Immobilization of phosphorus in sewage sludge using inorganic amendments

Sewage sludge contains large amount of water-soluble phosphorus, which is prone to runoff loss when sewage sludge is land applied. Phosphorus export from sewage sludge is an important cause for water eutrophication. Immobilization of phosphorus before sewage sludge land application seems necessary. In this study, three amendments including red mud (RM), lime and mixture of RM and lime were employed to immobilize phosphorus in fresh sewage sludge. It was found that phosphorus was effectively controlled by RM, lime and mixture of RM and lime. Sequential chemical extraction results indicate that the RM amendment transformed H₂O-P in the sewage sludge into the NaOH-P, while the lime amendment transformed H₂O-P in the sewage sludge into the HCl-P. Such transformations in phosphorus fractions would have little influence on phosphorus availability but would retard and reduce potential phosphorus loss following sewage sludge was land applied.     

Reuse of dewatered sewage sludge conditioned with skeleton builders as landfill cover material

High water and organic content of sewage sludge constricts its reuse and disposal. It is often necessary to solidify/stabilize the dewatered sludge with solidifying agents before landfill disposal. In this study, the sewage sludge was conditioned with skeleton builders, i.e., fly ash and lime combined with ferric chloride for the purpose of improving the dewatering efficiency. The dewatered sewage sludge was then directly reused as landfill cover materials since the skeleton builders also play a role in solidification of sludge. The geotechnical properties of the dewatered sewage sludge were investigated. The results show that the plasticity index of the dewatered sludge increases compared to that of the dewatered sludge without any conditioner, and the permeability coefficient changes from 10^?8 to 10^?5 cm s^?1. Furthermore, the strength of specimens increase with curing days. Microstructure analyses reveal that the main hydrated products are calcium silicate hydrate and ettringite, which contribute to the solidification/stabilization of the dewatered sludge. The results indicate that the dewatered sewage sludge conditioned with skeleton builders can be used as landfill covers. This study provides an alternative for traditional sewage sludge treatment and disposal.     

Agricultural use of sewage sludge under sub-humid Mediterranean conditions: effect on growth,yield, and metal content of a forage plant

A field experiment was carried out in order to investigate the effects of sewage sludge application on the growth and yield components of triticale (X Triticosecale Wittmack). Five treatments were compared: a control (C) without application of sludge or nitrogen fertilization; a mineral fertilization treatment (MF) applied as ammonium nitrate; and three sewage sludge treatments (SS), 6, 12, and 18 t ha^?1, applied 15 days prior to triticale sowing. The main results showed that SS application improved plant growth by increasing leaf area index, tillering capacity, accumulated aboveground dry matter, and plant height of triticale. As a result, 18 t ha^?1 of SS could be recommended the suitable dose for triticale, where dry matter production was more than twofold above the control value. No toxic effects arising from the heavy metals in triticale plants were observed. The Cu concentration was the only trace element that increased in the straw tissues with sludge application, although the values recorded were below critical environmental thresholds. Furthermore, growth and yield responses of triticale to all SS rates are comparable even sometimes more important than those for mineral fertilizer.     

Effects of sewage sludge and nitrogen fertilizer on herbage growth and soil fertility improvement in restoration of the abandoned opencast mining areas in Shanxi, China

A field trial was conducted to investigate the effects of application of sewage sludge and nitrogen fertilizer on herbage growth and fertility improvement of raw mixed-loess soils at the west waste dump of Antaibao surface mine (ATB) in Shanxi, China. Four indigenous species present in mining areas, including Kentucky bluegrass, Erect milkvetch, Alfalfa and Alfalfa–ryegrass mixture were selected as the herbaceous plants in the field trial. The results showed that applying sewage sludge and nitrogen fertilizer, biomasses of all the four grasses were significantly increased when compared with those in the control group. After 100 days growth, applying sewage sludge had the greatest effects on biomass increasing for Kentucky bluegrass (17.54 times in the overground yields and 13.94 times in underground yields when compared with the control group) or Alfalfa–ryegrass mixture (5.34 and 7.20 times, respectively); meanwhile, the combined application of sewage sludge and nitrogen fertilizer also had the best effects. It was concluded that Kentucky bluegrass is the best pioneer species for quickly establishing vegetation in ATB abandoned opencast mining areas; municipal sewage sludge is an effective bio-fertilizer for the fertility improvement of raw mixed-loess soils; and the combined application of sewage sludge and nitrogen fertilizer in plots revegetated with Alfalfa–ryegrass mixture is the best strategy to help quickly establish a self-sustaining vegetation system during the primary stage of reclamation in ATB abandoned opencast mining areas in China.     

Applicability of upflow anaerobic sludge blanket (UASB) reactor for typical sewage of a small community: its biomass reactivation after shutdown

In this study, the characteristics of sewage of small community were determined for 6 months to ascertain the type of treatment required in subtropical conditions. The results demarcated sewage of this community as a medium-strength wastewater (chemical oxygen demand: 475 mg/L, biochemical oxygen demand: 240 mg/L and total suspended solids: 434 mg/L). Chemical oxygen demand to sulphate ratio of the sewage (11.6) established that it was amenable to anaerobic digestion. The temperature, strength, biodegradability and components of sewage were suitable for anaerobic digestion, and thus, upflow anaerobic sludge blanket reactor (UASB) was selected for its treatment. These reactors are often shutdown in small communities due to environmental and/or socio-economic factors. The ability of two UASB reactors, seeded with cow dung (UASB_CD) and activated sludge of a dairy treatment plant (UASB_ASDIT) to restart after a long idle period of 12 months, was investigated along with sludge analysis by scanning electron microscope. Biomass in both reactors reactivated rapidly after shutdown period and within 30 days after substrate feeding achieved uniform removal efficiencies for chemical oxygen demand, total suspended solids, total dissolved solids, chloride and oil and grease. Chemical oxygen demand removal efficiency of both reactors became uniform and remained close to 80% after 30 days through reactivation of microbes in sludge bed due to adequate food and temperature conditions. During restart-up, at an average organic loading rate of 0.902 kg COD/m³ per day, methane yields of 0.091 and 0.084 m³/kg COD removed were achieved for UASB_CD and UASB_ASDIT reactors, respectively.     

Contribution of a sewage sludge application to the short-term carbon sequestration across a wide range of agricultural soils

The atmospheric levels of carbon dioxide (CO₂) and other greenhouse gases (GHGs) have increased dramatically since the industrial revolution. The atmospheric enrichment with CO₂ and other GHGs has resulted in multiple negative consequences: such as the increase in the average temperature and the rise of the sea level. Hence, there is a growing interest in developing feasible methods to reduce the atmospheric levels of these gases. One of these strategies is to enhance C sequestration through the increase of soil organic carbon (SOC) pool by the amendment of agricultural soils with sewage sludge. However, there is considerable uncertainty about the effects (positive or negative) of sewage sludge applications on the SOC pool. Thus, a simple approach developed under laboratory conditions is presented to discern the effect of a single sewage sludge application of 50 t ha⁻¹ on the short-term SOC pool in 60 contrasting agricultural soils. The role of soil factors in the C sequestration of the recently added carbon was also studied. The application of sewage sludge supposed a mean increase of 1.7 ± 1.6 g SOC kg⁻¹, with peak increases of up to 3.8 g SOC kg⁻¹ and decreases of up to 4.6 g SOC kg⁻¹. The initial SOC contents conditioned the C sequestration after sewage sludge application, and no other soil property was related.     

Anaerobic co-digestion of sewage and brewery sludge for biogas production and land application

In Thailand, sewage sludge production from the Bangkok metropolitan area can reach up to 63,000 ton/y by 2010. The Beer-Thai Company, Thailand, produces beer and generates lots of sludge as waste. Sewage sludge and brewery sludge can be used to generate energy which could be saved on the fossil fuels conventionally used as a source of energy. The possibility was explored to mix brewery sludge with sewage sludge at different mixing ratios for anaerobic digestion so that the energy can be generated as biogas and at the same time, digested sewage sludge can be used as fertilizer for agricultural applications. A batch anaerobic reactor under mesophilic condition for a digestion period of 40 days was used in the laboratory. The acrylic reactor was cylindrical with a working weight of 12 kg. The diameter was 23.7 cm and the height was 34.5 cm. Sludge mixtures at different ratios were fed into the reactors and the optimum mixing ratio was determined. Experimental results showed that the sludge mixture at ratio of 25:75 % by weight (sewage:brewery) yielded higher biogas production. A reduction in heavy metals and pathogens was observed at this ratio after the digestion indicating its safe use as fertilizer. Nitrogen content was about 4.95 % which is well above the commercial fertilizers. At optimum mixing ratio of 25:75, the amount of the generated biogas is 1.15×10⁶ m³/y. This large amount of biogas is equivalent to 1.44 million kWh/y of electricity, 561,000 L/y of diesel oil and 936,000 L/y of vehicle gasoline.     

Assessment of microbiological and biochemical properties of dairy sewage sludge

The rational utilisation of sludge as organic matter application into the soil permits enrichment in nutrients such as nitrogen and phosphorus. As dairy sewage sludge contains large amounts of organic matter and minerals, utilisation of such sludge in agriculture appears to be a noteworthy proposal. However, such waste can also be a source of toxic substances, heavy metals, inhibitors, xenobiotics and potentially pathogenic microorganisms. Therefore, it is so important to monitor its microbiological and biochemical properties in aspect of the safety for human health, natural environment preservation and a suitable level of agricultural production maintenance. The objective of study was the estimation of selected microbiological, biochemical and chemical properties of activated sludge (AS) and waste activated sludge (WAS) originating from the dairy sewage treatment plant. Nitrification and ammonification rates, respiratory, dehydrogenases, acid phosphatase, alkaline phosphatase, protease and urease activities were at significantly higher levels in the WAS than in the AS. The pH value of the AS and WAS oscillated within the range of neutral reaction.     

新型城市污泥固化土工程特性及微观机理

通过污泥固化技术可以将城市污泥转化为一种新型城市污泥固化土。为了研究污泥固化土工程特性,对新型城市污泥固化土进行无侧限强度试验、收缩特性试验、浸出毒性试验以及X射线衍射试验与微观结构测试。试验结果表明,城市污泥固化土无侧限抗压强度随期龄增加而增长,28 d后基本稳定;新型城市污泥固化土的线缩率随龄期的增大而增大,且28 d后趋于稳定值;与消化后城市污泥相比,城市污泥固化土中的浸出毒性明显减少,重金属浸出量均符合国家规范要求。消化城市污泥衍射峰中氢氧化钙峰值很高,但随着养护期龄的增长,城市污泥固化土中氢氧化钙的衍射峰值减小,碳酸钙的衍射峰值增大,说明固化土各成分反应越充分,强度越高。微结构测试研究表明,污泥固化土SEM图像中有大量的纤维状物质联结着土颗粒和颗粒团块,形成土骨架纤维的交互空间结构,提高了土体强度。     

Compacted sewage sludge as a barrier for tailing impoundment

The feasibility of compacted sewage sludge serving as a barrier for tailing impoundment was evaluated by the batch test and hydraulic conductivity test with respect to heavy metal retardation and impermeability. The batch test results showed that the effective removal of heavy metals approached 97.8 and 93.4% for Zn and Cd, respectively. Formation of precipitation of oxy(hydroxide) and carbonate minerals was mainly responsible for the attenuation of heavy metals in the early period of the test. Nevertheless, the further removal of heavy metals can be attributed to the sulfate reduction. The hydraulic conductivity test indicated that almost all of the heavy metals contained in simulated acid pore water were retarded by compacted sewage sludge. The hydraulic conductivity of the compacted sewage sludge ranged from 3.0 × 10⁻⁸ to 8.0 × 10⁻⁸ cm s⁻¹, lower than 1.0 × 10⁻⁷ cm s⁻¹, which is required by regulations for the hydraulic barrier in landfill sites. Thus, this study suggested that compacted sewage sludge could be used as a bottom barrier for tailing impoundment.     

Geological and environmental implications in the reclamation of limestone quarries in Sierra de Callosa (Alicante,Spain)

Sierra de Callosa have an area of 8 km² and a maximum altitude of 566 masl. Geologically, it is found to be primarily comprised of carbonated rocks. Mine spoils coming from limestone quarries extraction are often used in the working reclamation process. These materials could be actually employed profitably once conveniently amended with organic matter. A study on the temporary evolution of nutrients and several physical–chemical parameters in a mineral waste amended with municipal solid waste (MSW) compost has been carried out. The effect of incorporating such waste to mine spoils in an arid gravel quarry has been studied, quantifying the temporal evolution of nutrients and several physical–chemical parameters in the mixture. Three plots have been prepared with mine spoils proceeding from a limestone quarry located in the south of the province of Alicante (municipality of Redován). These plots have been amended with 3 kg/m² of MSW compost. Texture, pH, electrical conductivity, oxidizable organic matter, N-Kjeldahl, available P, Na, K, Ca, Mg, Fe, Mn, Cu and Zn were analysed. The results reflected the contribution of nutrients to the substrate after the MSW addition. The variability of the information indicated the heterogeneity of the MSW composition, as well as the difficulty of obtaining a homogeneous MSW mixture–mineral waste.     

Development and application of a soil organic matter-based soil quality index in mineralized terrane of the Western US

Soil quality indices provide a means of distilling large amounts of data into a single metric that evaluates the soil’s ability to carry out key ecosystem functions. Primarily developed in agroecosytems, then forested ecosystems, an index using the relation between soil organic matter and other key soil properties in more semi-arid systems of the Western US impacted by different geologic mineralization was developed. Three different sites in two different mineralization types, acid sulfate and Cu/Mo porphyry in California and Nevada, were studied. Soil samples were collected from undisturbed soils in both mineralized and nearby unmineralized terrane as well as waste rock and tailings. Eight different microbial parameters (carbon substrate utilization, microbial biomass-C, mineralized-C, mineralized-N and enzyme activities of acid phosphatase, alkaline phosphatase, arylsulfatase, and fluorescein diacetate) along with a number of physicochemical parameters were measured. Multiple linear regression models between these parameters and both total organic carbon and total nitrogen were developed, using the ratio of predicted to measured values as the soil quality index. In most instances, pooling unmineralized and mineralized soil data within a given study site resulted in lower model correlations. Enzyme activity was a consistent explanatory variable in the models across the study sites. Though similar indicators were significant in models across different mineralization types, pooling data across sites inhibited model differentiation of undisturbed and disturbed sites. This procedure could be used to monitor recovery of disturbed systems in mineralized terrane and help link scientific and management disciplines.     

13C/12C composition, a novel parameter to study the downward migration of paper sludge in soils?

δ ¹³C values of crop and forest soils were measured 8 years after disposal of paper sewage sludge. The carbon transfer from paper sludge downward to the first humic layer is evidenced by a ¹³C-enrichnient of up to + 5.6‰ due to the input of ¹³C-enriched sludge carbonates. ¹³C/¹²C composition is thus a novel, sensitive parameter to follow the downward transfer of paper sludge carbon.     

Organic matter degradation in paper sludge amendments over gold mine tailings

The long-term stability of paper sludge amendments as covers for reclaimed mine waste storage facilities must be assessed by the mining industry. This study examines a 6 yr old sequence of paper sludge amendments applied over wastes from historic Au mines located in Northern Ontario, Canada. As paper sludge is mostly comprised of C-rich organic compounds, elemental quantification, ¹³C cross polarization/magic angle spinning nuclear magnetic resonance (¹³C CP/MAS NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were used to examine the minimal changes in the C content and speciation observed of the amendments over time. These results suggest that paper sludge covers are suitable for use in medium to long-term mining reclamation strategies.     

Geotechnical properties of municipal sewage sludge

The geotechnical properties of municipal sewage sludge, in particular those pertinent to the handling and landfilling of the material, are presented. Index, drying, compaction, shear strength and consolidation tests were conducted on the material at different states of biodegradation. The organic content and specific gravity of solids were found to be inversely related, with typical organic contents of 50–70% and specific gravity of solids values of 1.55–1.80. The density of the compacted material was low in comparison with mineral soils. Standard Proctor compaction yielded a maximum dry density of 0.56 tonne/m³ at 85% water content. Laboratory vane-shear and triaxial compression tests indicated that, below about 180% water content, the shear strength of the sludge material increased exponentially with reducing water content. Consolidated-undrained triaxial compression tests on the pasteurised sludge material indicated an effective angle of shearing resistance of 32° for the moderately degraded material and 37° for the strongly degraded material. Biogas was produced at rates of up to 0.33 L/day/kg slurry due to ongoing biodegradation and the resulting pore pressure response must be taken into account in any stress analysis. Consolidation tests using the hydraulic consolidation cell, oedometer and triaxial apparatus indicated that the sludge material was highly compressible although practically impermeable, for example the coefficient of permeability for the moderately degraded slurry was of the order of 10⁻⁹m/s. However, creep deformation was significant with typical coefficient of secondary compression values of 0.02–0.08 for the compacted material. A more free-draining material was produced at higher states of biodegradation.     

The effect of long-term reclamation on enzyme activities and microbial community structure of saline soil at Shangyu, China

Reclamation of saline soil plays an important role in supporting high population growth in China. To evaluate the effects of reclamation and sustainability of salt-affected land production, soil chemical properties, enzyme activities, microbial community structure and function in sites reclaimed in 1976, 1984 and 1996 were characterized. The 2009 site was left to succession fallow and chosen as a control site. Results showed that electrical conductivity (EC) and pH decreased rapidly after the soil forming process started. An accumulation of soil organic C as a result of farming was observed. In all sites, inorganic N and available P were increased within 33 years after reclamation and commencement of agriculture. As a result of reclamation, soil enzyme activity (β-glucosidase, phosphatase, urease and arylsulfatase) was increased. There were no significant differences in soil enzyme activity between the sites reclaimed in 1976 and 1984, with the exception of phosphatase. Carbon source utilization patterns were less diverse in control soil than in treatment sites. The activities of reclamation resulted in synthesis of new phospholipid fatty acids (14:0, 17:1 c9, 16:0 2OH, 17:0 10Me, i17:0, 20:4 ω6c). Principal component analyses showed that the sites reclaimed in 1976 and 1984 clustered together and were distinct from 1996. Taken together, reclamation showed significantly increased soil quality and microbial activity. EC was the main limiting soil quality characteristic, which showed a comparative steady state after a reclamation time of 33 years. Differences in soil enzyme activity and microbial community function after long-term reclamation have potential to be reflected in soil functional integrity and ecosystem service.     

Improvement of Clayey Soil with Lime and Industrial Sludge

Industrial waste generation has reached up to millions of tons yearly. One way to solve the problems of the large accumulating amount of waste could be to incorporate it into the soil; thus, finding a way for the use of industrial waste could be a quest for soil improvement studies. Industrial sludge in certain pozzolanic form reacts with soil and possesses cementitious properties. This paper illustrates the utilization of lime, steel and copper sludge in improvement of high plasticity clayey soil. The influence of stabilizer type, different curing times and various ratios of lime to sludge are evaluated by Atterberg limits, standard proctor compaction, unconfined compressive strength and unconsolidated undrained strength in triaxial test. The  test results show that adding lime and sludge results in an increase in maximum strength. Moreover, the strength of soil increases with the increase of curing time. Utilizing stabilizers also influences plasticity index and compaction parameters. Finally, the results demonstrate that steel sludge has better performance than that of copper sludge in term of strength development.     

处置库污泥工程特性测试研究

对某填埋场污泥库中取样的污泥进行了岩土工程特性测试,包括有机质含量、含水率、界限含水率、颗粒级配、渗透系数、压缩固结特性及抗剪强度等。试验结果表明,与常规淤泥相比,污泥库中经一段时间降解后污泥有机质含量及含水率较高,平均值分别为45%和520%;污泥在历时2 a的生物降解作用下,污泥含水率、有机质含量沿深度呈较为明显的减少趋势;污泥具有极高的压缩性,压缩系数a100-200高达7 MPa-1;污泥的固结表现为非线性大变形特性,其固结系数在10-5～10-6 cm2/s,比淤泥低1～2个数量级,固结系数随压力的增加而显著减少;污泥的抗剪强度参数较小,其黏聚力为0,内摩擦角为14.7°。有机质含量高是污泥高含水率、高液塑性指数、高压缩性,低渗透性、低固结系数及低抗剪强度的本质原因。以上成果可为污泥库的固化处置、稳定分析等提供必要的参数。     

Impact of sewage sludge application on zinc desorption kinetics in some calcareous soils

Sewage sludge usually contains significant amount of Zinc (Zn) and is widely used in agricultural lands. A laboratory experiment was performed to determine Zn desorption characteristics in unamended and amended soils with sewage sludge. Ten calcareous soils were amended with 1 % (w/w) sewage sludge. Amended and unamended soils were incubated at field capacity at 25 ± 1 °C for 1 month. After incubation, the kinetics of Zn desorption in amended and unamended soils were determined by successive extraction with DTPA-TEA (diethylenetriaminepentaacetic acid-triethanolamine) in a period of 1–504 h at 25 ± 1 °C. The results of kinetics study showed that extracted Zn and desorption rate constants in the amended soils were significantly (p < 0.01) higher than in the unamended soils. The results showed that Zn desorption increased from 201 to 343 % in amended soil with respect to unamended soils. The amounts of desorbed Zn in the unamended soils ranged from 3.73 to 8.79 mg kg^?1, while the amounts of desorbed Zn in amended soils ranged from 11.47 to 17.66 mg kg^?1. Desorption kinetics of Zn in two soils conformed fairly well to first-order, parabolic diffusion and power function equations. The results of stepwise regression analysis indicated that calcium carbonate equivalent and clay could be used to estimate Zn desorption characteristics in DTPA-TEA solution in the amended and unamended calcareous soils. It can be concluded that sewage sludge applied to calcareous soils may enhance the source of Zn for the plants.     

The retention of heavy metals in sewage sludge applied to a freshwater tidal wetland

The hypothesis that freshwater tidal wetlands act as sinks for heavy metals was tested using sewage sludge applied biweekly from March to October 1981 at low treatment (25 g m^?2 wk^?1) and high treatment (100 g m^?1) levels. No differences in aboveground macrophyte standing crop were found except in June when high and low treatment sites had significantly higher (p=0.05) standing crops than control sites. Except for chromium, metal standing stocks in the vegetation on treatment sites did not increase as a result of sludge application. The March litter had significantly higher (p=0.05) concentrations of chromium, copper, lead, and nickel at all sites than the October vegetation, but only high and low treatment litter chromium levels were significantly higher (p=0.05) than control litter. When sludge application terminated in October, the top 5 cm of soil at the high and low treatment sites had retained, respectively, 47 and 43% of the cadmium, 53 and 28% of the chromium, 52 and 0% of the copper, 51 and 0% of the zinc, 31 and 0% of the lead, and 0 and 0% of the nickel applied; only cadmium (15 and 46%, respectively) and chromium (12 and 28%, respectively) were still retained the following March. Thus, freshwater tidal wetlands can retain significant quantities of heavy metals associated with sewage sludge. The vegetation and litter play minor roles while the soil plays a major role in heavy metal retention.