Potato absorption and phytoavailability of Cd, Ni, Cu, Zn and Pb in sierozem soils amended with municipal sludge compost

Effects of sludge utilization on the mobility and phytoavailability of heavy metals in soil-plant systems have attracted broad attention in recent years. In this study, we analyzed the effects of municipal sludge compost （MSC） on the solubility and pIant uptake of Cd, Ni, Cu, Zn and Pb in a soil-potato system to explore the mobility, potato plant uptake and enrichment of these five heavy metals in sierozem soils amended with MSC through a potato cultivation trial in Lanzhou University of China in 2014. Ridge regression analysis was conducted to investigate the phytoavailability of heavy metals in amended soils. Furthermore, CaC12, CH3COONH4, CH3COOH, diethylene triamine pentacetic acid （DTPA） and ethylene diamJne tetraacetic acid （EDTA） were used to extract the labile fraction of heavy metals from the amended soils. The results show that the MSC could not only improve the fertility but also increase the dissolved organic carbon （DOC） content of sierozem soils. The total concentrations and labile fraction proportions of heavy metals increase with increasing MSC percentage in sierozem soils. In amended soils, Cd has the highest solubility and mobility while Ni has the lowest solubility and mobility among the five heavy metals. The MSC increases the concentrations of heavy metals in the root, stem, peel and tuber of the potato plant, with the concentrations being much higher in the stem and root than in the peel and tuber. Among the five heavy metals, the bioconcentration factor value of Cd is the highest, while that of Ni is the lowest. The complexing agent （DTPA and EDTA） extractable fractions of heavy metals are the highest in terms of phytoavailability. Soil properties （including organic matter, pH and DOC） have important impacts on the phytoavailability of heavy metals. Our results suggest that in soil-potato systems, although the MSC may improve soil fertility, it can also increase the risk of soils exposed to heavy metals.

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.

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.

New mechanism of FA in composted sludge inducing Cu fixation on Albite in open-pit mine soil

Fulvic acid(FA),typical organic matter derived from humification process in composted sludge,possesses the potential to remediate mine soils contaminated by heavy metals.To understand the cooper(Cu)immobilizing process in open-pit mine soil induced by FA,changes of Cu speciation in mixture of open-pit mine soil and composted sludge was tracked over 180 days.It was observed that the organic-bound and residual fraction of Cu increased dramatically with the corresponding decrease of Fe/Mn oxide-bound Cu in the first 60 days,then the organic-bound fraction decreased to about its initial proportion during 60-120 days,while residual fraction still increased,and the proportion of residual Cu accounted for over85%and became stable after 120 days.To reveal the mechanism of FA inducing Cu fixation on Albite which is the main phase of soil primary ore,two groups of Cu adsorption experiments with and without FA were designed.With the addition of FA,the adsorption capacity of Cu by Albite increased by 1.55 times and the content of residual Cu in Albite increased by7.7 times.It was found that the Cu absorbed in smaller Albite particle induced by FA formed a secondary mineral——Chrysocolla,causing increase of residual fraction of Cu.These results revealed the mechanism:FA was absorbed on the surface of Albite after complexing with Cu ions in the solution,and then it induced Cu into the interlayer and pore channels of Albite.The Cu in the Albite was immobilized by forming Chrysocolla finally.

Effect of aeration rate on composting of penicillin mycelial dreg

Pilot scale experiments with forced aeration were conducted to estimate effects of aeration rates on the performance of composting penicillin mycelial dreg using sewage sludge as inoculation. Three aeration rates of 0.15, 0.50 and 0.90 L/（min·kg） organic matter（OM） were examined. The principal physicochemical parameters were monitored during the 32 day composting period. Results showed that the higher aeration rate of 0.90 L/（min·kg） did not corresponded to a longer thermophilic duration and higher rates of OM degradation;but the lower aeration rate of 0.15 L/（min·kg） did induce an accumulation of NH＋4-N contents due to the inhibition of nitrification. On the other hand, aeration rate has little effect on degradation of penicillin. The results show that the longest phase of thermophilic temperatures ≥ 55°C, the maximum NO-3-N content and seed germination, and the minimum C/N ratio were obtained with 0.50 L/（min·kg） OM. Therefore, aeration rates of0.50 L/（min·kg） OM can be recommended for composting penicillin mycelial dreg.

A new complex plant for carbonization and composting of municipal wastes

A new complex plant for carbonization and composting of municipal wastes proposed for Gero City is introduced. The separated combustible waste and non-separated combustible waste are carbonized in two fluidized carbonization furnaces in the plant, and the coke produced is used in steelworks. The separated garbage and forest-wastes are mixed with dried septic-tank sludge to produce high quality compost for farms. This use of waste materials in the complex plant considerably lowers the amount of waste going to land-fills, and in addition, creates lower total emission of dioxins and carbon dioxide into the environment.