Sewage Sludge Compost Research Articles

Substitution of mineral N fertilizers with organic wastes in two long‐term field experiments: Dynamics and drivers of crop yields

AbstractOrganic wastes (OW) are rich in nutrients, and their recycling into agriculture can substitute chemical fertilizers. The level of substitution (partial with mineral fertilizer or exclusive with only OW), along with the method, amount, and timing of OW application, as well as the crop type, can impact crop productivity. The temporal dynamics of crop productivity after repeated applications of OW remain uncertain. Thus, two French long‐term field experiments (QualiAgro and PROspective, started in 1998 and 2000, respectively) were used to evaluate the effect of repeated OW applications on crop yield dynamics and investigate the potential driving factors affecting crop yields. Six different OW were applied: urban sewage sludge (SLU), green waste and SLU compost (GWS), biowaste compost (BIO), municipal solid waste compost (MSW), farmyard manure (FYM), and composted FYM (FYMC). The OW were applied every 2 years in QualiAgro (~4 t C ha−1) and PROspective (~1.7 t C ha−1). QualiAgro was studied under high and low mineral N conditions, while PROspective was examined with and without mineral N fertilization. The results indicated that at the QualiAgro site, a combination of OW and high mineral N treatments resulted in higher maize and wheat yields compared to the mineral N control, while the combination of OW and low mineral N reached the same maize and wheat yield as the mineral N control after 3 and 6 applications of OW, respectively. At the PROspective site, partially substituting mineral fertilizer with OW maintained maize yields but decreased wheat yields, while full substitution led to a decrease in both maize and wheat yields compared to the mineral N control. Results from the gradient boosting model (GBM) showed that soil total N rather than mineral N input was the primary driver of the relative maize yield, while mineral N fertilizer input was more critical for wheat during the second year. We conclude that the joined use of OW and mineral fertilizers is superior to using OW or mineral fertilizer alone for maintaining high yields and soil fertility. We further suggest that OW full substitution of mineral fertilizer may need to apply OW more frequently to meet the crop demands, and/or to use OW with higher N availability like digestates.

Use of Corn Steep Liquor as a Biostimulant in Agriculture

Biostimulants are substances or microorganisms that are applied to plants, soil, or seeds, to improve the growth, development, performance, and quality of crops. Their application is mainly directed towards improving the resistance of crops against abiotic and biotic stresses. These compounds are formulated from a great variety of compounds: humic substances, complex organic materials (sewage sludge extracts, composts, and manure), chemical elements (Al, Co, Na, Se, and Si), inorganic salts including phosphite, seaweed extracts (brown, red, and green), amino acids, etc. As of today, it has been observed that corn steep liquor (CSL), which is obtained from the industrial process of corn transformation, may be a good ingredient for the formulation of biostimulant products. CSL contains a large amount of different chemical compounds with biological activity for the plants and soil. The use of CSL industrial waste, previously formulated, could have a direct or indirect effect on the physiological processes and metabolic routes of plants related to the adaptation to abiotic and biotic stresses, as their compounds are part of these metabolic pathways, act as elicitor compounds, and/or have their own biological activity in the plants. There is evidence that the application of CSL could protect plants from specific abiotic and biotic stresses, such as an excess of light or temperature, nutritional limitations, salinity, drought, or pathogens. In addition, it can improve the growth of the plant when these are grown in hydroponic systems, and can improve the health of soils. The present article is focused on describing the most relevant scientific aspects of CSL when used as an ingredient to formulate biostimulants for agriculture. It will discuss its chemical composition, the analytical techniques utilized to elucidate and quantify its compounds, its uses in agriculture, and mode of action in the plants.

Composted Sewage Sludge as a Substrate for Commercial Seedlings of Peltophorum dubium (Spreng.) Taub.

Sewage sludge in natura is rich in nutrients, water, and organic matter and is essential for plant development. However, sewage sludge is diluted with water when composted, which could hamper plant growth. Therefore, supplementation with chemical fertilization may be necessary. This study evaluated the performance of composted sewage sludge (CSS) in producing Peltophorum dubium (Spreng.) Taub. seedlings with and without chemical fertilization via fertigation. The experiment was completely randomized in a 3 × 4 factorial scheme, with four fertigation (Ca(NO3)2(H2O)x: 0.87; (NH4)(H2PO4): 0.21; KCl: 0.47; (NH4)2SO4: 0.11; CH₄N₂O: 0.54; MgSO4: 0.52; Fe (13%): 0.03; B(OH)3: 6.00; CuSO4: 0.60; ZnSO4: 1.40; MnSO4: 6.00; Na2MoO4: 0.16 g L−1) doses: zero, standard, duplicate, and quadruplicate. In addition, three substrates were used: commercial substrate as the control, sewage sludge composted with sugarcane bagasse (LBC), and sewage sludge composted with Eucalyptus bark (LCE). The development of the seedlings was measured through the following variables: height, stem diameter, shoot/root ratio, leaf dry mass, root dry mass, total dry mass, green color index, the Dickson Quality Index, and the accumulation of nutrients in plant tissue. The seedlings produced with LCE that were subjected to the standard dose (1×) and the quadruplicate dose (4×) had the statistically highest mean values for most variables. Nevertheless, supplementation with chemical fertilization was necessary. Composted sewage sludge with eucalyptus bark, at the standard dosage, can be used for the commercial production of P. dubium seedlings, thus preventing the dangerous disposal of waste and strongly decreasing associated environmental hazards.

Waste from sewage treatment plants used in soybean cultivation: its influence on crop development

The aim of the present study is to assess the effect of using composted sewage sludge (CSS) and wastewater from a sewage treatment plant (WW) on soybean plants’ development. Treatments were assessed through completely randomized design experiments carried out at split-plot arrangements based on nitrogen fertilization levels and types and on irrigation water nature – potable (WP) and wastewater (WW). Seven nitrogen fertilization levels were distributed into two plots represented by irrigation with WP and WW, namely: T0 = without nitrogen fertilization; T1 = 100% chemical nitrogen fertilization; T2 = 50% chemical nitrogen fertilization + 50% nitrogen fertilization via CSS; T3, T4, T5 and T6 corresponded to 100%, 150%, 200% and 250% CSS nitrogen fertilization, respectively. Conventional nitrogen fertilization replacement by CSS did not significantly change the behavior of the assessed variables: plant height and mass of 100 grains. This finding points towards the possibility of saving inputs by replacing chemical fertilization by organic fertilization. Irrigation with wastewater led to 37% increase in dry matter mass and 21% in mass of 100 grains.

Biological remediation treatments improve the health of a mixed contaminated soil before significantly reducing contaminant levels.

The remediation of mixed contaminated soil is challenging as it often requires actions to minimize metal-induced risks while degrading organic contaminants. Here, the effectiveness of different bioremediation strategies, namely, rhizoremediation with native plant species, mycoremediation with Pleurotus ostreatus spent mushroom substrate, and biostimulation with organic by-products (i.e., composted sewage sludge and spent mushroom substrate), for the recovery of a mixed contaminated soil from an abandoned gravel pit was studied. The combination of biostimulation and rhizoremediation led to the most significant increase in soil health, according to microbial indicator values. The application of composted sewage sludge led to the highest reduction in anthracene and polychlorinated biphenyls concentrations. None of the strategies managed to decrease contamination levels below regulatory limits, but they did enhance soil health. It was concluded that the biological remediation treatments improved soil functioning in a short time, before the concentration of soil contaminants was significantly reduced.

Assessing feasibility of sewage sludge composting in rotary drum reactor

In a year-long study, the efficacy of a manually operated rotary drum prototype, jointly developed by CEIT Spain and IIM Mumbai, was examined for sanitized compost production in Indian conditions. The prototype, a 200-liter horizontal plastic drum made of high-density polyethylene, incorporated a perforated polypropylene pipe for passive aeration of the composting mixture. Focused on optimizing composting of sewage sludge from a Municipal MBBR, the research targeted key process variables in the rotary drum reactor to attain the thermophilic phase. Wood shavings emerged as the optimal bulking agent, with a mixing ratio of three parts dewatered sewage sludge to one-part bulking agent. A turning frequency of every 12 h proved optimal for achieving the desired temperature of around 60 °C. The study concluded that the final sludge quality met prescribed standards, showcasing the viability of the rotary drum system for efficient compost production in Indian settings.

Growing of Phalaroides arundinacea L. and Bromopsis inermis Leyss for Biofuel Using Sewage Sludge Compost as a Fertilizer

Bromopsis inermis and Phalaroides arundinacea are increasingly grown not only for feed but also for other purposes, such as obtaining energy. Composting sewage sludge and using such compost to fertilize various plants is also becoming more popular. Therefore, the aim of our study was to investigate how the fertilization of the mentioned plants with sewage sludge compost (SSC) affects the biomass yield and biomass quality of these plants. It was also important to determine whether fertilization with SSC is possible in low-yielding soils of light texture without harming these soils There are no similar studies in Lithuania, and there are very few in Europe and the world. It was found that investigated grasses formed a small biomass DM yield (6.6 t/ha within three years). The biomass of B. inermis and Ph. arundinacea had a very high ash content and concentrations of nitrogen and potassium. This greatly reduced the quality of the biomass of these grasses as a solid biofuel. SSC performed poorly as a fertilizer. Fertilization with 125 t/ha SSC significantly increased the total biomass yield of Ph. arundinacea only. At the same time, using SSC as a fertilizer significantly increased the concentration of Cu, Zn, and Cd in the soil.

The inoculation of thermophilic heterotrophic nitrifiers improved the efficiency and reduced ammonia emission during sewage sludge composting

In this study, three thermophilic heterotrophic nitrifiers were isolated and inoculated into the semi-permeable membrane-covered composting of sewage sludge as thermophilic microbial (TM) agent. The physicochemical properties and microbial communities as well as the metabolism of microorganisms during composting were analyzed. Compared to CK, the inoculation of TM agent prolonged the thermophilic stage from 4 days to 7 days, increased the degradation of organic matters by 14.06 %, and promoted humification of compost. Meanwhile, TM agent reduced the NH3 emission by 34.64 % while the NO3−-N content was 2.72 folds that of CK, resulting lower nitrogen loss. Additionally, an obvious succession of microbial communities occurred and the inoculation of TM agent enriched organic matters-degrading microorganisms (Bacillus, Thermobispora, Planifilum and Tepidimicrobium) and decreased the abundance of pathogens (Aspergillus and Cephalotrichum). Besides, many microorganisms related to nitrogen transformation were detected during the composting. The analysis of functional genes revealed that the nitrification was facilitated while denitrification process might be inhibited, establishing an efficient nitrogen retention system. This research provided an effective agent for sludge composting and indicated that the inoculation of thermophilic nitrifiers was a promising strategy to improve composting efficiency and reduce nitrogen loss.

Physico-Chemical Properties and Phosphorus Solubilization of Organomineral Fertilizers Derived from Sewage Sludge

Sewage sludge (SS) is an organic waste that may potentially be used as a slow-release source of phosphorus (P), despite the necessity for pre-treatment and its lower P content compared to soluble mineral fertilizers. For these reasons, composted sewage sludge was used to manufacture pelletized organomineral fertilizers, by mixing it with the inorganic sources monoammonium phosphate (MAP) and AshDec® (ASD) (thermochemically incinerated SS). The fertilizers were physiochemically characterized and evaluated for their P solubilization dynamics and lability in the soil. The sources tested were as follows: organic compost of sewage sludge powder (SSC) and its pelletized form (SCP), pelletized organomineral SSC + MAP (S + MAP) and SSC + ASD (S + ASD), ASD alone, compared conventional MAP and a control (nil-P). These fertilizers were applied to columns containing 50 g of soil at the dose of 100 mg P column−1 and were leached daily with 30 mL of water or 2% citric acid for 30 days. We analyzed the leachates for pH and P content. Pelletizing process resulted in denser products and promoted more gradual P release. The organomineral S + MAP was the most water-soluble recycled source, solubilizing about 70% of the total P, while the others presented much lower solubilization (<20%). In contrast, all fertilizers showed high solubility in 2% citric acid (except for S + ASD). After leaching, soil P fractionation disclosed that the P leftover in the soil remained mostly in the labile and moderately labile pools. Composting and the ASD process produced materials with slow P solubilization, being favored in acidic soils and in plant’s rhizosphere. In turn, S + MAP resulted in a promising product with intermediate P solubility, better synchronized with crop demand, potentially increasing P-use efficiency. Our results shed light in the physico-chemical properties and on the solubilization dynamics of novel organomineral products in tropical soil conditions.

Residual effects of composted sewage sludge on nitrogen cycling and plant metabolism in a no-till common bean-palisade grass-soybean rotation.

In the context of increasing population and decreasing soil fertility, food security is one of humanity's greatest challenges. Large amounts of waste, such as sewage sludge, are produced annually, with their final disposal causing environmental pollution and hazards to human health. Sludge has high amounts of nitrogen (N), and, when safely recycled by applying it into the soil as composted sewage sludge (CSS), its residual effect may provide gradual N release to crops. A field study was conducted in the Brazilian Cerrado. The aims were to investigate the residual effect of successive applications of CSS as a source of N in the common bean (Phaseolus vulgaris L. cv. BRS Estilo)-palisade grass (Urochloa brizantha (A.Rich.) R.D. Webster)-soybean (Glycine max L.) rotation under no-tillage. Additionally, N cycling was monitored through changes in N metabolism; the efficiency of biological N2 fixation (BNF) and its implications for plant nutrition, development, and productivity, was also assessed. The experiment consisted of a randomized complete block design comparing four CSS rates (10, 15, 20, and 25 Mg ha-1, wet basis) to a control treatment (without adding mineral or organic fertilizer) over two crop years. Multiple plant and soil analyses (plant development and crop yield, Falker chlorophyll index (FCI), enzymatic, biochemical, 15N natural abundance, was evaluated, root and shoot N accumulation, etc.) were evaluated. Results showed that CSS: i) maintained adequate N levels for all crops, increasing their productivity; ii) promoted efficient BNF, due to the stability of ureide metabolism in plants and increased protein content; iii) increased the nitrate content and the nitrate reductase activity in soybean; iv) affected urease activity and ammonium content due to changes in the plant's urea metabolism; v) increased N accumulation in the aerial part of palisade grass. Composted sewage sludge can be used as an alternative source to meet crops' N requirements, promoting productivity gains and N cycling through forage and improving N metabolism.

Contamination of water, soil, and plants by micropollutants from reclaimed wastewater and sludge from a wastewater treatment plant

Several studies have shown that plants can absorb various micropollutants. The behavior of micropollutants from wastewater treatment plant resources was comprehensively investigated in raised beds in which either a mixture of vegetables or maize was grown. The beds were either irrigated with treated wastewater or enriched with sewage sludge or composted sewage sludge. Over the year, samples of wastewater, water drained from the beds, soils and plants were analyzed. Of the seventy-five analyzed substances, fifty-four, thirty-three and twenty-seven were quantified in wastewater, sewage sludge, and composted sludge, respectively. Alarmingly, approximately 20 % of the compounds from wastewater were also detected in the solutions leached from the beds irrigated with wastewater (e.g., gabapentin, tramadol, sertraline, carbamazepine, its metabolites, and benzotriazoles). In addition, a gradual increase in the content of four substances (telmisartan, venlafaxine, carbamazepine, citalopram) was recorded in these beds. The compounds from both biosolids used for soil enrichment tended to remain in the soils (e.g., telmisartan, venlafaxine, sertraline, its metabolite, citalopram, and its metabolite). Only four compounds (sertraline and three benzotriazoles) leached from these beds. Uptake of some chemicals (e.g., gabapentin, tramadol, carbamazepine and its metabolite, and venlafaxine and its metabolite) and their accumulation in plant tissues was observed mainly in vegetables grown on beds irrigated with wastewater. However, daily consumption values for edible plant parts and individual compounds did not indicate a direct threat to human health. Results of this innovative study show possible risks associated with the use of these resources in agriculture. Of particular concern is the possible micropollutants percolation towards groundwater, including those for which high sorption and thus low mobility in the soil environment is expected, such as sertraline. Soil and crop contamination cannot be neglected either.

Compost promotes biocrust and plant growth in greenhouse cocultures for dryland restoration

Biocrusts and plants are the main ground cover and provide multiple ecosystem functions in arid and semiarid areas. As land degradation worsens and waste management is ever more pressing, the use of composted waste appears as a sustainable restoration practice to enhance vegetation reestablishment, but its effects on biocrusts still remain largely understudied. Moreover, developing appropriate methods for the co‐introduction of plants and biocrusts can be an emerging approach to reconstruct the biocrust/plant interaction and their associated functions. We evaluated the effect of different compost types on biocrust and plant cocultivations. We performed a greenhouse mesocosm experiment using urban organic solid waste and sewage sludge composts to grow a moss‐dominated biocrust and seedlings of two pioneer shrubs (Senecio filaginoides and Acaena splendens) in the Patagonian steppe. Both compost types successfully enhanced biocrust cover and chlorophyll a development, with cultured biocrusts being compositionally similar to the natural inoculum. Only the addition of composted sewage sludge enhanced seedling growth, and biocrusts had significant but opposite effects (positive/negative) on the two plant species we used for experimentation. This difference in the biocrust/plant interaction outcome was likely mediated by the significant influence of biocrusts on the relative availability of ammonium and nitrate and possible plant species‐specific preferences for different inorganic nitrogen forms. We conclude that the application of sewage sludge compost effectively improves the success of biocrust and plant cocultures, but species‐specific differences in the performance of seedlings growing in biocrusted soils impose limits on attempts to promote biocrust and plant joint restoration.

Insights into effects of thermotolerant nitrifying and sulfur-oxidizing inoculants on nitrogen-sulfur co-metabolism in sewage sludge composting

In this study, high temperature thermotolerant nitrifying bacteria (TNB) and high temperature thermotolerant sulfide oxidizing bacteria (TSOB) were obtained from compost samples and inoculated into sewage sludge (SS) compost. The effects of inoculation on physical and chemical parameters, ammonia and hydrogen sulfide release, nitrogen form and sulfur compound content change and physical-chemical properties during nitrogen and sulfur conversion were studied. The results showed that inoculation of TNB and TSOB increased the temperature, pH, OM degradation, C/N ratio and germination index (GI) of compost. Compared with the control treatment (CK), the addition of inoculants reduced the release of NH3 and H2S, and transformed them into nitrogen and sulfur compounds, the hydrolysis of polymeric ferrous sulfate was promoted, resulting in relatively high content of sulfite and sulfate. At the same time, the physical and chemical properties of SS have a strong correlation with nitrogen and sulfur compounds.

Brown Coal Waste in Agriculture and Environmental Protection: A Review

Modern agricultural technologies have contributed to a significant reduction in the amount of soil organic matter. Brown coal waste (BCW), with low energy content, can be used to neutralize this process, contributing to the recuperation of soil fertility and to environmental protection. More studies need to be conducted on organomineral fertilizers based on BCW and applied to soils with low humus content. Apart from increasing soil production capacity in arable fields, BCW could be used for the reclamation of industrially contaminated areas and degraded soils, in the vicinity of motorways and in soilless agriculture. It can also be used as a sorbent of gases emitted from slurry during its storage such as NH3, H2S, mercaptans, volatile fulvic acids (FAs); as a component of sewage sludge compost; as a natural additive to calf feed; and for the production of adsorbents for sewage and wastewater treatment.

Microplastic Pollution in EU Farmland Soils: Preliminary Findings from Agricultural Soils (Southwestern Poland)

Agricultural soils are considered as “hot-spots” of plastic particles; however, due to a lack of standardized method of microplastic determination in soils, as well as no legal regulations requiring the monitoring of the soil environment in the context of microplastic contamination, the data on MP abundance and occurrence in European soils are very limited. In this first study of MPs pollution in agricultural soils in Poland, we developed a method of microplastic extraction from soil samples with different properties (particle size distribution, clay and organic matter content) and used optical microscopy for MP determination and quantification. In this study, we analyzed 44 soil samples from five sampling site locations with differing soil type, agricultural activity, including farmland soils on floodplains and past records of sewage sludge and compost applications. We found evidence that 93% of cultivated soils in the SW part of Poland contained MPs. The content of MP varied between soil types and present/former use of the land. Loamy and clay soils contained more MPs, 1540 ± 912 particles per kg soil and 933 ± 682 particles per kg, respectively, compared with sandy soils at 383 ± 188 particles per kg of soil. The highest MP concentrations were determined in soils amended with sewage sludge, wastewaters and green-waste composts (up to 4050 ± 2831 particles per kg of soil). The wide distribution of MPs with a dominance of plastic fibers (up to 60% of determined MP types) can be associated with agricultural sources such as soil mulching, the use of organic fertilizers, seed coating or unintentional waste dumping and air deposition.

Industrial-Scale Composting of Rice Straw and Sewage Sludge

Composting is an interesting option to recycle big quantities of organic waste because it helps to mitigate different environmental problems. Complementary characteristics of rice straw (RS) and sewage sludge (SS) create a suitable mixture to be used in a composting process. This work studies industrial-scale RS and SS composting to assess both its viability and optimization. Windrow composting was conducted during two seasons. The complete characterisation (moisture, pH, electrical conductivity, total, oxidisable and water-soluble organic carbon, humic substances, organic and mineral nitrogen, macronutrients, micronutrients, heavy metals) of starting materials, samples taken periodically and final composts were carried out. During the first season, an RS:SS ratio of 1:8 (w:w fresh weight) was used, which led to a process with adequate temperatures for biodegradation, but not for ensuring materials’ sanitation. During the second season, the RS:SS ratio was increased (1:6) to enhance the energy process and, thus, temperatures. Although this increase took place, degradation slowed down as oxidisable organic carbon and water-soluble organic carbon indicated. During both seasons, final composts presented adequate pH, high N-richness, and interesting macro- and micronutrient values. Notwithstanding, they also presented certain salinity and high ammonium contents, which must be considered for their field application. The obtained composts have interesting agronomic characteristics, which suggest their potential as an alternative to conventional fertilisers.

Unlocking fertilization potential of anaerobically digested sewage sludge centrate for protein-rich rice cultivation with composted sludge amendment

The use of composted sewage sludge (CSS) and centrate as alternatives to synthetic fertilizers in rice cultivation holds great promise. This study aims to determine the effects of varying doses and timings of centrate derived from anaerobically digested sewage sludge on rice yield, nutrient quality, and soil fertility when applied as a topdressing to rice fields fertilized with CSS. At the panicle initiation (PI) stage, 100, 300, and 500 kg N ha−1 of centrate topdressing (CT100, CT300, and CT500, respectively) was applied. In addition, different topdressing timings at a total dose of 500 kg N ha−1 were evaluated, including a two-split application (40% at active tillering (AT) and 60% at PI; CT500S2) and a three-split application (40% at AT + 40% at PI + 20% at heading; CT500S3). At a rate of 160 kg N ha−1, CSS was used as a base fertilizer in all treatments. A control treatment received synthetic fertilizers at a rate of 160 kg N ha−1 as a base application and 100 kg N ha−1 as a topdressing. Results showed that CSS-treated rice plants exhibited a lower N status and leaf chlorophyll content during the vegetative growth stage; however, the split application of centrate topdressing improved plant N status, resulting in an increase in biomass and grain yield. Centrate and CSS tended to increase the mineral content of rice; nevertheless, a significant accumulation of As in grains raised concerns about food safety. Combining CSS and centrate has the potential to increase rice production, improve grain nutritional value, and decrease reliance on synthetic fertilizers. However, it is essential to optimize this fertilization, mitigate environmental risks, and ensure food safety by employing appropriate fertilization dosing and timing as well as appropriate field management strategies.

Behavior and Biochemical Mechanism of High Iron Attapulgite Dosages Affecting Sewage Sludge Composting

We first revealed the behavior and biochemical mechanism of high iron attapulgite (HIAP) and different dosages affecting sewage sludge (SS) composting. HS/TOC ratio increased, but HA/TOC and HA/FA ratios reduced with the increase in HIAP dose. High-dose HIAP promoted the formation of more HS by weak catalytic effect but could bind more FA than HA by strong adsorption effect to inhibit the polymerization of the adsorbed FA into HA. Mixing SS with HIAP and subsequent composting as two consecutive processes during HIAP-amended composting significantly influenced the species distribution of heavy metals (HMs) Cu, Zn, and Cr. Each process roughly contributed one-half to HMs passivation. The bioavailable fraction (BF) of HMs reduced with the increase of HIAP dose. HIAP dose greatly affected the microbial community. Both 1% and 5% HIAP treatments promoted Proteobacteria and Firmicutes, but 10% HIAP promoted Actinobacteriota and Bacteroidota. At the thermophilic phase, HIAP dose greatly affected core thermophilic microbial genera, which were significantly correlated to pile temperature and pH value. In the maturity stage, core microbial genera in different treatments were basically similar and closely correlated to the bioavailable fraction (BF) of HMs and HA, and the influence order was BF–Cr > BF–Cu > BF–Zn > HA. The optimal 5% HIAP dose was recommended.

Effects of CuO nanoparticles in composted sewage sludge on rice-soil systems and their potential human health risks

The release of metal-based nanoparticles (MNPs) into sewage systems is worrisome due to their potential impact on crop-soil systems that are amended with sewage sludge. This study aimed to investigate the effects of copper oxide nanoparticles (CuO NPs) in composted sewage sludge (CSS) on rice-soil systems and to assess the health risks associated with consuming CuO NP-contaminated rice produced by CSS amendment. CSS was treated with three doses of CuO NPs, resulting in Cu levels below the sludge limits (1500 mg Cu kg−1) for reuse as a soil amendment. Results showed that CuO NPs in CSS at environmentally acceptable levels had no negative effect on rice growth and yield. In fact, they enhanced biomass production, tillering capacity, and soil fertility by increasing N and K levels in the soil. In addition, CuO NPs in CSS (450–1450 mg Cu kg−1) promoted the accumulation of macro- and micro-minerals in rice grains, thereby improving the nutritional value of rice. However, Cu contamination in CSS led to elevated levels of toxic metals, especially As, in rice grains, posing potential health risks to both adults and children. In the presence of higher CuO NPs contamination in CSS, the hazard quotient of As exceeded one, indicating an increased risks of toxic metal exposure via rice consumption. This study raises concerns about potential long-term threats to human health posed by MNPs contamination in CSS and highlights the need to reevaluate the permissible limits of hazardous elements in sludge to ensure its safe reuse in agriculture.

Investigation of heavy metal and micro-macro element speciation in biomass ash enriched sewage sludge compost

The objective of this study was to enrich the nutrient content of compost and to investigate the passivation and solubilization of plant micronutrients (Fe, Al, Cu, Ni, Zn, Na, Mn), macroelements (P, K, Mg, Ca), and heavy metals (Cr, Cd, Pb) during sewage sludge composting with nutrient-rich biomass ash additives. T0: 0%, T1: 3.5%, T2: 7.0%, and T3: 14.0% dry weight (DW), weight/weight (w/w) biomass ash was added to the sewage sludge + sawdust mixture (volume, 1:1) to obtain the final NPK content and monitored over a 45-day period. Sawdust was used as auxiliary material. The sequential extraction method was used to determine the elemental species. Cr, Cd and Pb showed higher affinity to the residual fraction and occluded in the oxide fraction, which decreased the bioavailability factor (BF) (<1% BF–Cr, 21% BF–Cd and 9% BF–Pb) compared to the control treatment (46% BF–Cr, 47% BF–Cd and 80% BF–Pb). As the amount of biomass ash increased (T1-T3), the percentages of residual Cr (Res-Cr) (10–65%), exchangeable Cd (Exc-Cd) and organically bound Cd (Org-Cd) (14% and 21%), and oxides-Pb (Oxi-Pb) (20–61%) increased. In all composts, Fe, Al, and Cu were associated with organically bound and oxides-entrapped fractions. More than 50% of total Mn and Mg were concentrated mainly in exchangeable fractions, suggesting high mobility and bioavailability (42% BF–Mn and 98% BF–Mg). Ni, Zn, and Na tended to be present in oxide-bound, organically bound, and residual fractions, while K and P were associated with exchangeable and organically bound fractions. The overall results suggest that composting sewage sludge with biomass ash may be the best strategy and technique to overcome soil application bottlenecks because it passivates heavy metals and improves the bioavailability of plant nutrients.