospira and Rhizomicrobium) and denitrifiers (Rhodanobacter and Thauera) simultaneously existed in the zeolite layer. The dominant existence of versatile organic degraders and nitrifiers/denitrifiers in the zeolite layer was related to the removal of most COD and nitrogen in this zone. The contribution of the possible nitrogen removal pathways in the CW was as follows: nitrification-denitrification (86.55%)>substrate adsorption (11.70%)>plant uptake (1.15%)>microbial assimilation (0.60%).     

A heterotrophic nitrification-aerobic denitrification bacterium Halomonas venusta TJPU05 suitable for nitrogen removal from high-salinity wastewater

• H. venusta TJPU05 showed excellent HN-AD ability at high salinity. • Successful expression of AMO, HAO, NAR and NIR confirmed the HN-AD ability of TJPU05. • H. venusta TJPU05 could tolerate high salt and high nitrogen environment. • H. venusta TJPU05 is a promising candidate for the bio-treatment of AW. A novel salt-tolerant heterotrophic nitrification and aerobic denitrification (HN-AD) bacterium was isolated and identified as Halomonas venusta TJPU05 (H. venusta TJPU05). The nitrogen removal performance of H. venusta TJPU05 in simulated water (SW) with sole or mixed nitrogen sources and in actual wastewater (AW) with high concentration of salt and nitrogen was investigated. The results showed that 86.12% of NH₄⁺-N, 95.68% of NO₃^–-N, 100% of NO₂^–-N and 84.57% of total nitrogen (TN) could be removed from SW with sole nitrogen sources within 24 h at the utmost. H. venusta TJPU05 could maximally remove 84.06% of NH₄⁺-N, 92.33% of NO₃^–-N, 92.9% of NO₂^–-N and 77.73% of TN from SW with mixed nitrogen source when the salinity was above 8%. The application of H. venusta TJPU05 in treating AW with high salt and high ammonia nitrogen led to removal efficiencies of 50.96%, 47.28% and 43.19% for NH₄⁺-N, NO₃^–-N and TN respectively without any optimization. Furthermore, the activities of nitrogen removal–related enzymes of the strain were also investigated. The successful detection of high level activities of ammonia oxygenase (AMO), hydroxylamine oxidase (HAO), nitrate reductase (NAR) and nitrite reductase (NIR) enzymes under high salinity condition further proved the HN-AD and salt-tolerance capacity of H. venusta TJPU05. These results demonstrated that the H. venusta TJPU05 has great potential in treating high-salinity nitrogenous wastewater.     

Nitrogen removal efficiencies and microbial communities in full-scale IFAS and MBBR municipal wastewater treatment plants at high COD:N ratio

• Two IFAS and two MBBR full-scale systems (high COD:N ratio 8:1) were characterized. • High specific surface area carriers grew and retained slow-growing nitrifiers. • High TN removal is related to high SRT and low DO concentration in anoxic tanks. The relative locations of AOB, NOB, and DNB were examined for three different kinds of carriers in two types of hybrid biofilm process configurations: integrated fixed-film activated sludge (IFAS) and moving bed biofilm reactor (MBBR) processes. IFAS water resource recovery facilities (WRRFs) used Anodkalness^TM K1 carriers (KC) at Broomfield, Colorado, USA and polypropylene resin carriers (RC) at Fukuoka, Japan, while MBBR WRRFs used KC carriers at South Adams County, Colorado, USA and sponge carriers (SC) at Saga, Japan. Influent COD to N ratios ranged from 8:1 to 15:1. The COD and BOD removal efficiencies were high (96%–98%); NH₄⁺-N and TN removal efficiencies were more varied at 72%–98% and 64%–77%, respectively. The extent of TN removal was higher at high SRT, high COD:N ratio and low DO concentration in the anoxic tank. In IFAS, RC with high specific surface area (SSA) maintained higher AOB population than KC. Sponge carriers with high SSA maintained higher overall bacteria population than KC in MBBR systems. However, the DNB were not more abundant in high SSA carriers. The diversity of AOB, NOB, and DNB was fairly similar in different carriers. Nitrosomonas sp. dominated over Nitrosospira sp. while denitrifying bacteria included Rhodobacter sp., Sulfuritalea sp., Rubrivivax sp., Paracoccus sp., and Pseudomonas sp. The results from this work suggest that high SRT, high COD:N ratio, low DO concentration in anoxic tanks, and carriers with greater surface area may be recommended for high COD, BOD and TN removal in WRRFs with IFAS and MBBR systems.     

Nitrate removal to its fate in wetland mesocosm filled with sponge iron: Impact of influent COD/N ratio

• CW-Fe allowed a high-performance of NO₃^‒-N removal at the COD/N ratio of 0. • Higher COD/N resulted in lower chem-denitrification and higher bio-denitrification. • The application of s-Fe⁰ contributed to TIN removal in wetland mesocosm. • s-Fe⁰ changed the main denitrifiers in wetland mesocosm. Sponge iron (s-Fe⁰) is a porous metal with the potential to be an electron donor for denitrification. This study aims to evaluate the feasibility of using s-Fe⁰ as the substrate of wetland mesocosms. Here, wetland mesocosms with the addition of s-Fe⁰ particles (CW-Fe) and a blank control group (CW-CK) were established. The NO₃^‒-N reduction property and water quality parameters (pH, DO, and ORP) were examined at three COD/N ratios (0, 5, and 10). Results showed that the NO₃^‒-N removal efficiencies were significantly increased by 6.6 to 58.9% in the presence of s-Fe⁰. NH₄⁺-N was mainly produced by chemical denitrification, and approximately 50% of the NO₃^‒-N was reduced to NH₄⁺-N, at the COD/ratio of 0. An increase of the influent COD/N ratio resulted in lower chemical denitrification and higher bio-denitrification. Although chemical denitrification mediated by s-Fe⁰ led to an accumulation of NH₄⁺-N at COD/N ratios of 0 and 5, the TIN removal efficiencies increased by 4.5%‒12.4%. Moreover, the effluent pH, DO, and ORP values showed a significant negative correlation with total Fe and Fe (II) (P<0.01). High-throughput sequencing analysis indicated that Trichococcus (77.2%) was the most abundant microorganism in the CW-Fe mesocosm, while Thauera, Zoogloea, and Herbaspirillum were the primary denitrifying bacteria. The denitrifiers, Simplicispira, Dechloromonas, and Denitratisoma, were the dominant bacteria for CW-CK. This study provides a valuable method and an improved understanding of NO₃^‒-N reduction characteristics of s-Fe⁰ in a wetland mesocosm.     

Sludge fermentation liquid addition attained advanced nitrogen removal in low C/N ratio municipal wastewater through short-cut nitrification-denitrification and partial anammox

• Sludge fermentation liquid addition resulted in a high NAR of 97.4%. • Extra NH₄⁺-N from SFL was removed by anammox in anoxic phase. • Nitrogen removal efficiency of 92.51% was achieved in municipal wastewater. • The novel system could efficiently treat low COD/N municipal wastewater. Biological nitrogen removal of wastewater with low COD/N ratio could be enhanced by the addition of wasted sludge fermentation liquid (SFL), but the performance is usually limited by the introducing ammonium. In this study, the process of using SFL was successfully improved by involving anammox process. Real municipal wastewater with a low C/N ratio of 2.8–3.4 was treated in a sequencing batch reactor (SBR). The SBR was operated under anaerobic-aerobic-anoxic (AOA) mode and excess SFL was added into the anoxic phase. Stable short-cut nitrification was achieved after 46d and then anammox sludge was inoculated. In the stable period, effluent total inorganic nitrogen (TIN) was less than 4.3 mg/L with removal efficiency of 92.3%. Further analysis suggests that anammox bacteria, mainly affiliated with Candidatus_Kuenenia, successfully reduced the external ammonia from the SFL and contributed approximately 28%–43% to TIN removal. Overall, this study suggests anammox could be combined with SFL addition, resulting in a stable enhanced nitrogen biological removal.     

Effect of chemical dose on phosphorus removal and membrane fouling control in a UCT-MBR

Phosphorus removal was enhanced effectively by dosing aluminum sulfate and effluent phosphorus concentration was lower than 0.5 mg/L. Sludge activity was not inhibited but improved slightly with addition of aluminum sulfate. EPS concentrations both in mixed liquid and on membrane surface were decreased, contributing to the effective mitigation of membrane fouling. To enhance phosphorus removal and make the effluent meet the strict discharge level of total phosphorus (TP, 0.5 mg/L), flocculant dosing is frequently applied. In this study, the performance of aluminum sulfate dosing in a University of Cape Town Membrane Bioreactor (UCT-MBR) was investigated, in terms of the nutrients removal performance, sludge characteristics and membrane fouling. The results indicated that the addition of aluminum sulfate into the aerobic reactor continuously had significantly enhanced phosphorus removal. Moreover, COD, NH₄⁺-N and TN removal were not affected and effluent all met the first level A criteria of GB18918-2002. In addition, the addition of aluminum sulfate had improved the sludge activity slightly and reduced trans-membrane pressure (TMP) increase rate from 1.13 KPa/d to 0.57 KPa/d effectively. The membrane fouling was alleviated attributed to the increased average particle sizes and the decreased accumulation of the small sludge particles on membrane surface. Furthermore, the decline of extracellular polymeric substance (EPS) concentration in mixed sludge liquid decreased its accumulation on membrane surface, resulting in the mitigation of membrane fouling directly.     

Removal of ammonium and nitrate through Anammox and FeS-driven autotrophic denitrification

● Simultaneous NH₄⁺/NO₃^– removal was achieved in the FeS denitrification system ● Anammox coupled FeS denitrification was responsible for NH₄⁺/NO₃^– removal ● Sulfammox, Feammox and Anammox occurred for NH₄⁺ removal ● Thiobacillus, Nitrospira , and Ca. Kuenenia were key functional microorganisms An autotrophic denitrifying bioreactor with iron sulfide (FeS) as the electron donor was operated to remove ammonium (NH₄⁺) and nitrate (NO₃⁻) synergistically from wastewater for more than 298 d. The concentration of FeS greatly affected the removal of NH₄⁺/NO₃⁻. Additionally, a low hydraulic retention time worsened the removal efficiency of NH₄⁺/NO₃⁻. When the hydraulic retention time was 12 h, the optimal removal was achieved with NH₄⁺ and NO₃⁻ removal percentages both above 88%, and the corresponding nitrogen removal loading rates of NH₄⁺ and NO₃⁻ were 49.1 and 44.0 mg/(L·d), respectively. The removal of NH₄⁺ mainly occurred in the bottom section of the bioreactor through sulfate/ferric reducing anaerobic ammonium oxidation (Sulfammox/Feammox), nitrification, and anaerobic ammonium oxidation (Anammox) by functional microbes such as Nitrospira, Nitrosomonas, and Candidatus Kuenenia. Meanwhile, NO₃⁻ was mainly removed in the middle and upper sections of the bioreactor through autotrophic denitrification by Ferritrophicum, Thiobacillus, Rhodanobacter, and Pseudomonas, which possessed complete denitrification-related genes with high relative abundances.     

Partial anammox achieved in full scale biofilm process for typical domestic wastewater treatment

• A full scale biofilm process was developed for typical domestic wastewater treatment. • The HRT was 8 h and secondary sedimentation tank was omitted. • Candidatus Brocadia were enriched in the HBR with an abundance of 2.89%. • Anammox enabled a stable ammonium removal of ~15% in the anoxic zone. The slow initiation of anammox for treating typical domestic wastewater and the relatively high footprint of wastewater treatment infrastructures are major concerns for practical wastewater treatment systems. Herein, a 300 m³/d hybrid biofilm reactor (HBR) process was developed and operated with a short hydraulic retention time (HRT) of 8 h. The analysis of the bacterial community demonstrated that anammox were enriched in the anoxic zone of the HBR process. The percentage abundance of Candidatus Brocadia in the total bacterial community of the anoxic zone increased from 0 at Day 1 to 0.33% at Day 130 and then to 2.89% at Day 213. Based upon the activity of anammox bacteria, the removal of ammonia nitrogen (NH₄⁺-N) in the anoxic zone was approximately 15%. This showed that the nitrogen transformation pathway was enhanced in the HBR system through partial anammox process in the anoxic zone. The final effluent contained 12 mg/L chemical oxygen demand (COD), 0.662 mg/L NH₄⁺-N, 7.2 mg/L total nitrogen (TN), and 6 mg/L SS, indicating the effectiveness of the HBR process for treating real domestic wastewater.     

Distribution and removal of antibiotic resistance genes during anaerobic sludge digestion with alkaline,thermal hydrolysis and ultrasonic pretreatments

Sludge digestion is critical to control the spread of ARGs from wastewater to soil. Fate of ARGs in three pretreatment-AD processes was investigated. UP was more efficient for ARGs removal than AP and THP in pretreatment-AD process. The total ARGs concentration showed significant correlation with 16S rRNA gene. The bacteria carrying ARGs could be mainly affiliated with Proteobacteria. Sewage sludge in the wastewater treatment plants contains considerable amount of antibiotic resistance genes (ARGs). A few studies have reported that anaerobic digestion (AD) could successfully remove some ARGs from sewage sludge, but information on the fate of ARGs in sludge pretreatment-AD process is still very limited. In this study, three sludge pretreatment methods, including alkaline, thermal hydrolysis and ultrasonic pretreatments, were compared to investigate the distribution and removal of ARGs in the sludge pretreatment-AD process. Results showed that the ARGs removal efficiency of AD itself was approximately 50.77%, and if these three sludge pretreatments were applied, the total ARGs removal efficiency of the whole pretreatment-AD process could be improved up to 52.50%–75.07%. The ultrasonic pretreatment was more efficient than alkaline and thermal hydrolysis pretreatments. Although thermal hydrolysis reduced ARGs obviously, the total ARGs rebounded considerably after inoculation and were only removed slightly in the subsequent AD process. Furthermore, it was found that the total ARGs concentration significantly correlated with the amount of 16S rRNA gene during the pretreatment and AD processes, and the bacteria carrying ARGs could be mainly affiliated with Proteobacteria.     

Scrap Iron Filings assisted nitrate and phosphate removal in low C/N waters using mixed microbial culture

• Microbes enhance denitrification under varying DO concentrations and SIF dosages. • Abiotic nitrate reduction rates are proportional to SIF age and dosage. • Over 80% of the simultaneously loaded NO₃⁻-N and PO₄³⁻ is removed biologically. This study focuses on identifying the factors under which mixed microbial seeds assist bio-chemical denitrification when Scrap Iron Filings (SIF) are used as electron donors and adsorbents in low C/N ratio waters. Batch studies were conducted in abiotic and biotic reactors containing fresh and aged SIF under different dissolved oxygen concentrations with NO₃⁻-N and/or PO₄^3- influent(s) and their nitrate/phosphate removal and by-product formations were studied. Batch reactors were seeded with a homogenized mixed microbial inoculum procured from natural sludges which were enriched over 6 months under denitrifying conditions in the presence of SIF. Results indicated that when influent containing 40 mg/L of NO₃⁻-N was treated with 5 g SIF, 79.9% nitrate reduction was observed in 8 days abiotically and 100% removal was accomplished in 20 days when the reactor was seeded. Both abiotic and seeded reactors removed more than 92% PO₄³⁻ under high DO conditions in 12 days. Abiotic and biochemical removal of NO₃⁻-N and abiotic removal of PO₄³⁻ were higher under independent NO₃⁻-N/PO₄³⁻ loading, while 99% PO₄^3- was removed biochemically under combined NO₃⁻-N and PO₄³⁻ loading. This study furthers the understandings of nitrate and phosphate removal in Zero Valent Iron (ZVI) assisted mixed microbial systems to encourage the application of SIF-supported bio-chemical processes in the simultaneous removals of these pollutants.     

Effect of nitrobenzene on the performance and bacterial community in an expanded granular sludge bed reactor treating high-sulfate organic wastewater

Less than 50 mg/L nitrobenzene brought little effect on anaerobic sulfate reduction. Kinetics of sulfate reduction under different nitrobenzene contents was studied. Increased nitrobenzene contents greatly changed the bacterial community structure. Genus Desulfovibrio played the key role in anaerobic sulfate reduction process. Nitrobenzene (NB) is frequently found in wastewaters containing sulfate and may affect biological sulfate reduction process, but information is limited on the responses of sulfate reduction efficiency and microbial community to the increased NB contents. In this study, a laboratory-scale expanded granular sludge bed reactor was operated continuously to treat high-sulfate organic wastewater with increased NB contents. Results successfully demonstrated that the presence of more than 50 mg/L NB depressed sulfate reduction and such inhibition was partly reversible. Bath experiments showed that the maximum specific desulfuration activity (SDA) decreased from 135.80 mg SO₄^2?/gVSS/d to 30.78 mg SO₄^2?/gVSS/d when the NB contents increased from none to 400 mg/L. High-throughput sequencing showed that NB also greatly affected bacterial community structure. Bacteroidetes dominated in the bioreactor. The abundance of Proteobacteria increased with NB addition while Firmicutes presented an opposite trend. Proteobacteria gradually replaced Firmicutes for the dominance in response to the increase of influent NB concentrations. The genus Desulfovibrio was the dominant sulfate-reducing bacteria (SRB) with absence or presence of NB, but was inhibited under high content of NB. The results provided better understanding for the biological sulfate reduction under NB stress.     

Methanation and chemolitrophic nitrogen removal by an anaerobic membrane bioreactor coupled partial nitrification and Anammox

● Efficient carbon methanation and nitrogen removal was achieved in AnMBR-PN/A system. ● AOB outcompeted NOB in PN section by limiting aeration and shortening SRT. ● The moderate residual organic matter of PN section triggered PD in anammox unit. ● AnAOB located at the bottom of UASB played an important role in nitrogen removal. An AnMBR-PN/A system was developed for mainstream sewage treatment. To verify the efficient methanation and subsequent chemolitrophic nitrogen removal, a long-term experiment and analysis of microbial activity were carried out. AnMBR performance was less affected by the change of hydraulic retention time (HRT), which could provide a stable influent for subsequent PN/A units. The COD removal efficiency of AnMBR was > 93% during the experiment, 85.5% of COD could be recovered in form of CH₄. With the HRT of PN/A being shortened from 10 to 6 h, nitrogen removal efficiency (NRE) of PN/A increased from 60.5% to 80.4%, but decreased to 68.8% when the HRT_PN/A further decreased to 4 h. Microbial analysis revealed that the highest specific ammonia oxidation activity (SAOA) and the ratio of SAOA to specific nitrate oxidation activity (SNOA) provide stable NO₂⁻-N/NH₄⁺-N for anammox, and anammox bacteria (mainly identified as Candidatus Brocadia) enriched at the bottom of Anammox-UASB might play an important role in nitrogen removal. In addition, the decrease of COD in Anammox-UASB indicated partial denitrification occurred, which jointly promoted nitrogen removal with anammox.     

Four kinds of capping materials for controlling phosphorus and nitrogen release from contaminated sediment using a static simulation experiment

• Lanthanum modified bentonite (LMB) can effectively absorb phosphorus (P). • Water treatment plant sludge (WTPS) capping is effective for controlling P release. •Aluminum-based P-inactivation agent (Al-PIA) is an efficient P control material. •The P adsorbed by WTPS and Al-PIA is mainly in the form of NAIP. We determined the effects of quartz sand (QS), water treatment plant sludge (WTPS), aluminum-based P-inactivation agent (Al-PIA), and lanthanum-modified bentonite (LMB) thin-layer capping on controlling phosphorus and nitrogen release from the sediment, using a static simulation experiment. The sediment in the experiment was sampled from Yundang Lagoon (Xiamen, Fujian Province, China), which is a eutrophic waterbody. The total phosphorus (TP), ammonium nitrogen (NH₄⁺-N), and total organic carbon (TOC) levels in the overlying water were measured at regular intervals, and the changes of different P forms in WTPS, Al-PIA, and sediment of each system were analyzed before and after the test. The average TP reduction rates of LMB, Al-PIA, WTPS, and QS were 94.82, 92.14, 86.88, and 10.68%, respectively, when the release strength of sediment TP was 2.26–9.19 mg/(m²·d) and the capping strength of the materials was 2 kg/m². Thin-layer capping of LMB, WTPS, and Al-PIA could effectively control P release from the sediment (P<0.05). However, thin-layer capping of LMB, Al-PIA, and QS did not significantly reduce the release of ammonium N and organic matter (P > 0.05). Based on our results, LMB, Al-PIA, and WTPS thin-layer capping promoted the migration and transformation of easily released P in sediment. The P adsorbed by WTPS and Al-PIA mainly occurred in the form of NAIP.     

Treating wastewater under zero waste principle using wetland mesocosms

• Smart wetland was designed to treat wastewater according to zero waste principle. • The system included a dynamic roughing filter, Cyperus papyrus (L.) and zeolite. • It removed 98.8 and 99.8% of chemical and bacterial pollutants in 3 days. • The effluent reused to irrigate a landscape and the sludge recycled as fertilizer. • The plant biomass is a profitable resource for antibacterial and antioxidants. The present investigation demonstrates the synergistic action of using a sedimentation unit together with Cyperus papyrus (L.) wetland enriched with zeolite mineral in one-year round experiment for treating wastewater. The system was designed to support a horizontal surface flow pattern and showed satisfactory removal efficiencies for both physicochemical and bacteriological contaminants within 3 days of residence time. The removal efficiencies ranged between 76.3% and 98.8% for total suspended solids, turbidity, iron, biological oxygen demand, and ammonia. The bacterial indicators (total and fecal coliforms, as well as fecal streptococci) and the potential pathogens (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa) showed removal efficiencies ranged between 96.9% and 99.8%. We expect the system to offer a smart management for every component according to zero waste principle. The treated effluent was reused to irrigate the landscape of pilot area, and the excess sludge was recycled as fertilizer and soil conditioner. The zeolite mineral did not require regeneration for almost 36 weeks of operation, and enhanced the density of shoots (14.11%) and the height of shoots (15.88%). The harvested plant biomass could be a profitable resource for potent antibacterial and antioxidant bioactive compounds. This could certainly offset part of the operation and maintenance costs and optimize the system implementation feasibility. Although the experiment was designed under local conditions, its results could provide insights to upgrade and optimize the performance of other analogous large-scale constructed wetlands.     

Anaerobic biodegradation of trimethoprim with sulfate as an electron acceptor

Anaerobic biodegradation of trimethoprim (TMP) coupled with sulfate reduction. Demethylation of TMP is the first step in the acclimated microbial consortia. The potential degraders and fermenters were enriched in the acclimated consortia. Activated sludge and river sediment had similar core microbiomes. Trimethoprim (TMP) is an antibiotic frequently detected in various environments. Microorganisms are the main drivers of emerging antibiotic contaminant degradation in the environment. However, the feasibility and stability of the anaerobic biodegradation of TMP with sulfate as an electron acceptor remain poorly understood. Here, TMP-degrading microbial consortia were successfully enriched from municipal activated sludge (AS) and river sediment (RS) as the initial inoculums. The acclimated consortia were capable of transforming TMP through demethylation, and the hydroxyl-substituted demethylated product (4-desmethyl-TMP) was further degraded. The biodegradation of TMP followed a 3-parameter sigmoid kinetic model. The potential degraders (Acetobacterium, Desulfovibrio, Desulfobulbus, and unidentified Peptococcaceae) and fermenters (Lentimicrobium and Petrimonas) were significantly enriched in the acclimated consortia. The AS- and RS-acclimated TMP-degrading consortia had similar core microbiomes. The anaerobic biodegradation of TMP could be coupled with sulfate respiration, which gives new insights into the antibiotic fate in real environments and provides a new route for the bioremediation of antibiotic-contaminated environments.     

Rapid control of black and odorous substances from heavily-polluted sediment by oxidation: Efficiency and effects

Oxidants were proposed to rapidly control black and odorous substances in sediments. NaClO and KMnO₄ had excellent efficiency to remove black and odorous substances. NaClO dramatically accelerated the release of organics, NH₄⁺-N, P, and heavy-metals. Moderate oxidation had a limited effect on microbial communities. NaClO of 0.2 mmol/g was viewed to be the optimum option. The control of black and odorous substances in sediments is of crucial importance to improve the urban ecological landscape and to restore water environments accordingly. In this study, chemical oxidation by the oxidants NaClO, H₂O₂, and KMnO₄ was proposed to achieve rapid control of black and odorous substances in heavily-polluted sediments. Results indicate that NaClO and KMnO₄ are effective at removing Fe(II) and acid volatile sulfides. The removal efficiencies of Fe(II) and AVS were determined to be 45.2%, 94.1%, and 93.7%, 89.5% after 24-h exposure to NaClO and KMnO₄ at 0.2 mmol/g, respectively. Additionally, rapid oxidation might accelerate the release of pollutants from sediment. The release of organic matters and phosphorus with the maximum ratios of 22.1% and 51.2% was observed upon NaClO oxidation at 0.4 mmol/g. Moreover, the introduction of oxidants contributed to changes in the microbial community composition in sediment. After oxidation by NaClO and KMnO₄ at 0.4 mmol/g, the Shannon index decreased from 6.72 to 5.19 and 4.95, whereas the OTU numbers decreased from 2904 to 1677 and 1553, respectively. Comparatively, H₂O₂ showed a lower effect on the removal of black and odorous substances, pollutant release, and changes in sediment microorganisms. This study illustrates the effects of oxidant addition on the characteristics of heavily polluted sediments and shows that chemical oxidants may be an option to achieve rapid control of black and odorous substances prior to remediation of water environments.     

Effects of Al3+ on pollutant removal and extracellular polymeric substances (EPS) under anaerobic,anoxic and oxic conditions

The highest removal efficiencies of COD and TN were achieved under 10 mg/L of Al³⁺. The highest TP removal efficiency occurred under 30 mg/L of Al³⁺. EPS, PS and PN concentrations increased with the addition of Al³⁺. Sludge properties significantly changed with the addition of Al³⁺. Aluminum ions produced by aluminum mining, electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge. They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation, as well as nitrogen and phosphorus removal. In this study, the effects of Al³⁺ on pollutant removal, sludge flocculation and the composition and structure of extracellular polymeric substances (EPS) were investigated under anaerobic, anoxic and oxic conditions. Results demonstrated that the highest chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies were detected for an Al³⁺ concentration of 10 mg/L. In addition, the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al³⁺. The highest removal efficiency of total phosphorus (TP) was achieved at an Al³⁺ concentration of 30 mg/L. The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones. The addition of Al³⁺ promoted the secretion of EPS. Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al³⁺. At the Al³⁺ concentration of 10 mg/L, fulvic acid and tryptophan fluorescence peaks began to appear, while the majority of protein species and the highest microbial activity were also detected. Low Al³⁺ concentrations (<10 mg/L) could promote the removal efficiencies of COD and TN, yet excessive Al³⁺ levels (>10 mg/L) weakened microbial activity. Higher Al³⁺ concentrations (>30 mg/L) also inhibited the release of phosphorus in the anaerobic zone by reacting with PO₄^3-.     

A novel sequence batch membrane carbonation photobioreactor developed for microalgae cultivation

A novel SBM-C-PBR was constructed for microalgae cultivation. Membrane fouling was greatly mitigated by membrane carbonation. NH₄⁺ and P removal rates were around 80% in SBM-C-PBR. Biomass was completely retained by membrane. In this study, a novel sequence batch membrane carbonation photobioreactor was developed for microalgae cultivation. Herein, membrane module was endowed functions as microalgae retention and CO₂ carbonation. The results in the batch experiments expressed that the relatively optimal pore size of membranes was 30 nm, photosynthetically active radiation was 36 W/m² and the CO₂ concentration was 10% (v/v). In long-term cultivation, the microalgal concentration separately accumulated up to 1179.0 mg/L and 1296.4 mg/L in two periods. The concentrations of chlorophyll a, chlorophyll b and carotenoids were increased about 23.2, 14.9 and 6.3 mg/L respectively in period I; meanwhile, the accumulation was about 25.0, 14.5, 6.6 mg/L respectively in the period II. Furthermore, the pH was kept about 5.5–7.5 due to intermittent carbonation mode, which was suitable for the growth of microalgae. Transmembrane pressure (TMP) was only increased by 0.19 and 0.16 bar in the end of periods I and II, respectively. The pure flux recovered to 75%–80% of the original value by only hydraulic cleaning. Scanning electron microscope images also illustrated that carbonation through membrane module could mitigate fouling levels greatly.     

Current status of municipal wastewater treatment plants in North-east China: implications for reforming and upgrading

● The performance and costs of 20 municipal WWTPs were analyzed. ● Effluent COD and NH₄⁺-N effluent exceed the limits more frequently in winter. ● Nitrification and refractory pollutant removal are limited at low temperatures. ● To meet the national standards, electricity cost must increase by > 42% in winter. ● Anammox, granular sludge, and aerobic denitrification are promising technologies. Climate affects the natural landscape, the economic productivity of societies, and the lifestyles of its inhabitants. It also influences municipal wastewater treatment. Biological processes are widely employed in municipal wastewater treatment plants (WWTPs), and the prolonged cold conditions brought by the winter months each year pose obstacles to meeting the national standards in relatively cold regions. Therefore, both a systematic analysis of existing technical bottlenecks as well as promising novel technologies are urgently needed for these cold regions. Taking North-east China as a case, this review studied and analyzed the main challenges affecting 20 municipal WWTPs. Moreover, we outlined the currently employed strategies and research issues pertaining to low temperature conditions. Low temperatures have been found to reduce the metabolism of microbes by 58% or more, thereby leading to chemical oxygen demand (COD) and NH₄⁺-N levels that have frequently exceeded the national standard during the winter months. Furthermore, the extracellular matrix tends to lead to activated sludge bulking issues. Widely employed strategies to combat these issues include increasing the aeration intensity, reflux volume, and flocculant addition; however, these strategies increase electricity consumption by > 42% in the winter months. Internationally, the processes of anaerobic ammonium oxidation (anammox), granular sludge, and aerobic denitrification have become the focus of research for overcoming low temperature. These have inspired us to review and propose directions for the further development of novel technologies suitable for cold regions, thereby overcoming the issues inherent in traditional processes that have failed to meet the presently reformed WWTP requirements.