Reclaimed water driven lettuce cultivation in a hydroponic system: the need of micropollutant removal by advanced wastewater treatment

Occurrence and dissipation mechanisms of organic contaminants during sewage sludge anaerobic digestion: A critical review

Sewage sludge, a complex mixture of contaminants and pathogenic agents, necessitates treatment or stabilization like anaerobic digestion (AD) before safe disposal. AD-derived products (solid digestate and liquid fraction) can be used as fertilizers. During AD, biogas is also produced, and used for energy purposes. All these fractions can be contaminated with various compounds, whose amount depends on the feedstocks used in AD (and their mutual proportions). This paper reviews studies on the distribution of organic contaminants across AD fractions (solid digestate, liquid fraction, and biogas), delving into the mechanisms behind contaminant dissipation and proposing future research directions. AD proves to be a relatively effective method for removing polychlorinated biphenyls, polycyclic aromatic hydrocarbons, pharmaceuticals, antibiotic resistance genes and hydrocarbons. Contaminants are predominantly removed through biodegradation, but many compounds, especially hydrophobic (e.g. per- and polyfluoroalkyl substances), are also sorbed onto digestate particles. The process of sorption is suggested to reduce the bioavailability of contaminants. As a result of sorption, contaminants accumulate in the largest amount in the solid digestate, whereas in smaller amounts in the other AD products. Polar pharmaceuticals (e.g. metformin) are particularly leached, while volatile methylsiloxanes and polycyclic aromatic hydrocarbons, characterized by a high Henry's law constant, are volatilized into the biogas. The removal of compounds can be affected by AD operational parameters, the type of sludge, physicochemical properties of contaminants, and the sludge pretreatment used.

Nutrient recovery from wastewater for hydroponic systems: A comparative analysis of fertilizer demand, recovery products, and supply potential of WWTPs

Nutrient recovery from wastewater treatment plants (WWTPs) for hydroponic cultivation holds promise for closing the nutrient loop and meeting rising food demands. However, most studies focus on solid products for soil-based agriculture, thus raising questions about their suitability for hydroponics. In this study, we address these questions by performing the first in-depth assessment of the extent to which state-of-the-art nutrient recovery processes can generate useful products for hydroponic application. Our results indicate that less than 11.5% of the required nutrients for crops grown hydroponically can currently be recovered. Potassium nitrate (KNO3), calcium nitrate (Ca(NO3)2), and magnesium sulfate (MgSO4), constituting over 75% of the total nutrient demand for hydroponics, cannot be recovered in appropriate form due to their high solubility, hindering their separated recovery from wastewater. To overcome this challenge, we outline a novel nutrient recovery approach that emphasizes the generation of multi-nutrient concentrates specifically designed to meet the requirements of hydroponic cultivation. Based on a theoretical assessment of nutrient and contaminant flows in a typical municipal WWTP, utilizing a steady-state model, we estimated that this novel approach could potentially supply up to 56% of the nutrient requirements of hydroponic systems. Finally, we outline fundamental design requirements for nutrient recovery systems based on this new approach. Achieving these nutrient recovery potentials could be technically feasible through a combination of activated sludge processes for nitrification, membrane-based desalination processes, and selective removal of interfering NaCl. However, given the limited investigation into such treatment trains, further research is essential to explore viable system designs for effective nutrient recovery for hydroponics.

Biogas slurry purification-lettuce growth nexus: Nutrients absorption and pollutants removal

As a main by-product of anaerobic digestion in biogas plants, biogas slurry contains a high concentration of mineral elements (such as ammonia‑nitrogen and potassium) and chemical oxygen demand (COD). So determining how to dispose the biogas slurry in a harmless and value-added ways is crucial from the perspective of ecological and environmental protections. This study explored a novel nexus between biogas slurry and lettuce, in which the biogas slurry was concentrated and saturated with carbon dioxide (CO2) to serve as a hydroponic solution for lettuce growth. Meanwhile, the lettuce was used to purify the biogas slurry through removing pollutants. Results showed that when concentrating the biogas slurry, the total nitrogen and ammonia nitrogen contents in the biogas slurry decreased with the increase of concentration factor. The CO2-rich 5-time-concentrated biogas slurry (CR-5CBS) was screened as the most suitable hydroponic solution for lettuce growth after comprehensively considering the nutrient element balance, energy consumption of concentrating the biogas slurry and CO2 absorption performance. The quality of lettuce cultivated in CR-5CBS was comparable to that of the Hoagland-Arnon nutrient solution in terms of physiological toxicity, nutritional quality, and mineral uptake. Obviously, the hydroponic lettuce could effectively utilize the nutrients in CR-5CBS to purify CR-5CBS, meeting the standard of reclaimed water quality for agricultural reuse. Interestingly, when the same yield of lettuce is targeted, using CR-5CBS as the hydroponic solution to cultivate lettuce can save about US $151/m3-CR-5CBS for lettuce production compared to the Hoagland-Arnon nutrient solution. This study might provide a feasible method for high-value utilization and harmless disposal of biogas slurry.

The Importance of Humic Substances in Transporting "Chemicals of Emerging Concern" in Water and Sewage Environments

In this study, we examined the sorption of selected "chemicals of emerging concern" (CEC) on humic substances commonly found in water and municipal wastewater. These were ibuprofen, diclofenac, caffeine, carbamazepine, estrone, triclosan, bisphenol A, and isoproturon. The humic substances (HSs) were synthetic and not contaminated by the tested organic substances. The elemental composition and content of mineral micropollutants, gravimetric curves, and the IR spectrum of HSs were determined. We determined a relationship between the process efficiency and the characteristics of a sorbent and sorbate using the properties of organic substances sorbed on HSs. This relationship was confirmed by sorption tests on the HS complex, i.e., the HS-organic micropollutant. It has been shown that the given complexes have a greater affinity for hydrophobic surfaces than hydrophilic surfaces. To confirm the nature of the sorbent surfaces, we determined their zeta potential dependence on the pH of the solution. Studies have shown that HSs are carriers of both mineral substances and CEC in water and sewage environments.

[Health risks from crop irrigation with treated wastewater containing antibiotic residues, resistance genes, and resistant microorganisms]

This review describes the effects and potential health risks of resistant microorganisms, resistance genes, and residues of drugs and biocides that occur when re-using wastewater for crop irrigation. It focusses on specific aspects of these contaminants and their interactions, but does not provide a general risk assessment of the microbial load when using reclaimed water.Antimicrobial residues, antimicrobial resistant microorganisms, and resistance genes are frequently detected in treated wastewater. They have effects on the soil and plant-associated microbiota (total associated microorganisms) and can be taken up by plants. An interaction of residues with microorganisms is mainly expected before using the water for irrigation. However, it may also occur as a combined effect on the plant microbiome and all the abundant resistance genes (resistome). Special concerns are raised as plants are frequently consumed raw, that is, without processing that might reduce the bacterial load. Washing fruits and vegetables only has minor effects on the plant microbiome. On the other hand, cutting and other processes may support growth of microorganisms. Therefore, after such process steps, cooling of the foods is required.Further progress has to be made in the treatment of wastewater that will be used for crop irrigation with respect to removing micropollutants and microorganisms to minimize the risk of an increased exposure of consumers to transferable resistance genes and resistant bacteria.

Selective accumulation of pharmaceutical residues from 6 different soils by plants: a comparative study on onion, radish, and spinach

The accumulation of six pharmaceuticals of different therapeutic uses has been thoroughly investigated and compared between onion, spinach, and radish plants grown in six soil types. While neutral molecules (e.g., carbamazepine (CAR) and some of its metabolites) were efficiently accumulated and easily translocated to the plant leaves (onion > radish > spinach), the same for ionic (both anionic and cationic) molecules seems to be minor to moderate. The maximum accumulation of CAR crosses 38,000 (onion), 42,000 (radish), and 7000 (spinach) ng g-1 (dry weight) respectively, in which the most majority of them happened within the plant leaves. Among the metabolites, the accumulation of carbamazepine 10,11-epoxide (EPC - a primary CAR metabolite) was approximately 19,000 (onion), 7000 (radish), and 6000 (spinach) ng g-1 (dry weight) respectively. This trend was considerably similar even when all these pharmaceuticals applied together. The accumulation of most other molecules (e.g., citalopram, clindamycin, clindamycin sulfoxide, fexofenadine, irbesartan, and sulfamethoxazole) was restricted to plant roots, except for certain cases (e.g., clindamycin and clindamycin sulfoxide in onion leaves). Our results clearly demonstrated the potential role of this accumulation process on the entrance of pharmaceuticals/metabolites into the food chain, which eventually becomes a threat to associated living biota.

Soil degradation kinetics of oxybenzone (Benzophenone-3) and toxicopathological assessment in the earthworm, Eisenia fetida

A preponderance of recent evidence indicates that oxybenzone and other personal-care product chemicals threaten the biota inhabiting various ecological niches. What is understudied is the ecotoxicological impact of oxybenzone, a UV filter in sunscreens and anti-aging products, to terrestrial/soil organisms that are keystone species in these habitats. In the present study, acute exposure (14-day) to oxybenzone resulted in earthworm mortality (LC₅₀ of 364 mg/kg) and growth rate inhibition. Environmentally relevant concentration of oxybenzone (3.64, 7.28 and 36.4 mg/kg) at exposures of 7-day, 14-day, 28-day induced oxidative stress and neurotoxicity followed by perturbations in reproduction processes and changes in vital organs. Decreased levels of superoxide dismutase (SOD) and catalase (CAT) activity were statistically lower than controls (p < 0.05) on day 14 for all three concentrations, while glutathione-s-transferase (GST) activity was significantly elevated from controls on days 7 and 14. On day 28, SOD and CAT activities were either not significantly different from the control or were higher, demonstrating a temporal multiphasic response of anti-oxidant enzymes. GST activity on day 28 was significantly reduced compared to controls. Acetylcholinesterase levels across the three-time points exhibited a complicated behaviour, with every exposure concentration being significantly different from the control. Chronic exposure negatively influences earthworm health status with elevated biomarker values analysed using IBRv2 index. This, in turn, impacted higher levels of hierarchical organization, significantly impairing reproduction and organismal homeostasis at the histological level and manifesting as decreasing cocoon formation and successful hatching events. Thus, the overall findings demonstrate that oxybenzone is toxic to Eisenia fetida at low-level, long-term exposure. Based on the concentration verification analysis and application of the EPA PestDF tool, oxybenzone undergoes single first-order kinetics degradation in OECD soil with DT50 and DT90 as 8.7-28.9 days, respectively.