It is desirable to establish an environmentally benign platform for disposing biomass from the phytoremediation process while recovering energy is of importance. To this end, the biochemical methane potential (BMP) tests were conducted using four different biomass samples (i.e., sunflower: Helianthus annuus) that were obtained from the different remediation sites. In particular, this study laid great emphasis on evaluating the inhibition for the anaerobic digestion (AD) process induced by endogenous heavy metal (Cd, Cu, Ni, Pb, and Zn) content in biomass. Despite the high levels of heavy metal contents (Cd: 58.4, Cu: 23.0, Ni: 2.01, Pb: 9.88, and Zn: 146 mg kg⁻¹) in the substrate for the AD process, the overall performance was comparable relative to the case of the references. Therefore, this study signified that the inhibition derived from heavy metals was nearly negligible, which suggested that biomass from the phytoremediation site could be used as a substrate for the AD process.

The prevalence of antibiotic resistance genes (ARGs) in waste sludge, especially for the pharmaceutical waste sludge, presents great potential risks to human health. Although ARGs and factors affecting their spreading are of major importance for human health, the factors influencing the fate of ARGs during sludge treatment, especially for pharmaceutical sludge treatment are not yet well understood. In order to be able to minimize ARGs spreading, it is important to find what is influencing their spreading. Therefore, certain factors, such as the sludge characteristics, bacterial diversity and community composition, and mobile genetic elements (MGEs) during the advanced AD of pharmaceutical sludge with different pretreatments were studied, and their affinity with ARGs was elucidated by Spearman correlation analysis. Furthermore, multiple linear regression was introduced to evaluate the importance of the various factors. Results showed that 59.7%–88.3% of the variations in individual ARGs and total ARGs can be explained by the corresponding factors. Bacterial diversity rather than specific bacterial community composition affected the fate of ARGs, whereas alkalinity was the most important factor on ARGs among all sludge characteristics investigated in this study. Besides, 66.4% of variation of total ARGs was driven by the changes of MGEs. Multiple linear regression models also reveal the collective effect of these factors on ARGs, and the contributions of each factor impact on ARGs. This study provides more comprehension about the factors impact on the fate of ARGs during pharmaceutical sludge treatment, and offers an approach to evaluate the importance of each factor, which method could be introduced for evaluation of factors influencing ARGs during other types of sludge or wastewater treatment.

We evaluated the chronic impact of oxytetracycline (OTC) on performance and antibiotic resistance development during the mesophilic anaerobic digestion (AD) of antibiotic-containing biomass. Mesophilic AD was conducted in a completely stirred tank reactor by constantly feeding municipal excess sludge spiked with increasing concentrations of OTC (0–1000 mg L−1) under a solid retention time of 20 days over a period of 265 days. Results showed that methane generation of mesophilic AD was inhibited when the OTC concentration in digested sludge was increased to around 18,000 mg kg−1 (OTC dose, 1000 mg L−1), due to the inhibition of fermenting and acidogenic bacteria. Metagenomic sequencing and high-throughput quantitative PCR analysis demonstrated that tetracycline resistance genes were the most dominant type (38.47–43.76%) in the resistome, with tetG, tetX, tetM, tetR, tetQ, tetO, and tetL as the dominant resistant subtypes throughout the whole experimental period. The relative abundance of these tet genes increased from 2.10 × 10−1 before spiking OTC (OTC concentration in digested sludge, 8.97 mg kg−1) to 2.83 × 10−1 (p < 0.05) after spiking OTC at a dose of 40 mg L−1 (OTC concentration in digested sludge, 528.52 mg kg−1). Furthermore, mobile genetic elements, including integrons, transposons, and plasmids, were also enriched with the increase in OTC dose. Based on partial canonical correspondence analysis, the contributions of horizontal (mobile element alteration) and vertical (bacterial community shift) gene transfer to antibiotic resistome variation were 29.35% and 21.51%, respectively. Thus, considering the inhibition of hydrolytic acidification and enrichment of antibiotic resistome, mesophilic AD is not suggested to directly treat the biomass containing OTC concentration higher than 200 mg L−1.

Manure treatment technologies are rapidly developing to minimize eutrophication of surrounding environments and potentially decrease the introduction of antibiotics and antibiotic resistant genes (ARGs) into the environment. While laboratory and pilot-scale manure treatment systems boast promising results, antibiotic and ARG removals in full-scale systems receiving continuous manure input have not been evaluated. The effect of treatment on ARGs is similarly lacking. This study examines the occurrence and transformation of sulfonamides, tetracyclines, tetracycline degradation products, and related ARGs throughout a full-scale advanced anaerobic digester (AAD) receiving continuous manure and antibiotic input. Manure samples were collected throughout the AAD system to evaluate baseline antibiotic and ARG input (raw manure), the effect of hygenization (post-pasteurized manure) and anaerobic digestion (post-digestion manure) on antibiotic and ARG levels. Antibiotics were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the ARGs tet(O), tet(W), sul1 and sul2 were analyzed by quantitative polymerase chain reaction (Q-PCR). Significant reductions in the concentrations of chlortetracycline, oxytetracycline, tetracycline and their degradation products were observed in manure liquids following treatment (p < 0.001), concomitant to significant increases in manure solids (p < 0.001). These results suggest sorption is the major removal route for tetracyclines during AAD. Significant decreases in the epimer-to-total residue ratios for chlortetracycline and tetracycline in manure solids further indicate degradation is desorption-limited. Moreover, sul1 and sul2 copies decreased significantly (p < 0.001) following AAD in the absence of sulfonamide antibiotics, while tetracyclines-resistant genes remained unchanged. A cross-sectional study of dairy farms utilizing natural aeration and liquid-solid separation treatments was additionally performed to compare levels of antibiotics and ARGs found in AAD with the levels in common manure management systems. The concentration of antibiotics in raw manure varied greatly between farms while minimal differences in ARGs were observed. However, significant (p < 0.01) differences in the levels of antibiotics and ARGs (except tet(W)) were observed in the effluents from the three different manure management systems.

Triclosan (TCS) is a broad-spectrum antimicrobial used in a variety of consumer products. While it was recently banned from hand soaps in the US, it is still a key ingredient in a top-selling toothpaste. TCS is a hydrophobic micropollutant that is recalcitrant under anaerobic digestion thereby resulting in high TCS concentrations in biosolids. The objective of this study was to determine the impact of TCS on the antibiotic resistome and potential cross-protection in lab-scale anaerobic digesters using shotgun metagenomics. It was hypothesized that metagenomics would reveal selection for antibiotic resistance genes (ARGs) not previously found in pure culture studies or mixed-culture studies using targeted qPCR. In this study, four different levels of TCS were continuously fed to triplicate lab-scale anaerobic digesters to assess the effect of TCS levels on the antibiotic resistance gene profiles (resistome). Blasting metagenomic reads against antibiotic/metal resistance gene database (BacMet) revealed that ARG diversity and abundance changed along the TCS concentration gradient. While loss of bacterial diversity and digester function were observed in the digester treated with the highest TCS concentration, FabV, which is a known TCS resistance gene, increased in this extremely high TCS environment. The abundance of several other known ARG or metal resistance genes (MRGs), including corA and arsB, also increased as the concentrations of TCS increased. Analysis of other functional genes using SEED database revealed the increase of potentially key genes for resistance including different types of transporters and transposons. These results indicate that antimicrobials can alter the abundance of multiple resistance genes in anaerobic digesters even when function (i.e. methane production) is maintained. This study also suggests that enriched ARGs could be released into environments with biosolids land application.

Animal manure is often anaerobically digested for the purpose of producing biogas. The digested manure, namely digestate, can be applied onto farmlands to enhance crop yields as it is abundant in nutrients. However, intensive livestock farming brings about manure exceeding the carrying capacity of lands nearby. Technologies focused on nutrient recovery from digestate have been studied recently, while many problems and challenges still remain unsolved. In this article, these recovery technologies are reviewed and compared, and challenges are deliberated. Ammonia stripping and struvite formation are easily operated technologies in comparison with membrane technologies. Amongst membrane technologies, electrodialysis reversal and forward osmosis are promising due to their high resistance to membrane fouling. Further studies should be focused on the operational cost, disposal of solid and liquid residuals and marketization of the recovered products.

In this study, different nitrogen doses (0, 16, 48, 64, 80, and 96 kg ha⁻¹) from two sources, biofertilizer (from anaerobic digestion of cattle wastewater) and urea, were applied to cultivate two sugarcane varieties (RB 867515 and SP 803280). °Brix values higher than 21% were obtained with application of 80 kg ha⁻¹ from biofertilizer. The mean productivity of the cultivar RB 867515 using biofertilizer was 147.5 ton ha⁻¹, while from urea it was 136.87 ton ha⁻¹. The cultivar SP 803280 produced an average yield of 152.25 ton ha⁻¹ when applying biofertilizer and 154.37 ton ha⁻¹ with use of urea. Significant differences (P ≤ 0.05) between the use of biofertilizer and urea were detected for cultivar RB 867515 in terms of crude protein concentration. The application of 80 kg of N ha⁻¹ was considered the ideal dose, corresponding to fertirrigation blades of 54 mm of biofertilizer. The experiment showed that the biofertilizer formulation analyzed can replace urea as a nitrogen source for growing sugarcane. Graphical Abstract ᅟ

This study investigated the biogas production and dewaterability of sewage sludge with alkaline pretreatment at mesophilic and thermophilic temperatures. The total suspended solids (TSS) and volatile suspended solids (VSS) of raw sludges were 21.1 ± 2.3 and 16.2 ± 1.5 g L⁻¹, respectively. Raw sludges were pretreated at uncontrolled, pH 8, pH 10, and pH 12 under mesophilic (Mu, M8, M10, and M12) and thermophilic (Tu, T8, T10, and T12) conditions, respectively. All the pretreatments last 6 days. The pH of pretreated sludges was adjusted to the pH 7.0 prior to inoculating with mesophilic anaerobic digested sludge and undergoing 60 days of anaerobic digestion. The ultimate biogas yield of Mu, M8, M10, M12, Tu, T8, T10, and T12 was 296.8, 384.8, 339.9, 323.1, 376.6, 322.4, 271.5, and 258.1 mL g⁻¹-VSₐddₑd, respectively. Both the pH of alkali treatment and temperature of thermal treatment affect the performance of anaerobic digestion. High hydrolysis pH (pH 10 and pH 12) resulted in high Na⁺ concentration (over 4000 mg L⁻¹), and Na⁺ inhibitory effect reduced the ultimate biogas yield. The normalized capillary suction time (NCST) found in the treatments of M8 and Tu were 11.8 ± 1.1 to 23.4 ± 1.7 and 27.9 ± 5.4 to 111.8 ± 1.7 s g⁻¹-TSS, respectively. The results suggest that both the pH of alkali treatment and temperatures of mild thermal treatment affect the performance of anaerobic digestion and sludge pretreated at pH 8.0 under mesophilic conditions could achieve high biogas yield and adequate dewaterability of digested sludge.

The aim of this study is to evaluate the influence of anaerobic digestion with pretreatment on the phytotoxicity of sewage sludge. The phytotoxicity was evaluated on sewage sludge (SS) and biosolids that came from conventional anaerobic digestion (CAD) and anaerobic digestion with a pretreatment by sequential ultrasound and low-thermal hydrolysis, called advance anaerobic digestion (AAD). To compare the phytotoxicity, eight elutriate concentrations (0.5–100% v/v) from SS, CAD, and AAD were studied on three testing plants: Lactuca sativa, Raphanus sativus, and Triticum aestivum. The percentages of seed germination inhibition, root elongation, and germination index (GI) were evaluated. GI is an phytotoxicity indicator that combines seed germination and root growth, therefore reflecting a more complete estimation of toxicity. Phytotoxicity assays showed that SS, CAD, and AAD elutriates have a beneficial effect on R. sativus. Similar results were observed for T. aestivum for CAD and AAD, with GI values up to 80% in both biosolids. Only for SS, moderate toxicity was observed in T. aestivum. Moreover, L. sativa showed GI values below 50% for SS and CAD, which reflected high toxicity. Only for AAD, no presence of phytotoxic substances was observed in L. sativa. This study concluded that biosolids from AAD improved the plants’ development with a GI above 78% with respect to biosolids from SS and CAD and reduced the phytotoxicity of sewage biosolid.