Sludge Batch Research Articles

Aquaculture sludge as feed for black soldier fly: Transfer of chemical and biological contaminants and nutrients

Aquaculture sludge (uneaten feed and faeces) is nutrient rich and has potential as feed for insects. The aim of this study was to investigate the transfer of chemical and biological contaminants, as well as nutrients, from aquaculture sludge to black soldier fly larvae. The larvae were reared on a sludge mixture made of different sludges collected from Norwegian freshwater salmonid facilities. The sludge was spiked with four common salmon pathogens: Infectious Pancreatic Necrosis Virus, Infectious Salmon Anemia virus, Yersinia ruckeri or Mycobacterium salmoniphilum. During the 15 days of growth on sludge, the black soldier fly larvae accumulated valuable nutrients including protein, fat, eicosapentaenoic acid, iron, manganese, zinc and selenium. The larvae also accumulated undesirable substances including cadmium, mercury, dioxins and polychlorinated biphenyls. The concentrations of dioxins exceeded the EU maximum level set for animal feed. None of the salmon pathogens that were spiked to the sludge were detected in the black soldier fly larvae. This study reports low risk of transfer of salmon pathogens from sludge to insect larvae, and showed that the transfer of heavy metals, minerals and metalloids are in accordance with earlier studies. The large variations in levels of heavy metals between batches of sludge can cause levels in BSF exceeding the EU maximum levels, and thus indicate a need for monitoring of the proposed value chain. The transfer of dioxins from sludge to insects, reported for the first time in this paper, would be of special interest for future research, with special focus on risk mitigation.

Advancing circular economy: A study of drinking water sludge for potential uses

The high demand for drinking water has increased the by-products from treatment plants, notably during coagulation-flocculation, leading to substantial sludges' accumulation. This study aims to focus on the characterization of drinking water treatment sludge (DWTS) batches from the three last years and statically studying it's uniformity, as exploring potential repurposing options. The samples were characterized using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Loss On Ignition (LOI), and Granulometric analysis. The results evinced that DWTS have a sandy nature, the organic fraction takes third of the DWTS’ chemical composition, the amount of Al2O3 + SiO2 + Fe2O3 is slightly different, with 55.84, 57.47, and 56.14 % for DWTS21, DWTS22, and DWTS23 respectively, as per ANOVA results, which exhibited the consistency sludge composition among the samples, providing valuable insights into repurposing DWTS, and contributing to sustainable and eco-friendly practices in the construction industry especially DWTS21, which presents higher content of CaO with 2.95 %.

Conventional activated sludge vs. photo-sequencing batch reactor for enhanced nitrogen removal in municipal wastewater: Microalgal-bacterial consortium and pathogenic load insights

Municipal wastewater treatment plants are mostly based on traditional activated sludge (AS) processes. These systems are characterised by major drawbacks: high energy consumption, large amount of excess sludge and high greenhouse gases emissions. Treatment through microalgal-bacterial consortia (MBC) is an alternative and promising solution thanks to lower energy consumption and emissions, biomass production and water sanitation. Here, microbial difference between a traditional anaerobic sludge (AS) and a consortium-based system (photo-sequencing batch reactor (PSBR)) with the same wastewater inlet were characterised through shotgun metagenomics. Stable nitrification was achieved in the PSBR ensuring ammonium removal > 95 % and significant total nitrogen removal thanks to larger flocs enhancing denitrification. The new system showed enhanced pathogen removal, a higher abundance of photosynthetic and denitrifying microorganisms with a reduced emissions potential identifying this novel PSBR as an effective alternative to AS.

Hydrochars as slow-release phosphorus fertilizers for enhancing corn and soybean growth in an agricultural soil

Hydrochars as carbonaceous amendments rich in porous structures and nutrients can be used as promising slow-release fertilizers and soil health amendments. Yet, the performance of hydrochars derived from different feedstocks in improving crop plant growth and soil phosphorus (P) availability is not well understood. Here, a batch of sewage sludge (SS) and chicken manure (CM) derived hydrochars (SSCs and CMCs) were produced at 125 and 225 °C (SS125/225 and CM125/225) to investigate their characteristics and performances in improving the seedling growth of two representative crops, soybean (Glycine max) and corn (Zea mays), as well as the P availability in an acidic agricultural soil in comparison with triple super phosphate (TSP), a conventional P fertilizer. Compared with CMCs, SSCs with more porous and rougher surfaces contained relatively lower contents of carbon (C; 32.3–33.3%), hydrogen (H; 3.9–4.69%), and potassium (K; 29.2–51 mg g−1), but higher contents of P (37.4–85.4%) and nitrogen (N; 2.26–4.9%), as well as more O-containing and N-containing functional groups. The impacts of hydrochars on soybean and corn growth showed distinct variations. The application of SSCs showed little effect on soybean growth (i.e., biomass, chlorophyl contents, and number of leaves), while CMCs significantly increased its total dry biomass by 23.2–66.2%. For corn, both SSCs and CMCs increased the total dry biomass by 32.8–92.4% and 21.8–69.7%, respectively, compared to those in the un-amended soils. In addition, compared with the higher temperature hydrochars (SS225 and CM225), the lower temperature ones (SS125 and CM125) increased the total dry biomass by 24.6% and 34.9% for soybean and 44.8% and 39.3% for corn, respectively. The significant improvement in crop growth by hydrochars was mainly due to the direct nutrient supply (particularly P) by the hydrochars, which was supported by the increased soil and shoot P concentrations. Moreover, hydrochar application led to a rise in soil water soluble P (WSP) levels. However, as time progressed, these levels fell due to the fixation and adsorption of P via precipitation, electrostatic attraction, and ion exchange on the hydrochars. Contrarily, TSP maintained persistently high soil WSP levels, increasing the leaching risk of P through the soil profile. Our results provide direct evidence for hydrochars as slow-release P fertilizers to enhance crop growth and production and give better insights for producing functionalized P-rich chars as an alternative to chemical P fertilizers to maintain sustainable agricultural production.Graphical

Water quality indicators influencing the formation and morphology of hydrostatically-formed photogranules

Initial water quality parameters in hydrostatic photogranulation determine photogranule shape (spherical or disk-shaped), impacting their physical traits and wastewater treatment effectiveness.

Inorganic carbon as a key factor governing competition between methanogens and acetogens in high-rate anaerobic treatment of methanol wastewater

The anaerobic treatment of methanolic wastewater has become a crucial issue. Sodium bicarbonate (NaHCO3), as a typical representative of inorganic carbon substances, not only provides alkalinity in the anaerobic treatment of methanol but also governs the competition between methanogens and acetogens. However, a suitable dosage has rarely been mentioned. In this study, we demonstrate the crucial role of NaHCO3 in the anaerobic treatment of methanol using a long-term operated up-flow anaerobic sludge blanket (UASB) reactor and batch tests. The UASB results revealed that by adding 3 to 5 g/L of NaHCO3 to the influent at a high organic loading rate of 50 gCOD/L/d, a significant accumulation of acetic acid was detected, with a maximum value of up to 1400 mg/L. In the context of microbial community evolution, this study profiled substrate competition between the acetogens Acetobacterium and Methanomethylovorans, which directly utilize methanol, as well as the synergistic effects of Acetobacterium and acetoclastic Methanosaeta. Abundance analysis of genes encoding relevant pathway enzymes also revealed that the acetic acid production pathway was significantly enhanced when more NaHCO3 was added. According to the dose–response mechanism in the batch test based on kinetic analysis, an acceptable threshold prediction scheme was beneficial in reasonably adding NaHCO3 to improve acid production capacity and rapid methanol degradation, and ensuring that the generated acetate could be rapidly degraded without inhibition, in the high-rate anaerobic treatment of methanolic wastewater.

Chemical characteristics and valuation of sewage sludge from four different wastewater treatment plants.

Sewage sludge contains plant nutrients and organic matter in its composition, making it a potential partial substitute for mineral fertilizers if it meets environmental, agronomic, and sanitary standards. The objective was to evaluate the content of nutrients and heavy metals in the sludge generated in four wastewater treatment stations (WWTPs) in Rio de Janeiro state and assess its potential value and usefulness. The samples of 19 batches from the WTTPs Alegria, Barra da Tijuca, Ilha do Governador, and Sarapuí were analyzed. The WWTPs differ in methods and processes used for treating sewage and sludge. The total contents of C, N, P, K, Ca, Mg, Fe, Al, Na, Co, Mn, As, Ba, Cd, Cr, Cu, Ni, Se, Pb, and Zn were evaluated, as well as the ratio C/N, pH, organic matter content, and electrical conductivity. The grouping of sludge samples was assessed using principal components (PCA) and cluster analysis. The economic valuation of sludge was conducted utilizing the substitute goods method, which compared the sludge's N-P-K contents with the prices of consolidated nutrient sources. All the evaluated sludge batches exhibited concentrations of heavy metals below the limits allowed by Brazilian law, along with high levels of nutrients and organic matter. Considering the chemical characteristics, all evaluated materials showed potential for agricultural use, but it is crucial to evaluate the microbiological characteristics of sludge batches before agriculture application. PCA and cluster analysis demonstrated that sludge samples from the same WWTP clustered close to each other, demonstrating higher similarity among themselves than with samples from other WWTPs. The sludge had an average added value of U$ 88.46 per megagram, considering the total contents of N, P, and K in its composition. Land application of sewage sludge can reduce the need to purchase mineral fertilizers, thereby supporting the feasibility of reusing this material in the agricultural sector.

Low tar yield and high energy conversion efficiency in a continuous pyrolysis reactor with modified ribbon screw conveyor

The high temperature batch and continuous pyrolysis of rice husk, sewage sludge, composite waste, hazelnut and apricot kernel shell were performed at 850 °C in a rotating batch reactor and a continuous reactor with a modified ribbon screw conveyor. Batch results were used in the continuous reactor design and comparison. At the continuous pyrolysis experiments, mixing and conveying efficiency of screw and thermal cracking performance of reactor, heated gas line and cyclone were investigated. Each material was fed into the reactor continuously with a feed rate of 4.5 kg/h for 3.5 h, and then the pipelines and reactor were monitored and collected tar and char were analyzed. The mixing unit and uninterrupted heated system showed excellent performance on tar reduction and tar yields were lower than 1.7 % for all materials. Separation of char dust from the gas without tar condensation in a heated cyclone prevented blocking in gas lines. With the secondary reactions syngas energy conversion efficiency for rice husk, sewage sludge, composite waste, hazelnut shell, and apricot kernel shell were 67.76 %, 59.22 %, 76.35 %, 56.96 %, 61.98 % respectively. With the new design with a modified ribbon screw, different types of materials were decomposed with minimum char yield in less than 15 min without mechanical problems. The high capacity of the installed reactor as 1–10 kg/h moved the technology readiness level (TRL) to 5 and set an example for demonstration in operational environment.

Partitioning and inactivation of enveloped and nonenveloped viruses in activated sludge, anaerobic and microalgae-based wastewater treatment systems

Anaerobic and microalgae-based technologies for municipal wastewater treatment have emerged as sustainable alternatives to activated sludge systems. However, viruses are a major sanitary concern for reuse applications of liquid and solid byproducts from these technologies. To assess their capacity to reduce viruses during secondary wastewater treatment, enveloped Phi6 and nonenveloped MS2 bacteriophages, typically used as surrogates of several types of wastewater viruses, were spiked into batch bioreactors treating synthetic municipal wastewater (SMWW). The decay of Phi6 and MS2 in anaerobic and microalgae-based reactors was compared with the decay in activated sludge batch reactors for 96 h (Phi6) and 144 h (MS2). In each reactor, bacteriophages in the soluble and solids fractions were titered, allowing the assessment of virus partitioning to biomass over time. Moreover, the influence of abiotic conditions such as agitation, oxygen absence and light excess in activated sludge, anaerobic and microalgae reactors, respectively, was assessed using dedicated SMWW control reactors. All technologies showed Phi6 and MS2 reductions. Phi6 was reduced in at least 4.7 to 6.5 log10 units, with 0 h concentrations ranging from 5.0 to 6.5 log10 PFU mL−1. Similarly, reductions achieved for MS2 were of at least 3.9 to 7.2 log10 units, from starting concentrations of 8.0 to 8.6 log10 PFU mL−1. Log-logistic models adjusted to bacteriophages’ decay indicated T90 values in activated sludge and microalgae reactors of 2.2 and 7.9 h for Phi6 and of 1.0 and 11.5 h for MS2, respectively, all within typical hydraulic retention times (HRT) of full-scale operation. In the case of the microalgae technology, T99 values for Phi6 and MS2 of 12.7 h and 13.6 h were also lower than typical operating HRTs (2–10 d), while activated sludge and anaerobic treatment achieved less than 99 % of Phi6 and 50 % of MS2 inactivation within 12 h of typical HRT, respectively. Thus, the microalgae-based treatment exhibited a higher potential to reduce the disinfection requirements of treated wastewater.

Real-time measurement of the moisture contents of dewatered sewage sludge during thermal drying using a low-cost ECH2O EC-5 soil moisture sensor

Real-time measurement of sewage sludge moisture content renders it possible to optimize the consumption of auxiliary fuel and the thermal treatment. Thus, we explored whether a dielectric soil moisture sensor could be used to measure real-time changes in sludge moisture content. This was possible with the aid of a unified calibration curve. The explanatory variable was the third-order sensor output voltage. The calibration curve well-fitted the data; the mean measurement error was 6.14 wt.%. The use of individual calibration curves for each sludge batch reduced the mean measurement error to 3.09 wt.%. The mean measurement error improves when multiple sensors are simultaneously used. The sensor operates very well when the moisture content is low; the results are minimally affected by the bulk density and Fe level. Considering feed-back to the process, it is ideal to measure sludge moisture content near the outlet of the thermal treatment.

INNOVATIVE SOLUTIONS FOR THE PRODUCTION OF BRICKS FROM WASTEWATER TREATMENT SLUDGE

Based on the need to recover various wastes such as waste from wastewater treatment plants, it is proposed to use sludge in the manufacture of various building materials as bricks. So far, bricks made of different materials and combinations of classical materials as burnt clay, cement, sand, but also of other unconventional materials, most of them coming from different wastes, are used in construction. In order to use the sludge for bricks fabrication, it is necessary to inert it and to obtain a moisture content below 80%. Also, the physico-chemical and ecological parameters must be suitable for sludge utilization and their values must be situated within the limits imposed by legislation. So, the sludge is centrifuged in order to reduce the moisture content from (90-95)% to a maximum of 80%, treated, then the sludge batches are characterised and finally the sludge is recovered by inert cement.

Wastewater sediment treatment facilities in a large region as a multi-component system

Introduction. The development of a sludge management technology requires the understanding of treatment facilities as complex multi-parameter systems having explicit correlations between the composition of wastewater and concentrated pollution. In this regard, the article discusses the establishment of environmentally friendly systems for the disposal of sewage sludge, taking into account the process features of treatment facilities.
 Materials and methods. The authors study the largest treatment facilities located in the Samara region, as well as various new and previously accumulated batches of sewage sludge in the area of their influence. The method of principal components is applied to solve the pre-set tasks.
 Results. Parametric criteria, used to evaluate the treatment facilities and the sludge they accumulate, are addressed in the article. The project also encompasses the calculation of environmental and resource parameters. Data centering and scaling were applied to the information obtained in the course of the project implementation, and the obtained data were further analyzed using the method of principal components. The results obtained with the help of the model, constructed using the method of principal components, are displayed in the graphs of accounts and loads, characterizing the relationship between the fields and parameters used to evaluate them.
 Conclusions. Following the analysis of 20 pre-selected sites of treatment facilities, 6 facilities were considered as rational, since they are characterized by the well-developed engineering infrastructure. The conditionally rational area includes 8 facilities. Sediment processing and disposal plants are to be established there upon completion of preliminary environmental surveys. The remaining 6 facilities are considered irrational, since their resource capacity is insufficient for efficient production processes. A systematic approach allows (1) arranging sewage sludge treatment facilities at wastewater treatment plants located in the rational and conditionally rational areas of development and (2) drafting process flow diagrams to ensure a higher involvement of sludge in reclamation processes.

Field investigation of antibiotic removal efficacies in different hospital wastewater treatment processes in Thailand

The removal efficacies of 19 antibiotics in different hospital wastewater treatment processes (WWTP) were investigated at various sizes of 60 hospitals across Thailand. The results showed slight differences in the total antibiotic removals (79–84%) among WWTP sizes. High antibiotics loading to all WWTP were amoxicillin, ciprofloxacin, tetracycline ampicillin, and norfloxacin, respectively. Amoxicillin and ampicillin were eliminated highly (90–99%) in every size of WWTP, while various efficacies showed for other antibiotics (0–93%). According to process comparison, activated sludge (CAS), oxidation ditch (OD), and sequencing batch reactor (SBR) systems showed similar removals of overall antibiotics (P>0.05). The attached growth systems such as submerged aerated fixed-film (SAFF) demonstrated relatively lower antibiotic removals. The natural processes such as aerated lagoon (AL), facultative pond (FP), and constructed wetland (CW) presented substantial biodegradation of some recalcitrant antibiotics such as fluoroquinolones, sulfamethoxazole, and trimethoprim. Post -chlorination provided additional elimination of some antibiotics such as amoxicillin and ampicillin. Finally, the top-five of antibiotics released into the water environment via discharged effluent are amoxicillin, tetracycline, ampicillin, ciprofloxacin, and imipenem, respectively, which mainly from the suspended growth systems.

Changes in BNR Microbial Community in Response to Different Selection Pressure

This study investigated structural changes in microbial community of biological nutrient removal (BNR) in response to changes in substrate composition (ammonium and phosphate), redox condition, and morphological characteristics (flocs to granules), with a focus on nitrification and phosphate removal. Analyzing treatment performance and 16S rRNA phylogenetic gene sequencing data suggested that heterotrophic nitrification (HN) and autotrophic nitrification (AN) potentially happened in aerobic organic-rich (HN_AS) and aerobic organic-deficient (AN_AS) activated sludge batch reactors, respectively. However, phosphate release and uptake were not observed under alternating anaerobic/aerobic regime. Phosphate release could not be induced even when anaerobic phase was extended, although Accumulibacter existed in the inoculum (5.1% of total bacteria). Some potential HN (e.g., Thauera, Acinetobacter, Flavobacterium), AN (e.g., Nitrosomonas (3.2%) and Nitrospira), and unconventional phosphate-accumulating organisms (PAOs) were identified. Putative HN bacteria (i.e., Thauera (29–36%) and Flavobacterium (18–25%)) were enriched in aerobic granular sludge (AGS) regardless of the granular reactor operation mode. Enrichment of HN organisms in the AGS was suspected to be mainly due to granulation, possibly due to the floc-forming ability of HN species. Thus, HN is likely to play a role in nitrogen removal in AGS reactors. This study is supposed to serve as a starting point for the investigation of the microbial communities of AS- and AGS-based BNR processes. It is recommended that the identified roles for the isolated bacteria are further investigated in future works.

Stereoselective profiling of methamphetamine in a full-scale wastewater treatment plant and its biotransformation in the activated sludge batch experiments

The stereoselective biotransformation of methamphetamine (METH), as a chiral compound, during biological treatment in wastewater treatment plants (WWTPs) is often ignored. In this study, a non-racemic form of METH was detected in the raw influent of a full-scale WWTP, with S-(+)-METH as the predominant enantiomer. Stereoselective biotransformation of METH in favor of S-(+)-METH occurred in anaerobic/anoxic and aerobic processes, resulting in the detection of R-(-)-METH as the only enantiomer in the secondary sedimentation tank. To evaluate the stereoselective biotransformation of METH in an activated sludge system, controlled laboratory experiments were conducted under aerobic and anaerobic conditions. Different stereoselective enrichment was observed in a racemic METH batch experiment at various initial concentrations. Batch experiment results with different initial concentrations of nutrient substances demonstrated that the biotransformation of S-(+)-METH occurred simultaneously with the biodegradation of COD and NH4+-N, proving its cometabolism nature. Enzymes released under microbial starvation stress likely stimulated R-(-)-METH biotransformation. Compared with the biotransformation rate of METH under the anaerobic condition, the presence of dissolved oxygen led to a higher biotransformation rate of METH under the aerobic condition.

Comprehensive investigation of SARS-CoV-2 fate in wastewater and finding the virus transfer and destruction route through conventional activated sludge and sequencing batch reactor

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA transmission route was thoroughly investigated in the hospital wastewater, sewage collection network, and wastewater treatment plants. Samples were taken on four occasions from December 2020 to April 2021. The performance of two different wastewater treatment processes of sequencing batch reactor (SBR) and conventional activated sludge (CAS) was studied for virus destruction. For this purpose, liquid phase, solid phase and bioaerosol samples were taken from different units of the investigated wastewater treatment plants (WWTPs). The results revealed that all untreated hospital wastewater samples were positive for SARS-CoV-2 RNA. The virus detection frequency increased when the number of hospitalized cases increased. Detection of viral RNA in the wastewater collection system exhibited higher load of virus in the generated wastewater in areas with poor socioeconomic conditions. Virus detection in the emitted bioaerosols in WWTPs showed that bioaerosols released from CAS with surface aeration contains SARS-CoV-2 RNA posing a potential threat to the working staff of the WWTPs. However, no viral RNA was detected in the bioaerosols of the SBR with diffused aeration system. Investigation of SARS-CoV-2 RNA in WWTPs showed high affinity of the virus to be accumulated in biosolids rather than transporting via liquid phase. Following the fate of virus in sludge revealed that it is completely destructed in anaerobic sludge treatment process. Therefore, based on the results of the present study, it can be concluded that receiving water resources could not be contaminated with virus, if the wastewater treatment processes work properly.

Biotransformation of Current-Use Progestin Dienogest and Drospirenone in Laboratory-Scale Activated Sludge Systems Forms High-Yield Products with Altered Endocrine Activity.

Dienogest (DIE) and drospirenone (DRO) are two fourth-generation synthetic progestins widely used as oral contraceptives. Despite their increasing detection in wastewaters and surface waters, their fate during biological wastewater treatment is unclear. Here, we investigated DIE and DRO biotransformation with representative activated sludge batch incubations and identified relevant transformation products (TPs) using high-resolution mass spectrometry. DIE exhibited slow biotransformation (16-30 h half-life) and proceeded through a quantitative aromatic dehydrogenation to form TP 309 (molar yields of ∼55%), an aromatic TP ∼30% estrogenic as 17β-estradiol. DRO experienced more rapid biotransformation (<0.5 h half-life), and 1,2-dehydrogenation formed the major TP 364 (molar yields of ∼40%), an antimineralocorticoid drug candidate named as spirorenone. Lactone ring hydrolysis was another important biotransformation pathway for DRO (molar yields of ∼20%) and generated pharmacologically inactive TP 384. Other minor pathways for DIE and DRO included hydroxylation, methoxylation, and 3-keto and C4(5) double-bond hydrogenation; distinct bioactivities are plausible for such TPs, including antigestagenic activity, antigonadotropic activity, and pregnancy inhibition effects. Thus, biotransformation products of DIE and DRO during wastewater treatment should be considered in environmental assessments of synthetic progestins, especially certain TPs such as the estrogenic TP 309 of DIE and the antimineralocorticoid spirorenone (TP 364) of DRO.

Environmental performance of extended activated sludge and sequential batch reactor using life cycle assessment

Abstract Although several studies have been published on the application of life cycle assessment (LCA) on wastewater treatment plants (WWTP), few have been reported from developing countries. In this study, the environmental impacts of a sequential batch reactor (SBR) and extended activated sludge process (EASP) treatment technologies were evaluated and analysed using LCA. SimaPro® 9.1.1.1 software was used, together with the ecoinvent 3.6 database, and the ReCiPe midpoint (H) methodology. A functional unit of 1 m3 of treated wastewater was used. Normalised results showed that freshwater eutrophication, freshwater ecotoxicity, and human toxicity were the key impact categories. EASP indicated the highest impact result on all evaluated impact categories. Electricity consumption was the main contributor to freshwater ecotoxicity and human toxicity impact categories. Residual phosphorus in the effluent stream was the dominant contributor to freshwater eutrophication. Primary treatment had the highest environmental burden of EASP, due to raw wastewater pumping. Secondary treatment had the highest environmental burden on SBR due to aeration. SBR was the preferable option as it scored less on all the key impact categories evaluated. The coal-based South African electricity mix was found to be highly influential on both the EASP and SBR.

Effect of nano-magnetite on the propionic acid degradation in anaerobic digestion system with acclimated sludge

In this study, a batch of acid-tolerant inoculation sludge was domesticated as inoculum, and different concentrations of nano-magnetite were added to the propionic acid (PA) anaerobic digestion system to explore its effect on the PA degradation. It was found the PA degradation rates of nano-magnetite groups were 10.96–74.62% higher than the control group without magnetite in the 6th day, especially with the dosage of 100 mg/L. Microbial community analysis showed some potential DIET participants of Chloroflexi, Proteobacteria and Bacteroidetes had the highest abundance, while metabolite analysis showed that nano-magnetite promoted the transformation of malic acid to oxaloacetic acid and the PA disproportionation to butyric acid. It indicated that nano-magnetite could effectively promote the early degradation of PA in the sludge acclimation system by accelerating DIET or PA disproportionation, so as to prevent the PA accumulation, which could provide reference for the acid accumulation regulation of anaerobic digestion system.

Ecotoxicity and biodegradation of the bacteriostatic 3,3′,4′,5-tetrachlorosalicylanilide (TSCA) compared to the structurally similar bactericide triclosan

This article studies the ecotoxicity of 3,3′,4′,5-tetrachlorosalicylanilide (TCSA) using different bioassays and examines its fate in activated sludge batch experiments. Despite of the common use of TCSA as chemical uncoupler in wastewater treatment systems and as preservative in several products, limited data has been published for its ecotoxicity, while no information is available for its biodegradation. Among different bioassays, the highest toxicity of TSCA was noticed for Daphna magna (48-h LC50: 0.054 mg L−1), followed by Vibrio fischeri (15-min EC50: 0.392 mg L−1), Lemna minor, (7-d EC50: 5.74 mg L−1) and activated sludge respiration rate (3-h EC50: 31.1 mg L−1). The half-life of TSCA was equal to 7.3 h in biodegradation experiments with activated sludge, while use of mass balances showed that 90% of this compound is expected to be removed in an aerobic activated sludge system, mainly due to biodegradation. A preliminary risk assessment of TSCA using the Risk Quotient methodology showed possible ecological threat in rivers where wastewater is diluted up to 100-fold. Comparison with the structurally similar 5-chloro-2-(2,4-dichlorophenoxy)phenol (triclosan, TCS) showed that both compounds have similar biodegradation potential and seem to cause analogous toxicity to Vibrio fischeri and activated sludge. Specifically, TCS was biodegraded quite rapidly by activated sludge (half-life: 6.2 h), while EC50 values equal to 0.134 mg L−1 and 39.9 mg L−1 were calculated for Vibrio fischeri, and activated sludge respiration rate. Future research should focus on monitoring of TSCA concentrations in the environment and study its effects in long-term toxicity and bioaccumulation tests.