Real Sludge Research Articles

Visual and photoelectrochemical analysis of antibiotic resistance genes enabled by surface-engineered ZIF-8@Au cascade nanozymes

The aggravation of antibiotic resistance genes (ARGs) in the environment has posed a significant global health crisis. Accurate evaluation of ARGs levels in a facile manner is a pressing issue for environmental surveillance. Here, we demonstrate a unique dumbbell-shaped cascade nanozyme for visual/photoelectrochemical (PEC) dual-mode detection of ARGs. Gold nanoparticles (AuNPs) with tunable exposed facets are controllably anchored onto ZIF-8 dodecahedrons, exhibiting glucose oxidase (GOx)-like (ZIF-8@Au/G) and peroxidase (POD)-like (ZIF-8@Au/P) activities. Upon the occurrence of ARGs, an asymmetric cascade-amplified “dumbbell” configuration is spontaneously generated via target-induced DNA hybridization, comprising GOx-like ZIF-8@Au/G with capture DNA on one side and POD-like ZIF-8@Au/P with signal DNA on the opposite side. Such a cascade nano-system can efficiently oxidize colorless 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) into its green oxidation state and synergistically decompose H2O2, realizing colorimetric/PEC dual-mode ARGs detection with a detection limit of 0.112 nM. The applicability of the present bioassay is validated through measuring ARGs in real sludge samples. This work suggests the possibility to rationally design task-specific nanozymes and develop target-responsive nano-cascade assays for environmental monitoring.

Unravelling the Role of Biochemical Compounds within the Hydrothermal Liquefaction Process of Real Sludge Mixtures

This paper aims to provide a contribution to understanding the role of sludge macro-components (lipids, proteins and carbohydrates) on the yield/quality of bio-crude obtained via hydrothermal liquefaction (HTL). This was pursued by analysing the HTL process of real sludges and the mixtures thereof at different compositions, a topic that has been explored in a very limited way in the pertinent literature. The HTL experiments were run with municipal sludge, tannery sludge and a mixture of them in 25:75, 50:50 and 75:25 weight ratios in a batch reactor at 350 °C and for different residence times. The outcomes for a single sludge showed a greater bio-crude yield for the municipal one (42.5% at 10 min), which is linked to its significant carbohydrate content. The results obtained from the sludge mixtures suggested that a carbohydrate-to-protein mass ratio of 2:1 would maximise the bio-crude yield (average value of about 38%). Moreover, LC-MS and NMR analyses highlighted that the mixed sludges contributed to the formation of a higher number of compounds after the HTL treatment, with respect to the pure municipal or tannery sludge, with an increase in amine, alcohols and aromatic compounds.

The use of hydrodynamic cavitation for waste-to-energy approach to enhance methane production from waste activated sludge

Anaerobic digestion in wastewater treatment plants converts its unwanted end product – waste activated sludge into biogas. Even if the process is well established, pre-treatment of the sludge can further improve its efficiency. In this study, four treatment regimes for increasing methane production through prior sludge disintegration were investigated using lab-scale cavitation generator and real sludge samples. Three different cavitating (attached cavitation regime, developed cloud shedding cavitation regime and cavitation in a wake regime) and one non-cavitating regime at elevated static pressure were studied in detail for their effectiveness on physical and chemical properties of sludge samples. Volume-weighted mean diameter D[4,3] of sludge's particles decreased by up to 92%, specific surface area increased by up to 611%, while viscosity (at a shear rate of 3.0 s−1) increased by up to 39% in the non-cavitating and decreased by up to 24% in all three cavitating regimes. Chemical changes were more pronounced in cavitating regimes, where released soluble chemical oxygen demand (sCOD) and increase of dissolved organic matter (DOM) compounds by up to 175% and 122% were achieved, respectively. Methane production increased in all four cases, with the highest increase of 70% corresponding to 312 mL CH4 g−1 COD. However, this treatment was not particularly efficient in terms of energy consumption. The best energy balance was found for the regime with a biochemical methane potencial increase of 43%.

Temperature-Responsive Nanocarrier-Regulated Alternative Release of "Cargos" for a Multiplex Photoelectrochemical Bioassay of Antibiotic-Resistant Genes.

A smart temperature stimuli-driven multiplex photoelectrochemical (PEC) assay was constructed for antibiotic resistance genes (ARGs) detection, where the stimuli-responsive gatekeeping by regulating the alternative release of "cargo" allowed for the simultaneous detection of multiple tetracycline resistance gene, using tetA (TDNA1) and tetC (TDNA2) as the model. Dual temperature-responsive nanoassemblies were embedded in the PEC bioassay as signal DNA tages: one thermoresponsive polymer (poly(N-isopropylacrylamide), PNIPAM)-capped mesoporous silica nanoparticles (MSN) with loading the "cargo" of HgO nanoparticles as signal DNA1 tags (SDNA1-PNIPAM@MSN@HgONPs) and the other antimony tartrate (SbT)-anchored silica nanospheres as signal DNA2 tags (SDNA2-SbT@SiO2NSs). At 20 °C, below the lower critical solution temperature (LCST) of PNIPAM, the "gatekeeper" PNIPAM in SDNA1-PNIPAM@MSN@HgONPs was in an ON state, igniting Hg2+ release through the pore of SiO2. While at above LCST (40 °C), it was in an OFF state. Likewise, the thermo-dependent dissociation of SbT endowed the grafted SDNA2 tags switching from the OFF (at 20 °C) to ON state (at 40 °C), igniting SbO+ release. The released Hg2+ and SbO+ triggered the amplified photocurrents due to the structure evolution of the photoactive layer into HgS/ZnS or Sb2S3/ZnS heterostructure, thus achieving sensitive detection of multiple ARGs: tetA, tetC, tetG, tetM, tetO, tetZ, tetX, and tetW. Combined with heat map analysis, rapid screening of the ARGs profiles in 12 samples could be realized. This bioassay is simple and accessible for multiple genes analysis with the detection limit down to 0.50 nM. And it was successfully applied for measuring tetracycline ARGs in real sludge samples.

Influence of operating parameters and membrane fouling on nutrient transport by FO membrane

The influence of operating parameters (i.e. membrane surface area and water flux) and membrane fouling on FO nutrient retention was examined. A higher water flux and larger membrane surface area significantly improved total ammonia nitrogen retention, owing to the uncoupling of solute and solvent flux and shorter filtration time, respectively. Phosphate retention remained high (>95%) for all experiments. Membrane fouling by real sludge centrate feed solution caused significant water flux decline, and a reduction in total ammonia nitrogen retention was observed at increasing water recovery. Organic fouling by sodium alginate and humic acid also caused significant water flux decline and a lower total ammonia nitrogen retention when compared to a pristine membrane at the same draw solution ionic concentration. However, total ammonia nitrogen retention at the same water flux for a fouled and clean membrane was similar, indicating that membrane fouling had minimal direct influence on nutrient transport. Osmotic backwashing was highly effective in recovering water flux (92% and 85% for model-foulant and real sludge centrate fouled membranes, respectively); however, the reverse salt flux of the membrane increased after fouling/cleaning, indicating possible changes to the membrane integrity.

A new protocol to assess the microplastics in sewage sludge

Pollution from plastics and their slow degradation are current problems that require urgent solutions. The natural degradation of plastics leads to its fragmentation, resulting not only in microplastics (MPs) but also in nanoplastics (NPs). In recent years, research and monitoring of MPs and NPs concentrations has increased. The monitoring of their concentrations in the environment, sampling sites, detection and quantification methods are not standardised due to the inherent properties of the materials and the origin of the samples, which tends to make the comparison of data between different studies difficult. In this study, we developed an H2O2-enzyme protocol for the extraction of MPs from sludge based on existing analytical methods in the literature, from sampling to quantification and detection. Our laboratory study consists of four protocols used to verify MPs recovery from doped sludge samples containing three polymers (polypropylene, polyethylene terephthalate and nylon). To emphasise the relevance of the optimal protocol, a triplicate test was performed for each of these protocols, all of them using sieve fractions between 100 and 500 μm, while isoporous polycarbonate membranes were used for the filtration of the samples. The percentage polymer distribution of H2O2-enzyme protocol was similar to the control (42% ± 8.49; 38% ± 2.83; 16% ± 11.31), with some limitations for the larger fraction. Data collection was carried out by optical visualisation and chemical identification using Fourier-transform infrared spectroscopy to record polymer spectra obtained for potential interpretation. Finally, a test was conducted to try all protocols on a real sludge from a local plant to confirm their efficiency.

Phosphorus and humic acid extraction from fermentation liquor of ferric phosphate sludge via layered double hydroxides: Efficiency and interaction mechanism

Iron salts are increasingly employed in wastewater treatment worldwide, generating ferric phosphate sludge with low phosphorus (P) bioavailability. The fermentation of ferric phosphate sludge effectively transfers P from the solid phase to the liquid phase and simultaneously releases high contents of ferrous cations (Fe2+) and humic acids (HA) into the sludge liquor. This study aimed to extract P from simulated and real sludge fermentation liquor via Mg/Al layered double hydroxide (LDH), evaluate the impact of co-existed Fe and explore the interaction mechanism between phosphate and HA adsorption. The Fe influence experiments explored the suitable organic matter concentration range for the LDH adsorbent to extract P without the concurrent precipitation of iron compounds. Thus, the residual ferrous species in sludge liquor can be reused as a flocculant. Moreover, the analysis of the adsorption kinetics of phosphate at 25, 35, and 55 °C showed that increasing temperature accelerated the phosphate adsorption rate but had minor effects on the P adsorption capacity. HA and phosphate were jointly adsorbed onto Mg/Al LDH. Investigations on isotherm, kinetics, and mechanism suggested that phosphate anions have a competitive advantage in the ion exchange process but are hindered by large-molecular-weight HA in surface adsorption because of limited adsorption sites. Subsequent adsorption experiments in sludge liquor and nutrient release test confirmed the possibility of using Mg/Al LDH to simultaneously recover P and organic matters from sludge fermentation liquid based on its stable P adsorption performance and intercalated anion slow-release property.

Achieving combined biological short-cut nitrogen and phosphorus removal in a one sludge system with side-stream sludge treatment

Biological nitrogen (N) removal via the short-cut pathway (NH4+-N→NO2−-N→N2) is economically attractive in wastewater treatment plants (WWTPs). However, biological phosphorus (P) removal processes remain a bottleneck in these systems due to the strong inhibitory effect of nitrite or its protonated form (HNO2, free nitrous acid - FNA) on polyphosphate accumulating organisms (PAOs). In this study, a novel combined nitrogen and phosphorus removal strategy was verified and achieved in a biological short-cut nitrogen removal system via side-stream sludge treatment with FNA, and the mechanisms impacting this process were investigated. The side-stream FNA treatment process applied here led to a significant reduction in the real sludge retention time (SRT) in the mainstream (approximately 2.7 days) based on the biocidal effect of FNA to the majority of the organisms. This work also found that around 40% of the P uptake activity was still maintained at a much higher FNA level of 38 μg N/L with potential PAOs, which highly broadened the current knowledge of PAOs community. An economic analysis revealed advantages of the proposed as compared to conventional biological nitrogen and phosphorus removal (13% savings in total cost), biological short-cut nitrogen removal (via FNA treatment) with chemical phosphorus precipitation (21% savings) and conventional biological nitrogen removal with chemical precipitation (27% savings). Overall, this study presents a novel and viable retrofit strategy in integrating biological short-cut nitrogen removal with EBPR for next generation WWTPs.

Magnetic nanostructures functionalized with a derived lysine coating applied to simultaneously remove heavy metal pollutants from environmental systems

ABSTRACT The pollution of environmental systems with heavy metals is becoming a serious problem worldwide. These contaminants are one of the main issues in sludge (which is considered waste) and can even have harmful effects if the sludge is not treated properly. Thus, the development of a novel functional magnetic nanoadsorbent based on a derived lysine is reported here, which can be efficiently applied for metal removal from sludge. Magnetic nanoparticles were coated with silica layer and further modified by covalent bonding of derived lysine. The morphology of the nanomaterial, its nano-size and the silica layer thickness were analyzed by transmission electron microscopy. The successful silanization of the lysine derivative to the silica-coated magnetic nanostructures was investigated by several physicochemical characterization techniques, while the magnetic properties were measured with a vibrating sample magnetometer. The synthesized nanostructures were used as adsorbents for simultaneous removal of most critical heavy metals (Cr, Zn, Cu) from real complex sludge suspensions. The main practical adsorption parameters, pH of the native stabilized sludge, adsorbent amount, time, and adsorbent regeneration were investigated. The results show promising adsorption properties among currently available adsorbents (the total equilibrium adsorption capacity was 24.5 mg/g) from the sludge with satisfactory nanoadsorbent reusability and its rapid removal. The stability of the nanoadsorbent in the sludge, an important but often neglected practical parameter for efficient removal, was verified. This work opens up new possibilities for the development of high-quality magnetic nanoadsorbents for metal pollutants applied in various complicated environmental fields and enables waste recovery.

Oil Sludge Deposition in Storage Tanks: A Case Study for Russian Crude Oil in Mo-he Station

The oil tank can form a considerable amount of sludge deposition after continuous accumulation, which cause a seriously negative impact on both the storage capacity and the safe operation of the oil tank. Therefore, it is important to anticipate the rate of sludge deposition in advance so that proper measures can be planned to remove this heavy layer on the bottom. This paper proposes a method using a relatively simple formula for predicting the sludge deposits. The sedimentation mechanism of wax and asphaltene is introduced and summarized from both the micro and macro aspects, the factors causing the interaction between particles and the influence on coalescence were analyzed. We applied our prediction methods to calculate the sludge deposition of four oil tanks in Mo-he Station and compared our results with the data measured by experiments. The results show that our method had a good general accuracy to experimental data and can be used directly for on-site engineers to anticipate real sludge height before measuring the oil level inside the tank.

Isolation and characterization of novel indigenous facultative quorum quenching bacterial strains for ambidextrous biofouling control

Quorum quenching (QQ), the disruption of microbial communication, has proven to be effective as an innovative anti-biofouling strategy for membrane bioreactors (MBRs). However, QQ bacteria for anaerobic environments have not been extensively analyzed in previous research. This study thus investigated facultative QQ bacterial strains that exhibit potential for use in aerobic and anaerobic MBRs. Two novel QQ strains from the genus Pseudomonas (KS2 and KS10) were isolated from anaerobic digester sludge using signal molecules as the sole carbon source. The two QQ strains exhibited significant signal molecule degradation depending on the oxygen levels and demonstrated endogenous QQ activity, with KS2 producing lactonase and KS10 producing acylase. The QQ strains significantly reduced the formation of the biofilm generated by both Pseudomonas aeruginosa (PAO1) and real sludge. Facultative QQ strains have the potential to offer a more flexible option for effective biofouling control in both aerobic and anaerobic MBRs.

Критерии выбора способа утилизации отходов очистных сооружений

Предложен обобщенный алгоритм исследования состава и выбора способа утилизации твердых отходов сточных вод, образующихся на городских и поселковых очистных сооружениях при биологической очистке или в результате вторичной очистки из биореакторов. Алгоритм апробирован на примере образцов реального осадка - отхода очистки сточных вод городских очистных сооружений хозяйственно-бытовых сточных вод. Полученные результаты его анализа с использованием комплекса современных физико-химических методов сравнивались с действующими нормативными показателями соответствующих параметров. Исследования физико-химических свойств образца осадка показали его радиологическую, химическую и биологическую безопасность, а также высокую энергоемкость. Это позволило отнести исследуемый образец к малоопасным и рекомендовать его использование для технической рекультивации нарушенных земель или применение в качестве энергобрикетов. A generalized algorithm for studying waste composition and choosing procedure for disposal of sewage sludge produced at urban and rural wastewater treatment plants after its biological treatment or secondary treatment in bioreactors is proposed. The algorithm was tested as exemplified for a sample of real sludge which was formed after wastewater purification at urban facilities for treatment of household wastewater. The results of the sewage sludge sample assays using a set of modern physicochemical methods of analysis were compared with the data taken from current standards for the relevant parameters. Studies of physicochemical characteristics for the sediment sample showed its radiological, chemical and biological safety, as well as high energy capacity level. The obtained results made it possible to classify the test sample as a low-hazard material and recommend its use for technical restoration of disturbed lands or production of energy briquettes.

Triclosan enhances short-chain fatty acid production from sludge fermentation by elevating transcriptional activity of acidogenesis bacteria

Triclosan (TCS) is an emerging contaminant in waste activated sludge (WAS). However, the effects of TCS on WAS anaerobic fermentation is still unknown. Herein, we investigated the impacts of different TCS levels on the short-chain fatty acid (SCFA) accumulation. TCS at 100 mg/kg TSS (total suspended solids) significantly (p < 0.05) enhanced SCFA production by 35.8 ± 4.1% through increasing the production of propionic and butyric acid, while the higher TCS level inhibited the SCFA production processes. The results of batch tests with real sludge showed that 100 mg/kg TSS TCS enhanced acidogenesis process and had no significant impact on other processes, while higher TCS level caused negative effects on acidogenesis, acetogenesis and methanogenesis. Generally, 2,4-dichlorophenol was considered as the main metabolic product of TCS under anaerobic condition. However, in this study, TCS was found to be converted into (Z)-4-(2,4-dichlorophenoxy)penta-1,3-dien-3-ol, 2,4-dichloro-1-(4-chloro-2-methoxyphenoxy)benzene and other substances, and its hypothetical metabolic pathway were reformulated. The microbial community structure in the WAS anaerobic fermentation system did not significantly change with TCS addition, but 100 mg/kg TSS TCS contributed to the modest enrichment of SCFA producers. Further analyses of key enzyme activity and abundance of enzyme-encoded genes revealed that TCS at 100 mg/kg TSS up-regulated the expression of enzyme-coding genes (i.e. butyrate kinase (BK) and oxaloacetic acid carboxylase (OAATC)), and this is the primary reason for the increased SCFA production. This work provides a new insight for pollutant effects in WAS anaerobic fermentation, which will help to reveal the impact of emerging contaminants and relearn the role of conventional pollutants.

The influence of selected pharmaceuticals on biogas production from laboratory and real anaerobic sludge.

The presented study summarizes laboratory tests results to define the inhibition effect of selected pharmaceuticals on biogas production under anaerobic digestion conditions. Two sets of inhibition tests were realized: (i) with real anaerobic sludge (from municipal wastewater treatment plant (WWTP) where sludge is present and includes a wide spectrum of pharmaceuticals over a long period) and (ii) with laboratory sludge (sludge without pharmaceuticals). Methanogenic tests lasting 20 days were performed with three analgesics (diclofenac, ibuprofen, and tramadol), two antibiotics (amoxicillin and ciprofloxacin), β-blocker (atenolol), three psychoactive compounds (carbamazepine, caffeine, and cotinine), and a mixture of these compounds. All tests were performed with two concentrations of pharmaceuticals (10 μg/L and 500 μg/L). Results of the methanogenic tests showed the different behaviors of the investigated sludges in the presence of individual pharmaceuticals. Stimulation of anaerobic digestion was mostly detected for laboratory (unadapted) sludge (e.g., the addition of ibuprofen at a concentration of 500 μg/L increased biogas production by 61%). On the other hand, pharmaceuticals inhibited biogas production for real sludge (e.g., the addition of ciprofloxacin 500 μg/L decreased biogas production by 52%).

Dynamics of humic substance composition during anaerobic digestion of excess activated sludge

Inhibition by humic substances (HSs) on anaerobic digestion of excess activated sludge is one of the limitations for converting more organics into biogas. In order to counteract the inhibition from HSs, the present study was initiated to understand the dynamic changes (content and structure) of HSs during the anaerobic digestion of synthetic and real sludge. For the first time, the present work studied the dynamics of HSs separately in the liquid and solid phases. These observations on HSs conversions by potentiometric titration, UV–Vis, FTIR, and two-dimensional infrared spectra, confirmed that the dynamic changes of HA and FA compositions were caused by losing aliphatic moieties and enriching aromatic moieties in the structural compositions. This changes increased the humification degree, aromaticity, and the amounts of oxygen-containing functional groups. Based on the observations, strategies to alleviate the inhibition effect were discussed.

Ammonium recovery from model solutions and sludge liquor with a combined ion exchange and air stripping process

The recovery of ammonium (NH4+) from model (NH4)2SO4 solutions as well as from sludge liquor of a communal waste water treatment plant was studied on the laboratory scale using the ion exchanger loop stripping process (ILS). The ILS process combines ion exchange and air stripping in a hybrid process and works with fixed bed columns containing natural zeolite (mainly clinoptilolite), which is alternately loaded and regenerated. The sodium hydroxide (NaOH) regeneration fluid is simultaneously air stripped. Ammonium is recovered in a subsequent acid scrubber as concentrated ammonium sulfate solution, which is a suitable reducing agent for industrial NOx recovery. Lab scale experiments with four loading and regeneration cycles demonstrate the technical feasibility of the process. The ammonium equilibrium increased after the first loading and regeneration cycles and ammonium uptake reached concentrations of 3 to 4 mg NH4+ L−1 over four consecutive cycles. NaOH regeneration at pH values >11.5 recovered nearly the total amount of previously adsorbed ammonium. The stripped amount of NH4+ increased over the investigated cycles and in the final regeneration sequence approximately the whole amount of desorbed ammonium was simultaneously stripped. Ammonium exchange and recovery characteristics did not significantly change when real sludge liquor samples were used.

СЖИГАНИЕ МОДЕЛЬНЫХ И РЕАЛЬНЫХ НЕФТЕШЛАМОВ В КИПЯЩЕМ СЛОЕ КАТАЛИЗАТОРА

Актуальность исследования обусловлена ежегодным образованием огромного количества нефтяных отходов (в основном нефтяных шламов и кислых гудронов). Развитие технологий переработки такого вида сырья является актуальным направлением исследования для многих научных коллективов. Несмотря на значительный вред для окружающей среды, отходы нефтепереработки заключают в себе огромный энергетический потенциал, в связи с чем необходимо создавать технологии, которые будут сочетать в себе как экологически чистую утилизацию, так и эффективное использование этого потенциала. На данный момент существует множество различных по своей природе способов утилизации рассматриваемых материалов. Основным из них является прямое сжигание отходов. Тем не менее практически все существующие подходы являются дорогостоящими и сложными в реализации. Кроме того, большинство из них не обеспечивают требуемой экологической безопасности процесса. Цель: демонстрация применимости метода сжигания в кипящем слое катализатора к процессу эффективной утилизации отходов нефтепереработки. Объекты: смеси нефть/вода различного соотношения компонентов, моделирующие отходы, образующиеся в результате процессов нефтепереработки (добычи, хранения, переработки в товарные продукты). Кроме того, исследованы образцы реальных отходов нефтепереработки – нефтешламы различного происхождения. Методы: анализ литературных источников на предмет определения основных подходов к утилизации отходов нефтепереработки, используемых на практике; физические эксперименты по определению зольности, влажности и содержания летучих компонентов в исследуемых образцах; физический эксперимент по сжиганию модельных и реальных нефтяных отходов. Результаты. Проведен анализ существующих методов термической переработки с достаточно подробным рассмотрением отдельных методов, применяемых на практике. Кроме того, была проведена серия физических экспериментов по сжиганию как модельных смесей нефть/вода в различном соотношении, так и реальных нефтяных шламов различного происхождения. Авторами работы показано, что сжигание как модельных, так и реальных нефтешламов в условиях кипящего слоя катализатора обеспечивает высокую экологическую безопасность процесса – содержание вредных выбросов (. Кроме того, исследования показали возможность реализации автотермического режима горения рассматриваемых отходов, что позволяет максимально эффективно использовать их энергетический потенциал.&#x0D;

Transparent polymers to emulate the rheological properties of primary, activated, and digested sludge

Understanding the rheological characteristics of sludge is important for design and operation of water and wastewater treatment units including stirrers, mixers, pumps, and separators. Studying the rheological characteristics of real sludge involves health risks and complexity due to opaque nature of sludge and its time evolution caused by microbial activity and aging. Researchers have applied various simulants such as clay, minerals, and gels to prepare synthetic sludge and to perform a lab-scale study on rheological properties and flow behaviour of real sludge. Some of previous studies have ignored the stability and rheological characteristics of simulant fluids, which might lead to less reliable results. Therefore, selection of a safe, cheap and stable alternative that can mimic rheological behaviour of real sludge is still open and challenging. The proposed study examined the pH sensitivity, zeta potential characteristics and rheological properties of sodium carboxymethyl cellulose, polyethylene glycol, sodium alginate, and xanthan gum as popular model fluids with different concentrations (0.1, 0.5, 1, 1.5, 2, and 3 wt%) in details. A comparison of rheological properties of these fluids with the rheology of different types of sludge indicated that xanthan gum is a preferred simulant fluid that mimic the behaviour of sludge for the shear rate below 100 s−1. Analysis of zeta potential and pH sensitivity indicates that xanthan gum is also a resistant solution to pH changes and agglomeration. In addition, it replicates sludge behaviour in terms of viscosity, flow curve, and Herschel–Bulkely parameters. Nevertheless, xanthan gum does not support thixotropy and viscoelastic characteristics of sludge.

Acute biotoxicity assessment of heavy metals in sewage sludge based on the glucose consumption of Escherichia coli.

As a simple and feasible method for acute biotoxicity assessment, personal glucose meter (PGM) can be successfully applied in the early warning of environmental pollutants in sewage. In this paper, the acute biotoxicity of single and joint heavy metals in sewage and real sludge samples was systematically described based on the glucose metabolism of Escherichia coli (E. coli). Results indicated that the biotoxicity order of five single heavy metals in sewage was Hg2+ > As3+ > Cu2+ > Zn2+ > Cd2+. The joint heavy metals of Cu2+ + Zn2+, Cu2+ + Cd2+, and Cu2+ + Hg2+ produced synergistic effects, while Cu2+ + As3+ and Cd2+ + Zn2+ possessed antagonistic effects for the combined biotoxicity. In spiked sludge, Cd2+ and Zn2+ owned higher biotoxicity than Cu2+ and As3+. Notably, the electroplate factory and housing estate sludge respectively showed the highest and lowest inhibition rates as 57.4% and 17.7% under the real sludge biotoxicity assessment. These results demonstrated that PGM was a sensitive and portable method, which could be widely used for acute biotoxicity assessment of heavy metals in sewage sludge.

Mechanisms of peroxymonosulfate pretreatment enhancing production of short-chain fatty acids from waste activated sludge

Peroxymonosulfate (PMS) has been recently used as an additive to pretreat waste activated sludge (WAS) to enhance short-chain fatty acids (SCFAs) production. However, the mechanisms of how PMS enhances SCFAs production remain largely unknown. This work therefore aims to explore the mechanisms through deeply understanding its impact on the disintegration of sludge cells, the biodegradability of organics released and the bioprocesses involved in anaerobic fermentation, and differentiating the contributions of its degradation intermediates to SCFAs production. This was demonstrated by a series of batch fermentation tests using either real sludge or model organic compounds as fermentation substrates. Experimental results showed that the maximal SCFAs yield increased from 29.69 to 311.67 mg COD/g VSS with PMS level increasing from 0 to 0.09 g/g TSS. No obvious increase in SCFAs yield was observed when PMS further increased. The mechanism explorations revealed that PMS pretreatment not only enhanced the disintegration of sludge cells but also promoted the biodegradability of organics released, thereby providing more biodegradable substrates for subsequent SCFAs production. PMS pretreatment decreased the percentages of fulvic acid-like and humic acid-like substances in the released organics. Moreover, the species and total detection frequency of other recalcitrant organics such as cyclopentasiloxane, heptasiloxane, and ethylene glycol, which were hardly degraded in ordinary anaerobic condition, also decreased remarkably. Although PMS caused harms to some extents to all the microbes in the anaerobic fermentation, its inhibitions to SCFAs consumers were much severer than that to SCFAs producers, probably due to the less tolerance of methanogens. Further analyses exhibited that 1O2, SO4•- and •OH were the major contributors to the increased SCFAs production, and their contributions were in the order of 1O2 > SO4•- > •OH. The findings obtained in this work provide insights into PMS-involved sludge fermentation process and might have important implication for further manipulation of WAS treatment in the future.