Incinerated Sewage Sludge Bottom Ash- Chemical processing, Leaching patterns and Toxicity testing

Perspectives on innovative non-fertilizer applications of sewage sludge for mitigating environmental and health hazards

As waste production increases and resources become limited, sewage sludge presents a valuable resource with potential beyond traditional land use and incineration. This review emphasizes exploring innovative non-fertilizer applications of sewage sludges and advocates for viewing wastewater treatment plants as sources of valuable feedstock and carbon sequestration. Innovative uses include integrating sewage sludge into construction materials such as asphalt pavements, geopolymer, cementitious composites, and masonry blocks. These methods not only immobilize heavy metals and mitigate environmental hazards but also support carbon sequestration, contrasting with incineration and land application methods that release carbon into the atmosphere. The review also addresses emerging technologies like bio-adhesives, bio-binders for asphalt, hydrogels, bioplastics, and corrosion inhibitors. It highlights the recovery of valuable materials from sewage sludge, including phosphorus, oils, metals, cellulose, and polyhydroxyalkanoates as well as enzyme production. By focusing on these non-fertilizer applications, this review presents a compelling case for re-envisioning wastewater treatment plants as sources of valuable feedstock and carbon sequestration, supporting global efforts to manage waste effectively and enhance sustainability.

Valorization of carbon soot ash for the selective capture of lead ions from industrial waste water-A waste to resource approach

Landfills are struggling to accommodate the increasing amounts of carbon soot ash waste from oil refineries. Due to extensive industrial productions, large quantities of lead ions are released into the environment, which not only pollutes the environment but also affects flora and fauna. In this work, these urgent environmental issues will be tackled by studying the use of modified carbon soot ash for specific heavy metal adsorption. Carbon soot ash modified with chemical leaching and physical ball-milling was loaded onto the surface of graphene oxide. This adsorbent was found to selectively adsorb and remove toxic lead ions (>99%) from a mixed heavy metal solution. The adsorption efficiency was found to increase with temperature (20-60 °C) and pH (2-8). Langmuir isotherm and pseudo-second order kinetics were found to fit the adsorption process through curve fitting, where the adsorbent reached a maximum capacity of 194.55 mg/g. Potential mechanisms for lead adsorption and metal specificity are also discussed here. This work aligns with the waste-to-resource pathway, where waste carbon soot ash is diverted from landfilling and is formulated as a specific heavy metal adsorbent, that shows promise for environmental remediation.

Understanding the biological impact of organic pollutants absorbed by nanoplastics

Many organisms are consuming food contaminated with micro- and nanoparticles of plastics, some of which absorb persistent organic pollutants (POPs) from the environment and acting as carrier vectors for increasing the bioavailability in living organisms. We recently reported that polymethylmethacrylate (PMMA) nanoparticles at low concentrations are not toxic to animal models tested. In this study, the toxicity of diphenylamine (DPA) incorporated PMMA nanoparticles are assessed using barnacle larvae as a model organism. The absorption capacity of DPA from water for commercially available virgin PMMA microparticles is relatively low (0.14 wt%) during a 48 h period, which did not induce exposure toxicity to barnacle nauplii. Thus, PMMA nanoparticles encapsulated with high concentrations of DPA (DPA-enc-PMMA) were prepared through a reported precipitation method to achieve 40% loading of DPA inside the particles. Toxicity of DPA-enc-PMMA nanoparticles were tested using freshly spawned acorn barnacle nauplii. The observed mortality of nauplii from DPA-enc-PMMA exposure was compared to the values obtained from pure DPA exposure in water. The mortality among the exposed acorn barnacle nauplii did not exceed 50% even at a high concentration of DPA inside the PMMA nanoparticles. The results suggest that the slow release of pollutants from polymer nanoparticles may not induce significant toxicity to the organism living in a dynamic environment. The impact of long-term exposure of DPA absorbed plastic nanoparticles need to be investigated in the future.

Towards understanding respiratory particle transport and deposition in the human respiratory system: Effects of physiological conditions and particle properties

Fly ash is a common solid residue of incineration plants and poses a great environmental concern because of its toxicity upon inhalation exposure. The inhalation health impacts of fly ash is closely related to its transport and deposition in the human respiratory system which warrants significant research for health guideline setting and inhalation exposure protection. In this study, a series of fly ash transport and deposition experiments have been carried out in a bifurcation airway model by optical aerosol sampling analysis. Three types of fly ash samples of different morphologies were tested and their respiratory deposition and transport processes were compared. The deposition efficiencies were calculated and relevant transport dynamics mechanisms were discussed. The influences of physiological conditions such as breathing rate, duration, and fly ash physical properties (size, morphology, and specific surface area) were investigated. The deposition characteristics of respiratory particles containing SARS-CoV-2 has also been analyzed, which could further provide some guidance on COVID-19 prevention. The results could potentially serve as a basis for setting health guidelines and recommending personal respiratory protective equipment for fly ash handlers and people who are in the high exposure risk environment for COVID-19 transmission.

Sewage sludge ash-based mortar as construction material: Mechanical studies, macrofouling, and marine toxicity

Incinerated sewage sludge ash is tested here as a cement and aggregate substitute in mortar blocks. It can be used at various percentages to reduce the overall cost of production and promote ash recycling. The compressive strength of the cast blocks was tested at 28 days to determine the optimal combination of ball milled ash (replacing cement) and sewage sludge ash (replacing sand). This was compared with a control block made of cement and sand only. The cast blocks with the optimal ash formulation were tested for their flexural strength and other properties such as surface functional groups, constituent phases and porosity. The control and ash mortars exhibited similar properties. A potential application of these blocks is to use them as part of seawalls. These blocks were thus suspended in the sea for 6 months. Marine organism attachment was observed over time in both control and ash mortar blocks. There was no significant difference between the mortars after 6 months. The mortar blocks were also subjected to leaching tests (NEN-7345). The leachates did not exhibit toxicity to microalgae. In contrast, mild toxicity was observed in the sea urchin embryo development assay. Overall, the study suggests that sewage sludge ash is a potential material to be used for seawall construction as it has the desirable mechanical properties. However, there remain some residual marine toxicity concerns that need to be further addressed.

An innovative accelerated carbonation process for treatment of incineration bottom ash and biogas upgrading

Incineration is the main technology used for the management of municipal solid waste, in parallel to various recycling programs. However, incineration should not be considered as the final step for waste management as the ash still needs to be treated and disposed properly. In this work, an innovative accelerated carbonation of incineration bottom ash (IBA) using simulated biogas composition from anaerobic digestion processes (a mixture of CH₄ and CO₂) has been applied to lower the leaching of heavy metals from the carbonated IBA and its associated toxicity. Various temperatures and reaction times were explored for carbonation optimization and it was found that the carbonation at 25 °C for 8 h was the optimal reaction condition by taking into account the degree of carbonation and time constraint. The mineral content, functional groups, thermal stability, leaching patterns and ecotoxicity of both raw IBA and carbonated IBA were tested. It was found that carbonated IBA leached out less heavy metals than the raw IBA due to the locking of heavy metals in the calcite matrix. Cost-benefit analysis was also conducted on the industrial-scale process with a capacity of processing 10 tons of IBA per day. The results indicated that the proposed process had great economic potential.

The cadmium decontamination and disposal of the harvested cadmium accumulator Amaranthus hypochondriacus L

The heavy metal accumulated biomass after phytoremediation needs to be decontaminated before disposal. Liquid extraction is commonly used to remove and recycle toxic heavy metals from contaminated biomass. In this study, we examined the cadmium (Cd) removal efficiency using different chemical reagents (hydrochloric acid, nitric acid, sulfuric acid, and ethylenediaminetetraacetic acid disodium) of the post-harvest Amaranthus hypochondriacus L. biomass. The purifications for the extracted liquids and ecological risk assessments for the extracted residues were also investigated. We have found that 77.8% of Cd in stems and 62.1% of Cd in leaves were removed by 0.25 M HCl after 24 h. In addition, K₂CO₃, KOH, and 4 Å molecular sieve could remove ≥89.0% of Cd in the extracted liquids. Finally, after we returned the extracted residues to the earthworm-incubated soil, the extracted biomass negatively affected the growth (weight loss ≥ 11.0%) and survival (mortality ≥ 33.3%) of Eisenia fetida. It should be noted that earthworms decreased soil available Cd concentrations from 0.14-0.05 mg kg^-1 to 0.11-0.04 mg kg^-1 and offset the negative effects of the Cd-contaminated biomass on soil microbes. Overall, given the cost of reagents, the Cd removal efficiency, and the ecological risks of the extracted biomass, using 0.25 M HCl for liquid extraction and K₂CO₃ for purification should be recommended. This work highlights the potential of liquid extraction for immediately and directly removing the Cd from fresh contaminated accumulator biomass and the resource cycling potential of the extracted liquids and biomass after purification.

Toxicity effects of size fractions of incinerated sewage sludge bottom ash on human cell lines

Sewage sludge bottom ash (SSBA) from the incineration plant used for the production of construction materials possibly possess heavy metals which might cause a negative impact on human health. Considering biosafety, we investigated the toxicity effects of 0.5-2 mm (aggregate substitute) and < 0.075 mm (cement substitute) in its solid and leachate form on human lung fibroblast cells (MRC-5) and human skin epidermal cells (HaCaT) on exposure through contact. MTS assay revealed the cellular responses of lung and skin cell lines to the leachates showing that the skin cells, which often interact with the external environment displayed better tolerance than the lung cells, whereas solid ash showed a concentration and size-dependent toxicity. Solid ash was found to downregulate the intracellular glutathione/superoxide dismutase activities and upregulate lactate dehydrogenase/lipid peroxidation activities thus inducing oxidative stress to the cell and subsequently resulting in the cell membrane leakage, destructive mitochondrial membrane potential (Δψm), apoptosis, and DNA damage, which is nearly 7-fold higher than the negative control. At a high concentration, DNA damage index of 1.09 and 1.29 was observed for the 0.5-2 mm sized ash leachate on skin cells and lung cells respectively, whereas for ash (<0.075 mm size) leachate, this fraction was 1.29 and 2.96, respectively. Overall, the ash leachate is found to be safer/biocompatible if they come in contact with humans as compared to SSBA in its solid form.

Extraction and Purification of Phosphorus from the Ashes of Incinerated Biological Sewage Sludge

Phosphorus depletion represents a significant problem. Ash of incinerated biological sewage sludge (BSS) contains P, but the presence of heavy metals (e.g., Fe and Al) is the main issue. Based on chemical characterization by SEM-EDS, ED-XRF and ICP-OES techniques, the characteristics and P content of bottom ash (BA) and fly ash (FA) of incinerated BSS were very similar. On BA, P extraction carried out in counter- current with an S:L ratio of 1:10 and H2SO4 0.5 M led to better extraction yields than those of a similar test with H2SO4 1 M and an S:L ratio of 1:5 (93% vs. 86%). Comparing yields with H2SO4 0.5 M (S:L ratio of 1:10), the counter-current method gave better results than those of the crossflow method (93% vs. 83.9%), also improving the performance obtained with HCl in crossflow (93% vs. 89.3%). The results suggest that the purification of the acid extract from heavy metals with pH variation was impractical due to metal precipitation as phosphates. Extraction with H2SO4 and subsequent treatment with isoamyl alcohol represented the best option to extract and purify P, leading to 81% extraction yields of P with low amounts of metals.