In-situ stabilisation followed by ex-situ composting for treatment and disposal of heavy metals polluted sediments

An innovative in-situ stabilisation treatment followed by ex-situ sediment composting was tested for its ability to treat and dispose of heavy-metal-polluted sediments in a river near the Chinese Pearl Delta. First, polluted sediments were treated in-situ to stabilise the heavy metals. Then the treated sediments were dredged, dewatered and sent for high temperature aerobic composting （HTAC） treatment. Finally, the compost products were used as a fertiliser for fiver bank plants. The stabilisation efficiency of heavy metals during the process was investigated and the results are as follows： （1） using in-situ stabilisation, the extraction concentrations of Cu, Zn and Pb were reduced by 65.0%, 82.2% and 90.0%, respectively, which are much lower than the national standard given in the Identification Standard for Hazardous Waste （GB5085.3-1996）; （2） chemical fraction analysis showed that heavy metals were further stabilized during the HTAC treatment; （3） the concentrations of Cu, Zn and Pb in rainwater leachate through the river bank met the level of class V in the Environmental Quality Standards for Surface Water in China （GB3838-2002）. Therefore, using this new process, the toxicities of heavy metals in sediments were reduced markedly.

Split Addition of Nitrogen-Rich Substrate at Thermophilic and Mesophilic Stages of Composting: Effect on Green House Gases Emission and Quality of Compost

Composting as a solution to the increasing generation of municipal solid waste (MSW), also contribute to GHGs emission when not controlled and could lack some basic nutrients, especially nitrogen. This study assessed the split-additions of nitrogen-rich substrate to composting materials and their effect on GHGs emissions as well as the quality of the composts. Nitrogen-rich substrates formulated from pig and goat manure were co-composted with MSW for a 12-weeks period by split adding at mesophilic (˚C) and thermophilic (>50˚C) stages in five different treatments. Representative samples from the compost were taken from each treatment for physicochemical, heavy metals and bacteriological analysis. In-situ CH4, CO2, N2O gas emissions were also analyzed weekly during composting. It was observed that all the treatments showed significant organic matter decomposition, reaching thermophilic temperatures in the first week of composting. The absence affects the suitable agronomic properties. All nitrogen-rich substrate applied at thermophilic stage (Treatment two) recorded the highest N, P and K concentrations of 1.34%, 0.97% and 2.45%, respectively with highest nitrogen retention. In terms of GHG emissions, CO2 was highest at the thermophilic stage when N-rich substrate was added in all treatment, while CH4 was highest in the mesophilic stage with N-rich substrate addition. N2O showed no specific trend in the treatments. Split addition of the N-rich substrate for co-composting of MSW produced compost which is stable, has less nutrient loss and low GHG emissions. Split addition of a nitrogen-rich substrate could be an option for increasing the fertilizer value of MSW compost.

Adsorption Properties of Adsorption Tower Filled with Calcium Superphosphate on NH_3 Emitted from Composting System of Animal Wastes

[Objective] This study aimed to investigate the adsorption properties of the adsorption tower filled with calcium superphosphate on ammonia volatilized with aer- ation. [Method] Adsorption tower filled with calcium superphosphate was adopted as experimental apparatus, which was constructed by poly vinyl chloride （PVC） circular tubes. With hartshorn as the source of ammonia volatilization, the effect of different ratios of height to diameter of the tower filled with equal amount of calcium super-phosphate on ammonia adsorption was investigated. In addition, adsorption tower with height-diameter ratio of 9.9 was selected to adsorb the ammonia emitted from the composting systems of pig manure and chicken manure with optimized and reg- ulated carbon-nitrogen ratio. [Result] Under certain volatilization rate, calcium super- phosphate particles in the adsorption tower could effectively adsorb the ammonia, and the adsorption efficiency was enhanced with the increase of height-diameter ra-tio, which could reach above 90% with height-diameter ratio of more than 1.1; the ammonia emitted from composting systems of pig manure and chicken manure with optimized and regulated carbon-nitrogen ratio could be completely absorbed using adsorption tower with height-diameter ratio of 9.9 filled with calcium superphosphate accounting for about 8% of the weight of composting materials. [Conclusion] Experi- mental results of this study provided reference for the application of adsorption tower filled with calcium superphosphate in the treatment of waste gas emitted from com- posting materials.

Effects of Superphosphate Addition on NH_3 and Greenhouse Gas Emissions During Vegetable Waste Composting

To study the effects of superphosphate（SP） on the NH_3 and greenhouse gas emissions,vegetable waste composting was performed for 27 days using 6 different treatments. In addition to the controls,five vegetable waste mixtures（0.77m^3 each） were treated with different amounts of the SP additive, namely, 5%, 10%,15%, 20% and 25%. The ammonia volatilization loss and greenhouse gas emissions were measured during composting.Results indicated that the SP additive significantly decreased the ammonia volatilization and greenhouse gas emissions during vegetable waste composting. The additive reduced the total NH_3 emission by 4.0% to 16.7%. The total greenhouse gas emissions（CO_2-eq） of all treatments with SP additives were decreased by 10.2% to 20.8%, as compared with the controls. The NH_3 emission during vegetable waste composting had the highest contribution to the greenhouse effect caused by the four different gases.The amount of NH_3（CO_2-eq）from each treatment ranged from 59.90 to 81.58 kg/t; NH_3（CO_2-eq） accounted for 69% to 77% of the total emissions from the four gases. Therefore, SP is a cost-effective phosphorus-based fertilizer that can be used as an additive during vegetable waste composting to reduce the NH_3 and greenhouse gas emissions as well as to improve the value of compost as a fertilizer.

STUDY ON DEGRADATION OF POLYETHYLENE FILMS CONTAINING ADDITIVES WITH FERROUS ION AT COMPOSTING TEMPERATURES

Polyethylene (PE) films with additives consisting mainly of oleic acid and ferrous ions were subjected to accelerated degradation at simulated composting temperatures.Based on Fourier transform infrared spectroscopy and measurements of mechanical properties and viscosity average molecular weight,the degradation of the films was characterized and the degradation mechanism was discussed.The films containing additives with ferrous ions represent considerable decreases in molecular weight,and the carbonyl groups and hydroperoxides in the aging films show different trends of increase with the aging time.These results indicate that the ferrous ion plays an important role in the degradation of PE films and accelerates the degradation of PE.

Microbiological parameters and maturity degree during composting of Posidonia oceanica residues mixed with vegetable wastes in semi-arid pedo-climatic condition

The aim of this study was to characterize the biological stability and maturity degree of compost during a controlled pile-composting trial of mixed vegetable residues （VR） collected from markets of Tunis City with residues of Posidonia oceanica （PoR）, collected from Tunis beaches. The accumulation in beaches （as well as their removal） constitutes a serious environmental problem in all Mediterranean countries particularly in Tunisia. Aerobic-thermophilic composting is the most reasonable way to profit highly-valuable content of organic matter in these wastes for agricultural purposes. The physical, chemical, and biological parameters were monitored during composting over 150 d. The most appropriate parameters were selected to establish the maturity degree. The main result of this research was the deduction of the following maturity criterion： （a） C/N ratio 〈 15; （b） NH4^＋-N 〈 400 mg/kg; （c） CO2-C 〈 2000 mg CO2-C/kg; （d） dehydrogenase activity 〈 1 mg TPF/g dry matter; （e） germination index （GI） 〉 80%. These five parameters, considered jointly are indicative of a high maturity degree and thus of a high-quality organic amendment which employed in a rational way, may improve soil fertility and soil quality. The mature compost was relatively rich in N （13.0 g/kg）, P （4.74 g/kg） and MgO （15.80 g/kg）. Thus composting definitively constitutes the most optimal option to exploit these wastes.

Effect of four crop straws on transformation of organic matter during sewage sludge composting

A 45-d laboratory experiment was conducted to compare the effect of four crop straws on the transformations of organic matter （OM） during composting of sewage sludge. The four crop straws included rape straw, wheat straw, maize straw and rice straw. The following parameters such as temperature, OM, humic-like substances （HS）, fulvic-like acids （FA） and humic-like acids （HA） were determined. The degradation of OM and the formation of HS and HA could be described well by the first-order kinetic model, while the FA content fluctuated during composting. The maximal degradation rates of OM in the compost piles added with rape straw, wheat straw, maize straw and rice straw were 34.7, 46.9, 54.7 and 52.8%, respectively, and the final contents of HS were 118, 128, 141 and 134 g kg-1, respectively, while the humification indices were higher in the compost piles added with maize straw and wheat straw than in those with rice straw and rape straw. The results indicate that a higher hemicellulose content and a lower C/N ratio in crop straw can result in a higher rate of OM degradation and higher contents of HS, while a higher content of lignin can lead to a higher polymerization degree of humic substances in compost piles. The final compost piles added with maize straw has the highest contents of OM, total nitrogen and humus substance as well as the highest values of polymerization degree, while compost piles with rape straw have the highest potassium content and those with rice straw have the highest pH values.

Changes of Cu, Zn, and Cd speciation in sewage sludge during composting

The potential toxicity risks from heavy metals depend on their chemical speciation. The four stages of the Tessier sequential extraction method were employed to investigate changes in heavy metal speciation （Cu, Zn, and Cd） of sewage sludge during forced aeration composting, and then to identify whether the composting process would reduce or enhance their toxicities. Throughout the composting process, the exchangeable, carbonate-bound, Fe-Mn oxide-bound, and organic matter-bound fractions of Cu were converted to the residual Cu fraction. The organic matter-bound Cu fraction greatly contributed to this transformation. Residual Zn fraction was transformed to the Fe-Mn oxide-bound and organic matter-bound fractions after composting. The residual Zn fraction was a major contributor to the organic matter-bound Zn fraction. The availability of Cu and Zn was reduced by composting such that the risk of heavy metal toxicity decreased with prolonged treatment times. Additionally, attention should be paid to the increased availability of Cd in sewage sludge after composting treatment.

Bioremediation of Soil Contaminated with Petroleum Using Forced-Aeration Composting

Laboratory simulation studies and composting pilot study wereconducted to evaluate the capacity of three strains of fungi,indigenous fungus Fusarium sp. And Phanerochaete chrysosporium andCoriolus Versicolor, to remediate petroleum-contaminated soils. Inlaboratory, the fungi were inoculated into a liquid Culture mediumand the petroleum-contaminated soil samples for incubation of 40 and50 days, respectively. In the 200-day pilot study, nutrient contentsand moisture were adjusted and maintained under aerobic Condition incomposting units using concrete container (118.5 cm×65.5 cm×12.5cm) designed specially For this study.

Fluorescence characteristic changes of dissolved organic matter during municipal solid waste composting

Dissolved organic matter（DOM） of municipal solid waste（MSW） consists of minerals, water, ash and humic substances, and is known to enhance plant growth. In this study, inoculating microbes（Z J, MS） were used in municipal solid wastes composting, and composting implemented a industrialized technology. During composting, dissolved organic matter was extracted from the compost and purified. The spectral characteristics of dissolved organic matter was determined by fluorescence emission, excitation, and synchronous spectroscopy. Fluorescence emission, excitation, and synchronous spectra characterized by different relative fluorescent intensities and peaks over time. Fluorescence spectra were similar to that of fulvic acid in sewage sludge, indicating the presence of dissolved organic matter with aromatic structures and a high degree of molecular polymerization. Compared with the controls with no microbial inoculation, the microbe-inoculated treatments exhibited the increase of aromatic polycondensation, in the following order： MS ＋ ZJ 〉 ZJ 〉 MS 〉 CK.

Nitrogen transformations during pig manure composting

Composting is now suggested as one of the environmentally and friendly alternative method for disposal of solid organic wastes, as it leads to minimization, stabilization, and utilization of organic waste. Transformations of nitrogen were investigated in co-composting of pig manure with different amendments, such as sawdust and leaves. Samples were analyzed for pH, total-N, soluble NH4-N, soluble NO3-N and soluble organic-N. The total-N increased after 63 days of composting, as well as the soluble NO3-N and soluble organic-N. Soluble NH4,-N increased significantly and showed peak values at day 7, thereafter decreased sharply and gradually to lower levels. Seed germination index (GI) showed that co-composting of pig manure with sawdust reached maturity after 49 days of composting, while co-composting of pig manure with sawdust and leases required shorter time for 35 days. Soluble NH4-N was significantly negatively ( P < 0.05) , while soluble NO3-N and soluble organic-N were significantly positively ( P < 0.05), correlated with seed germination index (GI). Addition of leaves in co-composting of pig manure with sawdust had no significant impacts on nitrogen transformations, but it was beneficial for maturity of pig manure compost.

Static aerobic composting of municipal sewage sludge with forced ventilation:Using matured compost as bulking conditioner

Static aerobic composting of municipal sewage sludge with forced ventilation or air ventilation using matured compost as bulking conditioner was investigated. Physical and chemical parame ,eters, e.g., temperature, moisture content, VSS, CODcr, pH, and germination index （GI）, were analyzed to characterize the composting process. Fermentation starts quickly in both forced and air ventilation compost heaps and reaches high-temperature stage after 2 d, owing to the bulking function of matured compost. Compared to air ventilation, however, forced ventilation enables the high-temperature stage to last longer for approximately 7 d. The moisture content of both compost bodies decreases from 62% to about 50% as a result of evaporation, and it decreases slightly faster in forced ventilation compost heap after 13 d due to the higher temperature and better ventilation condition. Although no obvious differences of VSS and pH are observed between both compost heaps, the soluble CODcr and GI show differences during the second half period of fermentation. In forced ventilation compost, the soluble CODcr has a small rebound after 13 d, and GI decreases from 46% to 35% but then increases. These results show that in general, the matured compost is a good conditioner and force ventilation with a proper air supply strategy can be more efficient than air ventilation.

Effect of bio-surfactant on municipal solid waste composting process

Bio-surfactant is a new type of surfactant that is produced in microbial metabolism. Adding bio-surfactant during composting process, especially to those contain some toxic substances, has been proved to be a promising way. In this study, Strains Ⅲ(2), a bacterial with high activity to produce bio-surfactant, were isolated firstly. Following comparison experiments with and without adding Strains Ⅲ(2), namely Run 1 and Run R, were conducted, respectively. The experimental results showed that, by adding Strains Ⅲ(2), the surface tension could reduce from 46.5 mN/m to 39.8 mN/m and the corresponding time to maintain the surface tension under 50 mN/m could prolong from 60 h to 90 h. The oxygen uptake rate and total accumulated oxygen consumption with Stains Ⅲ(2) were both higher than those without Strains Ⅲ(2), while the accumulation of H_2S in outlet gas was reduced to around 50% of Run R. Moreover, two additional experiments were also carried out to examine the effects of strains coming from different systems. One is adding Strains Ⅲ(2) with a dose of 0.4%(Run 2), and the other is seedling commercial Strains at the same conditions, the composting experiments showed that: Run 2 was more effective than Run 3, because the commercial Strains can be suppressed significantly in a complex composting system with different pH, high temperature and some of metals. The bio-surfactant was also added into the solid waste, which contained some toxic substances, the corresponding results showed that the remove rate of Hg and sodium pentachlorophenolate(PCP-Na) could be improved highly. Thus, the microenvironment, reactionrate and composting quality could be enhanced effectively by adding bio-surfactant to the composting process.

Effects of Biochar on Substrate Degradation and Ammonia Emission during Aerobic Composting of Chicken Manure

In this study, chicken manure and Caragana korshinskii Kom powder were used as the main raw materials with different amounts of biochar added to test four aerobic composting treatment groups A, B, C and D with laboratory composting fermenters and testing apparatus, and new insight into biochar’s nitrogen conservation mechanism was gotten, based on the experimental data and related exploration such as the physical and chemical properties of the final products, the changing interactions among nutrient elements and other elements, and the relationship between substrate degradation and the amount of biochar used as well as the best formula for reducing ammonia emission. The results showed that the proper proportion of the added biochar to the other elements was conducive to less ammonia emission and nitrogen loss during the aerobic composting. The composting effect of Treatment C （biochar at 20%） was the optimal in the test, where in the composting temperature rose the most rapid and the earliest to the maximum temperature 52.5℃, with the least nitrogen loss. An effective, safe and high-quality resource utilization of chicken manure was established through the aerobic composting with reasonable material mixture proportion.

Changes in Phosphorus Fractions and Nitrogen Forms During Composting of Pig Manure with Rice Straw

The study was conducted to reveal P fractions and N forms changing characters during composting of pig manure with rice straw.During composting,the NH 4 ＋-N concentration decreased and reached at a relatively low value（〈400 mg kg-1） in the final compost,while the NO 3--N concentration increased.Total N losses mainly occurred during thermophilic phase due to the high temperature,the high NH 4 ＋-N concentration and the increase of pH value.Labile inorganic P was dominated in the pig manure and initial compost mixture.During composting,the proportion of labile inorganic P of total extracted P decreased,while the proportion of Fe＋Al-bound P,Ca＋Mg-bound P and residual P increased.The evolutions of the proportion of labile inorganic P,Fe＋Al-bound P and Ca＋Mg-bound P were well correlated with the changes of pH value,organic matter and C/N ratio.Therefore,composting could increase the concentration of N and P and decrease the presence of NH 4 ＋-N and labile P fractions which might cause environmental issues following land application.

Effects of different loading rates and types of biochar on passivations of Cu and Zn via swine manure composting

Pollution of arable land caused by heavy metals in livestock and poultry manure has become a potential threaten to human health in China.Safe disposal of the contained toxic pollution with animal manure by co-composting with biochar is one of the alternative methods.Biochars from different sources(wheat straw,peanut shells and rice husks)amended with different loading rates were investigated for passivations of copper and zinc(Cu and Zn)in swine manure composting.Results showed that the passivation effects of the three types of biochar on Cu and Zn were enhanced with increasing biochar dose.Contents of Cu and Zn measured by diethylenetriaminepentaacetic acid(DTPA)and Community Bureau of Reference(CBR)showed that wheat straw biochar with the loading rates of 10%–13%(w/w)was superior to the other two types of biochar in this study.Compared with the control,sample from wheat straw biochar was more favorable for the bacterial growth of Proteobacteria,Firmicutes and Actinobacteria.In addition,pot experiment showed that organic fertilizer amended with wheat straw biochar could significantly improve the growth of Chinese pakchoi and enzyme activities(superoxide dismutase,peroxidase,polyphenol oxidase and catalase)as compared with the control.Cu and Zn contents of Chinese pakchoi in the organic fertilizer group containing wheat straw biochar reduced by 73.2%and 45.2%,65.8%and 33.6%,respectively,compared with the group without loading biochar.There was no significant difference in the contents of vitamin C and reducing sugar between the groups of organic fertilizer amended with/without wheat straw biochar,however,there was significant difference compared with the heavy metal addition group.The application of organic fertilizer formed by adding biochar can effectively reduce the adverse effects of heavy metals on crops.

Formation of Struvite Crystals in a Simulated Food Waste Aerobic Composting Process

Bench-scale treatments with three mixtures of Mg and P salts, including K3PO4＋MgSO4, K2HPO4＋MgSO4, and KH2PO4＋MgSO4 as additives in a simulated food waste aerobic composting process, were conducted to test the magnesium ammonium phosphate（MAP） formation, and the compost products were analyzed by X-ray diffraction（XRD）, Scanning electron microscopy（SEM）, and Energy dispersive X-ray spectroscopy（EDS） analyses. The comparison results between XRD, SEM, and EDS analyses of MAPs in the dried compost and synthesized MAPs confirm the formation of MAP crystals in the simulated food waste aerobic composting process. The analysis of the compost also indicates that the addition of all the three mixtures of Mg and P salts in the aerobic composting process can increase nitrogen conservation and decrease nitrogen loss because of the formation of MAPs. The mechanism of MAP formation was verified as the reaction of ammonium（NH4＋） with magnesium（Mg^2＋） and phosphate[HnPO4^（3-n） , n=0, 1, and 2）.

Application of Potent Actinomycete Strains for Bio-Degradation of Domestic Agro-Waste by Composting and Treatment of Pulp-Paper Mill Effluent

Actinomycetes are known to produce an extensive range of bioactive compounds as well as variety of enzymes having multiple biotechnological applications. They are an important source of lignocellulose hydrolyzing enzymes and constitute considerable proportion of the soil or aquatic micro-flora responsible for degradation of biomass in natural environment. Presently, most of the commercially exploited lignocellulases and commercial biodegradation processes rely mostly on fungal or bacterial micro-organisms. Actinomycetes are relatively less explored for biodegradation processes that utilize lignocellulases for solid agro-waste management and waste water treatment. There is also a need to search and explore novel actinomycete strains for various biodegradation applications. This study involved examining the possibility of using only potent actinomycetes strains for the composting process by creating the consortium of such strains that could produce thermo-tolerant and alkali-tolerant key enzymes necessary for the degradation of cellulose, hemi-cellulose and lignin. The newly developed actinomycete consortium was tested for the composting activity and the composting process was optimized. The analysis of the composted material generated under ideal condition, demonstrated desirable physical and chemical characteristics. Paper pulp effluent poses a hazard to waterways due to toxicity. The toxicity of this mill effluent can be attributed to a compound called lignin and its chlorinated derivatives that are let out during the treatment of lignocellulosic constituents. Current study also involves the use of a strain of actinomycete having ability to produce enzyme laccase, which is active under alkaline condition for the treatment of paper pulp effluent. Enzyme laccase is known for its ability to attack phenolic components of lignin and common hazardous component of effluent, polycyclic aromatic hydrocarbons (PAH). Aerobic treatment of effluent by actinomycete strain indicated 21% reduction in COD at pH 7.5 after 14 days under optimum condition. This strain was identified as Streptomyces rochei based on molecular fingerprinting and was reported to be the producer of laccase probably for the first time. LCMS analysis of the treated effluent sample showed the presence of degradation compounds forming after 7 and 14 days of treatment. These compounds showed the degradation of lignin components and other phenolic, non-phenolic components of the effluent by intra molecular re-arrangement, oxidation and ring opening reactions. Overall, potent thermo-tolerant and alkali-tolerant actinomycete strains were successfully isolated and applied for bio-degradation of domestic agro-waste by composting and treatment of pulp-paper mill effluent. The consortium of these strains may be further utilized for scale-up studies in order to assess its commercial feasibility for biodegradation processes.

Microbial community dynamics during composting of animal manures contaminated with arsenic,copper,and oxytetracycline

Effects of the heavy metal copper(Cu), the metalloid arsenic(As), and the antibiotic oxytetracycline(OTC) on bacterial community structure and diversity during cow and pig manure composting were investigated. Eight treatments were applied, four to each manure type, namely cow manure with:(1) no additives(control),(2) addition of heavy metal and metalloid,(3) addition of OTC and(4) addition of OTC with heavy metal and metalloid;and pig manure with:(5) no additives(control),(6) addition of heavy metal and metalloid,(7) addition of OTC and(8) addition of OTC with heavy metal and metalloid. After 35 days of composting, according to the alpha diversity indices, the combination treatment(OTC with heavy metal and metalloid) in pig manure was less harmful to microbial diversity than the control or heavy metal and metalloid treatments. In cow manure, the treatment with heavy metal and metalloid was the most harmful to the microbial community, followed by the combination and OTC treatments. The OTC and combination treatments had negative effects on the relative abundance of microbes in cow manure composts. The dominant phyla in both manure composts included Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. The microbial diversity relative abundance transformation was dependent on the composting time. Redundancy analysis(RDA) revealed that environmental parameters had the most influence on the bacterial communities. In conclusion, the composting process is the most sustainable technology for reducing heavy metal and metalloid impacts and antibiotic contamination in cow and pig manure. The physicochemical property variations in the manures had a significant effect on the microbial community during the composting process. This study provides an improved understanding of bacterial community composition and its changes during the composting process.

Phosphate rock reduces the bioavailability of heavy metals by influencing the bacterial communities during aerobic composting

Available information on the microbial mechanisms associated with heavy metal(HM)passivation during co-composting amended with phosphate rock(PR)remains limited.Thus,this study investigated the dynamic changes in bacterial communities and HM-fractions(Zn,Cu,Cd,Cr and Pb)during swine manure composting with maize straw,and ascertained the bacterial influence on HM-passivation.The results demonstrated that the addition of PR improved HM-passivation,especially for Zn and Cd,with their bioavailability factors(BFs)reduced by 247.41 and 176.25%,respectively.As for bacterial communities,the proportion of Firmicutes decreased,while the proportions of Proteobacteria,Bacteroidetes,DeinococcusThermus and Gemmatimonadetes increased in all treatments.PR significantly changed the primary bacterial phyla in the thermophilic phase.Bacteroidetes were the main bacterial component controlling the passivation of Zn,Cu and Cr,while Deinococcus-Thermus mainly regulated the mobility of Zn and Pb,and Proteobacteria only dominated the transformation among Cd-fractions.These results may provide a reference for the use of HM-passivation techniques during composting.