Preliminary screening of co-substrates for bioremediation of pyrene-contaminated soil through composting

The feasibility of using different organic amendments of different origin and properties in the bioremediation of pyrene-contaminated soil by means of composting has been tested. The selected pyrene concentration was 1 g of pyrene per kg of dry soil. The organic amendments used include: raw organic fraction of municipal solid wastes (OFMSW), industrial compost from OFMSW composting (COFMSW), compost derived from home composting of OFMSW (HCOFMSW), anaerobically digested sludge (ADS), non-digested activated sludge (NDS) and centrifuged non-digested activated sludge (CNDS). The degradation rate was related to the amendment properties that directly affected the composting process. Raw OFMSW was not capable to enhance pyrene degradation in comparison to control, but stable HCOFMSW exhibited the highest removal rate (69%). The amendments stability and the temperatures reached as a consequence influenced the process, and thermophilic temperatures showed an inhibition effect on the microbial activity related to pyrene degradation. Some of the tested wastes need to be further investigated to find inexpensive organic amendments for soil bioremediation

Optimization and enhancement of soil bioremediation by composting using the experimental design technique

The objective of this study was the application of the experimental design technique to optimize the conditions for the bioremediation of contaminated soil by means of composting. A low-cost material such as compost from the Organic Fraction of Municipal Solid Waste as amendment and pyrene as model pollutant were used. The effect of three factors was considered: pollutant concentration (0.1-2 g/kg), soil:compost mixing ratio (1:0.5-1:2 w/w) and compost stability measured as respiration index (0.78, 2.69 and 4.52 mg O2 g⁻¹ Organic Matter h⁻¹). Stable compost permitted to achieve an almost complete degradation of pyrene in a short time (10 days). Results indicated that compost stability is a key parameter to optimize PAHs biodegradation. A factor analysis indicated that the optimal conditions for bioremediation after 10, 20 and 30 days of process were (1.4, 0.78, 1:1.4), (1.4, 2.18. 1:1.3) and (1.3, 2.18, 1:1.3) for concentration (g/kg), compost stability (mg O₂ g−1 Organic Matter h−1) and soil:compost mixing ratio, respectively

Effects of compost stability and contaminant concentration on the bioremediation of PAHs contaminated soil through composting

The objective of this study was to investigate the effect of two factors: the stability degree (0.37-4.55 mg O₂ g⁻¹ Organic Matter h⁻¹) of different composts derived from the organic fraction of municipal solid wastes and the concentration of a complex mixture of PAHs including flourene, phenanthrene, anthracene, flouranthene, pyrene and benzo(a)anthracene in the bioremediation of soil. The two factors were systematically studied applying central composite design methodology. The obtained results demonstrated that compost stability degree was particularly important during the first stage of the process. Stable composts enhanced the levels of degradation in soil-compost mixture and a degradation rate of 92% was achieved in this period, but only 40% was degraded with the least stable compost. The PAHs concentration was also important during the process, since the degradation rates increased with the increase in the PAHs concentration. Moreover, all the individual PAHs demonstrated a notable decrease in their concentrations after the incubation period, but pyrene was degraded to lower levels in some treatments compared to others PAHs

Anaerobic degradation of PAHs in soil : impacts of concentration and amendment stability on the PAHs degradation and biogas production

In this study, the bioremediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil under strict anaerobic-methanogenic conditions was systematically studied applying the central composite design approach. The effect of PAHs concentration and the stability of the compost as an organic amendment for anaerobic digestion were examined. In all assays, the used methanogenic consortium was able to degrade the PAHs although some inhibition effects were observed during the initial stage in some cases. The degradation rates varied between 31.4 and 90.6% during 50 days incubation period. The study demonstrated that the PAHs concentration influences the degradation rate where more degradation was observed by increasing the concentration of PAHs. However, the biogas production as a result of the digestion process was more influenced by the compost stability which also has its effect on the degradation rates as more degradation occurred with more stable compost, but more biogas was produced with less stable compost, which indicates that the biogas is mainly produced by the anaerobic digestion of the amended compost. Finally, it seems that compost addition is required to improve the process in some cases but in other circumstances it does not greatly improve the bioremediation of PAHs

Performance of different systems for the composting of the source-selected organic fraction of municipal solid waste

Performance of three pile composting systems at field-scale were studied and compared in the composting of source-selected organic fraction of municipal solid waste (OFMSW): turned pile (TP), static forced-aerated pile (SAP) and turned forced-aerated pile (TAP). Routine parameters such as temperature, oxygen content, moisture and porosity were monitored. Temperature was found to be higher in turned systems whereas oxygen content was higher in forced-aerated systems. Although the initial air-filled porosity (AFP) for all mixtures was high, around 70%, the material tended to compact in the static system. A high degree of heterogeneity was found in the non-turned system. Extent of biodegradation was measured by respiration techniques (from 5.3 to 1.1 mg [O2] g [organic matter {OM}]−1 h−1 in TP and from 4.7 to 0.7 mg [O2] g [OM]−1 h−1 in turned forced-aerated pile). The non-turned compost showed a low level of stability (3.6 mg [O2] g [OM]−1 h−1) and the lowest maturity grade (I) measured by the self-heating test. In forced-aerated systems a low intermittent aeration rate of 1 l kg [volatile solids {VS}]−1 min−1 (5 min on, 30 min off) proved to be excessive, causing major water losses and hampering moisture control. Comparison of the results obtained for TP and TAP demonstrated that the investment cost in a forced-aeration system is not necessary for this waste. Hence, turned systems are recommended for OFMSW pile composting

Bioremediation of PAHs-contaminated soil through composting : influence of bioaugmentation and biostimulation on the contaminants biodegradation

The degradation of several polycyclic aromatic hydrocarbons (PAHs) in soil through composting was investigated. The selected PAHs included: fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, and chrysene, with concentrations simulating a real creosote sample. The degradation of PAHs (initial concentration 1 g of total PAHs kg⁻¹ dry soil) was assessed applying bioaugmentation with the white-rot fungi Trametes versicolor and biostimulation using compost of the source-selected organic fraction of municipal solid waste (OFMSW) and rabbit food as organic co-substrates. The process performance during 30 days of incubation was evaluated through different analyses including: dynamic respiration index (DRI), cumulative oxygen consumption during 5 days (AT₅), enzymatic activity, and fungal biomass. These analyses demonstrated that the introduced T. versicolor did not significantly enhance the degradation of PAHs. However, biostimulation was able to improve the PAHs degradation: 89% of the total PAHs were degraded by the end of the composting period (30 days) compared to the only 29.5% that was achieved by the soil indigenous microorganisms without any co-substrate (control, not amended). Indeed, the results showed that stable compost from the OFMSW has a greater potential to enhance the degradation of PAHs compared to non-stable co-substrates such as rabbit food

Bioremediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil: process evaluation through composting and anaerobic digestion approach

Among the different available remediation technologies, it is well-known that bioremediation methods which mainly depend on microorganisms to degrade, transform, detoxify or break down the contaminants, they are recognized as cost-effective and environmental-friendly methods. In fact, microorganisms “engine of bioremediation process” carry out their normal duty under aerobic or anaerobic conditions, which without doubt extends and motivates the desires to make use of such abilities to reduce environmental threats caused by various contaminants. However, to achieve satisfactory results during any bioremediation process, providing optimal conditions for microorganisms is considered as an essential/crucial task. Composting as one of the applied bioremediation technologies used to remediate soils contaminated with organic contaminants like PAHs still needs more investigation although a valuable effort has been devoted to elucidate the behaviour of this process in the remediation of PAHs-contaminated soils. However, till recently, anaerobically treatment of PAHs-contaminated soil received less attention as it was believed that PAHs are poorly or even impossible to be degraded under such conditions. Therefore, the present study tried to touch both aerobically bioremediation of PAH-contaminated soil through composting and anaerobically treatment of the same soil under strict methanogenic conditions. For both remediation approaches, the effect of some controlling factors had been also evaluated through experiment design methodology employing central design (CCD) technique. Regarding the composting process, the obtained results demonstrated that this technology is an advantageous and indisputable method to decontaminate PAHs-contaminated soils within short period. Additionally, compost derived from the organic fraction of municipal solid wastes (OFMSW) was found to enhance the contaminants (PAHs) removal rate to high extent. Moreover, a lucid correlation between the contaminants removal rate and the compost stability degree was observed, such that more stable composts better enhanced the remediation process as these composts are believed to have a considerable fraction of humic matter which facilitates the desorption of the contaminants, and get more available as a consequence. At the same time, treatments with stable composts do not produce high temperature during the composting process, and normally they are in the mesophilic ranges which are more favourable for such bioremediation process. Bioaugmentation of the process through introducing white-rot fungi with desired catalytic capacity (Trametes Versicolor) in attempt to accelerate the degradation process demonstrated that no effect or enhancement was achieved through such approach. In the second part of the research, anaerobically treatment of PAHs-contaminated soil has been investigated under strict methanogenic conditions employing two types of inocula; thermophilic and mesophilic. The obtained results demonstrated the effectiveness of such biological treatments in this field. Nevertheless, the process was relatively less effective compared with composting. Furthermore, under these conditions and due to unclear reasons, reversible results were obtained as PAHs concentrations were increased with prolonged incubation, indicating the reversed bioformation of PAHs under such oxygen-deficient conditions. Therefore, future work should be devoted to clarify the reasons behind this behaviour

Preliminary screening of co-substrates for bioremediation of pyrene-contaminated soil through composting

The feasibility of using different organic amendments of different origin and properties in the bioremediation of pyrene-contaminated soil by means of composting has been tested. The selected pyrene concentration was 1 g of pyrene per kg of dry soil. The organic amendments used include: raw organic fraction of municipal solid wastes (OFMSW), industrial compost from OFMSW composting (COFMSW), compost derived from home composting of OFMSW (HCOFMSW), anaerobically digested sludge (ADS), non-digested activated sludge (NDS) and centrifuged non-digested activated sludge (CNDS). The degradation rate was related to the amendment properties that directly affected the composting process. Raw OFMSW was not capable to enhance pyrene degradation in comparison to control, but stable HCOFMSW exhibited the highest removal rate (69%). The amendments stability and the temperatures reached as a consequence influenced the process, and thermophilic temperatures showed an inhibition effect on the microbial activity related to pyrene degradation. Some of the tested wastes need to be further investigated to find inexpensive organic amendments for soil bioremediation

Optimization and enhancement of soil bioremediation by composting using the experimental design technique

The objective of this study was the application of the experimental design technique to optimize the conditions for the bioremediation of contaminated soil by means of composting. A low-cost material such as compost from the Organic Fraction of Municipal Solid Waste as amendment and pyrene as model pollutant were used. The effect of three factors was considered: pollutant concentration (0.1-2 g/kg), soil:compost mixing ratio (1:0.5-1:2 w/w) and compost stability measured as respiration index (0.78, 2.69 and 4.52 mg O2 g⁻¹ Organic Matter h⁻¹). Stable compost permitted to achieve an almost complete degradation of pyrene in a short time (10 days). Results indicated that compost stability is a key parameter to optimize PAHs biodegradation. A factor analysis indicated that the optimal conditions for bioremediation after 10, 20 and 30 days of process were (1.4, 0.78, 1:1.4), (1.4, 2.18. 1:1.3) and (1.3, 2.18, 1:1.3) for concentration (g/kg), compost stability (mg O₂ g−1 Organic Matter h−1) and soil:compost mixing ratio, respectively

Effects of compost stability and contaminant concentration on the bioremediation of PAHs contaminated soil through composting

The objective of this study was to investigate the effect of two factors: the stability degree (0.37-4.55 mg O₂ g⁻¹ Organic Matter h⁻¹) of different composts derived from the organic fraction of municipal solid wastes and the concentration of a complex mixture of PAHs including flourene, phenanthrene, anthracene, flouranthene, pyrene and benzo(a)anthracene in the bioremediation of soil. The two factors were systematically studied applying central composite design methodology. The obtained results demonstrated that compost stability degree was particularly important during the first stage of the process. Stable composts enhanced the levels of degradation in soil-compost mixture and a degradation rate of 92% was achieved in this period, but only 40% was degraded with the least stable compost. The PAHs concentration was also important during the process, since the degradation rates increased with the increase in the PAHs concentration. Moreover, all the individual PAHs demonstrated a notable decrease in their concentrations after the incubation period, but pyrene was degraded to lower levels in some treatments compared to others PAHs