The behavior of melamine in biological wastewater treatment system

Melamine - A PMT/vPvM substance as a generic indicator for anthropogenic activity and urbanisation? An explorative study on melamine in the water cycle and soil

Melamine has a high production volume today and is spread ubiquitously in the anthropogenic technosphere. It is released steadily to the water cycle by many sources. Even though melamine has low direct toxicity, chronic exposure can cause nephrolithiasis and disrupt the endocrine system. Most data on melamine is based on case studies with, when compared, partially contradictive implications. As melamine is a compound of many sources (SMS), very persistent, mobile (vPvM), and toxic (PMT) it has the potential to break through natural barriers posing a potential risk to drinking water resources. This study combines existing data with own measurements gathered through various individual monitoring campaigns with the aim to gain new insights into its environmental behaviour and hotspots. Samples from surface water bodies, groundwater, wastewater (treated, untreated), and soil samples were analysed regarding their melamine concentration via liquid chromatography coupled with tandem mass spectrometry (LC-MSMS). Besides three drinking water samples, melamine could be found in all water samples (n = 632) of this study, with a maximum concentration of 1289 ng/L in drinking water and 1120 ng/L in groundwater. While a constant baseline melamine concentration with an event-based release could be observed in most surface water bodies, higher concentrations towards Western Europe (urbanisation and chemical industry) was observed for wastewater. A similar pattern was found in the spatial distribution of melamine in agricultural soils towards an urban/suburban area. As, in general, melamine concentrations were higher towards urbans centers melamine can also be classified as an indicator of anthropogenic activity and urbanisation, but also spotlights on these areas as hotspots for potentially many compounds of the human technosphere. We call policy to shift from the existing one-size-fits-all solution to more flexible and risk-based approaches to prepare for future challenges.

Dynamic Source Distribution and Emission Inventory of a Persistent, Mobile, and Toxic (PMT) Substance, Melamine, in China

Persistent, mobile, and toxic (PMT) substances are affecting the safety of drinking water and are threatening the environment and human health. Many PMT substances are used in industrial processing or consumer products, but their sources and emissions mostly remain unclear. This study presents a long-term source distribution and emission estimation of melamine, a high-production-volume PMT substance of emerging global concern. The results indicate that in China, approximately 1858.7 kilotonnes (kt) of melamine were released into the water (∼58.9%), air (∼27.0%), and soil systems (∼14.1%) between 1995 and 2020, mainly from its production and use in the decorative panels, textiles, and paper industries. The textile and paper industries have the highest emission-to-consumption ratios, with more than 90% emissions per unit consumption. Sewage treatment plants are the largest source of melamine in the environment for the time being, but in-use products and their wastes will serve as significant melamine sources in the future. The study prompts priority action to control the risk of PMT substances internationally.

Transformation of potentially persistent and mobile organic micropollutants in column experiments

The occurrence of potentially persistent and mobile (PM) organic micropollutants (OMP) in the aquatic environment is recognized as a severe threat to water resources and drinking water suppliers. The current study investigated long-term fate (persistency and bio-transformation) of several emerging contaminants in a simulated bank filtration (BF) for the first time. In parallel, four sand column systems were operated with groundwater and continuously spiked with an average concentration of 1 μg/L for 24 OMP. Each column system consisted of two sand columns connected in series. Presumably, biological activities in the first column were higher than in the second column, as dissolved oxygen utilization, dissolved organic matter (DOM) and UV absorbance at 254 nm (UV254) reduction rates were high in the first column. This study revealed that 9 out of 24 OMP were persistent and mobile throughout the study under oxic conditions and within a hydraulic retention time (HRT) of 12 days. However, 2 (out of 9) OMP were persistent but showed sorption behavior. 15 (out of 24) OMP displayed bio-transformation, 4 were eliminated entirely within 4.5 days of HRT. Others showed constant or improved degradation with the adaptation (or operation) time. Improved degradation with adaption was high in the bioactive sand columns. However, 8 OMP showed improved elimination at high HRT, even in low biologically active columns. In addition, no significant effect of the DOM on the eliminations of OMP was found except for 4-hydroxy-1-(2-hydroxyethyl)-2,2,6,6,-tetramethylpiperidine (HHTMP), 2-methyl-2-propene-1-sulfonic acid (MPSA) and sulfamethoxazole (SMX). The eliminations of HHTMP (Pearson's r > 0.80, p < 0.05), MPSA (Pearson's r > 0.70) and SMX (Pearson's r > 0.80) correlated with the removals of humic substances in the sand columns. Overall, adaptation time and HRT play a crucial role in the elimination of emerging OMP through BF, yet at the same time several OMP exhibit persistent behavior.

Pilot-scale removal of persistent and mobile organic substances in granular activated carbon filters and experimental predictability at lab-scale

Present knowledge about the fate of persistent and mobile (PM) substances in drinking water treatment is limited. Hence, this study assesses the potential of fixed-bed granular activated carbon (GAC) filters to fill the treatment gap for PM substances and the elimination predictability from lab-scale experiments. Two parallel pilot filters (GAC bed height 2 m, diameter 15 cm) with different GAC were operated for 1.5 years (ca. 47,000 BV throughput) alongside rapid small-scale column tests (RSSCT) designed based on the proportional diffusivity (PD) and the constant diffusivity (CD) approaches. Background dissolved organic matter (DOM) and a set of 17 target substances were investigated, among them 2-acrylamido-2-methylpropane sulfonate (AAMPS), adamantan-1-amine (ATA), melamine (MEL) and trifluoromethanesulfonic acid (TFMSA). Nine substances were predominantly present in the drinking water used as pilot filter influent (frequencies of detection above 80 %, median concentrations 0.003-1.868 μg/L) and their breakthrough behaviors could be observed: TFMSA was not retained at all, four substances including AAMPS and ATA reached complete breakthrough below 20,000 BV, three compounds were partially retained until the end of operation and oxypurinol was retained completely. The comparable PM candidate and DOM removal performances of both GAC aligns with their very similar surface characteristics and elemental compositions. The agreement of results between RSSCT with the pilot-scale filters were substance specific and no superior RSSCT design could be identified. However, CD-RSSCT provide a conservative removal prediction for most studied compounds. MEL adsorption was significantly underestimated by both RSSCT designs. Using the criterion of a carbon usage rate (with respect to 50 % breakthrough) below 25 mg_GAC/L_water for an economic retention by fixed-bed GAC filters, five (out of nine) substances met the requirement.

Primary amide-functionalized cyclotricatechylene covalent organic frameworks membrane for efficient enrichment of melamine and its derivatives in migration solution of food contact materials

A highly chemically stable primary amide-functionalized cyclotricatechylene covalent organic framework was synthesized by an irreversible reaction and a post-synthetic modification. It possessed a rod-like morphology and exhibited strong solvent stability owing to the polyether bonds. The material showed good adsorption performance for melamine and its derivatives and adsorption mechanism was investigated by molecular simulations. The adsorbent was coated on the nylon-66 membrane to prepare the enrichment membrane. Under optimized conditions, an in-syringe membrane-based extraction method, combined with ultra-high performance liquid chromatography-tandem mass spectrometry was developed for the analysis of melamine and six melamine derivatives in the migration solution. A good linearity was obtained with correlation coefficients ranging from 0.9924 to 0.9995. The limits of detection were 1-200 ng/L and the limits of quantification were 3-500 ng/L. This method was successfully applied to the migration solution of sushi bamboo rolling mats with spiked recoveries of 73.2%-115% and relative standard deviations of 0.9%-9.9%. This work shows a practical and perspective approach for the efficient enrichment of food contact material hazards.

Elevated emissions of melamine and its derivatives in the indoor environments of typical e-waste recycling facilities and adjacent communities and implications for human exposure

Melamine and its derivatives are used as additives in flame retardants. Moreover, melamine-containing consumables such as laminates, adhesives, glues, and plastics are extensively used in electronic products. Nevertheless, there is no information concerning the identification of melamine and its derivatives during e-waste recycling. In the present study, the occurrence of melamine and three of its derivatives (cyanuric acid, ammelide, and ammeline) was identified for the first time in indoor dust from typical e-waste recycling areas and adjacent rural communities. Urban communities situated about 80 kilometers away were used as a control. The target analytes were detected in almost all the dust samples, which were dominated by melamine and cyanuric acid. The total concentrations of melamine and its derivatives varied among sampling locations in the following order: e-waste workshops (geometric mean: 15,018 ng/g) > urban houses (9060 ng/g) > local rural houses (6204 ng/g) > local streets (201 ng/g). This suggested that e-waste dismantling/recycling activities mainly contributed to the abundant emission of melamine and its derivatives in e-waste dust. Correlation analysis indicated that melamine and its derivatives were similarly applied in electronic products and e-waste recycling resulted in common emissions. The combined toxicity of melamine and its derivatives on human bladder cancer cells was observed. Importantly, Monte Carlo analysis was used to determine that the estimated daily intakes of these chemicals via dust ingestion for occupational e-waste recycling workers were 2.5-9 times higher than the estimated daily intakes for adult residents in both adjacent local communities and urban areas. These results are the first to demonstrate that e-waste dismantling workers are more vulnerable to the exposure risk posed by the presence of melamine and its derivatives in e-waste dust, which deserves more research attention.

White Rot Fungi Produce Novel Tire Wear Compound Metabolites and Reveal Underappreciated Amino Acid Conjugation Pathways

There is increasing concern about tire wear compounds (TWCs) in surface water and stormwater as evidence grows on their toxicity and widespread detection in the environment. Because TWCs are prevalent in stormwater, there is a need to understand fate and treatment options including biotransformation in green infrastructure (e.g., bioretention). Particularly, fungal biotransformation is not well-studied in a stormwater context despite the known ability of certain fungi to remove recalcitrant contaminants. Here, we report the first study on fungal biotransformation of the TWCs acetanilide and hexamethoxymethylmelamine (HMMM). We found that the model white rot fungus, Trametes versicolor, removed 81.9% and 69.6% of acetanilide and HMMM, respectively, with no significant sorption to biomass. The bicyclic amine 1,3-diphenylguanidine was not removed. Additionally, we identified novel TWC metabolites using semi-untargeted metabolomics via high-resolution mass spectrometry. Key metabolites include multiple isomers of HMMM biotransformation products, melamine as a possible "dead-end" product of HMMM (verified with an authentic standard), and a glutamine-conjugated product of acetanilide. These metabolites have implications for environmental toxicity and treatment. Our discovery of the first fungal glutamine-conjugated product highlights the need to investigate amino acid conjugation as an important pathway in biotransformation of contaminants, with implications in other fields including natural products discovery.

Insights into how poly aluminum chloride and poly ferric sulfate affect methane production from anaerobic digestion of waste activated sludge

Poly aluminum chloride (PAC) and poly ferric sulfate (PFS) are widely used in wastewater treatment and sludge dewatering, resulting in their amounts being accumulated substantially in waste activated sludge (WAS). Till now, however, little information about their influence on WAS digestion is available. This work therefore aims to provide insights into how PAC and PFS affect sludge anaerobic digestion. The experimental results showed that PFS's inhibition to methane production was much severer than PAC, in control reactor (0 mg Al or Fe /g TSS), the maximum cumulative methane production was 152.99 ± 7.18 mL/g VSS, when flocculants concentration increased to 30 mg Al/g TSS or 30 mg Fe/g TSS, the yields decreased to 129.54 ± 6.18 mL/g VSS and 89.52 ± 4.82 mL/g VSS respectively. Mechanism explorations exhibited that protein in WAS could bond with flocculants, which would inhibit protein bioconversion. It was also observed that the apparent activation energy (AAE) of organic solubilisation of PAC and PFS-contained sludge were increased by 38.58% and 18.67% respectively. Meanwhile, compared to the PFS, PAC led to more serious suppression of hydrolysis and acidogenesis processes, with propionic acid used as substrate, PFS inhibit methanogenesis more severely than PAC. Illumina MiSeq sequencing analyses showed that the number of sulfate-reducing bacteria (SRB) enriched obviously in PFS reactor. The results revealed that although PFS reduced methane production more severely than PAC, the reduction was mainly enforced by the activity of SRB but not organic enmeshment. Furthermore, PAC severely suppresses acetotrophic methanogens but PFS depress hydrogenotrophic methanogenesis microorganism mainly. Additionally, malodor control and dewaterability enhancement of digested sludge can be realized with PAC existence. The finding obtained in this study would provide insights into the PFS or PAC-involved sludge anaerobic digestion system and might support the important implication for further manipulate WAS treatment in the future.

Melamine degradation to bioregenerate granular activated carbon

The industrial chemical melamine is often detected in surface water used for drinking water production, due to its wide application and insufficient removal in conventional wastewater treatment plants. Melamine can be removed from water by adsorption onto granular activated carbon (GAC), nevertheless, GAC needs periodic reactivation in costly and energy intense processes. As an alternative method, GAC can also be regenerated using biomass capable of degrading melamine in a process called bioregeneration. We assessed melamine biodegradation in batch experiments in fully oxic and anoxic, as well as in alternating oxic and anoxic conditions. Additionally, we studied the effect of an additional carbon source on the biodegradation. The most favourable conditions for melamine biodegradation were applied to bioregenerate GAC loaded with melamine. We demonstrate that melamine can be biodegraded in either oxic or anoxic conditions and that melamine degrading biomass can restore at least 28% of the original GAC adsorption capacity. Furthermore, our results indicate that bioregeneration occurs mainly in the largest pore fraction of GAC, impacting adsorption kinetics. Overall, we show that bioregeneration has a large potential for restoring GAC adsorption capacity in industrial wastewater.

Sensor Based on a Poly[2-(Dimethylamino)ethyl Methacrylate-Co-Styrene], Gold Nanoparticles, and Methylene Blue-Modified Glassy Carbon Electrode for Melamine Detection

Melamine has been used as a non-protein nitrogenous additive in food products to artificially increase the apparent “false” protein content. Melamine is known as a dangerous and poisonous substance for human health and it causes diverse diseases. An electrochemical sensor for melamine detection has been developed by modification of a glassy carbon electrode using copolymer poly[DMAEMA-co-styrene], gold nanoparticles, and methylene blue. The characterization of the modified electrode was conducted using several analysis techniques including cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The electrochemical detection of melamine was performed by impedance spectroscopy. Obtained results revealed that the developed sensor has a large detection range from 5.0 × 10⁻¹³ to 3.8 × 10⁻⁸ M with a low detection limit of 1.8 × 10⁻¹² M (at S/N = 3). Various interfering species such as phenol, hydroquinone, and bisphenol A have been used and their behavior on modified electrode has been studied.

The fate of triclocarban in activated sludge and its influence on biological wastewater treatment system

Triclocarban (TCC), a typical emerging contaminant, was abundantly released into environment and frequently detected in practical wastewater treatment plants. However it is also an important material when being added to personal skin care products as a antibacterial agent. In this work, the behavior of TCC in wastewater treatment process was investigated. Experiments showed that ~82% of influent TCC was removed by activated sludge adsorption and its adsorption isotherm was well fitted with Linear model and Freundich model. High levels of TCC had seriously impact on the settleability, dewaterability and extracellular polymetric substance (EPS) of activated sludge, even on effluent turbidity after a long-term exposure. Furthermore, the performance of biological wastewater treatment was damaged by TCC long-term exposure as well. The removal rates of total nitrogen and phosphorus decreased from 91.2 ± 2.1% to 72.6 ± 2.2% and from 94.7 ± 3.1% to 78.4 ± 2.3%, respectively, with TCC level increasing from 0 to 100 μg/L. Mechanism analysis showed that TCC exposure significantly inhibited the relevant biological processes, such as ammonia oxidation, denitrification, phosphorus release and uptake, which were closely relevant to nitrogen and phosphorus removal.

Norfloxacin-induced effect on enhanced biological phosphorus removal from wastewater after long-term exposure

In this study, long-term experiments were performed under synthetic wastewater conditions to evaluated the potential impacts of norfloxacin (NOR) (10, 100 and 500 μg/L) on enhanced biological phosphorus removal (EBPR). Experimental result showed that long-term exposure to 10 μg/L NOR induced negligible effects on phosphorus removal. The presence of 100 μg/L NOR slightly decreased phosphorus removal efficiency to 94.41 ± 1.59 %. However, when NOR level further increased to 500 μg/L, phosphorus removal efficiency was significantly decreased from 97.96 ± 0.8 5% (control) to 82.33 ± 3.07 %. The mechanism study revealed that the presence of 500 μg/L NOR inhibited anaerobic phosphorus release and acetate uptake as well as aerobic phosphorus uptake during long-term exposure. It was also found that 500 μg/L NOR exposure suppressed the activity of key enzymes related to phosphorus removal but promoted the transformations of intracellular polyhydroxyalkanoate and glycogen. Microbial analysis revealed that that the presence of 500 μg/L NOR reduced the abundances of polyphosphate accumulating organisms but increased glycogen accumulating organisms, as compared the control.

Exposure to melamine and its derivatives in childcare facilities

Melamine (MEL) and its derivatives are widely used in many consumer products, including furniture, kitchenware, and plastics. However, very limited knowledge exists on human exposure to MEL and its derivatives, especially in the indoor environment. Here, we determined the occurrence and distribution of 11 MEL derivatives in childcare facilities and estimated children's exposure through dust ingestion and dermal absorption. We analyzed dust and samples of nap mats, a commonly used item in many childcares, from eight facilities located in the United States. Eight MEL-based compounds were detected in dust, and total MEL concentrations ranged from 429 to 117,000 ng/g. The most abundant compounds found in the dust samples were MEL, cyanuric acid (CYA), ammeline (AMN), and ammelide (AMD), with median concentrations of 1620, 585, 1060, and 299 ng/g, respectively. MEL, CYA, AMN and 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine (TBMMAT) were also detected in nap mats with median concentrations of 45.6, 19.8, 1510 and 2.5 ng/g, respectively. ΣMEL concentrations in mat covers (median 709 ng/g) were significantly higher than those in mat foam (median 15.1 ng/g). Estimated daily intakes (EDIs) of MEL and its derivatives via dust ingestion were two orders of magnitude higher than the EDIs through dermal absorption, but both were below the established tolerable daily intake levels. This is the first report on exposure to MEL and its derivatives in the childcare environment.

Occurrence and distribution of melamine and its derivatives in surface water, drinking water, precipitation, wastewater, and swimming pool water

The extensive use of melamine and its three derivatives (i.e., ammeline, ammelide, and cyanuric acid) resulted in their widespread occurrence in the environment. Nevertheless, limited information is available on their distribution in the aquatic environment. In this study, concentrations and profiles of melamine and its derivatives were determined in 223 water samples, comprising river water, lake water, seawater, tap water, bottled water, rain water, wastewater, and swimming pool water, collected from New York State, USA. The sum concentrations of melamine and its derivatives (∑₄MELs) decreased in the following order: swimming pool water (median: 1.5 × 10⁷ ng/L) ≫ wastewater (1240) > precipitation (739) > tap water (512) > river water (370) > lake water (347) > seawater (186) > bottled water (98). Cyanuric acid was the major compound, accounting for 60-100% of ∑₄MELs concentrations in swimming pool water, wastewater, precipitation, tap water, seawater, and bottled water, whereas melamine dominated in river and lake water (54-64% of ∑₄MELs). Significant positive correlations (0.499 < R < 0.703, p < 0.002) were found between the concentrations of melamine and atrazine (a triazine herbicide) in surface waters. The geographic distribution in the concentrations of ∑₄MELs in river, lake, and tap water corresponded with the degree of urbanization, suggesting that human activities contribute to the sources melamine and cyanuric acid in the aquatic environments. A preliminary hazard assessment of melamine and cyanuric acid in waters suggested that their ecological or human health risks were minimal. This is the first study to document the occurrence and spatial distribution of melamine and its derivatives in waters from the United States.

Hexamethoxymethylmelamine - A precursor of persistent and mobile contaminants in municipal wastewater and the water cycle

Hexamethoxymethylmelamine (HMMM) is a crosslinker of melamine resins and widely used in the production of coatings and plastics, e.g. for cans, coils and automobiles. Despite its widespread application little is known about the occurrence of HMMM in municipal wastewater, the extent of its removal in wastewater treatment and the fate of transformation products that may be formed from it. A lab degradation experiment with activated sludge showed that HMMM is transformed but not mineralized under aerobic conditions. By LC-UV and LC-HRMS analyses 21 transformation products (TPs) were detected and tentatively identified, with modified di(methoxymethyl)amino side chains, and a pathway for their formation was proposed. The major TP after 28 days was methylol-1,3,5-triazin-2,4,6-triamin. LC-UV and LC-HRMS response of the TPs in the lab experiment was used to quantitatively assess the concentration of TPs also in environmental samples. In municipal wastewater HMMM and its two TPs TetraMMM and DiMMM added up to median concentrations of 2.8 μg/l (7.5 nmol/L) in three wastewater treatment plants (WWTPs), and to 17.9 μg/l (66 nmol/L) in another plant with a higher contribution of industrial wastewater. Their concentration increased in the WWTPs by a factor of 2-4, likely due to ongoing formation from HMMM-related precursor compounds. Also melamine concentrations increased in the four WWTPs (to 3-8 μg/L), but this did not seem to be linked to HMMM transformation. In surface water affected by WWTP discharges HMMM and 12 TPs were determined, at median total concentrations of 5 μg/L, with an even higher proportion of the TPs relative to HMMM compared to the WWTP effluents. During bank filtration HMMM, TetraMMM and DiMMM, together with some cationic TPs, were largely removed, while three TPs, all carrying one carbonylated side chain were eventually determined in raw waters used for drinking water production, in median concentrations ranging from 0.1 to 1 μg/L. It appears that HMMM, while falling under the exemptions of REACH registration, is a precursor for widely found persistent and mobile TPs, that can reach raw waters used for drinking water production.

Spatial and temporal trends of melamine and its derivatives in sediment from Lake Shihwa, South Korea

Occurrence, spatial distribution, and temporal trends of melamine and its derivatives (ammeline, ammelide, and cyanuric acid) were investigated in surface sediment and two sediment cores collected from Lake Shihwa, South Korea. ∑Melamine (sum of melamine and its three derivatives) was found in all surface sediment samples at concentrations that ranged from 16.6 to 4390 ng/g dry weight (dw), with an average value of 202 ng/g dw. ∑Melamine concentrations exhibited a clear spatial gradient, in decreasing order, as: creeks (mean: 577 ng/g dw) > inshore locations (41.9 ng/g dw) > offshore locations (24.3 ng/g dw). ∑Melamine concentrations were notably high in sediment collected near wastewater treatment plant (WWTP) outfalls. Melamine was the most prevalent compound in sediment collected from creeks (87%) and WWTP outfall locations (48%), whereas cyanuric acid was the dominant compound in sediment from inshore (51%) and offshore (63%) locations. The historical profiles of ∑Melamine in sediment cores corresponded with coastal development and environmental changes in this region. This is the first study to document the occurrence and temporal distribution of melamine in sediment cores, and this information is useful in understanding the fate of these relatively less-studied chemicals in the environment.

Free nitrous acid-based nitrifying sludge treatment in a two-sludge system obtains high polyhydroxyalkanoates accumulation and satisfied biological nutrients removal

A novel strategy to achieve substantial polyhydroxyalkanoates (PHA) accumulation in waste activated sludge (WAS) was developed, which was conducted in a two-sludge system consisted of an anaerobic/anoxic/oxic reactor (AAO-SBR) and a nitrifying reactor (N-SBR), where the nitrifying-sludge was treated by free nitrous acid (FNA). Initially, 0.98 ± 0.09 and 1.46 ± 0.10 mmol-c/g VSS of PHA were respectively determined in the control-SBR and AAO-SBR. When 1/16 of nitrifying sludge was daily treated with 1.49 mg N/L FNA for 24 h, ∼46.5% of nitrite was accumulated in the N-SBR, ∼2.43 ± 0.12 mmol-c/g VSS of PHA was accumulated in WAS in AAO-SBR without deteriorating nutrient removal. However, nutrient removal of control-SBR was completely collapsed after implementing the same FNA treatment. Further investigations revealed that the activity and abundance of nitrite oxidizing bacteria (NOB) was decreased significantly after FNA treatment. Finally, sludge with high PHA level to generate more methane was confirmed.

Effect of poly aluminum chloride on dark fermentative hydrogen accumulation from waste activated sludge

Poly aluminum chloride (PAC), an inorganic coagulant being accumulated in waste activated sludge (WAS) at substantial levels, are generally thought to inhibit WAS anaerobic fermentation. However, its effect on dark fermentative hydrogen accumulation has not been documented. This work therefore aimed to explore its effect on hydrogen accumulation and to elucidate the mechanism of how PAC affects hydrogen accumulation. Experimental results showed that with an increase of PAC addition from 0 to 20 mg Al per gram of total suspended solids (TSS), the maximal hydrogen yield from alkaline fermentation (pH 9.5) increased from 20.9 mL to 27.4 mL per gram volatile suspended solids (VSS) under the standard condition. Further increase of PAC to 30 mg Al/g TSS didn't cause a significant increase of hydrogen yield (p > 0.05). The mechanism explorations revealed that although PAC reduced the total short-chain fatty acid (SCFA) production, this reduction was mainly enforced to propionic acid fermentation type, which did not contribute hydrogen production. PAC suppressed all the microbial processes relevant to anaerobic fermentation to some extents, but its inhibition to hydrogen consumption was much severer than that to hydrogen production. Illumina Miseq sequencing analysis revealed that PAC did not affect the populations of SCFA and hydrogen producers, but the two hydrogen consumers, Acetoanaerobium and Desulfobulbus, were almost washed out by PAC. Among the three types of Al species present in the anaerobic fermentation systems, Ala (monomeric species) significantly affected the maximal hydrogen production potential while Alb (medium polymer species) and Alc (species of sol or gel) posed impacts on hydrogen production rate and the lag time.

A nationwide survey of the occurrence of melamine and its derivatives in archived sewage sludge from the United States

Melamine-based resins are used extensively in laminates, plastics, coatings, glues, and dinnerware. Little is known, however, about the occurrence of melamine and its derivatives in the environment. In this study, a nationwide survey of melamine and its derivatives, namely ammeline, ammelide, and cyanuric acid, was conducted, using archived sewage sludge samples collected from 68 wastewater treatment plants in the United States (U.S.). The sum concentrations of four target compounds in sludge ranged from 34 to 1800 ng/g dry weight (dw), with a mean concentration of 240 ng/g dw; melamine (46%) and cyanuric acid (40%) collectively accounted for 86% of the total mass of analytes. No significant geographical variation in the concentrations of melamine and its derivatives in sewage sludge was found. The estimated emission of melamine and its derivatives via land-application of sludge was approximately 1600 kg/yr in the U.S. The hazard quotient values for melamine in sludge-amended soils ranged from 2.2 × 10^-5 to 4.4 × 10^-3, indicating that the current levels of melamine in sludge pose a minimal risk to the soil environment.

Rate-controlled nano-layered assembly mechanism of melamine-induced melamine–uric acid stones and its inhibition and elimination methods

The formation of kidney stones induced by melamine is a rate-controlled nano-scale supramolecular layered assembly process.

Free nitrous acid promotes hydrogen production from dark fermentation of waste activated sludge

Simultaneous sludge fermentation and nitrite removal is an effective approach to enhance nutrient removal from low carbon-wastewater. It was found in this work that the presence of nitrite largely promoted hydrogen production from acidic fermentation of waste activated sludge (WAS). The results showed that with an increase of nitrite from 0 to 250 mg/L, the maximal hydrogen yield increased from 8.5 to 15.0 mL/g VSS at pH 5.5 fermentation and 8.1-13.0 mL/g VSS at pH 6 fermentation. However, the maximal hydrogen yield from WAS fermentation at pH 8 remained almost constant (2.9-3.7 mL/g VSS) when nitrite was in the range of 0-250 mg/L. Further analyses revealed that free nitrous acid (FNA) rather than nitrite was the major contributor to the promotion of hydrogen yield. The mechanism investigations showed that FNA not only accelerated the disruption of sludge cells but also promoted the biodegradability of organics released, thereby provided more biodegradable substrates for subsequent hydrogen production. Although FNA inhibited activities of all microbes involved in the anaerobic fermentation, its inhibitions to hydrogen consumers were much severer than those to hydrolytic microorganisms and hydrogen producers. Further investigations with microbial community showed that FNA increased the abundances of hydrogen producers (e.g., Citrobacter sp.) and denitrifiers (e.g., Dechloromonas sp.), but reduced the abundances of hydrogen consumers (e.g., Clostridium_aceticum). This work demonstrated for the first time that FNA in WAS fermentation systems enhanced hydrogen production. The findings obtained expand the application field of FNA and may provide supports for sustainable operation of wastewater treatment plants.

Effect of acetate to glycerol ratio on enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) is a sustainable and promising technology for phosphorus removal from wastewater. The efficiency of this technology, however, is often discounted due to the insufficient carbon sources in influent. In this work, the effect of acetate to glycerol ratio on the EBPR performance was evaluated. The experimental results showed when the ratio of acetate to glycerol decreased from 100/0% to 50/50%, the EBPR efficiency increased from 90.2% to 96.2%. Further decrease of acetate to glycerol ratio to 0/100% decreased the efficiency of EBPR to 30.5%. Fluorescence in situ hybridization analysis demonstrated appropriate increase of glycerol benefited to increase the relative abundance of phosphate accumulating organisms. Further investigation revealed the proper addition of glycerol increased the amount of polyhydroxyalkanoates synthesis, and then produced sufficient energy for oxic luxury phosphorus in the subsequent oxic phase.

The fate of cyanuric acid in biological wastewater treatment system and its impact on biological nutrient removal

Cyanuric acid (CA) is widely used in living and production. It is a kind of environmental priority pollutants which exists chronically in soil and water, but is difficult to be chemically hydrolyzed or oxidized. The behavior of CA at different levels of 0, 0.01, 0.10 and 1.00 mg L^-1 in biological wastewater treatment process was investigated in this paper. Experimental results showed that CA (0.01 and 0.10 mg L^-1) was removed in biological wastewater treatment process, which was mainly achieved by biodegradation of particular species (Acidovorax and Pseudomonas) in the anaerobic condition. However, 1.00 mg L^-1 CA was reluctant to be degraded in biological wastewater treatment system. With the CA level increase from 0 to 1.00 mg L^-1, total nitrogen removal efficiency decreased from 97.23 to 74.72%. The presence of CA promoted both the synthesis and decomposition metabolisms of poly-hydroxyalkanoates and glycogen, thereby providing the advantage for phosphorus removal. CA could inhibit nitrification process because of inhibition to nitrite oxidizing bacteria (NOB). Moreover, the microbial community of activated sludge was changed by the exposure of CA. Polyphosphate accumulating organisms, such as Bacteroidetes, Chloroflexi and Saccharibacteria increased, but the abundance of Nitrospirae was decreased.

The feasibility of enhanced biological phosphorus removal in the novel oxic/extended idle process using fermentation liquid from sludge fermentation

Carbon sources are essential for biological phosphorus removal (BPR); the carbon sources, however, are often inadequate in municipal wastewater treatment plants. This study demonstrated the feasibility of sludge fermentation liquid enhanced by biosurfactant alkylpolyglycosides (APG) as carbon sources to improve the performance of BPR in the novel oxic/extended idle (O/EI) reactor and the underlying mechanism was also investigated. The results showed that APG induced fermentation liquid could enhance the BPR performance in the O/EI reactor, and the BPR efficiency was 95.2%, which was significantly higher than that in the conventional anaerobic/oxic (A/O) reactor. Mechanism investigation showed that compared with the A/O reactor, the O/EI reactor enriched more polyphosphate accumulating organisms (PAOs) (38.2%), but less glycogen accumulating organisms (GAOs) when the APG-induced fermentation liquid was used as carbon source. The transformations of the polyhydroxyalkanoates (PHA) and glycogen in the O/EI reactor were lower than those in the A/O reactor. Further study found that the activities of polyphosphate kinase (PPK) and acetyl-CoA synthases (ACS) in the O/EI reactor were significantly higher than those of the A/O reactor, which was consistent with the higher BPR efficiency in the O/EI reactor.

Long-term effect of fermented liquid as carbon source on effluent COD and SOP in O/EI reactor.

Effect of ciprofloxacin on biological nitrogen and phosphorus removal from wastewater

In this work, both short-term and long-term experiments were therefore conducted to assess the effects of ciprofloxacin (0.2 and 2mg·L^-1) on wastewater nutrient removal. The results showed that both levels of ciprofloxacin had no acute and chronic adverse effects on the surface integrity and viability of activated sludge. Short-term exposure to all the ciprofloxacin levels induced negligible influences on wastewater nutrient removal. However, the prolonged exposure to ciprofloxacin decreased total phosphorus and nitrogen removal efficiencies from 96.8, 95.8% (control) to 91.7, 84.9% (0.2mg·L^-1) and 90.5%, 80.2% (2mg·L^-1), respectively. The mechanism study showed that ciprofloxacin exposure suppressed denitrification and phosphorus uptake processes. It was also found that ciprofloxacin affected the transformations of intracellular polyhydroxyalkanoates and glycogen in the oxic and anoxic stages. Moreover the activities of nitrite reductase and polyphosphate kinase were inhibited by the presence of ciprofloxacin. Further analysis with high-throughput sequencing revealed that compared with the control, the abundances of polyphosphate accumulating organisms, glycogen accumulating organisms and denitrifying bacteria in ciprofloxacin exposure reactors reduced, which were consistent with the decreased nutrient removal performance measured in these reactors.

Acute and chronic effects of roxarsone on biological nitrogen and phosphorus removal and its mechanism

Effect of roxarsone on the removal of nutrients from wastewater.

Phosphorus–nitrogen compounds. Part 37. Syntheses and structural characterizations, biological activities of mono and bis(4-fluorobenzyl)spirocyclotetraphosphazenes

The syntheses, spectroscopic and crystallographic properties, in vitro cytotoxic and antimicrobial activities of the cyclotetraphosphazenes were investigated.