Evolution of heavy metal speciation during the aerobic composting process of sewage sludge

The contents of heavy metals and their bioavailability to the soil-plant system were the major limitation to the application of sewage sludge compost in soil. This study was conducted to determine the evolution of heavy metal speciation in the course of an aerobic composting, and investigate the influence of changes of composting process parameters including pH, temperature and organic matter (OM) content on distribution of heavy metal speciation in composted sludge. The sequential extraction procedure developed by Tessier et al. was used in sludge compost to determine the heavy metal speciation. Results showed that, during composting, (1) 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; (2) 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; (3) 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 R(2) value was significantly increased by the inclusion of other variables such as pH, temperature and OM content.     

Ni2＋对活性污泥活性及群落多样性的影响

通过检测活性污泥的电子传递体系活性以及生物多样性，研究Ni2＋对活性污泥微生物活性及群落多样性的影响。结果表明：与对照系统相比，5mg／L的Ni2＋对2，3，5-lriphenylteItrazoliumchloride（TTC．ETS）活性未产生显著的影响；但当Ni2＋的浓度进一步增大到10、20和40mg／L后，其对序批式反应器内活性污泥TTC—ETS活性的抑制率分别达到（36．794-11．14）％、（55．88±13．90）％和（70．97±6．78）％。低浓度Ni2＋．能增强活性污泥微生物对碳源的利用，但高于10mg／L的Ni2＋则显著抑制了活性污泥微生物对碳源的利用。各个SBR系统中微生物群落最常见的物种相近，物种丰富度和均一性则均有所不同，其中群落物种丰富度随着Ni2＋浓度的增加而逐渐减小。TTC—ETS活性、平均每孔颜色变化率、Shan—liOn指数和Simpson指数，与Ni2＋的胁迫浓度之间的显著相关性表明，它们均可有效地表征Ni2＋胁迫对活性污泥微生物活性及群落多样性的影响程度。     

The influence of organic amendment and nickel pollution on tomato fruit yield and quality

The effects of organic fertilization (sludge application) and/or different levels of Ni pollution on tomato fruit yield, quality, nutrition, and Ni accumulation were investigated. The mass loading of sewage sludge solids used in this study for the amendment of a calcareous soil with low organic matter content was 2% (w/w). A control with no sewage sludge amendment was also included (S). Nickel was added to the sludge amended soil at 0, 60, 120 and 240 mg kg-1 concentrations. Sewage sludge addition to the calcareous soil significantly increased fruit yield but did not adversely affect the quality and nutritional status of the tomato fruit. The results demonstrated that sewage sludge could be successfully used as a horticultural fertilizer. Only the highest addition rate of Ni (240 mg kg-1) to an organic amended calcareous soil had negative effects on fruit yield and quality, and caused a Ni accumulation in fruit that could be considered as a hazard for human health. Thus, no toxic problems will be encountered in tomato fruit due to Ni pollution provided the total Ni (soil Ni plus Ni incorporated with sludge amendment) concentration is kept below the maximum concentration of Ni allowed for agricultural alkaline soils in Spain (112 mg Ni kg-1).     

Change of PCBs and forms of heavy metals in sewage sludge during thermophilic anaerobic digestion

Determination of seven congeners of PCBs was carried out for sewage sludge before, during and after thermophilic digestion. The overall content of heavy metals (Zn, Cu, Ni, Cd, Pb, Cr) in sludge before and after digestion was determined. Moreover the concentration of heavy metals in particular chemical fractions of the sludge was analyzed. After the thermophilic digestion total concentration of seven PCBs was reduced by 47%, which suggests that thermophilic digestion affects PCB reduction positively. On the 10th d of the process, concentration of lower chlorinated PCBs increased, whereas those of higher chlorinated PCBs decreased. The thermophilic digestion process showed no accumulation of the studied heavy metals in the mobile fractions (exchangeable and carbonate) of the stabilized sewage sludge, except for nickel. The highest increase in zinc, copper, cadmium, and chromium concentration was observed in the organic-sulfide fraction, whereas the highest increase in lead was found in the residual fraction of the sludge. In case of nickel both fractions of organic-sulfide and exchangeable-carbonate fractions were enriched.     

Tetracycline as a selector for resistant bacteria in activated sludge

Tetracycline, one of the most widely used antibiotics, is excreted into wastewater after consumption by humans and animals. The focus of this research was to evaluate the fate of tetracycline resistant bacteria in the activated sludge process as a function of tetracycline loading. The studies were conducted with aerobic biological sequencing batch reactors (SBRs). When comparing 250 microgl(-1) tetracycline fed SBRs with parallel SBRs having a background influent wastewater tetracycline concentration of approximately 1 microgl(-1), tetracycline fed reactors were found to have increased concentrations and production rates of tetracycline resistant bacteria, higher net growth rates of resistant bacteria, and higher percentages of tetracycline resistant bacteria, which were amplified by increase in organic loading and growth rates.     

Effects of sewage sludge amendment on heavy metal accumulation and consequent responses of Beta vulgaris plants

Use of sewage sludge, a biological residue produced from sewage treatment processes in agriculture is an alternative disposal technique of waste. To study the usefulness of sewage sludge amendment for palak (Beta vulgaris var. Allgreen H-1), a leafy vegetable and consequent heavy metal contamination, a pot experiment was conducted by mixing sewage sludge at 20% and 40% (w/w) amendment ratios to the agricultural soil. Soil pH decreased whereas electrical conductance, organic carbon, total N, available P and exchangeable Na, K and Ca increased in soil amended with sewage sludge in comparison to unamended soil. Sewage sludge amendment led to significant increase in Pb, Cr, Cd, Cu, Zn and Ni concentrations of soil. Cd concentration in soil was found above the Indian permissible limit in soil at both the amendment ratios.

The increased concentration of heavy metals in soil due to sewage sludge amendment led to increases in heavy metal uptake and shoot and root concentrations of Ni, Cd, Cu, Cr, Pb and Zn in plants as compared to those grown on unamended soil. Accumulation was more in roots than shoots for most of the heavy metals. Concentrations of Cd, Ni and Zn were more than the permissible limits of Indian standard in the edible portion of palak grown on different sewage sludge amendments ratios. Sewage sludge amendment in soil decreased root length, leaf area and root biomass of palak at both the amendment ratios, whereas shoot biomass and yield decreased significantly at 40% sludge amendment. Rate of photosynthesis, stomatal conductance and chlorophyll content decreased whereas lipid peroxidation, peroxidase activity and protein and proline contents, increased in plants grown in sewage sludge-amended soil as compared to those grown in unamended soil.

The study clearly shows that increase in heavy metal concentration in foliage of plants grown in sewage sludge-amended soil caused unfavorable changes in physiological and biochemical characteristics of plants leading to reductions in morphological characteristics, biomass accumulation and yield. The study concludes that sewage sludge amendment in soil for growing palak may not be a good option due to risk of contamination of Cd, Ni and Zn and also due to lowering of yield at higher mixing ratio.     

Sequential extraction of heavy metals during composting of sewage sludge

The major limitation of soil application of sewage sludge compost is the total heavy metal contents and their bioavailability to the soil-plant system. This study was conducted to determine the heavy metal speciation and the influence of changing the physico-chemical properties of the medium in the course of composting on the concentrations, bioavailability or chemical forms of Cu, Zn, Pb and Ni in sewage sludge. Principal physical and chemical properties and FTIR spectroscopical characterization of sludge compost during treatment show the stability and maturity of end product. The total metal contents in the final compost were much lower than the limit values of composts to be used as good soil fertilizer. Furthermore, it was observed by using a sequential extraction procedure in sludge compost at different steps of treatment, that a large proportion of the heavy metals were associated to the residual fraction (70-80%) and more resistant fractions to extraction X-NaOH, X-EDTA, X-HNO3 (12-29%). Less than 2% of metals bound to bioavailable fractions X-(KNO3+H2O). Heavy metal distribution and bioavailability show some changes during composting depending on the metal itself and the physico-chemical properties of the medium. Bioavailable fractions of all elements tend to decrease except Ni-H2O. Zn and mainly Cu present more affinity to organic and carbonate fractions. In contrast, Pb is usually preferentially bound to sulfide forms X-HNO3. Nickel shows a significant decrease of organic form. Significant degrees of correlation were found between heavy metal fractions and changes of some selected variables (e.g. pH, ash, organic matter, humic substance) during the course of composting. Mobile fractions of metals are poorly predictable from the total content. The R2 value was significantly increased by the inclusion of other variables such as the amount of organic matter (OM) and pH.     

中国部分城市污泥中矿质元素形态与生物可利用性研究

近年来随着城市污水处理厂数目迅速增加,低成本、高效率的污泥农用受到越来越多的关注。研究从北到南的五家污水处理厂消化污泥中矿质元素的含量和形态分布,为污泥资源化的合理利用提供科学参考。结果表明：消化污泥总体呈高有机质、高氮磷、低K、高矿质元素营养的相似性,但其理化性质如阳离子交换容量(CEC)、pH等差异较大,对矿质元素的形态分布与生物可利用性有明显的影响。同种元素在不同污泥中含量的差异较大,相差数倍,甚至十倍以上。污泥中不同元素含量明显不同,Fe的浓度最高,次之是Mg、Zn、B的浓度最低。连续提取研究表明,污泥pH对污泥中矿质元素的形态分布有明显影响,酸性污泥(厦门污水处理厂)中各矿质元素酸溶／交换态百分率明显高于其他污泥。Cu主要分布在氧化态;Zn的三态分布百分率均在10％以上;Mg、Mn的酸溶／交换态含量较高;Fe主要分布在残渣态;B氧化态和还原态的百分率较高。建议在全国范围内进行一次污水处理厂污泥品质调查,为污泥合理农用提供科学依据。     

溶解氧对活性污泥合成可生物降解塑料—PHB的影响

聚-β-羟基丁酸酯（polyhydroxybutyrate,PHB）是一种可完全生物降解和具有良好生物相容性的高分子材料，许多情况下可作为传统塑料的替代品。以活性污泥微生物作为PHB合成菌，研究了动态底物投加方式下，溶解氧对污泥贮存PHB过程的影响。结果表明，PHB的贮存过程相当程度上取决于氧的提供。溶解氧浓度的提高明显加快了底物乙酸的吸收，进而导致更大比例的乙酸被活性污泥贮存为PHB。试验中，溶解氧浓度由饱和浓度的10%提高到70%，PHB的产率由0.36 C mmol/C mmol 提高到0.56 C mmol/C mmol，PHB的胞内含量也由26%提高到37%。试验证明溶解氧是控制活性污泥合成PHB工艺的重要因素。     

低浓度LAS对活性污泥性质和去除污染物行为的影响

采用SBR处理模拟废水,考察了不同浓度阴离子表面活性剂——烷基苯磺酸钠（LAS）对反应器活性污泥的影响。实验结果表明,低浓度表面活性剂LAS的投加,有利于提高SBR中活性污泥对COD和氨氮处理效率,并且活性污泥的沉降性以及微生物活性也随着LAS投加浓度的升高而升高。但是,当LAS的投加浓度过高时（1 mg/L）,污泥表面产生起泡、乳化和微粒悬浮等现象,使大量固体陷入漂浮泡沫层,降低曝气池的充氧效率,最终导致污泥解体,沉降性变差,活性下降。     

调理剂对堆肥产品重金属生物有效性的影响

城市污泥中重金属含量及其生物有效性是限制污泥农用的主要因素,因此,研究污泥堆肥化处理过程中重金属生物有效性,对污泥的农用具有重要意义。实验以城市污泥为原料,以菌菇渣和秸秆为调理剂,设置4个处理:A(污泥∶菌菇渣∶秸秆=1∶0.4∶0.025)、B(污泥∶菌菇渣∶秸秆=1∶0.3∶0.025)、C(污泥∶秸秆=1∶0.12)和D(污泥∶秸秆=1∶0.09),进行好氧堆肥实验,采用BCR顺序提取法测定各种形态的重金属,研究堆肥前后重金属形态的变化规律。结果表明,城市污泥中Cu、Ni、Pb和Cr主要以可氧化态及残渣态存在,生物有效性较低,而Zn和Cd主要以酸溶态和可还原态存在,生物有效性较高;堆肥过程显著降低了Cu、Zn、Ni和Pb的生物有效性,并改变了Cu、Zn、Ni、Pb、Cr和Cd的形态分布,使污泥中的Cu、Zn、Ni、Pb和Cd向着更稳定的可氧化态或残渣态转变;污泥经过堆肥处理后,Cu、Zn和Ni 3种重金属生物有效性关系为:ABCD,与其他处理相比,处理A残渣态的Pb和Cr增加比例较多,综合来看,处理A对重金属生物有效性的降低最为明显,重金属钝化效果最佳。     

Anammox enrichment from different conventional sludges

Three sets of sequencing batch reactor (SBR) were used for Anammox enrichment from conventional sludges including upflow anaerobic sludge blanket, activated sludge, and anaerobic digestion sludge. After four months of operation, the Anammox activity occurred in all reactors allowing continuous removal of ammonium and nitrite. The morphology of the cultivated Anammox sludge was observed using scanning electron microscope. The photographs showed that the obtained culture was mostly spherical in shape, presumably Anammox culture. There were also filamentous-like bacteria co-existing in the system. Fluorescence in situ hybridization (FISH) analysis using 16S rRNA targeting oligonucleotide probes PLA46 and Amx820 showed that the dominant population developed in all SBRs was hybridized with both PLA46 and Amx820 gene probes. It means that the cultivated biomass in all SBRs was classified in the group of Planctomycetales bacteria with respect to the anaerobic ammonium-oxidizing bacteria, Candidatus Brocadia anammoxidans and Candidatus Kuenenia stuttgartiensis. Numerous time sequences were tested in this experiment. The shortest workable reaction time was found in the range from 5 to 7 h. Good quiescence of sludge was obtained at 30 min of settle period followed by a discharge period of 15 min. A long-term performance showed a near perfect removal of nitrite based on the influent NO2(-)-N concentration of 50-70 mg l(-1). The maximum ammonia removal efficiency was 80% with the influent NH4(+)-N concentration of 40-60 mg l(-1). It is, therefore, concluded that Anammox cultivation from conventional sludges was highly possible under control environment within four months.     

微量金属对废水厌氧处理效果的影响

以葡萄酒蒸馏废水的厌氧生物处理为例,研究了Fe、Ni、Co、Mo、Cu、Zn对厌氧反应器的COD去除率、出水中挥发性有机酸含量、气体产量、气体成分、pH缓冲能力和碱度等的影响.对比了微量金属投加前后,厌氧反应器污泥中微量金属含量的变化.得出微量金属具有提高厌氧运行效果的作用,其中,Co的作用要更大一些.Ni、Co、Mo在附着态、悬浮态污泥中具有逐渐积累的特点;Fe、Cu、Zn在附着态污泥中是淋失的,而在悬浮态污泥中变化不大.     

Formation of aerobic granules in the presence of a synthetic chelating agent

This paper examines the development of aerobic granular sludge in the presence of a synthetic chelating agent, nitrilotriacetic acid (NTA), in sequencing batch reactors (SBR). The growth of seed sludge at 0.26 mM, 0.52 mM and 1.05 mM of NTA was found to be significantly lower as compared to that in the absence of NTA. Aerobic granulation was significantly enhanced in the three SBRs (R2, R3 and R4), which were fed with 0.26 mM, 0.52 mM and 1.05 mM of NTA as a co-substrate, in comparison to the acetate-alone fed SBR (R1). After 2 months of operation, the mean diameter of the biomass stabilized at 0.35 mm in R1 (acetate alone), as compared to 2.18 mm in R4 (1.05 mM NTA+acetate). NTA degradation was established in SBRs, with almost complete removal during the SBR cycle. Batch experiments also showed efficient degradation of NTA by the aerobic granules.     

季铵化合物对好氧活性污泥吸附Ni2+的影响研究

以季铵化合物中最具潜在影响力、毒性较大的苄基季铵盐(BAC)为模型物,进行了BAC对好氧活性污泥吸附Ni2+的影响研究.结果表明,当反应液初始pH≤3时,不同浓度的BAC对好氧活性污泥吸附Ni2+的影响较小,当初始pH在3～9时,不同浓度的BAC对Ni2+吸附的抑制影响顺序为100 mg/L＞20 mg/L＞0 mg/...     

Metal associations in soils before and after EDTA extractive decontamination: implications for the effectiveness of further clean-up procedures

The distribution of Pb, Ni and Zn in two contaminated soils was determined before and after treating the soils with an EDTA solution. After the EDTA extraction, the proportion of Pb accumulated in the acid-extractable fraction considerably increased, which was related to the greater degree of metal extraction from the other fractions. EDTA was also able to extract certain amounts of Pb, Zn and Ni from the silicate matrix, which implied that these extractable amounts were not so strongly fixed to the residual fraction as previously supposed. As a consequence, after EDTA application, metal content (especially Pb) remained more weakly adsorbed to soil components (more easily leachable), potentially favouring the application of phytoremediation technologies. The extraction recoveries (for only one application) were generally low for the three metals (33-37% for Pb, 5-11% for Ni and 14-19% for Zn), although this fact is an advantage as plants would not be able to assimilate very high mobilised contents of metals.     

Implications of rhizospheric heavy metals and nutrients for the growth of alfalfa in sludge amended soil

Rhizospheric distribution of nutrients and heavy metals in sludge amended soil was investigated using the rhizobag technique to give an indication of the release of metals from wastewater sludge. DTPA-extractable Zn, Cd, Ni and Mn, and available P, K and NH4+-N in the rhizosphere were markedly depleted when soil was amended with sludge. There was no conspicuous depletion or accumulation of DTPA-extractable Cu in the rhizosphere when the soil was amended with sewage sludge but DTPA-extractable Fe accumulated in the rhizosphere when the soil was amended with increasing amounts of sludge. The pH value in the rhizosphere increased with distance from the roots when soil was amended with larger amounts of sludge. The exchangeable fraction of Cu in the rhizosphere was depleted whether or not the soil was treated with sludge. Carbonate, oxide, organic and residual fractions of Cu and Zn were depleted in the rhizosphere at a distance of 0-2 mm from the roots when soil was amended with 50% sludge. Application of sewage sludge had a positive effect on alfalfa growth. With an increase in sludge amounts, the concentrations of Fe, Cu and Zn in alfalfa shoots did not change. Soil amendments with less than 25% sludge did not increase the availability or mobility of heavy metals. The depletion in rhizospheric DTPA-extractable Zn, Cd and Ni indicates that with the sole exception of Cu, release of metals from sludge amended soil was very limited.     

Long-term effects of fertilization on the forms and availability of soil phosphorus in rice paddy

The changes in total P accumulation and P compounds with time in the plough layer in a paddy soil in southern Korea were investigated in relation to the continuous application of chemical fertilizers (NPK), straw based compost (Compost), combination these two (NPK+Compost) for 31 years. Continuous fertilization increased the total and inorganic P contents in plough layers. In NPK, inorganic P fraction did not change with time, but organic P content increased significantly. Long-term application of chemical fertilizer together with compost accelerated the decrease in the organic P fraction, presumably due to promoting microbial activity in the plow layer, and then increased significantly inorganic P fraction. Compost application decreased the residual P and Fe-P fractions and then increased inorganic P fraction, in spite of continuous compost application. Increase in total, inorganic and extractable P with time may be closely related to the increase in the availability of accumulated P for rice growth.     

Metal mobility at an old, heavily loaded sludge application site

This study was undertaken to determine the present distribution and mobility of sludge-applied metals at an old land application site. Trace metals concentrations were determined for soils (using 4 M HNO3 extracts), soil leachates (collected with passive wick lysimeters over a 2.5-year period), and plant tissue from a field site which received a heavy loading of wastewater sludge in 1978 and an adjacent control plot. Blue dye was used to indicate preferential percolate flowpaths in the sludge plot soil for sampling and comparison with bulk soil metals concentrations. After nearly 20 years, metals in the sludge plot leachate were found at significantly greater concentrations than in the control plot, exceeding drinking water standards for Cd, Ni, Zn, and B. Annual metals fluxes were only a fraction of the current soil metal contents, and do not account for the apparent substantial past metals losses determined in a related study. Elevated Cd, Cu, and Ni levels were found in grass growing on the sludge plot. Despite heavy loadings, fine soil texture (silty clay loam) and evidence of past and ongoing metals leaching, examination of the bulk subsoil indicated no statistically significant increases in metals concentrations (even in a calcareous subsoil horizon with elevated pH) when comparing pooled sludge plot soil profiles with controls. Sampling of dyed preferential flow paths in the sludge plot detected only slight increases in several metals. Preferential flow and metal complexation with soluble organics apparently allow leaching without easily detectable readsorption in the subsoil. The lack of significant metal deposition in subsoil may not be reliable evidence for immobility of sludge-applied metals.     

Impact of sewage sludge spreading on nickel mobility in a calcareous soil: adsorption–desorption through column experiments

A soil column adsorption–desorption study was performed on an agricultural calcareous soil to determine the impact of sewage sludge spreading on nickel mobility. Ni adsorption experiments were followed by desorption tests involving the following liquid extractants: water, calcium (100 mg/L), oxalic acid (525 mg/L equivalent to 100 mg carbon/L), and sludge extracts (0.5 and 2.5 g/L). Desorption tests were also conducted after sewage sludge spreading at three application rates (30, 75, and 150 t/ha). According to the breakthrough curve, Ni adsorption was irreversible and occurred mainly through interactions with calcite surface sites. Nickel desorption from the soil column was promoted in presence of significant dissolved organic carbon (DOC) concentration as observed with oxalic acid elution and sludge extract at 2.5 g/L. In sludge-amended soil columns, the maximum Ni levels occurred in first pore volumes, and they were positively correlated to the sludge application rate. The presence of DOC in leaching waters was the main factor controlling Ni desorption from the sludge-amended soil columns. This finding implies that DOC generated by sludge applied on calcareous soils might facilitate the leaching of Ni due to the formation of soluble Ni–organic complexes. Thus, sludge application can have potential environmental impacts in calcareous soils, since it promotes nickel transport by decreasing Ni retention by soil components.