Biosolids Compost Research Articles

Microbiome science of human excrement composting.

Linear waste management systems are unsustainable and contribute to environmental degradation, economic inequity, and health disparities. Among the array of environmental challenges stemming from anthropogenic impacts, the management of human excrement (human feces and urine) stands as a significant concern. Over two billion people do not have access to adequate sanitation, signifying a global public health crisis. Composting is the microbial biotechnology aimed at cycling organic waste, including human excrement, for improved public health, agricultural productivity and safety, and environmental sustainability. Applications of modern microbiome -omics and related technologies have the capacity to support continued advances in composting science and praxis. In this article, we review literature focused on applications of microbiome technologies to study composting systems and reactions. The studies we survey generally fall into the categories of animal manure composting, biosolids composting, and human excrement composting. We review experiments utilizing microbiome technologies to investigate strategies for enhancing pathogen suppression and accelerating the biodegradation of organic matter. Additionally, we explore studies focused on the bioengineering potential of microbes as inoculants to facilitate degradation of toxins such as pharmaceuticals or per- and polyfluoroalkyl substances. The findings from these studies underscore the importance of advancing our understanding of composting processes through the integration of emerging microbiome -omics technologies. We conclude that work to-date has demonstrated exciting basic and applied science potential from studying compost microbiomes, with promising implications for enhancing global environmental sustainability and public health.

Transformed biosolids promote ryegrass growth and microbial carbon cycling at the ‘cost’ of soil carbon

Soil carbon supports desirable ecosystem functions for global agricultural productivity and climate resilience objectives. Wastewater biosolids can be transformed into soil amendments that return carbon and nutrients to agricultural systems in stoichiometric ratios that support carbon stabilisation. However, practicable delivery that enhances stable soil carbon and plant yield remains challenging. Soil carbon stability and nutrient availability are mediated partly by microbial community composition and function, which are poorly understood in soils amended with transformed biosolids. We conducted a 56-day study in a temperature-controlled glasshouse, growing perennial ryegrass (Lolium perenne) in pasture soil amended with straw, straw supplemented with nutrients, or transformed biosolids (composted biosolids, dried biosolids or biosolids biochar), all with equal added carbon (3500 kg ha−1). Control soils, with and without supplementary nutrients, were also included. Plant dry mass, soil chemical characteristics, and soil carbon fractions were measured at harvest. 16S rRNA sequencing was used to infer the composition and putative function of rhizosphere bacterial communities. Shoot dry mass increased for composted biosolids (236%) and dried biosolids (559%), but total carbon in rhizosphere soil decreased for composted biosolids (16.3%), dried biosolids (13.3%) and biosolids biochar (12.7%) when compared to unamended soils. Fine-fraction carbon in rhizosphere soil decreased for straw with supplementary nutrients (6.8%), dried biosolids (6.3%) and biosolids biochar (4.6%). Rhizosphere bacterial communities clustered by treatment, with populations correlated with fine-fraction carbon distinct from those populations correlated with shoot and root dry mass. Path analysis linked fine-fraction carbon loss with increased putative carbon cycling genes, driven by available nutrients and plant growth. Transformed biosolids can trigger a microbial response that reallocates nutrients from organic matter to plants, disrupting soil carbon-nutrient stoichiometry and facilitating carbon loss. Understanding the carbon cost of this ecosystem service is fundamental when translating benefits of transformed biosolids to end users.

Risk management approach using ash-based amendment blends for remediation of lead-contaminated urban soils and protection of public health

Anthropogenic activities have left a legacy of contaminated vacant land, which disproportionately affects lower income communities and can have detrimental impacts on human health, particularly children. A management solution is needed to address this widespread lead contamination in urban soils of vacant lots. In this study, high-Fe biosolids incinerator ash (BIA) was evaluated for its ability to sequester soil Pb. Five blends were created using BIA and different amount of other products (dredge, biosolids compost, and yard waste compost) to determine the most effective treatment to reduce Pb bioaccessibility in the soil. The sorption capacity of the BIA for Pb was evaluated by mixing the BIA with Pb(NO3)2 at 1000 to 100,000 ​mg ​Pb/kg BIA. The contaminated soil from Cleveland, OH was treated with five BIA-based blends at a 1:1 (w/w) ratio, and Pb bioaccessibility was evaluated using USEPA Method 1340 ​at pH 2.5 and the Physiologically Based Extraction Test (PBET) at pH 2.5. BIA was a strong sorbent for Pb, sorbing ∼100% of the Pb from solution at 10,000 ​mg/L with only 41% bioaccessibility based on Method 1340 ​at pH 2.5. The blend containing 4.5%, 10%, or 19% BIA reduced the Pb bioaccessibility by 48% from the control based on both bioaccessibility methods. The bioaccessible Pb determined by PBET was less than that by USEPA Method 1340 ​at pH 2.5. However, similar reductions in bioaccessible Pb between blend-treated soils and the unamended soil were observed for all bioaccessibility methods. Plant growth assays showed the blends to have little to no significant impact on clover growth, mortality, or flower production, with the blend containing 10% BIA showing greater biomass yield. Results showed BIA-based blends were able to reduce bioaccessible Pb in the soil. This remediation approach may improve the urban living environment and protects public health.

Ineffectiveness of phosphorus-containing amendments to reduce Pb bioaccessibility in an urban alkaline soil.

Urban soils contaminated by historical and current anthropogenic activities present an alarming human health risk requiring redress. Federal and state governments continue to lower residential soil lead (Pb) screening standards, which will likely require new risk-based approaches to address urban soil Pb contamination. Phosphorus (P) soil amendments have long been presented as a solution to sequester Pb, thereby reducing exposure risk. In this study, P-containing sources (biosolids incinerator ash, poultry litter, biosolids compost, and triple superphosphate) of varying solubilities were assessed as soil amendments to reduce Pb bioaccessibility and serve as an inexpensive remediation strategy for urban soil. Contaminated soil (1624mg kg-1Pb, pH 7.43) from Cleveland, OH, was treated with the four P-containing soil amendments at a 1:5Pb:P molar ratio and two combination treatments at 1:10Pb:P molar ratio and incubated for 3 months. A batch equilibration analysis was also conducted to assess reduction in in vitro bioaccessible Pb (IVBA Pb). Pb bioaccessibility was evaluated using US EPA Method 1340 at pH 1.5 and the Physiologically Based Extraction Test pH 2.5 at 1 and 3 months. In general, treatments were ineffective in reducing IVBA Pb regardless of IVBA extraction method, incubation duration, batch equilibration analyses, or P source. The results of this study suggest P-containing amendments are not suitable to address Pb exposure in the study soil. Site-specific efficacy testing to determine reductions in IVBA Pb from P-containing amendments should be performed before making recommendations for remediation of Pb-contaminated urban soil.

A Novel Technosol Formulation for Sustainable Landfill Top Covers Using Non-Hazardous Wastes

This study explores the potential of non-hazardous wastes for crafting an engineered soil-like material (Technosol) suitable for landfill capping applications. Three distinct materials—waste foundry sand (WFS), washing aggregate sludge (WAS), and composted biosolids (CBS)—were strategically combined to develop this innovative Technosol. The formulation process involved a comprehensive analysis of their physical–chemical properties, mineral composition, leachate quality, and a series of geotechnical assessments to ensure compliance with landfill top cover construction standards. The blend 90WFS/10WAS showed optimal geotechnical properties for constructing a protective layer, including maximum dry density (1.77 g cm−3), void ratio (0.4), CBR index (23.2), cohesive strength (40 kPa), internal friction (ϕ = 30°), and permeability coefficient (k = 1.48 × 10−6 cm s−1). Further enhancement was achieved by adding 10% CBS, resulting in the development of a functional organo-mineral topsoil horizon (81WFS/9WAS/10CBS). Importantly, leachate analysis confirmed the negligible environmental footprint of this Technosol. Moreover, a pot-based experiment with Brassica juncea planting validated its capacity to support plant growth and establish a vegetative cover on the landfill surface.

Effects of Biochar and Compost on Turfgrass Establishment Rates

Organic soil amendments are a sustainable option for modifying soil structure and improving plant performance in the face of abiotic stressors such as drought and soil salinity. Of these amendments, biochar and compost have the added benefits of carbon sequestration and waste recycling. Establishment studies were conducted on tall fescue (Festuca arundinacea Schreb.) (syn., Schedonorus arundinaceus (Schreb.) Dumort and Lolium arundinaceum (Scop.) Holub) to assess the potential inhibition of establishment by compost and biochar products. Both green waste and biosolid compost impaired establishment rates, while biochar did not. In the field study, the green waste treatments were slower to reach 50% coverage than the untreated control or when biochar was added to the soil, but all treatments reached 75% and final coverage at a similar rate. Field application of compost had a positive effect on final root length and volume but a negative effect on tall fescue roots in the greenhouse. The negative effect of higher salts and volatiles in the biosolids compost was reduced when biosolids and biochar were incorporated into the soil simultaneously. This work represents one of the only large-scale field studies on turfgrass establishment comparing the impact of biochar and compost products on turfgrass establishment.

A review of the influence of heat drying, alkaline treatment, and composting on biosolids characteristics and their impacts on nitrogen dynamics in biosolids-amended soils

Application of biosolids to agricultural land has gained increasing attention due to their rich nutrient content. There are a variety of treatment processes for converting sewage sludge to biosolids. Different treatment processes can change the physicochemical properties of the raw sewage sludge and affect the dynamics of nutrient release in biosolids-amended soils. This paper reviews heat drying, alkaline treatment, and composting as biosolids treatment processes and discusses the effects of these treatments on biosolid nitrogen (N) content and availability. Most N in the biosolids remain in organic forms, regardless of biosolids treatment type but considerable variation exists in the mean values of total N and mineralizable N across different types of biosolids. The highest mean total N content was recorded in heat-dried biosolids (HDB) (4.92%), followed by composted biosolids (CB) (2.25%) and alkaline-treated biosolids (ATB) (2.14%). The mean mineralizable N value was similar between HDB and ATB, with a broader range of mineralizable N in ATB. The lowest N availability was observed in CB. Although many models have been extensively studied for predicting potential N mineralization in soils amended with organic amendments, limited research has attempted to model soil N mineralization following biosolids application. With biosolids being a popular, economical, and eco-friendly alternative to chemical N-fertilizers, understanding biosolids treatment effects on biosolids properties is important for developing a sound biosolids management system. Moreover, modeling N mineralization in biosolids-amended soils is essential for the adoption of sustainable farming practices that maximize the agronomic value of all types of biosolids.

Soil legacy and organic amendment role in promoting the resistance of contaminated soils to drought

The application of organic amendments is a common practice in the restoration of contaminated and degraded soils. We designed an experiment in pot mesocosms to study the effect of organic amendment (comparing a short-term addition of biosolid compost with soils amended 17 years ago) and soil legacy (comparing soils exposed or not to extensive grazing over a remediation process) on the resistance of a degraded Mediterranean soil against a simulated drought event. Pots were sown with a forage mixture (Lolium rigidum and Medicago polymorpha), and soil resistance was evaluated by measuring soil chemical properties, biological activity (soil enzyme activities and respiration rate), soil microbial community composition and plant production. Our results showed a positive effect of the organic amendment and the exposure to extensive grazing on soil properties, increasing soil water retention and the stability of plant production under drought conditions. The long-term amendment addition avoided the negative consequences of drought on L. rigidum production (the species with the lowest tolerance to water stress), while M. polymorpha biomass in soils exposed to grazing was 12 times the biomass in the non-amended and non-exposed soil. However, soil biological activity (enzyme activities and respiration rate) as well as microbial diversity were not limited by the simulated drought conditions under any type of soil management legacy, demonstrating the great adaptation of the microbial communities to water stress conditions in semiarid Mediterranean soils. Soils exposed to organic matter inputs in the long-term, through amendment addition or exposure to grazing, showed high similarities in terms of bacterial and fungal composition.

Effect of biosolid compost amended on Pb availability in soils cultivated with lettuce

Effect of biosolid compost amended on Pb availability in soils cultivated with lettuce

The interactive effect of environmental factors on methane oxidation in a continental landfill bio-cover

In the current study, the interactive effect of environmental factors was studied in an active bio-cover after two years of operation and experiencing a wide range of temperatures across the seasons (<0 ℃ to >45 ℃) in a continental climate condition. The studied environmental factors includes moisture content (MC), temperature, and initial CH4 concentration that were observed to have the most controlling effect on the CH4 oxidation in the bio-cover over two years of field-scale measurements. Therefore, selected environmental factors were modeled to determine their interactive effect on CH4 oxidation potential in the bio-cover material including Yard Waste and Leaf Compost (YWLC) and Biosolids Compost (BSC) (1:4). The compost was taken from the active bio-cover in October 2018 with a compost temperature between 10 and 15 ℃. The expectation was that the methanotrophic biomass would be adapted to the seasonal in situ conditions. While the effects of individual environmental factors on biological CH4 oxidation have been described in a previous long term study, their interactive effects in the bio-cover compost materials had not been explored. Therefore, interactive effects of environmental factors were investigated with a Box–Behnken Design adopting a Response Surface Methodology to develop a statistical model and determine the optimal conditions for the CH4 oxidation in the compost mixture sampled. To do so, 17 batch incubations were conducted at the MC of 20 %, 40 %, and 60 %, temperatures of 15, 30, and 45 ℃, and initial CH4 concentrations of 10 %, 20 %, and 30 %. The maximum value of CH4 oxidation rate obtained from the model was 2.20 mgCH4.gdw−1.d−1 with optimum MC of 47.4 %, temperature of 32.7 ℃, and initial CH4 concentration of 23.8 %. A parabolic curve for MC and temperature was observed simultaneously, and there was no significant difference between CH4 oxidation rates at 20 % and 30 % initial CH4 concentration. The model was then validated experimentally. The results of this study showed that the current compost mixture, collected from this bio-cover accustomed to fluctuations in temperature and MC, selected for a community of methanotrophs capable of effective operation over a wide range of summer compost temperatures and MCs, but was ill-adapted to spring and fall temperatures when the bio-cover temperature descends below 15 ℃, including when the bio-cover sample was taken for the current analyses.

Soil invertebrate and microbial activity rehabilitation by compost application after road construction and volcanic disturbance

Topsoil and plants had been removed for the construction of the “De los Siete Lagos” road when the June 2011 Puyehue–Cordón Caulle Complex volcanic eruption deposited 30 cm of tephra. Our objective was to study the active rehabilitation of substrate on roadsides simultaneously affected by road construction and volcanic eruption by compost addition. We studied two biological communities frequently forgotten by rehabilitation measures: invertebrates (density, richness) and microorganisms (enzymatic activities); both in the surface organic matter created by compost addition and the tephra substrate. In December 2012, we installed control, biosolids compost (BC) and municipal waste compost (MC) plots on roadside exclosures. Forest reference sites were also studied. Samplings were performed in spring 2013 and summer 2014. No surface organic matter was found in control plots, and no invertebrates were detected in the tephra layer of control plots in both samplings. BC and MC promoted the formation of a surface organic matter layer that harbored invertebrate and enzymatic activity in both sampling seasons. There were no significant differences in invertebrate density among BC, MC, and forest both in the surface organic matter and the tephra substrate. However, BC and MC invertebrate communities, dominated by springtails, did not resemble the forest community, where oribatids were the most common taxa. Statistically significant differences in total (surface organic matter + tephra substrate) microbial activities indicated a treatment order of forest &gt; BC ≥ MC &gt; control for enzymes related with the mineralization of nitrogen (leucine‐aminopeptidase) and phosphorus (acid phosphomonoesterase).

Leaching of select per-/poly-fluoroalkyl substances, pharmaceuticals, and hormones through soils amended with composted biosolids

The use of organic amendments to enhance soil health is increasingly being identified as a strategy to improve residential landscapes while also reducing the need for external inputs (e.g., fertilizers, irrigation). Composted biosolids are a re-purposed waste product that can be used in organic amendments to improve the overall sustainability of a municipality by enhancing residential soil carbon content while simultaneously reducing waste materials. However, the biosolids-based feedstock of these compost products has the potential to be a source of organic contaminants. We conducted a laboratory-based soil column experiment to evaluate the potential for different commercially available compost products to act as a source of emerging organic contaminants in residential landscapes. We compared two biosolids-based compost products, a manure-based compost product, and a control (no compost) treatment by irrigating soil columns for 30 days and collecting daily leachate samples to quantify leaching rates of six hormones, eight pharmaceuticals, and seven per- and polyfluoroalkyl substances (PFAS). Detection of hormones and pharmaceuticals was rare, suggesting that compost amendments are likely not a major source of these contaminants to groundwater resources. In contrast, we detected three of the seven PFAS compounds in leachate samples throughout the study. Perfluorohexanoic acid (PFHxA) was more likely to leach from biosolids-based compost treatments than other treatments (p < 0.05) and perfluorobutane sulfonate (PFBS) was only detected in biosolids-based treatments (although PFBS concentrations did not significantly differ among treatments). In contrast, perfluorooctanoic acid (PFOA) was commonly detected across all treatments (including controls), suggesting potential PFOA experimental contamination. Overall, these results demonstrate that commercially available composted biosolids amendments are likely not a major source of hormone and pharmaceutical contamination. The detection of PFHxA at significantly higher concentrations in biosolids treatments suggests that biosolids-based composts may act as sources of PFHxA to the environment. However, concentrations of multiple PFAS compounds found in leachate in this study were lower than concentrations found in known PFAS hotspots. Therefore, there is potential for environmental contamination from PFAS leaching from composted biosolids, but leachate concentrations are low which should be considered in risk-benefit analyses when considering whether or not to use composted biosolids as an organic amendment to enhance residential soil health.

Composted biosolids amendments for enhanced soil organic carbon and water storage in perennial pastures in Colorado

Land management of grasslands can play a significant role in climate change mitigation by influencing soil carbon (C) storage. Soil amendments, such as adding compost, have been shown to increase soil C storage while simultaneously increasing plant productivity and soil water holding capacity (WHC), factors that provide immediate benefits to ranchers. Research to date has mainly focused on temperate annual grasslands. However, little is known if irrigated perennial pasturelands in cold, arid climates respond similarly. This study’s objective was to determine the immediate effects of a 5 cm depth application of biosolids compost on plant productivity, soil moisture, and soil C storage. Research sites were established at four ranches in Gunnison, CO, a high-elevation, arid region. During the first year, there was a significant increase in total aboveground biomass (AGB) across three of the four sites (F3,32 = 62.3, p < 0.001), resulting in a difference in total AGB of 199.83 g·m−2 (95% CI 133.6 – 266.1 g·m−2) between the control and treatment, an average increase of 109% (SE ± 20%). There was a significant increase in soil moisture in the treatment plots relative to the controls at each site for most of the growing season (July-Oct). On average, soil organic matter (SOM) increased by 32% SE ± 10.5, with two sites demonstrating a significant increase. Soil C stocks increased across sites with biosolids, but this was only significant at one site (F1,32 = 7.05, p = 0.012), the most degraded of all four pasturelands. This study demonstrated that a single application of biosolids compost could elicit a significant increase in soil moisture throughout the growing season and increase plant biomass production. Biosolid applications can also increase SOC. However, this response's magnitude is site-specific and is associated with the degree of soil degradation, which might be related to land management history. Using biosolids compost on pasturelands seems to be a positive strategy to improve soil health and its associated co-benefits. Still, managers should consider the degree of degradation of their land when determining cost benefits.

Greenhouse gas emissions from decomposition of biosolids as affected by stabilization method and soil moisture

AbstractComputational models are useful to estimate agricultural greenhouse gas emissions at regional scales. However, empirically based parameter values are required for the models to accurately represent carbon (C) and nitrogen (N) mineralization rates of different organic amendments in more and less humid regions or during wet and dry periods of the growing season. A controlled environment study was conducted to assess the rates of C and N mineralization in differently processed sewage sludge (biosolids) in wet and dry soil. Parameter values were estimated for use in modelling the degradation of three types of biosolids. A loam soil with either 49% water‐filled pore space (WFPS) or 29% WFPS was amended with mesophilic anaerobically digested (digested), alkaline‐stabilized, or composted biosolids. Headspace samples were collected and analysed for carbon dioxide (CO2) and nitrous oxide (N2O), and soil samples for nitrate () and ammonium (). Four different first‐order models were fitted to the cumulative CO2–C and N2O–N data (R2 &gt; 0.98), and soil (R2 &gt; 0.65) and (R2 &gt; 0.93) concentrations. CO2–C data indicated that C mineralization was higher in soil with 49% WFPS than in soils with 29% WFPS. Seventy‐nine percent of the C compounds in digested biosolids degraded in soil with 49% WFPS, compared with 52% for alkaline‐stabilized biosolids and 8% for composted biosolids. The fitted coefficient values were similar for all of the four first‐order models used in this study and provide useful information for parameterizing more sophisticated mechanistic models of the degradation of biosolids in soil.

Ingestion of remediated lead-contaminated soils affects the fecal microbiome of mice.

The relationship between ingestion of diets amended with a Pb-contaminated soil and the composition of the fecal microbiome was examined in a mouse model. Mice consumed diets amended with a Pb-contaminated soil in its native (untreated) state or after treatment for remediation with phosphoric acid or triple superphosphate alone or in combination with iron-waste material or biosolids compost. Subacute dietary exposure of mice receiving treated soil resulted in modulation of the fecal intestinal flora, which coincided with reduced relative Pb bioavailability in the bone, blood and kidney and differences in Pb speciation compared to untreated soil. Shifts in the relative abundance of several phyla including Verrucomicrobia, Tenericutes, Firmicutes, Proteobacteria, and TM7 (Candidatus Saccharibacteria) were observed. Because the phyla persist in the presence of Pb, it is probable that they are resistant to Pb. This may enable members of the phyla to bind and limit Pb uptake in the intestine. Families Ruminococcaceae, Lachnospiraceae, Erysipelotrichaceae, Verrucomicrobiaceae, Prevotellaceae, Lactobacilaceae, and Bacteroidaceae, which have been linked to health or disease, also were modulated. This study is the first to explore the relationship between the murine fecal microbiome and ingested Pb contaminated soils treated with different remediation options designed to reduce bioavailability. Identifying commonalities in the microbiome that are correlated with more positive health outcomes may serve as biomarkers to assist in the selection of remediation approaches that are more effective and pose less risk.

The Clean Water Act and biosolids: A 45‐year chronological review of biosolids land application research in Colorado

The 1972 U.S. Clean Water Act set forth the generation of biosolids. In Colorado, biosolids land application research began in 1976 and continues today. Pastureland research suggested that sewage effluent could effectively be land applied to benefit aboveground plant growth and to polish water prior to reaching receiving waters. Forest wildfire-affected ecosystems can also benefit from biosolids applications; application rates of up to 80 Mg ha-1 can lead to greater plant establishment, soil microbial activity, and nutrient turnover and reduced nutrient and heavy metal concentrations in runoff below livestock and USEPA drinking water standards. Long-term (24-yr) observations in oil shale-mined lands showed that biosolids (up to 224 Mg ha-1 ) can have a positive effect on microbial-mediated nutrient cycling and, in turn, on aboveground plant community structure. Biosolids applications of up to 40 Mg ha-1 in high-elevation shrubland ecosystems, dominated by Mo-containing shale deposits, can aid in reducing imbalances between Mo and Cu in soils and plants; excessive plant Mo, when consumed by ruminants, can lead to molybdenosis. Biosolids and lime applications (both at 224 Mg ha-1 ) have been shown to improve long-term reclamation success on acid-generating, heavy metal-containing fluvial mine tailings. Thirty years of grazing land research, focused on soil and aboveground plant benefits, illustrate that soil health and plant productivity can be improved to the greatest extent at biosolids application rates close to 10 Mg ha-1 . Finally, 40 yr of dryland agroecosystem research (a) have helped identify biosolids N fertilizer equivalency (∼8kg N Mg-1 ) and thus dryland winter wheat application rates (e.g., 4.5-6.7 dry Mg ha-1 ); (b) have identified first-year mineralization rates of 25-32%; (c) dispute the "time bomb" theory by showing that plant metal uptake follows an exponential rise to a maximum; (d) showcase economic return to producers via increased wheat grain protein content; (e) suggest that biosolids-borne proteins and their degradation products are labile C and N sources; (f) have led to long-term tracking of micronutrients and heavy metals in soils and revealed that plants-soil concentrations will not lead to groundwater degradation and that plants are safe for human consumption; and (g) have shown that biosolids provide Zn, helping to overcome soil deficiencies and enhancing Zn biofortification in wheat grain. This latter point is important because ∼2 billion people globally suffer from Zn deficiencies. Forty-five years of research in Colorado have proven that biosolids can enhance environmental quality, improve soil health, and produce healthy food products.

Soil management and compost amendment are the main drivers of carbon sequestration in rainfed olive trees agroecosystems: An evaluation of chemical and biological markers

Traditional olive groves are considered at high risk of erosion and desertification due to low organic matter inputs and scarce vegetation cover coupled to highly intensity tillage, leading to a further decrease in soil organic carbon contents. In a context of climate change, carbon sequestration through waste management in the framework of a circular economy becomes of primary importance for rainfed Mediterranean agricultural soils. To unveil the mechanisms of carbon sequestration in those agroecosystems, we evaluated the effect of the application of two composts (olive waste “alperujo” and biosolid) at two different doses coupled to the sustainable soil management allowing spontaneous vegetation growing on the soil surface.With this aim, solid state nuclear magnetic resonance was used to trace the evolution of the chemical composition of compost-derived and soil-derived organic matter. Successively, the activity of soil microbial community after the compost addition was monitored by measuring two enzymatic activities (β-glucosidase and dehydrogenase) and soil CO2 respiration. Lastly, the adaptation of microbial communities was quantified using the genes encoding soil enzymes associated with C cycling -glucosidase and laccase-like multicopper oxidases. The results of this study show that biosolid compost has a higher potential for C storage at mid-term (24 to 30 months after first application) than alperujo compost, yielding up to 50% net C sequestration in the topsoil in addition to the compost-derived C applied. We attribute these results to biosolid compost chemical composition, closer to that of the native organic matter, which led to a less abrupt adaptation of soil microbial functioning (lower flushes of water soluble C, lower number of copies of genes encoding enzymatic activities) to the new C source, if compared to alperujo compost. The results encourage the reduction of soil perturbation and the use of organic amendments instead of mineral fertilizers to increase carbon storage and improve sustainability of olive groves in the Mediterranean agroecosystems.

Optimized design of a compost layer in a landfill biocover for CH4 oxidation

In this study, the mixture of two compost materials, including Yard Waste and Leaf Compost (YWLC) and Biosolids Compost (BSC) was optimized for methane (CH4) oxidation to be suitable for a field-scale landfill biocover. Laboratory column tests were conducted with CH4 and carbon dioxide (CO2) flowing through the column at 50:50 v:v to assess the CH4 oxidation in the vertical profile of the compost. The variation in CO2:CH4 ratio, indicating methanotrophic activity, was assessed during three column trials considering two different mixing ratios of 1:1 and 1:4 YWLC:BSC, moisture contents (MC) of 60%, 35%, and 40% ww, and the addition of a methanotroph-enriched compost extract. It was found that the main restricting factors for effective CH4 oxidation were high MC, Exopolymeric Substance (EPS) formation, and fine texture of the materials that limited oxygen (O2) diffusion into the biocover. Based on CH4 mass balance in the columns, the highest CH4 oxidation efficiency of 40% was observed in the column trial with the 1:4 mixing ratio of composts at a MC of 40% ww, with CH4 being oxidized throughout the entire height of the column. It can be concluded that this optimized design for YWLC and BSC mixture, removing a significant portion of the CH4 flowing through the landfill biocover, had the potential to be used in the real field conditions.

Biosolids increase phosphate adsorption of semi-arid Mediterranean soils

The impact of biosolid compost on the adsorption of orthophosphate (IP) to Mediterranean-type soils was studied. Eight soils were amended with a stable biosolid compost (ADSC) at 9:1 and 97:3 ratios (w/w). Four soils were amended with the dissolved organic matter (DOM) fraction of the ADSC at the amount added at the 9:1 mixture (810 mg C kg−1). Soils and their 9:1 soil‒ADSC mixtures were incubated for seven years. The maximum ADSC IP-adsorption capacity (SMAX, Langmuir model) at native pH (≈7.5) was 850 mg P kg−1. Mixing the ADSC with the soils increased their SMAX values by ca. 150 and 190 mg P kg−1 in the 9:1 and 97:3 mixtures, which exceeded additivity by 50% and 575%. The addition of DOM similarly increased the SMAX of three out of the four soils. Following the incubation, the soils' organic-C decreased by 34% and the ADSC-derived OC decreased by 60%. Still, the corresponding soil's and mixtures' average levels of labile IP either increased (by 60%) or remained steady (at ̴30% of total-P). Incubation increased the SMAX of three soils and five soil‒ADSC mixtures and decreased their binding affinity (k), trends which were also reflected in the quantity/intensity parameters. This study showed that amending semi-arid Mediterranean soils with stable biosolids, and their long-term oxidative co-stabilization is conducive to increase their IP binding capacity and bioavailability. Finally, the often similar effects of the compost and its DOM on IP adsorption merits further research regarding the role of cation (Ca+2) bridging in IP‒DOM‒solid phase interactions.

Methane oxidation in a landfill biowindow under wide seasonally fluctuating climatic conditions.

In the current study, a pilot biowindow was constructed in a closed cell of a Canadian Landfill, undergoing high seasonal fluctuations in the temperature from -30 in winter to 35 in summer. The biowindow was filled with biosolids compost amended with yard waste and leaf compost with the ratio of 4:1 as the substrate layer. Two years of monitoring of methane (CH4) oxidation in the biowindow led to remarkable expected observations including a thick, solid winter frost cover affecting gas exchange in winter and temperatures above 45 ℃ in the biowindow in late summer. A high influx compared to the reported values was observed into the biowindow with an average value of 1137 g.m-2.d-1, consisting of 64% of CH4 and 36% of carbon dioxide (CO2) in the landfill gas. The variations in the temperature and moisture content (MC) of the compost layer in addition to the influx fluctuations affected CH4 oxidation efficiency; however, a high average CH4 oxidation rate of 237 g.m-2.d-1 was obtained, with CH4 being mostly oxidized at top layers. The laboratory batch experiments verified that thermophilic methane-oxidizing bacteria (MOB) were active throughout the study period and oxidized CH4 with a higher rate than mesophilic MOB. The methanotrophic potential of the compost mixture showed an average value of 282 µmol.g-1.d-1 in the entire period of the study which is in the range of the highest reported maximum CH4 oxidation rates. The adopted compost mixture was suitable for CH4 oxidation if the MC was above 30%. The significance of MC variations on CH4 oxidation rate depended on the temperature range within the biowindow. At temperatures below 2 ℃, between 29 and 31℃, and above 45 ℃, MC was not a controlling factor for mesophilic CH4 oxidation.