Bioremediation of storage tank bottom sludge by using a two-stage composting system: Effect of mixing ratio and nutrients addition

Response of petroleum-contaminated soil to chemical oxidation combined with biostimulation

In this study, a microcosm experiment was conducted to investigate the effects of Na2S2O8 preoxidation combined with biostimulation on petroleum-contaminated soil remediation. The response of microbial community during this process was explored using BIOLOG ECO microplate carbon utilization method and 16 s rDNA high-throughput sequencing. The results showed that use of 10 mg/g Na2S2O8 removed 19.8 % of the petroleum hydrocarbons, reduced soil biotoxicity and did not affect soil microbial activity compared to other concentrations. Therefore, sodium persulfate of ca. 10 mg/g was used to oxidize petroleum in soil before the biostimulation experiment with organic and inorganic fertilizers. Our finding showed that the content of total petroleum hydrocarbons (TPHs) in soil was reduced by 43.3 % in inorganic fertilizer treatment after 60 days. The results of BIOLOG ECO microplate carbon utilization analysis and 16 S rDNA high-throughput sequencing further confirmed that biostimulation quickly restored the microbial activities in oxidant treated soil. The main marker bacteria in chemical oxidation combined with biostimulation remediation were Arthrobacter and Paenarthrobacter, and their relative abundances were both significantly negatively correlated with the content of petroleum hydrocarbons in soil.

Pilot-scale field studies on activated microbial remediation of petroleum-contaminated soil

Soil contamination by petroleum, including crude oil from various sources, is increasingly becoming a pressing global environmental concern, necessitating the exploration of innovative and sustainable remediation strategies. The present field-scale study developed a simple, cost-effective microbial remediation process for treating petroleum-contaminated soil. The soil treatment involves adding microbial activators to stimulate indigenous petroleum-degrading microorganisms, thereby enhancing the total petroleum hydrocarbons (TPH) degradation rate. The formulated microbial activator provided a growth-enhancing complex of nitrogen and phosphorus, trace elements, growth factors, biosurfactants, and soil pH regulators. The field trials, involving two 500 m3 soil samples with the initial TPH content of 5.01% and 2.15%, were reduced to 0.41% and 0.02% in 50 days, respectively, reaching the national standard for cultivated land category II. The treatment period was notably shorter than the commonly used composting and bioaugmentation methods (typically from 8 to 12 weeks). The results indicated that the activator could stimulate the functional microorganisms in the soil and reduce the phytotoxicity of the contaminated soil. After 40 days of treatment, the germination rate of rye seeds increased from 20 to 90%, indicating that the microbial activator could be effectively used for rapid on-site remediation of oil-contaminated soils.

Assessment of oily sludge biodegradation in lab scale composting and slurry bioreactor by bacterial consortium

The present study aimed to investigate biodegradability of oily sludge in lab scale composting and slurry bioreactor using a potential bacterial consortium isolated from petroleum-contaminated sites. The consortium used in the study consisted of bacterial genera, including Enterobacter, Bacillus, Microbacterium, Alcaligenes Pseudomonas, Ochrobactrum, Micrococcus, and Shinella which were obtained after rigorous screening using different hydrocarbons. The meticulously designed lab scale composting experiments were carried out and showed that the combination of 10% oily sludge (A1) exhibited the highest total carbon (TC) removal, which was 40.33% within 90 days. To assess the composting experiments' efficiency, the first (k₁) and second (k₂) order rate constants were evaluated and was found to be 0.0004-0.0067 per day and second (k₂) 0.0000008-0.00005 g/kg. day respectively. To further enhance the biodegradation rate of A1 combination, a slurry bioreactor was used. The maximum total petroleum hydrocarbon (TPH) removals in a slurry bioreactor for cycle-I and -II were 48.8% and 46.5%, respectively, on the 78th and 140th days of the treatment. The results obtained in the study will be a technological platform for the development of slurry phase treatment of petroleum waste in a sustainable and eco-friendly manner.

Bioremediation of heavy oily sludge: a microcosms study

Oily sludge is a residue from the petroleum industry composed of a mixture of sand, water, metals, and high content of hydrocarbons (HCs). The heavy oily sludge used in this study originated from Colombian crude oil with high density and low American Petroleum Institute (API) gravity. The residual waste from heavy oil processing was subject to thermal and centrifugal extraction, resulting in heavy oily sludge with very high density and viscosity. Biodegradation of the total petroleum hydrocarbons (TPH) was tested in microcosms using several bioremediation approaches, including: biostimulation with bulking agents and nutrients, the surfactant Tween 80, and bioaugmentation. Select HC degrading bacteria were isolated based on their ability to grow and produce clear zones on different HCs. Degradation of TPH in the microcosms was monitored gravimetrically and with gas chromatography (GC). The TPH removal in all treatments ranged between 2 and 67%, regardless of the addition of microbial consortiums, amendments, or surfactants within the tested parameters. The results of this study demonstrated that bioremediation of heavy oily sludge presents greater challenges to achieve regulatory requirements. Additional physicochemical treatments analysis to remediate this recalcitrant material may be required to achieve a desirable degradation rate.

The nitrogen cycle and mitigation strategies for nitrogen loss during organic waste composting: A review

Composting is a promising technology to decompose organic waste into humus-like high-quality compost, which can be used as organic fertilizer. However, greenhouse gases (N₂O, CO₂, CH₄) and odorous emissions (H₂S, NH₃) are major concerns as secondary pollutants, which may pose adverse environmental and health effects. During the composting process, nitrogen cycle plays an important role to the compost quality. This review aimed to (1) summarizes the nitrogen cycle of the composting, (2) examine the operational parameters, microbial activities, functions of enzymes and genes affecting the nitrogen cycle, and (3) discuss mitigation strategies for nitrogen loss. Operational parameters such as moisture, oxygen content, temperature, C/N ratio and pH play an essential role in the nitrogen cycle, and adjusting them is the most straightforward method to reduce nitrogen loss. Also, nitrification and denitrification are the most crucial processes of the nitrogen cycle, which strongly affect microbial community dynamics. The ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB), and heterotrophic and autotrophic denitrifiers play a vital role in nitrification and denitrification with the involvement of ammonia monooxygenase (amoA) gene, nitrate reductase genes (narG), and nitrous oxide reductase (nosZ). Furthermore, adding additives such as struvite salts (MgNH₄PO₄·6H₂O), biochar, and zeolites (clinoptilolite), and microbial inoculation, namely Bacillus cereus (ammonium strain), Pseudomonas donghuensis (nitrite strain), and Bacillus licheniformis (nitrogen fixer) can help control nitrogen loss. This review summarized critical issues of the nitrogen cycle and nitrogen loss in order to help future composting research with regard to compost quality and air pollution/odor control.

Cost reduction strategies in the remediation of petroleum hydrocarbon contaminated soil

Petroleum hydrocarbon spill on land pollutes soil and reduces its ecosystem. Hydrocarbon transport in the soil is aided by several biological, physical, and chemical processes. However, pore characteristics play a major role in the distribution within the soil matrix. Restoring land use after spills necessitates remediation using cost-effective technologies. Several remediation technologies have been demonstrated at different scales, and research is ongoing to improve their performances towards the reduction of treatment costs. The process of removing the contaminants in the soil is through one or a combination of containment, separation, and degradation methods under the influence of biological, physical, chemical, and electrically-dominated processes. Generally, performance improvement is achieved through the introduction of products/materials and/or energy. Nevertheless, the technologies can be categorized based on effectiveness period as short, medium, and long term. The treatment cost of short, medium, and long-term technologies are usually in the range of $39 - 331/t (/tonne), $22 - 131/t, and $8 - 131/t, respectively. However, the total cost depends on other factors such as site location, capital cost, and permitting. This review compiles cost-saving strategies reported for different techniques used in remediating petroleum hydrocarbon polluted soil. We discuss the principles of contaminant removal, performance enhancing methods, and the cost-effectiveness analysis of selected technologies.

Removal of Petroleum Contaminants Through Bioremediation with Integrated Concepts of Resource Recovery: A Review

There is an upsurge in industrial production to meet the rising demands of the rapidly growing population globally. The enormous energy demand of the growing economies still depends upon petroleum. It has also resulted in environmental pollution due to the release of petroleum origin pollutants. Soil and aquifers, especially in the direct impact zones of petroleum refineries, are the worst hit. The integrated concept of bioremediation and resource recovery offers a sustainable solution to mitigate environmental pollution. It involves biodegradation, a benign utilization of toxic wastes, and the recycling of natural resources. Bioremediation is considered an integral contributor to the emerging concepts of bio-economy and sustainable development goals. This review article aims to provide an updated overview of bioremediation involving petroleum-based contaminants. Microbial degradation is discussed as a promising strategy for petroleum refinery effluent and sludge treatment. The review also provides an insight into resource reuse and recovery as a holistic approach towards sustainable refinery waste treatment. Furthermore, the integrated technologies that deserve in-depth exploration for future study in the refinery sector are highlighted in the present study.

Assessment of the Suitability of Melilotus officinalis for Phytoremediation of Soil Contaminated with Petroleum Hydrocarbons (TPH and PAH), Zn, Pb and Cd Based on Toxicological Tests

The article presents issues related to the possibility of using toxicological tests as a tool to monitor the progress of soil treatment contaminated with petroleum substances (TPH, PAH), Zn, Pb and Cd in bio-phytoremediation processes. In order to reduce the high content of petroleum pollutants (TPH = 56,371 mg kg⁻¹ dry mass, PAH = 139.3 mg kg⁻¹ dry mass), the technology of stepwise soil treatment was applied, including basic bioremediation and inoculation with biopreparations based of indigenous non-pathogenic species of bacteria, fungi and yeasts. As a result of basic bioremediation in laboratory conditions (ex-situ method), the reduction of petroleum pollutants TPH by 33.9% and PAH by 9.5% was achieved. The introduction of inoculation with biopraparation-1 prepared on the basis of non-pathogenic species of indigenous bacteria made it possible to reduce the TPH content by 86.3%, PAH by 40.3%. The use of a biopreparation-1 enriched with indigenous non-pathogenic species of fungi and yeasts in the third series of inoculation increased to an increase in the degree of biodegradation of aliphatic hydrocarbons with long carbon chains and PAH by a further 28.9%. In the next stage of soil treatment after biodegradation processes, which was characterized by an increased content of heavy metals (Zn, Pb, Cd) and naphthalene, chrysene, benzo(a)anthracene and benzo(ghi)perylene belonging to polycyclic aromatic hydrocarbons, phytoremediation with the use of Melilotus officinalis was applied. After the six-month phytoremediation process, the following was achieved: Zn content by 25.1%, Pb by 27.9%, Cd by 23.2% and TPH by 42.2% and PAH by 49.9%. The rate of removal of individual groups of hydrocarbons was in the decreasing order: C₁₂–C₁₈ > C₆–C₁₂ > C₁₈–C₂₅ > C₂₅–C₃₆. PAHs tended to be removed in the following order: chrysene > naphthalene > benzo(a)anthracene > benzo(ghi)perylene. The TF and BCF coefficients were calculated to assess the capacity of M. officinalis to accumulate metal in tissues, uptake from soil and transfer from roots to shoots. The values of TF translocation coefficients were, respectively, for Zn (0.44), Pb (0.12), Cd (0.40). The calculated BCF concentration factors (BCF_roots > BCF_shoots) show that heavy metals taken up by M. officinalis are mainly accumulated in the root tissues in the following order Zn > Pb > Cd, revealing a poor metal translocation from the root to the shoots. This process was carried out in laboratory conditions for a period of 6 months. The process of phytoremediation of contaminated soil using M. officinalis assisted with fertilization was monitored by means of toxicological tests: Microtox, Ostracodtoxkit F^TM, MARA and Phytotoxkit^TM. The performed phytotoxicity tests have indicated variable sensitivity of the tested plants on contaminants occurring in the studied soils, following the sequence: Lepidium sativum < Sorghum saccharatum < Sinapis alba. The sensitivity of toxicological tests was comparable and increased in the order: MARA < Ostracodtoxkit F^TM < Microtox. The results of the toxicological monitoring as a function of the time of soil treatment, together with chemical analyses determining the content of toxicants in soil and biomass M. officinalis, clearly confirmed the effectiveness of the applied concept of bioremediation of soils contaminated with zinc, lead and cadmium in the presence of petroleum hydrocarbons.

Statistical Optimisation of Diesel Biodegradation at Low Temperatures by an Antarctic Marine Bacterial Consortium Isolated from Non-Contaminated Seawater

Hydrocarbon pollution is widespread around the globe and, even in the remoteness of Antarctica, the impacts of hydrocarbons from anthropogenic sources are still apparent. Antarctica’s chronically cold temperatures and other extreme environmental conditions reduce the rates of biological processes, including the biodegradation of pollutants. However, the native Antarctic microbial diversity provides a reservoir of cold-adapted microorganisms, some of which have the potential for biodegradation. This study evaluated the diesel hydrocarbon-degrading ability of a psychrotolerant marine bacterial consortium obtained from the coast of the north-west Antarctic Peninsula. The consortium’s growth conditions were optimised using one-factor-at-a-time (OFAT) and statistical response surface methodology (RSM), which identified optimal growth conditions of pH 8.0, 10 °C, 25 ppt NaCl and 1.5 g/L NH₄NO₃. The predicted model was highly significant and confirmed that the parameters’ salinity, temperature, nitrogen concentration and initial diesel concentration significantly influenced diesel biodegradation. Using the optimised values generated by RSM, a mass reduction of 12.23 mg/mL from the initial 30.518 mg/mL (4% (w/v)) concentration of diesel was achieved within a 6 d incubation period. This study provides further evidence for the presence of native hydrocarbon-degrading bacteria in non-contaminated Antarctic seawater.

Aerobic composting remediation of petroleum hydrocarbon-contaminated soil. Current and future perspectives

This article provides a comprehensive review on aerobic composting remediation of soil contaminated with total petroleum hydrocarbons (TPHs). The studies reviewed have demonstrated that composting technology can be applied to treat TPH contamination (as high as 380,000 mg kg^-1) in clay, silt, and sandy soils successfully. Most of these studies reported more than 70% removal efficiency, with a maximum of 99%. During the composting process, the bacteria use TPHs as carbon and energy sources, whereas the fungi produce enzymes that can catalyze oxidation reactions of TPHs. The mutualistic and competitive interactions between the bacteria and fungi are believed to sustain a robust biodegradation system. The highest biodegradation rate is observed during the thermophilic phase. However, the presence of a diverse and dynamic microbial community ensures that TPH degradation occurs in the entire composting process. Initial concentration, soil type, soil/compost ratio, aeration rate, moisture content, C/N ratio, pH, and temperature affect the composting process and should be monitored and controlled to ensure successful degradation. Nevertheless, there is insufficient research on optimizing these operational parameters, especially for large-scale composting. Also, toxic and odorous gas emissions during degradation of TPHs, usually unaddressed, can be potential air pollution sources and need further insightful characterization and mitigation/control research.

Bioremediation of oily sludge by solid complex bacterial agent with a combined two-step process

In the present research, a bioremediation process was developed using solid complex bacterial agents (SCBA) through a combined two-step biodegradation process. Four isolated strains showed high efficiency for the degradation of total petroleum hydrocarbons (TPH) and the reduction of COD of the oily sludge, at 96.6% and 92.6%, respectively. The mixed strains together with bran prepared in form of SCBA exhibited improved performance compared to individual strains, all of which had an optimal temperature of around 35 °C. The use of SCBA provided advantages over commonly used liquid media for storage and transportation. The two-step process, consisting of firstly biosurfactant-assisted oil recovery and secondly biodegradation of the remaining TPH with SCBA, demonstrated the capability for treating oily sludge with high TPH content (>10 wt%) and short process period (60 days). The large-scale (5 tons oily sludge) field test, achieving a TPH removal efficiency of 93.8% and COD reduction of 91.5%, respectively, confirmed the feasibility and superiority of the technology for industrial applications.

Treatment of petroleum refinery sludge by petroleum degrading bacterium Stenotrophomonas pavanii IRB19 as an efficient novel technology

Petroleum hydrocarbons (PHCs) in petroleum refinery sludge (PRS) are the most adverse components because of their toxic nature, which are harmful to human health and the aquatic ecosystem. This study aimed to identify and characterize an indigenous bacterium isolated from PRS of Indian oil corporation ltd. (IOCL), Haldia, India, and evaluate its performance for biodegradation of total petroleum hydrocarbon (TPH) of PRS. The bacterium molecularly characterized as Stenotrophomonas sp. IRB19 by 16S rRNA sequencing and phylogenetic analysis. The strain IRB19 showed a significant ability to utilize four different oils (kerosene, diesel, petrol and hexadecane) in-vitro. IRB19 could able to degrade up to 65 ± 2.4% of TPH in 28 d of incubation. Solvent extraction study showed that PRS contain 180.57 ± 3.44 g kg^-1 of TPH and maltene fraction composed of aliphatic, aromatics and polar components of 52 ± 4, 39 ± 2 and 9 ± 1%, respectively. The TPH degradation best fitted for the Gompertz model and followed the first-order kinetics having the rate constant (k) and half-life period (t _1/2) of 0.036 d^-1 and 19 d, respectively. Results of this study verified the suitability of the novel strain IRB19 for the biodegradation of PHCs.

Biogas slurry as an activator for the remediation of petroleum contaminated soils through composting mediated by humic acid

Soil pollution caused by petroleum hydrocarbons is a widespread environmental problem. Composting is one of the cost-effective solutions for petroleum hydrocarbons removal but limited by low efficiency of bioremediation, leading to high phytotoxicity. Given that biogas slurry as nutrients can alter the microbial activity, the aim of this study was to investigate the role of biogas slurry on the remediation of petroleum contaminated soils in composting. Herein, we added biogas slurry into the composting of hydrocarbon contaminated soil to investigate its effect on the biodegradation of petroleum hydrocarbons, humic acid (HA) transformation and the safety of product. The results showed that biogas slurry addition improved the degradation of organic matter and total petroleum hydrocarbons (TPH) (especially C > 16), but also increased 18.0% of germination index and the humification degree of HA. The estrone from biogas slurry was removed during composting and did not affect the phytotoxicity level of compost. Redundancy analysis and structural equation modeling indicated that TPH degradation was significantly related to the humification of HA components and total nitrogen from biogas slurry, which contributed to composting safety. Therefore, biogas slurry could be a possible activator for the remediation of petroleum contaminated soils through composting mediated by HA transformation, which is beneficial to obtain the composts with a lower phytotoxicity and higher maturity for soil application.

Co-treatment of an oily sludge and aged contaminated soil: permanganate oxidation followed by bioremediation

The bioremediation of an oily sludge (321 ± 30 mg of polycyclic aromatic hydrocarbons/kg_{DRY SLUDGE} and 13420 ± 1300 mg of aliphatic hydrocarbons/kg_{DRY SLUDGE}) by mixture with contaminated soil (23 ± 2 mg of polycyclic aromatic hydrocarbons/kg_{DRY SOIL} and 98 ± 10 mg of aliphatic hydrocarbons/kg_{DRY SOIL}) was studied. Furthermore, the effect of oxidative pretreatments (persulfate and permanganate) on the performance of the global process was examined. The treatments reached contamination levels lower than the original residues, indicating the presence of synergic processes between a highly contaminated sludge and soil with a selected hydrocarbon-degrading community. Pretreatment with permanganate significantly improved biodegradation, possibly due to the increase in bioavailability and biodegradability of petroleum hydrocarbons. Two months of incubation was enough to reach the complete elimination of polycyclic aromatic hydrocarbons and 92% elimination of aliphatic hydrocarbons. Monitoring using five parameters (concentration of total petroleum hydrocarbons, total cultivable heterotrophic bacteria count, lipase and dehydrogenase activities, and polycyclic aromatic hydrocarbon-degrading bacteria count) as an approach for a preliminary scanning of the effectiveness of a treatment is proposed based on principal components analysis.

Effect of immature and mature compost addition on petroleum contaminated soils composting: kinetics

PURPOSE

The kinetic studies and effect of amendment addition on the performance of the composting process in reduction of total petroleum hydrocarbons (TPH) from petroleum contaminated soils (PCS) were investigated in the present research.

METHODS

Seven composting experiments containing various mixing ratios of PCS to unfinished compost (UC) and finished compost (FC) were set up and operated for 14 weeks. The mixing rations consisted of 1:0 (as control experiment), 1:0.3, 1:0.6, and 1:1. The initial C/N/P and moisture contents of the composting piles were adjusted to 100/5/1 and 50-55%, respectively.

RESULTS

Results showed that 50.09-79.49% of TPH was removed in the composting experiments after 14 weeks. The highest and lowest removal rates were achieved in the ratios of 1:1 and 1:0.3, respectively. Moreover, application of UC as amendments and bulking agent is more efficient than FC. The biodecomposition of TPH was fitted to the first-order kinetic with the half lives and rate constants of 5.63-11.55 days and 0.060-0.123 d^-1, respectively. The bacteria detected from the composting treatments were Staphylococcus sp., Bacillus sp., and Pseudomonas sp.

CONCLUSIONS

The study confirmed the suitability of composting process for PCS bioremediation and superiority of UC than FC as bulking agent.

Biodegradation of high concentrations of petroleum compounds by using indigenous bacteria isolated from petroleum hydrocarbons-rich sludge: Effective scale-up from liquid medium to composting process

The scale-up of petroleum hydrocarbons-rich sludge (PHRS) bioremediation from liquid medium to a composting method bioaugmentated with two indigenous bacteria, capable of degrading high levels of crude oil, was surveyed. After isolating the strains (Sphingomonas olei strain KA1 and Acinetobacter radioresistens strain KA2) and determining their biomass production, emulsification index (E₂₄), bacterial adhesion to hydrocarbon (BATH), and crude oil degradation in liquid medium, they were inoculated into the composting experiments. In liquid medium, the removal rate of crude oil were 67.25, 70.86, 61.77, 42.13, and 27.92%, respectively for the initial oil levels of 1, 2, 3, 4, and 5% after 7 days. Degradation of 10, 20, 30, 40 and 50 g kg^-1 concentrations of total petroleum hydrocarbons (TPH) were also calculated to be 91.24, 87.23, 84.69, 74.08, and 60.14%, respectively after a composting duration of 12 weeks. The values of the rate constants (k) and half-lives (t_1/2) of petroleum hydrocarbons degradation were 0.083-0.212 day^-1 and 3.27-8.35 days for the first-order and 0.003-0.089 g kg^-1day^-1 and 1.12-6.67 days for the second-order model, respectively. This study verified the suitability of the isolated strains for PHRS bioremediation. Successful scale-up of PHRS bioremediation from a liquid medium to a composting process for degrading high amounts of TPH was also confirmed.

Gas chromatographic analysis of polychlorinated biphenyls in compost samples from different origin

Depending on the origin, the compost produced may contain not only nutrients but also pollutants, such as heavy metals and persistent organic pollutants. It is very important to determine them in soil-improving substances, because persistent organic pollutants show environmental toxic, cancerogenic, mutagenic effects and do not decompose for a long time. The aim of this study was to determine seven polychlorinated biphenyls concentrations in different kinds of composts produced in Lithuania and to evaluate the appliance of these composts in agricultural land. First, before routine analysis was done a gas chromatography with electron-capture detector method was developed. In this study 145 samples of green waste, sewage sludge, cattle manure, food waste, mixed municipal waste, digestate and composts made from mixed municipal waste after mechanical-biological treatment were analysed. Obtained results show that 28% of investigated cattle manure composts (CMCs) and 10.5% of food waste composts (FWCs) were free from polychlorinated biphenyls. Other kinds of composts investigated in this study (green waste compost (GWC), sewage sludge compost (SSC), mixed municipal waste compost (MMWC), mixed municipal waste compost after mechanical biological treatment (MMWCABMT) and digestate (DIG)) were contaminated 100% with polychlorinated biphenyls. Despite the fact that polychlorinated biphenyls were forbidden 25 years ago, their concentration varied from 2.70 to 163.7 µg kg^-1 in different kinds of composts produced in Lithuania. According to get an increasing average amount of Σ7 polychlorinated biphenyls, Lithuanian composts were distributed as follows CMC > GWC > DIG > FWC > SSC > MMWCABMT > MMWC.

Effects of waste lime and Chinese medicinal herbal residue amendments on physical, chemical, and microbial properties during green waste composting

Traditional composting is time-consuming and often results in a low-quality product. The objective of this study was to determine the effects of waste lime (WL; at 0, 2.5, and 3.5%) and/or Chinese medicinal herbal residues (CMHRs; at 0, 10, and 20%) as amendments on the two-stage composting of green waste (GW). The combination of WL and CMHRs improved compost particle-size distribution and pH, decreased nitrogen loss, and increased cation exchange capacity (CEC), nutrient content, and microbial numbers. The combination of WL and CMHRs also accelerated organic matter humification and lignocellulose degradation and therefore increased the germination index of the final compost. Relative to the non-amended compost, the optimal amendment (2.5% WL and 20% CMHRs) increased the percentage of particles of ideal size from 23.8 to 66.9%, the pH from 6.69 to 7.17, the CEC from 52 to 169 cmol/kg, the humic acid to fulvic acid ratio from 1.32 to 2.49, the hemicellulose degradation rate from 42 to 87%, and the cellulose degradation rate from 20 to 61%. The treatment with addition of 2.5% WL and 20% CMHRs to GW required only 21 days to generate the highest quality compost product.

Optimization of combined in-vessel composting process and chemical oxidation for remediation of bottom sludge of crude oil storage tanks

In this research, removal of petroleum hydrocarbons from oily sludge of crude oil storage tanks was investigated under the optimized conditions of in-vessel composting process and chemical oxidation with H₂O₂ and Fenton. After determining the optimum conditions, the sludge was pre-treated with the optimum state of the oxidation process. Then, the determined optimum ratios of the sludge to immature compost were composted at a C:N:P ratio of 100:5:1 and moisture content of 55% for a period of 10 weeks. Finally, both pre-treated and composted mixtures were again oxidized with the optimum conditions of the oxidants. Results showed that total petroleum hydrocarbons (TPH) removal of the 1:8 and 1:10 composting reactors which were pre-treated with H₂O₂ were 88.34% and 90.4%, respectively. In addition, reduction of TPH in 1:8 and 1:10 composting reactors which were pre-treated with Fenton were 83.90% and 84.40%, respectively. Without applying the pre-treatment step, the composting reactors had a removal rate of about 80%. Therefore, pre-treatment of the reactors increased the TPH removal. However, post-oxidation of both pre-treated and composted mixtures reduced only 13-16% of TPH. Based on the results, remarkable overall removal of TPH (about 99%) was achieved by using chemical oxidation and subsequent composting process. The study showed that chemical oxidation with H₂O₂ followed by in-vessel composting is a viable choice for the remediation of the sludge.

Evaluation of maifanite and silage as amendments for green waste composting

Composting is a popular method for recycling organic solid wastes including agricultural and forestry residues. However, traditional composting method is time consuming, generates foul smells, and produces an immature product. The effects of maifanite (MF; at 0%, 8.5%, and 13.5%) and/or silage (SG; at 0%, 25%, and 45%) as amendments on an innovative, two-stage method for composting green waste (GW) were investigated. The combined addition of MF and SG greatly improved composting conditions, reduced composting time, and enhanced compost quality in terms of composting temperature, bulk density, water-holding capacity, void ratio, pH, cation exchange capacity, ammonia nitrogen content, dissolved organic carbon content, crude fibre degradation, microbial numbers, enzyme activities, nutrient contents, and phytotoxicity. The two-stage composting of GW with 8.5% MF and 45% SG generated the highest quality and the most mature compost product and did so in only 21 days. With the optimized composting, the degradation rate of cellulose and hemicellulose reached 46.3 and 82.3%, respectively, and the germination index of Chinese cabbage and lucerne was 153 and 172%, respectively, which were all far higher than values obtained with the control. The combined effects of MF and SG on GW composting have not been previously explored, and this study therefore provided new and practical information. The comprehensive analyses of compost properties during and at the end of the process provided insight into underlying mechanisms. The optimized two-stage composting method may be a viable and sustainable alternative for GW management in that it converts the waste into a useful product.