Sludge Samples Research Articles

Systematic evaluation of the impact of standard storage conditions on plasmid conjugation behavior in wastewater samples

Filter mating experiment is widely used to study the conjugation behavior of plasmids and associated antibiotic resistance in environmental settings, however, the influence and biases brought by sample storage conditions (temperature and duration) were not yet systematically elaborated. This study systematically investigated the influence of standard storage conditions (4 °C, −20 °C, −80 °C) on plasmid conjugation behavior in influent (Inf) and activated sludge (AS) samples from sewage treatment plants (STP). The findings revealed a significant reduction in conjugation efficiency under all the tested storage conditions except for 1-week storage at 4 °C. Notably, storing at −80 °C maintained conjugation activities in activated sludge more effectively compared to −20 °C. However, the preservation performance was less effective for influent samples, which consist mainly of anaerobe-dominant communities. Systematic loss of IncH-type plasmids was observed in influent samples stored at 4 °C and −20 °C. Correspondingly, the plasmid-carrying resistome genotypes detected in the influent samples showed a clear downward trend with the increase in storage duration when stored at 4 °C and −20 °C. A relatively uniform composition in terms of incompatibility type and resistome profile was observed across activated sludge samples, regardless of the varied storage conditions. This study highlights the critical impact of storage conditions on plasmid conjugation behavior and resistome composition, offering valuable insights for optimal sample handling in resistome research.

Occurrence of selected pharmaceuticals in wastewater and sludge samples from wastewater treatment plants in Eastern Cape province of South Africa

ABSTRACT The occurrence of pharmaceuticals in various wastewater treatment plants (WWTPs) and their discharge into the surface water are existing global challenges. However, such challenges are more detrimental in developing countries due to the aging infrastructure and its vandalism influenced by poverty, resulting in the illegal breakdown of the WWTPs. This study investigated the presence of efavirenz, ibuprofen, naproxen, sulfamethoxazole, and trimethoprim in WWTPs. Ultrasound-assisted extraction (UAE) followed by solid-phase extraction (SPE) was used to extract these pharmaceuticals in sludge samples, with wastewater extracted with only the latter. This was followed with analysis using a high-performance liquid chromatography-photo-diode array detection system. Recoveries found after spiking the samples with analytes at different concentrations ranged from 56 to 117%. An antibiotic, sulfamethoxazole, was among the prominent drugs in untreated wastewater with its concentration reaching 77 ug L-1. All the analytes were detected in sludge samples, with naproxen having the highest concentration of 13.35 ng g-1. The pharmaceutical with the lowest removal efficiency (2-12%) in WWTPs was efavirenz, while other drugs were fairly removed from wastewater. Overall, the findings of this study indicate the dysfunctionality of selected WWTPs in the Eastern Cape province of South Africa due to the release of high amounts of pharmaceuticals into the surface water which can be detrimental to humans, animals, and aquatic life.

Biosurfactant-enhanced bioremediation of petroleum sludge: Unveiling the potential of Enterobacter cloacae AR-IASST (01)

Petroleum sludge is accidentally released in oil fields and refineries, which can harm the environment because it contains emerging contaminants such as PAHs, BTEX components, heavy metals, and asphaltenes. This study developed a method to eliminate petroleum sludge-related emerging contaminants using a novel bacterium, AR-IASST (01), which can produce biosurfactants (surface tension reduced to 26.4 mN/m). The potential bacterium was Gram-negative, and molecular characterization revealed that the bacterium belongs to Enterobacter cloacae with positive oxidase, catalase, gelatin, hemolytic, and negative glucose fermentation tests. After five days of culture incubation, a degradation of 86.9% was achieved, and biosurfactant production was also observed during the sludge degradation process. The peak numbers in the GC-MS analysis were reduced from 184 to 13 in the treated sample, indicating complete degradation of PAHs in the sludge. The biosurfactant was identified as a rhamnolipid in nature. The biosurfactant was emulsified well with several oils, and an E24 of 100% was achieved against crude oil. The biosurfactant was stable across a wide temperature and salt concentration range, though it was sensitive in highly acidic conditions. Furthermore, the bacterial treatment was found to remove heavy metals viz. nickel (Ni), zinc (Zn), lead (Pb), iron (Fe), chromium (Cr), and copper (Cu) from the sludge sample. Thus, the current study demonstrates that the novel bacterium is highly potent and can be widely used to restore petroleum sludge-contaminated sites.

Synergistic effect of innovative bentonite and poly aluminum chloride (PAC) combination for excess and digested sludge thickening and dewatering

Urban wastewater sludge dewatering is one of the challenging issues that wastewater treatment plants face today and needs sustainable solutions. This study aimed to evaluate the effectiveness of the bentonite and poly aluminum chloride (PAC) combination as physical and chemical conditioners for sludge conditioning. This research has shown that the optimal dose for conditioning untreated excess and anaerobically digested sludge is a 0.3% PAC-to-bentonite ratio (1.8 g/g PAC + 6 g/g bentonite for anaerobically digested sludge and 0.324 g/g PAC + 1.08 g/g bentonite for biological excess sludge). Additional tests on extracellular polymeric substances proved that this method can significantly affect parameters such as total organic carbon, protein, and polysaccharides in sludge samples. It was found that time to filtration and specific resistance to filtration parameters were also reduced by 78% and 72% in anaerobically digested sludge and by 90% and 66% in untreated excess sludge respectively when this combination was used. Significant changes in other parameters such as sludge particle size, zeta potential, and others demonstrate the effect of PAC and bentonite combination on sludge types. In addition, the cost for preparing the solutions of both polymers at the considered optimal concentrations was calculated. For each ton of conditioned sludge, the cost ranges between 77$ and 94$. It has been demonstrated that the combination of bentonite and PAC, along with other conventional materials such as acidic modified bentonite, facilitates the dewatering process effectively despite the smaller clots in the sludge after conditioning, which reduces the porosity of the sludge and prevents dewatering.

A comprehensive study on the physicochemical characteristics of faecal sludge from septic tank and single pit latrine facilities in a typical semi-urban Indian town: a case study of Rajasthan, India

Faecal sludge (FS) samples were analysed to assess their characteristics. FS has high chemical oxygen demand, ranging from 4406 to 160 000 mg l−1, influenced by sludge age, sanitation type, and inflow/outflow to onsite sanitation contaminants.

Analysis of fecal pollution load factor from septic tanks of residential area (study case: Bandung City, Indonesia)

According to the Ministry of Environment and Forestry, 2017, domestic waste is the most significant contributor to pollution sources in the Citarum watershed (62.16%) and Bandung City (94.15%). To overcome the problem, planning for infrastructure development and improvement of the domestic sewage treatment system is necessary. One of the essential characteristic parameters, which is the subject of this study, is the pollutant load factor parameter in the city of Bandung. Compared to sewage pipelines, the domination of domestic wastewater treatment in Bandung is the On-site Sanitation System (OSS) (38.47%), and the most widely used type of OSS is a septic tank. For this reason, thirty fecal sludge samples were taken from two fecal disposal points in Bandung City, and the concentrations of TSS, COD, BOD, and Ammonia were then analyzed. Based on the results of the study, the range of fecal sludge pollutant load factor for TSS in Bandung City is 57.28 g / person/day – 1,064 g / person/day with an average value of 546.39 g / person/day, the range for total COD is 30.06 g / person/day – 294.99 g /person/day with an average of 294.99 g / person/day, the total BOD range is 14.05 g /person/day – 504.97 g / person/day with an average of 175.5 g / person/day, and ammonia range 1.61 g/person/day – 3.11 g/person/day with an average of 2.62 g/person/day. Based on fecal sludge data, the result can be considered a recommendation to re-determine the main domestic wastewater pollution indicator generation. The new suggestions can be used to design an adequate domestic wastewater treatment system, especially in Bandung. The pollutant load factors can also be used to estimate the pollution loading of wastewater generated by present and future populations. It is important in urban growth planning.

Reevaluating the accuracy and specificity of EDTA-based polyphosphate quantification method

Feng et al. (2020) developed a simple, nondestructive, and cost-effective method to quantify polyphosphate (poly-P) in poly-P-accumulating organism (PAO)-enriched sludge samples through 30-h anaerobic exposure to 1 % (w/v) ethylenediaminetetraacetic acid (EDTA). This study optimized the N/P ratio (∼2) of the PAO culture medium in order to provide excess P for poly-P formation in PAO cells. Subsequently, the fluorescence microscopic observation of stained cells confirmed that Corynebacterium glutamicum was a PAO species capable of heterotrophic nitrification. Finally, this study reevaluated the accuracy and specificity of the EDTA-based quantification method, using two confirmed PAO biomass, three confirmed non-PAO biomass, and two sludge samples. The 1 % (w/v) EDTA treatment appears destructive to non-PAO cells, causes the release of other P forms, and is not effective for all PAO species. Under the conditions, the actual P release amount should be calculated by subtracting approximately 8 mg P g−1 total suspended solids from the determination. The amounts of P released from sludge samples was determined not only by the PAO fractions described by Feng et al. but also by PAO community structure and sludge P content.

WASTE LEMON PEEL AS A CIRCULAR SOLUTION FOR THE REMEDIATION OF LEAD-CONTAMINATED SLUDGE FOR LAND APPLICATION

Lead-contaminated sludge is a major environmental concern, as land application of this material can contaminate surfaces with toxic heavy metals. To address this, a novel approach to utilizing waste lemon peel (WLP) for the remediation of lead-contaminated sludge for land application with the circular economy in perspective is presented. The WLP was collected from local producers and characterized using Fourier transform infrared (FTIR) spectroscopy to determine the functional groups present. The hydroxyl, carboxyl, ether, and amide groups are the main functional groups in the sample and they have been identified as potential sites responsible for binding heavy metal ions to the biomass.
 The sludge samples were collected from the Ahmadu Bello University Water treatment plant and analyzed for contamination. The effects of WLP on the lead sorption were investigated using batch experiments. The results indicated that lead sorption onto the WLP was significantly as high as 90.5%. The WLP was found to effectively reduce the lead from the contaminated sludge. This study aimed to identify the capability of WLP as a low-cost and sustainable material for the remediation of lead-contaminated sludge for land application, indicating the potential for waste materials to be utilized in the circular economy. The Material Circularity Indicator of 0.835 indicated a highly circular system.

Degrading characteristics of oil‐degrading bacteria and its study of petroleum hydrocarbon metabolites

AbstractExploring the community characteristics of petroleum degrading bacteria and revealing the types of petroleum metabolites produced by degrading bacteria play an important role in solving the problem of oil pollution. In this study, the bacterial suspension was extracted from the sludge of the sewage treatment plant, and the efficient dominant bacteria were enriched and cultured by microbial screening. The optimal environmental conditions and kinetic behavior of microbial degradation of petroleum hydrocarbons in groundwater were discussed, and the metabolites of microbial degradation of petroleum hydrocarbons were analyzed. The results showed that the optimum degradation conditions of the strain were as follows: bacterial suspension inoculum: 2%, pH: 7, temperature: 30°C, initial concentration of contaminated water sample: 500 mg/L. Under these conditions, the microbial petroleum hydrocarbon degradation efficiency was 84.7% and followed the first‐order kinetics; qualitative and quantitative statistical analysis of the metabolites of the microbial degradation of petroleum hydrocarbons by gas chromatography‐time‐of‐flight mass spectrometry was performed. A total of 10 significantly upregulated products and 12 significantly downregulated products were screened, which were significantly different from the metabolites of the control group. Further microbial community analysis showed that Pseudomonas was dominant in the bacterial suspension, more than 99.5%, which was significantly different from the sludge sample, providing data support for the degradation of petroleum hydrocarbons by Pseudomonas. This study has provided a scientific basis for in situ remediation of petroleum pollution in groundwater.

Denitrification Capacity of Volatile Fatty Acids from Sludge Fermentation: Lab-Scale Testing and Full-Scale Assessment

This work provides insights into the possibility of integrating recovered volatile fatty acids (VFAs) into biological nitrogen removal processes. VFAs are the main products of the acidogenic fermentation of waste sludge and are an effective carbon source for denitrification in activated sludge processes. The assessment of denitrification rates and the utilisation hierarchy of different VFAs are relevant to evaluating the possibility of replacing external carbon sources with the fermented liquid, FL, from acidogenic fermentation. To this scope, single VFAs, FL collected from a full-scale waste sludge fermenter, and commercial hydroalcoholic solutions have been tested with manometric lab-scale tests. Regarding single acids, acetic acid showed the highest denitrification rates, up to 4 mg N-NO3 g VSS−1 h−1, while more complex acids usually showed a lower denitrification rate. The synthetic VFA mixture and FL showed a higher denitrification rate than the sole acetate (up to 134% of the acetate denitrification rate). Mass balances across the full-scale wastewater treatment plant demonstrated the positive role of FL dosage in enhancing the denitrification process in the activated sludge treatment, with an average nitrogen removal equal to 57% and 78% without and with FL dosage, respectively. Batch manometric tests proved to be an efficient and reliable tool to assess the quality of the carbon sources as well as the activity of denitrifying bacteria in activated sludge samples.

Sorption of methylene orange on biocarbon sorbent, obtained by pyroly-sis of wastewater sludge

Water pollution and deterioration of air and water quality is a rapidly growing problem directly related to the generation of waste water and the accumulation of significant amounts of wastewater sludge (WWS). One of the methods for recycling WWS is their pyrolytic processing into biochar adsorbents for purification from various pollutants. The type of adsorbent and its properties play a key role in the efficiency of the purification process, which explains the relevance of the search for alternative materials for water treatment processes. The purpose of the study was to create a biocarbon sorbent during the pyrolysis of wastewater sludge and determine its sorption capacity for the methylene orange dye. To obtain samples of biocarbon sorbent, dried and crushed samples of wastewater sludge were exposed to a temperature of 500 °C for 1.5 hours in a vacuum chamber with a heating rate to a given temperature of 5°C/min. Elemental analysis of the resulting sorbent allowed to establish a decrease in the content of carbon, oxygen, and sulphur: for C by 2.50 at.%, for O by 9.91 at.%, for S by 0.4 at.%, relative to WWS. Scanning electron microscopy confirmed a significant reduction in the particle size of biochar compared to the original WWS sample. In the initial WWS sample, after the sample preparation stage, the dispersion of particle sizes was 10-70 µm, and after pyrolysis of the sediment, the dispersion decreased to the range of 10-45 µm. The percentage of biochar yield was calculated, constituting 42% of the weight of the initial WWS and studies on the sorption of methylene orange were carried out. The sorption capacity of biochar for the anionic dye methylene orange after 120 min of sorption was 4.9 mg/g, the degree of solution purification reached 82%. The kinetics of dye sorption was correctly described by a pseudo-second-order equation and indicated the polymolecular nature of sorption.

Utilization of wastewater treatment sludge in the production of fired clay bricks: An approach towards sustainable development

Wastewater treatment sludge has increase due to the increasing of population and economic potential. Sludge generally contains heavy metals that could lead to environmental effect as well as to human health. This study is focus on utilization of sludges into incorporated fired clay brick. The samples of sludge were gathered from IWK in Perwira and Senggarang. The heavy metal concentration in the wastewater treatment sludge was identified using X-Ray Fluorescence. Sludges were incorporated into bricks at various percentages: 0 %, 1 %, 5 %, 10 %, 20 %, and 30 %. The physical and mechanical characteristics of brick after being integrated with both types of sludges were identified. Furthermore, heavy metals leachability of sludge bricks was tested. The findings reveal that Barium (Ba) has the highest heavy metal concentration in the raw materials, and the chemical composition is Silicon Dioxide (SiO2). Bricks with 5 % sludge content exhibited optimal physical and mechanical attributes for both sludge types. However, sludge from Senggarang exhibited the better results compared to Perwira sludge. In terms of leachability, heavy metals were analysed in bricks from both sludge types. Bricks containing up to 20 % sludge from Senggarang exhibited the lowest heavy metal leachability. Nevertheless, value of heavy metals from both sludges is complied with USEPA standard. In conclusion, 5 % of both sludges is the best percentage to be utilized into fired clay brick by considering it properties and leachability. This study also demonstrated that adopting cleaner production techniques for building bricks can make a substantial contribution towards attaining Sustainable Development Goals (SDGs).

Distinctive species interaction patterns under high nitrite stress shape inefficient denitrifying phosphorus removal performance

Denitrifying phosphorus removal using nitrite as an electron acceptor is an innovative, resource-efficient approach for nitrogen and phosphorus removal. However, the inhibitory effects of nitrite on anoxic phosphorus uptake and process stability are unclear. This study investigated the total phosphorus removal performance under nitrite stress and analyzed microbiome responses in 186 sludge samples. The results indicated that the total phosphorus removal rates and dominant taxon abundance were highly similar under nitrite stress. High nitrite stress induced a community-state shift, leading to unstable dynamics and decreased total phosphorus removal. This shift resulted from increased species cooperation. Notably, the shared genera OLB8 and Zoogloea under non-inhibitory nitrite stress, suggesting their vital roles in mitigating nitrite stress by enhancing carbon and energy metabolism. The response patterns of these bacterial communities to high nitrite stress can guide the design and optimization of high-nitrogen wastewater reactors.

Near-infrared reflectance spectroscopy for rapid prediction of biochemical methane potential of wastewater wasted sludge

The information of biochemical methane potential (BMP) of wasted sludge is essential to ensure the stable operation of sludge management processes. However, conventional anaerobic digestion (AD) approach for BMP test is time-consuming and labour-intensive. Currently, the technique of Near Infrared Spectroscopy (NIRS) is gaining prominence in the biogas production within AD process. Previous studies mostly focused on predicting BMP values for fibrous plant biomass and solid waste, with only a limited number of studies attempting to apply NIRS to obtain BMP values across a wide array of wasted sludge types. To obtain BMP values for this diverse range of wasted sludge efficiently and accurately, it is imperative to develop precise models for assessing BMP values using NIRS. In this study, the possibility of using NIRS to predict the BMP values of wasted sludge was evaluated. A total of 70 sludge samples from different sources were investigated to develop a BMP-prediction model by correlating the measured BMP values with the obtained NIR spectra. As a result, a reliable and successful BMP-prediction model was established with the determination coefficient of 0.90, residual prediction deviation of 3.50 and low root mean square error of prediction of 36.8 mL CH4/g VS. This BMP-prediction model is satisfactory for predicting BMP values of various types of sludge. It could provide support for plant operators to make decisions rapidly, thereby improving the process efficiency and optimizing sludge management procedures.

Assessment of polyhydroxyalkanoates and polysaccharides production in native phototrophic consortia under nitrogen and phosphorous-starved conditions

Growing demand for sustainable and eco-friendly alternatives to petroleum-based polymers has increased the interest in the microalgae-based production of polymers, specifically polyhydroxyalkanoates and polysaccharides. While most studies in microbial polymer production have primarily focused on axenic or genetically engineered cultures of cyanobacteria and eukaryotic algae, little is known about the potential of mixed phototrophic consortia. This study aimed to obtain and evaluate mixed photosynthetic consortia of different origins (natural and residual) as a novel approach for polyhydroxyalkanoates and polysaccharides accumulation. Activated sludge and freshwater samples were collected and inoculated in lab-scale photobioreactors to generate mixed photosynthetic consortia. After a preliminary screening for polymer-accumulating strains under nutrient-unbalanced conditions, the selected strains were subjected to a biphasic strategy (biomass accumulation and nutrient stress) to evaluate their polyhydroxyalkanoates and polysaccharide accumulation. First, cultures were subjected to a nutrient-rich phase to increase the biomass content and then deprived of nutrients (known as the polymer accumulation phase) to evaluate polyhydroxyalkanoates and polysaccharide yield. Findings in this study revealed that the highest polysaccharide yield for activated sludge biomass and freshwater consortia was 460 ± 16 and 320 ± 24 mg glucose g dried biomass−1, respectively. In contrast, the highest polyhydroxyalkanoates accumulation levels for both cultures were calculated at 5 mg polyhydroxyalkanoates g dried biomass−1. The efficacy of nutrient stress as a selective pressure strategy to develop mostly polysaccharides-accumulating consortia was demonstrated.

Optimizing sludge dewatering efficiency with ultrasonic Treatment: Insights into Parameters, Effects, and microstructural changes

Sludge dewatering plays a critical role in the efficient and cost-effective management of wastewater treatment plants. Ultrasonic treatment has emerged as a promising technique for improving dewatering processes. This study aims to evaluate the impact of ultrasonic treatment on sludge dewatering characteristics. A series of experiments were conducted to evaluate the dewatering characteristics of sludge under ultrasonic treatment. Experimental data was collected, and the effects of ultrasonic parameters on dewatering efficiency were analyzed. Ultrasound has the capacity to disintegrate sludge flocs, liberate tightly bound water, and enhance sludge dewatering capabilities. The application of ultrasound leads to the breakdown of sludge flocs, which facilitates a substantial amount of organic acids or carbonates. This, in turn, modifies the pH value of the sludge. Additionally, ultrasound induces instantaneous high temperature and pressure within the liquid phase, consequently elevating the temperature of the sludge slurry. Optimum ultrasound energy density and duration of ultrasound treatment exist. For the sludge samples analyzed in this investigation, it was determined that the optimal ultrasonic energy density is 9.8 W, while the optimal duration of ultrasound treatment is 30 s. Excessively escalating the sound energy density or prolonging the duration of ultrasound may yield unfavorable outcomes in terms of sludge dewatering effectiveness. To enhance sludge dewatering, it is crucial to select appropriate ultrasonic energy density and duration of ultrasonic treatment. This study demonstrates the positive impact of ultrasonic treatment on the dewatering characteristics of sludge. The findings provide valuable insights into the potential of ultrasonic technology for enhancing sludge dewatering.

Precise determination of the total nitrogen content in activated sludge by ultrasonic pre-treatment assisted wet method

ABSTRACT The study proposed a method for determining total nitrogen (TN) content in activated sludge by ultrasound pre-treatment assisted wet method. Based on the single-factor experiment, with the TN content as the response value, the response surface methodology was employed to examine the individual and interactive effects of three factors: the dilution multiple of the sludge mixture, ultrasonic time, and ultrasonic power. At the same time, the physico-chemical parameters and the digestion–oxidation parameters were optimised. The results indicated that the optimal parameters were as follows; sludge dilution multiple of 225 times, stirring rate of 400 r/min, ultrasonic time of 22 minutes, ultrasonic power of 720 W, and optimal added volume of potassium persulfate at 8 mL with a digestion time of 40 minutes. The relative standard deviation (RSD) for the parallel determination of TN in sludge samples using ultrasonic pre-treatment assisted wet method was ≤2.77%, with a spike recovery rate of 98.49–101.43%. The method, ultrasonic pre-treatment assisted wet method to determine TN concentration in activated sludge, was simpler to operate, more accurate.

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.

Conversion of dairy sludge into biodiesel via Non-Catalytic transesterification

Considering the current energy infrastructure utilizing renewable energy that is compatible with it will be advantageous. From the perspective of compatibility, the use of biodiesel is promising. Although practical implementation and commercialization of biodiesel have been prioritized, the valorization of dairy sludge into biodiesel via conventional conversion protocols (acid-/base-catalyzed (trans)esterification) has not yet been realized. Tolerance against free fatty acids (FFAs), saponified fatty acids (SFAs), and undefined impurities in acid-/base-catalyzed (trans)esterification are vulnerable. To overcome the technical inferiority of acid-/base-catalyzed (trans)esterification, this study adopted non-catalytic (trans)esterification, which can valorize dairy sludge into biodiesel with high efficiency in a reaction time of ≤ 1 min. The non-catalytic conversion platform used in this study is invulnerable to impurities, and its reaction kinetics are governed by the temperature. Biodiesel recovery by non-catalytic (trans)esterification ranged from 72 to 75.8 wt% of dairy sludge extracts at 380 ℃. One of the interesting findings is that biodiesel recoveries from non-catalytic (trans)esterification of dairy sludge extracts at ≥ 300 ℃ were nearly similar. This suggests that the yield of biodiesel was saturated at ≥ 300 ℃. From the perspective of the economic viability of biodiesel production, the direct conversion of dairy sludge into biodiesel without lipid extraction is desirable. Thus, non-catalytic (trans)esterification of the two dairy sludge samples was performed. Biodiesel recoveries from the two dairy sludge samples were 31.7 and 38.8 wt% at 380 ℃, respectively. This finding demonstrates the extraordinarily strong tolerance against impurities and technical superiority of the introduced biodiesel conversion platform.

Ecological and functional differences of abundant and rare sub-communities in wastewater treatment plants across China

The microbial community in activated sludge is composed of a small number of abundant sub-community with high abundance and a large number of rare sub-community with limited abundance. Our knowledge regarding the ecological properties of both abundant and rare sub-communities in activated sludge is limited. This article presented an analysis of functional prediction, assembly mechanisms, and biogeographic distribution characteristics of abundant and rare sub-communities in 211 activated sludge samples from 60 wastewater treatment plants across China. Moreover, this study investigated the dominant factors influencing the community structure of these two microbial groups. The results showed that the functions associated with carbon and nitrogen cycling were primarily detected in abundant sub-community, while rare sub-community were primarily involved in sulfur cycling. Both microbial groups were mainly influenced by dispersal limitation, which, to some extent, resulted in a distance-decay relationship in their biogeographic distribution. Moreover, a higher spatial turnover rate of rare sub-communities (0.0887) suggested that spatial differences in microbial community structure among different WWTPs may mainly result from rare sub-community. Moreover, SEM showed that geographic locations affected rare sub-communities greatly, which agreed with their higher dispersal limitation and turnover rate. In contrast, influent characteristics showed stronger correlations with abundant sub-communities, suggesting that abundant sub-community may contribute more to the removal of pollutants. This study enhanced our understanding of abundant and rare microorganisms in activated sludge especially the role of rare species and provided scientific evidence for precise regulation and control of wastewater treatment plants.