Pollutants In Sludge Research Articles

Behaviour of M. aeruginosa–Microplastic composite pollutants in coagulation and sludge storage

Microcystis aeruginosa (M. aeruginosa) blooms and microplastics pollution have been major global water pollution concern in lakes and reservoirs. In this study, the behaviour of M. aeruginosa–microplastic composite pollutants in inorganic coagulant (PACl) and organic coagulant (HTCC) treatment was investigated. Results showed that, in coagulation stage, the dissolved extracellular polymers secreted by M. aeruginosa could promote the adhesion of microplastics to algae, so as to combine them into the algal flocs, thus improving the sedimentation and removal efficiency of microplastics. On the other hand, whilst microplastics increased the size of algal flocs in PACl coagulation and improved algal removal efficiency, they had the opposite effect on HTCC coagulation. And the removal of algal metabolites including microcystins were improved by the presence of microplastics.In sludge storage stage, the oxidative and mechanical damage effects of microplastics promoted the rupture of M. aeruginosa cells in PACl sludge but not in HTCC sludge, which mean more potential risks in recycling of PACl sludge water. Besides, microplastics promoted the proliferation of beneficial bacteria such as Poterioochromonas and Coccomyxa, which contributed to the control of sludge pollution.

Sequential DBD plasma-assisted tandem tri-electrodes Fenton process for enhanced antibiotics treatment and denitrification

Ozone generated by dielectric barrier discharge (DBD) plasma has the potential for water treatment; however, its limitations, including water solubility, performance in complex matrices, and resistance to some pollutants. This study explored a sequential DBD plasma assisted by a tandem tri-electrode Fenton (S-PEF) process, using a three-stage treatment approach for degrading antibiotics (sulfamethoxazole, SMX; amoxicillin, AMX; and norfloxacin, NOF) in continuous flow mode for 220-bed volumes. Initially, antibiotics such as SMX and AMX underwent degradation in DBD plasma gas, which housed the mixing chamber. The more resilient NOF was removed by hydroxyl radicals (OH) in the following anodic chamber of the tandem trielectrodes by Fenton assisted oxidation. The continuous cyclic redox regeneration of Fe in tandem trielectrodes prevents secondary Fe sludge pollution. Finally, NO3-N and NO2-N were denitrified into N2 with 95 % selectivity in a cathodic chamber using copper oxide nanowires. This sequential treatment is crucial to mitigating the competitive effects of CO32− and humic acid in wastewater since O3 is less susceptible to them compared to OH. The S-PEF completely degraded all antibiotics regardless of water temperature (10 and 25 °C) compared to sole plasma treatment. Finally, toxicity assessments using an ecological structure–activity relationship (ECOSAR) and E. coli disinfection assays showed a significant reduction in toxicity. This study highlights the promising potential of the S-PEF as an advanced technology for wastewater treatment.

Spatial confined synthesis of submicron Fe-MoS2 with abundant surface cationic groups and sulfur vacancies for enhanced peroxymonosulfate activation

ABSTRACT The widespread use of emerging refractory organic contaminants poses a significant threat to human health, prompting the need for a cost-effective and efficient removal strategy. While the iron ions/PMS system effectively removes organic pollutants, slow Fe3+ to Fe2+ transformation hampers its efficiency, and the homogeneous distribution of iron ions complicates separation, resulting in secondary sludge pollution. Herein, we developed a novel submicron Fe-MoS2 (S-Fe-MoS2) catalyst with abundant surface cationic groups and sulfur vacancy through a cationic polyacrylamide aerogels (CPAMA) confined hydrothermal synthesis strategy. These features promote active site exposure, enhance reactant adsorption, and accelerate electron transfer between Mo and Fe sites, improving catalytic kinetics and promoting Fe3+/Fe2+ cycle for PMS activation. As a result, the S-Fe-MoS2/PMS system exhibited a high catalytic rate constant (k obs) of 0.32 min−1, in the degradation of 4-chlorophenol (4-CP), 1.5 times higher than that of the conventional Fe-MoS2/PMS system. It also achieved 82.9% total organic carbon (TOC) degradation within 60 min. Additionally, it possessed similar degradation performance for various organic pollutants, along with remarkable reusability (four cycles) and broad pH adaptability (2–8), indicating significant potential for widespread application. This study provided a new way for developing advanced heterogeneous catalysts with high efficiency for water treatment.

Novel strategy for efficient energy recovery and pollutant control from sewage sludge and food waste treatment

Considering the high organic matter contents and pollutants in sewage sludge (SS) and food waste (FW), seeking green and effective technology for energy recovery and pollutant control is a big challenge. In this study, we proposed a integrated technology combing SS mass separation by hydrothermal pretreatment, methane production from co-digestion of hydrothermally treated sewage sludge (HSS) centrate and FW, and biochar production from co-pyrolysis of HSS cake and digestate with heavy metal immobilization for synergistic utilization of SS and FW. The results showed that the co-digestion of HSS centrate with FW reduced the NH4+-N concentration and promoted volatile fatty acids conversion, leading to a more robust anaerobic system for better methane generation. Among the co-pyrolysis of HSS cake and digestate, digestate addition improved biochar quality with heavy metals immobilization and toxicity reduction. Following the lab-scale investigation, the pilot-scale verification was successfully performed (except the co-digestion process). The mass and energy balance revealed that the produced methane could supply the whole energy consumption of the integrated system with 26.2 t biochar generation for treating 300 t SS and 120 t FW. This study presents a new strategy and technology validation for synergistic treatment of SS and FW with resource recovery and pollutants control.

Biological treatment of swine wastewater—Conventional methods versus microalgal processes

BackgroundSwine wastewater (SWW) contains abundant organic carbon, nitrogen, and phosphorus, posing a significant risk of pollution and eutrophication with direct environmental release. Therefore, its proper treatment before environmental release is imperative. Conventional SWW treatment methods like stabilization ponds, aerobic processes, and anaerobic digestion are energy-intensive, with limited nitrogen and phosphorus removal and challenges in secondary sludge disposal. MethodsConventional methods described above, in addition to bacterial methods, have been discussed in detail. Microalgal bioremediation is an emerging technology for bioremediation and resource recovery from a circular economy perspective. Significant findingsConventional methods are dissimilatory and do not recover nutrients. On the other hand, the nutrients in SWW serve as a beneficial growth medium for microalgae. With its suitable nutritional composition, the resulting microalgal biomass can serve as supplements for livestock and aquaculture feed, generating additional revenue in microalgae-based SWW treatment. Microalgae-based processes enhance the SWW treatment efficiency and mitigate the common issue of secondary sludge pollution found in conventional treatment methods. This review offers comprehensive insights into traditional and microalgae-based SWW treatment methods and provides a comparative analysis of the various techniques and future research perspectives.

Quantification of linear alkylbenzene sulphonates in complex sludge samples: Influence of matrix effects in calibration methods

Linear Alkylbenzene Sulfonates (LAS) are among the priority organic pollutants in sludge owing to their high concentrations, due to its use as a major cleaning agent (surfactant) in laundry detergents and household cleaning products, and to the concentration limits of 2,600 mg/kg outlined in the EU directive draft for land application of sludge. In this work, a method has been optimized and validated for the accurate quantification of LAS homologues C10-C13 in different types of samples in the sludge treatment and disposal process including primary, secondary, and digested sludge, compost, and soil. The type of matrix had a significant impact on the method’s validation process, resulting in the need of the use of distinct dilution factors for each matrix. Overall, the procedure propose involves a cost-effective and user-friendly technique that combines both extraction and clean-up in a single step (ultrasound-assisted extraction and dispersive solid phase extraction). Analytical determination is conducted using liquid chromatography-tandem mass spectrometry. The method demonstrated excellent accuracy (relative recoveries exceeding 84.5 % across all types of sludge samples) and the limit of quantification enables the measurement of LAS concentrations up to 1000 times lower than the concentration limits stipulated in the EU directive draft. For an accurate quantification, three calibration approaches were tested (external calibration, standard addition, and matrix-matched calibration). Standard addition was the preferred method for quantitative analysis. It helps mitigate matrix effects that could otherwise distort the accuracy of analyte measurements, making it crucial for quality control, especially in monitoring applications where matrix effects may introduce bias into concentration calculations.

Sustainable Agriculture Practices: Utilizing Composted Sludge Fertilizer for Improved Crop Yield and Soil Health

It is desirable to recycle sewage sludge as fertilizer for agricultural fields. The application of sludge to agricultural soils is a measure that replaces chemical fertilizers and plays an important role in improving soil’s physicochemical and biological properties. However, there are concerns that the pollutants in sewage sludge will cause negative impacts on soil health. To closely monitor the soil–sludge interactions, a field study was conducted over a 20-year period in the North China Plain. In this study, the long-term effects of sewage sludge on the soil properties and soil microbial diversity were investigated. We examined the effects of various fertilization methods (control, chemical fertilizer, uncomposted sludge fertilizer, composted sludge fertilizer) on wheat production and several soil health indicators, such as the soil’s enzymatic activities, microbial biomass, microbial diversity, and crop yield. This long-term experiment supports that the composted sludge fertilizer increased crop production by 124.2% compared to the control treatment. The soil’s biological quality (e.g., the concentration of soil microbial biomass carbon) was also improved under the composted sludge fertilizer treatment. The concentrations of soil microbial biomass carbon under the uncomposted sludge fertilizer and composted sludge fertilizer treatments were 560.07 mg/kg and 551.07 mg/kg, respectively. The effect of the composted sludge fertilizer was greater than that of the uncomposted sludge fertilizer. The content of heavy metals did not exceed the national standard. The highest soil health index was 0.79 with the composted sludge fertilizer. Therefore, these results suggest that the application of composted sludge fertilizer has the potential to enhance long-term soil health and promote sustainable agricultural practices.

Assessment of the Polluting Status of Sludge from a Physicochemical Water Purification Unit and Their Impacts on the Soil: Case of the Yato Station (Littoral-Cameroon)

The Yato physicochemical water purification station is located in Dibombari District Council in the Littoral-Cameroon region. It is one of the largest drinking water production stations in the Central African sub-region. This work aims to evaluate, through the quantification of the concentrations of Trace Metal Elements (TMEs), the polluting status of the sludge from this drinking water production station and their impacts on the soil. To achieve this objective, mixed samples of sludge from sludge treatment ponds (taken according to the technique described in GIDS-A003 point 6 as explained in the Solid and pasty waste sampling strategy of Code of Good Practice No. 2) and samples of sludge from primary settling basins (taken in transparent bottles in polyethylene terephthalate of 1.5L) were analysed. Likewise, three soil wells were carried out and soil samples were taken on two levels of alteration then sent to the laboratory where physicochemical and TME analyses were carried out. The characteristics of the samples that were analysed are: particle size, texture (sand, silt, clay), physiochemistry (pH, electrical conductivity, temperature, phosphorus, nitrogen) and TME (chromium, copper, zinc, manganese). The results obtained show that the polluting status of the sludge from the Yato station is proven because their pollution index by heavy metals is greater than 1. The pollution index greater than 1 in the sludge from the treatment basins is due to the strong concentrations of TME originating from the accumulation of waste of all kinds in this location. Overall, TME concentrations in soils decrease for the most part from the surface towards depth. All the TMEs studied (Zn, Mn, Cu, Cr) are present in all horizons. There is multiple contamination of sludge by TMEs because their pollution index is greater than 1 (IP>1). Although the sludge pollution indices are greater than 1, those of the different horizons are much lower than 1. Thus, since the TMEs decrease with depth, the subsurface horizons would be less affected by the pollutants contained in the station sludge. marking a real pollution of the surface layers.

Simultaneous degradation of NSAIDs in aqueous and sludge stages by an electron-Fenton system derived from sediment microbial fuel cell based on a novel Fe@Mn biochar GDC

Electro-Fenton (e-Fenton) reactions boosted using microbial fuel cells (MFCs) can degrade contaminants with high efficiency, the treatment is generally performed in the aqueous phase and the sludge pollution is ignored in such MFCs. In this study, a sediment MFC e-Fenton (SMFC-e-Fenton) system was proposed for the degradation of nonsteroidal anti-inflammatory drugs (NSAIDs) in both aqueous and solid phases. A Fe@Mn-codoped biochar gas diffusion cathode was fabricated to produce hydroxyl radicals without any additional power input. The studied NSAIDs of ibuprofen (IBU), naproxen (NPX), and diclofenac (DCF) exhibited total degradation efficiencies (including aqueous and sludge phase) of 99.1%, 98.5%, and 80.6%, respectively, in the SMFC-e-Fenton system. Compared with sludge anaerobic digestion, the residual amounts of IBU, NPX, and DCF reduced from 10.2%, 24.6%, and 32.2% to 2.7%, 4.4%, and 8.5%, respectively, in the sludge phase. Moreover, the electricity generation and sludge reduction improved owing to the e-Fenton process. Using the SMFC-e-Fenton system, the effects of NSAIDs were reduced and the richness and diversity of the microbial community are maintained, improving the overall system performance. These results demonstrate that the SMFC-e-Fenton method is a high-efficiency, economic and environmental friendly technology for simultaneously treating NSAIDs in the aqueous and sludge phases.

Roles of extracellular polymeric substances in the adsorption and removal of norfloxacin during hydrothermal treatment of sewage sludge

Hydrothermal treatment (HT) is promising to remove antimicrobials from sewage sludge (SS); however, the mechanism of antimicrobial degradation during the HT of SS is not fully understood. In this study, the roles of extracellular polymeric substances (EPS) in the removal and transformation of norfloxacin (NOR) during the HT of SS at temperatures of 100 and 160 °C were investigated. The results indicated that the degradation of NOR increased with increasing HT temperature, with maximum NOR removal (52%) achieved at 160 °C. Furthermore, the NOR in sludge showed higher degradation efficiencies than the control as HT temperature was higher than 120 °C. Evident promotion effects of bound-EPS (B-EPS) in sludge were observed on the NOR degradation as HT temperature was higher than 120 °C, leading to the mineralization and deamination of protein-like components in EPS during HT. Beside, the adsorption capacity of NOR during the HT of SS decreased at temperatures higher than 120 °C. The evolution of the spatial structure of B-EPS was predominantly responsible for the adsorption of antimicrobials, a spontaneous process driven mainly by hydrophilic interactions. With the hydrothermal conversion of B-EPS, the electron transfer, and reactive species (3EPS* and ·OH) derived from B-EPS could facilitate the degradation of NOR. In particular, hydrogen bonds between B-EPS and NOR increased the apparent yield of ·OH and accelerated the decarboxylation of NOR during HT at temperatures higher than 120 °C. A toxicity evaluation suggested that HT for NOR degradation could attenuate toxicity, whereas deep oxidation or mineralization would be needed to promote ecosystem safety. These findings provide new insights into the hydrothermal activation of EPS and the interrelated hydrothermal fate of antimicrobials and other toxic pollutants in sludge.

Components of sludge from municipal wastewater treatment plants and its evaluation for land application in JiUJiang city of China

Municipal sewage sludge has a potential for widespread application on land, but the implementation of new standards for the agricultural use of sludge in China support a cautious approach. The organic matter, nutrients, and heavy metals in sewage sludge from four municipal wastewater treatment plants in Jiujiang City of China were continuously monitored. The feasibility for its land use was analyzed from three aspects such as sludge nutrients, heavy metal pollution levels, and potential ecological risks in soil. The average content of Cd, Cu, Zn, Cr, Ni, Pb, Hg and As in the sludge of Jiujiang City are 1.85, 305.25, 764.48, 170.57, 42.45, 42.27, 0.59, 28.79 mg∙kg-1, which are less than or close to mean value of heavy metals in China (except As), and all meet the minimum standards of heavy metal content in the sludge according to Chinese Quality of sludge from municipal wastewater treatment plant (GB24188-2009). The maximum content of Cu, Zn, Cr, and As exceed the control standards of pollutants in sludge for agricultural use, and the maximum value of Cu and Cr are close to the limit of landscaping standards. The average contents of organic matter, total nitrogen, total phosphorus, total potassium, and total nutrients in sludge are 385.16, 34.14, 11.05, 7.87, 53.06 g∙kg-1, respectively. The organic matter content meets the limit value (no less than 200 g∙kg-1) of Chinese Control standards of pollutants in sludge for agricultural use (GB 4284-2018), and the total nutrients content meets certain content limit (no less than 40 g∙kg-1) of total nutrients in China’s organic fertilizer. The single-factor pollution index and Nemerow’s synthetic pollution index methods were used to assess the pollution of heavy metals. The heavy metal pollution indexes (PI) are in descending order: Cd > Cu > Zn > Cr > As > Ni > Pb > Hg. The PI shows that Cd and Cu are in strong pollution level, Zn is in moderate pollution level, and As, Ni, Pb, Hg are in absolute safe level. The potential ecological risk levels of heavy metal are ranked in the following order: Cd> Cu> As> Ni> Zn> Cr > Pb. The monomial potential ecological risk coefficients reveal that Cd is in extremely strong ecological risk, Cu is in medium ecological risk and other heavy metals are in slight ecological risk. The results indicate that Cd and Cu are the main contributors to the pollution and potential ecological risks of heavy metals in soil, to which more attention should be paid during sludge disposal. Being rich in organic matter and inorganic plant nutrients，sewage sludge in Jiujiang City may be widely used on soil, but availability of potential toxic metals exceeding the limit value often restricts its uses. Before being harmlessly treated, the sludge in Jiujiang City should not be used on agricultural land and may be applied with highly caution on landscaping and land improvement, but it can be used as cover materials for co-landfilling.

Understanding how microbial electrolysis cell assisted anaerobic digestion enhances triclocarban dechlorination in sludge

Microbial electrolysis cell assisted anaerobic digestion (MEC-AD) has recently been considered as an efficient method for degradations of refractory pollutants. To date, however, knowledge about whether and how MEC-AD enhances the degradations of refractory pollutants in sludge remains largely unknown. This study therefore aims to fill this knowledge gap through investigating the transformation of triclocarban (TCC), a widely used antimicrobial agent, in MEC-AD reactors. Experimental results showed that over 83.3 % of TCC was dechlorinated to less toxic dichlorocarbanilide, monochlorocarbanilide and carbanilide in MEC-AD reactors. However, the mass loss of TCC in AD reactor (the electrodeless control) was merely 0.53 %. The presence of electrodes promoted TCC dechlorination in MEC-AD reactors, while the applied voltages (0.6 and 0.8 V) promoted hydrogenotrophic methanogenesis. H2-utilizing Nitrospira and homoacetogenic Acetobacterium were recognized as potential TCC dechlorinators, with their abundances in the planktonic sludge of MEC-AD reactors being 5.0–16.5 times higher than those in AD reactor. The carbon brush electrodes in MEC-AD reactors caused the enrichment of acetoclastic Methanothrix and the complete removal of acetic acid, which thereby thermodynamically accelerated homoacetogenesis and H2-producing acetogenesis in the planktonic sludge. Moreover, the direct interspecies electron transfer using hydrogenase as terminal electron acceptor was enhanced in the planktonic sludge of MEC-AD reactors, which could also improve H2 production rate and stimulate the growth and activity of TCC dechlorinators.

De-oiling characteristics and mechanism of oil-bearing sludge cleaned by CGAs

There hasn't been much study on using Colloidal Gas Aphrons (CGAs) to clean oily sludge. In addition, the efficacy and mechanism of CGAs-enhanced surfactant cleaning of oily sludge are not yet clear. Therefore, in this study, CGAs prepared from the compound surfactant solution were used to clean oily sludge in an oil field in Xinjiang. The performance of CGAs in terms of oil removal and particle size was both examined when building the surfactant compounding system. The removal abilities of CGAs from different crude oil components and an analysis of the chemical cleaning process of CGAs were studied. The results demonstrated that the interfacial tension was as low as 3.535 mN/m and the oil removal rate of CGAs was as high as 92.9% when the ideal ratio of sophorolipid (SL) to sodium dodecyl benzene sulfonate (SDBS) was 6: 4. The average particle size of CGAs was 90.57 µm at this ideal ratio. The Zeta potential and turbidity of the supernatant after CGAs cleaning was lower than those of chemical cleaning. Infrared analysis, two-dimensional fluorescence analysis, and thermogravimetric methods were used to characterize the oily sludge after CGAs cleaned. According to the analysis's findings, CGAs' enormous specific surface area allows them to adsorb more petroleum pollutants and improved the ability of those pollutants to migrate between the water phase and other phases of the atmosphere. Also, CGAs are particularly successful in adhering to petroleum-based pollutants in oil sludge for the removal of light constituents like n-alkanes and aromatic hydrocarbons due to the synergistic effects of hydrophobic and electrostatic effects on the functional surface of CGAs. This work provides useful information on the mechanism of the enhanced removal of crude oil from oily sludge by CGAs and provides a new idea for oily sludge cleaning.

Concentration of the main persistent organic pollutants in sewage sludge in relation to wastewater treatment plant parameters and sludge stabilisation

Concentration of 16 polycyclic aromatic hydrocarbons (PAHs), 7 polychlorinated biphenyls (PCBs), and 11 organochlorine pesticides (OCPs) in sewage sludge from 40 wastewater treatment plants (WWTPs) was investigated. Relationship between pollutant sludge contents, main WWTP parameters and type of sludge stabilisation was carefully evaluated. Average load of PAHs, PCBs, and OCPs in different sludges from Czech Republic was 3096, 95.7 and 76.1 μg/kg dry weight, respectively. There were moderate/strong correlations among the individual tested pollutants in sludge (r = 0.40–0.76). Relationship between total pollutant contents in sludge, common WWTP parameters and sludge stabilisation was not evident. Only individual pollutants such anthracene and PCB 52 correlated significantly (P < 0.05) with biochemical oxygen demand (r = −0.35) and chemical oxygen demand removal efficiencies (r = −0.35), suggesting recalcitrance to degradation during wastewater treatment. When sorted according to the design capacity, a linear correlation between WWTP size and pollutant contents in sludge was evident with growing WWTP capacity. Our study indicated that WWTPs with anaerobic digestion are prone to accumulate a statistically higher content of PAHs and PCBs (P < 0.05) in digested sludges compared to aerobically digested ones. The influence of anaerobic digestion temperature of treated sludge on tested pollutants was not evident.

Isolasi Dan Karakterisasi Bakteri Termofilik Dari Oil Sludge Asal Kalimantan Timur

Oil sludge is a product of petroleum mining activities and causes environmental pollution. However, oil sludge, including hazardous and toxic waste materials (B3), has been less effective in reducing oil sludge pollution. Thus, the researcher solved the issue by using hydrocarbonoclastic. It is necessary to use hydrocarbonoclastic bacteria isolated directly from their habitat (indigenous bacteria) as hydrocarbon degrading agents. Therefore, this study aimed to isolate and identify indigenous thermophilic bacteria from East Kalimantan Oil sludge. This study is an observational study that is analyzed descriptively. Procedure for isolation and identification of thermophilic bacteria from oil sludge grow on Synthetic Mineral Water media (SMW) with and without an autoclave. The Microbact Identification System Kit GNB 24E was used to characterize colonies macroscopically, microscopically, Gram staining, physiological tests (catalase, coagulase, and motility tests), and biochemically. The bacteria that were successfully isolated were later identified with Microbact Software and Bergey's book Manual of Determinative Bacteriology Ninth Edition. The results of the isolation and identification of thermophilic Indigenous bacteria from Oil Sludge Kalimantan Timur found Pseudomonas aeruginosa species with a similarity accuracy of 98.33%. The identified bacterial isolates can later be used as bioremediation agents on soils polluted with oil sludge. Keywords : Indigenous bacteria, Oil Sludge, Pseudomonas aeruginosa.

Biorefinery of Sewage Sludge: Overview of Possible Value-Added Products and Applicable Process Technologies

The disposal of excess biological sewage sludge from wastewater treatment is a growing environmental issue due to the vast quantities generated worldwide. For many years, sludge disposal has been considered an inevitable “nuisance” linked to the main task of wastewater treatment; recently, the issues relating to the presence of emerging pollutants in sludge have contributed to severe limitations on traditional disposal routes and increased process costs. As a consequence of the water industry’s approach to sustainability and circular economy principles, the investigation into options for sludge-embedded resource recovery has been increasing over time. Among these, the definition of biorefinery encompasses many processes used to process sewage sludge for biofuel and/or resource recovery. In addition to the “conventional” recovery of biogas and nutrients, biopolymers (PHAs and EPS), proteins, enzymes, biopesticides, and biofuels are among the “new” sludge extraction products that are being studied. Not all of the proposed technologies are, however, mature for industrial exploitation as yet. This paper presents an overview of possible product recovery from sludge biorefinery, with emphasis on recent developments, and on the benefits and limitations of applicable technologies for ensuring sustainability and environmental efficiency, through an analysis of the current literature.

Light and oxygen facilitating the directly treatment food wastewater and poly-β-hydroxybutyrate, 5-aminolevulinic acid, pigment productions by Rubrivivax gelatinosus.

Rubrivivax gelatinosus has the advantage of using wastewater to realize biomass recovery. However, they still cannot be applied large scale because they cannot directly treat the wastewater containing macromolecular organics. Thus, this article investigated the effects of light-oxygen conditions on R. gelatinosus by directly recycling wastewater containing macromolecular organics to produce biomass, poly-β-hydroxybutyrate (PHB), 5-aminolevulinic acid (5-ALA), and pigment. Results showed that R. gelatinosus directly treated the macromolecule organic (soybean protein and starch) wastewaters and achieved biomass recovery under light-anaerobic and light-micro-oxygen in six conditions. Chemical oxygen demand, protein, and starch removals for two wastewaters all reached above 70%. Renewable bio-resources such as biomass, PHB, 5-ALA, and pigment production were 10 times the initial content. Theoretical analysis indicated that light activated the synthesis of protease and amylase. However, oxygen concentration decided the number of enzymes. When oxygen was at micro-oxygen or anaerobic, the aforementioned expression and synthesis were conducted. In summary, this study expanded the viewpoint ignored by traditional theory. It was realized that R. gelatinosus directly treated wastewater and accumulated nutrients (biomass, PHB, pigment, and 5-ALA) for recycling, which reduced the secondary pollution of excess sludge into the environment.

Spatial Distribution Characteristics and Potential Risk Assessment of Heavy Metals in Sludge of Shanghai Sewage Treatment Plant: A Case Study

Sewage treatment is an important indicator of the urban environment and an important method of sustainable development. In this paper, the spatial distribution characteristics of 8 heavy metals in sewage sludge from 44 sewage treatment plants in Shanghai were analyzed. The pollution degree and potential ecological risk of heavy metals in sludge were evaluated by the Nemerow comprehensive pollution index and Hakanson potential ecological risk index. First, the single factor pollution index of heavy metals was ranked. The Nemerow comprehensive pollution index showed that five sewage treatment plants in Nanxiang, Dongqu, Liantang, Songjiang west, and Xinhe were heavily polluted. Second, the single factor potential ecological risk index of each heavy metal was analyzed. Finally, it is concluded that in the monitoring and control of sewage treatment, Shanghai should pay attention to the sewage treatment plants with high potential ecological risks and gain an excellent performance in the reduction in the emissions of pollution sources, so as to improve environmental quality and reduce the potential ecological risks. This paper provides the basis for studying the characteristics of heavy metal pollution of sewage sludge.

Preparation and resource utilization of sludge-based fire-preventive and extinguishing composite gel for coal mine

We prepared a sludge-based fire-preventive and extinguishing composite gel for coal mines using sludge, HPAM, water glass, and sodium bicarbonate as the main raw materials. Orthogonal test was used to analyze the effects of each component and its level on the performance of gel to determine the optimal ratio of gel and then tested its fire-preventive and extinguishing characteristics. Finally, the gelling mechanisms of the gel are discussed. The composite gel prepared at the optimal level showed that the gelling time can be maintained at about 55 s, the water retention can reach up to 58.6% in 12 h at 100 °C. The gel has a dense microstructure and uniform pores, and has the best inhibition rate of coal spontaneous combustion. As compared with other materials, the coal piled with gel did not reignite. TGA showed that the gel hinders oxidation and complete combustion of coal. The in-situ infrared analysis confirmed that the coal sample treated with gel has a low content of aliphatic hydrocarbon and hydroxyl group. Infrared spectroscopy analysis indicated that the sludge in the gel plays the role of filler. The organic-inorganic composite network structure formed by the sludge and the gel not only prevents the system from water loss and coal oxidation but also absorbs a large amount of sludge and realizes the resource utilization of sludge. Therefore, the preparation of composite gel reduces the secondary pollution of sludge and lowers the cost of the material, making it an economical and environmentally friendly fire-preventive and extinguishing material.

Improved Fe(II) regeneration from actual ferric sludge using a biocathode with granular sludge

Ferric sludge pollution and unsustainable utilization of Fe(II) reagent were tough nuts to crack for homogeneous Fenton treatment. Previous Fe(II) regeneration methods are still limited by high reagent consumption or low regeneration rate. In this work, granular sludge was introduced into the biocathode of microbial electrolysis cell (MEC), to improve Fe(II)-regeneration rate from actual ferric sludge at near neutral pH. Wastewater constituents in the bioanode of dual-chamber MEC were used as the reducing power to regenerate Fe(II). In the flow-through biocathode, 175 ± 16 mg/L of dissolved Fe(II) was efficiently regenerated from actual ferric sludge. The regeneration rate of dissolved Fe(II) was 7.2 times higher than that of the previously reported biocathode. Besides, the actual and synthetic ferric sludge had a similar Fe(II) regeneration performance. Interestingly, recalcitrant organics and 20 mg/L NO3–N in ferric sludge were removed by 96% and 100% during Fe(II) regeneration. The biomass in the granular sludge biocathode was 12 times that of the control biocathode, in which Clostridium sensu stricto dominated. These findings provide insights and theoretical support for developing a viable biotechnology platform, to close the gap for the efficient and sustainable iron cycle.