The influence of different temperature programmes on the bioremediation of polycyclic aromatic hydrocarbons (PAHs) in a coal-tar contaminated soil by in-vessel composting

Enhancement of microbial community dynamics and metabolism in compost through ammonifying cultures inoculation

The efficient use of livestock and poultry manure waste has become a global challenge, with microorganisms playing an important role. To investigate the impact of novel ammonifying microorganism cultures (NAMC) on microbial community dynamics and carbon and nitrogen metabolism, five treatments [5% (v/w) sterilized distilled water, Amm-1, Amm-2, Amm-3, and Amm-4] were applied to cow manure compost. Inoculation with NAMC improved the structure of bacterial and fungal communities, enriched the populations of the functional microorganisms, enhanced the role of specific microorganisms, and promoted the formation of tight modularity within the microbial network. Further functional predictions indicated a significant increase in both carbon metabolism (CMB) and nitrogen metabolism (NMB). During the thermophilic phase, inoculated NAMC treatments boosted carbon metabolism annotation by 10.55%-33.87% and nitrogen metabolism annotation by 26.69%-63.11. Structural equation modeling supported the NAMC-mediated enhancement of NMB and CMB. In conclusion, NAMC inoculation, particularly with Amm-4, enhanced the synergistic interaction between bacteria and fungi. This collaboration promoted enzymatic catabolic and synthetic processes, resultng in positive feedback loops with the endogenous microbial community. Understanding these mechanisms not only unravels how ammonifying microorganisms influence microbial communities but also paves the way for the development of the composting industry and global waste management practices.

Effects of different organic substrate compositions on the decontamination of aged PAH-polluted soils through outdoor co-composting

The effects of different organic substrate compositions on the efficiency of outdoor co-composting as a bioremediation technology for decontaminating soil polluted by polycyclic aromatic hydrocarbons (PAHs) were investigated. Four different substrate mixtures and two different aged PAH-contaminated soils were used in a semi-pilot-scale experiment that lasted nearly 700 days. The two soils (A and B) differed concerning both the initial concentrations of the Ʃ16 US EPA PAHs (5926 vs. 369 mg kg-1, respectively) and the type of predominant PAH group by molecular weight. The experiments revealed that while the composition of the organic substrate had an impact on the rate of PAH degradation, it did not significantly influence the final extent of PAH degradation. Notably, the organic substrate consisting of green waste and wood chips (GW) was found to facilitate the most rapid rate of PAH degradation (first-order rate constant k = 0.033 ± 0.000 d-1 with soil A over the initial 42 days of the experiment and k = 0.036 ± 0.000 d-1 with soil B over the initial 56 days). Despite the differences in organic substrate compositions and types of soil being treated, PAH degradation levels exceeded at least 95% in all the treatments after more than 680 days of co-composting. Regardless of the composition, the removal of low- and medium- molecular-weight (2-4 rings) PAHs was nearly complete by the end of the experiment. Furthermore, high-molecular-weight PAHs (5 rings and more) were significantly degraded during co-composting, with reductions ranging from 54% to 79% in soil A and from 59% to 68% in soil B. All composts were dominated by Proteobacteria, Firmicutes, and Actinobacteria, with significant differences in abundance between soils. Genera with PAH degradation potentials were detected in all samples. The results of a battery of toxicity tests showed that there was almost no toxicity associated with the final composts.

Effects of thermophilic bacteria inoculation on maturity, gaseous emission and bacterial community succession in hyperthermophilic composting

Hyperthermophilic composting, characterized by temperatures equal to or exceeding 75 °C, offers superior compost maturity and performance. Inoculation with thermophilic bacteria presents a viable approach to achieving hyperthermophilic composting. This study investigates the effects of inoculating thermophilic bacteria, isolated at different temperatures (50 °C, 60 °C, and 70 °C) into compost on maturity, gaseous emissions, and microbial community dynamics during co-composting. Results indicate that the thermophilic bacteria inoculation treatments exhibited peak temperature on Day 3, with the maximum temperature of 75 °C reached two days earlier than the control treatment. Furthermore, these treatments demonstrated increased bacterial richness and diversity, along with elevated relative abundances of Firmicutes and Proteobacteria. They also fostered mutualistic correlations among microbial species, enhancing network connectivity and complexity, thereby facilitating lignocellulose degradation. Specifically, inoculation with thermophilic bacteria at 60 °C increased the relative abundance of Thermobifida and unclassified-f-Thermomonosporaceae (Actinobacteriota), whereas Bacillus, a thermophilic bacterium, was enriched in the 70 °C inoculation treatment. Consequently, the thermophilic bacteria at 60 °C and 70 °C enhanced maturity by 36 %-50 % and reduced NH3 emissions by 1.08 %-27.50 % through the proliferation of thermophilic heterotrophic ammonia-oxidizing bacteria (Corynebacterium). Moreover, all inoculation treatments decreased CH4 emissions by 6 %-27 % through the enrichment of methanotrophic bacteria (Methylococcaceae) and reduced H2S, Me2S, and Me2SS emissions by 1 %-25 %, 47 %-63 %, and 15 %-53 %, respectively. However, the inoculation treatments led to increased N2O emissions through enhanced denitrification, as evidenced by the enrichment of Truepera and Pusillimonas. Overall, thermophilic bacteria inoculation promoted bacteria associated with compost maturity while attenuating the relationship between core bacteria and gaseous emissions during composting.

A review of the definition, influencing factors, and mechanisms of rapid composting of organic waste

Composting is a traditional method of treating organic waste. A growing number of studies have been focusing on accelerating the process to achieve "rapid composting." However, the specific definition and influencing factors of rapid composting remain unclear. Therefore, we aimed to gather more insight into the features of rapid composting by reviewing the literature concerning organic waste composting published in the Web of Science database in the past 5 years. We selected 1615 sample studies with "composting" as the subject word and analyzed the effective composting time stated in each study. We defined rapid composting within 15 days using the median test and quartile method. Based on this definition, we summarized the influencing factors of "rapid composting," namely materials, reactors, temperature, and microorganisms. Finally, we summarized two mechanisms related to humus formation during organic waste rapid composting: high temperature-promoting maturation and microbial driving mechanisms. This literature review compiled useful references to help promote the development of rapid composting technology and related equipment.

Exploring the bioremediation capability of petroleum-contaminated soils for enhanced environmental sustainability and minimization of ecotoxicological concerns

The bioremediation of soils contaminated with petroleum hydrocarbons (PHCs) has emerged as a promising approach, with its effectiveness contingent upon various types of PHCs, i.e., crude oil, diesel, gasoline, and other petroleum products. Strategies like genetically modified microorganisms, nanotechnology, and bioaugmentation hold potential for enhancing remediation of polycyclic aromatic hydrocarbon (PAH) contamination. The effectiveness of bioremediation relies on factors such as metabolite toxicity, microbial competition, and environmental conditions. Aerobic degradation involves enzymatic oxidative reactions, while bacterial anaerobic degradation employs reductive reactions with alternative electron acceptors. Algae employ monooxygenase and dioxygenase enzymes, breaking down PAHs through biodegradation and bioaccumulation, yielding hydroxylated and dihydroxylated intermediates. Fungi contribute via mycoremediation, using co-metabolism and monooxygenase enzymes to produce CO2 and oxidized products. Ligninolytic fungi transform PAHs into water-soluble compounds, while non-ligninolytic fungi oxidize PAHs into arene oxides and phenols. Certain fungi produce biosurfactants enhancing degradation of less soluble, high molecular-weight PAHs. Successful bioremediation offers sustainable solutions to mitigate petroleum spills and environmental impacts. Monitoring and assessing strategy effectiveness are vital for optimizing biodegradation in petroleum-contaminated soils. This review presents insights and challenges in bioremediation, focusing on arable land safety and ecotoxicological concerns.

Mechanisms and effects of novel ammonifying microorganisms on nitrogen ammonification in cow manure waste composting

It is essential to reduce nitrogen losses and to improve nitrogen conversion during organic waste composting because of environmental protection and sustainable development. To reveal newly domesticated ammonifying microorganisms (AM) cultures on the ammonification and nitrogen conversion during the composting, the screened microbial agents were inoculated at 5 % concentration (in weight basis) into cow manure compost under five different treatments: sterilized distilled water (Control), Amm-1 (mesophilic fungus-F1), Amm-2 (mesophilic bacterium-Z1), Amm-3 (thermotolerant bacterium-Z2), and Amm-4 (consortium: F1, Z1, and Z2), and composted for 42 days. Compared to control, AM inoculation prolonged the thermophilic phases to 9-19 days, increased the content of NH4+-N to 1.60-1.96 g/kg in the thermophilic phase, reduced N2O and NH3 emissions by 22.85-61.13 % and 8.45-23.29 %, increased total Kjeldahl nitrogen, and improved cell count and viability by 12.09-71.33 % and 66.71-72.91 %. AM was significantly associated with different nitrogen and microbial compositions. The structural equation model (SEM) reveals NH4+-N is the preferable nitrogen for the majority of bacterial and fungal growth and that AM is closely associated with the conversion between NH3 and NH4+-N. Among the treatments, inoculation with Amm-4 was more effective, as it significantly enhanced the driving effect of the critical microbial composition on nitrogen conversion and accelerated nitrogen ammonification and sequestration. This study provided new concepts for the dynamics of microbial in the ammonification process of new AM bacterial agents in cow manure compost, and an understanding of the ecological mechanism underlying the ammonification process and its contribution to nitrogen (N) cycling from the perspective of microbial communities.

Advanced remediation of pyrene contaminated soil by double dielectric barrier discharge (DDBD) plasma and subsequent composting process

Due to increasing industrialization, soils are increasingly contaminated by polycyclic aromatics such as pyrene and need gentle treatment to keep the soil functioning. This study applied a double dielectric barrier discharge (DDBD) plasma reactor and composting reactor to remediate pyrene-contaminated soil. The effect of peak-to-peak applied voltages on the remediation efficiency of pyrene was investigated. The experimental results illustrate that pyrene remediation efficiency increased from 43% to 85% when the peak-to-peak applied voltage was increased from 28.0 to 35.8 kV. When using the combined method of DDBD and composting, 90-99% of pyrene could be removed, while a reduction of 76.5% was achieved using only composting, indicating the superiority of the combined system. Moreover, the authors could demonstrate that DDBD plasma treatment improves humification in the post-composting process as humic acid (HA) concentrations increased to 7.7 mg/g with an applied voltage of 35.8 kV; when composting was used as the sole treatment method, only 3.4 mg/g HA were produced. The microbial activity in the DDBD plasma-treated soil peaked on the 5th day and had a 2nd rise afterwards. The authors demonstrate that the combined technology of DDBD plasma and composting is a promising method for soil remediation with persistent organic pollutants. This treatment approach improves pollutant degradation efficiency and facilitates further humification, potentially restoring the function of contaminated soil. This approach could be considered a cost-effective and green strategy for soil remediation with persistent organic pollutants.

Thermally enhanced bioremediation: A review of the fundamentals and applications in soil and groundwater remediation

Thermally enhanced bioremediation (TEB), a new concept proposed in recent years, explores the combination of thermal treatment and bioremediation to address the challenges of the low efficiency and long duration of bioremediation. This study presented a comprehensive review regarding the fundamentals of TEB and its applications in soil and groundwater remediation. The temperature effects on the bioremediation of contaminants were systematically reviewed. The thermal effects on the physical, chemical and biological characteristics of soil, and the corresponding changes of contaminants bioavailability and microbial metabolic activities were summarized. Specifically, the increase in temperature within a suitable range can proliferate enzymes enrichment, extracellular polysaccharides and biosurfactants production, and further enhancing bioremediation. Furthermore, a systematic evaluation of TEB applications by utilizing traditional in situ heating technologies, as well as renewable energy (e.g., stored aquifer thermal energy and solar energy), was provided. Additionally, TEB has been applied as a biological polishing technology post thermal treatment, which can be a cost-effective method to address the contaminants rebounds in groundwater remediation. However, there are still various challenges to be addressed in TEB, and future research perspectives to further improve the basic understanding and applications of TEB for the remediation of contaminated soil and groundwater are presented.

Assessment of the use of compost stability as an indicator of alkane and aromatic hydrocarbon degrader abundance in green waste composting materials and finished composts for soil bioremediation application

Green waste composting materials and finished composts were collected from different commercial ex situ composting sites all treating source segregated green waste feedstocks. Stability of each material was determined using the standard ORG0020 dynamic respiration test. To assess whether stability could be used as an indicator for the potential suitability of green waste composting materials and finished composts as amendments for soil bioremediation, comparison was made with alkane and aromatic hydrocarbon degrader abundance determined using a quantitative PCR (qPCR) approach. Specifically, primers targeting alkB and, polyaromatic hydrocarbon ring-hydroxylating dioxygenases genes (PAH-RHD) of Gram positive (GP) and Gram negative (GN) populations were used for qPCR analysis. The results showed no direct correction between compost stability and gene abundance. Further, increase in alkB gene abundance was not linked to PAH-RHD gene abundance. The results support the use of qPCR as a tool for screening organic amendments on a site by site basis for soil bioremediation treatment.

Decreased enzyme activities, ammonification rate and ammonifiers contribute to higher nitrogen retention in hyperthermophilic pretreatment composting

Hyperthermophilic pretreatment composting (HPC) is superior to traditional composting (TC) with shortened maturity period and increased nitrogen (N) retention. However, the mechanism associated with N retention in HPC remains unclear. In this study, we compared the impact of HPC and TC on N retention, and found the proportion of N retained in the final compost was 83.3% and 67.2% for HPC and TC, respectively. Decreased ammonification rate, urease and protease activities together with an elevated temperature were found in HPC. Illumina amplicon sequencing showed that HPC caused a major decline in microbial community richness and diversity in the thermophilic phase. Notably, bacterial (Pseudomonas and Bacillus) and fungal ammonifiers (Acremonium, Alternaria and Penicillium) decreased remarkably in HPC during this phase. Changes in the microbial community could be related to unfavorable modifications of environment from HPC, and which resulted in decreased ammonification and enzyme activities and improved N retention.

The distinctive microbial community improves composting efficiency in a full-scale hyperthermophilic composting plant

The application of conventional thermophilic composting (TC) is limited by poor efficiency. Newly-developed hyperthermophilic composting (HTC) is expected to overcome this shortcoming. However, the characterization of microbial communities associated with HTC remains unclear. Here, we compared the performance of HTC and TC in a full-scale sludge composting plant, and found that HTC running at the hyperthermophilic and thermophilic phases for 21 days, led to higher composting efficiency and techno-economic advantages over TC. Results of high-throughput sequencing showed drastic changes in the microbial community during HTC. Thermaceae (35.5-41.7%) was the predominant family in the hyperthermophilic phase, while the thermophilic phase was dominated by both Thermaceae (28.0-53.3%) and Thermoactinomycetaceae (29.9-36.1%). The change of microbial community could be the cause of continuous high temperature in HTC, and thus improve composting efficiency by accelerating the maturation process. This work has provided theoretical and practical guidance for managing sewage sludge by HTC.

Polycyclic aromatic hydrocarbons degradation and microbial community shifts during co-composting of creosote-treated wood

The feasibility of decontaminating creosote-treated wood (CTW) by co-composting with agricultural wastes was investigated using two bulking agents, grass cuttings (GC) and broiler litter (BL), each employed at a 1:1 ratio with the matrix. The initial concentration of total polycyclic aromatic hydrocarbons (PAHs) in CTW (26,500 mg kg(-1)) was reduced to 3 and 19% after 240 d in GC and BL compost, respectively. PAH degradation exceeded the predicted bioaccesible threshold, estimated through sequential supercritical CO2 extraction, together with significant detoxification, assessed by contact tests using Vibrio fisheri and Hordeum vulgare. GC composting was characterized by high microbial biomass growth in the early phases, as suggested by phospholipid fatty acid analyses. Based on the 454-pyrosequencing results, fungi (mostly Saccharomycetales) constituted an important portion of the microbial community, and bacteria were characterized by rapid shifts (from Firmicutes (Bacilli) and Actinobacteria to Proteobacteria). However, during BL composting, larger amounts of prokaryotic and eukaryotic PLFA markers were observed during the cooling and maturation phases, which were dominated by Proteobacteria and fungi belonging to the Ascomycota and those putatively related to the Glomeromycota. This work reports the first in-depth analysis of the chemical and microbiological processes that occur during the co-composting of a PAH-contaminated matrix.

Activity of Arylsulphatase in Soil Contaminated with Polycyclic Aromatic Hydrocarbons

An experiment has been performed to determine the activity of arylsulphatase in soil submitted to pressure of four polycyclic aromatic hydrocarbons: naphthalene, phenanthrene, anthracene, and pyrene, in the amount of: 0, 1,000, 2,000, and 4,000 mg kg^-1 dm of soil. Soil samples were also applied some organic substances, such as: cellulose, sucrose, and compost, in the amount of 0 and 9 g kg^-1 dm of soil. The experiment was run under laboratory conditions. It was established on soil which belonged to loamy sand. The soil resistance (RS) and resilience (RL) indices were computed. It has been discovered that the PAHs stimulated arylsulphatase activity, with anthracene raising the activity of the enzyme to the highest degree. The activity of arysulphatase depended significantly on the dose of a PAH, duration of pressure, and type of organic substances added to soil. The highest resistance (RS) was determined in soil exposed to phenanthrene, and the lowest one-in soil polluted with pyrene. Low values of the RL index prove that polycyclic aromatic hydrocarbons cause lasting disorders in the activity of arylsulphatase.

Effect of composting on the removal of semivolatile organic chemicals (SVOCs) from sewage sludge

In order to investigate the occurrence and removal of semivolatile organic chemicals (SVOCs) in the compost of sewage sludge, three different composting treatments, including manual turned compost (MTC), intermittent aerated compost (IAC), and naturally aerated compost (NAC) were conducted. Thirty SVOCs in composts were Soxhlet-extracted and analyzed by GC/MS. After 56 days of composting, the total concentrations of 16 polycyclic aromatic hydrocarbons (∑PAHs) ranged from 0.55 to 8.20 mg kg(-1) dry weight, decreasing in order of IAC>MTC>NAC. The total concentrations of six phthalic acid esters (∑PAEs), five chlorobenzenes or three nitroaromatic compounds were less than 5.0 mg kg(-1). Compared with the initial concentrations in sewage sludge, a significant reduction of ∑PAHs, ∑PAEs and chlorobenzenes was observed. The removal rates of ∑PAHs and ∑PAEs ranged from 54.6% to 75.9% and from 58.3% to 90.6%, respectively. Compared with different composting processes, MTC showed the highest potential for removal of SVOCs.

Remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soil through composting with fresh organic wastes

INTRODUCTION

Composting may enhance bioremediation of PAH-contaminated soils by providing organic substrates that stimulate the growth of potential microbial degraders. However, the influence of added organic matter (OM) together with the microbial activities on the dissipation of PAHs has not yet been fully assessed.

MATERIALS AND METHODS

An in-vessel composting-bioremediation experiment of a contaminated soil amended with fresh wastes was carried out. Four different experimental conditions were tested in triplicate during 60 days using laboratory-scale reactors: treatment S (100% soil), W (100% wastes), SW (soil/waste mixture), and SWB (soil/waste mixture with inoculation of degrading microorganisms).

RESULTS AND DISCUSSION

A dry mass loss of 35 ± 5% was observed in treatments with organic wastes during composting in all the treatments except treatment S. The dissipation of the 16 USEPA-listed PAHs was largely enhanced from no significant change to 50.5 ± 14.8% (for SW)/63.7 ± 10.0% (for SWB). More obvious dissipation was observed when fresh wastes were added at the beginning of composting to the contaminated soil, without significant difference between the inoculated and non-inoculated treatments. Phospholipid fatty acid (PLFA) profiling showed that fungi and G-bacteria dominated at the beginning of experiment and were probably involved in PAH dissipation. Subsequently, greater relative abundances of G + bacteria were observed as PAH dissipation slowed down.

CONCLUSIONS

The results suggest that improving the composting process with optimal organic compositions may be a feasible remediation strategy in PAH-contaminated soils through stimulation of active microbial populations.

Response of compost maturity and microbial community composition to pentachlorophenol (PCP)-contaminated soil during composting

Two composting piles were prepared by adding to a mixture of rice straw, vegetables and bran: (i) raw soil free from pentachlorophenol (PCP) contamination (pile A) and (ii) PCP-contaminated soil (pile B). It was shown by the results that compost maturity characterized by water soluble carbon (WSC), TOC/TN ratio, germination index (GI) and dehydrogenase activity (DA) was significantly affected by PCP exposure, which resulted in an inferior degree of maturity for pile B. DGGE analysis revealed an inhibited effect of PCP on compost microbial abundance. The bacteria community shifts were mainly consistent with composting factors such as temperature, pH, moisture content and substrates. By contrast, the fungal communities were more sensitive to PCP contamination due to the significant correlation between fungal community shifts and PCP removal. Therefore, the different microbial community compositions for properly evaluating the degree of maturity and PCP contamination were suggested.

Energy from Waste: Reuse of Compost Heat as a Source of Renewable Energy

An in-vessel tunnel composting facility in Scotland was used to investigate the potential for collection and reuse of compost heat as a source of renewable energy. The amount of energy offered by the compost was calculated and seasonal variations analysed. A heat exchanger was designed in order to collect and transfer the heat. This allowed heated water of C to be obtained. The temperature could be further increased to above C by passing it through multiple tunnels in series. Estimated costs for installing and running the system were calculated. In order to analyse these costs alternative solar thermal and ground source heat pump systems were also designed. The levels of supply and economic performance were then compared. A capital cost of 11,662 and operating cost of 1,039 per year were estimated, resulting in a cost of 0.50 per kWh for domestic water and 0.10 per kWh for spatial heat. Using the heat of the compost was found to provide the most reliable level of supply at a similar price to its rivals.

Remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic micropollutants which are resistant to environmental degradation due to their highly hydrophobic nature. Concerns over their adverse health effects have resulted in extensive studies on the remediation of soils contaminated with PAHs. This paper aims to provide a review of the remediation technologies specifically for PAH-contaminated soils. The technologies discussed here include solvent extraction, bioremediation, phytoremediation, chemical oxidation, photocatalytic degradation, electrokinetic remediation, thermal treatment and integrated remediation technologies. For each of these, the theories are discussed in conjunction with comparative evaluation of studies reported in the specialised literature.

Simulation of biopile processes using a hydraulics approach

Biopiles are a common treatment for the ex-situ remediation of contaminated soil. Much research has been carried out on understanding and modelling microbial degradation, but hitherto no study has attempted to model the effect on a biopile of its ambient surroundings. A hydraulics-based approach to simulating a biopile in the context of its ambient surroundings is presented, taking into account processes within the pile, external conditions of wind and temperature, the location of aeration pipes and the venting pressure, and considering the distribution of treatment over various regions within the pile. A system of add-ons to a commercial CFD code has been developed, and various example simulations have been carried out to examine the potential of the hydraulics approach for practical application. Results show that the model produces reasonable results, with biodegradation related to the temperature within the pile and the temperature in turn related to wind speed and aeration details. A number of counter-intuitive results are described, indicating that simulation of the type carried out will produce valuable insight into the practical design of biopiling systems. The simulation system also allows the total environmental footprint of biopiling to be considered, examining not just degradation of contaminant but also its removal via volatilization and the energy used in heating air for venting.

Biodegradation of phenanthrene and pyrene in compost-amended soil

This study investigated the biodegradation of the polycyclic aromatic hydrocarbons (PAHs) phenanthrene and pyrene in compost and compost-amended soil. The degradation rates of the two PAHs were phenanthrene>pyrene. The degradation of PAH was enhanced when the two PAHs were present simultaneously in the soil. The addition of either of the two types of compost (straw and animal manure) individually enhanced PAH degradation. Compost samples were separated into fractions with various particle size ranges, which spanned 2-50 microm, 50-105 microm, 105-500 microm, and 500-2000 microm. We observed that the compost fractions with smaller particle sizes demonstrated higher PAH degradation rates. However, when the different compost fractions were added to soil, compost particle size had no significant effect on the rate of PAH degradation. Of the micro-organisms isolated from the soil-compost mixtures, strains S1, S2, and S8, which were identified as Arthrobacter nicotianae, Pseudomonas fluorescens, and Bordetella Petrii, respectively, demonstrated the best degradation ability.

Characterization of water-extractable organic matter during the biostabilization of municipal solid waste

For the purpose of characterizing the evolution of water-extractable organic matter (WEOM) during the biostabilization of municipal solid waste (MSW) and investigating the correlation between biostability and WEOM characteristics, this study conducted 100-day investigation on biostabilization of MSW and applied various analytical approaches to characterize WEOM. The results showed that the respirometric activity of MSW was reduced by 93% to 10.7 mg kg(-1), and the dissolved organic carbon concentration of WEOM kept steady at around 4.0 g kg(-1) after day 44, when the MSW was considered to be stabilized. Moreover, the aromaticity of WEOM significantly increased and the high-molecular weight fraction became the main part of WEOM. Being highly related to the biostability of MSW, the excitation-emission matrix spectra indicated the stability by the fluorescence regional integration technique either by the presence of specific Ex/Em maxima (with wavelength pair of approximately 288/455) or by the rapid increase of normalized excitation-emission area volumes with respect to the humic substances.

Biodegradation of phthalate esters in compost-amended soil

In this study, we investigated the biodegradation of the phthalate acid esters (PAEs) di-n-butyl phthalate (DBP) and di-(2-ethyl hexyl) phthalate (DEHP) in compost and compost-amended soil. DBP (50 mg kg(-1)) and DEHP (50 mg kg(-1)) were added to the two types of compost (straw and animal manure) and subsequently added to the soil; they were tested as a single compound and in combination. Optimal PAE degradation in soil was at pH 7 and 30 degrees C. The degradation of PAE was enhanced when DBP and DEHP were simultaneously present in the soil. The addition of either of the two types of compost individually also improved the rate of PAE degradation. Compost samples were separated into fractions with various particle size ranges, which spanned from 0.1-0.45 to 500-2000 microm. We observed that the compost fractions with smaller particle sizes demonstrated higher PAE degradation rates. When the different compost fractions were added to soil, however, compost particle size had no significant effect on the rate of PAE degradation.

Microbial community dynamics during composting of sewage sludge and straw studied through phospholipid and neutral lipid analysis

The composting process involves a succession of different communities of microorganisms that decompose the initial material, transforming it into a stable final product. In this work, the levels of phospholipid fatty acid (PLFA), neutral lipid fatty acid (NLFA) and sterol were monitored in compost versus time, as indicators of the activity of various microorganisms (Gram-positive or Gram-negative bacteria, fungi, etc.). During composting, the PLFA and NLFA from Gram-negative bacteria and eukaryotes (2-OH 10; 3-OH 12; 2-OH 14; 13:0; 16:1; 18:1 trans) as well as some sterols of plant origin (e.g. monostearin sterols) decreased until the end of composting. In contrast, the branched fatty acids with iso- and anteiso-forms (i-15:0; a-15:0; i-16; i-17) increased mainly in the thermophilic phase, but decreased right after. The PLFA 18:2 (6; 9), which is used as an index of the occurrence of some fungi, rose strongly at the beginning of composting, but fell after peak heating. In contrast, the other main sterol indicative of fungi, ergosterol, decreased at the beginning of the thermophilic phase, but increased strongly by the end of composting. Accordingly, cluster and PCA analysis separated the PLFA of Gram-negative bacteria and eukaryotic cells from those of Gram-positive bacteria and long-chain fatty acids. The fungal PLFA considered, 18:2 (9, 12), was clustered more closely to iso- and anteiso-branched PLFAs. Stigmasterol, squalene and cholesterol occurred in the lower right part of the loading plot and were clustered more closely to iso-, anteiso-branched PLFAs and 18:2 w 6,9 suggesting their relationship to microbial activities. We also observed the tendency of resistance of fatty acid PLFAs and NLFAs of long chain (19:0 (cis-9); 20:0) and some recalcitrant sterols, e.g. sitosterol, at the end of composting. The presence of high levels of the latter in the final stage indicates their contribution to the structural stability of organic matter fractions. These recalcitrant components were more clustered and occurred in the lower right part of the loading plot.

Bioremediation of contaminated mixtures of desert mining soil and sawdust with fuel oil by aerated in-vessel composting in the Atacama Region (Chile)

Since early 1900s, with the beginning of mining operations and especially in the last decade, small, although repetitive spills of fuel oil had occurred frequently in the Chilean mining desert industry during reparation and maintenance of machinery, as well as casual accidents. Normally, soils and sawdust had been used as cheap readily available sorbent materials of spills of fuel oil, consisting of complex mixtures of aliphatic and aromatic hydrocarbons. Chilean legislation considers these fuel oil contaminated mixtures of soil and sawdust as hazardous wastes, and thus they must be contained. It remains unknown whether it would be feasible to clean-up Chilean desert soils with high salinity and metal content, historically polluted with different commercial fuel oil, and contained during years. Thus, this study evaluated the feasibility of aerated in-vessel composting at a laboratory scale as a bioremediation technology to clean-up contaminated desert mining soils (fuel concentration>50,000 mg kg(-1)) and sawdust (fuel concentration>225,000 mg kg(-1)) in the Atacama Region. The composting reactors were operated using five soil to sawdust ratios (S:SD, 1:0, 3:1, 1:1, 1:3, 0:1, on a dry weight basis) under mesophilic temperatures (30-40 degrees C), constant moisture content (MC, 50%) and continuous aeration (16 l min(-1)) during 56 days. Fuel oil concentration and physico-chemical changes in the composting reactors were monitored following standard procedures. The highest (59%) and the lowest (35%) contaminant removals were observed in the contaminated sawdust and contaminated soil reactors after 56 days of treatment, respectively. The S:SD ratio, time of treatment and interaction between both factors had a significant effect (p<0.050) on the contaminant removal. The results of this research indicate that bioremediation of an aged contaminated mixture of desert mining soil and sawdust with fuel oil is feasible. This study recommends a S:SD ratio 1:3 and a correct nutrient balance in order to achieve a maximum overall hydrocarbon removal of fuel oil in the weathered and aged contaminated wastes.