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.

Evolution of Heavy Metal Speciation During a Large-scale Sewage Sludge Composting

The evolution of metal species during sludge composting in aerobic reactor has been widely investigated,but little is known in large scale.In this study,the transformations of heavy metals speciation(Zn,Cu,Pb and Cd)in the process of sludge composting were studied in a bunker.Physico-chemical parameters,such as pH,moisture content(MC),organic matter(OM),humic acids(HA)and fulvic acids(FA)contents,were determined to evaluate their impacts on the redistribution of Zn,Cu,Pb and Cd in sludge compost.During the composting process,the contents of Cu,Pb,Zn and Cd in oxidizable and residual forms increased,whereas the contents of the exchangeable Cu,Pb,Zn and Cd decreased,with a slight increase in the total heavy metal contents.The contents of Cu,Zn and Cd in carbonate form and the reducible Cu,Zn and Pb falled;however,the content of Pb in carbonate formed and the reducible Cd increased.The results indicated that heavy metals(Zn,Cu,Pb and Cd)in sewage sludge could be passivated during composting process.The heavy metals speciation in the compost correlated with the physico-chemical parameters.In addition,linear regression analysis indicated that the content of mobile Pb could predict the total content of Pb.The contents of the residue fraction for Pb,Zn and Cd were decreased,but those for Ni and Cr were increased;the Cu residue fraction was almost constant.The contents of the total mobile fractions(including fractions 1-4)for Zn and Pb were significantly increased,but the increase of those for Cu and Ni were not so remarkable.There were significant degrees of correlation between heavy metal fractions and changes of some selected parameters(for example,pH,composting temperature and OM content).Only the content of the total mobile fractions for Cu could be predictable from its total content.For the prediction of the total mobile fractions of Zn,Ni,Cd and Cr,the R2 value was significantly increased by the inclusion of other variables such as pH,temperature and OM content.

Selecting and optimizing of the heavy metal inactivator in sewage sludge composting

In sewage sludge composting, adding ash from stove （FA20） inactivated active Cu effectively and the results were significantly better than control. For Zn, Mn, Pb and Cd, satisfying results was,achieved by adding ash from stove and phosphorite powder （FA20, PR10）, phosphorite powder and lime （PR15, CL10）, ash from stove and phosphorite powder （FA10, PR10）, and ash from stove and peat （FA20, PT 10）. Based on their effects of inactivating available forms of heavy metals, ash from stove, phosphorite powder and peat were supposed to be effective inactivators with optimum percentages of 20%, 15% and 10% （FA20, PR15, PT10）.

Stabilization of Spent Grains by Composting: Case of the BB Brewery in Lomé(Togo)

Brewery grains have a long history in animal feed. This use in animal feed nevertheless poses a problem, that of bad odors due to the sometimes too long shelf life of spent grains. The objective of this work is to recover spent grains from the BB brewery in Lomé by composting in order to stabilize them. A compost based solely on spent grains was produced after 5 months. The physico-chemical and spectroscopic characterizations at the end of the composting process revealed that the compost obtained has interesting properties with a pH = 7.01;a C/N ratio of 13.7 and a low level of heavy metals (Pb = 1.23 mg/kg, Cd = 0.04 mg/kg etc.).

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.

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.

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.

Sequential extraction of heavy metals during composting of urban waste

In urban waste (the first matter of compost), elements such as copper, nickel and lead may be found in metallic state (wire, pile, accumulator, etc.), which is considered as non-dependent state. The work undertaken at the laboratory of composting of the INRST in Henchir Lihoudia (Tunis) showed that the produced compost does not contain any mobile metallic element and the portion related to organic fraction (bioavailable) is tiny in size. We supposed that many reactions involving decomposition and complexation from elements related to the matrix components occurred during composting. The existence and importance of this phenomenon can be evaluated by studying the evolution of metal contents in the different fractions extracted sequentially during composting process.

Comparison of methods for evaluating stability and maturity of co-composting of municipal solid wastes and sewage sludge in semi-arid pedo-climatic condition

The step of maturation (around 60 days) appeared less active as compared to the first step of pre-fermentation (around 90 days) since the values of temperature, recorded during the second step of maturation, are found generally less important than those recorded during the first step. A similar tendency of C/N ratio values decrease is generally observed in the two piles of wastes during the two steps of composting and these C/N ratio values determined in the pile of wastes free of sewage sludge (W1) are generally slightly higher than those observed in the pile added with dry sewage sludge (W2). The amount of total heavy metals (order of content: Zn > Pb > Ni > Cu > Cr > Cd) appeared very heterogeneous and showed a large variation in the two piles of wastes. The use of sewage sludge in the pile W2 showed generally no apparent impact on the whole amount of total heavy metals recorded in the finished product and the values recorded are usually lower than the metal concentration limits imposed by several countries. Microbial inventory and total DNA extracted from composting materials followed during all the two steps of composting showed a net variation over time, and revealed specifically a good parallel progress according to the ambient temperature recorded inside the waste materials. It appeared also from this study that the microbial diversity is much nuanced in the case of windrow W2 added with sewage sludge as compared to that observed in the case of windrow W1 free of sewage sludge.

Effect of exogenous additives on heavy metal passivation and nitrogen retention in pig manure composting

The widespread use of feed additives in intensive and large-scale pig farming has resulted in high levels of heavy metals in pig manure.The long-term application of organic fertilizers containing high levels of heavy metals leads to the accumulation of heavy metals in the soil,which not only causes heavy metal pollution in the soil,and also affect food safety and endanger human health.Composting is an economical and effective technical measures to achieve environmentally-sustainable treatment of pig manure and is a practical method to reduce the problem of heavy metals and to improve the resource value of pig manure.The composting process is accompanied by high temperatures and the production and emission of gases,and also lead to changes in the nitrogen content of the compost and provide opportunity for heavy metal passivation additives.This paper summarizes the forms and types of heavy metals present in pig manure and reviews the progress of research as well as the techniques and problems of in the composting process,and provides recommendations for research on heavy metal passivation and nitrogen retention in pig manure composting.

Effect of lime on speciation of heavy metals during composting of water hyacinth

Composting is attractive and inexpensive method for treatment and biomass disposal of water hyacinth. However, the major disadvantage of water hyacinth composting is the high content of heavy metals in the final compost. Addition of lime sludge significantly reduced most bioavailable fractions （exchangeable and carbonate） of heavy metals. Studies were carried on composting of water hyacinth （Eichhornia crassipes） with cattle manure and sawdust （6：3：1 ratio） and effects of addition of lime （1%, 2% and 3%） on heavy metal speciation were evaluated during 30 days of composting period. The Tessier sequential extraction method was employed to investigate the changes in speciation of heavy metals such as Zinc （Zn）, Copper （Cu）, Manganese （Mn）, Iron （Fe）, Lead （Pb）, Nickel （Ni）, Cadmium （Cd） and Chromium （Cr） during water hyacinth composting. Effects of physicochemical parameters such as temperature, pH and organic matter on speciation of heavy metals were also studied during the process. Results showed that, the total metal content was increased during the composting process. The higher reduction in bioavailability factor （BF） of Cu, Fe, Ni, Cd and Cr was observed in lime 2 treatment about 62.1%, 64.4%, 71.9%, 62.1% and 58.9% respectively; however higher reduction in BF of Zn and Pb was observed in lime 1 treatment during the composting process. Reducible and oxidizable fractions of Ni, Pb and Cd were not observed during the process. Addition of lime was very effective for reduction ofbioavailability of heavy metals during composting of water hyacinth with cattle manure and sawdust.

Biochar mitigates the biotoxicity of heavy metals in livestock manure during composting

The addition of biochar could mitigate the bioavailability of heavy metals during livestock manure composting.However,the main action mechanism of biochar,such as how it worked,was ambiguous.Therefore,in this study,materials(biochar,alkali modified biochar,pretreated cotton ball)were added by embedding with nylon mesh bags to explore the adsorption performance of added materials and its influence on the composting process.The results showed that embedded materials promoted the formation of humic acid and reduced the distribution proportion of bioavailable fraction of heavy metals during composting(Cu:at least 15.72%;Zn:at least 33.44%).The surface of biochar extracted from composting contained attachments,however,the attachment of heavy metal was not detected and functional groups on the materials did no change significantly.This indicated that the addition of biochar did not directly adsorb heavy metals.Most notably,the microbial network changed after embedding materials,and the succession of microbial community promoted the formation of humic acid.Ultimately,structural equation models verified that embedded materials promoted the formation of humic acid through stable microbial groups,thereby accelerating the passivation of heavy metals during composting.This study provides theoretical and technical supports for mitigating the biotoxicity of heavy metals by biochar during composting.

The Effect of Planting Oilseed Rape and Compost Application on Heavy Metal Forms in Soil and Cd and Pb Uptake in Rice

Pot experiments were conducted under greenhouse condition to investigate whether Cd and Pb uptake by rice could be reduced when it was rotated with oilseed rape and compost application.The results showed that the rice grown after oilseed rape had significantly lower Cd and Pb concentrations in both straw and grains.Cd and Pb concentrations in the grains of the rice rotated with oilseed rape decreased by approximately 46-80% and 17-86%,respectively,although the Cd and Pb removal by oilseed rape ranged only from 2.39-3.67 and 0.032-0.13% of the total content in soil.Compost amendment also decreased the bioavailability of Cd and Pb in the soil and reduced Cd and Pb uptake by oilseed rapes and rice.The concentrations of Cd and Pb significantly decreased in the exchangeable and carbonate fractions and Pb concentration decreased in the organic matter and sulfide fractions in the contaminated soil after planting oilseed rapes.

A novel biosorbent: characterization of the spent mushroom compost and its application for removal of heavy metals

The spent mushroom compost of Lentinus edodes was used as a biosorbent for adsorbing cadmium, lead and chromium from solutions under batch conditions for the first time. Titration of the biomass revealed that it contained at least three types of functional groups. The Fourier transform infrared spectrometry showed that the carboxyl, phosphoryl, phenolic groups were the main groups. The simulated values of pK, and molar quantity were 5.00 and 0.44 mmol/g, 7.32 and 1.38 mmol/g, 10.45 and 1.44 mmol/g, respectively. The biosorption ability increased with pH in acid condition. When 10 mg/L biomass dosage was added in, there was no significant increment of metal uptake. The maximum uptake estimated with the Langmiur isotherm model were 833.33 mg/g for Cd（ Ⅱ ）, 1000.00 mg/g for Pb（ Ⅱ ） and 44.44 mg/g for Cr（ Ⅲ ）, respectively. All the results showed that vast potential sorption capacity was existed in the biomass for adsorbing these three kinds of metals studied.

Heavy metals and community structure of microorganism changes during livestock manure composting with inoculation of effective microorganisms

Effective microorganisms(EM)is usually used in composting to improve the composting process.However,the effect of EM on heavy metals evolution was still unclear.This study was performed to illustrate the microbial community changes that occur during composting with the addition of EM and to determine the evolution of heavy metal speciation during this process.The requirement of harmlessness for pig manure was met after the addition of EM at a dosage of 0.5%,with a germination index of 96.42%.The bacterial and fungal diversity were both found to decrease during the composting process.Additionally,the bioavailability of Cu and Pb decreased significantly during composting.Significant correlations were observed between the microbial composition and the percentage of different heavy metals fractions;however,the mechanism responsible for this correlation requires further investigation.This study has the potential to contribute to control of heavy metal contamination during the process of recycling pig manure through the controlled addition of EM.

Heavy metal accumulation of urban domestic rubbish compost in turfgrass by EDTA chelating

Seven kinds of heavy metal accumulation of rubbish compost in turfgrass by EDTA chelating were investigated. With EDTA application, heavy metal accumulation by two species of turfgrass was increased significantly. The enrichment coefficients of Lolium perenne L（L） and Festuca arundinacea L（F） to Cr reached 9.4.5 and 6.15 respectively. In the range of EDTA dosages given, heavy metal accumulation in turfgrass increased with increasing EDTA level. There were significant differences in remediation of different metals by applying EDTA. L had high ability to accumulate Cr, Cd, Ni and Zn, showing better remediation to heavy metals of rubbish compost. In contrast, F showed high ability to accumulate Cr, Ni, Cu and Zn. Low EDTA level increased aboveground net primary production （ANP） of turfgrass, but EDTA would considerably inhibit it when EDTA was higher than 20 mmol/kg. The results demonstrated that the optimum dosage of EDTA for remediating heavy metals in rubbish compost by turfgrass was between 10 mmol/kg and 20 mmol/kg.

Heavy Metal Remediation in Sludge Compost: Recent Progress

The safe and efficient disposal and utilization of sludge are major issues to be solved in solid waste treatment and environmental protection due to the complex characteristics of sludge and the low rate of innocuous treatments.Composting is a process of decomposing organic matter and transformed low-molecular organic acids into high-molecular humus substances under the action of microorganisms.Although land-use after composting has become an important direction for sludge treatment,heavy metal pollution is still the bottleneck problem restrict-ing land use of sludge compost.Adding zeolite,hydroxyapatite,and other conditioning agents to the composting process affects the concentration or form of some heavy metals and effectively reduces the environmental risk.Lime and phosphorus modifiers change heavy metal speciation in samples,playing a role in decreasing biological availability and mobility.In this study,the effects of sludge composting treatment and conditioning agents on the concentrations and forms of heavy metals are reviewed.This review will provide a theoretical basis to treat heavy metals in sludge composting and lay the foundation for the land utilization and waste recycling of sludge.

Effect of Compost Amendment on Heavy Metals, Nitrogen and Phosphorus in a Peat-Based Container Medium

A laboratory study was conducted to evaluate the effect of compost amendment on mobility and leaching potential of heavy metals, nitrogen （N） and phosphorus （P） from a peat-based commercial container medium containing 700 g kg^-1 peat, 200 g kg^-1 perlite and 100 g kg^-1 vermiculite at varying amendment rates of compost （0, 0.25, 0.50, 0.75 and 1.00 L L^-1）. Increasing compost amendment significantly and linearly increased the pH （P 〈 0.01）, the total concentrations of organic carbon （P 〈 0.05）, copper （Cu） （P 〈 0.01）, cadmium （ca） （P 〈 0.01）, and lead （Pb） （P 〈 0.01）, and increased the bulk density （P 〈 0.01） of the medium. The electrical conductivity （EC）, and total N and P of the medium increased significantly （P 〈 0.01） and quadratically with increasing compost amendment. The relationship of the C/N ratio of the medium with the compost amendment rate was decreasing, significant （P 〈 0.01） and cubic, while that of the total Zn was increasing, significant （P 〈 0.01） and cubic. Extractable P, NO3-N, and NH4-N increased initially with an increasing compost amendment of up to 0.50 L L^-1 and then decreased with further increasing compost rate. Increasing compost rates resulted in a highly significant （P 〈 0.01） and linear increase in total Cd, Cu, and Pb, and a highly significant （P 〈 0.01） and cubic increase in total Zn in the medium. Increasing compost rates also significantly （P 〈 0.01） increased extractable Cu （linearly） and Zn （quadratically）, but significantly （P 〈 0.01） decreased extractable Pb （linearly）. There was no significant effect of compost amendment on the extractable Cd concentration in the medium. However, with increasing compost rates from 0.25 to 1.00 L L^-1, extractability of P, Cd, Cu, Pb and Zn （extractable concentration as a percent of total） was decreased, indicating that compost amendment could lower the leachability of these elements from the medium.

The Effect of Water Hyacinth (<i>Eichhornia crassipes</i>) Compost on Tomato (<i>Lycopersicon esculentum</i>) Growth Attributes, Yield Potential and Heavy Metal Levels

The potential of different water hyacinth compost application rates in influencing growth attributes, yield and heavy metal accumulation of lead (Pb), copper (Cu), nickel (Ni) and zinc (Zn) in tomato fruit was studied in Masvingo. Four treatments of water hyacinth compost rates of 0, 37, 55.6 and 74.1 t·ha-1 were each replicated three times and applied in a randomized complete block design set up. Results showed that water hyacinth compost application rates significantly affected plant height, days to maturity and yield but had no influence on the number of tomato fruits per plant. The plant height at application rate of 74.1 t·ha-1 was 25%, 56% and 63% higher than the control at week 6, 9 and 12, respectively. At application rates of 56.6 t·ha-1, plant heights were 11%, 13% and 12% higher than the control whilst marginal plant height differences of -4%, 6% and 4% were recorded between application rate of 34.7 t·ha-1 and the control at week 6, 9 and 12, respectively. Tomato plants under compost rates of 34.7, 56.6 and 74.1 t·ha-1 in comparison to the control delayed maturity by 10, 17 and 20 days, respectively. Yields of 52, 55, 60 and 68 t·ha-1 were realized from hyacinth compost rates of 0, 34.7, 56.6 and 74.1 t·ha-1, respectively. Heavy metal concentrations increased with increase in the water hyacinth compost rate but at all application rates, the average concentrations were 85%, 93% and 86% lower than the Codex Alimentarious Commission permissible levels for Pb, Cu and Zn. Water hyacinth compost at a rate of 74 t·ha-1 therefore can be used for increased tomato yield without exposing consumers to heavy metal toxicity.

Heavy Metal Contents of Different Wastes Used for Compost

A study was conducted to assess the heavy metal (As, Pb, Cd, Cr, Cu, Zn and Hg) contents of different sources of wastes generated in Dhaka city which was further used for a compost plant. The study consisted of both field survey and laboratory analyses. Relevant primary and secondary sources of data were collected to identify the source and nature of wastes generated near the compost plant. A total of eight households, ten officers and ten waste collectors were surveyed for data collection. For laboratory analyses, wastes from various socio-economic niches (lower, lower middle, middle and high) were collected. The result showed that wastes generated in the lower income niche contained the minimum contents of heavy metals compared to middle and high niches. The increasing trend of heavy metal contents of the wastes from lower to high income groups has been found to be linked to the life style, attitude, profession, culture and food habit. Most of the heavy metals did not meet the standard level for almost all the niches. Most of the correlations were found to be insignificant between the contents of nutrient element (C, N and P) and heavy metals (As, Pb, Cd, Cr, Cu, Zn and Hg).