Sewage Sludge Compost Research Articles

Treatment of Sewage Sludge Compost Leachates on a Green Waste Biopile: A Case Study for an On-Site Application

This work proposes a suitable treatment for the leachates from a sewage sludge composting process using a specific windrow (biopile). The biopile’s evolution and organic content degradation were followed for 2 months with regular leachate spraying to assess the physico-chemical and biological impacts, and determine the risk of enrichment with certain monitored pollutants. The final objective was the valorization of the biopile substrates in the composting process, while respecting the quality standards of use in a circular economy way. Classical physico-chemical parameters (pH, conductivity, dissolved organic carbon (DOC), total dissolved nitrogen (TDN), etc.) were measured in the leachates and in the water-extractable and dry-solid fractions of the biopile, and the catabolic evolution of the micro-organisms (diversity and activities), as well as the enrichment with persistent organic pollutants (POPs) (prioritized PAHs (polycyclic aromatic hydrocarbons) and PCBs (polychlorinated biphenyls)), were determined. The results showed that the microbial populations that were already present in the biopile, and that are responsible for biodegradation, were not affected by leachate spraying. Even when the studied compost leachate was highly concentrated with ammonium nitrogen (10.4 gN L−1 on average), it significantly decreased in the biopile after 2 weeks. A study on the evolution of the isotopic signature (δ15 N) confirmed the loss of leachate nitrogen in its ammoniacal form. The bio-physico-chemical characteristics of the biopile at the end of the experiment were similar to those before the first spraying with leachate. Moreover, no significant enrichment with contaminants (metal trace elements, volatile fatty acids, or persistent organic pollutants) was observed. The results show that it would be possible for composting platforms to implement this inexpensive and sustainable process for the treatment of leachates.

Sewage Sludge and Municipal Solid Garbage Composting

Abstract: Co-compost could be gained by a mix of municipal solid garbage and sludge, that has been utilized in the agrarian grounds and solving municipal garbage and wastewater treatment plant issues. This investigation wants to present a method to set optimal situations like aeration speed, temperature, moisture range, C/N proportion, and particle size in composting procedure. Two pilots have been presented and in each pilot, various mixtures of municipal garbage, sludge, and wood pulp have been utilized. The size of the particle in mix and aeration speed were the distinctions between the 2 pilots. The outcomes demonstrated that the compost pile's pH has been almost ten in the start of the procedure and reduced to 7.25 slowly after seven days. The proper particle size has been 10 to 40 mm. The appropriate C/N proportion has been in the range of 25 and 35. It has been almost 33 in this experimentation. High temperatures lead to improving microbial movement in the start of the procedure. For homogenizing the temperature, it is essential for making an irritation of the compost pile each 4-6 days. An increase in co-compost temperature occurred while the moisture range has been from 50 to 60 percent. Aeration by 3 times of needed air has provided the best outcome. Ultimately, we have discovered that the moisture rate has more impact on microbial movement in comparison with the temperature. These outcomes support the utilization of the co-composting procedure by making up the size of particle and moisture abilities in preference to forced aeration-enclosed reactors.

An 18-year field experiment to assess how various types of organic waste used at European regulatory rates sustain crop yields and C, N, P, and K dynamics in a French calcareous soil

Recycling organic waste (OW) in agriculture can improve soil fertility and substitute chemical fertilizers depending on the OW and their treatment. The effects of OW have often been studied in simplified cropping systems to strengthen the observed effects. The objective of this study was thus to evaluate the long-term effects of different types of OW used at European regulatory rates on C storage, crop yields and N, P, and K dynamics. OW has been applied every 2 years at 170 kg N ha-1 since 2001 in the long-term field experiment PROspective in northeastern France on a silty loam calcosol. The 5 types of OW included urban sewage sludge (SLU), green waste and SLU compost (GWS), municipal biowaste compost (BIO), farmyard manure (FYM), and composted FYM (FYMC). The control treatment (CON) did not receive any OW. All treatments were studied after applying (N + ) or not applying (N-) mineral N fertilization at an annual optimal rate. Biowaste digestate was also applied after 2014 in N- treatments. OW application increased crop yield compared with the unfertilized control. Mineral N fertilizer partially substituted by OW allowed crop yield to be sustained compared with mineral fertilizer only, saving 18–54% mineral N fertilizer, 56–80% mineral P fertilizer and 14–76% mineral K fertilizer. No effects on crop grain N, P and K concentrations were found. The efficiency of OW to maintain SOC, total N, Olsen-P and exchangeable K contents in soils greatly varied with the type of OW. Except for SLU, the SOC stocks significantly increased from + 2.9 to + 7.0 t SOC ha-1 for FYMC_N- and BIO_N-, respectively. SLU and digestate had the greatest N fertilizer replacement value (58% and 69%, respectively). N-leaching risk did not increase with OW application in the long term. For a positive ∆P of 100 kg ha-1, Olsen-P increased by 2 mg P kg-1 in the GWS_N- and SLU_N- treatments, whereas Olsen-P decreased in other treatments. A surplus of + 100 kg ha-1∆K raised the exchangeable K stock by 20 and 21 kg K ha-1 in the FYM_N- and FYMC_N- treatments, respectively, whereas exchangeable K decreased in the BIO and GWS treatments. Our results highlight the ability of all tested types of OW to sustain crop yields in the long term when used at EU regulatory rates, while their effects on mineral fertilizer savings, SOC, soil mineral N, Olsen-P, and exchangeable K contents greatly varied according to the considered OW.

Improving the quality of organic compost of sewage sludge using grass cultivation followed by composting

Composting is one of the main processes of stabilization of sewage sludge and its association with cultivation in this residue has a great potential to produce stabilized organic fertilizer and, or substrate for plant development. The aim of this work was to evaluate the physical, chemical, and microbial attributes of sewage sludge (SS) aerated and cultivated with Pennisetum purpureum or Urochloa brizantha and, later, composted. The study was installed in a 2x2+2 factorial scheme, with four replications. The factors consisted of cultivation of P. purpureum or U. brizantha in SS for 90 days, with or without intermittent aeration for 60 days. The control treatments were SS without cultivation, with the presence or absence of aeration. After 90 days of cultivation, the grass was cut, crushed, and incorporated into the SS for composting for 60 days. The composted sewage sludge showed an increase of 26, 24, 17, 123, 19, 32, and 7.7% in the levels of P, Ca, Cu, Fe, Mn, Zn, and Pb; and a reduction of 22, 5.2, 26, 30, 8.8, and 70% in the levels of C, N, K, Mg, Ni, and Na, respectively. The levels of Cu, Ni, Zn, and Pb remained below the maximum limit allowed by environmental resolution. The degradation of SS decreased the particle diameter, increasing the bulk density and total porosity, improving the physical properties of the compost. The SS cultivation and composting, regardless of the grass, led to a reduction in pH, basal and accumulated respiration, nitrification index, and C/N ratio and an increase in the CEC/C ratio, showing adequate maturation of the compost produced. Thus, the SS cultivation and composting with grasses were effective for producing matured and quality organic compost with low risk of environmental contamination.

Composted Sewage Sludge Application Reduces Mineral Fertilization Requirements and Improves Soil Fertility in Sugarcane Seedling Nurseries

Sugarcane demands large amounts of nutrients to reach a high level of productivity. Nutrients are generally supplied by mineral fertilizers, but their high costs and negative environmental impacts have generated interest in greater use of organic nutrient sources such as composted sewage sludge (CSS). In this study, we evaluated changes in soil chemical properties after the application of CSS or CSS/mineral fertilizer (MF) combinations to soil containing sugarcane seedlings under nursery conditions. Treatments included: T1: conventional mineral fertilization (MF) without application of CSS, T2: 100% of the recommended MF (06–30–24); T3: application of 2.5 Mg−1 CSS; T4: 5.0 Mg−1 CSS, T5: 7.5 Mg−1 CSS, T6: 2.5 Mg−1 CSS and 50% MF, T7: 5.0 Mg−1 CSS and 50% MF, T8: 7.5 Mg−1 CSS and 50% MF, T9: 2.5 Mg−1 CSS and 100% MF, T10: 5.0 Mg−1 CSS and 100% MF, T11: 7.5 Mg−1 CSS and 100% MF. Soil chemical properties were evaluated from the soil surface (0.0–0.25 m) and subsurface (0.25–0.50 m) horizons. The results showed that the increase in CSS application did not affect soil organic matter content at either depth, while Zn concentrations increased in the soil subsurface horizon. The application of CSS at 5.0 Mg ha−1 with or without 50% MF resulted in the highest pH values, sum of bases, cation-exchange capacity, P, K, Ca, Mg, Cu, and Zn in surface horizons. The use of CSS as an organic fertilizer in sugarcane nurseries improves soil fertility, reduces mineral fertilizer requirements, and, thus, facilitates the sustainable disposal of sewage sludge.

Composted Sewage Sludge Application in a Sugarcane Seedling Nursery: Crop Nutritional Status, Productivity, and Technological Quality Implications

Composted sewage sludge (CSS) contains large amounts of organic matter and nutrients and can be used as an organic fertilizer to improve growth, yield, and quality of sugarcane. However, there is a lack of information regarding the impact of CSS application on sugarcane seedling performance in nursery environments. A field study was conducted using a randomized complete block design to evaluate the development, nutritional status, productivity, and technological quality of sugarcane seedlings after CSS application with or without mineral fertilizer. Morphological variables (stem height, diameter, and number, as well as leaf area), technological attributes (total recoverable sugar: ATR; quantity of sucrose in sugarcane juice: Pol; Brix: percentage (weight/weight) of soluble solids contained in juice; TAH: tons of sugar per hectare), nutritional status, and sugarcane productivity were evaluated. Treatments did not influence morphological and technological variables except for TAH but did positively alter nutritional status and seedling productivity. The application rates of 5.0 and 7.5 Mg ha−1 of CSS with or without mineral fertilizers (MF) provided the greatest increase in crop productivity. Our results indicate that CSS can be a sustainable nutritional management option in sugarcane seedling nurseries, resulting in greater crop productivity at lower mineral fertilization rates.

Initial Active Phase of In-Vessel Composting of Sewage Sludge, Leaves and Rice Straw

This work studied the characteristics of leaf, rice straw, and sewage sludge (SS) co-composting with the aim of determining the best composting ratio by monitoring temperature changes, oxygen (O2) concentration, carbon dioxide (CO2) concentration, ammonia (NH3) concentration, hydrogen sulfide (H2S) concentration, pH, electrical conductivity (EC), heavy metal content, carbon-nitrogen ratio (C/N ratio), germination index (GI), moisture content (MC), and volatile solids (VS) content during the composting process. Three composting piles with the mixture ratios of 4:1:1 (Pile A), 5:1:1 (Pile B), and 6:1:1(Pile C) (SS: leaf: rice straw) were tested. According to the temperature, C/N ratio, germination index, MC, and VS, the level of compost maturity in Pile B with a 5:1:1 mixing ratio was higher than that in Piles A and C. The contents of heavy metals in the composts were shown to meet the grade A standard in CJ/T 309-2009 (2009), except Cu and Zn, which was within the grade B standard.

Insight into Effects of Initial Moisture Content on the Heat-Up of Sewage Sludge Composting During Mesophilic Phase

The effects of initial moisture content (55%, 60% and 65%) on the heat-up of sewage sludge (SS) composting during the mesophilic phase were investigated. Monitoring results showed that low moisture content (55%) increased the heating rate, high initial moisture content (60% and 65%) significantly improved the activities of cellulase and peroxidase during the mesophilic phase. Furthermore, although high moisture content improved the diversity of bacteria during composting, there were no significant differences in the microbial structure during the process of succession. So, rather than inhibiting the activity of the bacterial population, the negative effect of high moisture content (60 and 65 per cent) on composting temperature heat up was attributable to the difficulty of heating produced by the specific heat capacity of water. The correlation index between initial moisture content and microorganisms was relatively low, while the temperature was the largest environmental factor affecting the bacterial community. This conclusion provided a hint to make an association between initial moisture content and composting temperature-rising stage.

Gaseous emissions and grain-heavy metal contents in rice paddies: A three-year partial organic substitution experiment

To reduce the utilization of chemical fertilisers, which cause substantial nitrogen loss and widespread nonpoint source pollution, the application of organic manure has become an increasingly popular alternative in rice agriculture. It plays key roles in improving soil quality and maintaining rice yields, but its integrated impacts on trace gas emissions and heavy metal contents in rice grains remain poorly documented. We conducted a three-year field experiment with two application ratios (25% and 50%) of sewage sludge compost (S) and pig manure compost (P) during the rice season in eastern China. The emissions of methane (CH4), nitrous oxide (N2O), ammonia (NH3), and the grain contents of nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) were measured. Compared with urea, partial organic application, particularly 50%S and 50%P, led to a considerable increase in CH4 emission (52%–71%), global warming potential (GWP, 50%–69%), and greenhouse gas intensity (46%–68%). However, it substantially decreased N2O emission and NH3 volatilisation, thus lowering the cumulative nitrogen loss by 32%–62%. Moreover, the average concentrations of Ni, Cu, Zn, Cd, and Pb in rice grains were 100–151 μg kg−1, 2.31–2.78 mg kg−1, 20.3–24.3 mg kg−1, 44.3–123 μg kg−1, and 8.69–15.2 μg kg−1, respectively, which were significantly lower than food standard limits for rice in China. Both 25%S and 50%S achieved the highest grain yields while significantly decreasing grain Ni and Cd contents. Health risk assessment showed that the target hazard quotient of all the metals was <1 (0.006–0.73), and the hazard index that represents additive effects of pollutants was higher than the threshold, except for 25%S and 50%S. The results suggested 25%S as a potential fertilisation practice in rice fields that not only maintains low GWP and high yields but also seldom poses grain pollution or health risks.

Feasibility of sewage sludge and food waste aerobic co-composting: Physicochemical properties, microbial community structures, and contradiction between microbial metabolic activity and safety risks

Co-composting of sludge and food waste eliminates the disadvantages of composting these waste products separately. Specifically, co-composing neutralizes the pollutants and improves the organic matter that occur in sewage sludge, and solves the problem of the low pH values and high moisture content of food waste. However, little is known about the functional microorganisms, microbial metabolic capacity, and biosecurity risks involved in sewage sludge and food waste co-composting. Therefore, this study established four lab-scale composting reactors [T1 (separate composting of food waste), T2 (separate composting of sewage sludge), T3 (sewage sludge and food waste co-composting at a C/N ratio of 25), and T4 (equal proportions composting of sewage sludge and food waste)] to assess the feasibility of sewage sludge and food waste aerobic co-composting. Our findings indicated that polysaccharides and proteins in T3 could be effectively degraded, and the total nutrient levels in T3 were higher than those in the other groups. After composting, the microbial diversity and richness of T3 were higher than that of T1. In later composting stages, the functional microorganisms in T1 maintained higher metabolic activity, however, it also had a higher biosecurity risk than T3 due to the presence of pathogenic bacteria such as Enterococcus_faecalis and Bacillus_circulan. Although the product of T3 could not be used as a microbial fertilizer, its biosecurity risk was lower than that of T1 and could therefore be used as an organic fertilizer. Redundancy analysis (RDA) results indicated that changing the microbial community structure by adjusting key environmental factors could improve composting quality and reduce microbial safety risks. Collectively, our results provide a theoretical basis for the development of co-composting strategies for the biodegradation of perishable solid organic waste, in addition to proposing the risk of pathogenic bacteria exposure that could endanger human and animal health.

Mechanisms controlling the stabilization of soil organic matter in agricultural soils as amended with contrasting organic amendments: Insights based on physical fractionation coupled with 13C NMR spectroscopy

Soil organic matter (SOM) has vital roles in the global carbon (C) cycle and the use of organic amendments (OAs) to maintain or improve SOM levels is a promising practice. However, the mechanisms underlying SOM stabilization in OA-amended soils remain insufficiently resolved. For more effective understanding on such issues, we examined soil samples from a long-term experimental plot (26–31 years) that included six treatments, namely, a chemical fertilizer (CF) alone (CF), a bark compost plus CF (BC + CF), a coffee residue compost plus CF (CRC + CF), a cattle manure compost plus CF (CMC + CF), and a cattle manure (CMC) or sewage sludge compost (SSC) alone at a higher application rate, using physical fractionation. In the fractionation, free particulate SOM (fSOM), free SOM occluded in aggregates (oSOM), and SOM weakly bound to minerals (wSOM; s.g. 1.6–2.0 g cm−3) and strongly (sSOM; s.g. >2.0 g cm−3) were separated and characterized using 13C nuclear magnetic resonance (NMR) along with OAs and bulk soil samples. The long-term OA applications enhanced the total C accumulation and the amount of C accumulated as oSOM, wSOM, and sSOM correlated positively with the total C content. The application of BC or CRC resulted in a greater accumulation of fSOM. Conversely, the continuous application of SSC or CMC, which has a high N content and a low C/N ratio, led to a greater accumulation of C, mainly as wSOM. Our findings suggest that both the quality and quantity of OAs control the forms of C that accumulate and this involves different mechanistic pathways. We suggest that the abundant alkyl C in the wSOM and sSOM fractions was SSC-derived SOM in the SSC soil while in the case of the CMC soil, this was due to the increased contribution of microbial-derived SOM.

A comparative study between the biofiltration for air contaminated with limonene or butyric acid using a combination of olfactometric, physico-chemical and genomic approaches

A multidisciplinary analysis based on physico-chemical, olfactometric and microbiological perspectives was performed to compare the biofiltration of air contaminated with limonene or butyric acid. Two biofilters were subjected to butyric acid gaseous streams: one was filled with wood chips and sewage sludge compost (BF B-1) and the other with wood chips only (BF B-2). Similarly, two other biofilters were subjected to a gaseous stream containing limonene, with the same beds (BF L-1 and BF L-2, respectively). Although the biofilters fed with butyric acid received higher odor loads (280–3280 ouE/m2·s for BF B-1 and 135–1460 ouE/m2·s for BF B-2) than the biofilters treating limonene (30–170 ouE/m2·s for BF L-1 and 15–130 ouE/m2·s for BF L-2), the first systems achieved odor removal efficiencies greater than 90% during most of the biofiltration time, whereas in the limonene biofilters, these efficiencies never exceeded 70%. Regarding the packed beds, genomic analysis of the microbial communities showed a wider distribution of phyla (Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria) in compost-wood biofilters than in wood chips systems where Proteobacteria was clearly predominant. This study reveals the importance of considering both the nature of the biofiltered compounds and the packed bed composition in biofiltration operations.

Heavy metal pollution and net greenhouse gas emissions in a rice-wheat rotation system as influenced by partial organic substitution

Substituting nitrogen fertilizer with organic manure is a common fertilization practice in farmland, but its potential effect on heavy metal pollution and greenhouse gas (GHG) emissions remains unclear. A three-year field experiment was conducted in the rice-wheat rotation system, with two different substitution ratios (25% and 50%) of sewage sludge compost (SS) and pig manure compost (PM). With the substitutions of SS and PM, the heavy metals, including Cu, Zn, Cd, and Pb were accumulated in the soil, but the pollution load index was <1 (0.39–0.66), indicating that soil was not polluted. Heavy metals Ni and Cu were mainly found in rice chaff, while Zn and Cd were accumulated in rice stalk, and the accumulation of Pb occurred in the leaf. For wheat, Ni, Cu, and Pb were accumulated in chaff, while grain and stalk had the highest concentrations of Zn and Cd, respectively. Moreover, the bioconcentration factor of heavy metals was 0–0.787, and their contents were below the standard limits for foods for rice and wheat in China, implying that the grains were unpolluted. Given the 5–8 fold increase in the sequestration rate of soil organic carbon with SS and PM substitutions, the annual net GHG emissions were reduced by 115–166%. Most importantly, 50% SS substitution exhibited the lowest net GHG emissions and highest rice and wheat yields. Overall, the results suggested that 50% SS substitution would be a feasible fertilization strategy that not only is unlikely to pose a high risk of soil and grain pollution but also significantly mitigates net GHG emissions and maintains high yields.

Differences of Enzymatic Activity During Composting and Vermicomposting of Sewage Sludge Mixed With Straw Pellets.

The study aims were focused on profiling eight hydrolytic enzymes by fluorescence method using a multifunctional modular reader and studying the proportion of basic microorganism groups during composting and vermicomposting of sewage sludge mixed with straw pellets in several proportions (0, 25, 50, 75, and 100%). The greatest decrease in enzymatic activity occurred in the first half of composting and vermicomposting. After 4 months of these processes, the least enzymatic activity was observed in the sludge with 50% and also 25% straw addition, indicating that straw is an important means for the rapid production of mature compost from sewage sludge. Enzymatic activity was usually less in the presence of earthworms than in the control treatment because some processes took place in the digestive tract of the earthworm. For the same reason, we observed reduced enzyme activity during fresh feedstock vermicomposting than precomposted material. The final vermicompost from fresh feedstocks exhibited less microbial biomass, and few fungi and G− bacteria compared to precomposted feedstock. The enzymatic activity during composting and vermicomposting of sewage sludge and their mixtures stabilized at the following values: β-D-glucosidase—50 μmol MUFG/h/g dw, acid phosphatase—200 μmol MUFP/h/g dw, arylsulphatase—10 μmol MUFS/h/g dw, lipase—1,000 μmol MUFY/h/g dw, chitinase—50 μmol MUFN/h/g dw, cellobiohydrolase—20 μmol MUFC/h/g dw, alanine aminopeptidase—50 μmol AMCA/h/g dw, and leucine aminopeptidase—50 μmol AMCL/h/g dw. At these and lesser values, these final products can be considered mature and stable.

Effects of Microbial Inoculum on Microbial Community and Enzyme Activity Involved in Nitrogen-Sulfur Metabolism During Sewage Sludge Composting

Effects of Microbial Inoculum on Microbial Community and Enzyme Activity Involved in Nitrogen-Sulfur Metabolism During Sewage Sludge Composting

Combined Addition of Bagasse and Zeolite Stabilizes Potentially Toxic Elements in Sewage Sludge Compost and Improves Eucalyptus Urophylla Seedling Growth

Combined Addition of Bagasse and Zeolite Stabilizes Potentially Toxic Elements in Sewage Sludge Compost and Improves Eucalyptus Urophylla Seedling Growth

Effects of Electro-Dewatering Pretreatment on Methane Emission, Methanogens, Methanotrophs and Related Functional Genes in Sewage Sludge Composting

Effects of Electro-Dewatering Pretreatment on Methane Emission, Methanogens, Methanotrophs and Related Functional Genes in Sewage Sludge Composting

Potential Usage of Sewage Sludge Compost (Scp) in Agricultural Practice: The Reduction of Antibiotics Resistance Genes in Lettuce and Soil Amended with Factory Scp

Potential Usage of Sewage Sludge Compost (Scp) in Agricultural Practice: The Reduction of Antibiotics Resistance Genes in Lettuce and Soil Amended with Factory Scp

High Nitrogen Addition after the Application of Sewage Sludge Compost Decreased the Bioavailability of Heavy Metals in Soil

High Nitrogen Addition after the Application of Sewage Sludge Compost Decreased the Bioavailability of Heavy Metals in Soil

Composted sewage sludge as an alternative substrate for forest seedlings production

The production of forest seedlings with adequate morphological and physiological characteristics is essential for the success of plantations. Substrates and irrigation are the major factors determining seedlings’ growth. Substrates made of urban and agricultural residues are a sustainable alternative to peat-based substrates. In this study, we evaluated how composted sewage sludge substrates affect the growth and gas exchange in seedlings of Cedrela fissilis Vell. Seedlings were produced under daily irrigation depths of 6, 9, and 12 mm, and on different substrates. The substrates were based on sewage sludge composted with Eucalyptus bark or sugarcane bagasse, and a commercial substrate based on peat, involving a double factorial design with 12 treatments (3 irrigation depths × 3 substrates). Both physical and chemical characteristics of substrates were analyzed, and morphological traits and gas exchanges of seedlings were measured. Sewage sludge-based substrates presented different characteristics according to the material it was mixed. Eucalyptus bark provided higher bulk density (0.19 g cm-3) and lower total porosity (75%) to the substrate, while sugarcane bagasse increased macroporosity up to 60%. Seedlings produced in sewage sludge-based substrates presented a height up to 17.8 cm and stem diameters of between 8.39-10.29 mm. Higher shoot and root dry mass was obtained in sewage sludge-based substrates with irrigation depth of 9 mm, which were 3.71 and 2.01 g, respectively. Photosynthetic carbon assimilation varied between 2.26 and 3.23 µmol CO2 m-2 s-1, and water use efficiency varied from 2.058 to 3.395 µmol CO2 (mol H2O)-1, with the highest values being obtained in seedlings produced in sewage sludge-based substrates with irrigation depth of 6 mm. Our results demonstrate that sewage sludge-based substrates are an efficient alternative to commercial peat-based substrates for seedling production.