Effects of heavy metal wastewater on the anoxic/aerobic-membrane bioreactor bioprocess and membrane fouling

Typical heavy metals in wastewater treatment plants in Nanjing, China: perspective of abundance, removal, and microbial response

Heavy metals (HMs) are hazardous contaminants with persistence and bioaccumulation, attracting widespread attention. Wastewater treatment plants (WWTPs) play vital roles in the pollution control of sewage, closely related to human health and the biological environment. Therefore, eight HMs in three typical WWTPs of Nanjing were determined in this study. The results revealed that Cr, Ni, Cu, and Zn were high-level HMs in all WWTPs. Notably, the highest contents of high-level HMs were found in electroplating WWTP (EWWTP) influent among three WWTPs, probably causing their higher removal (19.34-55.32%) during their primary treatment. In contrast, most HMs could be removed in the secondary treatment stage of municipal WWTP (MWWTP) and industrial WWTP (IWWTP) with the highest removal of As (72.00-85.81%). Analogously, nutrients were mainly removed during the secondary stage, with superior performance in MWWTP. A decrease in HMs removal was observed in the tertiary treatment of MWWTP and IWWTP compared to the secondary stage, while higher HMs removal (0.51-29.15%) was found in EWWTP except Hg. The highest content of HMs in sludge was Zn and Cr, which was more abundant in EWWTP than other WWTPs. The results of Illumina Miseq sequencing demonstrated the inhibition of microbial richness and diversity of EWWTP and IWWTP by industrial wastewater. Besides, alterations of microbial community structure and components were also observed owing to various influent sources. More similarity was found between EWWTP and MWWTP, in which the abundance of dominant genera, including Saccharimonadales (7.60-9.56%), Raineyella (5.06-7.38%), and Thauera (2.48-4.45%) was much higher than IWWTP.

Comparison of the short- and long-term effects of zinc ions on the anaerobic mesophilic co-digestion of food waste and waste activated sludge: Digester performance, antibiotic resistance gene reduction and the microbial community

Heavy metals contained in waste activated sludge (WAS), especially zinc ions, have an inhibitory effect on the anaerobic digestion. However, the effects of zinc ions on digester performance, antibiotic resistance genes (ARGs) reduction, and the microbial community involved in the anaerobic mesophilic co-digestion (AcoD) of WAS and food waste (FW) have not been fully characterized. Therefore, batch trials and continuous stirred tank reactors were used under different zinc-ion concentrations. Findings showed that the AcoD system can tolerate a maximum zinc ion of 540 mg/L in a short-term batch and 470 mg/L in a long-term AcoD system, promoting methane production of approximately 1.0-17.0 %. Metagenomic analysis revealed that syntrophic H2 transfer occurred between Syntrophomonas and Methanoculleus and the aceticlastic and hydrogenotrophic methanogenic pathways were both enhanced by 1.18- and 1.16 times, respectively. Moreover, the relative abundance of Methanosarcina increased from 58.4 % to 72.5 % at 470 mg/L to adapt to the high zinc ion concentration during long-term continuous operation. These results revealed that AcoD with a low zinc ion concentration can effectively increase the removal percentage of ARGs. The results provide guidance for biogas recovery and use of mesophilic AcoD with FW and WAS containing high zinc ion concentrations without pretreatment process.

Short-term influence of polytetrafluoroethylene micro/nano-plastics on the inhibition of copper and/or ciprofloxacin on the nitrifying sludge activities based on concentration addition and independent action models

Short-term influence of polytetrafluoroethylene micro/nano-plastics (PTFE-MPs/NPs) on the inhibition of copper (Cu2+) and/or ciprofloxacin (CIP) on the nitrifying sludge activities was explored based on concentration addition (CA) and independent action (IA) models. The half maximal inhibitory concentration (IC50) of Cu2+, CIP, PTFE-MPs (3 μm), and PTFE-NPs (800 nm) on the specific ammonium oxidation rate (SAOR) of nitrifying sludge was 64.57, 51.29, 102.33 and 93.33 mg L-1, respectively, while those on the specific nitrite oxidation rate (SNOR) of nitrifying sludge were 77.62, 32.36, 104.70 and 97.72 mg L-1, respectively. Among the five binary mixtures and two ternary mixtures composed by Cu2+, CIP, and/or PTFE-MPs/NPs, it was found that the two joint inhibitory actions from ternary mixtures on the SAOR and SNOR of the sludge showed time-dependent characteristics by analyzing of CA and IA models, while the five combined inhibitory effects from different binary mixtures did not all have time-dependent features. The two joint inhibition actions from diverse ternary mixtures on the SAOR at the exposure time of 60 min and on the SNOR at 90 min showed always concentration-dependent features, while the combined inhibitions with concentration-dependent characteristics had never been observed in the binary Cu2+ and PTFE-NPs mixtures at different exposure time. The Cu2+, CIP, and PTFE-MPs mixtures (or Cu2+, CIP, and PTFE-NPs mixtures) had synergistic actions on the SAOR at 90 min and antagonistic effects on the SNOR at 60 min based on CA and IA models, and these combined inhibitions did not exhibit concentration-dependent characteristics. In contrast, the joint inhibitory effects (on the SAOR and SNOR) with concentration-dependent features were found in the binary mixtures of CIP and PTFE-MPs at different exposure time, and the join inhibition changed from synergism to antagonism as the increasing concentration of mixed CIP and PTFE-MPs. This study provides novel perspectives for understanding the combined influence of plastic particles with different sizes, antibiotics, and heavy metals on the biological wastewater treatment process.

Effect of Cd(II) shock loading on performance, microbial enzymatic activity and microbial community in a sequencing batch reactor

The performance, microbial enzymatic activity and microbial community of a sequencing batch reactor (SBR) were explored under instantaneous Cd(II) shock loading. After a 24-h Cd(II) shock loading of 100 mg/L, the chemical oxygen demand and NH₄⁺-N removal efficiencies decreased significantly from 92.73% and 99.56% on day 22 to 32.73% and 43% on day 24, respectively, and then recovered to the normal values gradually. The specific oxygen utilization rate (SOUR), specific ammonia oxidation rate (SAOR), specific nitrite oxidation rate (SNOR), specific nitrite reduction rate (SNIRR) and specific nitrate reduction rate (SNRR) decreased by 64.81%, 73.28%, 77.77%, 56.84% and 52.46% on day 23 in comparison with the absence of Cd(II) shock loading, respectively, and they gradually returned to the normal levels. The changing trends of their associated microbial enzymatic activities including dehydrogenase, ammonia monooxygenase, nitrite oxidoreductase, nitrite reductase and nitrate reductase were in accordance with SOUR, SAOR, SNOR, SNIRR and SNRR, respectively. Cd(II) shock loading promoted the microbial reactive oxygen species production and lactate dehydrogenase release, indicating that instantaneous shock caused oxidative stress and damaged to cell membranes of the activated sludge. The microbial richness and diversity, and the relative abundance of Nitrosomonas and Thauera obviously decreased under the stress of Cd(II) shock loading. PICRUSt prediction showed that Cd (II) shock loading significantly affected Amino acid biosynthesis, Nucleoside and nucleotide biosynthesis. The present results are conducive to take adequate precautions to reduce the adverse effect on bioreactor performance in wastewater treatment systems.

Effects of antibiotics and heavy metals on denitrification in shallow eutrophic lakes

Antibiotic and heavy metal residues in shallow lakes caused by aquaculture and human activities such as sewage discharge have attracted much attention and public concern. However, mechanisms by which these environmental pollutants affect the microorganism-mediated biogeochemical cycle are unknown. This study focused on the effects of antibiotics, heavy metal, and antibiotic resistance genes (ARGs) on denitrification in shallow lakes. The results showed that antibiotics and metal elements had inhibitory effects on denitrification, whereas AGRs exhibited stimulating effects. Specifically, the enrofloxacin concentration showed a significant negative correlation with the copy number of denitrifying bacteria, whereas the copy number of the ARGs sulI, sulII, and tetG showed significant positive correlations. In addition, tetG was closely related to the community structure of nirS-type denitrifiers, and nirS-type denitrifiers were significantly correlated with the potential denitrification rate (PDR). Furthermore, the ARGs sulI, sulII, and tetG were positively correlated with PDR (P < 0.05). By contrast, the metal elements arsenic, manganese, cobalt, and antimony were negatively correlated with the copy number of denitrifying bacteria. Arsenic was significantly correlated with the community composition of nirK-type denitrifiers, but nirK-type denitrifiers did not show a significant correlation with the PDR. This work extends our understanding of the effects of antibiotics and heavy metals on denitrification, but further studies are needed to determine the interaction effects of pollutants.

Evaluation of partial nitrification efficiency as a response to cadmium concentration and microplastic polyvinylchloride abundance during landfill leachate treatment

The partial nitrification efficiency response to the presence of cadmium (Cd²⁺) and microplastics was investigated. Microplastics polyvinylchloride (PVC) abundance was 0-10,000 particles/L, and Cd²⁺ concentration was 0-10 mg/L. Cd-only inhibited the NH₄⁺-N oxidation rate 1.21, 1.23, and 1.18 times with concentrations at 1, 5, and 10 mg/L, respectively. PVC-only inhibited NH₄⁺-N oxidation rate 1.01, 1.21 and 1.05 times with PVC abundance at 1000, 5000 and 10,000 particles/L, respectively. The ammonia oxidation rate was improved with the co-existence of PVC and Cd²⁺ at the conditions PVC1000 and PVC5000, which could be attributed to the PVC. PVC at 1000 particles/L could act as carrier and mitigate the negative effect of Cd²⁺ to the partial nitrification process. Moreover, the partial nitrification process was largely inhibited with PVC abundance at 10,000 particles/L. First-order kinetic models could simulate the NH₄⁺-N, NO₂^-N, and NO₃^--N changes in the partial nitrification process.

Effect of heavy metals on the performance and bacterial profiles of activated sludge in a semi-continuous reactor

Heavy metals are toxic to microorganisms at specific concentrations and can have a serious effect on the efficiency of biological wastewater treatment plants. The wastewater treatment performance and bacterial communities of activated sludge were investigated at different heavy metal concentrations (0.1-10 mg L^-1 for Cd(II), Pb(II) and 1-100 mg L^-1 for Cu(II)) in a well-controlled semi-continuous reactor in 30 d period. Glucose was added once every 8 h as the carbon source throughout the experiment. The heavy metal toxicity was related to chemical oxygen demand (COD), total organic carbon (TOC), three-dimensional fluorescence excitation-emission matrix (EEM) spectroscopy, bacterial activity and community composition. The first-order consumption rate for glucose showed that the activity was decreasing in comparison to the control. The COD removal efficiency was also decreased from 87% to 26% in all the reactors under different heavy metal concentrations treatment. The PCR-DGGE and sequencing results revealed that the bacterial diversity showed evident variations under heavy metal stress owing to the potential toxicity of heavy metals. At the genus level, Pedobacter steynii and Flavobacterium, were only tolerant to Cu(II) at 100 mg L^-1, while Rhodanobacter thiooxydans resisted to all heavy metal concentrations except Cu(II) 100 mg L^-1. Cluster analysis and Principal component analysis (PCA) revealed that the microbial community in Cu(II) was different from the sludge samples treated with Cd(II) and Pb(II) concentrations. The study indicated that it is necessary to identify the metal tolerant species of bacteria for maintaining good performance of biological wastewater treatment plants.

Long term effects of Pb2+ on the membrane fouling in a hydrolytic-anoxic-oxic-membrane bioreactor treating synthetic electroplating wastewater

Long-term effects of Pb²⁺ on the operating performance and membrane fouling of two hydrolytic-anoxic-oxic-membrane bioreactors treating synthetic electroplating wastewater were investigated. The COD, NH₄⁺-N and TN removal efficiencies decreased by 5.5%, 10.4% and 7.9% with long-term exposure of 2 mg L^-1 Pb²⁺, while serious decreases achieved 25.4%, 35.0% and 26.2% with 6 mg L^-1 Pb²⁺ exposure, respectively. 2 mg L^-1 Pb²⁺ mitigated the cake layer fouling rate by 25.4% but increased the pore blocking rate by 69.1%, which was contributed by the increase of low and moderate molecular weight (MW) components in the soluble and colloidal foulants (SCFs). 6 mg L^-1 Pb²⁺ accelerated the cake layer fouling rate by 101.1%, but mitigated the pore blocking rate by 6.4% due to the increase of high MW SCFs (especially polysaccharides). Thermodynamic analyses showed that Pb²⁺ regulated the concentration and protein/polysaccharide ratio of loosely bound extracellular polymeric substances, thus changing the flocs hydrophobicity and aggregation capacity, leading the cake layer fouling rate variation.

Investigating the effect of copper and magnesium ions on nitrogen removal capacity of pure cultures by modified non-competitive inhibition model

Copper, a common heavy metal, may be beneficial for or poisonous to microbial activity. The objective of this study was to determine the effect of different copper ion concentrations on the nitrogen removal performance of Arthrobacter arilaitensis strain Y-10 and Pseudomonas taiwanensis strain J488. The non-competitive inhibition model was employed to evaluate the 50% inhibition concentrations (IC₅₀ values) of copper ions toward the pure strains. In the absence of magnesium ions, a low concentration of copper (0.1 mg/L) significantly enhanced the ammonium removal ability of strain Y-10 and its removal efficiency increased by 10.88% compared with the control treatment. Copper ranging from 0 to 0.1 mg/L had no significant effect on the ammonium removal capacity of strain J488. After adding 9.90 mg/L of magnesium to the basal medium, the effects of copper on nitrification of ammonium or denitrification of nitrate or nitrite were also assessed. In these conditions, 0.25 mg/L copper ions could strongly inhibit the ammonium, nitrate and nitrite removal activities for strain Y-10. For strain J488, no clear deterioration in ammonium removal efficiency was observed at copper ion concentrations below 0.5 mg/L, but 0.25 mg/L copper ions significantly inhibited nitrate and nitrite removal efficiencies, which were only 45.88% and 6.35%, respectively. The IC₅₀ values of copper ions for nitrate and nitrite removal by strain Y-10 were 0.195 and 0.090 mg/L respectively; for strain J488, the IC₅₀ values were 0.175 and 0.196 mg/L. The magnesium ions could improve the cell growth, nitrogen removal efficiency and copper ion resistance of bacteria.

Characteristics of Heterotrophic Nitrifying and Aerobic Denitrifying Arthrobacter nicotianae D51 Strain in the Presence of Copper

A heterotrophic nitrification and aerobic denitrification bacterium, strain D51, was identified as Arthrobacter nicotianae based on morphological, phospholipid fatty acids (PLFAs), and 16S rRNA gene sequence analyses. Further tests demonstrated that strain D51 had the capability to use nitrite, nitrate, or ammonium as the sole nitrogen source in the presence of Cu2+. The maximum removal efficiencies of nitrite, nitrate and ammonium were 68.97%, 78.32%, and 98.70%, respectively. Additionally, the maximum growth rate and denitrification capacity of this strain occurred in the presence of 0.05 mg·L−1 of Cu2+.However, the growth and aerobic denitrification capacity were intensively inhibited by Cu2+ at ≥0.1 mg·L−1. Moreover, gas chromatography indicated that a portion of the nitrogen was transformed into N2O when the nitrite, nitrate, and ammonium were separately used as the sole nitrogen source. This is the first study of the nitrification and denitrification ability of Arthrobacter nicotianae under aerobic conditions, and the first experiment to investigate the impact of Cu2+ concentration on the growth and denitrification ability of this bacteria. The results presented herein extend the known varieties of heterotrophic nitrifying–aerobic denitrifying bacteria and provide useful information regarding the specific bacteria for nitrogen bioremediation of industrial wastewater containing Cu2+.

Treatment of low-level Cu(II) wastewater and regeneration through a novel capacitive deionization-electrodeionization (CDI-EDI) technology

It was difficult for mature technologies to manage the low-level heavy metal wastewater due to low efficiency, secondary pollution and difficult enrichment. In this study, a novel capacitive deionization-electrodeionization (CDI-EDI) technology was developed through coordination mechanism of electromigration, electro-adsorption and ion exchange. Based on this technique, the low-content heavy metal ions in high-salinity wastewater could be removed efficiently. Moreover, a higher electro-adsorption CDI electrode was applied in the CDI-EDI stack. EDI device was optimized by decreasing ion exchange membranes from 4 to 2, thus reduced the stack cost. Based on the CDI-EDI stack, the simulated Cu(II) wastewater (C₀ = 42.9 mg/L) was treated, and its average removal rate in 1st cycle cathode- and anode-effluent was 95.7% and 87.6%, respectively, under optimal direct current (DC) of 1.5 mA for 1.5 min, followed by electroregeneration of resin and electrode. Besides, the actual electroplating wastewater containing Ni(II) (389.4 mg/L) was treated via this device after precipitation to verify its feasibility. The results indicated that Ni(II) in the anode- and cathode-compartments were removed by 1.61 mg/L and 2.01 mg/L, respectively, only via one-stage CDI-EDI device under the operating voltage (0.10-0.20 V) and direct current (2.0-4.0 mA). It was possible to improve desalination efficiency of low-concentration heavy metal using tandem-type multistage devices. The CDI-EDI technique could not only ensure stable effluent and lower regenerations cost, but also enrich heavy metal from regeneration fluid to achieve resource recovery. This study would have obvious implications in treatment of low-content and salt-containing heavy metal wastewater with high efficiency and low energy consumption.

Characterization of the Evolution of Crystallization Fouling in Membranes

Liquid-to-air membrane energy exchangers (LAMEEs) are promising in heating, ventilating, and air-conditioning applications because they are able to use semipermeable membranes to transfer heat and moisture between air and liquid desiccant streams. However, the development of crystallization fouling in membranes may pose a great risk to the long-term performance of LAMEEs. The main aim of this paper is to characterize the evolution of crystallization fouling in membranes through the use of both noninvasive and invasive methods. Noninvasive methods are used to study the development of fouling in the LAMEE by monitoring the changes in moisture flux through the membrane and overall moisture-transfer resistance of the LAMEE. On the other hand, invasive methods are implemented to characterize fouled membranes by using optical microscopy and scanning electron microscopy (SEM) to depict the morphology of crystal deposits and energy-dispersive X-ray spectroscopy (EDX) to identify the composition of the deposits. Experiments are performed by using air to dehydrate MgCl₂(aq) at two operating conditions of low and high fouling rates. The results show that the moisture flux decreases and the moisture-transfer resistance increases more considerably during the test at the high fouling rate than in the test at the low fouling rate. SEM micrographs show that cake crystal deposits cover the membrane surface in the test at the high fouling rate, whereas only few crystal particles are observed on the membrane in the test at the low fouling rate. Furthermore, the crystal deposits undergo more structural changes in the tests at the high fouling rate than in the tests at the low fouling rate, possibly because of the higher moisture transfer rate through the membrane in the tests at the high fouling rate. Finally, the SEM-EDX analysis confirms that the crystal deposits primarily consist of Mg, Cl, and O elements.

Effect of Cu, Ni and Zn on Fe(II)-driven autotrophic denitrification

Fe(II)-mediated autotrophic denitrification in the presence of copper (Cu), nickel (Ni) and zinc (Zn) with four different microbial cultures was investigated in batch bioassays. In the absence of metals, complete nitrate removal and Fe(II) oxidation were achieved with a Thiobacillus-dominated mixed culture and Pseudogulbenkiania sp. 2002 after 7 d. A nitrate removal of 96 and 91% was observed with a pure culture of T. denitrificans and an activated sludge enrichment, respectively, after 10 d of incubation. Cu, Ni and Zn were then supplemented at an initial concentration of 5, 10, 20 and 40 mg Me/L. A decrease of approximately 50% of the soluble metal concentrations occurred in the first 4 d of denitrification, due to metal precipitation, co-precipitation, sorption onto iron (hydr)oxides, and probably sorption onto biomass. A higher sensitivity to metal toxicity was observed for the microbial pure cultures. Pseudogulbenkiania sp. 2002 was the least tolerant among the biomasses tested, resulting in only 6, 8 and 6% nitrate removal for the highest Cu, Ni and Zn concentrations, respectively. In contrast, the highest nitrate removal efficiency and specific rates were achieved with the Thiobacillus-dominated mixed culture, which better tolerated the presence of metals. Averagely, Cu resulted in the highest inhibition of nitrate removal, followed by Zn and Ni.

Influence of elevated Zn (II) on Anammox system: Microbial variation and zinc tolerance

Nitrogen removal by anaerobic ammonium oxidation (Anammox) has attracted increasing attention in nowadays. An Anammox biofilter was subjected to a continuous loading of elevated Zn (II). The influence of Zn (II) on the nitrogen removal, microbial community and biofilm property was investigated in the condition of 23-26 °C and 3.5 h HRT. The nitrogen removal greatly decreased to 0.054 from the initial 0.502 kg m^-3 d^-1, with the Zn (II) addition. Anaerobic ammonia-oxidizing bacteria (AAOB) had self-adaption to Zn (II) in 1-10 mg L^-1 and was significantly enhanced after long-term acclimatization, while the suppression threshold was 20 mg L^-1. Soluble microbial products (SMP) increased correspondingly with Zn (II), while extracellular polymeric substance (EPS) climbed up initially and then decreased. Anammox biofilm performed the highest zinc adsorption as 158.27 mg g^-1 SS in biofilm. High Zn (II) improved the microbial diversity and lowered the Candidatus Kuenenia abuandance to 1.38% from 20.89%.

Mechanisms of microbial community structure and biofouling shifts under multivalent cations stress in membrane bioreactors

Five lab-scale membrane bioreactors (MBRs) were continuously operated to investigate the mechanisms and linkages of the microbial community and membrane fouling with trivalent metal cations (Fe(III) and Al(III)) and bivalent metal cations (Ca(II) and Mg(II)) shock loads. COD and NH₄⁺-N removals showed recovery trends along with treatment process in the presence of metals. Trivalent metal cations reduced trans-membrane pressure (TMP) as well as fouling rate (dTMP/dt) and extended membrane module replacement period by binding activated sludge extracellular polymeric substance (EPS) and effluent soluble microbial product (SMP) productions. Illunima sequencing of 16S rRNA gene showed that metal stress stimulated specific metal-tolerance bacteria in the MBRs. Canonical correspondence analysis indicated that EPS and SMP made different contributions to the distribution of microbial community structure in Fe(III) and Al (III) systems, respectively. Under bivalent metal conditions, microbial community shifts and Ca(II) binding bridge worked together to inhibit EPS and SMP, while filamentous bacteria stimulated by Mg(II) that mainly controlled membrane fouling. This study has shown that the comparison of tri- and bivalent metals for membrane fouling control with binding bridge and functional microorganisms can provide a strategy for practical membrane bioreactor applications.

Short-term and long-term effects of Zn (II) on the microbial activity and sludge property of partial nitrification process

Autotrophic nitrogen removal was an innovative and economical nitrogen removal technology with less oxygen and no organics consumption, in which partial nitrification (PN) is the key component. It is necessary to clear the impact of metal ions on PN since the development of industry increased their opportunity for entering into wastewater. In this study, PN process was successfully started-up in an SBR, the short-term and long-term effects of Zn (II) on microbial bioactivity and the sludge adsorption ability for Zn (II) were investigated. Results suggested that low Zn (II) were favorable for AOB bioactivity, while the long-term effect also induced NOB bioactivity. The suppression threshold of Zn (II) on AOB in short-term effect was 10mgL^-1, which rose to 50mgL^-1 in the long-term effect due to the self-adaption. The PN sludge presented prominent absorbability for zinc and performed a quadratic relation with the Zn (II) concentration.

Study on the mechanism of copper-ammonia complex decomposition in struvite formation process and enhanced ammonia and copper removal

Heavy metals and ammonia are difficult to remove from wastewater, as they easily combine into refractory complexes. The struvite formation method (SFM) was applied for the complex decomposition and simultaneous removal of heavy metal and ammonia. The results indicated that ammonia deprivation by SFM was the key factor leading to the decomposition of the copper-ammonia complex ion. Ammonia was separated from solution as crystalline struvite, and the copper mainly co-precipitated as copper hydroxide together with struvite. Hydrogen bonding and electrostatic attraction were considered to be the main surface interactions between struvite and copper hydroxide. Hydrogen bonding was concluded to be the key factor leading to the co-precipitation. In addition, incorporation of copper ions into the struvite crystal also occurred during the treatment process.

Recovery of nitrification in cadmium-inhibited activated sludge system by bio-accelerators

Cadmium (Cd) is toxic to nitrifying bacteria, but current studies on recovery process in Cd-inhibited activated sludge system are limited, especially on intensify-recovery processes with developing and optimizing nontoxic bio-accelerators. In this study, bioactivity recovery effects were demonstrated with respect to effluent NH4(+)-N, NO2(-)-N, NO3(-)-N concentrations, specific oxygen uptake rates and cadmium distribution in five parallel SBRs. Results indicated that bioactivity of nitrifying bacteria was mainly inhibited by surface-bound Cd. Dosing biotin, l-aspartic acid and cytokinin simultaneously was the most effective. Linear chain, together with amide (NH) and carboxyl (COOH) groups, may be important factors in fast nitrification recovery process. In terms of dosage and dosing mode, six-multiple dosage of optimal mixture with dosing at each cycle evenly was the most effective and bioactivities of nitrifying bacteria could 100% recovered within 7days. The bio-accelerators and optimum usage can be potentially applied to cope with heavy metal shock-loading emergency situations.

Eggshell: A green adsorbent for heavy metal removal in an MBR system

Presence of heavy metals as well as different metal ions in treated wastewater is a problem for the environment as well as human health. This paper aims to investigate the possibility to combine an MBR (membrane biological reactor) with an adsorption process onto powdered eggshell and eggshell membrane in order to improve metal removal from wastewater. The first step of the experimental analysis consists of the evaluation of the compatibility between the two processes. Then, a study about sorbent concentration and size effect on fouling was conducted, because the use of this kind of sorbent could affect membrane performance. The second step of the work concerns the check up of eggshell removal capacity as a function of sorbent size, achieved treating an aqueous solution containing Al(3+), Fe(2+) and Zn(2+) as water pollutants. Finally, synthetic wastewater, containing the metal species, was treated by two alternative process schemes: one of them performs the metal uptake in a dedicated adsorption unit, before the MBR. In the second, the two processes take place in the same unit. Results demonstrate that the optimization of the first option could be a solution to MBR upgrading.

Structure and distribution of inorganic components in the cake layer of a membrane bioreactor treating municipal wastewater

A laboratory-scale submerged anoxic-oxic membrane bioreactor treating municipal wastewater was operated to investigate the structure and distribution of the inorganic cake layer buildup on the membrane. BCR (European Community Bureau of Reference) sequential extraction, X-ray photoelectron spectroscopy (XPS), and both map and line scan of energy-dispersive X-ray analysis (EDX) were performed for cake layer characterization. BCR results showed that Si, Al, Ca, Mg, Fe, and Ba were the predominant inorganic elements in the cake layer, and they occurred mostly as crystal particles. Crystal SiO2 was the dominant inorganic compound while Ca in the form of CaSO4 (dominant) and CaCO3 were also present, but exerted little effect on the cake layer structure because most of these compounds were deposited as precipitates on the reactor bottom. EDX results indicated that Si and Al accumulated together along the cross-sectional cake layer in the form of Si-Al (SiO2-Al2O3) crystal particles.

Toxicants inhibiting anaerobic digestion: a review

Anaerobic digestion is increasingly being used to treat wastes from many sources because of its manifold advantages over aerobic treatment, e.g. low sludge production and low energy requirements. However, anaerobic digestion is sensitive to toxicants, and a wide range of compounds can inhibit the process and cause upset or failure. Substantial research has been carried out over the years to identify specific inhibitors/toxicants, and their mechanism of toxicity in anaerobic digestion. In this review we present a detailed and critical summary of research on the inhibition of anaerobic processes by specific organic toxicants (e.g., chlorophenols, halogenated aliphatics and long chain fatty acids), inorganic toxicants (e.g., ammonia, sulfide and heavy metals) and in particular, nanomaterials, focusing on the mechanism of their inhibition/toxicity. A better understanding of the fundamental mechanisms behind inhibition/toxicity will enhance the wider application of anaerobic digestion.

Effect of zinc on anammox activity and performance of simultaneous partial nitrification, anammox and denitrification (SNAD) process

In the present study, short-term effects of zinc on anammox activities and long-term effect of zinc on the performance of simultaneous partial nitrification, anammox and denitrification (SNAD) process were evaluated. The anammox activity decreased with increasing zinc concentration and exposure time in short-term tests. The IC50 value of zinc was found to be 6.9mg/L. However, the presence of zinc (<10mg/L) in wastewater stimulated the microbial activities and nitrogen removal performance of SNAD process in sequencing batch biofilm reactor (SBBR). At first, inhibition of SNAD process was observed when influent zinc concentration increased to 20mg/L. The system recovered immediately, suggesting the acclimatization of microbial communities of SNAD process. The results showed that SBBR was well acclimatized under high zinc concentration (50-100mg/L) achieving 98% NH4(+)-N, 96% TN and 87% COD removal efficiencies.