Impact of sludge conditioning treatment on the bioavailability of pyrene in sewage sludge

Polyaromatic hydrocarbons (PAHs) in the water environment: A review on toxicity, microbial biodegradation, systematic biological advancements, and environmental fate

Polycyclic aromatic hydrocarbons (PAHs) are considered a major class of organic contaminants or pollutants, which are poisonous, mutagenic, genotoxic, and/or carcinogenic. Due to their ubiquitous occurrence and recalcitrance, PAHs-related pollution possesses significant public health and environmental concerns. Increasing the understanding of PAHs' negative impacts on ecosystems and human health has encouraged more researchers to focus on eliminating these pollutants from the environment. Nutrients available in the aqueous phase, the amount and type of microbes in the culture, and the PAHs' nature and molecular characteristics are the common factors influencing the microbial breakdown of PAHs. In recent decades, microbial community analyses, biochemical pathways, enzyme systems, gene organization, and genetic regulation related to PAH degradation have been intensively researched. Although xenobiotic-degrading microbes have a lot of potential for restoring the damaged ecosystems in a cost-effective and efficient manner, their role and strength to eliminate the refractory PAH compounds using innovative technologies are still to be explored. Recent analytical biochemistry and genetically engineered technologies have aided in improving the effectiveness of PAHs' breakdown by microorganisms, creating and developing advanced bioremediation techniques. Optimizing the key characteristics like the adsorption, bioavailability, and mass transfer of PAH boosts the microorganisms' bioremediation performance, especially in the natural aquatic water bodies. This review's primary goal is to provide an understanding of recent information about how PAHs are degraded and/or transformed in the aquatic environment by halophilic archaea, bacteria, algae, and fungi. Furthermore, the removal mechanisms of PAH in the marine/aquatic environment are discussed in terms of the recent systemic advancements in microbial degradation methodologies. The review outputs would assist in facilitating the development of new insights into PAH bioremediation.

Phytoremediation of a pyrene-contaminated soil by Cannabis sativa L. at different initial pyrene concentrations

This study proposes the phytoremediation of a pyrene (PYR)-contaminated soil by Cannabis sativa L. The experimental campaign was conducted along a 60 days period using three different initial PYR concentrations (i.e., 50, 100 and 150 mg kg TS^-1 of soil) in 300 mL volume pots under greenhouse conditions (18-25 °C and 45-55% humidity). After 60 days of hemp growth and flourishing, the highest PYR removal reached approximately 95% in planted soil, 35% higher than in the unplanted control. PYR accumulation was observed in both roots and aerial parts of the plant, with a higher PYR uptake at increasing initial PYR concentrations in soil. The initial PYR concentration affected the growth and, thus, the phytoremediation potential of C. sativa L., which was the result of different removal mechanisms. Overall, the lowest initial PYR concentration was the one that resulted in the highest PYR removal. The interaction between the plant roots and microorganisms in rhizosphere was likely associated with PYR removal in this study. The highest DHO activity of 66.26 μg INTF g^-1 TS^-1 was observed in the soil spiked with 50 mg PYR·kg TS^-1.

Impact of initial sludge pH on enhancing the dewaterability of waste activated sludge by zero-valent iron-activated peroxydisulphate

In this study, the usefulness of the ZVI/S2O82- system in enhancing the dewaterability of waste activated sludge was studied at different initial sludge pH levels to reveal the associated mechanisms. Results showed that conditioning of sludge by the ZVI/S2O82- system at acidic initial sludge pHs enhanced sludge filterability and the dryness of dewatered sludge cake, while only the sludge filterability was improved at neutral initial sludge pH. In particular, the conditioning treatment using 0.353 g/g DS of ZVI and Na₂S₂O₈ with a mole ratio of 1.25:1, at initial sludge pH 2.52, was the optimum condition to improve sludge dewaterability, which reduced the moisture content of dewatered sludge cake to only 69.8% and meanwhile reduced sludge CST and SRF to only 70.9% and 40.7% of that of raw sludge, respectively. During the conditioning treatment, sludge microbial cell lysis resulting from decreasing the initial sludge pH led to the reduction in the moisture content of dewatered sludge cake, while the oxidation of sludge EPS and the coagulation of the disrupted sludge flocs achieved by the ZVI/S2O82- system improved sludge filterability. A kaolin suspension experiment revealed that with a decrease in system pH, the oxidation effect was gradually inhibited and the coagulation effect offset the disruption effect on sludge flocs to improve the filterability of sludge. Therefore, the conditioning of waste activated sludge using the ZVI/Na₂S₂O₈ system at acidic initial sludge pHs is useful to enhance the sludge filterability and the dryness of dewatered sludge cake, both of which are crucial for improving sludge dewatering performance.

Degradation of fluorescent dye-Solvent Green 7 (HPTS) in wastewater by advanced oxidation process

Solvent Green 7 (HPTS) is a widely used fluorescent dye. As a kind of polycyclic aromatic hydrocarbon (PAHs) derivative, HPTS would cause pollution when it is discharged into the environment. This study adopted advanced oxidation processes (UV/H₂O₂) to degrade the HPTS in aqueous solution and investigated the effects of various factors on the degradation. The results showed that: the initial concentration and the fluorescence characteristics of HPTS reduced the degradation efficiency. When the oxidant concentration of H₂O₂ was 3 mg/L, the degradation efficiency and cost of HPTS (20 mg/L) were the most appropriate; when there were various inorganic anions in the solution, the degradations were not affected, but when the solution was strong acid and there existed a lot of chloride ions, the degradation of HPTS was inhibited. The degradation pathways indicated HPTS degraded into naphthalene derivatives, benzene derivatives through oxidation and decarboxylation reactions, finally into water and carbon dioxide. Further research for substances similar to HPTS structure will make progress in understanding the degradation process of PAHs.

Role of extracellular polymeric substances in sludge dewatering under modified corn-core powder and sludge-based biochar pretreatments

Extracellular polymeric substances (EPS) which wrapped on sludge particles were deemed to hinder the outflowing of combined water in sludge system. The complex composition of EPS was the bottleneck for revealing its relationship with sludge dewaterability. In this study, a combined modified corn-core powder (MCCP) and sludge-based biochar (SBB) condition was executed to treat sludge for enhancing dehydration performance, and the concentration and the form distribution of organics in EPS, the variances of protein secondary structures were investigated. Correlation between the sludge dewaterability and EPS components were performed, found strong correlations among the net sludge solids yield (YN) and the specific resistance of filtration (SRF) (R = -0.923), Zeta potential (R = -0.971). Furthermore, the relationship between the secondary structures of protein and dehydration performance were strong related. With the optimal dosage of SBB and MCCP, aggregated strands and α -helix were released, indicated that the unfolding and despiralization in soluble EPS (S-EPS) were improved, disordered the sludge network, reduced the flowing resistance of bound water, finally enhancing sludge dewaterability.

Conditioning with zero-valent iron or Fe2+ activated peroxydisulfate at an acidic initial sludge pH removed intracellular antibiotic resistance genes but increased extracellular antibiotic resistance genes in sewage sludge

Sulfate radical (SO₄^-)-based conditioning methods, such as zero-valent iron (ZVI, i.e., Fe⁰) or ferrous iron (Fe²⁺) activated peroxydisulfate (S₂O₈^2-), have recently developed to improve sludge dewaterability, but it remains unclear how they impact the intracellular and extracellular antibiotic resistance genes (ARGs) in sewage sludge. In this study, it was found that conditioning treatments that used ZVI/S₂O₈^2- or Fe²⁺/S₂O₈^2- system, at an acidic initial sludge pH, removed the intracellular ARGs and intI1 and the extracellular intI1 from sewage sludge, but led to the accumulation of extracellular ARGs of aadA-01, aadA-02, aadA1, aadA2-03, and strB in conditioned sludge. During sludge conditioning with ZVI/S₂O₈^2- or Fe²⁺/S₂O₈^2-, bacterial hosts of ARGs and intI1 were seriously lysed to release the intracellular ARGs and intI1 to the extracellular environment, thus removing intracellular ARGs and intI1 in sludge, while the released ARGs and intI1 were primarily degraded by the produced SO₄^- to attenuate most extracellular ARGs and intI1. However, the relatively lower degradation ability of SO₄^- for extracellular ARGs of aadA-01, aadA-02, aadA1, aadA2-03, and strB led to their accumulation in conditioned sludge. Therefore, SO₄^--based conditioning methods can be employed to reduce ARGs in sludge, but the subsequent treatment of sludge dewatering filtrate requires more attention.

Comprehensive review of polycyclic aromatic hydrocarbons in water sources, their effects and treatments

Polycyclic aromatic hydrocarbons (PAHs) are principally derived from the incomplete combustion of fossil fuels. This study investigated the occurrence of PAHs in aquatic environments around the world, their effects on the environment and humans, and methods for their removal. Polycyclic aromatic hydrocarbons have a great negative impact on the humans and environment, and can even cause cancer in humans. Use of good methods and equipment are essential to monitoring PAHs, and GC/MS and HPLC are usually used for their analysis in aqueous solutions. In aquatic environments, the PAHs concentrations range widely from 0.03 ng/L (seawater; Southeastern Japan Sea, Japan) to 8,310,000 ng/L (Domestic Wastewater Treatment Plant, Siloam, South Africa). Moreover, bioaccumulation of ∑16PAHs in fish has been reported to range from 11.2 ng/L (Cynoscion guatucupa, South Africa) to 4207.5 ng/L (Saurida undosquamis, Egypt). Several biological, physical and chemical and biological techniques have been reported to treat water contaminated by PAHs, but adsorption and combined treatment methods have shown better removal performance, with some methods removing up to 99.99% of PAHs.

Biosolids and sludge management

The advancements in the field of sludge and biosolids have been made over the past year. This review outlines the major contributions of researchers that have been published in peer-reviewed journals and conference proceedings throughout 2018. The review is organized in sections including regulatory developments and market analysis; analysis and quantification of characteristics including microconstituents and metals; treatment advances for the conversion of sludge to biosolids including pretreatment and sludge minimization, conditioning and dewatering, digestion, composting, and innovative technologies; product development and reuse including adsorbents and thermal products, agricultural and other uses, and innovative uses; odor and air emissions; and energy factors. PRACTITIONER POINTS: Summary of advances in the field of residuals and biosolids research in 2018. This review outlines the major contributions of researchers that have been published in peer-reviewed journals and conference proceedings. Topics covered range from regulation to innovation.

Highly efficient nickel (II) removal by sewage sludge biochar supported α-Fe2O3 and α-FeOOH: Sorption characteristics and mechanisms

A novel approach was employed to load α-Fe₂O₃ and α-FeOOH onto sewage sludge biochar (SBC) with the purpose of efficient nickel (Ni) removal. A high Ni(II) adsorption capacity of 35.50 mg·g^-1 in 100 ppm Ni(II) solution with 10 mg modified sewage sludge biochar (MSBC) was achieved. The adsorption kinetic and isotherm were fitted well by the pseudo-second-order model and the Langmuir model, respectively. The optimal pH was found around a neutral pH of 7. The adsorption mechanisms of Ni(II) onto MSBC were described as the synergistic effects of electrostatic attraction, ion exchange, inner-sphere complexation and co-precipitation. The initial rapid adsorption phenomenon could be attributed to electrostatic attraction and ion exchange, and then inner-sphere complexation and co-precipitation acted as a crucial role in the following step. The remarkable performance of MSBC provides an effective waste utilization approach to simultaneous sewage sludge recycle and Ni removal from aqueous solution.

Bioleaching conditioning increased the bioavailability of polycyclic aromatic hydrocarbons to promote their removal during co-composting of industrial and municipal sewage sludges

Conditioning treatments are extensively employed in wastewater treatment plants (WWTPs) to enhance sludge dewaterability, thereby improving the sludge dehydration during mechanical dewatering. However, it remains unclear whether the sludge conditioning treatments would influence the removal of polycyclic aromatic hydrocarbons (PAHs) during the dewatered sludge composting. In this study, the influences of three sludge conditioning methods, including bioleaching conditioning driven by Acidithiobacillus ferrooxidans, chemical conditioning with Fe[III]/CaO, and chemical conditioning with polyacrylamide (PAM), on the bioavailability of PAHs in dewatered sludge and the PAH removal during the co-compositing of industrial and municipal sewage sludges were investigated. The results showed that bioleaching conditioning was capable to significantly increase the bioavailability of PAHs in dewatered sludge, which was not attained by the other two conditioning methods. During the 39 days composting of dewatered sludge, the total removal efficiency of six detected PAHs (∑PAHs) including acenaphthylene, fluorene, phenanthrene, anthracene, chrysene and benzo(k)fluoranthene was 58.7% in raw sludge, 58.5% in PAM-conditioned sludge, 76.4% in bioleached sludge, and 60.4% in Fe[III]/CaO-conditioned sludge, respectively, and the removal of acenaphthylene, chrysene and benzo(k)fluoranthene was much higher in bioleached sludge than in other sludges. During dewatered sludge composting, PAHs may mainly be degraded by the bacteria belonging to the genera Luteimonas, Glutamicibacter, Alcanivorax, Dechloromonas, Ferribacterium, Truepera and Sphingobacterium. Linear correlation analysis between PAH removal and their bioavailability revealed that the promoted PAH removal during the composting of dewatered bioleached sludge may ascribe to the enhanced bioavailability of individual PAH. Therefore, the combination of bioleaching conditioning and subsequent dewatered sludge composting is effective to remove PAHs in sewage sludge, thus alleviating the loads of PAHs during the land application of sludge compost products.

Importance of sludge conditioning in attenuating antibiotic resistance: Removal of antibiotic resistance genes by bioleaching and chemical conditioning with Fe[III]/CaO

Conditioning can drastically improve the dewaterability of sewage sludge and thus it is widely practiced in most wastewater treatment plants (WWTPs). In WWTPs, various antibiotic resistance genes (ARGs) present in sewage are concentrated in the sewage sludge, but the effect of sludge conditioning on ARGs in sewage sludge remains unclear. Here, we evaluated and compared the effectiveness of four sludge conditioning methods (namely chemical conditioning with polyacrylamide (PAM), chemical conditioning with Fe[III]/CaO, bioleaching conditioning, and chemical acidification conditioning) and an aerobic incubation control in removing 46 target ARGs and intI1 from a municipal sewage sludge. The damage of sludge microbial cells and the change in the sludge bacterial community during the various sludge conditioning treatments were also characterized. The results suggested that the chemical conditioning with PAM and aerobic incubation treatment did not remove ARGs and intI1 from the sewage sludge. The chemical acidification reduced the absolute abundances of most ARGs and intI1, but increased their relative abundances. However, the chemical conditioning with Fe[III]/CaO and bioleaching conditioning reduced both the absolute and relative abundances of most ARGs and removed a majority of extracellular ARGs in the sludge. During sludge conditioning treatments, the sludge microbial cells were severely damaged to decrease the total bacterial biomass in sludge, and accordingly the bacterial hosts carrying ARGs and intI were effectively damaged to reduce the absolute abundances of most ARGs and intI1. In addition, the sludge bacterial community in conditioned sludge determined the relative abundances of residual ARGs. Our findings suggest that sludge conditioning can be an important sludge treatment process in attenuating antibiotic resistance in sewage sludge, and bioleaching and chemical conditioning with Fe[III]/CaO can be employed as effective conditioning ways to reduce ARGs in sewage sludge, potentially limiting their release to the environment.