Anaerobic Biodegradation Processes Research Articles

Conductive adsorbents enhance phenol removal from wastewater by direct interspecies electron transfer "DIET"-based anaerobic biodegradation process

This study examined the hybrid adsorption and anaerobic biodegradation processes of phenol by using activated carbon cloth (CC) to stimulate direct interspecies electron transfer (DIET). Phenol biodegradation was tested over three sequential runs using 100 mL lab-scale bioreactors and compared with two different types of CC and granular activated carbons (GAC). The addition of the carbon adsorbents to the bioreactors significantly accelerated the methane production rate. This high rate of methane production was also accompanied by the complete removal of phenol, and a high COD(s) removal rate of about 95%, compared to 43.68% and 48.65% in the control sets in the first and second runs, respectively. The enhancement of the phenol biodegradation is attributed to the synergy of the adsorption and biodegradation processes. An initial adsorption stage has contributed to a significant and rapid reduction of phenol, leading to a lower inhibition effect of phenol, followed by anaerobic biodegradation of the adsorbed phenol stimulated by the DIET process. Specifically, the optimal concentration for Single Weave carbon cloth (CCSW) of 1.6 g L−1 promoted both the DIET and the adsorption processes. Microbial community composition analysis revealed that CCSW facilitated the growth of syntrophic bacterial groups (Rikenellae, Syntrophorhabdaceae, Gracilibacteraceae, and DTU014), and archaea (Methanosaetaceae and Methanoregulaceae), previously reported as key players in the DIET processes to promote phenol degradation. To the best of our knowledge, this is the first work that demonstrates the contribution of CC to stimulate DIET mechanism of anaerobic biodegradation synergistically combined with adsorption process for enhanced phenol removal.

Anaerobic and microaerobic biodegradation of benzene: Effect of important intermediates

The effect of important intermediates on the anaerobic and microaerobic benzene biodegradation was investigated. An up-flow anaerobic/microaerobic sludge blanket reactor was operated at a hydraulic retention time (HRT) of 24 h and fed with water contaminated with benzene (∼4.2 mg L−1) and ethanol (1 g COD L−1). Initially, reactor operating parameters such as variation of applied flow rates, microaeration application points, and effluent recirculation were studied to optimize microaeration. Secondly, the interference of benzene degradation intermediates (phenol, benzoate, and toluene) was investigated. The addition of low concentrations of oxygen (0.5–2 mL air min−1) ensured high benzene removals (∼76–86 %), with the best obtained for a flow rate of 1 mL of air min−1, for which there was a d% removal increase compared to the anaerobic stage. Although the contact time between the air bubbles was short, the best application point was close to the feed. Effluent recirculation was necessary to maintain good mass transfer and high benzene removal efficiencies. The loss by stripping was considered negligible, even at the microaerobic stages, proving the biological removal of this compound. Finally, the intermediates added to the contaminated water reduced benzene removal, with benzoate being the compound that most negatively influenced the benzene removal process, even under microaerobic conditions. Therefore, it is a key intermediate in the benzene anaerobic and microaerobic biodegradation process.

An approach for restoration of the water quality with emphasis on the removal of organochlorine pesticides and eutrophic conditions in tropical rivers

This work deals with an approach for the water quality restoration with emphasis on the removal of organochlorine pesticides and eutrophic conditions in tropical rivers, causing influence on the management of the central-regional aqueduct, as a source of water supply for human consumption (4 million people) and industrial production in the states of Carabobo, Cojedes and Aragua, Venezuela, testing the phytoremediation techniques through Vetiveria zizanioides (VZ) species and coupled bioreactors, Sequencing Batch Reactor (SBR) followed by an Upflow Anaerobic Filter in Three Separate Stages (UAF-3SS). Five rivers are involved known as Chirgua, Paito Guacara, Ereigüe, and Tucutunemo, whose waters have been classified as hypereutrophic, and containing organochlorine pesticides (OCPs). As a sample, for Tucutunemo River, OCPs included to DDT (dichlorodiphenyltrichloroethane) and its isomers and DRINs (Aldrin, Endrin and Dieldrin) dissolved in water and sorbed on sediments, which were measured during the dry and rainy seasons in the period 2013 to 2016, in three monitoring stations distributed in a reach of 15 km. The results indicated that p.p′-DDT concentration dissolved in water was increased up to 10 times from rainy to dry seasons, indicating that a permanent use of it is being carried out by farmers in the agricultural activity development. Steady concentrations of the DTT isomers (e.g., p.p′-DDD and p.p′-DDE) and Aldrin isomers (e.g., Dieldrin) demonstrated that the anaerobic and aerobic biodegradation processes occurred along the river and between climatic seasons. At experimental scale, VZ hydroponic system developed over a period of 6 months for the removal of nutrients demonstrated moderately low to high removal efficiencies. With respect coupled bioreactors, each bioreactor has been experimentally tested, demonstrating satisfactory performance in Chemical Oxygen Demand (COD) removal from industrial wastewater containing recalcitrant and inhibitory substances (46%–98%), which was estimated in the influent ranging from 3500 to 5500 mg/L, evidencing that coupling of bioreactors might lead to a effluent COD complying with environmental regulations.

Metagenomic Analysis of Bacterial, Archaeal and Fungal Diversity in Two-Stage Anaerobic Biodegradation for Production of Hydrogen and Methane from Corn Steep Liquor.

The main purpose of this study was to identify the microbial communities (bacterial, archaeal and fungal) in a two-stage system of anaerobic bioreactors for the production of hydrogen and methane from the waste substrate-corn steep liquor. Wastes from the food industry are valuable resources with potential in biotechnological production because of their high organic matter contents. In addition, the production of hydrogen and methane, volatile fatty acids, reducing sugars and cellulose content was monitored. Two-stage anaerobic biodegradation processes were performed by microbial populations in the first hydrogen generating bioreactor (working volume of 3 dm3) and in the second methane-generating reactor (working volume of 15 dm3). Cumulative hydrogen yield reached 2000 cm3 or 670 cm3/L a day, while the methane production reached a maximum quantity of 3300 cm3 or 220 cm3/L a day. Microbial consortia in anaerobic digestion systems play an essential role for process optimization and biofuel production enhancement. The obtained results showed the possibility of conducting two separate processes-the hydrogenic (hydrolysis and acidogenesis) and methanogenic (acetogenesis and methanogenesis)-as two stages of anaerobic digestion to favor energy production under controlled conditions with corn steep liquor. The diversity of microorganisms as main participants in the processes in the bioreactors of the two-stage system was followed using metagenome sequencing and bioinformatics analysis. The obtained metagenomic data showed that the most abundant phylum in both bacterial communities was Firmicutes-58.61% and 36.49% in bioreactors 1 and 2, respectively. Phylum Actinobacteria were found in significant quantities (22.91%) in the microbial community in Bioreactor 1, whereas in Bioreactor 2, they were 2.1%. Bacteroidetes are present in both bioreactors. Phylum Euryarchaeota made up 0.4% of the contents in the first bioreactor and 11.4% in the second. As the dominant genera among methanogenic archaea are Methanothrix (8.03%) and Methanosarcina (3.39%), the main fungal representatives were Saccharomyces cerevisiae. New knowledge of anaerobic digestion mediated by novel microbial consortia could be widely used to convert different wastes to green energy.

Novel synergistic metabolic processes for phenanthrene biodegradation by a nitrate-reducing phenanthrene-degrading culture and an anammox culture

The synergistic metabolism by anammox cultures and nitrate-reducers for anaerobic PAH biodegradation is largely unknown, including whether anammox culture and which kind of anammox bacterium can perform nitrogen metabolism in the anaerobic PAH biodegradation processes, the inhibitory effect of PAH on anammox activity and nitrite on PAH-degrading nitrate-reducers activity, and the synergistic metabolic processes. Herein, an anammox culture that can eliminate nitrite accumulation and decrease inorganic carbon emission during anaerobic phenanthrene (a model of PAH in this study) biodegradation, the synergistic mechanism for phenanthrene biodegradation by a nitrate-reducer and such anammox culture, and the inhibition effect of phenanthrene on such anammox culture and nitrite on a phenanthrene-degrading nitrate-reducer were newly discussed. The results showed that nitrite largely accumulated during anaerobic phenanthrene biodegradation (nitrate accumulation is a common phenomenon for the biodegradation of refractory matter, including PAHs, by nitrate-reducers) by a nitrate-reducer, PheN2, which mineralizes phenanthrene to inorganic carbon, and nitrite was verified as an inhibiting factor for further biodegradation. Anaerobic phenanthrene biodegradation rates and nitrite concentrations (0–7 mM) appeared to have a negative linear correlation. The anammox culture that mainly contained Candidatus Kuenenia was newly found to efficiently reduce nitrite accumulation and inorganic carbon emissions and significantly promote biodegradation efficiency by ∼1.94-fold. Our results showed that phenanthrene absorbed in and on anammox cells had a more direct relationship with the inhibitory effect on anammox activity than phenanthrene in the environment, and 15.2 mg/gVSS phenanthrene absorbed in and on the cells (4 mM concentration in the culture) showed nearly complete inhibition of anammox culture in this study. In addition, few (less than 2% abundance) anammox bacteria were found to be enough for the removal of nitrite produced from anaerobic phenanthrene biodegradation. In an ideal world, co-pollutants of ammonia, nitrate, phenanthrene, and nitrite could be converted to nitrogen gas and biomass by the synergistic metabolism of anammox cultures and nitrate reducers. Our study reveals a new synergistic process that may exist in our environments for PAH elimination by an anammox culture and a nitrate-reducer, which provides a new strategy for the bioremediation of PAH-polluted anoxic zones.

Oriented bio-feeding control of the anaerobic biodegradation of ethinyl estradiol

Up to 95% of hormones are excreted into domestic wastewater with urine or feces, but their macromolecules are difficult to biodegrade. This project studies the treatment of Ethinyl Estradiol (EE2) in swine wastewater in an Upstream Solids Reactor (USR), and explores a new method for oriented bio-feeding to regulate the anaerobic biodegradation process. It was found that the metabolism of lactic acid and propionic acid was accompanied by changes in EE2 content, but lactic acid molecules were not readily bioavailable, so adding propionic acid was more suitable. However, controlling the pH to lower (4.73) and higher (8.73) values inhibited further fermentation of acetic acid and propionic acid, which was not favorable for the removal of EE2. This is simply due to the fact that propionic acid as a carbon source changes the preference of the microbes for consuming EE2. The order of the effect of addition of propionic acid on the removal of EE2 was as follows: P400>P800>P0>P200 (addition of propionic acid). The P400 removal efficiency increased from 60% to 85%. In the metabolism of EE2, after oxidation, hydrolysis, ketosis, hydroxylation and enzymatic action, dienoic acid and oleic acid were generated, and there was no secondary pollution from EE2 metabolites. In conclusion, feeding microorganisms with propionic acid can enhance the anaerobic biodegradation of EE2, providing a new strategy for the anaerobic biodegradation and bioremediation of refractory pollutants.

A coupled compressible two-phase flow with the biological dynamics modeling the anaerobic biodegradation process of waste in a landfill

In this article, we present and study a new coupled model combining the biological and the mechanical aspects describing respectively the process of the biogas production and the compressible two-phase leachate-biogas flow during the anaerobic biodegradation of organic matters in a landfill, which is considered a reactive porous medium. The model obtained is governed by a reaction-diffusion system for the bacterial activity coupled with a compressible two-phase flow system of a non-homogeneous porous medium. We carry out the analysis and the numerical approximation of the model within a variational framework. We propose a full discrete system based on a second-order BDF-time scheme and P1-conforming finite element and we derive an efficient algorithm for the coupled system. We perform some numerical simulations in 2D and 3D examples in agreement with the theoretical analysis.

Impact of electron scavenging during electric current generation from propionate by a Geobacter co-culture

Propionate accumulates and inhibits anaerobic biodegradation processes. Technologies such as bioelectrochemical systems (BES) are being developed to remove this volatile fatty acid and convert it into bioenergy. Geobacter metallireducens is an electrogenic bacterium capable of oxidizing propionate, but slowly and inefficiently. Here, G. metallireducens was submitted to adaptive laboratory evolution (ALE) to improve its propionate metabolism. The adapted G. metallireducens, which harbors 62 mutations, reduced Fe(III) 3.6 times faster than the wild type with propionate as substrate. During growth, the adapted strain generated H2 at a rate of 25.4 μM h−1. To determine if quick H2 removal could accelerate propionate oxidation further, the adapted G. metallireducens was co-cultivated with a H2-oxidizing autotrophic Geobacter sulfurreducens strain. With Fe(III) as the electron acceptor, the co-culture oxidized propionate 2.2 times faster than the adapted G. metallireducens pure culture. In a BES, the co-culture outperformed the pure culture and generated a maximal current density of 2.34 A m−2. The anode of the co-culture-driven BES was coated by a thick biofilm reaching 116 μM made of both Geobacter species uniformly distributed. These results demonstrate that the combination of ALE and co-cultivating is an efficient strategy to optimize the metabolism of G. metallireducens for propionate-driven bioprocesses.

Anaerobic biodegradation of phenol in wastewater treatment: achievements and limits

Anaerobic biodegradation of toxic compounds found in industrial wastewater is an attractive solution allowing the recovery of energy and resources but it is still challenging due to the low kinetics making the anaerobic process not competitive against the aerobic one. In this review, we summarise the present state of knowledge on the anaerobic biodegradation process for phenol, a typical target compound employed in toxicity studies on industrial wastewater treatment. The objective of this article is to provide an overview on the microbiological and technological aspects of anaerobic phenol degradation and on the research needs to fill the gaps still hindering the diffusion of the anaerobic process. The first part is focused on the microbiology and extensively presents and characterises phenol-degrading bacteria and biodegradation pathways. In the second part, dedicated to process feasibility, anaerobic and aerobic biodegradation kinetics are analysed and compared, and strategies to enhance process performance, i.e. advanced technologies, bioaugmentation, and biostimulation, are critically analysed and discussed. The final section provides a summary of the research needs. Literature data analysis shows the feasibility of anaerobic phenol biodegradation at laboratory and pilot scale, but there is still a consistent gap between achieved aerobic and anaerobic performance. This is why current research demand is mainly related to the development and optimisation of powerful technologies and effective operation strategies able to enhance the competitiveness of the anaerobic process. Research efforts are strongly justified because the anaerobic process is a step forward to a more sustainable approach in wastewater treatment.Key points• Review of phenol-degraders bacteria and biodegradation pathways.• Anaerobic phenol biodegradation kinetics for metabolic and co-metabolic processes.• Microbial and technological strategies to enhance process performance.

New Frontiers of Anaerobic Hydrocarbon Biodegradation in the Multi-Omics Era.

The accumulation of petroleum hydrocarbons in the environment substantially endangers terrestrial and aquatic ecosystems. Many microbial strains have been recognized to utilize aliphatic and aromatic hydrocarbons under aerobic conditions. Nevertheless, most of these pollutants are transferred by natural processes, including rain, into the underground anaerobic zones where their degradation is much more problematic. In oxic zones, anaerobic microenvironments can be formed as a consequence of the intensive respiratory activities of (facultative) aerobic microbes. Even though aerobic bioremediation has been well-characterized over the past few decades, ample research is yet to be done in the field of anaerobic hydrocarbon biodegradation. With the emergence of high-throughput techniques, known as omics (e.g., genomics and metagenomics), the individual biodegraders, hydrocarbon-degrading microbial communities and metabolic pathways, interactions can be described at a contaminated site. Omics approaches provide the opportunity to examine single microorganisms or microbial communities at the system level and elucidate the metabolic networks, interspecies interactions during hydrocarbon mineralization. Metatranscriptomics and metaproteomics, for example, can shed light on the active genes and proteins and functional importance of the less abundant species. Moreover, novel unculturable hydrocarbon-degrading strains and enzymes can be discovered and fit into the metabolic networks of the community. Our objective is to review the anaerobic hydrocarbon biodegradation processes, the most important hydrocarbon degraders and their diverse metabolic pathways, including the use of various terminal electron acceptors and various electron transfer processes. The review primarily focuses on the achievements obtained by the current high-throughput (multi-omics) techniques which opened new perspectives in understanding the processes at the system level including the metabolic routes of individual strains, metabolic/electric interaction of the members of microbial communities. Based on the multi-omics techniques, novel metabolic blocks can be designed and used for the construction of microbial strains/consortia for efficient removal of hydrocarbons in anaerobic zones.

Anaerobic biodegradation of phenanthrene by a newly isolated nitrate-dependent Achromobacter denitrificans strain PheN1 and exploration of the biotransformation processes by metabolite and genome analyses.

Polycyclic aromatic hydrocarbons (PAHs) are widespread and harmful contaminants and are more persistent under anaerobic conditions. The bioremediation of PAHs in anaerobic zones has been enhanced by treating the contamination with nitrate, which is thermodynamically favourable, cost-effective, and highly soluble. However, anaerobic PAHs biotransformation processes that employ nitrate as an electron acceptor have not been fully explored. In this study, we investigated the anaerobic biotransformation of PAHs by strain PheN1, a newly isolated phenanthrene-degrading denitrifier, using phenanthrene as a model compound. PheN1 is phylogenetically closely related to Achromobacter denitrificans and reduces nitrate to nitrite (not N2 ) during the anaerobic phenanthrene degradation process. Phenanthrene biotransformation processes were detected using gas chromatography-mass spectrometry and were further examined by reverse transcription-quantitative PCR and genome analyses. Carboxylation and methylation were both found to be the initial steps in the phenanthrene degradation process. Downstream biotransformation processed benzene compounds and cyclohexane derivatives. This study describes the isolation of an anaerobic phenanthrene-degrading bacterium along with the pure-culture evidence of phenanthrene biotransformation processes with nitrate as an electron acceptor. The findings in this study can improve our understanding of anaerobic PAHs biodegradation processes and guide PAHs bioremediation by adding nitrate to anaerobic environments.

Unfolding microbial community intelligence in aerobic and anaerobic biodegradation processes using metagenomics.

Environmental factors and available nutrients influence microbial communities, and with that, there exists a dynamic shift in community structure and hierarchy in wastewater treatment systems. Of the various factors, the availability and gradient of oxygen selectively enrich a typical microbial community and also form the community stratification which could be established through metagenomics studies. In recent years, metagenomics with various sets of bioinformatics tools has assisted in exploration and better insight into the organization and relation of the taxonomical and functional composition and associate physiological intelligence of the microbial communities. The microbial communities, under defined conditions acquire a typicalhierarchy with flexible butactivenetwork of themetabolicroute, which ensures the survival needs ofeverymember residing in that community and their abundance. This knowledge of community functional organization defines the rule in designing and improving biodegradation processes in case of both aerobic and anaerobic systems.

Global stabilizability of an anaerobic biodegradation process via piecewise constant feedback

SummaryWe consider a nonlinear model of an anaerobic digestion process with methane production. We propose a stabilizing control law involving piecewise constant feedback and study the asymptotic stability of the obtained closed‐loop system. An extremum seeking algorithm is applied to maximize the output. Numerical simulation results are also presented to illustrate the theoretical investigations.

Geochemistry of fluids discharged from mud volcanoes in SE Caspian Sea (Gorgan Plain, Iran)

ABSTRACT A geochemical study was carried out on gas, water and mud samples from four mud volcanoes in Gorgan Plain, SE Caspian Sea (Iran) in order to investigate fluid primary sources and secondary processes controlling fluid chemistry. The chemical composition of light alkanes and the isotopic feature of methane indicated an origin related to a thermogenic source. Gases discharged from Neftlijeh evidenced anaerobic biodegradation processes with addition of secondary microbial methane. Chemical composition of discharged waters revealed two main groups i) brine-type Na+–Cl− waters from Gharenyaregh and Neftlijeh mud volcanoes, which were marked by relatively high Na+/Cl−, B/Cl− and Li/Cl− ratios and low Ca2+/Cl−, Mg2+/Cl− and K+/Cl− ratios, ii) waters from Sofikam and Inche, characterized by relatively low Na+/Cl−, B/Cl− and Li/Cl− ratios and relatively high Ca2+/Cl−, Mg2+/Cl− and K+/Cl− ratios. The chemical and isotopic characteristics of the discharged waters suggest that evaporated Caspian seawater trapped in sediments is likely representing a reliable water source. The maximum formation depth at Gharenyaregh and Neftlijeh mud volcanoes were estimated at about 6 km depth whereas the generation depth of the rest was significantly shallower. Thus, the observed compositional differences can be related to the different depths of the fluid source feeding them.

Denitrifying Microbial Community Structure and bamA Gene Diversity of Phenol Degraders in Soil Contaminated from the Coking Process.

Phenolic compounds are the dominant pollutants in soils contaminated by the coking industry. Ring opening by the hydroxylase gene (bamA) is the key step in the benzoyl-CoA degradation pathway under anaerobic conditions, and a broad spectrum of microorganisms possesses this functional gene, including denitrifiers. The present study analyzed the community structure of denitrifying bacteria and the diversity of the bamA gene for mixed cultures enriched from soil collected at a coking industrial site and then grown under nitrate-reducing conditions on phenol or p-hydroxybenzoate (4HBA), a key intermediate product of anaerobic phenol degradation. Illumina sequencing of the 16S rRNA gene showed different bacterial compositions between the two cultures. The dominant phyla were Proteobacteria, Armatimonadetes, and Planctomycetes in the phenol culture and Proteobacteria and Bacteroidetes in the 4HBA culture. Phylogenetic analysis further demonstrated that bamA genes were associated with four clusters of bacteria, three of known bacteria and one of uncultured bacteria. The diversity of the bamA gene differed from that reported in anaerobic aromatic degradation cultures, suggesting that these enriched cultures may contain new strains unique to coking-contaminated soils. The present study further validates the potential application of this functional gene as a marker for anaerobic biodegradation processes in enrichment cultures from contaminated soil.

Numerical model of aerobic bioreactor landfill considering aerobic-anaerobic condition and bio-stable zone development.

Aeration by airflow technology is a reliable method to accelerate waste biodegradation and stabilization and hence shorten the aftercare period of a landfill. To simulate hydro-biochemical behaviors in this type of landfills, this study develops a model coupling multi-phase flow, multi-component transport and aerobic-anaerobic biodegradation using a computational fluid dynamics (CFD) method. The uniqueness of the model is that it can well describe the evolution of aerobic zone, anaerobic zone, and temperature during aeration and evaluate aeration efficiency considering aerobic and anaerobic biodegradation processes. After being verified using existing in situ and laboratory test results, the model is then employed to reveal the bio-stable zone development, aerobic biochemical reactions around vertical well (VW), and anaerobic reactions away from VW. With an increase in the initial organic matter content (0.1 to 0.4), the bio-stable zone expands at a decreasing speed but with all the horizontal ranges larger than 17 m after an intermittent aeration for 1000 days. When waste intrinsic permeability is equal or greater than 10-11 m2, aeration using a low pressure between 4 and 8 kPa is appropriate. The aeration efficiency would be underestimated if anaerobic biodegradation is neglected because products of anaerobic biodegradation would be oxidized more easily. A horizontal spacing of 17 m is suggested for aeration VWs with a vertical spacing of 10 m for screens. Since a lower aeration frequency can give greater aeration efficiency, a 20-day aeration/20-day leachate recirculation scenario is recommended considering the maximum temperature over a reasonable range. For wet landfills with low temperature, the proportion of aeration can be increased to 0.67 (20-day aeration/10-day leachate recirculation) or an even higher value.

Recent biotechnological advances in petroleum hydrocarbons degradation under cold climate conditions: A review

In recent years, there have been advances in bioremediation of pollutants with the goal of effective clean-up of environments in an eco-friendly and cost-effective approach. For contamination removal at cold climate sites, bioremediation approaches are appealing due to their potential to be more cost-effective and efficient than alternative, more energy intensive approaches. Recent studies showed both aerobic and anaerobic biodegradation processes are important at cold climate sites. Most of these works are focused on biostimulation and bioaugmentation involved in adding nutrients and hydrocarbon degraders at cold climate sites, but studies on other methods such as the use of biosurfactant, genetically engineered bacteria, cold-adapted enzymes and immobilization method are still limited. This review selectively provides information on bioremediation under aerobic and anaerobic conditions and recent biotechnological advances in bioremediation at cold climate sites. However, the limitations and challenges for petroleum hydrocarbons bioremediation in cold climate remain at large. Further research and field demonstrations are required to determine which method is more effective for biodegradation of petroleum contaminates under such conditions.

Evaluation of the effects of bio stabilised waste on soil in terms of heavy metal accumulation and leaching

This work evaluated and compared potential impacts related to the accumulation and/or release of heavy metals resulting from the application of different types of stabilized waste to soil. Namely, the following three types of flows were considered: waste produced by aerobic bio-stabilization of municipal solid waste at a Mechanical Biological Treatment (MBT) plant, and compost produced either from aerobic composting or from a combination of anaerobic and aerobic biodegradation processes. After a preliminary characterization of the materials (organic matter content, volatile solid, and heavy metals content), heavy metal accumulation in soil caused by possible long-term application of these organic materials was evaluated by implementing a discretized mass balance based on the total content of the heavy metals in each type of solid matrix investigated. In addition, results of percolation leaching tests performed on each type of material were presented and discussed. Results highlight that although the total content of heavy metals of the three types of materials differed considerably, with the MBT waste presenting the highest concentrations, the results of the leaching percolation tests were quite similar.

Investigating the leaching properties of MBT wastes and composts from aerobic/anaerobic processes

This work assessed and compared the leaching properties of two types of compost and stabilized waste from a mechanical-biological treatment (MBT) plant. The first type of compost and the MBT waste were produced by aerobic treatments, while the second type of compost was generated from a combination of anaerobic and aerobic biodegradation processes. Both static-batch leaching tests, carried out applying a single liquid to solid (L/S) ratio equal to 10 L kg-1, and dynamic column percolation tests, investigating constituents release as a function of different L/S ratios, were performed. The three materials were also characterized in order to investigate their biological stability degree, organic matter content, and metals total content. As expected, due to the differences in feed input waste or treatment conditions, the three types of samples showed different characteristics and leaching concentrations. However, the leaching behavior of the three types of treated materials presented similar trends of dissolved organic carbon (DOC) and metals (Cu, Ni, Pb, Zn) leaching as a function of the L/S ratio. A screening model proposed and developed for MBT waste in a previous study, which allows the description DOC release as a function of the L/S ratio, was applied and discussed. The comparison of model predictions with the experimental leaching data highlighted that for all three samples the screening model describes quite well the release trends of metals.

Global Asymptotic Stability of a Functional Differential Model with Time Delay of an Anaerobic Biodegradation Process

We study a nonlinear functional differential model of an anaerobicdigestion process of wastewater treatment with biogas production. Themodel equations of biomass include two different discrete time delays. Amathematical analysis of the model is completed including existence andlocal stability of nontrivial equilibrium points, existence and boundednessof the model solutions as well as global stabilizability towards an admissibleequilibrium point. We propose and apply a numerical extremum seekingalgorithm for maximizing the biogas flow rate in real time. Numerical simulation results are also included.ACM Computing Classification System (1998): D.2.6, G.1.10, J.2.